{"collection":"philosophy-ethics","full_text_available":true,"graph_url":"https://unchartedknowledge.5gfusion.net/v2/api/page/gutenberg_1909/graph","html_url":"https://unchartedknowledge.5gfusion.net/v2/page/gutenberg_1909","id":"gutenberg_1909","license":"Public Domain (US)","rights_basis":"gutenberg_metadata_copyright_false","source":"gutenberg","source_url":"https://www.gutenberg.org/ebooks/1909","summary":null,"tags":["Biology","Category: Essays, Letters & Speeches","Category: Philosophy & Ethics","Category: Science - Biology","Darwin, Charles, 1809-1882","Evolution (Biology)","Science -- History"],"text":"Produced by Sue Asscher\n\n\n\n\n\nDARWIN AND MODERN SCIENCE\n\nESSAYS IN COMMEMORATION OF THE CENTENARY OF THE BIRTH OF CHARLES DARWIN\nAND OF THE FIFTIETH ANNIVERSARY OF THE PUBLICATION OF \"THE ORIGIN OF\nSPECIES\"\n\n\nBy A.C. Seward\n\n\n\n\"My success as a man of science, whatever this may have amounted to,\nhas been determined, as far as I can judge, by complex and diversified\nmental qualities and conditions. Of these, the most important have\nbeen--the love of science--unbounded patience in long reflecting over\nany subject--industry in observing and collecting facts--and a fair\nshare of invention as well as of common sense. With such moderate\nabilities as I possess, it is truly surprising that I should have\ninfluenced to a considerable extent the belief of scientific men on some\nimportant points.\"\n\nAutobiography (1881); \"The Life and Letters of Charles Darwin\", Vol. 1.\npage 107.\n\n\n\n\nPREFACE\n\nAt the suggestion of the Cambridge Philosophical Society, the Syndics\nof the University Press decided in March, 1908, to arrange for the\npublication of a series of Essays in commemoration of the Centenary\nof the birth of Charles Darwin and of the Fiftieth anniversary of the\npublication of \"The Origin of Species\". The preliminary arrangements\nwere made by a committee consisting of the following representatives of\nthe Council of the Philosophical Society and of the Press Syndicate:\nDr H.K. Anderson, Prof. Bateson, Mr Francis Darwin, Dr Hobson, Dr Marr,\nProf. Sedgwick, Mr David Sharp, Mr Shipley, Prof. Sorley, Prof. Seward.\nIn the course of the preparation of the volume, the original scheme and\nlist of authors have been modified: a few of those invited to contribute\nessays were, for various reasons, unable to do so, and some alterations\nhave been made in the titles of articles. For the selection of authors\nand for the choice of subjects, the committee are mainly responsible,\nbut for such share of the work in the preparation of the volume as\nusually falls to the lot of an editor I accept full responsibility.\n\nAuthors were asked to address themselves primarily to the educated\nlayman rather than to the expert. It was hoped that the publication\nof the essays would serve the double purpose of illustrating the\nfar-reaching influence of Darwin's work on the progress of knowledge and\nthe present attitude of original investigators and thinkers towards the\nviews embodied in Darwin's works.\n\nIn regard to the interpretation of a passage in \"The Origin of Species\"\nquoted by Hugo de Vries, it seemed advisable to add an editorial\nfootnote; but, with this exception, I have not felt it necessary to\nrecord any opinion on views stated in the essays.\n\nIn reading the essays in proof I have availed myself freely of the\nwilling assistance of several Cambridge friends, among whom I wish more\nespecially to thank Mr Francis Darwin for the active interest he\nhas taken in the preparation of the volume. Mrs J.A. Thomson kindly\nundertook the translation of the essays by Prof. Weismann and Prof.\nSchwalbe; Mrs James Ward was good enough to assist me by translating\nProf. Bougle's article on Sociology, and to Mr McCabe I am indebted for\nthe translation of the essay by Prof. Haeckel. For the translation\nof the botanical articles by Prof. Goebel, Prof. Klebs and Prof.\nStrasburger, I am responsible; in the revision of the translation of\nProf. Strasburger's essay Madame Errera of Brussels rendered valuable\nhelp. Mr Wright, the Secretary of the Press Syndicate, and Mr Waller,\nthe Assistant Secretary, have cordially cooperated with me in my\neditorial work; nor can I omit to thank the readers of the University\nPress for keeping watchful eyes on my shortcomings in the correction of\nproofs.\n\nThe two portraits of Darwin are reproduced by permission of Messrs Maull\nand Fox and Messrs Elliott and Fry. The photogravure of the study at\nDown is reproduced from an etching by Mr Axel Haig, lent by Mr Francis\nDarwin; the coloured plate illustrating Prof. Weismann's essay was\noriginally published by him in his \"Vortrage uber Descendenztheorie\"\nwhich afterwards appeared (1904) in English under the title \"The\nEvolution Theory\". Copies of this plate were supplied by Messrs Fischer\nof Jena.\n\nThe Syndics of the University Press have agreed, in the event of\nthis volume being a financial success, to hand over the profits to a\nUniversity fund for the endowment of biological research.\n\nIt is clearly impossible to express adequately in a single volume of\nEssays the influence of Darwin's contributions to knowledge on the\nsubsequent progress of scientific inquiry. As Huxley said in 1885:\n\"Whatever be the ultimate verdict of posterity upon this or that opinion\nwhich Mr Darwin has propounded; whatever adumbrations or anticipations\nof his doctrines may be found in the writings of his predecessors; the\nbroad fact remains that, since the publication and by reason of the\npublication of \"The Origin of Species\" the fundamental conceptions\nand the aims of the students of living Nature have been completely\nchanged... But the impulse thus given to scientific thought rapidly\nspread beyond the ordinarily recognised limits of Biology. Psychology,\nEthics, Cosmology were stirred to their foundations, and 'The Origin of\nSpecies' proved itself to be the fixed point which the general doctrine\nneeded in order to move the world.\"\n\nIn the contributions to this Memorial Volume, some of the authors\nhave more especially concerned themselves with the results achieved by\nDarwin's own work, while others pass in review the progress of research\non lines which, though unknown or but little followed in his day, are\nthe direct outcome of his work.\n\nThe divergence of views among biologists in regard to the origin of\nspecies and as to the most promising directions in which to seek for\ntruth is illustrated by the different opinions of contributors. Whether\nDarwin's views on the modus operandi of evolutionary forces receive\nfurther confirmation in the future, or whether they are materially\nmodified, in no way affects the truth of the statement that, by\nemploying his life \"in adding a little to Natural Science,\" he\nrevolutionised the world of thought. Darwin wrote in 1872 to Alfred\nRussel Wallace: \"How grand is the onward rush of science: it is enough\nto console us for the many errors which we have committed, and for our\nefforts being overlaid and forgotten in the mass of new facts and new\nviews which are daily turning up.\" In the onward rush, it is easy for\nstudents convinced of the correctness of their own views and equally\nconvinced of the falsity of those of their fellow-workers to forget the\nlessons of Darwin's life. In his autobiographical sketch, he tells us,\n\"I have steadily endeavoured to keep my mind free so as to give up any\nhypothesis, however much beloved...as soon as facts are shown to be\nopposed to it.\" Writing to Mr J. Scott, he says, \"It is a golden rule,\nwhich I try to follow, to put every fact which is opposed to one's\npreconceived opinion in the strongest light. Absolute accuracy is the\nhardest merit to attain, and the highest merit. Any deviation is ruin.\"\n\nHe acted strictly in accordance with his determination expressed in a\nletter to Lyell in 1844, \"I shall keep out of controversy, and just\ngive my own facts.\" As was said of another son of Cambridge, Sir George\nStokes, \"He would no more have thought of disputing about priority,\nor the authorship of an idea, than of writing a report for a company\npromoter.\" Darwin's life affords a striking confirmation of the truth\nof Hazlitt's aphorism, \"Where the pursuit of truth has been the habitual\nstudy of any man's life, the love of truth will be his ruling passion.\"\nGreat as was the intellect of Darwin, his character, as Huxley wrote,\nwas even nobler than his intellect.\n\nA.C. SEWARD.\n\nBotany School, Cambridge, March 20, 1909.\n\n\n\nCONTENTS\nI. INTRODUCTORY LETTER TO THE EDITOR from SIR JOSEPH DALTON HOOKER, O.M.\n\nII. DARWIN'S PREDECESSORS:  J. ARTHUR THOMSON, Professor of Natural\nHistory in the University of Aberdeen.\n\nIII. THE SELECTION THEORY:  AUGUST WEISMANN, Professor of Zoology in the\nUniversity of Freiburg (Baden).\n\nIV. VARIATION:  HUGO DE VRIES, Professor of Botany in the University of\nAmsterdam.\n\nV. HEREDITY AND VARIATION IN MODERN LIGHTS:  W. BATESON, Professor of\nBiology in the University of Cambridge.\n\nVI. THE MINUTE STRUCTURE OF CELLS IN RELATION TO HEREDITY:  EDUARD\nSTRASBURGER, Professor of Botany in the University of Bonn.\n\nVII. \"THE DESCENT OF MAN\":  G. SCHWALBE, Professor of Anatomy in the\nUniversity of Strassburg.\n\nVIII. CHARLES DARWIN AS AN ANTHROPOLOGIST:  ERNST HAECKEL, Professor of\nZoology in the University of Jena.\n\nIX. SOME PRIMITIVE THEORIES OF THE ORIGIN OF MAN:  J.G. FRAZER, Fellow\nof Trinity College, Cambridge.\n\nX. THE INFLUENCE OF DARWIN ON THE STUDY OF ANIMAL EMBRYOLOGY:  A.\nSEDGWICK, Professor of Zoology and Comparative Anatomy in the University\nof Cambridge.\n\nXI. THE PALAEONTOLOGICAL RECORD. I. ANIMALS:  W.B. SCOTT, Professor of\nGeology in the University of Princeton.\n\nXII. THE PALAEONTOLOGICAL RECORD. II. PLANTS:  D.H. SCOTT, President of\nthe Linnean Society of London.\n\nXIII. THE INFLUENCE OF ENVIRONMENT ON THE FORMS OF PLANTS:  GEORG KLEBS,\nProfessor of Botany in the University of Heidelberg.\n\nXIV. EXPERIMENTAL STUDY OF THE INFLUENCE OF ENVIRONMENT ON ANIMALS:\nJACQUES LOEB, Professor of Physiology in the University of California.\n\nXV. THE VALUE OF COLOUR IN THE STRUGGLE FOR LIFE:  E.B. POULTON, Hope\nProfessor of Zoology in the University of Oxford.\n\nXVI. GEOGRAPHICAL DISTRIBUTION OF PLANTS:  SIR WILLIAM THISELTON-DYER.\n\nXVII. GEOGRAPHICAL DISTRIBUTION OF ANIMALS:  HANS GADOW, Strickland\nCurator and Lecturer on Zoology in the University of Cambridge.\n\nXVIII. DARWIN AND GEOLOGY:  J.W. JUDD.\n\nXIX. DARWIN'S WORK ON THE MOVEMENTS OF PLANTS:  FRANCIS DARWIN.\n\nXX. THE BIOLOGY OF FLOWERS:  K. GOEBEL, Professor of Botany in the\nUniversity of Munich.\n\nXXI. MENTAL FACTORS IN EVOLUTION:  C. LLOYD MORGAN, Professor of\nPsychology at University College, Bristol.\n\nXXII. THE INFLUENCE OF THE CONCEPTION OF EVOLUTION ON MODERN PHILOSOPHY:\nH. HOFFDING, Professor of Philosophy in the University of Copenhagen.\n\nXXIII. DARWINISM AND SOCIOLOGY:  C. BOUGLE, Professor of Social\nPhilosophy in the University of Toulouse, and Deputy-Professor at the\nSorbonne, Paris.\n\nXXIV. THE INFLUENCE OF DARWIN UPON RELIGIOUS THOUGHT:  REV. P.N.\nWAGGETT.\n\nXXV. THE INFLUENCE OF DARWINISM ON THE STUDY OF RELIGIONS:  JANE ELLEN\nHARRISON, Staff-Lecturer and sometime Fellow of Newnham College,\nCambridge.\n\nXXVI. EVOLUTION AND THE SCIENCE OF LANGUAGE:  P. GILES, Reader in\nComparative Philology in the University of Cambridge.\n\nXXVII. DARWINISM AND HISTORY:  J.B. BURY, Regius Professor of Modern\nHistory in the University of Cambridge.\n\nXXVIII. THE GENESIS OF DOUBLE STARS:  SIR GEORGE DARWIN, Plumian\nProfessor of Astronomy and Experimental Philosophy in the University of\nCambridge.\n\nXXIX. THE EVOLUTION OF MATTER:  W.C.D. WHETHAM, Fellow of Trinity\nCollege, Cambridge.\n\nINDEX.\n\n\n\n\nDATES OF THE PUBLICATION Of CHARLES DARWIN'S BOOKS AND OF THE PRINCIPAL\nEVENTS IN HIS LIFE\n\n1809:\n\nCharles Darwin born at Shrewsbury, February 12.\n\n1817:\n\n\"At 8 1/2 years old I went to Mr Case's school.\" (A day-school at\nShrewsbury kept by the Rev G. Case, Minister of the Unitarian Chapel.)\n\n1818:\n\n\"I was at school at Shrewsbury under a great scholar, Dr Butler; I\nlearnt absolutely nothing, except by amusing myself by reading and\nexperimenting in Chemistry.\"\n\n1825:\n\n\"As I was doing no good at school, my father wisely took me away at\na rather earlier age than usual, and sent me (Oct. 1825) to Edinburgh\nUniversity with my brother, where I stayed for two years.\"\n\n1828:\n\nBegan residence at Christ's College, Cambridge.\n\n\"I went to Cambridge early in the year 1828, and soon became acquainted\nwith Professor Henslow...Nothing could be more simple, cordial and\nunpretending than the encouragement which he afforded to all young\nnaturalists.\"\n\n\"During the three years which I spent at Cambridge my time was wasted,\nas far as the academical studies were concerned, as completely as at\nEdinburgh and at school.\"\n\n\"In order to pass the B.A. Examination, it was...necessary to get up\nPaley's 'Evidences of Christianity,' and his 'Moral Philosophy'... The\ncareful study of these works, without attempting to learn any part by\nrote, was the only part of the academical course which...was of the\nleast use to me in the education of my mind.\"\n\n1831:\n\nPassed the examination for the B.A. degree in January and kept the\nfollowing terms.\n\n\"I gained a good place among the oi polloi or crowd of men who do not go\nin for honours.\"\n\n\"I am very busy,...and see a great deal of Henslow, whom I do not know\nwhether I love or respect most.\"\n\nDec. 27. \"Sailed from England on our circumnavigation,\" in H.M.S.\n\"Beagle\", a barque of 235 tons carrying 6 guns, under Capt. FitzRoy.\n\n\"There is indeed a tide in the affairs of men.\"\n\n1836:\n\nOct. 4. \"Reached Shrewsbury after absence of 5 years and 2 days.\"\n\n\"You cannot imagine how gloriously delightful my first visit was at\nhome; it was worth the banishment.\"\n\nDec. 13. Went to live at Cambridge (Fitzwilliam Street).\n\n\"The only evil I found in Cambridge was its being too pleasant.\"\n\n1837:\n\n\"On my return home (in the 'Beagle') in the autumn of 1836 I immediately\nbegan to prepare my journal for publication, and then saw how many facts\nindicated the common descent of species... In July (1837) I opened my\nfirst note-book for facts in relation to the Origin of Species, about\nwhich I had long reflected, and never ceased working for the next twenty\nyears... Had been greatly struck from about the month of previous\nMarch on character of South American fossils, and species on Galapagos\nArchipelago. These facts (especially latter), origin of all my views.\"\n\n\"On March 7, 1837 I took lodgings in (36) Great Marlborough Street in\nLondon, and remained there for nearly two years, until I was married.\"\n\n1838:\n\n\"In October, that is fifteen months after I had begun my systematic\nenquiry, I happened to read for amusement 'Malthus on Population,'\nand being well prepared to appreciate the struggle for existence which\neverywhere goes on from long-continued observation of the habits of\nanimals and plants, it at once struck me that under these circumstances\nfavourable variations would tend to be preserved, and unfavourable\nones to be destroyed. The result of this would be the formation of new\nspecies. Here then I had at last got a theory by which to work; but I\nwas so anxious to avoid prejudice, that I determined not for some time\nto write even the briefest sketch of it.\"\n\n1839:\n\nMarried at Maer (Staffordshire) to his first cousin Emma Wedgwood,\ndaughter of Josiah Wedgwood.\n\n\"I marvel at my good fortune that she, so infinitely my superior in\nevery single moral quality, consented to be my wife. She has been my\nwise adviser and cheerful comforter throughout life, which without\nher would have been during a very long period a miserable one\nfrom ill-health. She has earned the love of every soul near her\"\n(Autobiography).\n\nDec. 31. \"Entered 12 Upper Gower street\" (now 110 Gower street, London).\n\"There never was so good a house for me, and I devoutly trust you (his\nfuture wife) will approve of it equally. The little garden is worth its\nweight in gold.\"\n\nPublished \"Journal and Researches\", being Vol. III. of the \"Narrative of\nthe Surveying Voyage of H.M.S. 'Adventure' and 'Beagle'\"...\n\nPublication of the \"Zoology of the Voyage of H.M.S. 'Beagle'\", Part\nII., \"Mammalia\", by G.R. Waterhouse, with a \"Notice of their habits and\nranges\", by Charles Darwin.\n\n1840:\n\nContributed Geological Introduction to Part I. (\"Fossil Mammalia\") of\nthe \"Zoology of the Voyage of H.M.S. 'Beagle'\" by Richard Owen.\n\n1842:\n\n\"In June 1842 I first allowed myself the satisfaction of writing a very\nbrief abstract of my (species) theory in pencil in 35 pages; and this\nwas enlarged during the summer of 1844 into one of 230 pages, which I\nhad fairly copied out and still (1876) possess.\" (The first draft of\n\"The Origin of Species\", edited by Mr Francis Darwin, will be published\nthis year (1909) by the Syndics of the Cambridge University Press.)\n\nSept. 14. Settled at the village of Down in Kent.\n\n\"I think I was never in a more perfectly quiet country.\"\n\nPublication of \"The Structure and Distribution of Coral Reefs\"; being\nPart I. of the \"Geology of the Voyage of the Beagle\".\n\n1844:\n\nPublication of \"Geological Observations on the Volcanic Islands visited\nduring the Voyage of H.M.S. 'Beagle'\"; being Part II. of the \"Geology of\nthe Voyage of the 'Beagle'\".\n\n\"I think much more highly of my book on Volcanic Islands since Mr Judd,\nby far the best judge on the subject in England, has, as I hear, learnt\nmuch from it.\" (Autobiography, 1876.)\n\n1845:\n\nPublication of the \"Journal of Researches\" as a separate book.\n\n1846:\n\nPublication of \"Geological Observations on South America\"; being Part\nIII. of the \"Geology of the Voyage of the 'Beagle'\".\n\n1851:\n\nPublication of a \"Monograph of the Fossil Lepadidae\" and of a \"Monograph\nof the sub-class Cirripedia\".\n\n\"I fear the study of the Cirripedia will ever remain 'wholly unapplied,'\nand yet I feel that such study is better than castle-building.\"\n\n1854:\n\nPublication of Monographs of the Balanidae and Verrucidae.\n\n\"I worked steadily on this subject for...eight years, and ultimately\npublished two thick volumes, describing all the known living\nspecies, and two thin quartos on the extinct species... My work was of\nconsiderable use to me, when I had to discuss in the \"Origin of Species\"\nthe principles of a natural classification. Nevertheless, I doubt\nwhether the work was worth the consumption of so much time.\"\n\n\"From September 1854 I devoted my whole time to arranging my huge\npile of notes, to observing, and to experimenting in relation to the\ntransmutation of species.\"\n\n1856:\n\n\"Early in 1856 Lyell advised me to write out my views pretty fully, and\nI began at once to do so on a scale three or four times as extensive as\nthat which was afterwards followed in my 'Origin of Species'.\"\n\n1858:\n\nJoint paper by Charles Darwin and Alfred Russel Wallace \"On the Tendency\nof Species to form Varieties; and on the perpetuation of Varieties and\nSpecies by Natural Means of Selection,\" communicated to the Linnean\nSociety by Sir Charles Lyell and Sir Joseph Hooker.\n\n\"I was at first very unwilling to consent (to the communication of his\nMS. to the Society) as I thought Mr Wallace might consider my doing so\nunjustifiable, for I did not then know how generous and noble was his\ndisposition.\"\n\n\"July 20 to Aug. 12 at Sandown (Isle of Wight) began abstract of Species\nbook.\"\n\n1859:\n\nNov. 24. Publication of \"The Origin of Species\" (1250 copies).\n\n\"Oh, good heavens, the relief to my head and body to banish the whole\nsubject from my mind!... But, alas, how frequent, how almost universal it\nis in an author to persuade himself of the truth of his own dogmas.\nMy only hope is that I certainly see many difficulties of gigantic\nstature.\"\n\n1860:\n\nPublication of the second edition of the \"Origin\" (3000 copies).\n\nPublication of a \"Naturalist's Voyage\".\n\n1861:\n\nPublication of the third edition of the \"Origin\" (2000 copies).\n\n\"I am going to write a little book... on Orchids, and to-day I hate them\nworse than everything.\"\n\n1862:\n\nPublication of the book \"On the various contrivances by which Orchids\nare fertilised by Insects\".\n\n1865:\n\nRead paper before the Linnean Society \"On the Movements and Habits of\nClimbing plants\". (Published as a book in 1875.)\n\n1866:\n\nPublication of the fourth edition of the \"Origin\" (1250 copies).\n\n1868:\n\n\"I have sent the MS. of my big book, and horridly, disgustingly big it\nwill be, to the printers.\"\n\nPublication of the \"Variation of Animals and Plants under\nDomestication\".\n\n\"About my book, I will give you (Sir Joseph Hooker) a bit of advice.\nSkip the whole of Vol. I, except the last chapter, (and that need only\nbe skimmed), and skip largely in the 2nd volume; and then you will say\nit is a very good book.\"\n\n\"Towards the end of the work I give my well-abused hypothesis of\nPangenesis. An unverified hypothesis is of little or no value; but if\nanyone should hereafter be led to make observations by which some such\nhypothesis could be established, I shall have done good service, as an\nastonishing number of isolated facts can be thus connected together and\nrendered intelligible.\"\n\n1869:\n\nPublication of the fifth edition of the \"Origin\".\n\n1871:\n\nPublication of \"The Descent of Man\".\n\n\"Although in the 'Origin of Species' the derivation of any particular\nspecies is never discussed, yet I thought it best, in order that no\nhonourable man should accuse me of concealing my views, to add that by\nthe work 'light would be thrown on the origin of man and his history'.\"\n\n1872:\n\nPublication of the sixth edition of the \"Origin\".\n\nPublication of \"The Expression of the Emotions in Man and Animals\".\n\n1874:\n\nPublication of the second edition of \"The Descent of Man\".\n\n\"The new edition of the \"Descent\" has turned out an awful job. It took\nme ten days merely to glance over letters and reviews with criticisms\nand new facts. It is a devil of a job.\"\n\nPublication of the second edition of \"The Structure and Distribution of\nCoral Reefs\".\n\n1875:\n\nPublication of \"Insectivorous Plants\".\n\n\"I begin to think that every one who publishes a book is a fool.\"\n\nPublication of the second edition of \"Variation in Animals and Plants\".\n\nPublication of \"The Movements and Habits of Climbing Plants\" as a\nseparate book.\n\n1876:\n\nWrote Autobiographical Sketch (\"Life and Letters\", Vol. I., Chap II.).\n\nPublication of \"The Effects of Cross and Self fertilisation\".\n\n\"I now (1881) believe, however,...that I ought to have insisted more\nstrongly than I did on the many adaptations for self-fertilisation.\"\n\nPublication of the second edition of \"Observations on Volcanic Islands\".\n\n1877:\n\nPublication of \"The Different Forms of Flowers on Plants of the same\nspecies\".\n\n\"I do not suppose that I shall publish any more books... I cannot endure\nbeing idle, but heaven knows whether I am capable of any more good\nwork.\"\n\nPublication of the second edition of the Orchid book.\n\n1878:\n\nPublication of the second edition of \"The Effects of Cross and Self\nfertilisation\".\n\n1879:\n\nPublication of an English translation of Ernst Krause's \"Erasmus\nDarwin\", with a notice by Charles Darwin. \"I am EXTREMELY glad that\nyou approve of the little 'Life' of our Grandfather, for I have been\nrepenting that I ever undertook it, as the work was quite beyond my\ntether.\" (To Mr Francis Galton, Nov. 14, 1879.)\n\n1880:\n\nPublication of \"The Power of Movement in Plants\".\n\n\"It has always pleased me to exalt plants in the scale of organised\nbeings.\"\n\nPublication of the second edition of \"The Different Forms of Flowers\".\n\n1881:\n\nWrote a continuation of the Autobiography.\n\nPublication of \"The Formation of Vegetable Mould, through the Action of\nWorms\".\n\n\"It is the completion of a short paper read before the Geological\nSociety more than forty years ago, and has revived old geological\nthoughts... As far as I can judge it will be a curious little book.\"\n\n1882:\n\nCharles Darwin died at Down, April 19, and was buried in Westminster\nAbbey, April 26, in the north aisle of the Nave a few feet from the\ngrave of Sir Isaac Newton.\n\n\"As for myself, I believe that I have acted rightly in steadily\nfollowing and devoting my life to Science. I feel no remorse from having\ncommitted any great sin, but have often and often regretted that I have\nnot done more direct good to my fellow creatures.\"\n\nThe quotations in the above Epitome are taken from the Autobiography and\npublished Letters:--\n\n\"The Life and Letters of Charles Darwin\", including an Autobiographical\nChapter. Edited by his son, Francis Darwin, 3 Vols., London, 1887.\n\n\"Charles Darwin\": His life told in an Autobiographical Chapter, and in\na selected series of his published Letters. Edited by his son, Francis\nDarwin, London, 1902.\n\n\"More Letters of Charles Darwin\". A record of his work in a series of\nhitherto unpublished Letters. Edited by Francis Darwin and A.C. Seward,\n2 Vols., London, 1903.\n\n\n\n\nI. INTRODUCTORY LETTER From Sir Joseph Dalton Hooker, O.M., G.C.S.I.,\nC.B., M.D., D.C.L., LL.D., F.R.S., ETC.\n\n\nThe Camp,\n\nnear Sunningdale,\n\nJanuary 15, 1909.\n\nDear Professor Seward,\n\nThe publication of a Series of Essays in Commemoration of the century\nof the birth of Charles Darwin and of the fiftieth anniversary of the\npublication of \"The Origin of Species\" is assuredly welcome and is a\nsubject of congratulation to all students of Science.\n\nThese Essays on the progress of Science and Philosophy as affected by\nDarwin's labours have been written by men known for their ability to\ndiscuss the problems which he so successfully worked to solve. They\ncannot but prove to be of enduring value, whether for the information of\nthe general reader or as guides to investigators occupied with problems\nsimilar to those which engaged the attention of Darwin.\n\nThe essayists have been fortunate in having for reference the five\npublished volumes of Charles Darwin's Life and Correspondence. For there\nis set forth in his own words the inception in his mind of the problems,\ngeological, zoological and botanical, hypothetical and theoretical,\nwhich he set himself to solve and the steps by which he proceeded to\ninvestigate them with the view of correlating the phenomena of life with\nthe evolution of living things. In his letters he expressed himself in\nlanguage so lucid and so little burthened with technical terms that they\nmay be regarded as models for those who were asked to address themselves\nprimarily to the educated reader rather than to the expert.\n\nI may add that by no one can the perusal of the Essays be more vividly\nappreciated than by the writer of these lines. It was my privilege for\nforty years to possess the intimate friendship of Charles Darwin and to\nbe his companion during many of his working hours in Study, Laboratory,\nand Garden. I was the recipient of letters from him, relating mainly to\nthe progress of his researches, the copies of which (the originals are\nnow in the possession of his family) cover upwards of a thousand pages\nof foolscap, each page containing, on an average, three hundred words.\n\nThat the editorship of these Essays has been entrusted to a Cambridge\nProfessor of Botany must be gratifying to all concerned in their\nproduction and in their perusal, recalling as it does the fact that\nCharles Darwin's instructor in scientific methods was his lifelong\nfriend the late Rev. J.S. Henslow at that time Professor of Botany in\nthe University. It was owing to his recommendation that his pupil was\nappointed Naturalist to H.M.S. \"Beagle\", a service which Darwin himself\nregarded as marking the dawn of his scientific career.\n\nVery sincerely yours,\n\nJ.D. HOOKER.\n\n\n\n\nII. DARWIN'S PREDECESSORS. By J. Arthur Thomson.\n\nProfessor of Natural History in the University of Aberdeen.\n\n\nIn seeking to discover Darwin's relation to his predecessors it is\nuseful to distinguish the various services which he rendered to the\ntheory of organic evolution.\n\n(I) As everyone knows, the general idea of the Doctrine of Descent\nis that the plants and animals of the present-day are the lineal\ndescendants of ancestors on the whole somewhat simpler, that these again\nare descended from yet simpler forms, and so on backwards towards the\nliteral \"Protozoa\" and \"Protophyta\" about which we unfortunately know\nnothing. Now no one supposes that Darwin originated this idea, which in\nrudiment at least is as old as Aristotle. What Darwin did was to make\nit current intellectual coin. He gave it a form that commended itself\nto the scientific and public intelligence of the day, and he won\nwide-spread conviction by showing with consummate skill that it was\nan effective formula to work with, a key which no lock refused. In\na scholarly, critical, and pre-eminently fair-minded way, admitting\ndifficulties and removing them, foreseeing objections and forestalling\nthem, he showed that the doctrine of descent supplied a modal\ninterpretation of how our present-day fauna and flora have come to be.\n\n(II) In the second place, Darwin applied the evolution-idea to\nparticular problems, such as the descent of man, and showed what a\npowerful organon it is, introducing order into masses of uncorrelated\nfacts, interpreting enigmas both of structure and function, both\nbodily and mental, and, best of all, stimulating and guiding further\ninvestigation. But here again it cannot be claimed that Darwin was\noriginal. The problem of the descent or ascent of man, and other\nparticular cases of evolution, had attracted not a few naturalists\nbefore Darwin's day, though no one (except Herbert Spencer in the\npsychological domain (1855)) had come near him in precision and\nthoroughness of inquiry.\n\n(III) In the third place, Darwin contributed largely to a knowledge of\nthe factors in the evolution-process, especially by his analysis of what\noccurs in the case of domestic animals and cultivated plants, and by\nhis elaboration of the theory of Natural Selection, which Alfred Russel\nWallace independently stated at the same time, and of which there had\nbeen a few previous suggestions of a more or less vague description.\nIt was here that Darwin's originality was greatest, for he revealed to\nnaturalists the many different forms--often very subtle--which natural\nselection takes, and with the insight of a disciplined scientific\nimagination he realised what a mighty engine of progress it has been and\nis.\n\n(IV) As an epoch-marking contribution, not only to Aetiology but to\nNatural History in the widest sense, we rank the picture which\nDarwin gave to the world of the web of life, that is to say, of\nthe inter-relations and linkages in Nature. For the Biology of the\nindividual--if that be not a contradiction in terms--no idea is more\nfundamental than that of the correlation of organs, but Darwin's most\ncharacteristic contribution was not less fundamental,--it was the idea\nof the correlation of organisms. This, again, was not novel; we find\nit in the works of naturalist like Christian Conrad Sprengel, Gilbert\nWhite, and Alexander von Humboldt, but the realisation of its full\nimport was distinctively Darwinian.\n\nAS REGARDS THE GENERAL IDEA OF ORGANIC EVOLUTION.\n\nWhile it is true, as Prof. H.F. Osborn puts it, that \"'Before and after\nDarwin' will always be the ante et post urbem conditam of biological\nhistory,\" it is also true that the general idea of organic evolution\nis very ancient. In his admirable sketch \"From the Greeks to Darwin\"\n(\"Columbia University Biological Series\", Vol. I. New York and London,\n1894. We must acknowledge our great indebtness to this fine piece of\nwork.), Prof. Osborn has shown that several of the ancient philosophers\nlooked upon Nature as a gradual development and as still in process of\nchange. In the suggestions of Empedocles, to take the best instance,\nthere were \"four sparks of truth,--first, that the development of life\nwas a gradual process; second, that plants were evolved before animals;\nthird, that imperfect forms were gradually replaced (not succeeded)\nby perfect forms; fourth, that the natural cause of the production of\nperfect forms was the extinction of the imperfect.\" (Op. cit. page\n41.) But the fundamental idea of one stage giving origin to another was\nabsent. As the blue Aegean teemed with treasures of beauty and threw\nmany upon its shores, so did Nature produce like a fertile artist what\nhad to be rejected as well as what was able to survive, but the idea of\none species emerging out of another was not yet conceived.\n\nAristotle's views of Nature (See G.J. Romanes, \"Aristotle as a\nNaturalist\", \"Contemporary Review\", Vol. LIX. page 275, 1891; G. Pouchet\n\"La Biologie Aristotelique\", Paris, 1885; E. Zeller, \"A History of\nGreek Philosophy\", London, 1881, and \"Ueber die griechischen Vorganger\nDarwin's\", \"Abhandl. Berlin Akad.\" 1878, pages 111-124.) seem to have\nbeen more definitely evolutionist than those of his predecessors, in\nthis sense, at least, that he recognised not only an ascending scale,\nbut a genetic series from polyp to man and an age-long movement towards\nperfection. \"It is due to the resistance of matter to form that Nature\ncan only rise by degrees from lower to higher types.\" \"Nature produces\nthose things which, being continually moved by a certain principle\ncontained in themselves, arrive at a certain end.\"\n\nTo discern the outcrop of evolution-doctrine in the long interval\nbetween Aristotle and Bacon seems to be very difficult, and some of\nthe instances that have been cited strike one as forced. Epicurus and\nLucretius, often called poets of evolution, both pictured animals as\narising directly out of the earth, very much as Milton's lion long\nafterwards pawed its way out. Even when we come to Bruno who wrote that\n\"to the sound of the harp of the Universal Apollo (the World Spirit),\nthe lower organisms are called by stages to higher, and the lower stages\nare connected by intermediate forms with the higher,\" there is great\nroom, as Prof. Osborn points out (op. cit. page 81.), for difference of\nopinion as to how far he was an evolutionist in our sense of the term.\n\nThe awakening of natural science in the sixteenth century brought the\npossibility of a concrete evolution theory nearer, and in the early\nseventeenth century we find evidences of a new spirit--in the embryology\nof Harvey and the classifications of Ray. Besides sober naturalists\nthere were speculative dreamers in the sixteenth and seventeenth\ncenturies who had at least got beyond static formulae, but, as Professor\nOsborn points out (op. cit. page 87.), \"it is a very striking fact, that\nthe basis of our modern methods of studying the Evolution problem was\nestablished not by the early naturalists nor by the speculative writers,\nbut by the Philosophers.\" He refers to Bacon, Descartes, Leibnitz, Hume,\nKant, Lessing, Herder, and Schelling. \"They alone were upon the main\ntrack of modern thought. It is evident that they were groping in the\ndark for a working theory of the Evolution of life, and it is remarkable\nthat they clearly perceived from the outset that the point to which\nobservation should be directed was not the past but the present\nmutability of species, and further, that this mutability was simply the\nvariation of individuals on an extended scale.\"\n\nBacon seems to have been one of the first to think definitely about the\nmutability of species, and he was far ahead of his age in his suggestion\nof what we now call a Station of Experimental Evolution. Leibnitz\ndiscusses in so many words how the species of animals may be changed\nand how intermediate species may once have linked those that now seem\ndiscontinuous. \"All natural orders of beings present but a single\nchain\"... \"All advances by degrees in Nature, and nothing by leaps.\"\nSimilar evolutionist statements are to be found in the works of the\nother \"philosophers,\" to whom Prof. Osborn refers, who were, indeed,\nmore scientific than the naturalists of their day. It must be borne in\nmind that the general idea of organic evolution--that the present is\nthe child of the past--is in great part just the idea of human history\nprojected upon the natural world, differentiated by the qualification\nthat the continuous \"Becoming\" has been wrought out by forces inherent\nin the organisms themselves and in their environment.\n\nA reference to Kant (See Brock, \"Die Stellung Kant's zur\nDeszendenztheorie,\" \"Biol. Centralbl.\" VIII. 1889, pages 641-648. Fritz\nSchultze, \"Kant und Darwin\", Jena, 1875.) should come in historical\norder after Buffon, with whose writings he was acquainted, but he seems,\nalong with Herder and Schelling, to be best regarded as the culmination\nof the evolutionist philosophers--of those at least who interested\nthemselves in scientific problems. In a famous passage he speaks of\n\"the agreement of so many kinds of animals in a certain common plan of\nstructure\"... an \"analogy of forms\" which \"strengthens the supposition\nthat they have an actual blood-relationship, due to derivation from a\ncommon parent.\" He speaks of \"the great Family of creatures, for as\na Family we must conceive it, if the above-mentioned continuous and\nconnected relationship has a real foundation.\" Prof. Osborn alludes to\nthe scientific caution which led Kant, biology being what it was, to\nrefuse to entertain the hope \"that a Newton may one day arise even to\nmake the production of a blade of grass comprehensible, according\nto natural laws ordained by no intention.\" As Prof. Haeckel finely\nobserves, Darwin rose up as Kant's Newton. (Mr Alfred Russel Wallace\nwrites: \"We claim for Darwin that he is the Newton of natural history,\nand that, just so surely as that the discovery and demonstration by\nNewton of the law of gravitation established order in place of chaos and\nlaid a sure foundation for all future study of the starry heavens, so\nsurely has Darwin, by his discovery of the law of natural selection and\nhis demonstration of the great principle of the preservation of useful\nvariations in the struggle for life, not only thrown a flood of light\non the process of development of the whole organic world, but\nalso established a firm foundation for all future study of nature.\"\n(\"Darwinism\", London, 1889, page 9). See also Prof. Karl Pearson's\n\"Grammar of Science\" (2nd edition), London, 1900, page 32. See Osborn,\nop. cit. Page 100.))\n\nThe scientific renaissance brought a wealth of fresh impressions and\nsome freedom from the tyranny of tradition, and the twofold stimulus\nstirred the speculative activity of a great variety of men from old\nClaude Duret of Moulins, of whose weird transformism (1609) Dr Henry\nde Varigny (\"Experimental Evolution\". London, 1892. Chap. 1. page 14.)\ngives us a glimpse, to Lorenz Oken (1799-1851) whose writings are such\nmixtures of sense and nonsense that some regard him as a\nfar-seeing prophet and others as a fatuous follower of intellectual\nwill-o'-the-wisps. Similarly, for De Maillet, Maupertuis, Diderot,\nBonnet, and others, we must agree with Professor Osborn that they were\nnot actually in the main Evolution movement. Some have been included in\nthe roll of honour on very slender evidence, Robinet for instance, whose\nevolutionism seems to us extremely dubious. (See J. Arthur Thomson,\n\"The Science of Life\". London, 1899. Chap. XVI. \"Evolution of Evolution\nTheory\".)\n\nThe first naturalist to give a broad and concrete expression to the\nevolutionist doctrine of descent was Buffon (1707-1788), but it\nis interesting to recall the fact that his contemporary Linnaeus\n(1707-1778), protagonist of the counter-doctrine of the fixity\nof species (See Carus Sterne (Ernest Krause), \"Die allgemeine\nWeltanschauung in ihrer historischen Entwickelung\". Stuttgart, 1889.\nChapter entitled \"Bestandigkeit oder Veranderlichkeit der Naturwesen\".),\nwent the length of admitting (in 1762) that new species might arise\nby intercrossing. Buffon's position among the pioneers of the\nevolution-doctrine is weakened by his habit of vacillating between his\nown conclusions and the orthodoxy of the Sorbonne, but there is no doubt\nthat he had a firm grasp of the general idea of \"l'enchainement des\netres.\"\n\nErasmus Darwin (1731-1802), probably influenced by Buffon, was another\nfirm evolutionist, and the outline of his argument in the \"Zoonomia\"\n(\"Zoonomia, or the Laws of Organic Life\", 2 vols. London, 1794; Osborn\nop. cit. page 145.) might serve in part at least to-day. \"When we\nrevolve in our minds the metamorphoses of animals, as from the tadpole\nto the frog; secondly, the changes produced by artificial cultivation,\nas in the breeds of horses, dogs, and sheep; thirdly, the changes\nproduced by conditions of climate and of season, as in the sheep of\nwarm climates being covered with hair instead of wool, and the hares and\npartridges of northern climates becoming white in winter: when,\nfurther, we observe the changes of structure produced by habit, as seen\nespecially in men of different occupations; or the changes produced by\nartificial mutilation and prenatal influences, as in the crossing\nof species and production of monsters; fourth, when we observe the\nessential unity of plan in all warm-blooded animals,--we are led to\nconclude that they have been alike produced from a similar living\nfilament\"... \"From thus meditating upon the minute portion of time in\nwhich many of the above changes have been produced, would it be too bold\nto imagine, in the great length of time since the earth began to exist,\nperhaps millions of years before the commencement of the history of\nmankind, that all warm-blooded animals have arisen from one living\nfilament?\"... \"This idea of the gradual generation of all things seems to\nhave been as familiar to the ancient philosophers as to the modern\nones, and to have given rise to the beautiful hieroglyphic figure of the\nproton oon, or first great egg, produced by night, that is, whose origin\nis involved in obscurity, and animated by Eros, that is, by Divine Love;\nfrom whence proceeded all things which exist.\"\n\nLamarck (1744-1829) seems to have become an evolutionist independently\nof Erasmus Darwin's influence, though the parallelism between them is\nstriking. He probably owed something to Buffon, but he developed his\ntheory along a different line. Whatever view be held in regard to that\ntheory there is no doubt that Lamarck was a thorough-going evolutionist.\nProfessor Haeckel speaks of the \"Philosophie Zoologique\" as \"the first\nconnected and thoroughly logical exposition of the theory of descent.\"\n(See Alpheus S. Packard, \"Lamarck, the Founder of Evolution, His Life\nand Work, with Translations of his writings on Organic Evolution\".\nLondon, 1901.)\n\nBesides the three old masters, as we may call them, Buffon, Erasmus\nDarwin, and Lamarck, there were other quite convinced pre-Darwinian\nevolutionists. The historian of the theory of descent must take account\nof Treviranus whose \"Biology or Philosophy of Animate Nature\" is full of\nevolutionary suggestions; of Etienne Geoffroy St Hilaire, who in\n1830, before the French Academy of Sciences, fought with Cuvier, the\nfellow-worker of his youth, an intellectual duel on the question of\ndescent; of Goethe, one of the founders of morphology and the greatest\npoet of Evolution--who, in his eighty-first year, heard the tidings\nof Geoffroy St Hilaire's defeat with an interest which transcended the\npolitical anxieties of the time; and of many others who had gained with\nmore or less confidence and clearness a new outlook on Nature. It\nwill be remembered that Darwin refers to thirty-four more or less\nevolutionist authors in his Historical Sketch, and the list might be\nadded to. Especially when we come near to 1858 do the numbers increase,\nand one of the most remarkable, as also most independent champions of\nthe evolution-idea before that date was Herbert Spencer, who not only\nmarshalled the arguments in a very forcible way in 1852, but applied the\nformula in detail in his \"Principles of Psychology\" in 1855. (See Edward\nClodd, \"Pioneers of Evolution\", London, page 161, 1897.)\n\nIt is right and proper that we should shake ourselves free from all\ncreationist appreciations of Darwin, and that we should recognise the\nservices of pre-Darwinian evolutionists who helped to make the time\nripe, yet one cannot help feeling that the citation of them is apt to\nsuggest two fallacies. It may suggest that Darwin simply entered into\nthe labours of his predecessors, whereas, as a matter of fact, he knew\nvery little about them till after he had been for years at work. To\nwrite, as Samuel Butler did, \"Buffon planted, Erasmus Darwin and Lamarck\nwatered, but it was Mr Darwin who said 'That fruit is ripe,' and shook\nit into his lap\"... seems to us a quite misleading version of the facts\nof the case. The second fallacy which the historical citation is\na little apt to suggest is that the filiation of ideas is a simple\nproblem. On the contrary, the history of an idea, like the pedigree\nof an organism, is often very intricate, and the evolution of the\nevolution-idea is bound up with the whole progress of the world. Thus\nin order to interpret Darwin's clear formulation of the idea of organic\nevolution and his convincing presentation of it, we have to do more than\ngo back to his immediate predecessors, such as Buffon, Erasmus Darwin,\nand Lamarck; we have to inquire into the acceptance of evolutionary\nconceptions in regard to other orders of facts, such as the earth and\nthe solar system (See Chapter IX. \"The Genetic View of Nature\" in J.T.\nMerz's \"History of European Thought in the Nineteenth Century\", Vol. 2,\nEdinburgh and London, 1903.); we have to realise how the growing success\nof scientific interpretation along other lines gave confidence to those\nwho refused to admit that there was any domain from which science could\nbe excluded as a trespasser; we have to take account of the development\nof philosophical thought, and even of theological and religious\nmovements; we should also, if we are wise enough, consider social\nchanges. In short, we must abandon the idea that we can understand\nthe history of any science as such, without reference to contemporary\nevolution in other departments of activity.\n\nWhile there were many evolutionists before Darwin, few of them were\nexpert naturalists and few were known outside a small circle; what\nwas of much more importance was that the genetic view of nature was\ninsinuating itself in regard to other than biological orders of facts,\nhere a little and there a little, and that the scientific spirit had\nripened since the days when Cuvier laughed Lamarck out of court. How was\nit that Darwin succeeded where others had failed? Because, in the first\nplace, he had clear visions--\"pensees de la jeunesse, executees par\nl'age mur\"--which a University curriculum had not made impossible, which\nthe \"Beagle\" voyage made vivid, which an unrivalled British doggedness\nmade real--visions of the web of life, of the fountain of change within\nthe organism, of the struggle for existence and its winnowing, and of\nthe spreading genealogical tree. Because, in the second place, he put\nso much grit into the verification of his visions, putting them to the\nproof in an argument which is of its kind--direct demonstration being\nout of the question--quite unequalled. Because, in the third place,\nhe broke down the opposition which the most scientific had felt to\nthe seductive modal formula of evolution by bringing forward a more\nplausible theory of the process than had been previously suggested.\nNor can one forget, since questions of this magnitude are human and not\nmerely academic, that he wrote so that all men could understand.\n\nAS REGARDS THE FACTORS OF EVOLUTION.\n\nIt is admitted by all who are acquainted with the history of biology\nthat the general idea of organic evolution as expressed in the Doctrine\nof Descent was quite familiar to Darwin's grandfather, and to others\nbefore and after him, as we have briefly indicated. It must also be\nadmitted that some of these pioneers of evolutionism did more than apply\nthe evolution-idea as a modal formula of becoming, they began to inquire\ninto the factors in the process. Thus there were pre-Darwinian theories\nof evolution, and to these we must now briefly refer. (See Prof. W.A.\nLocy's \"Biology and its Makers\". New York, 1908. Part II. \"The Doctrine\nof Organic Evolution\".)\n\nIn all biological thinking we have to work with the categories\nOrganism--Function--Environment, and theories of evolution may be\nclassified in relation to these. To some it has always seemed that the\nfundamental fact is the living organism,--a creative agent, a striving\nwill, a changeful Proteus, selecting its environment, adjusting\nitself to it, self-differentiating and self-adaptive. The necessity of\nrecognising the importance of the organism is admitted by all Darwinians\nwho start with inborn variations, but it is open to question whether the\nwhole truth of what we might call the Goethian position is exhausted in\nthe postulate of inherent variability.\n\nTo others it has always seemed that the emphasis should be laid on\nFunction,--on use and disuse, on doing and not doing. Practice makes\nperfect; c'est a force de forger qu'on devient forgeron. This is one of\nthe fundamental ideas of Lamarckism; to some extent it met with Darwin's\napproval; and it finds many supporters to-day. One of the ablest\nof these--Mr Francis Darwin--has recently given strong reasons for\ncombining a modernised Lamarckism with what we usually regard as sound\nDarwinism. (Presidential Address to the British Association meeting at\nDublin in 1908.)\n\nTo others it has always seemed that the emphasis should be laid on the\nEnvironment, which wakes the organism to action, prompts it to change,\nmakes dints upon it, moulds it, prunes it, and finally, perhaps, kills\nit. It is again impossible to doubt that there is truth in this\nview, for even if environmentally induced \"modifications\" be not\ntransmissible, environmentally induced \"variations\" are; and even if\nthe direct influence of the environment be less important than\nmany enthusiastic supporters of this view--may we call them\nBuffonians--think, there remains the indirect influence which Darwinians\nin part rely on,--the eliminative process. Even if the extreme view\nbe held that the only form of discriminate elimination that counts is\ninter-organismal competition, this might be included under the rubric of\nthe animate environment.\n\nIn many passages Buffon (See in particular Samuel Butler, \"Evolution\nOld and New\", London, 1879; J.L. de Lanessan, \"Buffon et Darwin\",\n\"Revue Scientifique\", XLIII. pages 385-391, 425-432, 1889.) definitely\nsuggested that environmental influences--especially of climate and\nfood--were directly productive of changes in organisms, but he did not\ndiscuss the question of the transmissibility of the modifications so\ninduced, and it is difficult to gather from his inconsistent writings\nwhat extent of transformation he really believed in. Prof. Osborn\nsays of Buffon: \"The struggle for existence, the elimination of the\nleast-perfected species, the contest between the fecundity of certain\nspecies and their constant destruction, are all clearly expressed in\nvarious passages.\" He quotes two of these (op. cit. page 136.):\n\n\"Le cours ordinaire de la nature vivante, est en general toujours\nconstant, toujours le meme; son mouvement, toujours regulier, roule\nsur deux points inebranlables: l'un, la fecondite sans bornes donnee\na toutes les especes; l'autre, les obstacles sans nombre qui reduisent\ncette fecondite a une mesure determinee et ne laissent en tout temps\nqu'a peu pres la meme quantite d'individus de chaque espece\"... \"Les\nespeces les moins parfaites, les plus delicates, les plus pesantes,\nles moins agissantes, les moins armees, etc., ont deja disparu ou\ndisparaitront.\"\n\nErasmus Darwin (See Ernst Krause and Charles Darwin, \"Erasmus Darwin\",\nLondon, 1879.) had a firm grip of the \"idea of the gradual formation and\nimprovement of the Animal world,\" and he had his theory of the process.\nNo sentence is more characteristic than this: \"All animals undergo\ntransformations which are in part produced by their own exertions, in\nresponse to pleasures and pains, and many of these acquired forms or\npropensities are transmitted to their posterity.\" This is Lamarckism\nbefore Lamarck, as his grandson pointed out. His central idea is that\nwants stimulate efforts and that these result in improvements, which\nsubsequent generations make better still. He realised something of the\nstruggle for existence and even pointed out that this advantageously\nchecks the rapid multiplication. \"As Dr Krause points out, Darwin just\nmisses the connection between this struggle and the Survival of the\nFittest.\" (Osborn op. cit. page 142.)\n\nLamarck (1744-1829) (See E. Perrier \"La Philosophie Zoologique avant\nDarwin\", Paris, 1884; A. de Quatrefages, \"Darwin et ses Precurseurs\nFrancais\", Paris, 1870; Packard op. cit.; also Claus, \"Lamarck als\nBegrunder der Descendenzlehre\", Wien, 1888; Haeckel, \"Natural History\nof Creation\", English translation London, 1879; Lang \"Zur Charakteristik\nder Forschungswege von Lamarck und Darwin\", Jena, 1889.) seems to have\nthought out his theory of evolution without any knowledge of Erasmus\nDarwin's which it closely resembled. The central idea of his theory\nwas the cumulative inheritance of functional modifications. \"Changes\nin environment bring about changes in the habits of animals. Changes in\ntheir wants necessarily bring about parallel changes in their habits. If\nnew wants become constant or very lasting, they form new habits, the new\nhabits involve the use of new parts, or a different use of old\nparts, which results finally in the production of new organs and the\nmodification of old ones.\" He differed from Buffon in not attaching\nimportance, as far as animals are concerned, to the direct influence of\nthe environment, \"for environment can effect no direct change whatever\nupon the organisation of animals,\" but in regard to plants he agreed\nwith Buffon that external conditions directly moulded them.\n\nTreviranus (1776-1837) (See Huxley's article \"Evolution in Biology\",\n\"Encyclopaedia Britannica\" (9th edit.), 1878, pages 744-751, and Sully's\narticle, \"Evolution in Philosophy\", ibid. pages 751-772.), whom Huxley\nranked beside Lamarck, was on the whole Buffonian, attaching chief\nimportance to the influence of a changeful environment both in modifying\nand in eliminating, but he was also Goethian, for instance in his idea\nthat species like individuals pass through periods of growth, full\nbloom, and decline. \"Thus, it is not only the great catastrophes of\nNature which have caused extinction, but the completion of cycles\nof existence, out of which new cycles have begun.\" A characteristic\nsentence is quoted by Prof. Osborn: \"In every living being there exists\na capability of an endless variety of form-assumption; each possesses\nthe power to adapt its organisation to the changes of the outer world,\nand it is this power, put into action by the change of the universe,\nthat has raised the simple zoophytes of the primitive world to\ncontinually higher stages of organisation, and has introduced a\ncountless variety of species into animate Nature.\"\n\nGoethe (1749-1832) (See Haeckel, \"Die Naturanschauung von Darwin, Goethe\nund Lamarck\", Jena, 1882.), who knew Buffon's work but not Lamarck's, is\npeculiarly interesting as one of the first to use the evolution-idea as\na guiding hypothesis, e.g. in the interpretation of vestigial structures\nin man, and to realise that organisms express an attempt to make a\ncompromise between specific inertia and individual change. He gave the\nfinest expression that science has yet known--if it has known it--of\nthe kernel-idea of what is called \"bathmism,\" the idea of an \"inherent\ngrowth-force\"--and at the same time he held that \"the way of life\npowerfully reacts upon all form\" and that the orderly growth of form\n\"yields to change from externally acting causes.\"\n\nBesides Buffon, Erasmus Darwin, Lamarck, Treviranus, and Goethe,\nthere were other \"pioneers of evolution,\" whose views have been often\ndiscussed and appraised. Etienne Geoffroy Saint-Hilaire (1772-1844),\nwhose work Goethe so much admired, was on the whole Buffonian,\nemphasising the direct action of the changeful milieu. \"Species\nvary with their environment, and existing species have descended by\nmodification from earlier and somewhat simpler species.\" He had a\nglimpse of the selection idea, and believed in mutations or sudden\nleaps--induced in the embryonic condition by external influences. The\ncomplete history of evolution-theories will include many instances\nof guesses at truth which were afterwards substantiated, thus the\ngeographer von Buch (1773-1853) detected the importance of the Isolation\nfactor on which Wagner, Romanes, Gulick and others have laid great\nstress, but we must content ourselves with recalling one other pioneer,\nthe author of the \"Vestiges of Creation\" (1844), a work which passed\nthrough ten editions in nine years and certainly helped to harrow the\nsoil for Darwin's sowing. As Darwin said, \"it did excellent service in\nthis country in calling attention to the subject, in removing prejudice,\nand in thus preparing the ground for the reception of analogous views.\"\n(\"Origin of Species\" (6th edition), page xvii.) Its author, Robert\nChambers (1802-1871) was in part a Buffonian--maintaining\nthat environment moulded organisms adaptively, and in part a\nGoethian--believing in an inherent progressive impulse which lifted\norganisms from one grade of organisation to another.\n\nAS REGARDS NATURAL SELECTION.\n\nThe only thinker to whom Darwin was directly indebted, so far as the\ntheory of Natural Selection is concerned, was Malthus, and we may once\nmore quote the well-known passage in the Autobiography: \"In October,\n1838, that is, fifteen months after I had begun my systematic enquiry,\nI happened to read for amusement 'Malthus on Population', and being well\nprepared to appreciate the struggle for existence which everywhere goes\non from long-continued observation of the habits of animals and\nplants, it at once struck me that under these circumstances favourable\nvariations would tend to be preserved, and unfavourable ones to be\ndestroyed. The result of this would be the formation of new species.\"\n(\"The Life and Letters of Charles Darwin\", Vol. 1. page 83. London,\n1887.)\n\nAlthough Malthus gives no adumbration of the idea of Natural Selection\nin his exposition of the eliminative processes which go on in mankind,\nthe suggestive value of his essay is undeniable, as is strikingly\nborne out by the fact that it gave to Alfred Russel Wallace also \"the\nlong-sought clue to the effective agent in the evolution of organic\nspecies.\" (A.R. Wallace, \"My Life, A Record of Events and Opinions\",\nLondon, 1905, Vol. 1. page 232.) One day in Ternate when he was resting\nbetween fits of fever, something brought to his recollection the work of\nMalthus which he had read twelve years before. \"I thought of his clear\nexposition of 'the positive checks to increase'--disease, accidents,\nwar, and famine--which keep down the population of savage races to\nso much lower an average than that of more civilized peoples. It then\noccurred to me that these causes or their equivalents are continually\nacting in the case of animals also; and as animals usually breed much\nmore rapidly than does mankind, the destruction every year from these\ncauses must be enormous in order to keep down the numbers of each\nspecies, since they evidently do not increase regularly from year to\nyear, as otherwise the world would long ago have been densely crowded\nwith those that breed most quickly. Vaguely thinking over the enormous\nand constant destruction which this implied, it occurred to me to ask\nthe question, Why do some die and some live? And the answer was clearly,\nthat on the whole the best fitted live. From the effects of disease the\nmost healthy escaped; from enemies the strongest, the swiftest, or\nthe most cunning; from famine the best hunters or those with the\nbest digestion; and so on. Then it suddenly flashed upon me that this\nself-acting process would necessarily IMPROVE THE RACE, because in every\ngeneration the inferior would inevitably be killed off and the superior\nwould remain--that is, THE FITTEST WOULD SURVIVE.\" (Ibid. Vol. 1. page\n361.) We need not apologise for this long quotation, it is a tribute\nto Darwin's magnanimous colleague, the Nestor of the evolutionist\ncamp,--and it probably indicates the line of thought which Darwin\nhimself followed. It is interesting also to recall the fact that in\n1852, when Herbert Spencer wrote his famous \"Leader\" article on \"The\nDevelopment Hypothesis\" in which he argued powerfully for the thesis\nthat the whole animate world is the result of an age-long process of\nnatural transformation, he wrote for \"The Westminster Review\" another\nimportant essay, \"A Theory of Population deduced from the General Law of\nAnimal Fertility\", towards the close of which he came within an ace\nof recognising that the struggle for existence was a factor in organic\nevolution. At a time when pressure of population was practically\ninteresting men's minds, Darwin, Wallace, and Spencer were being\nindependently led from a social problem to a biological theory. There\ncould be no better illustration, as Prof. Patrick Geddes has pointed\nout, of the Comtian thesis that science is a \"social phenomenon.\"\n\nTherefore, as far more important than any further ferreting out of vague\nhints of Natural Selection in books which Darwin never read, we would\nindicate by a quotation the view that the central idea in Darwinism\nis correlated with contemporary social evolution. \"The substitution\nof Darwin for Paley as the chief interpreter of the order of nature is\ncurrently regarded as the displacement of an anthropomorphic view by a\npurely scientific one: a little reflection, however, will show that\nwhat has actually happened has been merely the replacement of the\nanthropomorphism of the eighteenth century by that of the nineteenth.\nFor the place vacated by Paley's theological and metaphysical\nexplanation has simply been occupied by that suggested to Darwin and\nWallace by Malthus in terms of the prevalent severity of industrial\ncompetition, and those phenomena of the struggle for existence which the\nlight of contemporary economic theory has enabled us to discern, have\nthus come to be temporarily exalted into a complete explanation\nof organic progress.\" (P. Geddes, article \"Biology\", \"Chambers's\nEncyclopaedia\".) It goes without saying that the idea suggested by\nMalthus was developed by Darwin into a biological theory which was then\npainstakingly verified by being used as an interpretative formula, and\nthat the validity of a theory so established is not affected by what\nsuggested it, but the practical question which this line of thought\nraises in the mind is this: if Biology did thus borrow with such\nsplendid results from social theory, why should we not more deliberately\nrepeat the experiment?\n\nDarwin was characteristically frank and generous in admitting that the\nprinciple of Natural Selection had been independently recognised by\nDr W.C. Wells in 1813 and by Mr Patrick Matthew in 1831, but he had no\nknowledge of these anticipations when he published the first edition\nof \"The Origin of Species\". Wells, whose \"Essay on Dew\" is still\nremembered, read in 1813 before the Royal Society a short paper entitled\n\"An account of a White Female, part of whose skin resembles that of a\nNegro\" (published in 1818). In this communication, as Darwin said, \"he\nobserves, firstly, that all animals tend to vary in some degree, and,\nsecondly, that agriculturists improve their domesticated animals by\nselection; and then, he adds, but what is done in this latter case\n'by art, seems to be done with equal efficacy, though more slowly, by\nnature, in the formation of varieties of mankind, fitted for the country\nwhich they inhabit.'\" (\"Origin of Species\" (6th edition) page xv.)\nThus Wells had the clear idea of survival dependent upon a favourable\nvariation, but he makes no more use of the idea and applies it only\nto man. There is not in the paper the least hint that the author ever\nthought of generalising the remarkable sentence quoted above.\n\nOf Mr Patrick Matthew, who buried his treasure in an appendix to a work\non \"Naval Timber and Arboriculture\", Darwin said that \"he clearly saw\nthe full force of the principle of natural selection.\" In 1860 Darwin\nwrote--very characteristically--about this to Lyell: \"Mr Patrick\nMatthew publishes a long extract from his work on \"Naval Timber and\nArboriculture\", published in 1831, in which he briefly but completely\nanticipates the theory of Natural Selection. I have ordered the book,\nas some passages are rather obscure, but it is certainly, I think, a\ncomplete but not developed anticipation. Erasmus always said that surely\nthis would be shown to be the case some day. Anyhow, one may be excused\nin not having discovered the fact in a work on Naval Timber.\" (\"Life and\nLetters\" II. page 301.)\n\nDe Quatrefages and De Varigny have maintained that the botanist Naudin\nstated the theory of evolution by natural selection in 1852. He explains\nvery clearly the process of artificial selection, and says that in the\ngarden we are following Nature's method. \"We do not think that Nature\nhas made her species in a different fashion from that in which we\nproceed ourselves in order to make our variations.\" But, as Darwin said,\n\"he does not show how selection acts under nature.\" Similarly it must\nbe noted in regard to several pre-Darwinian pictures of the struggle\nfor existence (such as Herder's, who wrote in 1790 \"All is in\nstruggle... each one for himself\" and so on), that a recognition of this\nis only the first step in Darwinism.\n\nProfs. E. Perrier and H.F. Osborn have called attention to a remarkable\nanticipation of the selection-idea which is to be found in the\nspeculations of Etienne Geoffroy St Hilaire (1825-1828) on the evolution\nof modern Crocodilians from the ancient Teleosaurs. Changing environment\ninduced changes in the respiratory system and far-reaching consequences\nfollowed. The atmosphere, acting upon the pulmonary cells, brings about\n\"modifications which are favourable or destructive ('funestes'); these\nare inherited, and they influence all the rest of the organisation of\nthe animal because if these modifications lead to injurious effects,\nthe animals which exhibit them perish and are replaced by others of a\nsomewhat different form, a form changed so as to be adapted to (a la\nconvenance) the new environment.\"\n\nProf. E.B. Poulton (\"Science Progress\", New Series, Vol. I. 1897. \"A\nRemarkable Anticipation of Modern Views on Evolution\". See also\nChap. VI. in \"Essays on Evolution\", Oxford, 1908.) has shown that the\nanthropologist James Cowles Prichard (1786-1848) must be included, even\nin spite of himself, among the precursors of Darwin. In some passages\nof the second edition of his \"Researches into the Physical History of\nMankind\" (1826), he certainly talks evolution and anticipates Prof.\nWeismann in denying the transmission of acquired characters. He is,\nhowever, sadly self-contradictory and his evolutionism weakens in\nsubsequent editions--the only ones that Darwin saw. Prof. Poulton finds\nin Prichard's work a recognition of the operation of Natural Selection.\n\"After enquiring how it is that 'these varieties are developed and\npreserved in connection with particular climates and differences of\nlocal situation,' he gives the following very significant answer: 'One\ncause which tends to maintain this relation is obvious. Individuals and\nfamilies, and even whole colonies, perish and disappear in climates for\nwhich they are, by peculiarity of constitution, not adapted. Of this\nfact proofs have been already mentioned.'\" Mr Francis Darwin and Prof.\nA.C. Seward discuss Prichard's \"anticipations\" in \"More Letters of\nCharles Darwin\", Vol. I. page 43, and come to the conclusion that the\nevolutionary passages are entirely neutralised by others of an opposite\ntrend. There is the same difficulty with Buffon.\n\nHints of the idea of Natural Selection have been detected elsewhere.\nJames Watt (See Prof. Patrick Geddes's article \"Variation and\nSelection\", \"Encyclopaedia Britannica (9th edition) 1888.), for\ninstance, has been reported as one of the anticipators (1851). But we\nneed not prolong the inquiry further, since Darwin did not know of any\nanticipations until after he had published the immortal work of 1859,\nand since none of those who got hold of the idea made any use of it.\nWhat Darwin did was to follow the clue which Malthus gave him, to\nrealise, first by genius and afterwards by patience, how the complex\nand subtle struggle for existence works out a natural selection of\nthose organisms which vary in the direction of fitter adaptation to the\nconditions of their life. So much success attended his application of\nthe Selection-formula that for a time he regarded Natural Selection\nas almost the sole factor in evolution, variations being pre-supposed;\ngradually, however, he came to recognise that there was some validity in\nthe factors which had been emphasized by Lamarck and by Buffon, and in\nhis well-known summing up in the sixth edition of the \"Origin\" he\nsays of the transformation of species: \"This has been effected chiefly\nthrough the natural selection of numerous successive, slight, favourable\nvariations; aided in an important manner by the inherited effects of\nthe use and disuse of parts; and in an unimportant manner, that is, in\nrelation to adaptive structures, whether past or present, by the direct\naction of external conditions, and by variations which seem to us in our\nignorance to arise spontaneously.\"\n\nTo sum up: the idea of organic evolution, older than Aristotle, slowly\ndeveloped from the stage of suggestion to the stage of verification, and\nthe first convincing verification was Darwin's; from being an a priori\nanticipation it has become an interpretation of nature, and Darwin is\nstill the chief interpreter; from being a modal interpretation it has\nadvanced to the rank of a causal theory, the most convincing part of\nwhich men will never cease to call Darwinism.\n\n\n\n\nIII. THE SELECTION THEORY, By August Weismann.\n\nProfessor of Zoology in the University of Freiburg (Baden).\n\n\nI. THE IDEA OF SELECTION.\n\nMany and diverse were the discoveries made by Charles Darwin in the\ncourse of a long and strenuous life, but none of them has had so\nfar-reaching an influence on the science and thought of his time as the\ntheory of selection. I do not believe that the theory of evolution would\nhave made its way so easily and so quickly after Darwin took up the\ncudgels in favour of it, if he had not been able to support it by a\nprinciple which was capable of solving, in a simple manner, the greatest\nriddle that living nature presents to us,--I mean the purposiveness\nof every living form relative to the conditions of its life and its\nmarvellously exact adaptation to these.\n\nEveryone knows that Darwin was not alone in discovering the principle\nof selection, and that the same idea occurred simultaneously and\nindependently to Alfred Russel Wallace. At the memorable meeting of the\nLinnean Society on 1st July, 1858, two papers were read (communicated by\nLyell and Hooker) both setting forth the same idea of selection. One\nwas written by Charles Darwin in Kent, the other by Alfred Wallace\nin Ternate, in the Malay Archipelago. It was a splendid proof of\nthe magnanimity of these two investigators, that they thus, in all\nfriendliness and without envy, united in laying their ideas before a\nscientific tribunal: their names will always shine side by side as two\nof the brightest stars in the scientific sky.\n\nBut it is with Charles Darwin that I am here chiefly concerned, since\nthis paper is intended to aid in the commemoration of the hundredth\nanniversary of his birth.\n\nThe idea of selection set forth by the two naturalists was at the time\nabsolutely new, but it was also so simple that Huxley could say of it\nlater, \"How extremely stupid not to have thought of that.\" As Darwin was\nled to the general doctrine of descent, not through the labours of\nhis predecessors in the early years of the century, but by his own\nobservations, so it was in regard to the principle of selection. He was\nstruck by the innumerable cases of adaptation, as, for instance, that\nof the woodpeckers and tree-frogs to climbing, or the hooks and\nfeather-like appendages of seeds, which aid in the distribution of\nplants, and he said to himself that an explanation of adaptations was\nthe first thing to be sought for in attempting to formulate a theory of\nevolution.\n\nBut since adaptations point to CHANGES which have been undergone by the\nancestral forms of existing species, it is necessary, first of all, to\ninquire how far species in general are VARIABLE. Thus Darwin's attention\nwas directed in the first place to the phenomenon of variability, and\nthe use man has made of this, from very early times, in the breeding of\nhis domesticated animals and cultivated plants. He inquired carefully\nhow breeders set to work, when they wished to modify the structure and\nappearance of a species to their own ends, and it was soon clear to him\nthat SELECTION FOR BREEDING PURPOSES played the chief part.\n\nBut how was it possible that such processes should occur in free\nnature? Who is here the breeder, making the selection, choosing out one\nindividual to bring forth offspring and rejecting others? That was the\nproblem that for a long time remained a riddle to him.\n\nDarwin himself relates how illumination suddenly came to him. He had\nbeen reading, for his own pleasure, Malthus' book on Population, and, as\nhe had long known from numerous observations, that every species gives\nrise to many more descendants than ever attain to maturity, and that,\ntherefore, the greater number of the descendants of a species perish\nwithout reproducing, the idea came to him that the decision as to which\nmember of a species was to perish, and which was to attain to maturity\nand reproduction might not be a matter of chance, but might be\ndetermined by the constitution of the individuals themselves, according\nas they were more or less fitted for survival. With this idea the\nfoundation of the theory of selection was laid.\n\nIn ARTIFICIAL SELECTION the breeder chooses out for pairing only such\nindividuals as possess the character desired by him in a somewhat higher\ndegree than the rest of the race. Some of the descendants inherit this\ncharacter, often in a still higher degree, and if this method be pursued\nthroughout several generations, the race is transformed in respect of\nthat particular character.\n\nNATURAL SELECTION depends on the same three factors as ARTIFICIAL\nSELECTION: on VARIABILITY, INHERITANCE, and SELECTION FOR BREEDING, but\nthis last is here carried out not by a breeder but by what Darwin called\nthe \"struggle for existence.\" This last factor is one of the special\nfeatures of the Darwinian conception of nature. That there are\ncarnivorous animals which take heavy toll in every generation of the\nprogeny of the animals on which they prey, and that there are herbivores\nwhich decimate the plants in every generation had long been known, but\nit is only since Darwin's time that sufficient attention has been paid\nto the facts that, in addition to this regular destruction, there exists\nbetween the members of a species a keen competition for space and food,\nwhich limits multiplication, and that numerous individuals of each\nspecies perish because of unfavourable climatic conditions. The\n\"struggle for existence,\" which Darwin regarded as taking the place\nof the human breeder in free nature, is not a direct struggle between\ncarnivores and their prey, but is the assumed competition for survival\nbetween individuals OF THE SAME species, of which, on an average, only\nthose survive to reproduce which have the greatest power of resistance,\nwhile the others, less favourably constituted, perish early. This\nstruggle is so keen, that, within a limited area, where the conditions\nof life have long remained unchanged, of every species, whatever be the\ndegree of fertility, only two, ON AN AVERAGE, of the descendants of each\npair survive; the others succumb either to enemies, or to disadvantages\nof climate, or to accident. A high degree of fertility is thus not an\nindication of the special success of a species, but of the numerous\ndangers that have attended its evolution. Of the six young brought forth\nby a pair of elephants in the course of their lives only two survive in\na given area; similarly, of the millions of eggs which two thread-worms\nleave behind them only two survive. It is thus possible to estimate the\ndangers which threaten a species by its ratio of elimination, or, since\nthis cannot be done directly, by its fertility.\n\nAlthough a great number of the descendants of each generation fall\nvictims to accident, among those that remain it is still the greater\nor lesser fitness of the organism that determines the \"selection\nfor breeding purposes,\" and it would be incomprehensible if, in this\ncompetition, it were not ultimately, that is, on an average, the best\nequipped which survive, in the sense of living long enough to reproduce.\n\nThus the principle of natural selection is THE SELECTION OF THE BEST FOR\nREPRODUCTION, whether the \"best\" refers to the whole constitution,\nto one or more parts of the organism, or to one or more stages of\ndevelopment. Every organ, every part, every character of an animal,\nfertility and intelligence included, must be improved in this manner,\nand be gradually brought up in the course of generations to its highest\nattainable state of perfection. And not only may improvement of parts\nbe brought about in this way, but new parts and organs may arise,\nsince, through the slow and minute steps of individual or \"fluctuating\"\nvariations, a part may be added here or dropped out there, and thus\nsomething new is produced.\n\nThe principle of selection solved the riddle as to how what was\npurposive could conceivably be brought about without the intervention\nof a directing power, the riddle which animate nature presents to our\nintelligence at every turn, and in face of which the mind of a Kant\ncould find no way out, for he regarded a solution of it as not to be\nhoped for. For, even if we were to assume an evolutionary force that is\ncontinually transforming the most primitive and the simplest forms of\nlife into ever higher forms, and the homogeneity of primitive times into\nthe infinite variety of the present, we should still be unable to infer\nfrom this alone how each of the numberless forms adapted to particular\nconditions of life should have appeared PRECISELY AT THE RIGHT MOMENT\nIN THE HISTORY OF THE EARTH to which their adaptations were appropriate,\nand precisely at the proper place in which all the conditions of life to\nwhich they were adapted occurred: the humming-birds at the same time as\nthe flowers; the trichina at the same time as the pig; the bark-coloured\nmoth at the same time as the oak, and the wasp-like moth at the same\ntime as the wasp which protects it. Without processes of selection we\nshould be obliged to assume a \"pre-established harmony\" after the famous\nLeibnitzian model, by means of which the clock of the evolution of\norganisms is so regulated as to strike in exact synchronism with that of\nthe history of the earth! All forms of life are strictly adapted to the\nconditions of their life, and can persist under these conditions alone.\n\nThere must therefore be an intrinsic connection between the conditions\nand the structural adaptations of the organism, and, SINCE THE\nCONDITIONS OF LIFE CANNOT BE DETERMINED BY THE ANIMAL ITSELF, THE\nADAPTATIONS MUST BE CALLED FORTH BY THE CONDITIONS.\n\nThe selection theory teaches us how this is conceivable, since it\nenables us to understand that there is a continual production of what is\nnon-purposive as well as of what is purposive, but the purposive alone\nsurvives, while the non-purposive perishes in the very act of arising.\nThis is the old wisdom taught long ago by Empedocles.\n\nII. THE LAMARCKIAN PRINCIPLE.\n\nLamarck, as is well known, formulated a definite theory of evolution at\nthe beginning of the nineteenth century, exactly fifty years before\nthe Darwin-Wallace principle of selection was given to the world.\nThis brilliant investigator also endeavoured to support his theory by\ndemonstrating forces which might have brought about the transformations\nof the organic world in the course of the ages. In addition to other\nfactors, he laid special emphasis on the increased or diminished use\nof the parts of the body, assuming that the strengthening or weakening\nwhich takes place from this cause during the individual life, could be\nhanded on to the offspring, and thus intensified and raised to the rank\nof a specific character. Darwin also regarded this LAMARCKIAN PRINCIPLE,\nas it is now generally called, as a factor in evolution, but he was not\nfully convinced of the transmissibility of acquired characters.\n\nAs I have here to deal only with the theory of selection, I need not\ndiscuss the Lamarckian hypothesis, but I must express my opinion that\nthere is room for much doubt as to the cooperation of this principle in\nevolution. Not only is it difficult to imagine how the transmission of\nfunctional modifications could take place, but, up to the present time,\nnotwithstanding the endeavours of many excellent investigators, not\na single actual proof of such inheritance has been brought forward.\nSemon's experiments on plants are, according to the botanist Pfeffer,\nnot to be relied on, and even the recent, beautiful experiments made\nby Dr Kammerer on salamanders, cannot, as I hope to show elsewhere,\nbe regarded as proof, if only because they do not deal at all with\nfunctional modifications, that is, with modifications brought about by\nuse, and it is to these ALONE that the Lamarckian principle refers.\n\nIII. OBJECTIONS TO THE THEORY OF SELECTION.\n\n(a) Saltatory evolution.\n\nThe Darwinian doctrine of evolution depends essentially on THE\nCUMULATIVE AUGMENTATION of minute variations in the direction of\nutility. But can such minute variations, which are undoubtedly\ncontinually appearing among the individuals of the same species,\npossess any selection-value; can they determine which individuals are\nto survive, and which are to succumb; can they be increased by natural\nselection till they attain to the highest development of a purposive\nvariation?\n\nTo many this seems so improbable that they have urged a theory of\nevolution by leaps from species to species. Kolliker, in 1872, compared\nthe evolution of species with the processes which we can observe in the\nindividual life in cases of alternation of generations. But a polyp only\ngives rise to a medusa because it has itself arisen from one, and there\ncan be no question of a medusa ever having arisen suddenly and de\nnovo from a polyp-bud, if only because both forms are adapted in their\nstructure as a whole, and in every detail to the conditions of their\nlife. A sudden origin, in a natural way, of numerous adaptations is\ninconceivable. Even the degeneration of a medusoid from a free-swimming\nanimal to a mere brood-sac (gonophore) is not sudden and saltatory, but\noccurs by imperceptible modifications throughout hundreds of years, as\nwe can learn from the numerous stages of the process of degeneration\npersisting at the same time in different species.\n\nIf, then, the degeneration to a simple brood-sac takes place only by\nvery slow transitions, each stage of which may last for centuries, how\ncould the much more complex ASCENDING evolution possibly have taken\nplace by sudden leaps? I regard this argument as capable of further\nextension, for wherever in nature we come upon degeneration, it is\ntaking place by minute steps and with a slowness that makes it not\ndirectly perceptible, and I believe that this in itself justifies us in\nconcluding that THE SAME MUST BE TRUE OF ASCENDING evolution. But in the\nlatter case the goal can seldom be distinctly recognised while in cases\nof degeneration the starting-point of the process can often be inferred,\nbecause several nearly related species may represent different stages.\n\nIn recent years Bateson in particular has championed the idea of\nsaltatory, or so-called discontinuous evolution, and has collected a\nnumber of cases in which more or less marked variations have suddenly\nappeared. These are taken for the most part from among domesticated\nanimals which have been bred and crossed for a long time, and it is\nhardly to be wondered at that their much mixed and much influenced\ngerm-plasm should, under certain conditions, give rise to remarkable\nphenomena, often indeed producing forms which are strongly suggestive of\nmonstrosities, and which would undoubtedly not survive in free nature,\nunprotected by man. I should regard such cases as due to an intensified\ngerminal selection--though this is to anticipate a little--and from this\npoint of view it cannot be denied that they have a special interest. But\nthey seem to me to have no significance as far as the transformation\nof species is concerned, if only because of the extreme rarity of their\noccurrence.\n\nThere are, however, many variations which have appeared in a sudden and\nsaltatory manner, and some of these Darwin pointed out and discussed\nin detail: the copper beech, the weeping trees, the oak with \"fern-like\nleaves,\" certain garden-flowers, etc. But none of them have persisted in\nfree nature, or evolved into permanent types.\n\nOn the other hand, wherever enduring types have arisen, we find traces\nof a gradual origin by successive stages, even if, at first sight, their\norigin may appear to have been sudden. This is the case with SEASONAL\nDIMORPHISM, the first known cases of which exhibited marked differences\nbetween the two generations, the winter and the summer brood. Take\nfor instance the much discussed and studied form Vanessa (Araschnia)\nlevana-prorsa. Here the differences between the two forms are so great\nand so apparently disconnected, that one might almost believe it to be\na sudden mutation, were it not that old transition-stages can be called\nforth by particular temperatures, and we know other butterflies, as for\ninstance our Garden Whites, in which the differences between the\ntwo generations are not nearly so marked; indeed, they are so little\napparent that they are scarcely likely to be noticed except by experts.\nThus here again there are small initial steps, some of which, indeed,\nmust be regarded as adaptations, such as the green-sprinkled or lightly\ntinted under-surface which gives them a deceptive resemblance to parsley\nor to Cardamine leaves.\n\nEven if saltatory variations do occur, we cannot assume that these HAVE\nEVER LED TO FORMS WHICH ARE CAPABLE OF SURVIVAL UNDER THE CONDITIONS\nOF WILD LIFE. Experience has shown that in plants which have suddenly\nvaried the power of persistence is diminished. Korschinksky attributes\nto them weaknesses of organisation in general; \"they bloom late, ripen\nfew of their seeds, and show great sensitiveness to cold.\" These are not\nthe characters which make for success in the struggle for existence.\n\nWe must briefly refer here to the views--much discussed in the last\ndecade--of H. de Vries, who believes that the roots of transformation\nmust be sought for in SALTATORY VARIATIONS ARISING FROM INTERNAL CAUSES,\nand distinguishes such MUTATIONS, as he has called them, from ordinary\nindividual variations, in that they breed true, that is, with strict\ninbreeding they are handed on pure to the next generation. I have\nelsewhere endeavoured to point out the weaknesses of this theory\n(\"Vortrage uber Descendenztheorie\", Jena, 1904, II. 269. English\nTranslation London, 1904, II. page 317.), and I am the less inclined\nto return to it here that it now appears (See Poulton, \"Essays on\nEvolution\", Oxford, 1908, pages xix-xxii.) that the far-reaching\nconclusions drawn by de Vries from his observations on the Evening\nPrimrose, Oenothera lamarckiana, rest upon a very insecure\nfoundation. The plant from which de Vries saw numerous \"species\"--his\n\"mutations\"--arise was not, as he assumed, a WILD SPECIES that had been\nintroduced to Europe from America, but was probably a hybrid form which\nwas first discovered in the Jardin des Plantes in Paris, and which does\nnot appear to exist anywhere in America as a wild species.\n\nThis gives a severe shock to the \"Mutation theory,\" for the other\nACTUALLY WILD species with which de Vries experimented showed no\n\"mutations\" but yielded only negative results.\n\nThus we come to the conclusion that Darwin (\"Origin of Species\" (6th\nedition), pages 176 et seq.) was right in regarding transformations as\ntaking place by minute steps, which, if useful, are augmented in\nthe course of innumerable generations, because their possessors more\nfrequently survive in the struggle for existence.\n\n(b) SELECTION-VALUE OF THE INITIAL STEPS.\n\nIs it possible that the significant deviations which we know as\n\"individual variations\" can form the beginning of a process of\nselection? Can they decide which is to perish and which to survive? To\nuse a phrase of Romanes, can they have SELECTION-VALUE?\n\nDarwin himself answered this question, and brought together many\nexcellent examples to show that differences, apparently insignificant\nbecause very small, might be of decisive importance for the life of the\npossessor. But it is by no means enough to bring forward cases of this\nkind, for the question is not merely whether finished adaptations have\nselection-value, but whether the first beginnings of these, and whether\nthe small, I might almost say minimal increments, which have led up\nfrom these beginnings to the perfect adaptation, have also had\nselection-value. To this question even one who, like myself, has been\nfor many years a convinced adherent of the theory of selection, can only\nreply: WE MUST ASSUME SO, BUT WE CANNOT PROVE IT IN ANY CASE. It is not\nupon demonstrative evidence that we rely when we champion the doctrine\nof selection as a scientific truth; we base our argument on quite other\ngrounds. Undoubtedly there are many apparently insignificant features,\nwhich can nevertheless be shown to be adaptations--for instance, the\nthickness of the basin-shaped shell of the limpets that live among the\nbreakers on the shore. There can be no doubt that the thickness of these\nshells, combined with their flat form, protects the animals from the\nforce of the waves breaking upon them,--but how have they become so\nthick? What proportion of thickness was sufficient to decide that of two\nvariants of a limpet one should survive, the other be eliminated? We can\nsay nothing more than that we infer from the present state of the shell,\nthat it must have varied in regard to differences in shell-thickness,\nand that these differences must have had selection-value,--no proof\ntherefore, but an assumption which we must show to be convincing.\n\nFor a long time the marvellously complex RADIATE and LATTICE-WORK\nskeletons of Radiolarians were regarded as a mere outflow of \"Nature's\ninfinite wealth of form,\" as an instance of a purely morphological\ncharacter with no biological significance. But recent investigations\nhave shown that these, too, have an adaptive significance (Hacker). The\nsame thing has been shown by Schutt in regard to the lowly unicellular\nplants, the Peridineae, which abound alike on the surface of the ocean\nand in its depths. It has been shown that the long skeletal processes\nwhich grow out from these organisms have significance not merely as a\nsupporting skeleton, but also as an extension of the superficial area,\nwhich increases the contact with the water-particles, and prevents\nthe floating organisms from sinking. It has been established that the\nprocesses are considerably shorter in the colder layers of the ocean,\nand that they may be twelve times as long (Chun, \"Reise der Valdivia\",\nLeipzig, 1904.) in the warmer layers, thus corresponding to the greater\nor smaller amount of friction which takes place in the denser and less\ndense layers of the water.\n\nThe Peridineae of the warmer ocean layers have thus become long-rayed,\nthose of the colder layers short-rayed, not through the direct effect\nof friction on the protoplasm, but through processes of selection, which\nfavoured the longer rays in warm water, since they kept the organism\nafloat, while those with short rays sank and were eliminated. If we put\nthe question as to selection-value in this case, and ask how great\nthe variations in the length of processes must be in order to possess\nselection-value; what can we answer except that these variations must\nhave been minimal, and yet sufficient to prevent too rapid sinking\nand consequent elimination? Yet this very case would give the\nideal opportunity for a mathematical calculation of the minimal\nselection-value, although of course it is not feasible from lack of data\nto carry out the actual calculation.\n\nBut even in organisms of more than microscopic size there must\nfrequently be minute, even microscopic differences which set going the\nprocess of selection, and regulate its progress to the highest possible\nperfection.\n\nMany tropical trees possess thick, leathery leaves, as a protection\nagainst the force of the tropical rain drops. The DIRECT influence\nof the rain cannot be the cause of this power of resistance, for the\nleaves, while they were still thin, would simply have been torn to\npieces. Their toughness must therefore be referred to selection, which\nwould favour the trees with slightly thicker leaves, though we cannot\ncalculate with any exactness how great the first stages of increase in\nthickness must have been. Our hypothesis receives further support from\nthe fact that, in many such trees, the leaves are drawn out into a\nbeak-like prolongation (Stahl and Haberlandt) which facilitates the\nrapid falling off of the rain water, and also from the fact that the\nleaves, while they are still young, hang limply down in bunches which\noffer the least possible resistance to the rain. Thus there are here\nthree adaptations which can only be interpreted as due to selection.\nThe initial stages of these adaptations must undoubtedly have had\nselection-value.\n\nBut even in regard to this case we are reasoning in a circle, not giving\n\"proofs,\" and no one who does not wish to believe in the selection-value\nof the initial stages can be forced to do so. Among the many pieces of\npresumptive evidence a particularly weighty one seems to me to be THE\nSMALLNESS OF THE STEPS OF PROGRESS which we can observe in certain\ncases, as for instance in leaf-imitation among butterflies, and\nin mimicry generally. The resemblance to a leaf, for instance of a\nparticular Kallima, seems to us so close as to be deceptive, and yet we\nfind in another individual, or it may be in many others, a spot added\nwhich increases the resemblance, and which could not have become fixed\nunless the increased deceptiveness so produced had frequently led to\nthe overlooking of its much persecuted possessor. But if we take the\nselection-value of the initial stages for granted, we are confronted\nwith the further question which I myself formulated many years ago: How\ndoes it happen THAT THE NECESSARY BEGINNINGS OF A USEFUL VARIATION ARE\nALWAYS PRESENT? How could insects which live upon or among green leaves\nbecome all green, while those that live on bark become brown? How have\nthe desert animals become yellow and the Arctic animals white? Why were\nthe necessary variations always present? How could the green locust lay\nbrown eggs, or the privet caterpillar develop white and lilac-coloured\nlines on its green skin?\n\nIt is of no use answering to this that the question is wrongly\nformulated (Plate, \"Selektionsprinzip u. Probleme der Artbildung\" (3rd\nedition), Leipzig, 1908.) and that it is the converse that is true; that\nthe process of selection takes place in accordance with the variations\nthat present themselves. This proposition is undeniably true, but so\nalso is another, which apparently negatives it: the variation required\nhas in the majority of cases actually presented itself. Selection cannot\nsolve this contradiction; it does not call forth the useful variation,\nbut simply works upon it. The ultimate reason why one and the same\ninsect should occur in green and in brown, as often happens in\ncaterpillars and locusts, lies in the fact that variations towards brown\npresented themselves, and so also did variations towards green: THE\nKERNEL OF THE RIDDLE LIES IN THE VARYING, and for the present we\ncan only say, that small variations in different directions present\nthemselves in every species. Otherwise so many different kinds of\nvariations could not have arisen. I have endeavoured to explain this\nremarkable fact by means of the intimate processes that must take place\nwithin the germ-plasm, and I shall return to the problem when dealing\nwith \"germinal selection.\"\n\nWe have, however, to make still greater demands on variation, for it\nis not enough that the necessary variation should occur in isolated\nindividuals, because in that case there would be small prospect of its\nbeing preserved, notwithstanding its utility. Darwin at first believed,\nthat even single variations might lead to transformation of the species,\nbut later he became convinced that this was impossible, at least\nwithout the cooperation of other factors, such as isolation and sexual\nselection.\n\nIn the case of the GREEN CATERPILLARS WITH BRIGHT LONGITUDINAL STRIPES,\nnumerous individuals exhibiting this useful variation must have been\nproduced to start with. In all higher, that is, multicellular organisms,\nthe germ-substance is the source of all transmissible variations, and\nthis germ-plasm is not a simple substance but is made up of many primary\nconstituents. The question can therefore be more precisely stated thus:\nHow does it come about that in so many cases the useful variations\npresent themselves in numbers just where they are required, the white\noblique lines in the leaf-caterpillar on the under surface of the body,\nthe accompanying coloured stripes just above them? And, further, how has\nit come about that in grass caterpillars, not oblique but longitudinal\nstripes, which are more effective for concealment among grass and\nplants, have been evolved? And finally, how is it that the same\nHawk-moth caterpillars, which to-day show oblique stripes, possessed\nlongitudinal stripes in Tertiary times? We can read this fact from the\nhistory of their development, and I have before attempted to show\nthe biological significance of this change of colour. (\"Studien\nzur Descendenz-Theorie\" II., \"Die Enstehung der Zeichnung bei den\nSchmetterlings-raupen,\" Leipzig, 1876.)\n\nFor the present I need only draw the conclusion that one and the same\ncaterpillar may exhibit the initial stages of both, and that it depends\non the manner in which these marking elements are INTENSIFIED and\nCOMBINED by natural selection whether whitish longitudinal or oblique\nstripes should result. In this case then the \"useful variations\"\nwere actually \"always there,\" and we see that in the same group of\nLepidoptera, e.g. species of Sphingidae, evolution has occurred in both\ndirections according to whether the form lived among grass or on broad\nleaves with oblique lateral veins, and we can observe even now that the\nspecies with oblique stripes have longitudinal stripes when young, that\nis to say, while the stripes have no biological significance. The white\nplaces in the skin which gave rise, probably first as small spots,\nto this protective marking could be combined in one way or another\naccording to the requirements of the species. They must therefore either\nhave possessed selection-value from the first, or, if this was not\nthe case at their earliest occurrence, there must have been SOME OTHER\nFACTORS which raised them to the point of selection-value. I shall\nreturn to this in discussing germinal selection. But the case may be\nfollowed still farther, and leads us to the same alternative on a still\nmore secure basis.\n\nMany years ago I observed in caterpillars of Smerinthus populi (the\npoplar hawk-moth), which also possess white oblique stripes, that\ncertain individuals showed RED SPOTS above these stripes; these spots\noccurred only on certain segments, and never flowed together to form\ncontinuous stripes. In another species (Smerinthus tiliae) similar\nblood-red spots unite to form a line-like coloured seam in the last\nstage of larval life, while in S. ocellata rust-red spots appear in\nindividual caterpillars, but more rarely than in S. Populi, and they\nshow no tendency to flow together.\n\nThus we have here the origin of a new character, arising from small\nbeginnings, at least in S. tiliae, in which species the coloured stripes\nare a normal specific character. In the other species, S. populi and\nS. ocellata, we find the beginnings of the same variation, in one more\nrarely than in the other, and we can imagine that, in the course of\ntime, in these two species, coloured lines over the oblique stripes will\narise. In any case these spots are the elements of variation, out\nof which coloured lines MAY be evolved, if they are combined in this\ndirection through the agency of natural selection. In S. populi the\nspots are often small, but sometimes it seems as though several had\nunited to form large spots. Whether a process of selection in this\ndirection will arise in S. populi and S. ocellata, or whether it is\nnow going on cannot be determined, since we cannot tell in advance what\nbiological value the marking might have for these two species. It is\nconceivable that the spots may have no selection-value as far as these\nspecies are concerned, and may therefore disappear again in the course\nof phylogeny, or, on the other hand, that they may be changed in another\ndirection, for instance towards imitation of the rust-red fungoid\npatches on poplar and willow leaves. In any case we may regard the\nsmallest spots as the initial stages of variation, the larger as a\ncumulative summation of these. Therefore either these initial stages\nmust already possess selection-value, or, as I said before: THERE MUST\nBE SOME OTHER REASON FOR THEIR CUMULATIVE SUMMATION. I should like to\ngive one more example, in which we can infer, though we cannot directly\nobserve, the initial stages.\n\nAll the Holothurians or sea-cucumbers have in the skin calcareous bodies\nof different forms, usually thick and irregular, which make the\nskin tough and resistant. In a small group of them--the species of\nSynapta--the calcareous bodies occur in the form of delicate anchors of\nmicroscopic size. Up till 1897 these anchors, like many other delicate\nmicroscopic structures, were regarded as curiosities, as natural\nmarvels. But a Swedish observer, Oestergren, has recently shown that\nthey have a biological significance: they serve the footless Synapta as\nauxiliary organs of locomotion, since, when the body swells up in the\nact of creeping, they press firmly with their tips, which are embedded\nin the skin, against the substratum on which the animal creeps, and thus\nprevent slipping backwards. In other Holothurians this slipping is\nmade impossible by the fixing of the tube-feet. The anchors act\nautomatically, sinking their tips towards the ground when the\ncorresponding part of the body thickens, and returning to the original\nposition at an angle of 45 degrees to the upper surface when the part\nbecomes thin again. The arms of the anchor do not lie in the same plane\nas the shaft, and thus the curve of the arms forms the outermost part\nof the anchor, and offers no further resistance to the gliding of the\nanimal. Every detail of the anchor, the curved portion, the little teeth\nat the head, the arms, etc., can be interpreted in the most beautiful\nway, above all the form of the anchor itself, for the two arms prevent\nit from swaying round to the side. The position of the anchors, too, is\ndefinite and significant; they lie obliquely to the longitudinal axis of\nthe animal, and therefore they act alike whether the animal is creeping\nbackwards or forwards. Moreover, the tips would pierce through the skin\nif the anchors lay in the longitudinal direction. Synapta burrows in the\nsand; it first pushes in the thin anterior end, and thickens this again,\nthus enlarging the hole, then the anterior tentacles displace more sand,\nthe body is worked in a little farther, and the process begins anew. In\nthe first act the anchors are passive, but they begin to take an\nactive share in the forward movement when the body is contracted again.\nFrequently the animal retains only the posterior end buried in the sand,\nand then the anchors keep it in position, and make rapid withdrawal\npossible.\n\nThus we have in these apparently random forms of the calcareous bodies,\ncomplex adaptations in which every little detail as to direction, curve,\nand pointing is exactly determined. That they have selection-value in\ntheir present perfected form is beyond all doubt, since the animals\nare enabled by means of them to bore rapidly into the ground and so to\nescape from enemies. We do not know what the initial stages were, but we\ncannot doubt that the little improvements, which occurred as variations\nof the originally simple slimy bodies of the Holothurians, were\npreserved because they already possessed selection-value for the\nSynaptidae. For such minute microscopic structures whose form is so\ndelicately adapted to the role they have to play in the life of the\nanimal, cannot have arisen suddenly and as a whole, and every new\nvariation of the anchor, that is, in the direction of the development\nof the two arms, and every curving of the shaft which prevented the tips\nfrom projecting at the wrong time, in short, every little adaptation\nin the modelling of the anchor must have possessed selection-value. And\nthat such minute changes of form fall within the sphere of fluctuating\nvariations, that is to say, THAT THEY OCCUR is beyond all doubt.\n\nIn many of the Synaptidae the anchors are replaced by calcareous rods\nbent in the form of an S, which are said to act in the same way. Others,\nsuch as those of the genus Ankyroderma, have anchors which project\nconsiderably beyond the skin, and, according to Oestergren, serve \"to\ncatch plant-particles and other substances\" and so mask the animal. Thus\nwe see that in the Synaptidae the thick and irregular calcareous bodies\nof the Holothurians have been modified and transformed in various ways\nin adaptation to the footlessness of these animals, and to the peculiar\nconditions of their life, and we must conclude that the earlier stages\nof these changes presented themselves to the processes of selection in\nthe form of microscopic variations. For it is as impossible to think of\nany origin other than through selection in this case as in the case of\nthe toughness, and the \"drip-tips\" of tropical leaves. And as these\nlast could not have been produced directly by the beating of the heavy\nrain-drops upon them, so the calcareous anchors of Synapta cannot have\nbeen produced directly by the friction of the sand and mud at the bottom\nof the sea, and, since they are parts whose function is PASSIVE the\nLamarckian factor of use and disuse does not come into question. The\nconclusion is unavoidable, that the microscopically small variations of\nthe calcareous bodies in the ancestral forms have been intensified\nand accumulated in a particular direction, till they have led to the\nformation of the anchor. Whether this has taken place by the action\nof natural selection alone, or whether the laws of variation and the\nintimate processes within the germ-plasm have cooperated will become\nclear in the discussion of germinal selection. This whole process of\nadaptation has obviously taken place within the time that has\nelapsed since this group of sea-cucumbers lost their tube-feet, those\ncharacteristic organs of locomotion which occur in no group except the\nEchinoderms, and yet have totally disappeared in the Synaptidae.\nAnd after all what would animals that live in sand and mud do with\ntube-feet?\n\n(c) COADAPTATION.\n\nDarwin pointed out that one of the essential differences between\nartificial and natural selection lies in the fact that the former can\nmodify only a few characters, usually only one at a time, while Nature\npreserves in the struggle for existence all the variations of a species,\nat the same time and in a purely mechanical way, if they possess\nselection-value.\n\nHerbert Spencer, though himself an adherent of the theory of selection,\ndeclared in the beginning of the nineties that in his opinion the range\nof this principle was greatly over-estimated, if the great changes which\nhave taken place in so many organisms in the course of ages are to\nbe interpreted as due to this process of selection alone, since no\ntransformation of any importance can be evolved by itself; it is always\naccompanied by a host of secondary changes. He gives the familiar\nexample of the Giant Stag of the Irish peat, the enormous antlers of\nwhich required not only a much stronger skull cap, but also greater\nstrength of the sinews, muscles, nerves and bones of the whole anterior\nhalf of the animal, if their mass was not to weigh down the animal\naltogether. It is inconceivable, he says, that so many processes of\nselection should take place SIMULTANEOUSLY, and we are therefore\nforced to fall back on the Lamarckian factor of the use and disuse of\nfunctional parts. And how, he asks, could natural selection follow two\nopposite directions of evolution in different parts of the body at the\nsame time, as for instance in the case of the kangaroo, in which the\nforelegs must have become shorter, while the hind legs and the tail were\nbecoming longer and stronger?\n\nSpencer's main object was to substantiate the validity of the Lamarckian\nprinciple, the cooperation of which with selection had been doubted\nby many. And it does seem as though this principle, if it operates\nin nature at all, offers a ready and simple explanation of all such\nsecondary variations. Not only muscles, but nerves, bones, sinews,\nin short all tissues which function actively, increase in strength\nin proportion as they are used, and conversely they decrease when the\nclaims on them diminish. All the parts, therefore, which depend on the\npart that varied first, as for instance the enlarged antlers of the\nIrish Elk, must have been increased or decreased in strength, in exact\nproportion to the claims made upon them,--just as is actually the case.\n\nBut beautiful as this explanation would be, I regard it as untenable,\nbecause it assumes the TRANSMISSIBILITY OF FUNCTIONAL MODIFICATIONS\n(so-called \"acquired\" characters), and this is not only undemonstrable,\nbut is scarcely theoretically conceivable, for the secondary variations\nwhich accompany or follow the first as correlative variations, occur\nalso in cases in which the animals concerned are sterile and THEREFORE\nCANNOT TRANSMIT ANYTHING TO THEIR DESCENDANTS. This is true of WORKER\nBEES, and particularly of ANTS, and I shall here give a brief survey of\nthe present state of the problem as it appears to me.\n\nMuch has been written on both sides of this question since the published\ncontroversy on the subject in the nineties between Herbert Spencer and\nmyself. I should like to return to the matter in detail, if the space\nat my disposal permitted, because it seems to me that the arguments I\nadvanced at that time are equally cogent to-day, notwithstanding all the\nobjections that have since been urged against them. Moreover, the matter\nis by no means one of subordinate interest; it is the very kernel of the\nwhole question of the reality and value of the principle of selection.\nFor if selection alone does not suffice to explain \"HARMONIOUS\nADAPTATION\" as I have called Spencer's COADAPTATION, and if we require\nto call in the aid of the Lamarckian factor it would be questionable\nwhether selection could explain any adaptations whatever. In this\nparticular case--of worker bees--the Lamarckian factor may be excluded\naltogether, for it can be demonstrated that here at any rate the effects\nof use and disuse cannot be transmitted.\n\nBut if it be asked why we are unwilling to admit the cooperation of\nthe Darwinian factor of selection and the Lamarckian factor, since this\nwould afford us an easy and satisfactory explanation of the phenomena,\nI answer: BECAUSE THE LAMARCKIAN PRINCIPLE IS FALLACIOUS, AND BECAUSE BY\nACCEPTING IT WE CLOSE THE WAY TOWARDS DEEPER INSIGHT. It is not a spirit\nof combativeness or a desire for self-vindication that induces me to\ntake the field once more against the Lamarckian principle, it is the\nconviction that the progress of our knowledge is being obstructed by the\nacceptance of this fallacious principle, since the facile explanation it\napparently affords prevents our seeking after a truer explanation and a\ndeeper analysis.\n\nThe workers in the various species of ants are sterile, that is to say,\nthey take no regular part in the reproduction of the species, although\nindividuals among them may occasionally lay eggs. In addition to this\nthey have lost the wings, and the receptaculum seminis, and their\ncompound eyes have degenerated to a few facets. How could this last\nchange have come about through disuse, since the eyes of workers are\nexposed to light in the same way as are those of the sexual insects and\nthus in this particular case are not liable to \"disuse\" at all? The same\nis true of the receptaculum seminis, which can only have been disused\nas far as its glandular portion and its stalk are concerned, and also\nof the wings, the nerves tracheae and epidermal cells of which could\nnot cease to function until the whole wing had degenerated, for the\nchitinous skeleton of the wing does not function at all in the active\nsense.\n\nBut, on the other hand, the workers in all species have undergone\nmodifications in a positive direction, as, for instance, the greater\ndevelopment of brain. In many species large workers have evolved,--the\nso-called SOLDIERS, with enormous jaws and teeth, which defend the\ncolony,--and in others there are SMALL workers which have taken over\nother special functions, such as the rearing of the young Aphides. This\nkind of division of the workers into two castes occurs among several\ntropical species of ants, but it is also present in the Italian species,\nColobopsis truncata. Beautifully as the size of the jaws could be\nexplained as due to the increased use made of them by the \"soldiers,\" or\nthe enlarged brain as due to the mental activities of the workers, the\nfact of the infertility of these forms is an insurmountable obstacle\nto accepting such an explanation. Neither jaws nor brain can have been\nevolved on the Lamarckian principle.\n\nThe problem of coadaptation is no easier in the case of the ant than in\nthe case of the Giant Stag. Darwin himself gave a pretty illustration to\nshow how imposing the difference between the two kinds of workers in one\nspecies would seem if we translated it into human terms. In regard to\nthe Driver ants (Anomma) we must picture to ourselves a piece of work,\n\"for instance the building of a house, being carried on by two kinds of\nworkers, of which one group was five feet four inches high, the other\nsixteen feet high.\" (\"Origin of Species\" (6th edition), page 232.)\n\nAlthough the ant is a small animal as compared with man or with the\nIrish Elk, the \"soldier\" with its relatively enormous jaws is hardly\nless heavily burdened than the Elk with its antlers, and in the ant's\ncase, too, a strengthening of the skeleton, of the muscles, the nerves\nof the head, and of the legs must have taken place parallel with the\nenlargement of the jaws. HARMONIOUS ADAPTATION (coadaptation) has here\nbeen active in a high degree, and yet these \"soldiers\" are sterile!\nThere thus remains nothing for it but to refer all their adaptations,\npositive and negative alike, to processes of selection which have taken\nplace in the rudiments of the workers within the egg and sperm-cells\nof their parents. There is no way out of the difficulty except the one\nDarwin pointed out. He himself did not find the solution of the riddle\nat once. At first he believed that the case of the workers among social\ninsects presented \"the most serious special difficulty\" in the way of\nhis theory of natural selection; and it was only after it had become\nclear to him, that it was not the sterile insects themselves but their\nparents that were selected, according as they produced more or less\nwell adapted workers, that he was able to refer to this very case of the\nconditions among ants \"IN ORDER TO SHOW THE POWER OF NATURAL SELECTION\"\n(\"Origin of Species\", page 233; see also edition 1, page 242.). He\nexplains his view by a simple but interesting illustration. Gardeners\nhave produced, by means of long continued artificial selection, a\nvariety of Stock, which bears entirely double, and therefore infertile\nflowers (Ibid. page 230.). Nevertheless the variety continues to be\nreproduced from seed, because in addition to the double and infertile\nflowers, the seeds always produce a certain number of single, fertile\nblossoms, and these are used to reproduce the double variety. These\nsingle and fertile plants correspond \"to the males and females of an\nant-colony, the infertile plants, which are regularly produced in large\nnumbers, to the neuter workers of the colony.\"\n\nThis illustration is entirely apt, the only difference between the two\ncases consisting in the fact that the variation in the flower is not\na useful, but a disadvantageous one, which can only be preserved\nby artificial selection on the part of the gardener, while the\ntransformations that have taken place parallel with the sterility of the\nants are useful, since they procure for the colony an advantage in the\nstruggle for existence, and they are therefore preserved by\nnatural selection. Even the sterility itself in this case is not\ndisadvantageous, since the fertility of the true females has at the same\ntime considerably increased. We may therefore regard the sterile forms\nof ants, which have gradually been adapted in several directions to\nvarying functions, AS A CERTAIN PROOF that selection really takes place\nin the germ-cells of the fathers and mothers of the workers, and that\nSPECIAL COMPLEXES OF PRIMORDIA (IDS) are present in the workers and in\nthe males and females, and these complexes contain the primordia of the\nindividual parts (DETERMINANTS). But since all living entities vary, the\ndeterminants must also vary, now in a favourable, now in an unfavourable\ndirection. If a female produces eggs, which contain favourably varying\ndeterminants in the worker-ids, then these eggs will give rise to\nworkers modified in the favourable direction, and if this happens with\nmany females, the colony concerned will contain a better kind of worker\nthan other colonies.\n\nI digress here in order to give an account of the intimate processes,\nwhich, according to my view, take place within the germ-plasm, and which\nI have called \"GERMINAL SELECTION.\" These processes are of importance\nsince they form the roots of variation, which in its turn is the root\nof natural selection. I cannot here do more than give a brief outline of\nthe theory in order to show how the Darwin-Wallace theory of selection\nhas gained support from it.\n\nWith others, I regard the minimal amount of substance which is contained\nwithin the nucleus of the germ-cells, in the form of rods, bands, or\ngranules, as the GERM-SUBSTANCE or GERM-PLASM, and I call the individual\ngranules IDS. There is always a multiplicity of such ids present in the\nnucleus, either occurring individually, or united in the form of rods\nor bands (chromosomes). Each id contains the primary constituents of a\nWHOLE individual, so that several ids are concerned in the development\nof a new individual.\n\nIn every being of complex structure thousands of primary constituents\nmust go to make up a single id; these I call DETERMINANTS, and I mean\nby this name very small individual particles, far below the limits of\nmicroscopic visibility, vital units which feed, grow, and multiply\nby division. These determinants control the parts of the developing\nembryo,--in what manner need not here concern us. The determinants\ndiffer among themselves, those of a muscle are differently constituted\nfrom those of a nerve-cell or a glandular cell, etc., and every\ndeterminant is in its turn made up of minute vital units, which I\ncall BIOPHORS, or the bearers of life. According to my view, these\ndeterminants not only assimilate, like every other living unit, but they\nVARY in the course of their growth, as every living unit does; they may\nvary qualitatively if the elements of which they are composed vary, they\nmay grow and divide more or less rapidly, and their variations give rise\nto CORRESPONDING variations of the organ, cell, or cell-group which they\ndetermine. That they are undergoing ceaseless fluctuations in regard to\nsize and quality seems to me the inevitable consequence of their unequal\nnutrition; for although the germ-cell as a whole usually receives\nsufficient nutriment, minute fluctuations in the amount carried to\ndifferent parts within the germ-plasm cannot fail to occur.\n\nNow, if a determinant, for instance of a sensory cell, receives for a\nconsiderable time more abundant nutriment than before, it will grow more\nrapidly--become bigger, and divide more quickly, and, later, when the\nid concerned develops into an embryo, this sensory cell will become\nstronger than in the parents, possibly even twice as strong. This is an\ninstance of a HEREDITARY INDIVIDUAL VARIATION, arising from the germ.\n\nThe nutritive stream which, according to our hypothesis, favours the\ndeterminant N by chance, that is, for reasons unknown to us, may remain\nstrong for a considerable time, or may decrease again; but even in\nthe latter case it is conceivable that the ascending movement of the\ndeterminant may continue, because the strengthened determinant now\nACTIVELY nourishes itself more abundantly,--that is to say, it attracts\nthe nutriment to itself, and to a certain extent withdraws it from its\nfellow-determinants. In this way, it may--as it seems to me--get into\nPERMANENT UPWARD MOVEMENT, AND ATTAIN A DEGREE OF STRENGTH FROM WHICH\nTHERE IS NO FALLING BACK. Then positive or negative selection sets in,\nfavouring the variations which are advantageous, setting aside those\nwhich are disadvantageous.\n\nIn a similar manner a DOWNWARD variation of the determinants may take\nplace, if its progress be started by a diminished flow of nutriment. The\ndeterminants which are weakened by this diminished flow will have less\naffinity for attracting nutriment because of their diminished strength,\nand they will assimilate more feebly and grow more slowly, unless chance\nstreams of nutriment help them to recover themselves. But, as will\npresently be shown, a change of direction cannot take place at EVERY\nstage of the degenerative process. If a certain critical stage of\ndownward progress be passed, even favourable conditions of food-supply\nwill no longer suffice permanently to change the direction of\nthe variation. Only two cases are conceivable; if the determinant\ncorresponds to a USEFUL organ, only its removal can bring back the\ngerm-plasm to its former level; therefore personal selection removes the\nid in question, with its determinants, from the germ-plasm, by causing\nthe elimination of the individual in the struggle for existence. But\nthere is another conceivable case; the determinants concerned may be\nthose of an organ which has become USELESS, and they will then continue\nunobstructed, but with exceeding slowness, along the downward path,\nuntil the organ becomes vestigial, and finally disappears altogether.\n\nThe fluctuations of the determinants hither and thither may thus be\ntransformed into a lasting ascending or descending movement; and THIS IS\nTHE CRUCIAL POINT OF THESE GERMINAL PROCESSES.\n\nThis is not a fantastic assumption; we can read it in the fact of the\ndegeneration of disused parts. USELESS ORGANS ARE THE ONLY ONES WHICH\nARE NOT HELPED TO ASCEND AGAIN BY PERSONAL SELECTION, AND THEREFORE IN\nTHEIR CASE ALONE CAN WE FORM ANY IDEA OF HOW THE PRIMARY CONSTITUENTS\nBEHAVE, WHEN THEY ARE SUBJECT SOLELY TO INTRA-GERMINAL FORCES.\n\nThe whole determinant system of an id, as I conceive it, is in a state\nof continual fluctuation upwards and downwards. In most cases the\nfluctuations will counteract one another, because the passive streams of\nnutriment soon change, but in many cases the limit from which a return\nis possible will be passed, and then the determinants concerned will\ncontinue to vary in the same direction, till they attain positive or\nnegative selection-value. At this stage personal selection intervenes\nand sets aside the variation if it is disadvantageous, or favours--that\nis to say, preserves--it if it is advantageous. Only THE DETERMINANT\nOF A USELESS ORGAN IS UNINFLUENCED BY PERSONAL SELECTION, and,\nas experience shows, it sinks downwards; that is, the organ that\ncorresponds to it degenerates very slowly but uninterruptedly till,\nafter what must obviously be an immense stretch of time, it disappears\nfrom the germ-plasm altogether.\n\nThus we find in the fact of the degeneration of disused parts the proof\nthat not all the fluctuations of a determinant return to equilibrium\nagain, but that, when the movement has attained to a certain strength,\nit continues IN THE SAME DIRECTION. We have entire certainty in regard\nto this as far as the downward progress is concerned, and we must\nassume it also in regard to ascending variations, as the phenomena of\nartificial selection certainly justify us in doing. If the Japanese\nbreeders were able to lengthen the tail feathers of the cock to\nsix feet, it can only have been because the determinants of the\ntail-feathers in the germ-plasm had already struck out a path of\nascending variation, and this movement was taken advantage of by the\nbreeder, who continually selected for reproduction the individuals in\nwhich the ascending variation was most marked. For all breeding depends\nupon the unconscious selection of germinal variations.\n\nOf course these germinal processes cannot be proved mathematically,\nsince we cannot actually see the play of forces of the passive\nfluctuations and their causes. We cannot say how great these\nfluctuations are, and how quickly or slowly, how regularly or\nirregularly they change. Nor do we know how far a determinant must be\nstrengthened by the passive flow of the nutritive stream if it is to\nbe beyond the danger of unfavourable variations, or how far it must be\nweakened passively before it loses the power of recovering itself by its\nown strength. It is no more possible to bring forward actual proofs in\nthis case than it was in regard to the selection-value of the initial\nstages of an adaptation. But if we consider that all heritable\nvariations must have their roots in the germ-plasm, and further, that\nwhen personal selection does not intervene, that is to say, in the case\nof parts which have become useless, a degeneration of the part, and\ntherefore also of its determinant must inevitably take place; then we\nmust conclude that processes such as I have assumed are running their\ncourse within the germ-plasm, and we can do this with as much certainty\nas we were able to infer, from the phenomena of adaptation, the\nselection-value of their initial stages. The fact of the degeneration\nof disused parts seems to me to afford irrefutable proof that the\nfluctuations within the germ-plasm ARE THE REAL ROOT OF ALL HEREDITARY\nVARIATION, and the preliminary condition for the occurrence of the\nDarwin-Wallace factor of selection. Germinal selection supplies the\nstones out of which personal selection builds her temples and\npalaces: ADAPTATIONS. The importance for the theory of the process of\ndegeneration of disused parts cannot be over-estimated, especially when\nit occurs in sterile animal forms, where we are free from the doubt as\nto the alleged LAMARCKIAN FACTOR which is apt to confuse our ideas in\nregard to other cases.\n\nIf we regard the variation of the many determinants concerned in the\ntransformation of the female into the sterile worker as having come\nabout through the gradual transformation of the ids into worker-ids,\nwe shall see that the germ-plasm of the sexual ants must contain three\nkinds of ids, male, female, and worker ids, or if the workers have\ndiverged into soldiers and nest-builders, then four kinds. We understand\nthat the worker-ids arose because their determinants struck out a useful\npath of variation, whether upward or downward, and that they continued\nin this path until the highest attainable degree of utility of the parts\ndetermined was reached. But in addition to the organs of positive or\nnegative selection-value, there were some which were indifferent as far\nas the success and especially the functional capacity of the workers was\nconcerned: wings, ovarian tubes, receptaculum seminis, a number of the\nfacets of the eye, perhaps even the whole eye. As to the ovarian tubes\nit is possible that their degeneration was an advantage for the workers,\nin saving energy, and if so selection would favour the degeneration; but\nhow could the presence of eyes diminish the usefulness of the workers to\nthe colony? or the minute receptaculum seminis, or even the wings? These\nparts have therefore degenerated BECAUSE THEY WERE OF NO FURTHER VALUE\nTO THE INSECT. But if selection did not influence the setting aside of\nthese parts because they were neither of advantage nor of disadvantage\nto the species, then the Darwinian factor of selection is here\nconfronted with a puzzle which it cannot solve alone, but which at once\nbecomes clear when germinal selection is added. For the determinants\nof organs that have no further value for the organism, must, as we have\nalready explained, embark on a gradual course of retrograde development.\n\nIn ants the degeneration has gone so far that there are no\nwing-rudiments present in ANY species, as is the case with so many\nbutterflies, flies, and locusts, but in the larvae the imaginal discs of\nthe wings are still laid down. With regard to the ovaries, degeneration\nhas reached different levels in different species of ants, as has been\nshown by the researches of my former pupil, Elizabeth Bickford. In many\nspecies there are twelve ovarian tubes, and they decrease from that\nnumber to one; indeed, in one species no ovarian tube at all is present.\nSo much at least is certain from what has been said, that in this\ncase EVERYTHING depends on the fluctuations of the elements of the\ngerm-plasm. Germinal selection, here as elsewhere, presents the\nvariations of the determinants, and personal selection favours or\nrejects these, or,--if it be a question of organs which have become\nuseless,--it does not come into play at all, and allows the descending\nvariation free course.\n\nIt is obvious that even the problem of COADAPTATION IN STERILE\nANIMALS can thus be satisfactorily explained. If the determinants are\noscillating upwards and downwards in continual fluctuation, and\nvarying more pronouncedly now in one direction now in the other, useful\nvariations of every determinant will continually present themselves\nanew, and may, in the course of generations, be combined with one\nanother in various ways. But there is one character of the determinants\nthat greatly facilitates this complex process of selection, that,\nafter a certain limit has been reached, they go on varying in the same\ndirection. From this it follows that development along a path once\nstruck out may proceed without the continual intervention of personal\nselection. This factor only operates, so to speak, at the beginning,\nwhen it selects the determinants which are varying in the right\ndirection, and again at the end, when it is necessary to put a check\nupon further variation. In addition to this, enormously long periods\nhave been available for all these adaptations, as the very gradual\ntransition stages between females and workers in many species plainly\nshow, and thus this process of transformation loses the marvellous and\nmysterious character that seemed at the first glance to invest it,\nand takes rank, without any straining, among the other processes of\nselection. It seems to me that, from the facts that sterile animal forms\ncan adapt themselves to new vital functions, their superfluous parts\ndegenerate, and the parts more used adapt themselves in an ascending\ndirection, those less used in a descending direction, we must draw\nthe conclusion that harmonious adaptation here comes about WITHOUT\nTHE COOPERATION OF THE LAMARCKIAN PRINCIPLE. This conclusion once\nestablished, however, we have no reason to refer the thousands of cases\nof harmonious adaptation, which occur in exactly the same way among\nother animals or plants, to a principle, the ACTIVE INTERVENTION OF\nWHICH IN THE TRANSFORMATION OF SPECIES IS NOWHERE PROVED. WE DO NOT\nREQUIRE IT TO EXPLAIN THE FACTS, AND THEREFORE WE MUST NOT ASSUME IT.\n\nThe fact of coadaptation, which was supposed to furnish the strongest\nargument against the principle of selection, in reality yields the\nclearest evidence in favour of it. We MUST assume it, BECAUSE NO OTHER\nPOSSIBILITY OF EXPLANATION IS OPEN TO US, AND BECAUSE THESE ADAPTATIONS\nACTUALLY EXIST, THAT IS TO SAY, HAVE REALLY TAKEN PLACE. With this\nconviction I attempted, as far back as 1894, when the idea of germinal\nselection had not yet occurred to me, to make \"harmonious adaptation\"\n(coadaptation) more easily intelligible in some way or other, and so\nI was led to the idea, which was subsequently expounded in detail by\nBaldwin, and Lloyd Morgan, and also by Osborn, and Gulick as ORGANIC\nSELECTION. It seemed to me that it was not necessary that all the\ngerminal variations required for secondary variations should have\noccurred SIMULTANEOUSLY, since, for instance, in the case of the\nstag, the bones, muscles, sinews, and nerves would be incited by\nthe increasing heaviness of the antlers to greater activity in THE\nINDIVIDUAL LIFE, and so would be strengthened. The antlers can only have\nincreased in size by very slow degrees, so that the muscles and bones\nmay have been able to keep pace with their growth in the individual\nlife, until the requisite germinal variations presented themselves. In\nthis way a disharmony between the increasing weight of the antlers and\nthe parts which support and move them would be avoided, since time would\nbe given for the appropriate germinal variations to occur, and so to set\nagoing the HEREDITARY variation of the muscles, sinews, and bones.\n(\"The Effect of External Influences upon Development\", Romanes Lecture,\nOxford, 1894.)\n\nI still regard this idea as correct, but I attribute less importance\nto \"organic selection\" than I did at that time, in so far that I do\nnot believe that it ALONE could effect complex harmonious adaptations.\nGerminal selection now seems to me to play the chief part in bringing\nabout such adaptations. Something the same is true of the principle\nI have called \"Panmixia\". As I became more and more convinced, in the\ncourse of years, that the LAMARCKIAN PRINCIPLE ought not to be called in\nto explain the dwindling of disused parts, I believed that this process\nmight be simply explained as due to the cessation of the conservative\neffect of natural selection. I said to myself that, from the moment in\nwhich a part ceases to be of use, natural selection withdraws its\nhand from it, and then it must inevitably fall from the height of its\nadaptiveness, because inferior variants would have as good a chance of\npersisting as better ones, since all grades of fitness of the part in\nquestion would be mingled with one another indiscriminately. This is\nundoubtedly true, as Romanes pointed out ten years before I did, and\nthis mingling of the bad with the good probably does bring about a\ndeterioration of the part concerned. But it cannot account for the\nsteady diminution, which always occurs when a part is in process of\nbecoming rudimentary, and which goes on until it ultimately disappears\naltogether. The process of dwindling cannot therefore be explained as\ndue to panmixia alone; we can only find a sufficient explanation in\ngerminal selection.\n\nIV. DERIVATIVES OF THE THEORY OF SELECTION.\n\nThe impetus in all directions given by Darwin through his theory of\nselection has been an immeasurable one, and its influence is still felt.\nIt falls within the province of the historian of science to enumerate\nall the ideas which, in the last quarter of the nineteenth century, grew\nout of Darwin's theories, in the endeavour to penetrate more deeply into\nthe problem of the evolution of the organic world. Within the narrow\nlimits to which this paper is restricted, I cannot attempt to discuss\nany of these.\n\nV. ARGUMENTS FOR THE REALITY OF THE PROCESSES OF SELECTION.\n\n(a) SEXUAL SELECTION.\n\nSexual selection goes hand in hand with natural selection. From the\nvery first I have regarded sexual selection as affording an extremely\nimportant and interesting corroboration of natural selection, but,\nsingularly enough, it is precisely against this theory that an adverse\njudgment has been pronounced in so many quarters, and it is only quite\nrecently, and probably in proportion as the wealth of facts in proof of\nit penetrates into a wider circle, that we seem to be approaching a\nmore general recognition of this side of the problem of adaptation. Thus\nDarwin's words in his preface to the second edition (1874) of his book,\n\"The Descent of Man and Sexual Selection\", are being justified: \"My\nconviction as to the operation of natural selection remains unshaken,\"\nand further, \"If naturalists were to become more familiar with the idea\nof sexual selection, it would, I think, be accepted to a much greater\nextent, and already it is fully and favourably accepted by many\ncompetent judges.\" Darwin was able to speak thus because he was already\nacquainted with an immense mass of facts, which, taken together,\nyield overwhelming evidence of the validity of the principle of sexual\nselection.\n\nNATURAL SELECTION chooses out for reproduction the individuals that are\nbest equipped for the struggle for existence, and it does so at every\nstage of development; it thus improves the species in all its stages and\nforms. SEXUAL SELECTION operates only on individuals that are already\ncapable of reproduction, and does so only in relation to the attainment\nof reproduction. It arises from the rivalry of one sex, usually the\nmale, for the possession of the other, usually the female. Its influence\ncan therefore only DIRECTLY affect one sex, in that it equips it\nbetter for attaining possession of the other. But the effect may\nextend indirectly to the female sex, and thus the whole species may be\nmodified, without, however, becoming any more capable of resistance\nin the struggle for existence, for sexual selection only gives rise to\nadaptations which are likely to give their possessor the victory over\nrivals in the struggle for possession of the female, and which are\ntherefore peculiar to the wooing sex: the manifold \"secondary sexual\ncharacters.\" The diversity of these characters is so great that I cannot\nhere attempt to give anything approaching a complete treatment of them,\nbut I should like to give a sufficient number of examples to make the\nprinciple itself, in its various modes of expression, quite clear.\n\nOne of the chief preliminary postulates of sexual selection is the\nunequal number of individuals in the two sexes, for if every male\nimmediately finds his mate there can be no competition for the\npossession of the female. Darwin has shown that, for the most part, the\ninequality between the sexes is due simply to the fact that there are\nmore males than females, and therefore the males must take some pains\nto secure a mate. But the inequality does not always depend on the\nnumerical preponderance of the males, it is often due to polygamy; for,\nif one male claims several females, the number of females in proportion\nto the rest of the males will be reduced. Since it is almost always\nthe males that are the wooers, we must expect to find the occurrence\nof secondary sexual characters chiefly among them, and to find it\nespecially frequent in polygamous species. And this is actually the\ncase.\n\nIf we were to try to guess--without knowing the facts--what means the\nmale animals make use of to overcome their rivals in the struggle for\nthe possession of the female, we might name many kinds of means, but it\nwould be difficult to suggest any which is not actually employed in some\nanimal group or other. I begin with the mere difference in strength,\nthrough which the male of many animals is so sharply distinguished from\nthe female, as, for instance, the lion, walrus, \"sea-elephant,\" and\nothers. Among these the males fight violently for the possession of the\nfemale, who falls to the victor in the combat. In this simple case no\none can doubt the operation of selection, and there is just as little\nroom for doubt as to the selection-value of the initial stages of the\nvariation. Differences in bodily strength are apparent even among human\nbeings, although in their case the struggle for the possession of the\nfemale is no longer decided by bodily strength alone.\n\nCombats between male animals are often violent and obstinate, and the\nemployment of the natural weapons of the species in this way has led\nto perfecting of these, e.g. the tusks of the boar, the antlers of the\nstag, and the enormous, antler-like jaws of the stag-beetle. Here again\nit is impossible to doubt that variations in these organs presented\nthemselves, and that these were considerable enough to be decisive in\ncombat, and so to lead to the improvement of the weapon.\n\nAmong many animals, however, the females at first withdraw from the\nmales; they are coy, and have to be sought out, and sometimes held by\nforce. This tracking and grasping of the females by the males has given\nrise to many different characters in the latter, as, for instance,\nthe larger eyes of the male bee, and especially of the males of the\nEphemerids (May-flies), some species of which show, in addition to the\nusual compound eyes, large, so-called turban-eyes, so that the whole\nhead is covered with seeing surfaces. In these species the females are\nvery greatly in the minority (1-100), and it is easy to understand that\na keen competition for them must take place, and that, when the insects\nof both sexes are floating freely in the air, an unusually wide range\nof vision will carry with it a decided advantage. Here again the actual\nadaptations are in accordance with the preliminary postulates of the\ntheory. We do not know the stages through which the eye has passed\nto its present perfected state, but, since the number of simple eyes\n(facets) has become very much greater in the male than in the female,\nwe may assume that their increase is due to a gradual duplication of\nthe determinants of the ommatidium in the germ-plasm, as I have already\nindicated in regard to sense-organs in general. In this case, again,\nthe selection-value of the initial stages hardly admits of doubt; better\nvision DIRECTLY secures reproduction.\n\nIn many cases THE ORGAN OF SMELL shows a similar improvement. Many lower\nCrustaceans (Daphnidae) have better developed organs of smell in the\nmale sex. The difference is often slight and amounts only to one or two\nolfactory filaments, but certain species show a difference of nearly\na hundred of these filaments (Leptodora). The same thing occurs among\ninsects.\n\nWe must briefly consider the clasping or grasping organs which have\ndeveloped in the males among many lower Crustaceans, but here natural\nselection plays its part along with sexual selection, for the union\nof the sexes is an indispensable condition for the maintenance of the\nspecies, and as Darwin himself pointed out, in many cases the two forms\nof selection merge into each other. This fact has always seemed to me to\nbe a proof of natural selection, for, in regard to sexual selection,\nit is quite obvious that the victory of the best-equipped could have\nbrought about the improvement only of the organs concerned, the factors\nin the struggle, such as the eye and the olfactory organ.\n\nWe come now to the EXCITANTS; that is, to the group of sexual characters\nwhose origin through processes of selection has been most frequently\ncalled in question. We may cite the LOVE-CALLS produced by many male\ninsects, such as crickets and cicadas. These could only have arisen in\nanimal groups in which the female did not rapidly flee from the male,\nbut was inclined to accept his wooing from the first. Thus, notes like\nthe chirping of the male cricket serve to entice the females. At first\nthey were merely the signal which showed the presence of a male in the\nneighbourhood, and the female was gradually enticed nearer and nearer\nby the continued chirping. The male that could make himself heard to the\ngreatest distance would obtain the largest following, and would transmit\nthe beginnings, and, later, the improvement of his voice to the greatest\nnumber of descendants. But sexual excitement in the female\nbecame associated with the hearing of the love-call, and then the\nsound-producing organ of the male began to improve, until it attained to\nthe emission of the long-drawn-out soft notes of the mole-cricket or\nthe maenad-like cry of the cicadas. I cannot here follow the process\nof development in detail, but will call attention to the fact that the\noriginal purpose of the voice, the announcing of the male's presence,\nbecame subsidiary, and the exciting of the female became the chief goal\nto be aimed at. The loudest singers awakened the strongest excitement,\nand the improvement resulted as a matter of course. I conceive of the\norigin of bird-song in a somewhat similar manner, first as a means of\nenticing, then of exciting the female.\n\nOne more kind of secondary sexual character must here be mentioned: the\nodour which emanates from so many animals at the breeding season. It is\npossible that this odour also served at first merely to give notice\nof the presence of individuals of the other sex, but it soon became an\nexcitant, and as the individuals which caused the greatest degree of\nexcitement were preferred, it reached as high a pitch of perfection as\nwas possible to it. I shall confine myself here to the comparatively\nrecently discovered fragrance of butterflies. Since Fritz Muller found\nout that certain Brazilian butterflies gave off fragrance \"like a\nflower,\" we have become acquainted with many such cases, and we now know\nthat in all lands, not only many diurnal Lepidoptera but nocturnal ones\nalso give off a delicate odour, which is agreeable even to man.\nThe ethereal oil to which this fragrance is due is secreted by the\nskin-cells, usually of the wing, as I showed soon after the discovery\nof the SCENT-SCALES. This is the case in the males; the females have no\nSPECIAL scent-scales recognisable as such by their form, but they must,\nnevertheless, give off an extremely delicate fragrance, although our\nimperfect organ of smell cannot perceive it, for the males become aware\nof the presence of a female, even at night, from a long distance off,\nand gather round her. We may therefore conclude, that both sexes have\nlong given forth a very delicate perfume, which announced their presence\nto others of the same species, and that in many species (NOT IN ALL)\nthese small beginnings became, in the males, particularly strong\nscent-scales of characteristic form (lute, brush, or lyre-shaped). At\nfirst these scales were scattered over the surface of the wing, but\ngradually they concentrated themselves, and formed broad, velvety bands,\nor strong, prominent brushes, and they attained their highest pitch of\nevolution when they became enclosed within pits or folds of the skin,\nwhich could be opened to let the delicious fragrance stream forth\nsuddenly towards the female. Thus in this case also we see that\ncharacters, the original use of which was to bring the sexes together,\nand so to maintain the species, have been evolved in the males into\nmeans for exciting the female. And we can hardly doubt, that the females\nare most readily enticed to yield to the butterfly that sends out the\nstrongest fragrance,--that is to say, that excites them to the highest\ndegree. It is a pity that our organs of smell are not fine enough to\nexamine the fragrance of male Lepidoptera in general, and to compare it\nwith other perfumes which attract these insects. (See Poulton, \"Essays\non Evolution\", 1908, pages 316, 317.) As far as we can perceive them\nthey resemble the fragrance of flowers, but there are Lepidoptera\nwhose scent suggests musk. A smell of musk is also given off by several\nplants: it is a sexual excitant in the musk-deer, the musk-sheep, and\nthe crocodile.\n\nAs far as we know, then, it is perfumes similar to those of flowers that\nthe male Lepidoptera give off in order to entice their mates, and this\nis a further indication that animals, like plants, can to a large extent\nmeet the claims made upon them by life, and produce the adaptations\nwhich are most purposive,--a further proof, too, of my proposition\nthat the useful variations, so to speak, are ALWAYS THERE. The flowers\ndeveloped the perfumes which entice their visitors, and the male\nLepidoptera developed the perfumes which entice and excite their mates.\n\nThere are many pretty little problems to be solved in this connection,\nfor there are insects, such as some flies, that are attracted by smells\nwhich are unpleasant to us, like those from decaying flesh and carrion.\nBut there are also certain flowers, some orchids for instance, which\ngive forth no very agreeable odour, but one which is to us repulsive\nand disgusting; and we should therefore expect that the males of such\ninsects would give off a smell unpleasant to us, but there is no case\nknown to me in which this has been demonstrated.\n\nIn cases such as we have discussed, it is obvious that there is no\npossible explanation except through selection. This brings us to the\nlast kind of secondary sexual characters, and the one in regard to\nwhich doubt has been most frequently expressed,--decorative colours\nand decorative forms, the brilliant plumage of the male pheasant, the\nhumming-birds, and the bird of Paradise, as well as the bright colours\nof many species of butterfly, from the beautiful blue of our little\nLycaenidae to the magnificent azure of the large Morphinae of Brazil. In\na great many cases, though not by any means in all, the male butterflies\nare \"more beautiful\" than the females, and in the Tropics in particular\nthey shine and glow in the most superb colours. I really see no reason\nwhy we should doubt the power of sexual selection, and I myself stand\nwholly on Darwin's side. Even though we certainly cannot assume that\nthe females exercise a conscious choice of the \"handsomest\" mate, and\ndeliberate like the judges in a court of justice over the perfections\nof their wooers, we have no reason to doubt that distinctive forms\n(decorative feathers) and colours have a particularly exciting effect\nupon the female, just as certain odours have among animals of so many\ndifferent groups, including the butterflies. The doubts which existed\nfor a considerable time, as a result of fallacious experiments, as to\nwhether the colours of flowers really had any influence in attracting\nbutterflies have now been set at rest through a series of more careful\ninvestigations; we now know that the colours of flowers are there on\naccount of the butterflies, as Sprengel first showed, and that the\nblossoms of Phanerogams are selected in relation to them, as Darwin\npointed out.\n\nCertainly it is not possible to bring forward any convincing proof of\nthe origin of decorative colours through sexual selection, but there\nare many weighty arguments in favour of it, and these form a body of\npresumptive evidence so strong that it almost amounts to certainty.\n\nIn the first place, there is the analogy with other secondary sexual\ncharacters. If the song of birds and the chirping of the cricket have\nbeen evolved through sexual selection, if the penetrating odours of male\nanimals,--the crocodile, the musk-deer, the beaver, the carnivores, and,\nfinally, the flower-like fragrances of the butterflies have been evolved\nto their present pitch in this way, why should decorative colours\nhave arisen in some other way? Why should the eye be less sensitive\nto SPECIFICALLY MALE colours and other VISIBLE signs ENTICING TO THE\nFEMALE, than the olfactory sense to specifically male odours, or the\nsense of hearing to specifically male sounds? Moreover, the decorative\nfeathers of birds are almost always spread out and displayed before\nthe female during courtship. I have elsewhere (\"The Evolution Theory\",\nLondon, 1904, I. page 219.) pointed out that decorative colouring and\nsweet-scentedness may replace one another in Lepidoptera as well as\nin flowers, for just as some modestly coloured flowers (mignonette and\nviolet) have often a strong perfume, while strikingly coloured ones are\nsometimes quite devoid of fragrance, so we find that the most beautiful\nand gaily-coloured of our native Lepidoptera, the species of Vanessa,\nhave no scent-scales, while these are often markedly developed in grey\nnocturnal Lepidoptera. Both attractions may, however, be combined in\nbutterflies, just as in flowers. Of course, we cannot explain why both\nmeans of attraction should exist in one genus, and only one of them in\nanother, since we do not know the minutest details of the conditions\nof life of the genera concerned. But from the sporadic distribution of\nscent-scales in Lepidoptera, and from their occurrence or absence in\nnearly related species, we may conclude that fragrance is a relatively\nMODERN acquirement, more recent than brilliant colouring.\n\nOne thing in particular that stamps decorative colouring as a product of\nselection is ITS GRADUAL INTENSIFICATION by the addition of new spots,\nwhich we can quite well observe, because in many cases the colours have\nbeen first acquired by the males, and later transmitted to the females\nby inheritance. The scent-scales are never thus transmitted, probably\nfor the same reason that the decorative colours of many birds are often\nnot transmitted to the females: because with these they would be exposed\nto too great elimination by enemies. Wallace was the first to point out\nthat in species with concealed nests the beautiful feathers of the male\noccurred in the female also, as in the parrots, for instance, but\nthis is not the case in species which brood on an exposed nest. In the\nparrots one can often observe that the general brilliant colouring of\nthe male is found in the female, but that certain spots of colour are\nabsent, and these have probably been acquired comparatively recently by\nthe male and have not yet been transmitted to the female.\n\nIsolation of the group of individuals which is in process of varying\nis undoubtedly of great value in sexual selection, for even a solitary\nconspicuous variation will become dominant much sooner in a small\nisolated colony, than among a large number of members of a species.\n\nAnyone who agrees with me in deriving variations from germinal selection\nwill regard that process as an essential aid towards explaining the\nselection of distinctive courtship-characters, such as coloured spots,\ndecorative feathers, horny outgrowths in birds and reptiles, combs,\nfeather-tufts, and the like, since the beginnings of these would\nbe presented with relative frequency in the struggle between the\ndeterminants within the germ-plasm. The process of transmission of\ndecorative feathers to the female results, as Darwin pointed out and\nillustrated by interesting examples, in the COLOUR-TRANSFORMATION OF A\nWHOLE SPECIES, and this process, as the phyletically older colouring\nof young birds shows, must, in the course of thousands of years, have\nrepeated itself several times in a line of descent.\n\nIf we survey the wealth of phenomena presented to us by secondary sexual\ncharacters, we can hardly fail to be convinced of the truth of the\nprinciple of sexual selection. And certainly no one who has accepted\nnatural selection should reject sexual selection, for, not only do the\ntwo processes rest upon the same basis, but they merge into one another,\nso that it is often impossible to say how much of a particular character\ndepends on one and how much on the other form of selection.\n\n(b) NATURAL SELECTION.\n\nAn actual proof of the theory of sexual selection is out of the\nquestion, if only because we cannot tell when a variation attains to\nselection-value. It is certain that a delicate sense of smell is of\nvalue to the male moth in his search for the female, but whether the\npossession of one additional olfactory hair, or of ten, or of twenty\nadditional hairs leads to the success of its possessor we are unable\nto tell. And we are groping even more in the dark when we discuss the\nexcitement caused in the female by agreeable perfumes, or by striking\nand beautiful colours. That these do make an impression is beyond doubt;\nbut we can only assume that slight intensifications of them give any\nadvantage, and we MUST assume this SINCE OTHERWISE SECONDARY SEXUAL\nCHARACTERS REMAIN INEXPLICABLE.\n\nThe same thing is true in regard to natural selection. It is not\npossible to bring forward any actual proof of the selection-value of\nthe initial stages, and the stages in the increase of variations, as has\nbeen already shown. But the selection-value of a finished adaptation can\nin many cases be statistically determined. Cesnola and Poulton have made\nvaluable experiments in this direction. The former attached forty-five\nindividuals of the green, and sixty-five of the brown variety of the\npraying mantis (Mantis religiosa), by a silk thread to plants, and\nwatched them for seventeen days. The insects which were on a surface of\na colour similar to their own remained uneaten, while twenty-five green\ninsects on brown parts of plants had all disappeared in eleven days.\n\nThe experiments of Poulton and Sanders (\"Report of the British\nAssociation\" (Bristol, 1898), London, 1899, pages 906-909.) were made\nwith 600 pupae of Vanessa urticae, the \"tortoise-shell butterfly.\" The\npupae were artificially attached to nettles, tree-trunks, fences, walls,\nand to the ground, some at Oxford, some at St Helens in the Isle of\nWight. In the course of a month 93 per cent of the pupae at Oxford were\nkilled, chiefly by small birds, while at St Helens 68 per cent perished.\nThe experiments showed very clearly that the colour and character of the\nsurface on which the pupa rests--and thus its own conspicuousness--are\nof the greatest importance. At Oxford only the four pupae which were\nfastened to nettles emerged; all the rest--on bark, stones and the\nlike--perished. At St Helens the elimination was as follows: on fences\nwhere the pupae were conspicuous, 92 per cent; on bark, 66 per cent; on\nwalls, 54 per cent; and among nettles, 57 per cent. These interesting\nexperiments confirm our views as to protective coloration, and show\nfurther, THAT THE RATIO OF ELIMINATION IN THE SPECIES IS A VERY HIGH\nONE, AND THAT THEREFORE SELECTION MUST BE VERY KEEN.\n\nWe may say that the process of selection follows as a logical necessity\nfrom the fulfilment of the three preliminary postulates of the theory:\nvariability, heredity, and the struggle for existence, with its enormous\nratio of elimination in all species. To this we must add a fourth\nfactor, the INTENSIFICATION of variations which Darwin established as\na fact, and which we are now able to account for theoretically on\nthe basis of germinal selection. It may be objected that there is\nconsiderable uncertainty about this LOGICAL proof, because of our\ninability to demonstrate the selection-value of the initial stages and\nthe individual stages of increase. We have therefore to fall back on\nPRESUMPTIVE EVIDENCE. This is to be found in THE INTERPRETATIVE VALUE OF\nTHE THEORY. Let us consider this point in greater detail.\n\nIn the first place, it is necessary to emphasise what is often\noverlooked, namely, that the theory not only explains the\nTRANSFORMATIONS of species, it also explains THEIR REMAINING THE SAME;\nin addition to the principle of varying, it contains within itself that\nof PERSISTING. It is part of the essence of selection, that it not\nonly causes a part to VARY till it has reached its highest pitch of\nadaptation, but that it MAINTAINS IT AT THIS PITCH. THIS CONSERVING\nINFLUENCE OF NATURAL SELECTION is of great importance, and was early\nrecognised by Darwin; it follows naturally from the principle of the\nsurvival of the fittest.\n\nWe understand from this how it is that a species which has become\nfully adapted to certain conditions of life ceases to vary, but remains\n\"constant,\" as long as the conditions of life FOR IT remain unchanged,\nwhether this be for thousands of years, or for whole geological epochs.\nBut the most convincing proof of the power of the principle of selection\nlies in the innumerable multitude of phenomena which cannot be explained\nin any other way. To this category belong all structures which are only\nPASSIVELY of advantage to the organism, because none of these can have\narisen by the alleged LAMARCKIAN PRINCIPLE. These have been so often\ndiscussed that we need do no more than indicate them here. Until quite\nrecently the sympathetic coloration of animals--for instance, the\nwhiteness of Arctic animals--was referred, at least in part, to\nthe DIRECT influence of external factors, but the facts can best be\nexplained by referring them to the processes of selection, for then it\nis unnecessary to make the gratuitous assumption that many species are\nsensitive to the stimulus of cold and that others are not. The great\nmajority of Arctic land-animals, mammals and birds, are white, and this\nproves that they were all able to present the variation which was most\nuseful for them. The sable is brown, but it lives in trees, where\nthe brown colouring protects and conceals it more effectively. The\nmusk-sheep (Ovibos moschatus) is also brown, and contrasts sharply\nwith the ice and snow, but it is protected from beasts of prey by its\ngregarious habit, and therefore it is of advantage to be visible from\nas great a distance as possible. That so many species have been able to\ngive rise to white varieties does not depend on a special sensitiveness\nof the skin to the influence of cold, but to the fact that Mammals and\nBirds have a general tendency to vary towards white. Even with us, many\nbirds--starlings, blackbirds, swallows, etc.--occasionally produce white\nindividuals, but the white variety does not persist, because it readily\nfalls a victim to the carnivores. This is true of white fawns, foxes,\ndeer, etc. The whiteness, therefore, arises from internal causes, and\nonly persists when it is useful. A great many animals living in a\nGREEN ENVIRONMENT have become clothed in green, especially insects,\ncaterpillars, and Mantidae, both persecuted and persecutors.\n\nThat it is not the direct effect of the environment which calls forth\nthe green colour is shown by the many kinds of caterpillar which rest on\nleaves and feed on them, but are nevertheless brown. These feed by night\nand betake themselves through the day to the trunk of the tree, and hide\nin the furrows of the bark. We cannot, however, conclude from this that\nthey were UNABLE to vary towards green, for there are Arctic animals\nwhich are white only in winter and brown in summer (Alpine hare, and\nthe ptarmigan of the Alps), and there are also green leaf-insects which\nremain green only while they are young and difficult to see on the leaf,\nbut which become brown again in the last stage of larval life, when they\nhave outgrown the leaf. They then conceal themselves by day, sometimes\nonly among withered leaves on the ground, sometimes in the earth itself.\nIt is interesting that in one genus, Chaerocampa, one species is brown\nin the last stage of larval life, another becomes brown earlier, and in\nmany species the last stage is not wholly brown, a part remaining green.\nWhether this is a case of a double adaptation, or whether the green is\nbeing gradually crowded out by the brown, the fact remains that the same\nspecies, even the same individual, can exhibit both variations. The case\nis the same with many of the leaf-like Orthoptera, as, for instance, the\npraying mantis (Mantis religiosa) which we have already mentioned.\n\nBut the best proofs are furnished by those often-cited cases in which\nthe insect bears a deceptive resemblance to another object. We now know\nmany such cases, such as the numerous imitations of green or withered\nleaves, which are brought about in the most diverse ways, sometimes by\nmere variations in the form of the insect and in its colour, sometimes\nby an elaborate marking, like that which occurs in the Indian\nleaf-butterflies, Kallima inachis. In the single butterfly-genus Anaea,\nin the woods of South America, there are about a hundred species which\nare all gaily coloured on the upper surface, and on the reverse side\nexhibit the most delicate imitation of the colouring and pattern of a\nleaf, generally without any indication of the leaf-ribs, but extremely\ndeceptive nevertheless. Anyone who has seen only one such butterfly\nmay doubt whether many of the insignificant details of the marking can\nreally be of advantage to the insect. Such details are for instance the\napparent holes and splits in the apparently dry or half-rotten leaf,\nwhich are usually due to the fact that the scales are absent on a\ncircular or oval patch so that the colourless wing-membrane lies bare,\nand one can look through the spot as through a window. Whether the\nbird which is seeking or pursuing the butterflies takes these holes for\ndewdrops, or for the work of a devouring insect, does not affect\nthe question; the mirror-like spot undoubtedly increases the general\ndeceptiveness, for the same thing occurs in many leaf-butterflies,\nthough not in all, and in some cases it is replaced in quite a peculiar\nmanner. In one species of Anaea (A. divina), the resting butterfly looks\nexactly like a leaf out of the outer edge of which a large semicircular\npiece has been eaten, possibly by a caterpillar; but if we look more\nclosely it is obvious that there is no part of the wing absent, and that\nthe semicircular piece is of a clear, pale yellow colour, while the rest\nof the wing is of a strongly contrasted dark brown.\n\nBut the deceptive resemblance may be caused in quite a different manner.\nI have often speculated as to what advantage the brilliant white C\ncould give to the otherwise dusky-coloured \"Comma butterfly\" (Grapta C.\nalbum). Poulton's recent observations (\"Proc. Ent. Soc\"., London, May 6,\n1903.) have shown that this represents the imitation of a crack such as\nis often seen in dry leaves, and is very conspicuous because the light\nshines through it.\n\nThe utility obviously lies in presenting to the bird the very familiar\npicture of a broken leaf with a clear shining slit, and we may conclude,\nfrom the imitation of such small details, that the birds are very sharp\nobservers and that the smallest deviation from the usual arrests their\nattention and incites them to closer investigation. It is obvious that\nsuch detailed--we might almost say such subtle--deceptive resemblances\ncould only have come about in the course of long ages through the\nacquirement from time to time of something new which heightened the\nalready existing resemblance.\n\nIn face of facts like these there can be no question of chance, and no\none has succeeded so far in finding any other explanation to replace\nthat by selection. For the rest, the apparent leaves are by no means\nperfect copies of a leaf; many of them only represent the torn or\nbroken piece, or the half or two-thirds of a leaf, but then the leaves\nthemselves frequently do not present themselves to the eye as a whole,\nbut partially concealed among other leaves. Even those butterflies\nwhich, like the species of Kallima and Anaea, represent the whole of\na leaf with stalk, ribs, apex, and the whole breadth, are not actual\ncopies which would satisfy a botanist; there is often much wanting.\nIn Kallima the lateral ribs of the leaf are never all included in the\nmarkings; there are only two or three on the left side and at most four\nor five on the right, and in many individuals these are rather obscure,\nwhile in others they are comparatively distinct. This furnishes us with\nfresh evidence in favour of their origin through processes of selection,\nfor a botanically perfect picture could not arise in this way; there\ncould only be a fixing of such details as heightened the deceptive\nresemblance.\n\nOur postulate of origin through selection also enables us to understand\nwhy the leaf-imitation is on the lower surface of the wing in the\ndiurnal Lepidoptera, and on the upper surface in the nocturnal forms,\ncorresponding to the attitude of the wings in the resting position of\nthe two groups.\n\nThe strongest of all proofs of the theory, however, is afforded by\ncases of true \"mimicry,\" those adaptations discovered by Bates in 1861,\nconsisting in the imitation of one species by another, which becomes\nmore and more like its model. The model is always a species that enjoys\nsome special protection from enemies, whether because it is unpleasant\nto taste, or because it is in some way dangerous.\n\nIt is chiefly among insects and especially among butterflies that we\nfind the greatest number of such cases. Several of these have been\nminutely studied, and every detail has been investigated, so that it is\ndifficult to understand how there can still be disbelief in regard\nto them. If the many and exact observations which have been carefully\ncollected and critically discussed, for instance by Poulton (\"Essays\non Evolution\", 1889-1907, Oxford, 1908, passim, e.g. page 269.) were\nthoroughly studied, the arguments which are still frequently urged\nagainst mimicry would be found untenable; we can hardly hope to find\nmore convincing proof of the actuality of the processes of selection\nthan these cases put into our hands. The preliminary postulates of\nthe theory of mimicry have been disputed, for instance, that diurnal\nbutterflies are persecuted and eaten by birds, but observations\nspecially directed towards this point in India, Africa, America and\nEurope have placed it beyond all doubt. If it were necessary I could\nmyself furnish an account of my own observations on this point.\n\nIn the same way it has been established by experiment and observation\nin the field that in all the great regions of distribution there\nare butterflies which are rejected by birds and lizards, their\nchief enemies, on account of their unpleasant smell or taste. These\nbutterflies are usually gaily and conspicuously coloured and thus--as\nWallace first interpreted it--are furnished with an easily recognisable\nsign: a sign of unpalatableness or WARNING COLOURS. If they were not\nthus recognisable easily and from a distance, they would frequently be\npecked at by birds, and then rejected because of their unpleasant taste;\nbut as it is, the insect-eaters recognise them at once as unpalatable\nbooty and ignore them. Such IMMUNE (The expression does not refer to all\nthe enemies of this butterfly; against ichneumon-flies, for instance,\ntheir unpleasant smell usually gives no protection.) species, wherever\nthey occur, are imitated by other palatable species, which thus acquire\na certain degree of protection.\n\nIt is true that this explanation of the bright, conspicuous colours\nis only a hypothesis, but its foundations,--unpalatableness, and the\nliability of other butterflies to be eaten,--are certain, and its\nconsequences--the existence of mimetic palatable forms--confirm it in\nthe most convincing manner. Of the many cases now known I select\none, which is especially remarkable, and which has been thoroughly\ninvestigated, Papilio dardanus (merope), a large, beautiful, diurnal\nbutterfly which ranges from Abyssinia throughout the whole of Africa to\nthe south coast of Cape Colony.\n\nThe males of this form are everywhere ALMOST the same in colour and in\nform of wings, save for a few variations in the sparse black markings on\nthe pale yellow ground. But the females occur in several quite different\nforms and colourings, and one of these only, the Abyssinian form, is\nlike the male, while the other three or four are MIMETIC, that is to\nsay, they copy a butterfly of quite a different family the Danaids,\nwhich are among the IMMUNE forms. In each region the females have thus\ncopied two or three different immune species. There is much that is\ninteresting to be said in regard to these species, but it would be out\nof keeping with the general tenor of this paper to give details of this\nvery complicated case of polymorphism in P. dardanus. Anyone who is\ninterested in the matter will find a full and exact statement of the\ncase in as far as we know it, in Poulton's \"Essays on Evolution\" (pages\n373-375). (Professor Poulton has corrected some wrong descriptions which\nI had unfortunately overlooked in the Plates of my book \"Vortrage uber\nDescendenztheorie\", and which refer to Papilio dardanus (merope).\nThese mistakes are of no importance as far as and understanding of the\nmimicry-theory is concerned, but I hope shortly to be able to correct\nthem in a later edition.) I need only add that three different mimetic\nfemale forms have been reared from the eggs of a single female in South\nAfrica. The resemblance of these forms to their immune models goes so\nfar that even the details of the LOCAL forms of the models are copied by\nthe mimetic species.\n\nIt remains to be said that in Madagascar a butterfly, Papilio meriones,\noccurs, of which both sexes are very similar in form and markings to\nthe non-mimetic male of P. dardanus, so that it probably represents the\nancestor of this latter species.\n\nIn face of such facts as these every attempt at another explanation must\nfail. Similarly all the other details of the case fulfil the preliminary\npostulates of selection, and leave no room for any other interpretation.\nThat the males do not take on the protective colouring is easily\nexplained, because they are in general more numerous, and the females\nare more important for the preservation of the species, and must also\nlive longer in order to deposit their eggs. We find the same state of\nthings in many other species, and in one case (Elymnias undularis)\nin which the male is also mimetically coloured, it copies quite a\ndifferently coloured immune species from the model followed by the\nfemale. This is quite intelligible when we consider that if there were\nTOO MANY false immune types, the birds would soon discover that there\nwere palatable individuals among those with unpalatable warning colours.\nHence the imitation of different immune species by Papilio dardanus!\n\nI regret that lack of space prevents my bringing forward more examples\nof mimicry and discussing them fully. But from the case of Papilio\ndardanus alone there is much to be learnt which is of the highest\nimportance for our understanding of transformations. It shows us chiefly\nwhat I once called, somewhat strongly perhaps, THE OMNIPOTENCE OF\nNATURAL SELECTION in answer to an opponent who had spoken of its\n\"inadequacy.\" We here see that one and the same species is capable of\nproducing four or five different patterns of colouring and marking;\nthus the colouring and marking are not, as has often been supposed,\na necessary outcome of the specific nature of the species, but a\ntrue adaptation, which cannot arise as a direct effect of climatic\nconditions, but solely through what I may call the sorting out of the\nvariations produced by the species, according to their utility. That\ncaterpillars may be either green or brown is already something more than\ncould have been expected according to the old conception of species, but\nthat one and the same butterfly should be now pale yellow, with black;\nnow red with black and pure white; now deep black with large, pure white\nspots; and again black with a large ochreous-yellow spot, and many small\nwhite and yellow spots; that in one sub-species it may be tailed like\nthe ancestral form, and in another tailless like its Danaid model,--all\nthis shows a far-reaching capacity for variation and adaptation that\nwide never have expected if we did not see the facts before us. How\nit is possible that the primary colour-variations should thus be\nintensified and combined remains a puzzle even now; we are reminded of\nthe modern three-colour printing,--perhaps similar combinations of the\nprimary colours take place in this case; in any case the direction of\nthese primary variations is determined by the artist whom we know as\nnatural selection, for there is no other conceivable way in which the\nmodel could affect the butterfly that is becoming more and more like it.\nThe same climate surrounds all four forms of female; they are subject\nto the same conditions of nutrition. Moreover, Papilio dardanus is by\nno means the only species of butterfly which exhibits different kinds of\ncolour-pattern on its wings. Many species of the Asiatic genus Elymnias\nhave on the upper surface a very good imitation of an immune Euploeine\n(Danainae), often with a steel-blue ground-colour, while the under\nsurface is well concealed when the butterfly is at rest,--thus there are\ntwo kinds of protective coloration each with a different meaning! The\nsame thing may be observed in many non-mimetic butterflies, for\ninstance in all our species of Vanessa, in which the under side shows\na grey-brown or brownish-black protective coloration, but we do not yet\nknow with certainty what may be the biological significance of the gaily\ncoloured upper surface.\n\nIn general it may be said that mimetic butterflies are comparatively\nrare species, but there are exceptions, for instance Limenitis archippus\nin North America, of which the immune model (Danaida plexippus) also\noccurs in enormous numbers.\n\nIn another mimicry-category the imitators are often more numerous than\nthe models, namely in the case of the imitation of DANGEROUS INSECTS by\nharmless species. Bees and wasps are dreaded for their sting, and they\nare copied by harmless flies of the genera Eristalis and Syrphus, and\nthese mimics often occur in swarms about flowering plants without damage\nto themselves or to their models; they are feared and are therefore left\nunmolested.\n\nIn regard also to the FAITHFULNESS OF THE COPY the facts are quite in\nharmony with the theory, according to which the resemblance must have\narisen and increased BY DEGREES. We can recognise this in many\ncases, for even now the mimetic species show very VARYING DEGREES OF\nRESEMBLANCE to their immune model. If we compare, for instance, the\nmany different imitators of Danaida chrysippus we find that, with their\nbrownish-yellow ground-colour, and the position and size, and more or\nless sharp limitation of their clear marginal spots, they have reached\nvery different degrees of nearness to their model. Or compare the female\nof Elymnias undularis with its model Danaida genutia; there is a general\nresemblance, but the marking of the Danaida is very roughly imitated in\nElymnias.\n\nAnother fact that bears out the theory of mimicry is, that even when the\nresemblance in colour-pattern is very great, the WING-VENATION, which is\nso constant, and so important in determining the systematic position\nof butterflies, is never affected by the variation. The pursuers of the\nbutterfly have no time to trouble about entomological intricacies.\n\nI must not pass over a discovery of Poulton's which is of great\ntheoretical importance--that mimetic butterflies may reach the same\neffect by very different means. (\"Journ. Linn. Soc. London (Zool.)\",\nVol. XXVI. 1898, pages 598-602.) Thus the glass-like transparency of the\nwing of a certain Ithomiine (Methona) and its Pierine mimic (Dismorphia\norise) depends on a diminution in the size of the scales; in the Danaine\ngenus Ituna it is due to the fewness of the scales, and in a third\nimitator, a moth (Castnia linus var. heliconoides) the glass-like\nappearance of the wing is due neither to diminution nor to absence of\nscales, but to their absolute colourlessness and transparency, and to\nthe fact that they stand upright. In another moth mimic (Anthomyza) the\narrangement of the transparent scales is normal. Thus it is not some\nunknown external influence that has brought about the transparency of\nthe wing in these five forms, as has sometimes been supposed. Nor is it\na hypothetical INTERNAL evolutionary tendency, for all three vary in a\ndifferent manner. The cause of this agreement can only lie in selection,\nwhich preserves and intensifies in each species the favourable\nvariations that present themselves. The great faithfulness of the copy\nis astonishing in these cases, for it is not THE WHOLE wing which is\ntransparent; certain markings are black in colour, and these contrast\nsharply with the glass-like ground. It is obvious that the pursuers\nof these butterflies must be very sharp-sighted, for otherwise the\nagreement between the species could never have been pushed so far. The\nless the enemies see and observe, the more defective must the imitation\nbe, and if they had been blind, no visible resemblance between the\nspecies which required protection could ever have arisen.\n\nA seemingly irreconcilable contradiction to the mimicry theory is\npresented in the following cases, which were known to Bates, who,\nhowever, never succeeded in bringing them into line with the principle\nof mimicry.\n\nIn South America there are, as we have already said, many mimics of the\nimmune Ithomiinae (or as Bates called them Heliconidae). Among these\nthere occur not merely species which are edible, and thus require the\nprotection of a disguise, but others which are rejected on account of\ntheir unpalatableness. How could the Ithomiine dress have developed in\ntheir case, and of what use is it, since the species would in any case\nbe immune? In Eastern Brazil, for instance, there are four butterflies,\nwhich bear a most confusing resemblance to one another in colour,\nmarking, and form of wing, and all four are unpalatable to birds. They\nbelong to four different genera and three sub-families, and we have to\ninquire: Whence came this resemblance and what end does it serve? For\na long time no satisfactory answer could be found, but Fritz Muller\n(In \"Kosmos\", 1879, page 100.), seventeen years after Bates, offered a\nsolution to the riddle, when he pointed out that young birds could not\nhave an instinctive knowledge of the unpalatableness of the Ithomiines,\nbut must learn by experience which species were edible and which\ninedible. Thus each young bird must have tasted at least one individual\nof each inedible species and discovered its unpalatability, before it\nlearnt to avoid, and thus to spare the species. But if the four species\nresemble each other very closely the bird will regard them all as of\nthe same kind, and avoid them all. Thus there developed a process\nof selection which resulted in the survival of the Ithomiine-like\nindividuals, and in so great an increase of resemblance between the four\nspecies, that they are difficult to distinguish one from another even in\na collection. The advantage for the four species, living side by side\nas they do e.g. in Bahia, lies in the fact that only one individual\nfrom the MIMICRY-RING (\"inedible association\") need be tasted by a young\nbird, instead of at least four individuals, as would otherwise be the\ncase. As the number of young birds is great, this makes a considerable\ndifference in the ratio of elimination.\n\nThese interesting mimicry-rings (trusts), which have much significance\nfor the theory, have been the subject of numerous and careful\ninvestigations, and at least their essential features are now fully\nestablished. Muller took for granted, without making any investigations,\nthat young birds only learn by experience to distinguish between\ndifferent kinds of victims. But Lloyd Morgan's (\"Habit and Instinct\",\nLondon, 1896.) experiments with young birds proved that this is really\nthe case, and at the same time furnished an additional argument against\nthe LAMARCKIAN PRINCIPLE.\n\nIn addition to the mimicry-rings first observed in South America, others\nhave been described from Tropical India by Moore, and by Poulton and\nDixey from Africa, and we may expect to learn many more interesting\nfacts in this connection. Here again the preliminary postulates of the\ntheory are satisfied. And how much more that would lead to the same\nconclusion might be added!\n\nAs in the case of mimicry many species have come to resemble one another\nthrough processes of selection, so we know whole classes of phenomena\nin which plants and animals have become adapted to one another, and have\nthus been modified to a considerable degree. I refer particularly to the\nrelation between flowers and insects; but as there is an article on \"The\nBiology of Flowers\" in this volume, I need not discuss the subject, but\nwill confine myself to pointing out the significance of these remarkable\ncases for the theory of selection. Darwin has shown that the originally\ninconspicuous blossoms of the phanerogams were transformed into flowers\nthrough the visits of insects, and that, conversely, several large\norders of insects have been gradually modified by their association\nwith flowers, especially as regards the parts of their body actively\nconcerned. Bees and butterflies in particular have become what they\nare through their relation to flowers. In this case again all that is\napparently contradictory to the theory can, on closer investigation, be\nbeautifully interpreted in corroboration of it. Selection can give rise\nonly to what is of use to the organism actually concerned, never to what\nis of use to some other organism, and we must therefore expect to find\nthat in flowers only characters of use to THEMSELVES have arisen, never\ncharacters which are of use to insects only, and conversely that in the\ninsects characters useful to them and not merely to the plants would\nhave originated. For a long time it seemed as if an exception to this\nrule existed in the case of the fertilisation of the yucca blossoms by\na little moth, Pronuba yuccasella. This little moth has a sickle-shaped\nappendage to its mouth-parts which occurs in no other Lepidopteron,\nand which is used for pushing the yellow pollen into the opening of\nthe pistil, thus fertilising the flower. Thus it appears as if a new\nstructure, which is useful only to the plant, has arisen in the insect.\nBut the difficulty is solved as soon as we learn that the moth lays\nits eggs in the fruit-buds of the Yucca, and that the larvae, when they\nemerge, feed on the developing seeds. In effecting the fertilisation\nof the flower the moth is at the same time making provision for its own\noffspring, since it is only after fertilisation that the seeds begin to\ndevelop. There is thus nothing to prevent our referring this structural\nadaptation in Pronuba yuccasella to processes of selection, which\nhave gradually transformed the maxillary palps of the female into the\nsickle-shaped instrument for collecting the pollen, and which have at\nthe same time developed in the insect the instinct to press the pollen\ninto the pistil.\n\nIn this domain, then, the theory of selection finds nothing but\ncorroboration, and it would be impossible to substitute for it any\nother explanation, which, now that the facts are so well known, could\nbe regarded as a serious rival to it. That selection is a factor, and\na very powerful factor in the evolution of organisms, can no longer be\ndoubted. Even although we cannot bring forward formal proofs of it IN\nDETAIL, cannot calculate definitely the size of the variations which\npresent themselves, and their selection-value, cannot, in short,\nreduce the whole process to a mathematical formula, yet we must assume\nselection, because it is the only possible explanation applicable to\nwhole classes of phenomena, and because, on the other hand, it is made\nup of factors which we know can be proved actually to exist, and\nwhich, IF they exist, must of logical necessity cooperate in the manner\nrequired by the theory. WE MUST ACCEPT IT BECAUSE THE PHENOMENA OF\nEVOLUTION AND ADAPTATION MUST HAVE A NATURAL BASIS, AND BECAUSE IT IS\nTHE ONLY POSSIBLE EXPLANATION OF THEM. (This has been discussed in many\nof my earlier works. See for instance \"The All-Sufficiency of Natural\nSelection, a reply to Herbert Spencer\", London, 1893.)\n\nMany people are willing to admit that selection explains adaptations,\nbut they maintain that only a part of the phenomena are thus explained,\nbecause everything does not depend upon adaptation. They regard\nadaptation as, so to speak, a special effort on the part of Nature,\nwhich she keeps in readiness to meet particularly difficult claims\nof the external world on organisms. But if we look at the matter more\ncarefully we shall find that adaptations are by no means exceptional,\nbut that they are present everywhere in such enormous numbers, that it\nwould be difficult in regard to any structure whatever, to prove that\nadaptation had NOT played a part in its evolution.\n\nHow often has the senseless objection been urged against selection that\nit can create nothing, it can only reject. It is true that it cannot\ncreate either the living substance or the variations of it; both must be\ngiven. But in rejecting one thing it preserves another, intensifies\nit, combines it, and in this way CREATES what is new. EVERYTHING in\norganisms depends on adaptation; that is to say, everything must be\nadmitted through the narrow door of selection, otherwise it can take\nno part in the building up of the whole. But, it is asked, what of the\ndirect effect of external conditions, temperature, nutrition, climate\nand the like? Undoubtedly these can give rise to variations, but they\ntoo must pass through the door of selection, and if they cannot do this\nthey are rejected, eliminated from the constitution of the species.\n\nIt may, perhaps, be objected that such external influences are often of\na compelling power, and that every animal MUST submit to them, and that\nthus selection has no choice and can neither select nor reject. There\nmay be such cases; let us assume for instance that the effect of the\ncold of the Arctic regions was to make all the mammals become black; the\nresult would be that they would all be eliminated by selection, and\nthat no mammals would be able to live there at all. But in most cases a\ncertain percentage of animals resists these strong influences, and\nthus selection secures a foothold on which to work, eliminating the\nunfavourable variation, and establishing a useful colouring, consistent\nwith what is required for the maintenance of the species.\n\nEverything depends upon adaptation! We have spoken much of adaptation\nin colouring, in connection with the examples brought into prominence by\nDarwin, because these are conspicuous, easily verified, and at the same\ntime convincing for the theory of selection. But is it only desert and\npolar animals whose colouring is determined through adaptation? Or the\nleaf-butterflies, and the mimetic species, or the terrifying markings,\nand \"warning-colours\" and a thousand other kinds of sympathetic\ncolouring? It is, indeed, never the colouring alone which makes up\nthe adaptation; the structure of the animal plays a part, often a very\nessential part, in the protective disguise, and thus MANY variations may\ncooperate towards ONE common end. And it is to be noted that it is by\nno means only external parts that are changed; internal parts are ALWAYS\nmodified at the same time--for instance, the delicate elements of the\nnervous system on which depend the INSTINCT of the insect to hold its\nwings, when at rest, in a perfectly definite position, which, in the\nleaf-butterfly, has the effect of bringing the two pieces on which\nthe marking occurs on the anterior and posterior wing into the same\ndirection, and thus displaying as a whole the fine curve of the midrib\non the seeming leaf. But the wing-holding instinct is not regulated in\nthe same way in all leaf-butterflies; even our indigenous species\nof Vanessa, with their protective ground-colouring, have quite a\ndistinctive way of holding their wings so that the greater part of the\nanterior wing is covered by the posterior when the butterfly is at rest.\nBut the protective colouring appears on the posterior wing and on the\ntip of the anterior, TO PRECISELY THE DISTANCE TO WHICH IT IS LEFT\nUNCOVERED. This occurs, as Standfuss has shown, in different degree in\nour two most nearly allied species, the uncovered portion being\nsmaller in V. urticae than in V. polychloros. In this case, as in most\nleaf-butterflies, the holding of the wing was probably the primary\ncharacter; only after that was thoroughly established did the protective\nmarking develop. In any case, the instinctive manner of holding the\nwings is associated with the protective colouring, and must remain as it\nis if the latter is to be effective. How greatly instincts may change,\nthat is to say, may be adapted, is shown by the case of the Noctuid\n\"shark\" moth, Xylina vetusta. This form bears a most deceptive\nresemblance to a piece of rotten wood, and the appearance is greatly\nincreased by the modification of the innate impulse to flight common to\nso many animals, which has here been transformed into an almost contrary\ninstinct. This moth does not fly away from danger, but \"feigns death,\"\nthat is, it draws antennae, legs and wings close to the body, and\nremains perfectly motionless. It may be touched, picked up, and thrown\ndown again, and still it does not move. This remarkable instinct must\nsurely have developed simultaneously with the wood-colouring; at all\nevents, both cooperating variations are now present, and prove that both\nthe external and the most minute internal structure have undergone a\nprocess of adaptation.\n\nThe case is the same with all structural variations of animal parts,\nwhich are not absolutely insignificant. When the insects acquired wings\nthey must also have acquired the mechanism with which to move them--the\nmusculature, and the nervous apparatus necessary for its automatic\nregulation. All instincts depend upon compound reflex mechanisms and are\njust as indispensable as the parts they have to set in motion, and all\nmay have arisen through processes of selection if the reasons which I\nhave elsewhere given for this view are correct. (\"The Evolution Theory\",\nLondon, 1904, page 144.)\n\nThus there is no lack of adaptations within the organism, and\nparticularly in its most important and complicated parts, so that we may\nsay that there is no actively functional organ that has not undergone a\nprocess of adaptation relative to its function and the requirements of\nthe organism. Not only is every gland structurally adapted, down to the\nvery minutest histological details, to its function, but the function\nis equally minutely adapted to the needs of the body. Every cell in the\nmucous lining of the intestine is exactly regulated in its relation to\nthe different nutritive substances, and behaves in quite a different way\ntowards the fats, and towards nitrogenous substances, or peptones.\n\nI have elsewhere called attention to the many adaptations of the whale\nto the surrounding medium, and have pointed out--what has long been\nknown, but is not universally admitted, even now--that in it a great\nnumber of important organs have been transformed in adaptation to the\npeculiar conditions of aquatic life, although the ancestors of the whale\nmust have lived, like other hair-covered mammals, on land. I cited a\nnumber of these transformations--the fish-like form of the body, the\nhairlessness of the skin, the transformation of the fore-limbs to fins,\nthe disappearance of the hind-limbs and the development of a tail fin,\nthe layer of blubber under the skin, which affords the protection\nfrom cold necessary to a warm-blooded animal, the disappearance of the\near-muscles and the auditory passages, the displacement of the external\nnares to the forehead for the greater security of the breathing-hole\nduring the brief appearance at the surface, and certain remarkable\nchanges in the respiratory and circulatory organs which enable the\nanimal to remain for a long time under water. I might have added many\nmore, for the list of adaptations in the whale to aquatic life is by no\nmeans exhausted; they are found in the histological structure and in the\nminutest combinations in the nervous system. For it is obvious that a\ntail-fin must be used in quite a different way from a tail, which serves\nas a fly-brush in hoofed animals, or as an aid to springing in the\nkangaroo or as a climbing organ; it will require quite different\nreflex-mechanisms and nerve-combinations in the motor centres.\n\nI used this example in order to show how unnecessary it is to assume a\nspecial internal evolutionary power for the phylogenesis of species, for\nthis whole order of whales is, so to speak, MADE UP OF ADAPTATIONS; it\ndeviates in many essential respects from the usual mammalian type, and\nall the deviations are adaptations to aquatic life. But if precisely the\nmost essential features of the organisation thus depend upon adaptation,\nwhat is left for a phyletic force to do, since it is these essential\nfeatures of the structure it would have to determine? There are few\npeople now who believe in a phyletic evolutionary power, which is not\nmade up of the forces known to us--adaptation and heredity--but the\nconviction that EVERY part of an organism depends upon adaptation has\nnot yet gained a firm footing. Nevertheless, I must continue to regard\nthis conception as the correct one, as I have long done.\n\nI may be permitted one more example. The feather of a bird is a\nmarvellous structure, and no one will deny that as a whole it depends\nupon adaptation. But what part of it DOES NOT depend upon adaptation?\nThe hollow quill, the shaft with its hard, thin, light cortex, and the\nspongy substance within it, its square section compared with the round\nsection of the quill, the flat barbs, their short, hooked barbules\nwhich, in the flight-feathers, hook into one another with just\nsufficient firmness to resist the pressure of the air at each wing-beat,\nthe lightness and firmness of the whole apparatus, the elasticity of\nthe vane, and so on. And yet all this belongs to an organ which is only\npassively functional, and therefore can have nothing to do with the\nLAMARCKIAN PRINCIPLE. Nor can the feather have arisen through some\nmagical effect of temperature, moisture, electricity, or specific\nnutrition, and thus selection is again our only anchor of safety.\n\nBut--it will be objected--the substance of which the feather consists,\nthis peculiar kind of horny substance, did not first arise through\nselection in the course of the evolution of the birds, for it formed the\ncovering of the scales of their reptilian ancestors. It is quite true\nthat a similar substance covered the scales of the Reptiles, but why\nshould it not have arisen among them through selection? Or in what other\nway could it have arisen, since scales are also passively useful parts?\nIt is true that if we are only to call adaptation what has been acquired\nby the species we happen to be considering, there would remain a great\ndeal that could not be referred to selection; but we are postulating an\nevolution which has stretched back through aeons, and in the course of\nwhich innumerable adaptations took place, which had not merely ephemeral\npersistence in a genus, a family or a class, but which was continued\ninto whole Phyla of animals, with continual fresh adaptations to\nthe special conditions of each species, family, or class, yet with\npersistence of the fundamental elements. Thus the feather, once\nacquired, persisted in all birds, and the vertebral column, once gained\nby adaptation in the lowest forms, has persisted in all the Vertebrates,\nfrom Amphioxus upwards, although with constant readaptation to the\nconditions of each particular group. Thus everything we can see in\nanimals is adaptation, whether of to-day, or of yesterday, or of ages\nlong gone by; every kind of cell, whether glandular, muscular, nervous,\nepidermic, or skeletal, is adapted to absolutely definite and specific\nfunctions, and every organ which is composed of these different kinds\nof cells contains them in the proper proportions, and in the particular\narrangement which best serves the function of the organ; it is thus\nadapted to its function.\n\nAll parts of the organism are tuned to one another, that is, THEY ARE\nADAPTED TO ONE ANOTHER, and in the same way THE ORGANISM AS A WHOLE IS\nADAPTED TO THE CONDITIONS OF ITS LIFE, AND IT IS SO AT EVERY STAGE OF\nITS EVOLUTION.\n\nBut all adaptations CAN be referred to selection; the only point that\nremains doubtful is whether they all MUST be referred to it.\n\nHowever that may be, whether the LAMARCKIAN PRINCIPLE is a factor that\nhas cooperated with selection in evolution, or whether it is altogether\nfallacious, the fact remains, that selection is the cause of a great\npart of the phyletic evolution of organisms on our earth. Those\nwho agree with me in rejecting the LAMARCKIAN PRINCIPLE will regard\nselection as the only GUIDING factor in evolution, which creates what\nis new out of the transmissible variations, by ordering and arranging\nthese, selecting them in relation to their number and size, as the\narchitect does his building-stones so that a particular style must\nresult. (\"Variation under Domestication\", 1875 II. pages 426, 427.) But\nthe building-stones themselves, the variations, have their basis in the\ninfluences which cause variation in those vital units which are handed\non from one generation to another, whether, taken together they form the\nWHOLE organism, as in Bacteria and other low forms of life, or only\na germ-substance, as in unicellular and multicellular organisms. (The\nAuthor and Editor are indebted to Professor Poulton for kindly assisting\nin the revision of the proof of this Essay.)\n\n\n\n\nIV. VARIATION. By HUGO DE VRIES.\n\nProfessor of Botany in the University of Amsterdam.\n\n\nI. DIFFERENT KINDS OF VARIABILITY.\n\nBefore Darwin, little was known concerning the phenomena of variability.\nThe fact, that hardly two leaves on a tree were exactly the same, could\nnot escape observation: small deviations of the same kind were met with\neverywhere, among individuals as well as among the organs of the same\nplant. Larger aberrations, spoken of as monstrosities, were for a\nlong time regarded as lying outside the range of ordinary phenomena. A\nspecial branch of inquiry, that of Teratology, was devoted to them, but\nit constituted a science by itself, sometimes connected with morphology,\nbut having scarcely any bearing on the processes of evolution and\nheredity.\n\nDarwin was the first to take a broad survey of the whole range of\nvariations in the animal and vegetable kingdoms. His theory of Natural\nSelection is based on the fact of variability. In order that this\nfoundation should be as strong as possible he collected all the facts,\nscattered in the literature of his time, and tried to arrange them in a\nscientific way. He succeeded in showing that variations may be grouped\nalong a line of almost continuous gradations, beginning with simple\ndifferences in size and ending with monstrosities. He was struck by the\nfact that, as a rule, the smaller the deviations, the more frequently\nthey appear, very abrupt breaks in characters being of rare occurrence.\n\nAmong these numerous degrees of variability Darwin was always on the\nlook out for those which might, with the greatest probability, be\nconsidered as affording material for natural selection to act upon in\nthe development of new species. Neither of the extremes complied with\nhis conceptions. He often pointed out, that there are a good many small\nfluctuations, which in this respect must be absolutely useless. On the\nother hand, he strongly combated the belief, that great changes would be\nnecessary to explain the origin of species. Some authors had propounded\nthe idea that highly adapted organs, e.g. the wings of a bird, could\nnot have been developed in any other way than by a comparatively sudden\nmodification of a well defined and important kind. Such a conception\nwould allow of great breaks or discontinuity in the evolution of highly\ndifferentiated animals and plants, shortening the time for the evolution\nof the whole organic kingdom and getting over numerous difficulties\ninherent in the theory of slow and gradual progress. It would, moreover,\naccount for the genetic relation of the larger groups of both animals\nand plants. It would, in a word, undoubtedly afford an easy means of\nsimplifying the problem of descent with modification.\n\nDarwin, however, considered such hypotheses as hardly belonging to the\ndomain of science; they belong, he said, to the realm of miracles. That\nspecies have a capacity for change is admitted by all evolutionists; but\nthere is no need to invoke modifications other than those represented by\nordinary variability. It is well known that in artificial selection this\ntendency to vary has given rise to numerous distinct races, and there is\nno reason for denying that it can do the same in nature, by the aid of\nnatural selection. On both lines an advance may be expected with equal\nprobability.\n\nHis main argument, however, is that the most striking and most highly\nadapted modifications may be acquired by successive variations. Each\nof these may be slight, and they may affect different organs, gradually\nadapting them to the same purpose. The direction of the adaptations\nwill be determined by the needs in the struggle for life, and natural\nselection will simply exclude all such changes as occur on opposite\nor deviating lines. In this way, it is not variability itself which is\ncalled upon to explain beautiful adaptations, but it is quite sufficient\nto suppose that natural selection has operated during long periods in\nthe same way. Eventually, all the acquired characters, being transmitted\ntogether, would appear to us, as if they had all been simultaneously\ndeveloped.\n\nCorrelations must play a large part in such special evolutions: when\none part is modified, so will be other parts. The distribution of\nnourishment will come in as one of the causes, the reactions of\ndifferent organs to the same external influences as another. But no\ndoubt the more effective cause is that of the internal correlations,\nwhich, however, are still but dimly understood. Darwin repeatedly laid\ngreat stress on this view, although a definite proof of its correctness\ncould not be given in his time. Such proof requires the direct\nobservation of a mutation, and it should be stated here that even\nthe first observations made in this direction have clearly confirmed\nDarwin's ideas. The new evening primroses which have sprung in my garden\nfrom the old form of Oenothera Lamarckiana, and which have evidently\nbeen derived from it, in each case, by a single mutation, do not differ\nfrom their parent species in one character only, but in almost all their\norgans and qualities. Oenothera gigas, for example, has stouter stems\nand denser foliage; the leaves are larger and broader; its thick\nflower-buds produce gigantic flowers, but only small fruits with large\nseeds. Correlative changes of this kind are seen in all my new forms,\nand they lend support to the view that in the gradual development of\nhighly adapted structures, analogous correlations may have played a\nlarge part. They easily explain large deviations from an original type,\nwithout requiring the assumption of too many steps.\n\nMonstrosities, as their name implies, are widely different in character\nfrom natural species; they cannot, therefore, be adduced as evidence in\nthe investigation of the origin of species. There is no doubt that they\nmay have much in common as regards their manner of origin, and that the\norigin of species, once understood, may lead to a better understanding\nof the monstrosities. But the reverse is not true, at least not as\nregards the main lines of development. Here, it is clear, monstrosities\ncannot have played a part of any significance.\n\nReversions, or atavistic changes, would seem to give a better support\nto the theory of descent through modifications. These have been of\nparamount importance on many lines of evolution of the animal as well\nas of the vegetable kingdom. It is often assumed that monocotyledons are\ndescended from some lower group of dicotyledons, probably allied to that\nwhich includes the buttercup family. On this view the monocotyledons\nmust be assumed to have lost the cambium and all its influence on\nsecondary growth, the differentiation of the flower into calyx and\ncorolla, the second cotyledon or seed-leaf and several other characters.\nLosses of characters such as these may have been the result of abrupt\nchanges, but this does not prove that the characters themselves have\nbeen produced with equal suddenness. On the contrary, Darwin shows very\nconvincingly that a modification may well be developed by a series of\nsteps, and afterwards suddenly disappear. Many monstrosities, such as\nthose represented by twisted stems, furnish direct proofs in support of\nthis view, since they are produced by the loss of one character and this\nloss implies secondary changes in a large number of other organs and\nqualities.\n\nDarwin criticises in detail the hypothesis of great and abrupt changes\nand comes to the conclusion that it does not give even a shadow of\nan explanation of the origin of species. It is as improbable as it is\nunnecessary.\n\nSports and spontaneous variations must now be considered. It is well\nknown that they have produced a large number of fine horticultural\nvarieties. The cut-leaved maple and many other trees and shrubs with\nsplit leaves are known to have been produced at a single step; this\nis true in the case of the single-leaf strawberry plant and of the\nlaciniate variety of the greater celandine: many white flowers, white\nor yellow berries and numerous other forms had a similar origin. But\nchanges such as these do not come under the head of adaptations, as they\nconsist for the most part in the loss of some quality or organ belonging\nto the species from which they were derived. Darwin thinks it impossible\nto attribute to this cause the innumerable structures, which are so well\nadapted to the habits of life of each species. At the present time we\nshould say that such adaptations require progressive modifications,\nwhich are additions to the stock of qualities already possessed by\nthe ancestors, and cannot, therefore, be explained on the ground of\na supposed analogy with sports, which are for the most part of a\nretrogressive nature.\n\nExcluding all these more or less sudden changes, there remains a long\nseries of gradations of variability, but all of these are not assumed by\nDarwin to be equally fit for the production of new species. In the\nfirst place, he disregards all mere temporary variations, such as size,\nalbinism, etc.; further, he points out that very many species have\nalmost certainly been produced by steps, not greater, and probably not\nvery much smaller, than those separating closely related varieties. For\nvarieties are only small species. Next comes the question of polymorphic\nspecies: their occurrence seems to have been a source of much doubt and\ndifficulty in Darwin's mind, although at present it forms one of\nthe main supports of the prevailing explanation of the origin of new\nspecies. Darwin simply states that this kind of variability seems to\nbe of a peculiar nature; since polymorphic species are now in a stable\ncondition their occurrence gives no clue as to the mode of origin of\nnew species. Polymorphic species are the expression of the result\nof previous variability acting on a large scale; but they now simply\nconsist of more or less numerous elementary species, which, as far as we\nknow, do not at present exhibit a larger degree of variability than any\nother more uniform species. The vernal whitlow-grass (Draba verna) and\nthe wild pansy are the best known examples; both have spread over almost\nthe whole of Europe and are split up into hundreds of elementary\nforms. These sub-species show no signs of any extraordinary degree\nof variability, when cultivated under conditions necessary for the\nexclusion of inter-crossing. Hooker has shown, in the case of some ferns\ndistributed over still wider areas, that the extinction of some of the\nintermediate forms in such groups would suffice to justify the elevation\nof the remaining types to the rank of distinct species. Polymorphic\nspecies may now be regarded as the link which unites ordinary\nvariability with the historical production of species. But it does not\nappear that they had this significance for Darwin; and, in fact, they\nexhibit no phenomena which could explain the processes by which one\nspecies has been derived from another. By thus narrowing the limits\nof the species-producing variability Darwin was led to regard small\ndeviations as the source from which natural selection derives material\nupon which to act. But even these are not all of the same type, and\nDarwin was well aware of the fact.\n\nIt should here be pointed out that in order to be selected, a change\nmust first have been produced. This proposition, which now seems\nself-evident, has, however, been a source of much difference of opinion\namong Darwin's followers. The opinion that natural selection produces\nchanges in useful directions has prevailed for a long time. In other\nwords, it was assumed that natural selection, by the simple means of\nsingling out, could induce small and useful changes to increase and\nto reach any desired degree of deviation from the original type. In\nmy opinion this view was never actually held by Darwin. It is\nin contradiction with the acknowledged aim of all his work,--the\nexplanation of the origin of species by means of natural forces and\nphenomena only. Natural selection acts as a sieve; it does not single\nout the best variations, but it simply destroys the larger number of\nthose which are, from some cause or another, unfit for their present\nenvironment. In this way it keeps the strains up to the required\nstandard, and, in special circumstances, may even improve them.\n\nReturning to the variations which afford the material for the\nsieving-action of natural selection, we may distinguish two main kinds.\nIt is true that the distinction between these was not clear at the time\nof Darwin, and that he was unable to draw a sharp line between them.\nNevertheless, in many cases, he was able to separate them, and he often\ndiscussed the question which of the two would be the real source of\nthe differentiation of species. Certain variations constantly occur,\nespecially such as are connected with size, weight, colour, etc. They\nare usually too small for natural selection to act upon, having hardly\nany influence in the struggle for life: others are more rare, occurring\nonly from time to time, perhaps once or twice in a century, perhaps even\nonly once in a thousand years. Moreover, these are of another type, not\nsimply affecting size, number or weight, but bringing about something\nnew, which may be useful or not. Whenever the variation is useful\nnatural selection will take hold of it and preserve it; in other cases\nthe variation may either persist or disappear.\n\nIn his criticism of miscellaneous objections brought forward against the\ntheory of natural selection after the publication of the first edition\nof \"The Origin of Species\", Darwin stated his view on this point very\nclearly:--\"The doctrine of natural selection or the survival of the\nfittest, which implies that when variations or individual differences of\na beneficial nature happen to arise, these will be preserved.\" (\"Origin\nof Species\" (6th edition), page 169, 1882.) In this sentence the words\n\"HAPPEN TO ARISE\" appear to me of prominent significance. They are\nevidently due to the same general conception which prevailed in Darwin's\nPangenesis hypothesis. (Cf. de Vries, \"Intracellulare Pangenesis\", page\n73, Jena, 1889, and \"Die Mutationstheorie\", I. page 63. Leipzig, 1901.)\n\nA distinction is indicated between ordinary fluctuations which are\nalways present, and such variations as \"happen to arise\" from time to\ntime. ((I think it right to point out that the interpretation of this\npassage from the \"Origin\" by Professor de Vries is not accepted as\ncorrect either by Mr Francis Darwin or by myself. We do not believe that\nDarwin intended to draw any distinction between TWO TYPES of variation;\nthe words \"when variations or individual differences of a beneficial\nnature happen to arise\" are not in our opinion meant to imply a\ndistinction between ordinary fluctuations and variations which \"happen\nto arise,\" but we believe that \"or\" is here used in the sense of ALIAS.\nWith the permission of Professor de Vries, the following extract is\nquoted from a letter in which he replied to the objection raised to his\nreading of the passage in question:\n\n\"As to your remarks on the passage on page 6, I agree that it is now\nimpossible to see clearly how far Darwin went in his distinction of the\ndifferent kinds of variability. Distinctions were only dimly guessed at\nby him. But in our endeavour to arrive at a true conception of his view\nI think that the chapter on Pangenesis should be our leading guide,\nand that we should try to interpret the more difficult passages by that\nchapter. A careful and often repeated study of the Pangenesis hypothesis\nhas convinced me that Darwin, when he wrote that chapter, was well aware\nthat ordinary variability has nothing to do with evolution, but that\nother kinds of variation were necessary. In some chapters he comes\nnearer to a clear distinction than in others. To my mind the expression\n'happen to arise' is the sharpest indication of his inclining in this\ndirection. I am quite convinced that numerous expressions in his book\nbecome much clearer when looked at in this way.\"\n\nThe statement in this passage that \"Darwin was well aware that ordinary\nvariability has nothing to do with evolution, but that other kinds\nof variation were necessary\" is contradicted by many passages in the\n\"Origin\". A.C.S.)) The latter afford the material for natural selection\nto act upon on the broad lines of organic development, but the first\ndo not. Fortuitous variations are the species-producing kind, which the\ntheory requires; continuous fluctuations constitute, in this respect, a\nuseless type.\n\nOf late, the study of variability has returned to the recognition of\nthis distinction. Darwin's variations, which from time to time happen\nto arise, are MUTATIONS, the opposite type being commonly designed\nfluctuations. A large mass of facts, collected during the last few\ndecades, has confirmed this view, which in Darwin's time could only be\nexpressed with much reserve, and everyone knows that Darwin was always\nvery careful in statements of this kind.\n\nFrom the same chapter I may here cite the following paragraph: \"Thus\nas I am inclined to believe, morphological differences,... such as\nthe arrangement of the leaves, the divisions of the flower or of the\novarium, the position of the ovules, etc.--first appeared in many cases\nas fluctuating variations, which sooner or later became constant through\nthe nature of the organism and of the surrounding conditions... but NOT\nTHROUGH NATURAL SELECTION (The italics are mine (H. de V.).); for as\nthese morphological characters do not affect the welfare of the species,\nany slight deviation in them could not have been governed or accumulated\nthrough this latter agency.\" (\"Origin of Species\" (6th edition), page\n176.) We thus see that in Darwin's opinion, all small variations had\nnot the same importance. In favourable circumstances some could become\nconstant, but others could not.\n\nSince the appearance of the first edition of \"The Origin of Species\"\nfluctuating variability has been thoroughly studied by Quetelet. He\ndiscovered the law, which governs all phenomena of organic life falling\nunder this head. It is a very simple law, and states that individual\nvariations follow the laws of probability. He proved it, in the first\nplace, for the size of the human body, using the measurements published\nfor Belgian recruits; he then extended it to various other measurements\nof parts of the body, and finally concluded that it must be of universal\nvalidity for all organic beings. It must hold true for all characters in\nman, physical as well as intellectual and moral qualities; it must hold\ntrue for the plant kingdom as well as for the animal kingdom; in short,\nit must include the whole living world.\n\nQuetelet's law may be most easily studied in those cases where the\nvariability relates to measure, number and weight, and a vast number of\nfacts have since confirmed its exactness and its validity for all kinds\nof organisms, organs and qualities. But if we examine it more closely,\nwe find that it includes just those minute variations, which, as Darwin\nrepeatedly pointed out, have often no significance for the origin of\nspecies. In the phenomena, described by Quetelet's law nothing \"happens\nto arise\"; all is governed by the common law, which states that small\ndeviations from the mean type are frequent, but that larger aberrations\nare rare, the rarer as they are larger. Any degree of variation will\nbe found to occur, if only the number of individuals studied is large\nenough: it is even possible to calculate before hand, how many\nspecimens must be compared in order to find a previously fixed degree of\ndeviation.\n\nThe variations, which from time to time happen to appear, are evidently\nnot governed by this law. They cannot, as yet, be produced at will: no\nsowings of thousands or even of millions of plants will induce them,\nalthough by such means the chance of their occurring will obviously\nbe increased. But they are known to occur, and to occur suddenly and\nabruptly. They have been observed especially in horticulture, where they\nare ranged in the large and ill-defined group called sports. Korschinsky\nhas collected all the evidence which horticultural literature affords\non this point. (S. Korschinsky, \"Heterogenesis und Evolution\", \"Flora\",\nVol. LXXXIX. pages 240-363, 1901.) Several cases of the first appearance\nof a horticultural novelty have been recorded: this has always happened\nin the same way; it appeared suddenly and unexpectedly without any\ndefinite relation to previously existing variability. Dwarf types are\none of the commonest and most favourite varieties of flowering plants;\nthey are not originated by a repeated selection of the smallest\nspecimens, but appear at once, without intermediates and without any\nprevious indication. In many instances they are only about half the\nheight of the original type, thus constituting obvious novelties. So it\nis in other cases described by Korschinsky: these sports or mutations\nare now recognised to be the main source of varieties of horticultural\nplants.\n\nAs already stated, I do not pretend that the production of horticultural\nnovelties is the prototype of the origin of new species in nature. I\nassume that they are, as a rule, derived from the parent species by the\nloss of some organ or quality, whereas the main lines of the evolution\nof the animal and vegetable kingdom are of course determined by\nprogressive changes. Darwin himself has often pointed out this\ndifference. But the saltatory origin of horticultural novelties is as\nyet the simplest parallel for natural mutations, since it relates to\nforms and phenomena, best known to the general student of evolution.\n\nThe point which I wish to insist upon is this. The difference between\nsmall and ever present fluctuations and rare and more sudden variations\nwas clear to Darwin, although the facts known at his time were too\nmeagre to enable a sharp line to be drawn between these two great\nclasses of variability. Since Darwin's time evidence, which proves\nthe correctness of his view, has accumulated with increasing rapidity.\nFluctuations constitute one type; they are never absent and follow the\nlaw of chance, but they do not afford the material from which to build\nnew species. Mutations, on the other hand, only happen to occur from\ntime to time. They do not necessarily produce greater changes than\nfluctuations, but such as may become, or rather are from their very\nnature, constant. It is this constancy which is the mark of specific\ncharacters, and on this basis every new specific character may be\nassumed to have arisen by mutation.\n\nSome authors have tried to show that the theory of mutation is opposed\nto Darwin's views. But this is erroneous. On the contrary, it is in\nfullest harmony with the great principle laid down by Darwin. In order\nto be acted upon by that complex of environmental forces, which Darwin\nhas called natural selection, the changes must obviously first be there.\nThe manner in which they are produced is of secondary importance and has\nhardly any bearing on the theory of descent with modification. (\"Life\nand Letters\" II. 125.)\n\nA critical survey of all the facts of variability of plants in nature as\nwell as under cultivation has led me to the conviction, that Darwin was\nright in stating that those rare beneficial variations, which from time\nto time happen to arise,--the now so-called mutations--are the real\nsource of progress in the whole realm of the organic world.\n\nII. EXTERNAL AND INTERNAL CAUSES OF VARIABILITY.\n\nAll phenomena of animal and plant life are governed by two sets of\ncauses; one of these is external, the other internal. As a rule the\ninternal causes determine the nature of a phenomenon--what an organism\ncan do and what it cannot do. The external causes, on the other hand,\ndecide when a certain variation will occur, and to what extent its\nfeatures may be developed.\n\nAs a very clear and wholly typical instance I cite the cocks-combs\n(Celosia). This race is distinguished from allied forms by its faculty\nof producing the well-known broad and much twisted combs. Every single\nindividual possesses this power, but all individuals do not exhibit\nit in its most complete form. In some cases this faculty may not be\nexhibited at the top of the main stem, although developed in lateral\nbranches: in others it begins too late for full development. Much\ndepends upon nourishment and cultivation, but almost always the\nhorticulturist has to single out the best individuals and to reject\nthose which do not come up to the standard.\n\nThe internal causes are of a historical nature. The external ones may be\ndefined as nourishment and environment. In some cases nutrition is\nthe main factor, as, for instance, in fluctuating variability, but in\nnatural selection environment usually plays the larger part.\n\nThe internal or historical causes are constant during the life-time of\na species, using the term species in its most limited sense, as\ndesignating the so-called elementary species or the units out of which\nthe ordinary species are built up. These historical causes are simply\nthe specific characters, since in the origin of a species one or more of\nthese must have been changed, thus producing the characters of the new\ntype. These changes must, of course, also be due partly to internal and\npartly to external causes.\n\nIn contrast to these changes of the internal causes, the ordinary\nvariability which is exhibited during the life-time of a species\nis called fluctuating variability. The name mutations or mutating\nvariability is then given to the changes in the specific characters.\nIt is desirable to consider these two main divisions of variability\nseparately.\n\nIn the case of fluctuations the internal causes, as well as the external\nones, are often apparent. The specific characters may be designated as\nthe mean about which the observed forms vary. Almost every character may\nbe developed to a greater or a less degree, but the variations of the\nsingle characters producing a small deviation from the mean are usually\nthe commonest. The limits of these fluctuations may be called wide or\nnarrow, according to the way we look at them, but in numerous cases the\nextreme on the favoured side hardly surpasses double the value of that\non the other side. The degree of this development, for every individual\nand for every organ, is dependent mainly on nutrition. Better\nnourishment or an increased supply of food produces a higher\ndevelopment; only it is not always easy to determine which direction\nis the fuller and which is the poorer one. The differences among\nindividuals grown from different seeds are described as examples of\nindividual variability, but those which may be observed on the same\nplant, or on cuttings, bulbs or roots derived from one individual\nare referred to as cases of partial variability. Partial variability,\ntherefore, determines the differences among the flowers, fruits, leaves\nor branches of one individual: in the main, it follows the same laws\nas individual variability, but the position of a branch on a plant also\ndetermines its strength, and the part it may take in the nourishment of\nthe whole. Composite flowers and umbels therefore have, as a rule,\nfewer rays on weak branches than on the strong main ones. The number of\ncarpels in the fruits of poppies becomes very small on the weak lateral\nbranches, which are produced towards the autumn, as well as on crowded,\nand therefore on weakened individuals. Double flowers follow the same\nrule, and numerous other instances could easily be adduced.\n\nMutating variability occurs along three main lines. Either a character\nmay disappear, or, as we now say, become latent; or a latent character\nmay reappear, reproducing thereby a character which was once prominent\nin more or less remote ancestors. The third and most interesting case\nis that of the production of quite new characters which never existed in\nthe ancestors. Upon this progressive mutability the main development of\nthe animal and vegetable kingdom evidently depends. In contrast to this,\nthe two other cases are called retrogressive and degressive mutability.\nIn nature retrogressive mutability plays a large part; in agriculture\nand in horticulture it gives rise to numerous varieties, which have\nin the past been preserved, either on account of their usefulness or\nbeauty, or simply as fancy-types. In fact the possession of numbers\nof varieties may be considered as the main character of domesticated\nanimals and cultivated plants.\n\nIn the case of retrogressive and degressive mutability the internal\ncause is at once apparent, for it is this which causes the disappearance\nor reappearance of some character. With progressive mutations the case\nis not so simple, since the new character must first be produced and\nthen displayed. These two processes are theoretically different, but\nthey may occur together or after long intervals. The production of the\nnew character I call premutation, and the displaying mutation. Both of\ncourse must have their external as well as their internal causes, as\nI have repeatedly pointed out in my work on the Mutation Theory. (\"Die\nMutationstheorie\", 2 vols., Leipzig, 1901.)\n\nIt is probable that nutrition plays as important a part among the\nexternal causes of mutability as it does among those of fluctuating\nvariability. Observations in support of this view, however, are too\nscanty to allow of a definite judgment. Darwin assumed an accumulative\ninfluence of external causes in the case of the production of new\nvarieties or species. The accumulation might be limited to the life-time\nof a single individual, or embrace that of two or more generations.\nIn the end a degree of instability in the equilibrium of one or more\ncharacters might be attained, great enough for a character to give\nway under a small shock produced by changed conditions of life. The\ncharacter would then be thrown over from the old state of equilibrium\ninto a new one.\n\nCharacters which happen to be in this state of unstable equilibrium are\ncalled mutable. They may be either latent or active, being in the\nformer case derived from old active ones or produced as new ones (by the\nprocess, designated premutation). They may be inherited in this mutable\ncondition during a long series of generations. I have shown that in the\ncase of the evening primrose of Lamarck this state of mutability\nmust have existed for at least half a century, for this species was\nintroduced from Texas into England about the year 1860, and since then\nall the strains derived from its first distribution over the several\ncountries of Europe show the same phenomena in producing new forms.\nThe production of the dwarf evening primrose, or Oenothera nanella,\nis assumed to be due to one of the factors, which determines the tall\nstature of the parent form, becoming latent; this would, therefore,\nafford an example of retrogressive mutation. Most of the other types\nof my new mutants, on the other hand, seem to be due to progressive\nmutability.\n\nThe external causes of this curious period of mutability are as yet\nwholly unknown and can hardly be guessed at, since the origin of the\nOenothera Lamarckiana is veiled in mystery. The seeds, introduced into\nEngland about 1860, were said to have come from Texas, but whether from\nwild or from cultivated plants we do not know. Nor has the species been\nrecorded as having been observed in the wild condition. This, however,\nis nothing peculiar. The European types of Oenothera biennis and O.\nmuricata are in the same condition. The first is said to have been\nintroduced from Virginia, and the second from Canada, but both probably\nfrom plants cultivated in the gardens of these countries. Whether the\nsame elementary species are still growing on those spots is unknown,\nmainly because the different sub-species of the species mentioned have\nnot been systematically studied and distinguished.\n\nThe origin of new species, which is in part the effect of mutability,\nis, however, due mainly to natural selection. Mutability provides the\nnew characters and new elementary species. Natural selection, on the\nother hand, decides what is to live and what to die. Mutability seems to\nbe free, and not restricted to previously determined lines. Selection,\nhowever, may take place along the same main lines in the course of long\ngeological epochs, thus directing the development of large branches of\nthe animal and vegetable kingdom. In natural selection it is evident\nthat nutrition and environment are the main factors. But it is probable\nthat, while nutrition may be one of the main causes of mutability,\nenvironment may play the chief part in the decisions ascribed to natural\nselection. Relations to neighbouring plants and to injurious or useful\nanimals, have been considered the most important determining factors\never since the time when Darwin pointed out their prevailing influence.\n\nFrom this discussion of the main causes of variability we may derive the\nproposition that the study of every phenomenon in the field of heredity,\nof variability, and of the origin of new species will have to be\nconsidered from two standpoints; on one hand we have the internal\ncauses, on the other the external ones. Sometimes the first are more\neasily detected, in other cases the latter are more accessible to\ninvestigation. But the complete elucidation of any phenomenon of life\nmust always combine the study of the influence of internal with that of\nexternal causes.\n\nIII. POLYMORPHIC VARIABILITY IN CEREALS.\n\nOne of the propositions of Darwin's theory of the struggle for life\nmaintains that the largest amount of life can be supported on any area,\nby great diversification or divergence in the structure and constitution\nof its inhabitants. Every meadow and every forest affords a proof of\nthis thesis. The numerical proportion of the different species of the\nflora is always changing according to external influences. Thus, in a\ngiven meadow, some species will flower abundantly in one year and then\nalmost disappear, until, after a series of years, circumstances allow\nthem again to multiply rapidly. Other species, which have taken their\nplaces, will then become rare. It follows from this principle, that\nnotwithstanding the constantly changing conditions, a suitable\nselection from the constituents of a meadow will ensure a continued\nhigh production. But, although the principle is quite clear, artificial\nselection has, as yet, done very little towards reaching a really high\nstandard.\n\nThe same holds good for cereals. In ordinary circumstances a field\nwill give a greater yield, if the crop grown consists of a number of\nsufficiently differing types. Hence it happens that almost all older\nvarieties of wheat are mixtures of more or less diverging forms. In the\nsame variety the numerical composition will vary from year to year, and\nin oats this may, in bad years, go so far as to destroy more than half\nof the harvest, the wind-oats (Avena fatua), which scatter their grain\nto the winds as soon as it ripens, increasing so rapidly that they\nassume the dominant place. A severe winter, a cold spring and other\nextreme conditions of life will destroy one form more completely\nthan another, and it is evident that great changes in the numerical\ncomposition of the mixture may thus be brought about.\n\nThis mixed condition of the common varieties of cereals was well known\nto Darwin. For him it constituted one of the many types of variability.\nIt is of that peculiar nature to which, in describing other groups,\nhe applies the term polymorphy. It does not imply that the single\nconstituents of the varieties are at present really changing their\ncharacters. On the other hand, it does not exclude the possibility of\nsuch changes. It simply states that observation shows the existence of\ndifferent forms; how these have originated is a question which it\ndoes not deal with. In his well-known discussion of the variability of\ncereals, Darwin is mainly concerned with the question, whether under\ncultivation they have undergone great changes or only small ones.\nThe decision ultimately depends on the question, how many forms have\noriginally been taken into cultivation. Assuming five or six initial\nspecies, the variability must be assumed to have been very large, but\non the assumption that there were between ten and fifteen types, the\nnecessary range of variability is obviously much smaller. But in regard\nto this point, we are of course entirely without historical data.\n\nFew of the varieties of wheat show conspicuous differences, although\ntheir number is great. If we compare the differentiating characters of\nthe smaller types of cereals with those of ordinary wild species, even\nwithin the same genus or family, they are obviously much less marked.\nAll these small characters, however, are strictly inherited, and this\nfact makes it very probable that the less obvious constituents of the\nmixtures in ordinary fields must be constant and pure as long as they do\nnot intercross. Natural crossing is in most cereals a phenomenon of rare\noccurrence, common enough to admit of the production of all possible\nhybrid combinations, but requiring the lapse of a long series of years\nto reach its full effect.\n\nDarwin laid great stress on this high amount of variability in the\nplants of the same variety, and illustrated it by the experience of\nColonel Le Couteur (\"On the Varieties, Properties, and Classification of\nWheat\", Jersey, 1837.) on his farm on the isle of Jersey, who cultivated\nupwards of 150 varieties of wheat, which he claimed were as pure as\nthose of any other agriculturalist. But Professor La Gasca of Madrid,\nwho visited him, drew attention to aberrant ears, and pointed out, that\nsome of them might be better yielders than the majority of plants in the\ncrop, whilst others might be poor types. Thence he concluded that the\nisolation of the better ones might be a means of increasing his crops.\nLe Couteur seems to have considered the constancy of such smaller types\nafter isolation as absolutely probable, since he did not even discuss\nthe possibility of their being variable or of their yielding a\nchangeable or mixed progeny. This curious fact proves that he considered\nthe types, discovered in his fields by La Gasca to be of the same kind\nas his other varieties, which until that time he had relied upon as\nbeing pure and uniform. Thus we see, that for him, the variability of\ncereals was what we now call polymorphy. He looked through his fields\nfor useful aberrations, and collected twenty-three new types of wheat.\nHe was, moreover, clear about one point, which, on being rediscovered\nafter half a century, has become the starting-point for the new Swedish\nprinciple of selecting agricultural plants. It was the principle of\nsingle-ear sowing, instead of mixing the grains of all the selected ears\ntogether. By sowing each ear on a separate plot he intended not only\nto multiply them, but also to compare their value. This comparison\nultimately led him to the choice of some few valuable sorts, one of\nwhich, the \"Bellevue de Talavera,\" still holds its place among the\nprominent sorts of wheat cultivated in France. This variety seems to be\nreally a uniform type, a quality very useful under favourable conditions\nof cultivation, but which seems to have destroyed its capacity for\nfurther improvement by selection.\n\nThe principle of single-ear sowing, with a view to obtain pure and\nuniform strains without further selection, has, until a few years ago,\nbeen almost entirely lost sight of. Only a very few agriculturists have\napplied it: among these are Patrick Shirreff (\"Die Verbesserung der\nGetreide-Arten\", translated by R. Hesse, Halle, 1880.) in Scotland\nand Willet M. Hays (\"Wheat, varieties, breeding, cultivation\", Univ.\nMinnesota, Agricultural Experimental Station, Bull. no. 62, 1899.) in\nMinnesota. Patrick Shirreff observed the fact, that in large fields of\ncereals, single plants may from time to time be found with larger ears,\nwhich justify the expectation of a far greater yield. In the course of\nabout twenty-five years he isolated in this way two varieties of wheat\nand two of oats. He simply multiplied them as fast as possible, without\nany selection, and put them on the market.\n\nHays was struck by the fact that the yield of wheat in Minnesota was far\nbeneath that in the neighbouring States. The local varieties were Fife\nand Blue Stem. They gave him, on inspection, some better specimens,\n\"phenomenal yielders\" as he called them. These were simply isolated and\npropagated, and, after comparison with the parent-variety and with some\nother selected strains of less value, were judged to be of sufficient\nimportance to be tested by cultivation all over the State of Minnesota.\nThey have since almost supplanted the original types, at least in most\nparts of the State, with the result that the total yield of wheat in\nMinnesota is said to have been increased by about a million dollars\nyearly.\n\nDefinite progress in the method of single-ear sowing has, however, been\nmade only recently. It had been foreshadowed by Patrick Shirreff, who\nafter the production of the four varieties already mentioned, tried\nto carry out his work on a larger scale, by including numerous minor\ndeviations from the main type. He found by doing so that the chances\nof obtaining a better form were sufficiently increased to justify\nthe trial. But it was Nilsson who discovered the almost inexhaustible\npolymorphy of cereals and other agricultural crops and made it the\nstarting-point for a new and entirely trustworthy method of the highest\nutility. By this means he has produced during the last fifteen years a\nnumber of new and valuable races, which have already supplanted the old\ntypes on numerous farms in Sweden and which are now being introduced on\na large scale into Germany and other European countries.\n\nIt is now twenty years since the station at Svalof was founded. During\nthe first period of its work, embracing about five years, selection was\npractised on the principle which was then generally used in Germany. In\norder to improve a race a sample of the best ears was carefully selected\nfrom the best fields of the variety. These ears were considered as\nrepresentatives of the type under cultivation, and it was assumed that\nby sowing their grains on a small plot a family could be obtained, which\ncould afterwards be improved by a continuous selection. Differences\nbetween the collected ears were either not observed or disregarded. At\nSvalof this method of selection was practised on a far larger scale than\non any German farm, and the result was, broadly speaking, the same.\nThis may be stated in the following words: improvement in a few cases,\nfailure in all the others. Some few varieties could be improved and\nyielded excellent new types, some of which have since been introduced\ninto Swedish agriculture and are now prominent races in the southern\nand middle parts of the country. But the station had definite aims, and\namong them was the improvement of the Chevalier barley. This, in\nMiddle Sweden, is a fine brewer's barley, but liable to failure during\nunfavourable summers on account of its slender stems. It was selected\nwith a view of giving it stiffer stems, but in spite of all the care and\nwork bestowed upon it no satisfactory result was obtained.\n\nThis experience, combined with a number of analogous failures, could\nnot fail to throw doubt upon the whole method. It was evident that good\nresults were only exceptions, and that in most cases the principle\nwas not one that could be relied upon. The exceptions might be due\nto unknown causes, and not to the validity of the method; it became\ntherefore of much more interest to search for the causes than to\ncontinue the work along these lines.\n\nIn the year 1892 a number of different varieties of cereals were\ncultivated on a large scale and a selection was again made from\nthem. About two hundred samples of ears were chosen, each apparently\nconstituting a different type. Their seeds were sown on separate plots\nand manured and treated as much as possible in the same manner. The\nplots were small and arranged in rows so as to facilitate the comparison\nof allied types. During the whole period of growth and during the\nripening of the ears the plots were carefully studied and compared: they\nwere harvested separately; ears and kernels were counted and weighed,\nand notes were made concerning layering, rust and other cereal pests.\n\nThe result of this experiment was, in the main, no distinct improvement.\nNilsson was especially struck by the fact that the plots, which should\nrepresent distinct types, were far from uniform. Many of them were as\nmultiform as the fields from which the parent-ears were taken. Others\nshowed variability in a less degree, but in almost all of them it was\nclear that a pure race had not been obtained. The experiment was a fair\none, inasmuch as it demonstrated the polymorphic variability of cereals\nbeyond all doubt and in a degree hitherto unsuspected; but from the\nstandpoint of the selectionist it was a failure. Fortunately there were,\nhowever, one or two exceptions. A few lots showed a perfect uniformity\nin regard to all the stalks and ears: these were small families. This\nfact suggested the idea that each might have been derived from a single\near. During the selection in the previous summer, Nilsson had tried to\nfind as many ears as possible of each new type which he recognised in\nhis fields. But the variability of his crops was so great, that he was\nrarely able to include more than two or three ears in the same group,\nand, in a few cases, he found only one representative of the supposed\ntype. It might, therefore, be possible that those small uniform plots\nwere the direct progeny of ears, the grains of which had not been mixed\nwith those from other ears before sowing. Exact records had, of course,\nbeen kept of the chosen samples, and the number of ears had been noted\nin each case. It was, therefore, possible to answer the question and it\nwas found that those plots alone were uniform on which the kernels of\none single ear only had been sown. Nilsson concluded that the mixture\nof two or more ears in a single sowing might be the cause of the lack of\nuniformity in the progeny. Apparently similar ears might be different in\ntheir progeny.\n\nOnce discovered, this fact was elevated to the rank of a leading\nprinciple and tested on as large a scale as possible. The fields were\nagain carefully investigated and every single ear, which showed a\ndistinct divergence from the main type in one character or another,\nwas selected. A thousand samples were chosen, but this time each sample\nconsisted of one ear only. Next year, the result corresponded to the\nexpectation. Uniformity prevailed almost everywhere; only a few\nlots showed a discrepancy, which might be ascribed to the accidental\nselection of hybrid ears. It was now clear that the progeny of single\nears was, as a rule, pure, whereas that of mixed ears was impure.\nThe single-ear selection or single-ear sowing, which had fallen into\ndiscredit in Germany and elsewhere in Europe, was rediscovered. It\nproved to be the only trustworthy principle of selection. Once isolated,\nsuch single-parent races are constant from seed and remain true to their\ntype. No further selection is needed; they have simply to be multiplied\nand their real value tested.\n\nPatrick Shirreff, in his early experiments, Le Couteur, Hays and others\nhad observed the rare occurrence of exceptionally good yielders and the\nvalue of their isolation to the agriculturist. The possibility of error\nin the choice of such striking specimens and the necessity of judging\ntheir value by their progeny were also known to these investigators, but\nthey had not the slightest idea of all the possibilities suggested by\ntheir principle. Nilsson, who is a botanist as well as an agriculturist,\ndiscovered that, besides these exceptionably good yielders, every\nvariety of a cereal consists of hundreds of different types, which find\nthe best conditions for success when grown together, but which, after\nisolation, prove to be constant. Their preference for mixed growth is so\ndefinite, that once isolated, their claims on manure and treatment\nare found to be much higher than those of the original mixed variety.\nMoreover, the greatest care is necessary to enable them to retain\ntheir purity, and as soon as they are left to themselves they begin to\ndeteriorate through accidental crosses and admixtures and rapidly return\nto the mixed condition.\n\nReverting now to Darwin's discussion of the variability of cereals, we\nmay conclude that subsequent investigation has proved it to be exactly\nof the kind which he describes. The only difference is that in reality\nit reaches a degree, quite unexpected by Darwin and his contemporaries.\nBut it is polymorphic variability in the strictest sense of the word.\nHow the single constituents of a variety originate we do not see. We\nmay assume, and there can hardly be a doubt about the truth of the\nassumption, that a new character, once produced, will slowly but surely\nbe combined through accidental crosses with a large number of\npreviously existing types, and so will tend to double the number of the\nconstituents of the variety. But whether it first appears suddenly or\nwhether it is only slowly evolved we cannot determine. It would, of\ncourse, be impossible to observe either process in such a mixture. Only\ncultures of pure races, of single-parent races as we have called them,\ncan afford an opportunity for this kind of observation. In the fields of\nSvalof new and unexpected qualities have recently been seen, from time\nto time, to appear suddenly. These characters are as distinct as the\nolder ones and appear to be constant from the moment of their origin.\n\nDarwin has repeatedly insisted that man does not cause variability. He\nsimply selects the variations given to him by the hand of nature. He may\nrepeat this process in order to accumulate different new characters\nin the same family, thus producing varieties of a higher order. This\nprocess of accumulation would, if continued for a longer time, lead to\nthe augmentation of the slight differences characteristic of varieties\ninto the greater differences characteristic of species and genera. It is\nin this way that horticultural and agricultural experience contribute\nto the problem of the conversion of varieties into species, and to the\nexplanation of the admirable adaptations of each organism to its complex\nconditions of life. In the long run new forms, distinguished from their\nallies by quite a number of new characters, would, by the extermination\nof the older intermediates, become distinct species.\n\nThus we see that the theory of the origin of species by means of natural\nselection is quite independent of the question, how the variations to\nbe selected arise. They may arise slowly, from simple fluctuations, or\nsuddenly, by mutations; in both cases natural selection will take hold\nof them, will multiply them if they are beneficial, and in the course of\ntime accumulate them, so as to produce that great diversity of organic\nlife, which we so highly admire.\n\nDarwin has left the decision of this difficult and obviously subordinate\npoint to his followers. But in his Pangenesis hypothesis he has given us\nthe clue for a close study and ultimate elucidation of the subject under\ndiscussion.\n\n\n\n\nV. HEREDITY AND VARIATION IN MODERN LIGHTS. By W. Bateson, M.A., F.R.S.\n\nProfessor of Biology in the University of Cambridge.\n\n\nDarwin's work has the property of greatness in that it may be admired\nfrom more aspects than one. For some the perception of the principle of\nNatural Selection stands out as his most wonderful achievement to which\nall the rest is subordinate. Others, among whom I would range myself,\nlook up to him rather as the first who plainly distinguished, collected,\nand comprehensively studied that new class of evidence from which\nhereafter a true understanding of the process of Evolution may be\ndeveloped. We each prefer our own standpoint of admiration; but I think\nthat it will be in their wider aspect that his labours will most command\nthe veneration of posterity.\n\nA treatise written to advance knowledge may be read in two moods. The\nreader may keep his mind passive, willing merely to receive the impress\nof the writer's thought; or he may read with his attention strained and\nalert, asking at every instant how the new knowledge can be used in a\nfurther advance, watching continually for fresh footholds by which to\nclimb higher still. Of Shelley it has been said that he was a poet\nfor poets: so Darwin was a naturalist for naturalists. It is when his\nwritings are used in the critical and more exacting spirit with which\nwe test the outfit for our own enterprise that we learn their full value\nand strength. Whether we glance back and compare his performance with\nthe efforts of his predecessors, or look forward along the course which\nmodern research is disclosing, we shall honour most in him not the\nrounded merit of finite accomplishment, but the creative power by which\nhe inaugurated a line of discovery endless in variety and extension.\nLet us attempt thus to see his work in true perspective between the past\nfrom which it grew, and the present which is its consequence. Darwin\nattacked the problem of Evolution by reference to facts of three\nclasses: Variation; Heredity; Natural Selection. His work was not as the\nlaity suppose, a sudden and unheralded revelation, but the first fruit\nof a long and hitherto barren controversy. The occurrence of variation\nfrom type, and the hereditary transmission of such variation had of\ncourse been long familiar to practical men, and inferences as to the\npossible bearing of those phenomena on the nature of specific difference\nhad been from time to time drawn by naturalists. Maupertuis, for\nexample, wrote \"Ce qui nous reste a examiner, c'est comment d'un seul\nindividu, il a pu naitre tant d'especes si differentes.\" And again \"La\nNature contient le fonds de toutes ces varietes: mais le hasard ou l'art\nles mettent en oeuvre. C'est ainsi que ceux dont l'industrie s'applique\na satisfaire le gout des curieux, sont, pour ainsi dire, creatures\nd'especes nouvelles.\" (\"Venus Physique, contenant deux Dissertations,\nl'une sur l'origine des Hommes et des Animaux: Et l'autre sur l'origine\ndes Noirs\" La Haye, 1746, pages 124 and 129. For an introduction to the\nwritings of Maupertuis I am indebted to an article by Professor Lovejoy\nin \"Popular Sci. Monthly\", 1902.)\n\nSuch passages, of which many (though few so emphatic) can be found in\neighteenth century writers, indicate a true perception of the mode of\nEvolution. The speculations hinted at by Buffon (For the fullest account\nof the views of these pioneers of Evolution, see the works of Samuel\nButler, especially \"Evolution, Old and New\" (2nd edition) 1882. Butler's\nclaims on behalf of Buffon have met with some acceptance; but after\nreading what Butler has said, and a considerable part of Buffon's own\nworks, the word \"hinted\" seems to me a sufficiently correct description\nof the part he played. It is interesting to note that in the chapter on\nthe Ass, which contains some of his evolutionary passages, there is a\nreference to \"plusieurs idees tres-elevees sur la generation\" contained\nin the Letters of Maupertuis.), developed by Erasmus Darwin, and\nindependently proclaimed above all by Lamarck, gave to the doctrine of\ndescent a wide renown. The uniformitarian teaching which Lyell deduced\nfrom geological observation had gained acceptance. The facts of\ngeographical distribution (See especially W. Lawrence, \"Lectures on\nPhysiology\", London, 1823, pages 213 f.) had been shown to be obviously\ninconsistent with the Mosaic legend. Prichard, and Lawrence, following\nthe example of Blumenbach, had successfully demonstrated that the races\nof Man could be regarded as different forms of one species, contrary\nto the opinion up till then received. These treatises all begin, it is\ntrue, with a profound obeisance to the sons of Noah, but that performed,\nthey continue on strictly modern lines. The question of the mutability\nof species was thus prominently raised.\n\nThose who rate Lamarck no higher than did Huxley in his contemptuous\nphrase \"buccinator tantum,\" will scarcely deny that the sound of the\ntrumpet had carried far, or that its note was clear. If then there were\nfew who had already turned to evolution with positive conviction,\nall scientific men must at least have known that such views had been\npromulgated; and many must, as Huxley says, have taken up his own\nposition of \"critical expectancy.\" (See the chapter contributed to the\n\"Life and Letters of Charles Darwin\" II. page 195. I do not clearly\nunderstand the sense in which Darwin wrote (Autobiography, ibid. I. page\n87): \"It has sometimes been said that the success of the \"Origin\" proved\n'that the subject was in the air,' or 'that men's minds were prepared\nfor it.' I do not think that this is strictly true, for I occasionally\nsounded not a few naturalists, and never happened to come across a\nsingle one who seemed to doubt about the permanence of species.\" This\nexperience may perhaps have been an accident due to Darwin's isolation.\nThe literature of the period abounds with indications of \"critical\nexpectancy.\" A most interesting expression of that feeling is given in\nthe charming account of the \"Early Days of Darwinism\" by Alfred Newton,\n\"Macmillan's Magazine\", LVII. 1888, page 241. He tells how in 1858\nwhen spending a dreary summer in Iceland, he and his friend, the\nornithologist John Wolley, in default of active occupation, spent\ntheir days in discussion. \"Both of us taking a keen interest in Natural\nHistory, it was but reasonable that a question, which in those days\nwas always coming up wherever two or more naturalists were gathered\ntogether, should be continually recurring. That question was, 'What is\na species?' and connected therewith was the other question, 'How did a\nspecies begin?'... Now we were of course fairly well acquainted with what\nhad been published on these subjects.\" He then enumerates some of these\npublications, mentioning among others T. Vernon Wollaston's \"Variation\nof Species\"--a work which has in my opinion never been adequately\nappreciated. He proceeds: \"Of course we never arrived at anything like\na solution of these problems, general or special, but we felt very\nstrongly that a solution ought to be found, and that quickly, if the\nstudy of Botany and Zoology was to make any great advance.\" He then\ndescribes how on his return home he received the famous number of the\n\"Linnean Journal\" on a certain evening. \"I sat up late that night to\nread it; and never shall I forget the impression it made upon me. Herein\nwas contained a perfectly simple solution of all the difficulties which\nhad been troubling me for months past... I went to bed satisfied that a\nsolution had been found.\")\n\nWhy, then, was it, that Darwin succeeded where the rest had failed?\nThe cause of that success was two-fold. First, and obviously, in the\nprinciple of Natural Selection he had a suggestion which would work. It\nmight not go the whole way, but it was true as far as it went. Evolution\ncould thus in great measure be fairly represented as a consequence of\ndemonstrable processes. Darwin seldom endangers the mechanism he devised\nby putting on it strains much greater than it can bear. He at least was\nunder no illusion as to the omnipotence of Selection; and he introduces\nnone of the forced pleading which in recent years has threatened to\ndiscredit that principle.\n\nFor example, in the latest text of the \"Origin\" (\"Origin\", (6th edition\n(1882), page 421.)) we find him saying:\n\n\"But as my conclusions have lately been much misrepresented, and it has\nbeen stated that I attribute the modification of species exclusively\nto natural selection, I may be permitted to remark that in the first\nedition of this work, and subsequently, I placed in a most conspicuous\nposition--namely, at the close of the Introduction--the following words:\n'I am convinced that natural selection has been the main but not the\nexclusive means of modification.'\"\n\nBut apart from the invention of this reasonable hypothesis, which may\nwell, as Huxley estimated, \"be the guide of biological and psychological\nspeculation for the next three or four generations,\" Darwin made a more\nsignificant and imperishable contribution. Not for a few generations,\nbut through all ages he should be remembered as the first who showed\nclearly that the problems of Heredity and Variation are soluble by\nobservation, and laid down the course by which we must proceed to\ntheir solution. (Whatever be our estimate of the importance of Natural\nSelection, in this we all agree. Samuel Butler, the most brilliant, and\nby far the most interesting of Darwin's opponents--whose works are at\nlength emerging from oblivion--in his Preface (1882) to the 2nd edition\nof \"Evolution, Old and New\", repeats his earlier expression of homage to\none whom he had come to regard as an enemy: \"To the end of time, if\nthe question be asked, 'Who taught people to believe in Evolution?' the\nanswer must be that it was Mr. Darwin. This is true, and it is hard to\nsee what palm of higher praise can be awarded to any philosopher.\") The\nmoment of inspiration did not come with the reading of Malthus, but with\nthe opening of the \"first note-book on Transmutation of Species.\" (\"Life\nand Letters\", I. pages 276 and 83.) Evolution is a process of Variation\nand Heredity. The older writers, though they had some vague idea that\nit must be so, did not study Variation and Heredity. Darwin did, and so\nbegat not a theory, but a science.\n\nThe extent to which this is true, the scientific world is only beginning\nto realise. So little was the fact appreciated in Darwin's own time that\nthe success of his writings was followed by an almost total cessation of\nwork in that special field. Of the causes which led to this remarkable\nconsequence I have spoken elsewhere. They proceeded from circumstances\npeculiar to the time; but whatever the causes there is no doubt that\nthis statement of the result is historically exact, and those who\nmake it their business to collect facts elucidating the physiology of\nHeredity and Variation are well aware that they will find little to\nreward their quest in the leading scientific Journals of the Darwinian\nepoch.\n\nIn those thirty years the original stock of evidence current and in\ncirculation even underwent a process of attrition. As in the story of\nthe Eastern sage who first wrote the collected learning of the universe\nfor his sons in a thousand volumes, and by successive compression and\nburning reduced them to one, and from this by further burning distilled\nthe single ejaculation of the Faith, \"There is no god but God and\nMohamed is the Prophet of God,\" which was all his maturer wisdom deemed\nessential:--so in the books of that period do we find the corpus of\ngenetic knowledge dwindle to a few prerogative instances, and these at\nlast to the brief formula of an unquestioned creed.\n\nAnd yet in all else that concerns biological science this period was,\nin very truth, our Golden Age, when the natural history of the earth was\nexplored as never before; morphology and embryology were exhaustively\nransacked; the physiology of plants and animals began to rival chemistry\nand physics in precision of method and in the rapidity of its advances;\nand the foundations of pathology were laid.\n\nIn contrast with this immense activity elsewhere the neglect which befel\nthe special physiology of Descent, or Genetics as we now call it, is\nastonishing. This may of course be interpreted as meaning that the\nfavoured studies seemed to promise a quicker return for effort, but it\nwould be more true to say that those who chose these other pursuits did\nso without making any such comparison; for the idea that the physiology\nof Heredity and Variation was a coherent science, offering possibilities\nof extraordinary discovery, was not present to their minds at all. In\na word, the existence of such a science was well nigh forgotten. It is\ntrue that in ancillary periodicals, as for example those that treat of\nentomology or horticulture, or in the writings of the already isolated\nsystematists (This isolation of the systematists is the one most\nmelancholy sequela of Darwinism. It seems an irony that we should\nread in the peroration to the \"Origin\" that when the Darwinian view\nis accepted \"Systematists will be able to pursue their labours as at\npresent; but they will not be incessantly haunted by the shadowy doubt\nwhether this or that form be a true species. This, I feel sure, and I\nspeak after experience, will be no slight relief. The endless disputes\nwhether or not some fifty species of British brambles are good species\nwill cease.\" \"Origin\", 6th edition (1882), page 425. True they have\nceased to attract the attention of those who lead opinion, but anyone\nwho will turn to the literature of systematics will find that they have\nnot ceased in any other sense. Should there not be something disquieting\nin the fact that among the workers who come most into contact with\nspecific differences, are to be found the only men who have failed to\nbe persuaded of the unreality of those differences?), observations with\nthis special bearing were from time to time related, but the class of\nfact on which Darwin built his conceptions of Heredity and Variation was\nnot seen in the highways of biology. It formed no part of the official\ncurriculum of biological students, and found no place among the subjects\nwhich their teachers were investigating.\n\nDuring this period nevertheless one distinct advance was made, that\nwith which Weismann's name is prominently connected. In Darwin's genetic\nscheme the hereditary transmission of parental experience and its\nconsequences played a considerable role. Exactly how great that role was\nsupposed to be, he with his habitual caution refrained from specifying,\nfor the sufficient reason that he did not know. Nevertheless much of\nthe process of Evolution, especially that by which organs have become\ndegenerate and rudimentary, was certainly attributed by Darwin to\nsuch inheritance, though since belief in the inheritance of acquired\ncharacters fell into disrepute, the fact has been a good deal\noverlooked. The \"Origin\" without \"use and disuse\" would be a materially\ndifferent book. A certain vacillation is discernible in Darwin's\nutterances on this question, and the fact gave to the astute Butler\nan opportunity for his most telling attack. The discussion which best\nillustrates the genetic views of the period arose in regard to the\nproduction of the rudimentary condition of the wings of many beetles\nin the Madeira group of islands, and by comparing passages from the\n\"Origin\" (6th edition pages 109 and 401. See Butler, \"Essays on Life,\nArt, and Science\", page 265, reprinted 1908, and \"Evolution, Old and\nNew\", chapter XXII. (2nd edition), 1882.) Butler convicts Darwin\nof saying first that this condition was in the main the result of\nSelection, with disuse aiding, and in another place that the main cause\nof degeneration was disuse, but that Selection had aided. To Darwin\nhowever I think the point would have seemed one of dialectics merely. To\nhim the one paramount purpose was to show that somehow an Evolution\nby means of Variation and Heredity might have brought about the facts\nobserved, and whether they had come to pass in the one way or the other\nwas a matter of subordinate concern.\n\n\nTo us moderns the question at issue has a diminished significance. For\nover all such debates a change has been brought by Weismann's challenge\nfor evidence that use and disuse have any transmitted effects at all.\nHitherto the transmission of many acquired characteristics had seemed\nto most naturalists so obvious as not to call for demonstration. (W.\nLawrence was one of the few who consistently maintained the contrary\nopinion. Prichard, who previously had expressed himself in the same\nsense, does not, I believe repeat these views in his later writings, and\nthere are signs that he came to believe in the transmission of acquired\nhabits. See Lawrence, \"Lect. Physiol.\" 1823, pages 436-437, 447\nPrichard, Edin. Inaug. Disp. 1808 (not seen by me), quoted ibid. and\n\"Nat. Hist. Man\", 1843, pages 34 f.) Weismann's demand for facts in\nsupport of the main proposition revealed at once that none having real\ncogency could be produced. The time-honoured examples were easily shown\nto be capable of different explanations. A few certainly remain\nwhich cannot be so summarily dismissed, but--though it is manifestly\nimpossible here to do justice to such a subject--I think no one will\ndispute that these residual and doubtful phenomena, whatever be their\ntrue nature, are not of a kind to help us much in the interpretation\nof any of those complex cases of adaptation which on the hypothesis of\nunguided Natural Selection are especially difficult to understand. Use\nand disuse were invoked expressly to help us over these hard places; but\nwhatever changes can be induced in offspring by direct treatment of the\nparents, they are not of a kind to encourage hope of real assistance\nfrom that quarter. It is not to be denied that through the collapse of\nthis second line of argument the Selection hypothesis has had to take\nan increased and perilous burden. Various ways of meeting the difficulty\nhave been proposed, but these mostly resolve themselves into improbable\nattempts to expand or magnify the powers of Natural Selection.\n\nWeismann's interpellation, though negative in purpose, has had a lasting\nand beneficial effect, for through his thorough demolition of the old\nloose and distracting notions of inherited experience, the ground has\nbeen cleared for the construction of a true knowledge of heredity based\non experimental fact.\n\nIn another way he made a contribution of a more positive character,\nfor his elaborate speculations as to the genetic meaning of cytological\nappearances have led to a minute investigation of the visible phenomena\noccurring in those divisions by which germ-cells arise. Though the\nparticular views he advocated have very largely proved incompatible\nwith the observed facts of heredity, yet we must acknowledge that it was\nchiefly through the stimulus of Weismann's ideas that those advances\nin cytology were made; and though the doctrine of the continuity of\ngerm-plasm cannot be maintained in the form originally propounded, it is\nin the main true and illuminating. (It is interesting to see how nearly\nButler was led by natural penetration, and from absolutely opposite\nconclusions, back to this underlying truth: \"So that each ovum when\nimpregnate should be considered not as descended from its ancestors, but\nas being a continuation of the personality of every ovum in the chain\nof its ancestry, which every ovum IT ACTUALLY IS quite as truly as the\noctogenarian IS the same identity with the ovum from which he has been\ndeveloped. This process cannot stop short of the primordial cell,\nwhich again will probably turn out to be but a brief resting-place. We\ntherefore prove each one of us to BE ACTUALLY the primordial cell which\nnever died nor dies, but has differentiated itself into the life of the\nworld, all living beings whatever, being one with it and members one of\nanother,\" \"Life and Habit\", 1878, page 86.) Nevertheless in the present\nstate of knowledge we are still as a rule quite unable to connect\ncytological appearances with any genetic consequence and save in one\nrespect (obviously of extreme importance--to be spoken of later) the two\nsets of phenomena might, for all we can see, be entirely distinct.\n\nI cannot avoid attaching importance to this want of connection between\nthe nuclear phenomena and the features of bodily organisation. All\nattempts to investigate Heredity by cytological means lie under\nthe disadvantage that it is the nuclear changes which can alone be\neffectively observed. Important as they must surely be, I have never\nbeen persuaded that the rest of the cell counts for nothing. What we\nknow of the behaviour and variability of chromosomes seems in my opinion\nquite incompatible with the belief that they alone govern form, and are\nthe sole agents responsible in heredity. (This view is no doubt contrary\nto the received opinion. I am however interested to see it lately\nmaintained by Driesch (\"Science and Philosophy of the Organism\", London,\n1907, page 233), and from the recent observations of Godlewski it has\nreceived distinct experimental support.)\n\nIf, then, progress was to be made in Genetics, work of a different kind\nwas required. To learn the laws of Heredity and Variation there is\nno other way than that which Darwin himself followed, the direct\nexamination of the phenomena. A beginning could be made by collecting\nfortuitous observations of this class, which have often thrown a\nsuggestive light, but such evidence can be at best but superficial and\nsome more penetrating instrument of research is required. This can only\nbe provided by actual experiments in breeding.\n\nThe truth of these general considerations was becoming gradually clear\nto many of us when in 1900 Mendel's work was rediscovered. Segregation,\na phenomenon of the utmost novelty, was thus revealed. From that moment\nnot only in the problem of the origin of species, but in all the great\nproblems of biology a new era began. So unexpected was the discovery\nthat many naturalists were convinced it was untrue, and at once\nproclaimed Mendel's conclusions as either altogether mistaken, or if\ntrue, of very limited application. Many fantastic notions about the\nworkings of Heredity had been asserted as general principles before:\nthis was probably only another fancy of the same class.\n\nNevertheless those who had a preliminary acquaintance with the facts\nof Variation were not wholly unprepared for some such revelation. The\nessential deduction from the discovery of segregation was that the\ncharacters of living things are dependent on the presence of definite\nelements or factors, which are treated as units in the processes of\nHeredity. These factors can thus be recombined in various ways. They act\nsometimes separately, and sometimes they interact in conjunction with\neach other, producing their various effects. All this indicates a\ndefiniteness and specific order in heredity, and therefore in variation.\nThis order cannot by the nature of the case be dependent on Natural\nSelection for its existence, but must be a consequence of the\nfundamental chemical and physical nature of living things. The study of\nVariation had from the first shown that an orderliness of this kind was\npresent. The bodies and the properties of living things are cosmic,\nnot chaotic. No matter how low in the scale we go, never do we find the\nslightest hint of a diminution in that all-pervading orderliness, nor\ncan we conceive an organism existing for a moment in any other state.\nMoreover not only does this order prevail in normal forms, but again\nand again it is to be seen in newly-sprung varieties, which by general\nconsent cannot have been subjected to a prolonged Selection. The\ndiscovery of Mendelian elements admirably coincided with and at once\ngave a rationale of these facts. Genetic Variation is then primarily the\nconsequence of additions to, or omissions from, the stock of\nelements which the species contains. The further investigation of\nthe species-problem must thus proceed by the analytical method which\nbreeding experiments provide.\n\nIn the nine years which have elapsed since Mendel's clue became\ngenerally known, progress has been rapid. We now understand the process\nby which a polymorphic race maintains its polymorphism. When a family\nconsists of dissimilar members, given the numerical proportions in\nwhich these members are occurring, we can represent their composition\nsymbolically and state what types can be transmitted by the various\nmembers. The difficulty of the \"swamping effects of intercrossing\" is\npractically at an end. Even the famous puzzle of sex-limited inheritance\nis solved, at all events in its more regular manifestations, and we know\nnow how it is brought about that the normal sisters of a colour-blind\nman can transmit the colour-blindness while his normal brothers cannot\ntransmit it.\n\nWe are still only on the fringe of the inquiry. It can be seen extending\nand ramifying in many directions. To enumerate these here would be\nimpossible. A whole new range of possibilities is being brought into\nview by study of the interrelations between the simple factors. By\nfollowing up the evidence as to segregation, indications have been\nobtained which can only be interpreted as meaning that when many factors\nare being simultaneously redistributed among the germ-cells, certain of\nthem exert what must be described as a repulsion upon other factors. We\ncannot surmise whither this discovery may lead.\n\nIn the new light all the old problems wear a fresh aspect. Upon the\nquestion of the nature of Sex, for example, the bearing of Mendelian\nevidence is close. Elsewhere I have shown that from several sets of\nparallel experiments the conclusion is almost forced upon us that, in\nthe types investigated, of the two sexes the female is to be regarded as\nheterozygous in sex, containing one unpaired dominant element, while the\nmale is similarly homozygous in the absence of that element. (In other\nwords, the ova are each EITHER female, OR male (i.e. non-female), but\nthe sperms are all non-female.) It is not a little remarkable that on\nthis point--which is the only one where observations of the nuclear\nprocesses of gameto-genesis have yet been brought into relation with\nthe visible characteristics of the organisms themselves--there should be\ndiametrical opposition between the results of breeding experiments and\nthose derived from cytology.\n\nThose who have followed the researches of the American school will\nbe aware that, after it had been found in certain insects that the\nspermatozoa were of two kinds according as they contained or did not\ncontain the accessory chromosome, E.B. Wilson succeeded in proving that\nthe sperms possessing this accessory body were destined to form FEMALES\non fertilisation, while sperms without it form males, the eggs being\napparently indifferent. Perhaps the most striking of all this series\nof observations is that lately made by T.H. Morgan (Morgan, \"Proc. Soc.\nExp. Biol. Med.\" V. 1908, and von Baehr, \"Zool. Anz.\" XXXII. page 507,\n1908.), since confirmed by von Baehr, that in a Phylloxeran two kinds\nof spermatids are formed, respectively with and without an accessory\n(in this case, DOUBLE) chromosome. Of these, only those possessing the\naccessory body become functional spermatozoa, the others degenerating.\nWe have thus an elucidation of the puzzling fact that in these forms\nfertilisation results in the formation of FEMALES only. How the\nmales are formed--for of course males are eventually produced by the\nparthenogenetic females--we do not know.\n\nIf the accessory body is really to be regarded as bearing the factor\nfor femaleness, then in Mendelian terms female is DD and male is DR. The\neggs are indifferent and the spermatozoa are each male, OR female.\nBut according to the evidence derived from a study of the sex-limited\ndescent of certain features in other animals the conclusion seems\nequally clear that in them female must be regarded as DR and male as\nRR. The eggs are thus each either male or female and the spermatozoa are\nindifferent. How this contradictory evidence is to be reconciled we\ndo not yet know. The breeding work concerns fowls, canaries, and the\nCurrant moth (Abraxas grossulariata). The accessory chromosome has been\nnow observed in most of the great divisions of insects (As Wilson has\nproved, the unpaired body is not a universal feature even in those\norders in which it has been observed. Nearly allied types may differ.\nIn some it is altogether unpaired. In others it is paired with a body of\nmuch smaller size, and by selection of various types all gradations can\nbe demonstrated ranging to the condition in which the members of the\npair are indistinguishable from each other.), except, as it happens,\nLepidoptera. At first sight it seems difficult to suppose that a feature\napparently so fundamental as sex should be differently constituted\nin different animals, but that seems at present the least improbable\ninference. I mention these two groups of facts as illustrating the\nnature and methods of modern genetic work. We must proceed by minute and\nspecific analytical investigation. Wherever we look we find traces of\nthe operation of precise and specific rules.\n\nIn the light of present knowledge it is evident that before we can\nattack the Species-problem with any hope of success there are vast\narrears to be made up. He would be a bold man who would now assert that\nthere was no sense in which the term Species might not have a strict and\nconcrete meaning in contradistinction to the term Variety. We have been\ntaught to regard the difference between species and variety as one of\ndegree. I think it unlikely that this conclusion will bear the test of\nfurther research. To Darwin the question, What is a variation? presented\nno difficulties. Any difference between parent and offspring was a\nvariation. Now we have to be more precise. First we must, as de Vries\nhas shown, distinguish real, genetic, variation from FLUCTUATIONAL\nvariations, due to environmental and other accidents, which cannot\nbe transmitted. Having excluded these sources of error the variations\nobserved must be expressed in terms of the factors to which they are due\nbefore their significance can be understood. For example, numbers of the\nvariations seen under domestication, and not a few witnessed in nature,\nare simply the consequence of some ingredient being in an unknown way\nomitted from the composition of the varying individual. The variation\nmay on the contrary be due to the addition of some new element, but to\nprove that it is so is by no means an easy matter. Casual observation\nis useless, for though these latter variations will always be dominants,\nyet many dominant characteristics may arise from another cause, namely\nthe meeting of complementary factors, and special study of each case\nin two generations at least is needed before these two phenomena can be\ndistinguished.\n\nWhen such considerations are fully appreciated it will be realised that\nmedleys of most dissimilar occurrences are all confused together under\nthe term Variation. One of the first objects of genetic analysis is to\ndisentangle this mass of confusion.\n\nTo those who have made no study of heredity it sometimes appears that\nthe question of the effect of conditions in causing variation is one\nwhich we should immediately investigate, but a little thought will\nshow that before any critical inquiry into such possibilities can be\nattempted, a knowledge of the working of heredity under conditions as\nfar as possible uniform must be obtained. At the time when Darwin was\nwriting, if a plant brought into cultivation gave off an albino variety,\nsuch an event was without hesitation ascribed to the change of life. Now\nwe see that albino GAMETES, germs, that is to say, which are destitute\nof the pigment-forming factor, may have been originally produced by\nindividuals standing an indefinite number of generations back in the\nancestry of the actual albino, and it is indeed almost certain that the\nvariation to which the appearance of the albino is due cannot have taken\nplace in a generation later than that of the grandparents. It is true\nthat when a new DOMINANT appears we should feel greater confidence\nthat we were witnessing the original variation, but such events are\nof extreme rarity, and no such case has come under the notice of an\nexperimenter in modern times, as far as I am aware. That they must have\nappeared is clear enough. Nothing corresponding to the Brown-breasted\nGame fowl is known wild, yet that colour is a most definite dominant,\nand at some moment since Gallus bankiva was domesticated, the element on\nwhich that special colour depends must have at least once been formed in\nthe germ-cell of a fowl; but we need harder evidence than any which has\nyet been produced before we can declare that this novelty came through\nover-feeding, or change of climate, or any other disturbance consequent\non domestication. When we reflect on the intricacies of genetic problems\nas we must now conceive them there come moments when we feel almost\nthankful that the Mendelian principles were unknown to Darwin. The time\ncalled for a bold pronouncement, and he made it, to our lasting profit\nand delight. With fuller knowledge we pass once more into a period of\ncautious expectation and reserve.\n\nIn every arduous enterprise it is pleasanter to look back at\ndifficulties overcome than forward to those which still seem\ninsurmountable, but in the next stage there is nothing to be gained by\ndisguising the fact that the attributes of living things are not what\nwe used to suppose. If they are more complex in the sense that the\nproperties they display are throughout so regular (I have in view, for\nexample, the marvellous and specific phenomena of regeneration,\nand those discovered by the students of \"Entwicklungsmechanik\". The\ncircumstances of its occurrence here preclude any suggestion that this\nregularity has been brought about by the workings of Selection. The\nattempts thus to represent the phenomena have resulted in mere parodies\nof scientific reasoning.) that the Selection of minute random variations\nis an unacceptable account of the origin of their diversity, yet by\nvirtue of that very regularity the problem is limited in scope and thus\nsimplified.\n\nTo begin with, we must relegate Selection to its proper place. Selection\npermits the viable to continue and decides that the non-viable shall\nperish; just as the temperature of our atmosphere decides that no liquid\ncarbon shall be found on the face of the earth: but we do not suppose\nthat the form of the diamond has been gradually achieved by a process of\nSelection. So again, as the course of descent branches in the successive\ngenerations, Selection determines along which branch Evolution shall\nproceed, but it does not decide what novelties that branch shall bring\nforth. \"La Nature contient le fonds de toutes ces varietes, mais le\nhazard ou l'art les mettent en oeuvre,\" as Maupertuis most truly said.\n\nNot till knowledge of the genetic properties of organisms has attained\nto far greater completeness can evolutionary speculations have more than\na suggestive value. By genetic experiment, cytology and physiological\nchemistry aiding, we may hope to acquire such knowledge. In 1872\nNathusius wrote (\"Vortrage uber Viehzucht und Rassenerkenntniss\", page\n120, Berlin, 1872.): \"Das Gesetz der Vererbung ist noch nicht erkannt;\nder Apfel ist noch nicht vom Baum der Erkenntniss gefallen, welcher,\nder Sage nach, Newton auf den rechten Weg zur Ergrundung der\nGravitationsgesetze fuhrte.\" We cannot pretend that the words are not\nstill true, but in Mendelian analysis the seeds of that apple-tree at\nlast are sown.\n\nIf we were asked what discovery would do most to forward our inquiry,\nwhat one bit of knowledge would more than any other illuminate the\nproblem, I think we may give the answer without hesitation. The greatest\nadvance that we can foresee will be made when it is found possible to\nconnect the geometrical phenomena of development with the chemical. The\ngeometrical symmetry of living things is the key to a knowledge of\ntheir regularity, and the forces which cause it. In the symmetry of\nthe dividing cell the basis of that resemblance we call Heredity is\ncontained. To imitate the morphological phenomena of life we have to\ndevise a system which can divide. It must be able to divide, and to\nsegment as--grossly--a vibrating plate or rod does, or as an icicle can\ndo as it becomes ribbed in a continuous stream of water; but with\nthis distinction, that the distribution of chemical differences and\nproperties must simultaneously be decided and disposed in orderly\nrelation to the pattern of the segmentation. Even if a model which would\ndo this could be constructed it might prove to be a useful beginning.\n\nThis may be looking too far ahead. If we had to choose some one piece of\nmore proximate knowledge which we would more especially like to acquire,\nI suppose we should ask for the secret of interracial sterility. Nothing\nhas yet been discovered to remove the grave difficulty, by which Huxley\nin particular was so much oppressed, that among the many varieties\nproduced under domestication--which we all regard as analogous to the\nspecies seen in nature--no clear case of interracial sterility has\nbeen demonstrated. The phenomenon is probably the only one to which the\ndomesticated products seem to afford no parallel. No solution of the\ndifficulty can be offered which has positive value, but it is perhaps\nworth considering the facts in the light of modern ideas. It should be\nobserved that we are not discussing incompatibility of two species to\nproduce offspring (a totally distinct phenomenon), but the sterility of\nthe offspring which many of them do produce.\n\nWhen two species, both perfectly fertile severally, produce on crossing\na sterile progeny, there is a presumption that the sterility is due to\nthe development in the hybrid of some substance which can only be formed\nby the meeting of two complementary factors. That some such account is\ncorrect in essence may be inferred from the well-known observation that\nif the hybrid is not totally sterile but only partially so, and thus is\nable to form some good germ-cells which develop into new individuals,\nthe sterility of these daughter-individuals is sensibly reduced or may\nbe entirely absent. The fertility once re-established, the sterility\ndoes not return in the later progeny, a fact strongly suggestive of\nsegregation. Now if the sterility of the cross-bred be really the\nconsequence of the meeting of two complementary factors, we see that the\nphenomenon could only be produced among the divergent offspring of\none species by the acquisition of at least TWO new factors; for if the\nacquisition of a single factor caused sterility the line would then\nend. Moreover each factor must be separately acquired by distinct\nindividuals, for if both were present together, the possessors would by\nhypothesis be sterile. And in order to imitate the case of species each\nof these factors must be acquired by distinct breeds. The factors need\nnot, and probably would not, produce any other perceptible effects;\nthey might, like the colour-factors present in white flowers, make\nno difference in the form or other characters. Not till the cross was\nactually made between the two complementary individuals would either\nfactor come into play, and the effects even then might be unobserved\nuntil an attempt was made to breed from the cross-bred.\n\nNext, if the factors responsible for sterility were acquired, they would\nin all probability be peculiar to certain individuals and would not\nreadily be distributed to the whole breed. Any member of the breed\nalso into which BOTH the factors were introduced would drop out of the\npedigree by virtue of its sterility. Hence the evidence that the various\ndomesticated breeds say of dogs or fowls can when mated together produce\nfertile offspring, is beside the mark. The real question is, Do they\never produce sterile offspring? I think the evidence is clearly that\nsometimes they do, oftener perhaps than is commonly supposed. These\nsuggestions are quite amenable to experimental tests. The most obvious\nway to begin is to get a pair of parents which are known to have had any\nsterile offspring, and to find the proportions in which these steriles\nwere produced. If, as I anticipate, these proportions are found to be\ndefinite, the rest is simple.\n\nIn passing, certain other considerations may be referred to. First, that\nthere are observations favouring the view that the production of totally\nsterile cross-breds is seldom a universal property of two species, and\nthat it may be a matter of individuals, which is just what on the view\nhere proposed would be expected. Moreover, as we all know now, though\nincompatibility may be dependent to some extent on the degree to which\nthe species are dissimilar, no such principle can be demonstrated to\ndetermine sterility or fertility in general. For example, though all our\nFinches can breed together, the hybrids are all sterile. Of Ducks some\nspecies can breed together without producing the slightest sterility;\nothers have totally sterile offspring, and so on. The hybrids between\nseveral genera of Orchids are perfectly fertile on the female side, and\nsome on the male side also, but the hybrids produced between the Turnip\n(Brassica napus) and the Swede (Brassica campestris), which, according\nto our estimates of affinity should be nearly allied forms, are totally\nsterile. (See Sutton, A.W., \"Journ. Linn. Soc.\" XXXVIII. page 341,\n1908.) Lastly, it may be recalled that in sterility we are almost\ncertainly considering a meristic phenomenon. FAILURE TO DIVIDE is,\nwe may feel fairly sure, the immediate \"cause\" of the sterility. Now,\nthough we know very little about the heredity of meristic differences,\nall that we do know points to the conclusion that the less-divided is\ndominant to the more-divided, and we are thus justified in supposing\nthat there are factors which can arrest or prevent cell-division. My\nconjecture therefore is that in the case of sterility of cross-breds we\nsee the effect produced by a complementary pair of such factors. This\nand many similar problems are now open to our analysis.\n\nThe question is sometimes asked, Do the new lights on Variation and\nHeredity make the process of Evolution easier to understand? On the\nwhole the answer may be given that they do. There is some appearance of\nloss of simplicity, but the gain is real. As was said above, the time\nis not ripe for the discussion of the origin of species. With faith in\nEvolution unshaken--if indeed the word faith can be used in application\nto that which is certain--we look on the manner and causation of adapted\ndifferentiation as still wholly mysterious. As Samuel Butler so truly\nsaid: \"To me it seems that the 'Origin of Variation,' whatever it is, is\nthe only true 'Origin of Species'\" (\"Life and Habit\", London, page\n263, 1878.), and of that Origin not one of us knows anything. But given\nVariation--and it is given: assuming further that the variations are not\nguided into paths of adaptation--and both to the Darwinian and to\nthe modern school this hypothesis appears to be sound if unproven--an\nevolution of species proceeding by definite steps is more, rather than\nless, easy to imagine than an evolution proceeding by the accumulation\nof indefinite and insensible steps. Those who have lost themselves in\ncontemplating the miracles of Adaptation (whether real or spurious) have\nnot unnaturally fixed their hopes rather on the indefinite than on the\ndefinite changes. The reasons are obvious. By suggesting that the\nsteps through which an adaptative mechanism arose were indefinite and\ninsensible, all further trouble is spared. While it could be said that\nspecies arise by an insensible and imperceptible process of variation,\nthere was clearly no use in tiring ourselves by trying to perceive that\nprocess. This labour-saving counsel found great favour. All that had\nto be done to develop evolution-theory was to discover the good in\neverything, a task which, in the complete absence of any control or test\nwhereby to check the truth of the discovery, is not very onerous. The\ndoctrine \"que tout est au mieux\" was therefore preached with fresh\nvigour, and examples of that illuminating principle were discovered with\na facility that Pangloss himself might have envied, till at last even\nthe spectators wearied of such dazzling performances.\n\nBut in all seriousness, why should indefinite and unlimited variation\nhave been regarded as a more probable account of the origin of\nAdaptation? Only, I think, because the obstacle was shifted one plane\nback, and so looked rather less prominent. The abundance of Adaptation,\nwe all grant, is an immense, almost an unsurpassable difficulty in\nall non-Lamarckian views of Evolution; but if the steps by which\nthat adaptation arose were fortuitous, to imagine them insensible is\nassuredly no help. In one most important respect indeed, as has often\nbeen observed, it is a multiplication of troubles. For the smaller\nthe steps, the less could Natural Selection act upon them. Definite\nvariations--and of the occurrence of definite variations in abundance we\nhave now the most convincing proof--have at least the obvious merit\nthat they can make and often do make a real difference in the chances of\nlife.\n\nThere is another aspect of the Adaptation problem to which I can only\nallude very briefly. May not our present ideas of the universality and\nprecision of Adaptation be greatly exaggerated? The fit of organism to\nits environment is not after all so very close--a proposition unwelcome\nperhaps, but one which could be illustrated by very copious evidence.\nNatural Selection is stern, but she has her tolerant moods.\n\nWe have now most certain and irrefragable proof that much definiteness\nexists in living things apart from Selection, and also much that\nmay very well have been preserved and so in a sense constituted by\nSelection. Here the matter is likely to rest. There is a passage in the\nsixth edition of the \"Origin\" which has I think been overlooked. On page\n70 Darwin says \"The tuft of hair on the breast of the wild turkey-cock\ncannot be of any use, and it is doubtful whether it can be ornamental in\nthe eyes of the female bird.\" This tuft of hair is a most definite and\nunusual structure, and I am afraid that the remark that it \"cannot be\nof any use\" may have been made inadvertently; but it may have been\nintended, for in the first edition the usual qualification was given and\nmust therefore have been deliberately excised. Anyhow I should like to\nthink that Darwin did throw over that tuft of hair, and that he felt\nrelief when he had done so. Whether however we have his great authority\nfor such a course or not, I feel quite sure that we shall be rightly\ninterpreting the facts of nature if we cease to expect to find\npurposefulness wherever we meet with definite structures or patterns.\nSuch things are, as often as not, I suspect rather of the nature of\ntool-marks, mere incidents of manufacture, benefiting their possessor\nnot more than the wire-marks in a sheet of paper, or the ribbing on the\nbottom of an oriental plate renders those objects more attractive in our\neyes.\n\nIf Variation may be in any way definite, the question once more arises,\nmay it not be definite in direction? The belief that it is has had many\nsupporters, from Lamarck onwards, who held that it was guided by need,\nand others who, like Nageli, while laying no emphasis on need, yet were\nconvinced that there was guidance of some kind. The latter view under\nthe name of \"Orthogenesis,\" devised I believe by Eimer, at the present\nday commends itself to some naturalists. The objection to such a\nsuggestion is of course that no fragment of real evidence can be\nproduced in its support. On the other hand, with the experimental proof\nthat variation consists largely in the unpacking and repacking of an\noriginal complexity, it is not so certain as we might like to think\nthat the order of these events is not pre-determined. For instance\nthe original \"pack\" may have been made in such a way that at the nth\ndivision of the germ-cells of a Sweet Pea a colour-factor might be\ndropped, and that at the n plus n prime division the hooded variety be\ngiven off, and so on. I see no ground whatever for holding such a view,\nbut in fairness the possibility should not be forgotten, and in the\nlight of modern research it scarcely looks so absurdly improbable as\nbefore.\n\nNo one can survey the work of recent years without perceiving that\nevolutionary orthodoxy developed too fast, and that a great deal has\ngot to come down; but this satisfaction at least remains, that in the\nexperimental methods which Mendel inaugurated, we have means of reaching\ncertainty in regard to the physiology of Heredity and Variation upon\nwhich a more lasting structure may be built.\n\n\n\n\nVI. THE MINUTE STRUCTURE OF CELLS IN RELATION TO HEREDITY. By Eduard\nStrasburger.\n\nProfessor of Botany in the University of Bonn.\n\nSince 1875 an unexpected insight has been gained into the internal\nstructure of cells. Those who are familiar with the results of\ninvestigations in this branch of Science are convinced that any modern\ntheory of heredity must rest on a basis of cytology and cannot be at\nvariance with cytological facts. Many histological discoveries, both\nsuch as have been proved correct and others which may be accepted as\nprobably well founded, have acquired a fundamental importance from the\npoint of view of the problems of heredity.\n\nMy aim is to describe the present position of our knowledge of Cytology.\nThe account must be confined to essentials and cannot deal with\nfar-reaching and controversial questions. In cases where difference of\nopinion exists, I adopt my own view for which I hold myself responsible.\nI hope to succeed in making myself intelligible even without the aid of\nillustrations: in order to convey to the uninitiated an adequate idea\nof the phenomena connected with the life of a cell, a greater number\nof figures would be required than could be included within the scope of\nthis article.\n\nSo long as the most eminent investigators (As for example the\nillustrious Wilhelm Hofmeister in his \"Lehre von der Pflanzenzelle\"\n(1867).) believed that the nucleus of a cell was destroyed in the course\nof each division and that the nuclei of the daughter-cells were produced\nde novo, theories of heredity were able to dispense with the nucleus.\nIf they sought, as did Charles Darwin, who showed a correct grasp of\nthe problem in the enunciation of his Pangenesis hypothesis, for\nhistological connecting links, their hypotheses, or at least the best of\nthem, had reference to the cell as a whole. It was known to Darwin\nthat the cell multiplied by division and was derived from a similar\npre-existing cell. Towards 1870 it was first demonstrated that\ncell-nuclei do not arise de novo, but are invariably the result of\ndivision of pre-existing nuclei. Better methods of investigation\nrendered possible a deeper insight into the phenomena accompanying cell\nand nuclear divisions and at the same time disclosed the existence of\nremarkable structures. The work of O. Butschli, O. Hertwig, W. Flemming\nH. Fol and of the author of this article (For further reference to\nliterature, see my article on \"Die Ontogenie der Zelle seit 1875\",\nin the \"Progressus Rei Botanicae\", Vol. I. page 1, Jena, 1907.), have\nfurnished conclusive evidence in favour of these facts. It was found\nthat when the reticular framework of a nucleus prepares to divide, it\nseparates into single segments. These then become thicker and denser,\ntaking up with avidity certain stains, which are used as aids to\ninvestigation, and finally form longer or shorter, variously bent,\nrodlets of uniform thickness. In these organs which, on account of their\nspecial property of absorbing certain stains, were styled Chromosomes\n(By W. Waldeyer in 1888.), there may usually be recognised a separation\ninto thicker and thinner discs; the former are often termed Chromomeres.\n(Discovered by W. Pfitzner in 1880.) In the course of division of the\nnucleus, the single rows of chromomeres in the chromosomes are doubled\nand this produces a band-like flattening and leads to the longitudinal\nsplitting by which each chromosome is divided into two exactly equal\nhalves. The nuclear membrane then disappears and fibrillar cell-plasma\nor cytoplasm invades the nuclear area. In animal cells these fibrillae\nin the cytoplasm centre on definite bodies (Their existence and their\nmultiplication by fission were demonstrated by E. van Beneden and Th.\nBoveri in 1887.), which it is customary to speak of as Centrosomes.\nRadiating lines in the adjacent cell-plasma suggest that these bodies\nconstitute centres of force. The cells of the higher plants do not\npossess such individualised centres; they have probably disappeared in\nthe course of phylogenetic development: in spite of this, however, in\nthe nuclear division-figures the fibrillae of the cell-plasma are seen\nto radiate from two opposite poles. In both animal and plant cells a\nfibrillar bipolar spindle is formed, the fibrillae of which grasp the\nlongitudinally divided chromosomes from two opposite sides and arrange\nthem on the equatorial plane of the spindle as the so-called nuclear\nor equatorial plate. Each half-chromosome is connected with one of the\nspindle poles only and is then drawn towards that pole. (These important\nfacts, suspected by W. Flemming in 1882, were demonstrated by E. Heuser,\nL. Guignard, E. van Beneden, M. Nussbaum, and C. Rabl.)\n\nThe formation of the daughter-nuclei is then effected. The changes\nwhich the daughter-chromosomes undergo in the process of producing the\ndaughter-nuclei repeat in the reverse order the changes which they went\nthrough in the course of their progressive differentiation from the\nmother-nucleus. The division of the cell-body is completed midway\nbetween the two daughter-nuclei. In animal cells, which possess no\nchemically differentiated membrane, separation is effected by simple\nconstriction, while in the case of plant cells provided with a definite\nwall, the process begins with the formation of a cytoplasmic separating\nlayer.\n\nThe phenomena observed in the course of the division of the nucleus show\nbeyond doubt that an exact halving of its substance is of the greatest\nimportance. (First shown by W. Roux in 1883.) Compared with the method\nof division of the nucleus, that of the cytoplasm appears to be very\nsimple. This led to the conception that the cell-nucleus must be the\nchief if not the sole carrier of hereditary characters in the organism.\nIt is for this reason that the detailed investigation of fertilisation\nphenomena immediately followed researches into the nucleus. The\nfundamental discovery of the union of two nuclei in the sexual act was\nthen made (By O. Hertwig in 1875.) and this afforded a new support for\nthe correct conception of the nuclear functions. The minute study of the\nbehaviour of the other constituents of sexual cells during fertilisation\nled to the result, that the nucleus alone is concerned with handing on\nhereditary characters (This was done by O. Hertwig and the author of\nthis essay simultaneously in 1884.) from one generation to another.\nEspecially important, from the point of view of this conclusion, is\nthe study of fertilisation in Angiosperms (Flowering plants); in these\nplants the male sexual cells lose their cell-body in the pollen-tube and\nthe nucleus only--the sperm-nucleus--reaches the egg. The cytoplasm of\nthe male sexual cell is therefore not necessary to ensure a transference\nof hereditary characters from parents to offspring. I lay stress on the\ncase of the Angiosperms because researches recently repeated with\nthe help of the latest methods failed to obtain different results.\nAs regards the descendants of angiospermous plants, the same laws of\nheredity hold good as for other sexually differentiated organisms; we\nmay, therefore, extend to the latter what the Angiosperms so clearly\nteach us.\n\nThe next advance in the hitherto rapid progress in our knowledge of\nnuclear division was delayed, because it was not at once recognised that\nthere are two absolutely different methods of nuclear division. All\nsuch nuclear divisions were united under the head of indirect or\nmitotic divisions; these were also spoken of as karyo-kineses, and\nwere distinguished from the direct or amitotic divisions which are\ncharacterised by a simple constriction of the nuclear body. So long\nas the two kinds of indirect nuclear division were not clearly\ndistinguished, their correct interpretation was impossible. This was\naccomplished after long and laborious research, which has recently\nbeen carried out and with results which should, perhaps, be regarded as\nprovisional.\n\nSoon after the new study of the nucleus began, investigators were struck\nby the fact that the course of nuclear division in the mother-cells, or\nmore correctly in the grandmother-cells, of spores, pollen-grains, and\nembryo-sacs of the more highly organised plants and in the spermatozoids\nand eggs of the higher animals, exhibits similar phenomena, distinct\nfrom those which occur in the somatic cells.\n\nIn the nuclei of all those cells which we may group together as\ngonotokonts (At the suggestion of J.P. Lotsy in 1904.) (i.e. cells\nconcerned in reproduction) there are fewer chromosomes than in the\nadjacent body-cells (somatic cells). It was noticed also that there is a\npeculiarity characteristic of the gonotokonts, namely the occurrence of\ntwo nuclear divisions rapidly succeeding one another. It was afterwards\nrecognised that in the first stage of nuclear division in\nthe gonotokonts the chromosomes unite in pairs: it is these\nchromosome-pairs, and not the two longitudinal halves of single\nchromosomes, which form the nuclear plate in the equatorial plane of\nthe nuclear spindle. It has been proposed to call these pairs gemini.\n(J.E.S. Moore and A.L. Embleton, \"Proc. Roy. Soc.\" London, Vol. LXXVII.\npage 555, 1906; V. Gregoire, 1907.) In the course of this division\nthe spindle-fibrillae attach themselves to the gemini, i.e. to entire\nchromosomes and direct them to the points where the new daughter-nuclei\nare formed, that is to those positions towards which the longitudinal\nhalves of the chromosomes travel in ordinary nuclear divisions. It\nis clear that in this way the number of chromosomes which the\ndaughter-nuclei contain, as the result of the first stage in division\nin the gonotokonts, will be reduced by one half, while in ordinary\ndivisions the number of chromosomes always remains the same. The first\nstage in the division of the nucleus in the gonotokonts has therefore\nbeen termed the reduction division. (In 1887 W. Flemming termed this the\nheterotypic form of nuclear division.) This stage in division determines\nthe conditions for the second division which rapidly ensues. Each of the\npaired chromosomes of the mother-nucleus has already, as in an ordinary\nnuclear division, completed the longitudinal fission, but in this case\nit is not succeeded by the immediate separation of the longitudinal\nhalves and their allotment to different nuclei. Each chromosome,\ntherefore, takes its two longitudinal halves into the same\ndaughter-nucleus. Thus, in each daughter-nucleus the longitudinal halves\nof the chromosomes are present ready for the next stage in the\ndivision; they only require to be arranged in the nuclear plate and then\ndistributed among the granddaughter-nuclei. This method of division,\nwhich takes place with chromosomes already split, and which have only\nto provide for the distribution of their longitudinal halves to the next\nnuclear generation, has been called homotypic nuclear division. (The\nname was proposed by W. Flemming in 1887; the nature of this type of\ndivision was, however, not explained until later.)\n\nReduction division and homotypic nuclear division are included together\nunder the term allotypic nuclear division and are distinguished from the\nordinary or typical nuclear division. The name Meiosis (By J. Bretland\nFarmer and J.E.S. Moore in 1905.) has also been proposed for these two\nallotypic nuclear divisions. The typical divisions are often spoken of\nas somatic.\n\nObservers who were actively engaged in this branch of recent\nhistological research soon noticed that the chromosomes of a given\norganism are differentiated in definite numbers from the nuclear\nnetwork in the course of division. This is especially striking in the\ngonotokonts, but it applies also to the somatic tissues. In the latter,\none usually finds twice as many chromosomes as in the gonotokonts. Thus\nthe conclusion was gradually reached that the doubling of chromosomes,\nwhich necessarily accompanies fertilisation, is maintained in the\nproduct of fertilisation, to be again reduced to one half in the\ngonotokonts at the stage of reduction-division. This enabled us to form\na conception as to the essence of true alternation of generations, in\nwhich generations containing single and double chromosomes alternate\nwith one another.\n\nThe single-chromosome generation, which I will call the HAPLOID, must\nhave been the primitive generation in all organisms; it might also\npersist as the only generation. Every sexual differentiation in\norganisms, which occurred in the course of phylogenetic development, was\nfollowed by fertilisation and therefore by the creation of a diploid or\ndouble-chromosome product. So long as the germination of the product\nof fertilisation, the zygote, began with a reducing process, a special\nDIPLOID generation was not represented. This, however, appeared later\nas a product of the further evolution of the zygote, and the reduction\ndivision was correspondingly postponed. In animals, as in plants, the\ndiploid generation attained the higher development and gradually assumed\nthe dominant position. The haploid generation suffered a proportional\nreduction, until it finally ceased to have an independent existence and\nbecame restricted to the role of producing the sexual products within\nthe body of the diploid generation. Those who do not possess the\nnecessary special knowledge are unable to realise what remains of the\nfirst haploid generation in a phanerogamic plant or in a vertebrate\nanimal. In Angiosperms this is actually represented only by the short\ndevelopmental stages which extend from the pollen mother-cells to the\nsperm-nucleus of the pollen-tube, and from the embryo-sac mother-cell to\nthe egg and the endosperm tissue. The embryo-sac remains enclosed in\nthe diploid ovule, and within this from the fertilised egg is formed\nthe embryo which introduces the new diploid generation. On the full\ndevelopment of the diploid embryo of the next generation, the diploid\novule of the preceding diploid generation is separated from the latter\nas a ripe seed. The uninitiated sees in the more highly organised plants\nonly a succession of diploid generations. Similarly all the higher\nanimals appear to us as independent organisms with diploid nuclei only.\nThe haploid generation is confined in them to the cells produced as the\nresult of the reduction division of the gonotokonts; the development of\nthese is completed with the homotypic stage of division which succeeds\nthe reduction division and produces the sexual products.\n\nThe constancy of the numbers in which the chromosomes separate\nthemselves from the nuclear network during division gave rise to the\nconception that, in a certain degree, chromosomes possess individuality.\nIndeed the most careful investigations (Particularly those of V.\nGregoire and his pupils.) have shown that the segments of the nuclear\nnetwork, which separate from one another and condense so as to produce\nchromosomes for a new division, correspond to the segments produced from\nthe chromosomes of the preceding division. The behaviour of such nuclei\nas possess chromosomes of unequal size affords confirmatory evidence of\nthe permanence of individual chromosomes in corresponding sections of an\napparently uniform nuclear network. Moreover at each stage in division\nchromosomes with the same differences in size reappear. Other cases are\nknown in which thicker portions occur in the substance of the resting\nnucleus, and these agree in number with the chromosomes. In this\nnetwork, therefore, the individual chromosomes must have retained\ntheir original position. But the chromosomes cannot be regarded as the\nultimate hereditary units in the nuclei, as their number is too small.\nMoreover, related species not infrequently show a difference in the\nnumber of their chromosomes, whereas the number of hereditary units\nmust approximately agree. We thus picture to ourselves the carriers of\nhereditary characters as enclosed in the chromosomes; the transmitted\nfixed number of chromosomes is for us only the visible expression of\nthe conception that the number of hereditary units which the chromosomes\ncarry must be also constant. The ultimate hereditary units may, like\nthe chromosomes themselves, retain a definite position in the resting\nnucleus. Further, it may be assumed that during the separation of the\nchromosomes from one another and during their assumption of the rod-like\nform, the hereditary units become aggregated in the chromomeres and\nthat these are characterised by a constant order of succession.\nThe hereditary units then grow, divide into two and are uniformly\ndistributed by the fission of the chromosomes between their longitudinal\nhalves.\n\nAs the contraction and rod-like separation of the chromosomes serve\nto isnure the transmission of all hereditary units in the products of\ndivision of a nucleus, so, on the other hand, the reticular distension\nof each chromosome in the so-called resting nucleus may effect a\nseparation of the carriers of hereditary units from each other and\nfacilitate the specific activity of each of them.\n\nIn the stages preliminary to their division, the chromosomes become\ndenser and take up a substance which increases their staining capacity;\nthis is called chromatin. This substance collects in the chromomeres\nand may form the nutritive material for the carriers of hereditary units\nwhich we now believe to be enclosed in them. The chromatin cannot itself\nbe the hereditary substance, as it afterwards leaves the chromosomes,\nand the amount of it is subject to considerable variation in the\nnucleus, according to its stage of development. Conjointly with the\nmaterials which take part in the formation of the nuclear spindle and\nother processes in the cell, the chromatin accumulates in the resting\nnucleus to form the nucleoli.\n\nNaturally connected with the conclusion that the nuclei are the carriers\nof hereditary characters in the organism, is the question whether\nenucleate organisms can also exist. Phylogenetic considerations give an\naffirmative answer to this question. The differentiation into nucleus\nand cytoplasm represents a division of labour in the protoplast. A\nstudy of organisms which belong to the lowest class of the organic world\nteaches us how this was accomplished. Instead of well-defined nuclei,\nscattered granules have been described in the protoplasm of several of\nthese organisms (Bacteria, Cyanophyceae, Protozoa.), characterised by\nthe same reactions as nuclear material, provided also with a nuclear\nnetwork, but without a limiting membrane. (This is the result of the\nwork of R. Hertwig and of the most recently published investigations.)\nThus the carriers of hereditary characters may originally have been\ndistributed in the common protoplasm, afterwards coming together and\neventually assuming a definite form as special organs of the cell. It\nmay be also assumed that in the protoplasm and in the primitive types\nof nucleus, the carriers of the same hereditary unit were represented in\nconsiderable quantity; they became gradually differentiated to an extent\ncommensurate with newly acquired characters. It was also necessary that,\nin proportion as this happened, the mechanism of nuclear division must\nbe refined. At first processes resembling a simple constriction would\nsuffice to provide for the distribution of all hereditary units to each\nof the products of division, but eventually in both organic kingdoms\nnuclear division, which alone insured the qualitative identity of the\nproducts of division, became a more marked feature in the course of\ncell-multiplication.\n\nWhere direct nuclear division occurs by constriction in the higher\norganisms, it does not result in the halving of hereditary units. So far\nas my observations go, direct nuclear division occurs in the more highly\norganised plants only in cells which have lost their specific\nfunctions. Such cells are no longer capable of specific reproduction. An\ninteresting case in this connection is afforded by the internodal cells\nof the Characeae, which possess only vegetative functions. These cells\ngrow vigorously and their cytoplasm increases, their growth being\naccompanied by a correspondingly direct multiplication of the nuclei.\nThey serve chiefly to nourish the plant, but, unlike the other\ncells, they are incapable of producing any offspring. This is a very\ninstructive case, because it clearly shows that the nuclei are not only\ncarriers of hereditary characters, but that they also play a definite\npart in the metabolism of the protoplasts.\n\nAttention was drawn to the fact that during the reducing division of\nnuclei which contain chromosomes of unequal size, gemini are constantly\nproduced by the pairing of chromosomes of the same size. This led to\nthe conclusion that the pairing chromosomes are homologous, and that one\ncomes from the father, the other from the mother. (First stated by T.H.\nMontgomery in 1901 and by W.S. Sutton in 1902.) This evidently applies\nalso to the pairing of chromosomes in those reduction-divisions in\nwhich differences in size do not enable us to distinguish the individual\nchromosomes. In this case also each pair would be formed by two\nhomologous chromosomes, the one of paternal, the other of maternal\norigin. When the separation of these chromosomes and their distribution\nto both daughter-nuclei occur a chromosome of each kind is provided for\neach of these nuclei. It would seem that the components of each pair\nmight pass to either pole of the nuclear spindle, so that the paternal\nand maternal chromosomes would be distributed in varying proportion\nbetween the daughter-nuclei; and it is not impossible that one\ndaughter-nucleus might occasionally contain paternal chromosomes only\nand its sister-nucleus exclusively maternal chromosomes.\n\nThe fact that in nuclei containing chromosomes of various sizes, the\nchromosomes which pair together in reduction-division are always of\nequal size, constitutes a further and more important proof of their\nqualitative difference. This is supported also by ingenious experiments\nwhich led to an unequal distribution of chromosomes in the products of\ndivision of a sea-urchin's egg, with the result that a difference was\ninduced in their further development. (Demonstrated by Th. Boveri in\n1902.)\n\nThe recently discovered fact that in diploid nuclei the chromosomes are\narranged in pairs affords additional evidence in favour of the unequal\nvalue of the chromosomes. This is still more striking in the case of\nchromosomes of different sizes. It has been shown that in the first\ndivision-figure in the nucleus of the fertilised egg the chromosomes of\ncorresponding size form pairs. They appear with this arrangement in all\nsubsequent nuclear divisions in the diploid generation. The longitudinal\nfissions of the chromosomes provide for the unaltered preservation\nof this condition. In the reduction nucleus of the gonotokonts the\nhomologous chromosomes being near together need not seek out one\nanother; they are ready to form gemini. The next stage is their\nseparation to the haploid daughter-nuclei, which have resulted from the\nreduction process.\n\nPeculiar phenomena in the reduction nucleus accompany the formation of\ngemini in both organic kingdoms. (This has been shown more particularly\nby the work of L. Guignard, M. Mottier, J.B. Farmer, C.B. Wilson, V.\nHacker and more recently by V. Gregoire and his pupil C.A. Allen, by the\nresearches conducted in the Bonn Botanical Institute, and by A. and\nK.E. Schreiner.) Probably for the purpose of entering into most\nintimate relation, the pairs are stretched to long threads in which the\nchromomeres come to lie opposite one another. (C.A. Allen, A. and K.E.\nSchreiner, and Strasburger.) It seems probable that these are homologous\nchromomeres, and that the pairs afterwards unite for a short time, so\nthat an exchange of hereditary units is rendered possible. (H. de Vries\nand Strasburger.) This cannot be actually seen, but certain facts of\nheredity point to the conclusion that this occurs. It follows from\nthese phenomena that any exchange which may be effected must be one of\nhomologous carriers of hereditary units only. These units continue to\nform exchangeable segments after they have undergone unequal changes;\nthey then constitute allelotropic pairs. We may thus calculate what sum\nof possible combinations the exchange of homologous hereditary units\nbetween the pairing chromosomes provides for before the reduction\ndivision and the subsequent distribution of paternal and maternal\nchromosomes in the haploid daughter-nuclei. These nuclei then transmit\ntheir characters to the sexual cells, the conjugation of which in\nfertilization again produces the most varied combinations. (A. Weismann\ngave the impulse to these ideas in his theory on \"Amphimixis\".) In this\nway all the cooperations which the carriers of hereditary characters are\ncapable of in a species are produced; this must give it an appreciable\nadvantage in the struggle for life.\n\nThe admirers of Charles Darwin must deeply regret that he did not live\nto see the results achieved by the new Cytology. What service would they\nhave been to him in the presentation of his hypothesis of Pangenesis;\nwhat an outlook into the future would they have given to his active\nmind!\n\nThe Darwinian hypothesis of Pangenesis rests on the conception that all\ninheritable properties are represented in the cells by small invisible\nparticles or gemmules and that these gemmules increase by division.\nCytology began to develop on new lines some years after the publication\nin 1868 of Charles Darwin's \"Provisional hypothesis of Pangenesis\"\n(\"Animals and Plants under Domestication\", London, 1868, Chapter\nXXVII.), and when he died in 1882 it was still in its infancy. Darwin\nwould have soon suggested the substitution of the nuclei for his\ngemmules. At least the great majority of present-day investigators in\nthe domain of cytology have been led to the conclusion that the nucleus\nis the carrier of hereditary characters, and they also believe that\nhereditary characters are represented in the nucleus as distinct units.\nSuch would be Darwin's gemmules, which in conformity with the name\nof his hypothesis may be called pangens (So called by H. de Vries in\n1889.): these pangens multiply by division. All recently adopted\nviews may be thus linked on to this part of Darwin's hypothesis. It is\notherwise with Darwin's conception to which Pangenesis owes its name,\nnamely the view that all cells continually give off gemmules, which\nmigrate to other places in the organism, where they unite to form\nreproductive cells. When Darwin foresaw this possibility, the continuity\nof the germinal substance was still unknown (Demonstrated by Nussbaum in\n1880, by Sachs in 1882, and by Weismann in 1885.), a fact which excludes\na transference of gemmules.\n\nBut even Charles Darwin's genius was confined within finite boundaries\nby the state of science in his day.\n\nIt is not my province to deal with other theories of development which\nfollowed from Darwin's Pangenesis, or to discuss their histological\nprobabilities. We can, however, affirm that Charles Darwin's idea that\ninvisible gemmules are the carriers of hereditary characters and that\nthey multiply by division has been removed from the position of a\nprovisional hypothesis to that of a well-founded theory. It is supported\nby histology, and the results of experimental work in heredity, which\nare now assuming extraordinary prominence, are in close agreement with\nit.\n\n\n\n\nVII. \"THE DESCENT OF MAN\". By G. Schwalbe.\n\nProfessor of Anatomy in the University of Strassburg.\n\nThe problem of the origin of the human race, of the descent of man, is\nranked by Huxley in his epoch-making book \"Man's Place in Nature\", as\nthe deepest with which biology has to concern itself, \"the question\nof questions,\"--the problem which underlies all others. In the same\nbrilliant and lucid exposition, which appeared in 1863, soon after the\npublication of Darwin's \"Origin of Species\", Huxley stated his own views\nin regard to this great problem. He tells us how the idea of a natural\ndescent of man gradually grew up in his mind, it was especially the\nassertions of Owen in regard to the total difference between the human\nand the simian brain that called forth strong dissent from the great\nanatomist Huxley, and he easily succeeded in showing that Owen's\nsupposed differences had no real existence; he even established, on the\nbasis of his own anatomical investigations, the proposition that the\nanatomical differences between the Marmoset and the Chimpanzee are much\ngreater than those between the Chimpanzee and Man.\n\nBut why do we thus introduce the study of Darwin's \"Descent of Man\",\nwhich is to occupy us here, by insisting on the fact that Huxley had\ntaken the field in defence of the descent of man in 1863, while Darwin's\nbook on the subject did not appear till 1871? It is in order that we may\nclearly understand how it happened that from this time onwards Darwin\nand Huxley followed the same great aim in the most intimate association.\n\nHuxley and Darwin working at the same Problema maximum! Huxley fiery,\nimpetuous, eager for battle, contemptuous of the resistance of a dull\nworld, or energetically triumphing over it. Darwin calm, weighing every\nproblem slowly, letting it mature thoroughly,--not a fighter, yet having\nthe greater and more lasting influence by virtue of his immense mass of\ncritically sifted proofs. Darwin's friend, Huxley, was the first to do\nhim justice, to understand his nature, and to find in it the reason why\nthe detailed and carefully considered book on the descent of man made\nits appearance so late. Huxley, always generous, never thought of\nclaiming priority for himself. In enthusiastic language he tells how\nDarwin's immortal work, \"The Origin of Species\", first shed light for\nhim on the problem of the descent of man; the recognition of a vera\ncausa in the transformation of species illuminated his thoughts as with\na flash. He was now content to leave what perplexed him, what he could\nnot yet solve, as he says himself, \"in the mighty hands of Darwin.\"\nHappy in the bustle of strife against old and deep-rooted prejudices,\nagainst intolerance and superstition, he wielded his sharp weapons on\nDarwin's behalf; wearing Darwin's armour he joyously overthrew adversary\nafter adversary. Darwin spoke of Huxley as his \"general agent.\" (\"Life\nand Letters of Thomas Henry Huxley\", Vol. I. page 171, London, 1900.)\nHuxley says of himself \"I am Darwin's bulldog.\" (Ibid. page 363.)\n\nThus Huxley openly acknowledged that it was Darwin's \"Origin of Species\"\nthat first set the problem of the descent of man in its true light, that\nmade the question of the origin of the human race a pressing one. That\nthis was the logical consequence of his book Darwin himself had long\nfelt. He had been reproached with intentionally shirking the application\nof his theory to Man. Let us hear what he says on this point in his\nautobiography: \"As soon as I had become, in the year 1837 or 1838,\nconvinced that species were mutable productions, I could not avoid the\nbelief that man must come under the same law. Accordingly I collected\nnotes on the subject for my own satisfaction, and not for a long time\nwith any intention of publishing. Although in the 'Origin of Species'\nthe derivation of any particular species is never discussed, yet I\nthought it best, in order THAT NO HONOURABLE MAN SHOULD ACCUSE ME OF\nCONCEALING MY VIEWS (No italics in original.), to add that by the work\n'light would be thrown on the origin of man and his history.' It would\nhave been useless and injurious to the success of the book to have\nparaded, without giving any evidence, my conviction with respect to his\norigin.\" (\"Life and Letters of Charles Darwin\", Vol. 1. page 93.)\n\nIn a letter written in January, 1860, to the Rev. L. Blomefield, Darwin\nexpresses himself in similar terms. \"With respect to man, I am very far\nfrom wishing to obtrude my belief; but I thought it dishonest to quite\nconceal my opinion.\" (Ibid. Vol. II. page 263.)\n\nThe brief allusion in the \"Origin of Species\" is so far from prominent\nand so incidental that it was excusable to assume that Darwin had not\ntouched upon the descent of man in this work. It was solely the desire\nto have his mass of evidence sufficiently complete, solely Darwin's\ngreat characteristic of never publishing till he had carefully weighed\nall aspects of his subject for years, solely, in short, his most\nfastidious scientific conscience that restrained him from challenging\nthe world in 1859 with a book in which the theory of the descent of man\nwas fully set forth. Three years, frequently interrupted by ill-health,\nwere needed for the actual writing of the book (\"Life and Letters\", Vol.\nI. page 94.): the first edition, which appeared in 1871, was followed in\n1874 by a much improved second edition, the preparation of which he very\nreluctantly undertook. (Ibid. Vol. III. page 175.)\n\nThis, briefly, is the history of the work, which, with the \"Origin of\nSpecies\", marks an epoch in the history of biological sciences--the work\nwith which the cautious, peace-loving investigator ventured forth from\nhis contemplative life into the arena of strife and unrest, and\nlaid himself open to all the annoyances that deep-rooted belief and\nprejudice, and the prevailing tendency of scientific thought at the time\ncould devise.\n\nDarwin did not take this step lightly. Of great interest in this\nconnection is a letter written to Wallace on Dec. 22, 1857 (Ibid. Vol.\nII. page 109.), in which he says \"You ask whether I shall discuss\n'man.' I think I shall avoid the whole subject, as so surrounded\nwith prejudices; though I fully admit that it is the highest and most\ninteresting problem for the naturalist.\" But his conscientiousness\ncompelled him to state briefly his opinion on the subject in the \"Origin\nof Species\" in 1859. Nevertheless he did not escape reproaches for\nhaving been so reticent. This is unmistakably apparent from a letter to\nFritz Muller dated February 22 (1869?), in which he says: \"I am thinking\nof writing a little essay on the Origin of Mankind, as I have been\ntaunted with concealing my opinions.\" (Ibid. Vol. III. page 112.)\n\nIt might be thought that Darwin behaved thus hesitatingly, and was so\nslow in deciding on the full publication of his collected material in\nregard to the descent of man, because he had religious difficulties to\novercome.\n\nBut this was not the case, as we can see from his admirable confession\nof faith, the publication of which we owe to his son Francis. (Ibid.\nVol. I. pages 304-317.) Whoever wishes really to understand the lofty\ncharacter of this great man should read these immortal lines in which he\nunfolds to us in simple and straightforward words the development of his\nconception of the universe. He describes how, though he was still quite\northodox during his voyage round the world on board the \"Beagle\", he\ncame gradually to see, shortly afterwards (1836-1839) that the Old\nTestament was no more to be trusted than the Sacred Books of the\nHindoos; the miracles by which Christianity is supported, the\ndiscrepancies between the accounts in the different Gospels, gradually\nled him to disbelieve in Christianity as a divine revelation. \"Thus,\" he\nwrites (\"Life and Letters\", Vol. 1. page 309.), \"disbelief crept over me\nat a very slow rate, but was at last complete. The rate was so slow that\nI felt no distress.\" But Darwin was too modest to presume to go beyond\nthe limits laid down by science. He wanted nothing more than to be able\nto go, freely and unhampered by belief in authority or in the Bible, as\nfar as human knowledge could lead him. We learn this from the concluding\nwords of his chapter on religion: \"The mystery of the beginning of all\nthings is insoluble by us; and I for one must be content to remain an\nAgnostic.\" (Loc. cit. page 313.)\n\nDarwin was always very unwilling to give publicity to his views in\nregard to religion. In a letter to Asa Gray on May 22, 1860 (Ibid. Vol.\nII. page 310.), he declares that it is always painful to him to have\nto enter into discussion of religious problems. He had, he said, no\nintention of writing atheistically.\n\nFinally, let us cite one characteristic sentence from a letter from\nDarwin to C. Ridley (Ibid. Vol. III. page. 236. (\"C. Ridley,\" Mr Francis\nDarwin points out to me, should be H.N. Ridley. A.C.S.)) (Nov. 28,\n1878.) A clergyman, Dr Pusey, had asserted that Darwin had written\nthe \"Origin of Species\" with some relation to theology. Darwin writes\nemphatically, \"Many years ago, when I was collecting facts for the\n'Origin', my belief in what is called a personal God was as firm as that\nof Dr Pusey himself, and as to the eternity of matter I never troubled\nmyself about such insoluble questions.\" The expression \"many years ago\"\nrefers to the time of his voyage round the world, as has already been\npointed out. Darwin means by this utterance that the views which had\ngradually developed in his mind in regard to the origin of species were\nquite compatible with the faith of the Church.\n\nIf we consider all these utterances of Darwin in regard to religion and\nto his outlook on life (Weltanschauung), we shall see at least so much,\nthat religious reflection could in no way have influenced him in regard\nto the writing and publishing of his book on \"The Descent of Man\".\nDarwin had early won for himself freedom of thought, and to this freedom\nhe remained true to the end of his life, uninfluenced by the customs and\nopinions of the world around him.\n\nDarwin was thus inwardly fortified and armed against the host of\ncalumnies, accusations, and attacks called forth by the publication of\nthe \"Origin of Species\", and to an even greater extent by the appearance\nof the \"Descent of Man\". But in his defence he could rely on the aid of\na band of distinguished auxiliaries of the rarest ability. His faithful\nconfederate, Huxley, was joined by the botanist Hooker, and, after\nlonger resistance, by the famous geologist Lyell, whose \"conversion\"\nafforded Darwin peculiar satisfaction. All three took the field with\nenthusiasm in defence of the natural descent of man. From Wallace, on\nthe other hand, though he shared with him the idea of natural selection,\nDarwin got no support in this matter. Wallace expressed himself in a\nstrange manner. He admitted everything in regard to the morphological\ndescent of man, but maintained, in a mystic way, that something else,\nsomething of a spiritual nature must have been added to what man\ninherited from his animal ancestors. Darwin, whose esteem for Wallace\nwas extraordinarily high, could not understand how he could give\nutterance to such a mystical view in regard to man; the idea seemed\nto him so \"incredibly strange\" that he thought some one else must have\nadded these sentences to Wallace's paper.\n\nEven now there are thinkers who, like Wallace, shrink from applying to\nman the ultimate consequences of the theory of descent. The idea\nthat man is derived from ape-like forms is to them unpleasant and\nhumiliating.\n\nSo far I have been depicting the development of Darwin's work on the\ndescent of man. In what follows I shall endeavour to give a condensed\nsurvey of the contents of the book.\n\nIt must at once be said that the contents of Darwin's work fall into two\nparts, dealing with entirely different subjects. \"The Descent of Man\"\nincludes a very detailed investigation in regard to secondary sexual\ncharacters in the animal series, and on this investigation Darwin\nfounded a new theory, that of sexual selection. With astonishing\npatience he gathered together an immense mass of material, and showed,\nin regard to Arthropods and Vertebrates, the wide distribution of\nsecondary characters, which develop almost exclusively in the male, and\nwhich enable him, on the one hand, to get the better of his rivals in\nthe struggle for the female by the greater perfection of his weapons,\nand on the other hand, to offer greater allurements to the female\nthrough the higher development of decorative characters, of song, or of\nscent-producing glands. The best equipped males will thus crowd out the\nless well-equipped in the matter of reproduction, and thus the relevant\ncharacters will be increased and perfected through sexual selection.\nIt is, of course, a necessary assumption that these secondary sexual\ncharacters may be transmitted to the female, although perhaps in\nrudimentary form.\n\nAs we have said, this theory of sexual selection takes up a great deal\nof space in Darwin's book, and it need only be considered here in so far\nas Darwin applied it to the descent of man. To this latter problem the\nwhole of Part I is devoted, while Part III contains a discussion of\nsexual selection in relation to man, and a general summary. Part II\ntreats of sexual selection in general, and may be disregarded in our\npresent study. Moreover, many interesting details must necessarily be\npassed over in what follows, for want of space.\n\nThe first part of the \"Descent of Man\" begins with an enumeration of\nthe proofs of the animal descent of man taken from the structure of\nthe human body. Darwin chiefly emphasises the fact that the human body\nconsists of the same organs and of the same tissues as those of the\nother mammals; he shows also that man is subject to the same diseases\nand tormented by the same parasites as the apes. He further dwells\non the general agreement exhibited by young, embryonic forms, and\nhe illustrates this by two figures placed one above the other, one\nrepresenting a human embryo, after Eaker, the other a dog embryo, after\nBischoff. (\"Descent of Man\" (Popular Edition, 1901), fig. 1, page 14.)\n\nDarwin finds further proofs of the animal origin of man in the\nreduced structures, in themselves extremely variable, which are either\nabsolutely useless to their possessors, or of so little use that they\ncould never have developed under existing conditions. Of such vestiges\nhe enumerates: the defective development of the panniculus carnosus\n(muscle of the skin) so widely distributed among mammals, the\near-muscles, the occasional persistence of the animal ear-point in man,\nthe rudimentary nictitating membrane (plica semilunaris) in the human\neye, the slight development of the organ of smell, the general hairiness\nof the human body, the frequently defective development or entire\nabsence of the third molar (the wisdom tooth), the vermiform appendix,\nthe occasional reappearance of a bony canal (foramen supracondyloideum)\nat the lower end of the humerus, the rudimentary tail of man (the\nso-called taillessness), and so on. Of these rudimentary structures\nthe occasional occurrence of the animal ear-point in man is most fully\ndiscussed. Darwin's attention was called to this interesting structure\nby the sculptor Woolner. He figures such a case observed in man, and\nalso the head of an alleged orang-foetus, the photograph of which he\nreceived from Nitsche.\n\nDarwin's interpretation of Woolner's case as having arisen through a\nfolding over of the free edge of a pointed ear has been fully borne out\nby my investigations on the external ear. (G. Schwalbe, \"Das Darwin'sche\nSpitzohr beim menschlichen Embryo\", \"Anatom. Anzeiger\", 1889, pages\n176-189, and other papers.) In particular, it was established by these\ninvestigations that the human foetus, about the middle of its embryonic\nlife, possesses a pointed ear somewhat similar to that of the monkey\ngenus Macacus. One of Darwin's statements in regard to the head of the\norang-foetus must be corrected. A LARGE ear with a point is shown in\nthe photograph (\"Descent of Man\", fig.3, page 24.), but it can easily be\ndemonstrated--and Deniker has already pointed this out--that the figure\nis not that of an orang-foetus at all, for that form has much smaller\nears with no point; nor can it be a gibbon-foetus, as Deniker supposes,\nfor the gibbon ear is also without a point. I myself regard it as that\nof a Macacus-embryo. But this mistake, which is due to Nitsche, in no\nway affects the fact recognised by Darwin, that ear-forms showing the\npoint characteristic of the animal ear occur in man with extraordinary\nfrequency.\n\nFinally, there is a discussion of those rudimentary structures which\noccur only in ONE sex, such as the rudimentary mammary glands in the\nmale, the vesicula prostatica, which corresponds to the uterus of the\nfemale, and others. All these facts tell in favour of the common descent\nof man and all other vertebrates. The conclusion of this section is\ncharacteristic: \"IT IS ONLY OUR NATURAL PREJUDICE, AND THAT ARROGANCE\nWHICH MADE OUR FOREFATHERS DECLARE THAT THEY WERE DESCENDED FROM\nDEMI-GODS, WHICH LEADS US TO DEMUR TO THIS CONCLUSION. BUT THE TIME WILL\nBEFORE LONG COME, WHEN IT WILL BE THOUGHT WONDERFUL THAT NATURALISTS,\nWHO WERE WELL ACQUAINTED WITH THE COMPARATIVE STRUCTURE AND DEVELOPMENT\nOF MAN, AND OTHER MAMMALS, SHOULD HAVE BELIEVED THAT EACH WAS THE WORK\nOF A SEPARATE ACT OF CREATION.\" (Ibid. page 36.)\n\nIn the second chapter there is a more detailed discussion, again based\nupon an extraordinary wealth of facts, of the problem as to the manner\nin which, and the causes through which, man evolved from a lower form.\nPrecisely the same causes are here suggested for the origin of man, as\nfor the origin of species in general. Variability, which is a necessary\nassumption in regard to all transformations, occurs in man to a high\ndegree. Moreover, the rapid multiplication of the human race creates\nconditions which necessitate an energetic struggle for existence, and\nthus afford scope for the intervention of natural selection. Of the\nexercise of ARTIFICIAL selection in the human race, there is nothing\nto be said, unless we cite such cases as the grenadiers of Frederick\nWilliam I, or the population of ancient Sparta. In the passages already\nreferred to and in those which follow, the transmission of acquired\ncharacters, upon which Darwin does not dwell, is taken for granted.\nIn man, direct effects of changed conditions can be demonstrated (for\ninstance in regard to bodily size), and there are also proofs of the\ninfluence exerted on his physical constitution by increased use or\ndisuse. Reference is here made to the fact, established by Forbes,\nthat the Quechua-Indians of the high plateaus of Peru show a striking\ndevelopment of lungs and thorax, as a result of living constantly at\nhigh altitudes.\n\nSuch special forms of variation as arrests of development\n(microcephalism) and reversion to lower forms are next discussed. Darwin\nhimself felt (\"Descent of Man\", page 54.) that these subjects are so\nnearly related to the cases mentioned in the first chapter, that many\nof them might as well have been dealt with there. It seems to me that it\nwould have been better so, for the citation of additional instances\nof reversion at this place rather disturbs the logical sequence of his\nideas as to the conditions which have brought about the evolution of\nman from lower forms. The instances of reversion here discussed\nare microcephalism, which Darwin wrongly interpreted as atavistic,\nsupernumerary mammae, supernumerary digits, bicornuate uterus, the\ndevelopment of abnormal muscles, and so on. Brief mention is also made\nof correlative variations observed in man.\n\nDarwin next discusses the question as to the manner in which man\nattained to the erect position from the state of a climbing quadruped.\nHere again he puts the influence of Natural Selection in the first\nrank. The immediate progenitors of man had to maintain a struggle for\nexistence in which success was to the more intelligent, and to those\nwith social instincts. The hand of these climbing ancestors, which\nhad little skill and served mainly for locomotion, could only undergo\nfurther development when some early member of the Primate series came to\nlive more on the ground and less among trees.\n\nA bipedal existence thus became possible, and with it the liberation\nof the hand from locomotion, and the one-sided development of the human\nfoot. The upright position brought about correlated variations in the\nbodily structure; with the free use of the hand it became possible\nto manufacture weapons and to use them; and this again resulted in a\ndegeneration of the powerful canine teeth and the jaws, which were then\nno longer necessary for defence. Above all, however, the intelligence\nimmediately increased, and with it skull and brain. The nakedness of\nman, and the absence of a tail (rudimentariness of the tail vertebrae)\nare next discussed. Darwin is inclined to attribute the nakedness of\nman, not to the action of natural selection on ancestors who originally\ninhabited a tropical land, but to sexual selection, which, for aesthetic\nreasons, brought about the loss of the hairy covering in man, or\nprimarily in woman. An interesting discussion of the loss of the tail,\nwhich, however, man shares with the anthropoid apes, some other monkeys\nand lemurs, forms the conclusion of the almost superabundant material\nwhich Darwin worked up in the second chapter. His object was to\nshow that some of the most distinctive human characters are in all\nprobability directly or indirectly due to natural selection. With\ncharacteristic modesty he adds (\"Descent of Man\", page 92.): \"Hence, if\nI have erred in giving to natural selection great power, which I am\nvery far from admitting, or in having exaggerated its power, which is in\nitself probable, I have at least, as I hope, done good service in aiding\nto overthrow the dogma of separate creations.\" At the end of the chapter\nhe touches upon the objection as to man's helpless and defenceless\ncondition. Against this he urges his intelligence and social instincts.\n\nThe two following chapters contain a detailed discussion of the\nobjections drawn from the supposed great differences between the mental\npowers of men and animals. Darwin at once admits that the differences\nare enormous, but not that any fundamental difference between the two\ncan be found. Very characteristic of him is the following passage:\n\"In what manner the mental powers were first developed in the\nlowest organisms, is as hopeless an enquiry as how life itself first\noriginated. These are problems for the distant future, if they are ever\nto be solved by man.\" (Ibid. page 100.)\n\nAfter some brief observations on instinct and intelligence, Darwin\nbrings forward evidence to show that the greater number of the emotional\nstates, such as pleasure and pain, happiness and misery, love and hate\nare common to man and the higher animals. He goes on to give various\nexamples showing that wonder and curiosity, imitation, attention, memory\nand imagination (dreams of animals), can also be observed in the higher\nmammals, especially in apes. In regard even to reason there are\nno sharply defined limits. A certain faculty of deliberation is\ncharacteristic of some animals, and the more thoroughly we know an\nanimal the more intelligence we are inclined to credit it with. Examples\nare brought forward of the intelligent and deliberate actions of apes,\ndogs and elephants. But although no sharply defined differences exist\nbetween man and animals, there is, nevertheless, a series of other\nmental powers which are characteristics usually regarded as absolutely\npeculiar to man. Some of these characteristics are examined in detail,\nand it is shown that the arguments drawn from them are not conclusive.\nMan alone is said to be capable of progressive improvement; but against\nthis must be placed as something analogous in animals, the fact that\nthey learn cunning and caution through long continued persecution. Even\nthe use of tools is not in itself peculiar to man (monkeys use sticks,\nstones and twigs), but man alone fashions and uses implements DESIGNED\nFOR A SPECIAL PURPOSE. In this connection the remarks taken from Lubbock\nin regard to the origin and gradual development of the earliest\nflint implements will be read with interest; these are similar to the\nobservations on modern eoliths, and their bearing on the development of\nthe stone-industry. It is interesting to learn from a letter to Hooker\n(\"Life and Letters\", Vol. II. page 161, June 22, 1859.), that Darwin\nhimself at first doubted whether the stone implements discovered\nby Boucher de Perthes were really of the nature of tools. With the\nrelentless candour as to himself which characterised him, he writes four\nyears later in a letter to Lyell in regard to this view of Boucher de\nPerthes' discoveries: \"I know something about his errors, and looked at\nhis book many years ago, and am ashamed to think that I concluded the\nwhole was rubbish! Yet he has done for man something like what Agassiz\ndid for glaciers.\" (Ibid. Vol. III. page 15, March 17, 1863.)\n\nTo return to Darwin's further comparisons between the higher mental\npowers of man and animals. He takes much of the force from the argument\nthat man alone is capable of abstraction and self-consciousness by his\nown observations on dogs. One of the main differences between man and\nanimals, speech, receives detailed treatment. He points out that various\nanimals (birds, monkeys, dogs) have a large number of different sounds\nfor different emotions, that, further, man produces in common with\nanimals a whole series of inarticulate cries combined with gestures, and\nthat dogs learn to understand whole sentences of human speech. In regard\nto human language, Darwin expresses a view contrary to that held by Max\nMuller (\"Descent of Man\", page 132.): \"I cannot doubt that language owes\nits origin to the imitation and modification of various natural sounds,\nthe voices of other animals, and man's own instinctive cries, aided by\nsigns and gestures.\" The development of actual language presupposes a\nhigher degree of intelligence than is found in any kind of ape. Darwin\nremarks on this point (Ibid. pages 136, 137.): \"The fact of the higher\napes not using their vocal organs for speech no doubt depends on their\nintelligence not having been sufficiently advanced.\"\n\nThe sense of beauty, too, has been alleged to be peculiar to man. In\nrefutation of this assertion Darwin points to the decorative colours of\nbirds, which are used for display. And to the last objection, that man\nalone has religion, that he alone has a belief in God, it is answered\n\"that numerous races have existed, and still exist, who have no idea of\none or more gods, and who have no words in their languages to express\nsuch an idea.\" (Ibid. page 143.)\n\nThe result of the investigations recorded in this chapter is to show\nthat, great as the difference in mental powers between man and the\nhigher animals may be, it is undoubtedly only a difference \"of degree\nand not of kind.\" (\"Descent of Man\", page 193.)\n\nIn the fourth chapter Darwin deals with the MORAL SENSE or CONSCIENCE,\nwhich is the most important of all differences between man and animals.\nIt is a result of social instincts, which lead to sympathy for other\nmembers of the same society, to non-egoistic actions for the good\nof others. Darwin shows that social tendencies are found among many\nanimals, and that among these love and kin-sympathy exist, and he gives\nexamples of animals (especially dogs) which may exhibit characters that\nwe should call moral in man (e.g. disinterested self-sacrifice for the\nsake of others). The early ape-like progenitors of the human race were\nundoubtedly social. With the increase of intelligence the moral sense\ndevelops farther; with the acquisition of speech public opinion arises,\nand finally, moral sense becomes habit. The rest of Darwin's detailed\ndiscussions on moral philosophy may be passed over.\n\nThe fifth chapter may be very briefly summarised. In it Darwin shows\nthat the intellectual and moral faculties are perfected through natural\nselection. He inquires how it can come about that a tribe at a low level\nof evolution attains to a higher, although the best and bravest among\nthem often pay for their fidelity and courage with their lives without\nleaving any descendants. In this case it is the sentiment of glory,\npraise and blame, the admiration of others, which bring about the\nincrease of the better members of the tribe. Property, fixed dwellings,\nand the association of families into a community are also indispensable\nrequirements for civilisation. In the longer second section of the\nfifth chapter Darwin acts mainly as recorder. On the basis of numerous\ninvestigations, especially those of Greg, Wallace, and Galton, he\ninquires how far the influence of natural selection can be demonstrated\nin regard to civilised nations. In the final section, which deals with\nthe proofs that all civilised nations were once barbarians, Darwin again\nuses the results gained by other investigators, such as Lubbock and\nTylor. There are two sets of facts which prove the proposition in\nquestion. In the first place, we find traces of a former lower state\nin the customs and beliefs of all civilised nations, and in the second\nplace, there are proofs to show that savage races are independently able\nto raise themselves a few steps in the scale of civilisation, and that\nthey have thus raised themselves.\n\nIn the sixth chapter of the work, Morphology comes into the foreground\nonce more. Darwin first goes back, however, to the argument based on the\ngreat difference between the mental powers of the highest animals and\nthose of man. That this is only quantitative, not qualitative, he has\nalready shown. Very instructive in this connection is the reference to\nthe enormous difference in mental powers in another class. No one\nwould draw from the fact that the cochineal insect (Coccus) and the ant\nexhibit enormous differences in their mental powers, the conclusion that\nthe ant should therefore be regarded as something quite distinct, and\nwithdrawn from the class of insects altogether.\n\nDarwin next attempts to establish the SPECIFIC genealogical tree of\nman, and carefully weighs the differences and resemblances between the\ndifferent families of the Primates. The erect position of man is an\nadaptive character, just as are the various characters referable to\naquatic life in the seals, which, notwithstanding these, are ranked as\na mere family of the Carnivores. The following utterance is very\ncharacteristic of Darwin (\"Descent of Man\", page 231.): \"If man had\nnot been his own classifier, he would never have thought of founding\na separate order for his own reception.\" In numerous characters not\nmentioned in systematic works, in the features of the face, in the form\nof the nose, in the structure of the external ear, man resembles the\napes. The arrangement of the hair in man has also much in common with\nthe apes; as also the occurrence of hair on the forehead of the human\nembryo, the beard, the convergence of the hair of the upper and under\narm towards the elbow, which occurs not only in the anthropoid apes, but\nalso in some American monkeys. Darwin here adopts Wallace's explanation\nof the origin of the ascending direction of the hair in the forearm of\nthe orang,--that it has arisen through the habit of holding the hands\nover the head in rain. But this explanation cannot be maintained when we\nconsider that this disposition of the hair is widely distributed among\nthe most different mammals, being found in the dog, in the sloth, and in\nmany of the lower monkeys.\n\nAfter further careful analysis of the anatomical characters Darwin\nreaches the conclusion that the New World monkeys (Platyrrhine) may\nbe excluded from the genealogical tree altogether, but that man is\nan offshoot from the Old World monkeys (Catarrhine) whose progenitors\nexisted as far back as the Miocene period. Among these Old World monkeys\nthe forms to which man shows the greatest resemblance are the anthropoid\napes, which, like him, possess neither tail nor ischial callosities. The\nplatyrrhine and catarrhine monkeys have their primitive ancestor among\nextinct forms of the Lemuridae. Darwin also touches on the question of\nthe original home of the human race and supposes that it may have been\nin Africa, because it is there that man's nearest relatives, the gorilla\nand the chimpanzee, are found. But he regards speculation on this point\nas useless. It is remarkable that, in this connection, Darwin regards\nthe loss of the hair-covering in man as having some relation to a\nwarm climate, while elsewhere he is inclined to make sexual selection\nresponsible for it. Darwin recognises the great gap between man and\nhis nearest relatives, but similar gaps exist at other parts of the\nmammalian genealogical tree: the allied forms have become extinct. After\nthe extermination of the lower races of mankind, on the one hand, and of\nthe anthropoid apes on the other, which will undoubtedly take place, the\ngulf will be greater than ever, since the baboons will then bound it on\nthe one side, and the white races on the other. Little weight need be\nattached to the lack of fossil remains to fill up this gap, since the\ndiscovery of these depends upon chance. The last part of the chapter is\ndevoted to a discussion of the earlier stages in the genealogy of\nman. Here Darwin accepts in the main the genealogical tree, which had\nmeantime been published by Haeckel, who traces the pedigree back through\nMonotremes, Reptiles, Amphibians, and Fishes, to Amphioxus.\n\nThen follows an attempt to reconstruct, from the atavistic characters,\na picture of our primitive ancestor who was undoubtedly an arboreal\nanimal. The occurrence of rudiments of parts in one sex which only come\nto full development in the other is next discussed. This state of things\nDarwin regards as derived from an original hermaphroditism. In regard to\nthe mammary glands of the male he does not accept the theory that they\nare vestigial, but considers them rather as not fully developed.\n\nThe last chapter of Part I deals with the question whether the different\nraces of man are to be regarded as different species, or as sub-species\nof a race of monophyletic origin. The striking differences between\nthe races are first emphasised, and the question of the fertility or\ninfertility of hybrids is discussed. That fertility is the more usual\nis shown by the excessive fertility of the hybrid population of Brazil.\nThis, and the great variability of the distinguishing characters of\nthe different races, as well as the fact that all grades of transition\nstages are found between these, while considerable general agreement\nexists, tell in favour of the unity of the races and lead to the\nconclusion that they all had a common primitive ancestor.\n\nDarwin therefore classifies all the different races as sub-species of\nONE AND THE SAME SPECIES. Then follows an interesting inquiry into the\nreasons for the extinction of human races. He recognises as the ultimate\nreason the injurious effects of a change of the conditions of life,\nwhich may bring about an increase in infantile mortality, and a\ndiminished fertility. It is precisely the reproductive system, among\nanimals also, which is most susceptible to changes in the environment.\n\nThe final section of this chapter deals with the formation of the races\nof mankind. Darwin discusses the question how far the direct effect of\ndifferent conditions of life, or the inherited effects of increased use\nor disuse may have brought about the characteristic differences between\nthe different races. Even in regard to the origin of the colour of the\nskin he rejects the transmitted effects of an original difference of\nclimate as an explanation. In so doing he is following his tendency to\nexclude Lamarckian explanations as far as possible. But here he makes\ngratuitous difficulties from which, since natural selection fails, there\nis no escape except by bringing in the principle of sexual selection, to\nwhich, he regarded it as possible, skin-colouring, arrangement of\nhair, and form of features might be traced. But with his characteristic\nconscientiousness he guards himself thus: \"I do not intend to assert\nthat sexual selection will account for all the differences between the\nraces.\" (\"Descent of Man\", page 308.)\n\nI may be permitted a remark as to Darwin's attitude towards Lamarck.\nWhile, at an earlier stage, when he was engaged in the preliminary\nlabours for his immortal work, \"The Origin of Species\", Darwin expresses\nhimself very forcibly against the views of Lamarck, speaking of\nLamarckian \"nonsense,\" (\"Life and Letters\", Vol. II. page 23.), and\nof Lamarck's \"absurd, though clever work\" (Loc. cit. page 39.) and\nexpressly declaring, \"I attribute very little to the direct action of\nclimate, etc.\" (Loc. cit. (1856), page 82.) yet in later life he became\nmore and more convinced of the influence of external conditions. In\n1876, that is, two years after the appearance of the second edition of\n\"The Descent of Man\", he writes with his usual candid honesty: \"In my\nopinion the greatest error which I have committed, has been not allowing\nsufficient weight to the direct action of the environment, i.e. food,\nclimate, etc. independently of natural selection.\" (Ibid. Vol. III. page\n159.) It is certain from this change of opinion that, if he had been\nable to make up his mind to issue a third edition of \"The Descent of\nMan\", he would have ascribed a much greater influence to the effect of\nexternal conditions in explaining the different characters of the races\nof man than he did in the second edition. He would also undoubtedly have\nattributed less influence to sexual selection as a factor in the origin\nof the different bodily characteristics, if indeed he would not have\nexcluded it altogether.\n\nIn Part III of the \"Descent\" two additional chapters are devoted to the\ndiscussion of sexual selection in relation to man. These may be very\nbriefly referred to. Darwin here seeks to show that sexual selection has\nbeen operative on man and his primitive progenitor. Space fails me to\nfollow out his interesting arguments. I can only mention that he is\ninclined to trace back hairlessness, the development of the beard in\nman, and the characteristic colour of the different human races to\nsexual selection. Since bareness of the skin could be no advantage, but\nrather a disadvantage, this character cannot have been brought about by\nnatural selection. Darwin also rejected a direct influence of climate as\na cause of the origin of the skin-colour. I have already expressed the\nopinion, based on the development of his views as shown in his letters,\nthat in a third edition Darwin would probably have laid more stress on\nthe influence of external environment. He himself feels that there are\ngaps in his proofs here, and says in self-criticism: \"The views here\nadvanced, on the part which sexual selection has played in the history\nof man, want scientific precision.\" (\"Descent of Man\", page 924.) I\nneed here only point out that it is impossible to explain the graduated\nstages of skin-colour by sexual selection, since it would have produced\nraces sharply defined by their colour and not united to other races\nby transition stages, and this, it is well known, is not the case.\nMoreover, the fact established by me (\"Die Hautfarbe des Menschen\",\n\"Mitteilungen der Anthropologischen Gesellschaft in Wien\", Vol. XXXIV.\npages 331-352.), that in all races the ventral side of the trunk is\npaler than the dorsal side, and the inner surface of the extremities\npaler than the outer side, cannot be explained by sexual selection in\nthe Darwinian sense.\n\nWith this I conclude my brief survey of the rich contents of Darwin's\nbook. I may be permitted to conclude by quoting the magnificent final\nwords of \"The Descent of Man\": \"We must, however, acknowledge, as it\nseems to me, that man, with all his noble qualities, with sympathy which\nfeels for the most debased, with benevolence which extends not only\nto other men but to the humblest living creature, with his god-like\nintellect which has penetrated into the movements and constitution of\nthe solar system--with all these exalted powers--Man still bears in his\nbodily frame the indelible stamp of his lowly origin.\" (Ibid. page 947.)\n\nWhat has been the fate of Darwin's doctrines since his great\nachievement? How have they been received and followed up by the\nscientific and lay world? And what do the successors of the mighty hero\nand genius think now in regard to the origin of the human race?\n\nAt the present time we are incomparably more favourably placed than\nDarwin was for answering this question of all questions. We have at our\ncommand an incomparably greater wealth of material than he had at his\ndisposal. And we are more fortunate than he in this respect, that we\nnow know transition-forms which help to fill up the gap, still great,\nbetween the lowest human races and the highest apes. Let us consider\nfor a little the more essential additions to our knowledge since the\npublication of \"The Descent of Man\".\n\nSince that time our knowledge of animal embryos has increased\nenormously. While Darwin was obliged to content himself with comparing\na human embryo with that of a dog, there are now available the youngest\nembryos of monkeys of all possible groups (Orang, Gibbon, Semnopithecus,\nMacacus), thanks to Selenka's most successful tour in the East Indies in\nsearch of such material. We can now compare corresponding stages of\nthe lower monkeys and of the Anthropoid apes with human embryos, and\nconvince ourselves of their great resemblance to one another, thus\nstrengthening enormously the armour prepared by Darwin in defence of his\nview on man's nearest relatives. It may be said that Selenka's material\nfils up the blanks in Darwin's array of proofs in the most satisfactory\nmanner.\n\nThe deepening of our knowledge of comparative anatomy also gives us much\nsurer foundations than those on which Darwin was obliged to build. Just\nof late there have been many workers in the domain of the anatomy of\napes and lemurs, and their investigations extend to the most different\norgans. Our knowledge of fossil apes and lemurs has also become much\nwider and more exact since Darwin's time: the fossil lemurs have been\nespecially worked up by Cope, Forsyth Major, Ameghino, and others.\nDarwin knew very little about fossil monkeys. He mentions two or three\nanthropoid apes as occurring in the Miocene of Europe (\"Descent of\nMan\", page 240.), but only names Dryopithecus, the largest form from\nthe Miocene of France. It was erroneously supposed that this form was\nrelated to Hylobates. We now know not only a form that actually stands\nnear to the gibbon (Pliopithecus), and remains of other anthropoids\n(Pliohylobates and the fossil chimpanzee, Palaeopithecus), but also\nseveral lower catarrhine monkeys, of which Mesopithecus, a form nearly\nrelated to the modern Sacred Monkeys (a species of Semnopithecus) and\nfound in strata of the Miocene period in Greece, is the most important.\nQuite recently, too, Ameghino's investigations have made us acquainted\nwith fossil monkeys from South America (Anthropops, Homunculus), which,\naccording to their discoverer, are to be regarded as in the line of\nhuman descent.\n\nWhat Darwin missed most of all--intermediate forms between apes\nand man--has been recently furnished. (E. Dubois, as is well known,\ndiscovered in 1893, near Trinil in Java, in the alluvial deposits of\nthe river Bengawan, an important form represented by a skull-cap, some\nmolars, and a femur. His opinion--much disputed as it has been--that in\nthis form, which he named Pithecanthropus, he has found a long-desired\ntransition-form is shared by the present writer. And although the\ngeological age of these fossils, which, according to Dubois, belong to\nthe uppermost Tertiary series, the Pliocene, has recently been fixed\nat a later date (the older Diluvium)), the MORPHOLOGICAL VALUE of\nthese interesting remains, that is, the intermediate position of\nPithecanthropus, still holds good. Volz says with justice (\"Das\ngeologische Alter der Pithecanthropus-Schichten bei Trinil, Ost-Java\".\n\"Neues Jahrb. f.Mineralogie\". Festband, 1907.), that even if\nPithecanthropus is not THE missing link, it is undoubtedly _A_ missing\nlink.\n\nAs on the one hand there has been found in Pithecanthropus a form which,\nthough intermediate between apes and man, is nevertheless more closely\nallied to the apes, so on the other hand, much progress has been made\nsince Darwin's day in the discovery and description of the older\nhuman remains. Since the famous roof of a skull and the bones of the\nextremities belonging to it were found in 1856 in the Neandertal near\nDusseldorf, the most varied judgments have been expressed in regard\nto the significance of the remains and of the skull in particular.\nIn Darwin's \"Descent of Man\" there is only a passing allusion to them\n(\"Descent of Man\", page 82.) in connection with the discussion of the\nskull-capacity, although the investigations of Schaaffhausen, King, and\nHuxley were then known. I believe I have shown, in a series of papers,\nthat the skull in question belongs to a form different from any of the\nraces of man now living, and, with King and Cope, I regard it as at\nleast a different species from living man, and have therefore designated\nit Homo primigenius. The form unquestionably belongs to the older\nDiluvium, and in the later Diluvium human forms already appear, which\nagree in all essential points with existing human races.\n\nAs far back as 1886 the value of the Neandertal skull was greatly\nenhanced by Fraipont's discovery of two skulls and skeletons from Spy in\nBelgium. These are excellently described by their discoverer (\"La race\nhumaine de Neanderthal ou de Canstatt en Belgique\". \"Arch. de Biologie\",\nVII. 1887.), and are regarded as belonging to the same group of forms\nas the Neandertal remains. In 1899 and the following years came the\ndiscovery by Gorjanovic-Kramberger of different skeletal parts of\nat least ten individuals in a cave near Krapina in Croatia.\n(Gorjanovic-Kramberger \"Der diluviale Mensch von Krapina in Kroatien\",\n1906.) It is in particular the form of the lower jaw which is different\nfrom that of all recent races of man, and which clearly indicates\nthe lowly position of Homo primigenius, while, on the other hand, the\nlong-known skull from Gibraltar, which I (\"Studien zur Vorgeschichte des\nMenschen\", 1906, pages 154 ff.) have referred to Homo primigenius, and\nwhich has lately been examined in detail by Sollas (\"On the cranial and\nfacial characters of the Neandertal Race\". \"Trans. R. Soc.\" London, vol.\n199, 1908, page 281.), has made us acquainted with the surprising shape\nof the eye-orbit, of the nose, and of the whole upper part of the face.\nIsolated lower jaws found at La Naulette in Belgium, and at Malarnaud\nin France, increase our material which is now as abundant as could be\ndesired. The most recent discovery of all is that of a skull dug up in\nAugust of this year (1908) by Klaatsch and Hauser in the lower grotto\nof the Le Moustier in Southern France, but this skull has not yet\nbeen fully described. Thus Homo primigenius must also be regarded as\noccupying a position in the gap existing between the highest apes and\nthe lowest human races, Pithecanthropus, standing in the lower part of\nit, and Homo primigenius in the higher, near man. In order to prevent\nmisunderstanding, I should like here to emphasise that in arranging this\nstructural series--anthropoid apes, Pithecanthropus, Homo primigenius,\nHomo sapiens--I have no intention of establishing it as a direct\ngenealogical series. I shall have something to say in regard to the\ngenetic relations of these forms, one to another, when discussing the\ndifferent theories of descent current at the present day. ((Since\nthis essay was written Schoetensack has discovered near Heidelberg\nand briefly described an exceedingly interesting lower jaw from rocks\nbetween the Pliocene and Diluvial beds. This exhibits interesting\ndifferences from the forms of lower jaw of Homo primigenius.\n(Schoetensack \"Der Unterkiefer des Homo heidelbergensis\". Leipzig,\n1908.) G.S.))\n\nIn quite a different domain from that of morphological relationship,\nnamely in the physiological study of the blood, results have recently\nbeen gained which are of the highest importance to the doctrine of\ndescent. Uhlenhuth, Nuttall, and others have established the fact\nthat the blood-serum of a rabbit which has previously had human blood\ninjected into it, forms a precipitate with human blood. This biological\nreaction was tried with a great variety of mammalian species, and it was\nfound that those far removed from man gave no precipitate under these\nconditions. But as in other cases among mammals all nearly related forms\nyield an almost equally marked precipitate, so the serum of a rabbit\ntreated with human blood and then added to the blood of an anthropoid\nape gives ALMOST as marked a precipitate as in human blood; the reaction\nto the blood of the lower Eastern monkeys is weaker, that to the Western\nmonkeys weaker still; indeed in this last case there is only a slight\nclouding after a considerable time and no actual precipitate. The blood\nof the Lemuridae (Nuttall) gives no reaction or an extremely weak one,\nthat of the other mammals none whatever. We have in this not only a\nproof of the literal blood-relationship between man and apes, but the\ndegree of relationship with the different main groups of apes can be\ndetermined beyond possibility of mistake.\n\nFinally, it must be briefly mentioned that in regard to remains of human\nhandicraft also, the material at our disposal has greatly increased of\nlate years, that, as a result of this, the opinions of archaeologists\nhave undergone many changes, and that, in particular, their views in\nregard to the age of the human race have been greatly influenced. There\nis a tendency at the present time to refer the origin of man back to\nTertiary times. It is true that no remains of Tertiary man have been\nfound, but flints have been discovered which, according to the opinion\nof most investigators, bear traces either of use, or of very primitive\nworkmanship. Since Rutot's time, following Mortillet's example,\ninvestigators have called these \"eoliths,\" and they have been traced\nback by Verworn to the Miocene of the Auvergne, and by Rutot even to the\nupper Oligocene. Although these eoliths are even nowadays the subject of\nmany different views, the preoccupation with them has kept the problem\nof the age of the human race continually before us.\n\nGeology, too, has made great progress since the days of Darwin and\nLyell, and has endeavoured with satisfactory results to arrange the\nhuman remains of the Diluvial period in chronological order (Penck). I\ndo not intend to enter upon the question of the primitive home of the\nhuman race; since the space at my disposal will not allow of my\ntouching even very briefly upon all the departments of science which are\nconcerned in the problem of the descent of man. How Darwin would have\nrejoiced over each of the discoveries here briefly outlined! What use\nhe would have made of the new and precious material, which would have\nprevented the discouragement from which he suffered when preparing the\nsecond edition of \"The Descent of Man\"! But it was not granted to him to\nsee this progress towards filling up the gaps in his edifice of which he\nwas so painfully conscious.\n\nHe did, however, have the satisfaction of seeing his ideas steadily\ngaining ground, notwithstanding much hostility and deep-rooted\nprejudice. Even in the years between the appearance of \"The Origin\nof Species\" and of the first edition of the \"Descent\", the idea of a\nnatural descent of man, which was only briefly indicated in the work of\n1859, had been eagerly welcomed in some quarters. It has been already\npointed out how brilliantly Huxley contributed to the defence and\ndiffusion of Darwin's doctrines, and how in \"Man's Place in Nature\"\nhe has given us a classic work as a foundation for the doctrine of\nthe descent of man. As Huxley was Darwin's champion in England, so in\nGermany Carl Vogt, in particular, made himself master of the Darwinian\nideas. But above all it was Haeckel who, in energy, eagerness for\nbattle, and knowledge may be placed side by side with Huxley, who took\nover the leadership in the controversy over the new conception of the\nuniverse. As far back as 1866, in his \"Generelle Morphologie\", he had\ninquired minutely into the question of the descent of man, and not\ncontent with urging merely the general theory of descent from lower\nanimal forms, he drew up for the first time genealogical trees showing\nthe close relationships of the different animal groups; the last of\nthese illustrated the relationships of Mammals, and among them of all\ngroups of the Primates, including man. It was Haeckel's genealogical\ntrees that formed the basis of the special discussion of the\nrelationships of man, in the sixth chapter of Darwin's \"Descent of Man\".\n\nIn the last section of this essay I shall return to Haeckel's conception\nof the special descent of man, the main features of which he still\nupholds, and rightly so. Haeckel has contributed more than any one else\nto the spread of the Darwinian doctrine.\n\nI can only allow myself a few words as to the spread of the theory\nof the natural descent of man in other countries. The Parisian\nanthropological school, founded and guided by the genius of Broca, took\nup the idea of the descent of man, and made many notable contributions\nto it (Broca, Manouvrier, Mahoudeau, Deniker and others). In England\nitself Darwin's work did not die. Huxley took care of that, for he, with\nhis lofty and unprejudiced mind, dominated and inspired English biology\nuntil his death on June 29, 1895. He had the satisfaction shortly before\nhis death of learning of Dubois' discovery, which he illustrated by a\nhumorous sketch. (\"Life and Letters of Thomas Henry Huxley\", Vol. II.\npage 394.) But there are still many followers in Darwin's footsteps\nin England. Keane has worked at the special genealogical tree of the\nPrimates; Keith has inquired which of the anthropoid apes has the\ngreatest number of characters in common with man; Morris concerns\nhimself with the evolution of man in general, especially with\nhis acquisition of the erect position. The recent discoveries of\nPithecanthropus and Homo primigenius are being vigorously discussed; but\nthe present writer is not in a position to form an opinion of the\nextent to which the idea of descent has penetrated throughout England\ngenerally.\n\nIn Italy independent work in the domain of the descent of man is being\nproduced, especially by Morselli; with him are associated, in the\ninvestigation of related problems, Sergi and Giuffrida-Ruggeri. From\nthe ranks of American investigators we may single out in particular the\neminent geologist Cope, who championed with much decision the idea\nof the specific difference of Homo neandertalensis (primigenius) and\nmaintained a more direct descent of man from the fossil Lemuridae. In\nSouth America too, in Argentina, new life is stirring in this department\nof science. Ameghino in Buenos Ayres has awakened the fossil primates\nof the Pampas formation to new life; he even believes that in\nTetraprothomo, represented by a femur, he has discovered a direct\nancestor of man. Lehmann-Nitsche is working at the other side of the\ngulf between apes and men, and he describes a remarkable first cervical\nvertebra (atlas) from Monte Hermoso as belonging to a form which\nmay bear the same relation to Homo sapiens in South America as Homo\nprimigenius does in the Old World. After a minute investigation he\nestablishes a human species Homo neogaeus, while Ameghino ascribes this\natlas vertebra to his Tetraprothomo.\n\nThus throughout the whole scientific world there is arising a new\nlife, an eager endeavour to get nearer to Huxley's problema maximum,\nto penetrate more deeply into the origin of the human race. There are\nto-day very few experts in anatomy and zoology who deny the animal\ndescent of man in general. Religious considerations, old prejudices,\nthe reluctance to accept man, who so far surpasses mentally all\nother creatures, as descended from \"soulless\" animals, prevent a few\ninvestigators from giving full adherence to the doctrine. But there are\nvery few of these who still postulate a special act of creation for\nman. Although the majority of experts in anatomy and zoology accept\nunconditionally the descent of man from lower forms, there is much\ndiversity of opinion among them in regard to the special line of\ndescent.\n\nIn trying to establish any special hypothesis of descent, whether by\nthe graphic method of drawing up genealogical trees or otherwise, let us\nalways bear in mind Darwin's words (\"Descent of Man\", page 229.) and use\nthem as a critical guiding line: \"As we have no record of the lines of\ndescent, the pedigree can be discovered only by observing the degrees of\nresemblance between the beings which are to be classed.\" Darwin carries\nthis further by stating \"that resemblances in several unimportant\nstructures, in useless and rudimentary organs, or not now functionally\nactive, or in an embryological condition, are by far the most\nserviceable for classification.\" (Loc. cit.) It has also to be\nremembered that NUMEROUS separate points of agreement are of much\ngreater importance than the amount of similarity or dissimilarity in a\nfew points.\n\nThe hypotheses as to descent current at the present day may be divided\ninto two main groups. The first group seeks for the roots of the human\nrace not among any of the families of the apes--the anatomically nearest\nforms--nor among their very similar but less specialised ancestral\nforms, the fossil representatives of which we can know only in part,\nbut, setting the monkeys on one side, it seeks for them lower down among\nthe fossil Eocene Pseudo-lemuridae or Lemuridae (Cope), or even among\nthe primitive pentadactylous Eocene forms, which may either have led\ndirectly to the evolution of man (Adloff), or have given rise to an\nancestral form common to apes and men (Klaatsch (Klaatsch in his last\npublications speaks in the main only of an ancestral form common to men\nand anthropoid apes.), Giuffrida-Ruggeri). The common ancestral form,\nfrom which man and apes are thus supposed to have arisen independently,\nmay explain the numerous resemblances which actually exist between\nthem. That is to say, all the characters upon which the great structural\nresemblance between apes and man depends must have been present in their\ncommon ancestor. Let us take an example of such a common character. The\nbony external ear-passage is in general as highly developed in the lower\nEastern monkeys and the anthropoid apes as in man. This character must,\ntherefore, have already been present in the common primitive form. In\nthat case it is not easy to understand why the Western monkeys have\nnot also inherited the character, instead of possessing only a tympanic\nring. But it becomes more intelligible if we assume that forms with a\nprimitive tympanic ring were the original type, and that from these were\nevolved, on the one hand, the existing New World monkeys with persistent\ntympanic ring, and on the other an ancestral form common to the lower\nOld World monkeys, the anthropoid apes and man. For man shares with\nthese the character in question, and it is also one of the \"unimportant\"\ncharacters required by Darwin. Thus we have two divergent lines arising\nfrom the ancestral form, the Western monkeys (Platyrrhine) on the one\nhand, and an ancestral form common to the lower Eastern monkeys, the\nanthropoid apes, and man, on the other. But considerations similar to\nthose which showed it to be impossible that man should have developed\nfrom an ancestor common to him and the monkeys, yet outside of and\nparallel with these, may be urged also against the likelihood of a\nparallel evolution of the lower Eastern monkeys, the anthropoid apes,\nand man. The anthropoid apes have in common with man many characters\nwhich are not present in the lower Old World monkeys. These characters\nmust therefore have been present in the ancestral form common to the\nthree groups. But here, again, it is difficult to understand why the\nlower Eastern monkeys should not also have inherited these characters.\nAs this is not the case, there remains no alternative but to assume\ndivergent evolution from an indifferent form. The lower Eastern monkeys\nare carrying on the evolution in one direction--I might almost say\ntowards a blind alley--while anthropoids and men have struck out a\nprogressive path, at first in common, which explains the many points of\nresemblance between them, without regarding man as derived directly\nfrom the anthropoids. Their many striking points of agreement indicate a\ncommon descent, and cannot be explained as phenomena of convergence.\n\nI believe I have shown in the above sketch that a theory which derives\nman directly from lower forms without regarding apes as transition-types\nleads ad absurdum. The close structural relationship between man and\nmonkeys can only be understood if both are brought into the same line\nof evolution. To trace man's line of descent directly back to the old\nEocene mammals, alongside of, but with no relation to these very similar\nforms, is to abandon the method of exact comparison, which, as Darwin\nrightly recognised, alone justifies us in drawing up genealogical trees\non the basis of resemblances and differences. The farther down we go the\nmore does the ground slip from beneath our feet. Even the Lemuridae\nshow very numerous divergent conditions, much more so the Eocene\nmammals (Creodonta, Condylarthra), the chief resemblance of which to man\nconsists in the possession of pentadactylous hands and feet! Thus the\nfarther course of the line of descent disappears in the darkness of the\nancestry of the mammals. With just as much reason we might pass by the\nVertebrates altogether, and go back to the lower Invertebrates, but\nin that case it would be much easier to say that man has arisen\nindependently, and has evolved, without relation to any animals, from\nthe lowest primitive form to his present isolated and dominant position.\nBut this would be to deny all value to classification, which must after\nall be the ultimate basis of a genealogical tree. We can, as Darwin\nrightly observed, only infer the line of descent from the degree of\nresemblance between single forms. If we regard man as directly derived\nfrom primitive forms very far back, we have no way of explaining the\nmany points of agreement between him and the monkeys in general, and the\nanthropoid apes in particular. These must remain an inexplicable marvel.\n\nI have thus, I trust, shown that the first class of special theories\nof descent, which assumes that man has developed, parallel with the\nmonkeys, but without relation to them, from very low primitive forms\ncannot be upheld, because it fails to take into account the close\nstructural affinity of man and monkeys. I cannot but regard this\nhypothesis as lamentably retrograde, for it makes impossible any\napplication of the facts that have been discovered in the course of\nthe anatomical and embryological study of man and monkeys, and indeed\nprejudges investigations of that class as pointless. The whole method is\nperverted; an unjustifiable theory of descent is first formulated with\nthe aid of the imagination, and then we are asked to declare that all\nstructural relations between man and monkeys, and between the different\ngroups of the latter, are valueless,--the fact being that they are the\nonly true basis on which a genealogical tree can be constructed.\n\nSo much for this most modern method of classification, which has\nprobably found adherents because it would deliver us from the\nrelationship to apes which many people so much dislike. In contrast\nto it we have the second class of special hypotheses of descent, which\nkeeps strictly to the nearest structural relationships. This is the only\nbasis that justifies the drawing up of a special hypothesis of descent.\nIf this fundamental proposition be recognised, it will be admitted that\nthe doctrine of special descent upheld by Haeckel, and set forth in\nDarwin's \"Descent of Man\", is still valid to-day. In the genealogical\ntree, man's place is quite close to the anthropoid apes; these again\nhave as their nearest relatives the lower Old World monkeys, and their\nprogenitors must be sought among the less differentiated Platyrrhine\nmonkeys, whose most important characters have been handed on to the\npresent day New World monkeys. How the different genera are to be\narranged within the general scheme indicated depends in the main on\nthe classificatory value attributed to individual characters. This is\nparticularly true in regard to Pithecanthropus, which I consider as the\nroot of a branch which has sprung from the anthropoid ape root and has\nled up to man; the latter I have designated the family of the Hominidae.\n\nFor the rest, there are, as we have said, various possible ways of\nconstructing the narrower genealogy within the limits of this branch\nincluding men and apes, and these methods will probably continue to\nchange with the accumulation of new facts. Haeckel himself has modified\nhis genealogical tree of the Primates in certain details since the\npublication of his \"Generelle Morphologie\" in 1866, but its general\nbasis remains the same. (Haeckel's latest genealogical tree is to be\nfound in his most recent work, \"Unsere Ahnenreihe\". Jena, 1908.) All the\nspecial genealogical trees drawn up on the lines laid down by Haeckel\nand Darwin--and that of Dubois may be specially mentioned--are based, in\ngeneral, on the close relationship of monkeys and men, although they may\nvary in detail. Various hypotheses have been formulated on these lines,\nwith special reference to the evolution of man. \"Pithecanthropus\" is\nregarded by some authorities as the direct ancestor of man, by others as\na side-track failure in the attempt at the evolution of man. The problem\nof the monophyletic or polyphyletic origin of the human race has also\nbeen much discussed. Sergi (Sergi G. \"Europa\", 1908.) inclines towards\nthe assumption of a polyphyletic origin of the three main races of man,\nthe African primitive form of which has given rise also to the\ngorilla and chimpanzee, the Asiatic to the Orang, the Gibbon, and\nPithecanthropus. Kollmann regards existing human races as derived from\nsmall primitive races (pigmies), and considers that Homo primigenius\nmust have arisen in a secondary and degenerative manner.\n\nBut this is not the place, nor have I the space to criticise the various\nspecial theories of descent. One, however, must receive particular\nnotice. According to Ameghino, the South American monkeys (Pitheculites)\nfrom the oldest Tertiary of the Pampas are the forms from which have\narisen the existing American monkeys on the one hand, and on the other,\nthe extinct South American Homunculidae, which are also small forms.\nFrom these last, anthropoid apes and man have, he believes, been\nevolved. Among the progenitors of man, Ameghino reckons the form\ndiscovered by him (Tetraprothomo), from which a South American primitive\nman, Homo pampaeus, might be directly evolved, while on the other hand\nall the lower Old World monkeys may have arisen from older fossil\nSouth American forms (Clenialitidae), the distribution of which may\nbe explained by the bridge formerly existing between South America and\nAfrica, as may be the derivation of all existing human races from Homo\npampaeus. (See Ameghino's latest paper, \"Notas preliminares sobre el\nTetraprothomo argentinus\", etc. \"Anales del Museo nacional de Buenos\nAires\", XVI. pages 107-242, 1907.) The fossil forms discovered by\nAmeghino deserve the most minute investigation, as does also the fossil\nman from South America of which Lehmann-Nitsche (\"Nouvelles recherches\nsur la formation pampeenne et l'homme fossile de la Republique\nArgentine\". \"Rivista del Museo de la Plata\", T. XIV. pages 193-488.) has\nmade a thorough study.\n\nIt is obvious that, notwithstanding the necessity for fitting man's line\nof descent into the genealogical tree of the Primates, especially the\napes, opinions in regard to it differ greatly in detail. This could not\nbe otherwise, since the different Primate forms, especially the fossil\nforms, are still far from being exhaustively known. But one thing\nremains certain,--the idea of the close relationship between man and\nmonkeys set forth in Darwin's \"Descent of Man\". Only those who deny the\nmany points of agreement, the sole basis of classification, and thus of\na natural genealogical tree, can look upon the position of Darwin and\nHaeckel as antiquated, or as standing on an insufficient foundation.\nFor such a genealogical tree is nothing more than a summarised\nrepresentation of what is known in regard to the degree of resemblance\nbetween the different forms.\n\nDarwin's work in regard to the descent of man has not been surpassed;\nthe more we immerse ourselves in the study of the structural\nrelationships between apes and man, the more is our path illumined by\nthe clear light radiating from him, and through his calm and deliberate\ninvestigation, based on a mass of material in the accumulation of which\nhe has never had an equal. Darwin's fame will be bound up for all time\nwith the unprejudiced investigation of the question of all questions,\nthe descent of the human race.\n\n\n\n\nVIII. CHARLES DARWIN AS AN ANTHROPOLOGIST. By Ernst Haeckel.\n\nProfessor of Zoology in the University of Jena.\n\nThe great advance that anthropology has made in the second half of the\nnineteenth century is due in the first place, to Darwin's discovery of\nthe origin of man. No other problem in the whole field of research is so\nmomentous as that of \"Man's place in nature,\" which was justly described\nby Huxley (1863) as the most fundamental of all questions. Yet the\nscientific solution of this problem was impossible until the theory of\ndescent had been established.\n\nIt is now a hundred years since the great French biologist Jean Lamarck\npublished his \"Philosophie Zoologique\". By a remarkable coincidence the\nyear in which that work was issued, 1809, was the year of the birth of\nhis most distinguished successor, Charles Darwin. Lamarck had\nalready recognised that the descent of man from a series of other\nVertebrates--that is, from a series of Ape-like Primates--was\nessentially involved in the general theory of transformation which\nhe had erected on a broad inductive basis; and he had sufficient\npenetration to detect the agencies that had been at work in the\nevolution of the erect bimanous man from the arboreal and quadrumanous\nape. He had, however, few empirical arguments to advance in support\nof his hypothesis, and it could not be established until the further\ndevelopment of the biological sciences--the founding of comparative\nembryology by Baer (1828) and of the cell-theory by Schleiden and\nSchwann (1838), the advance of physiology under Johannes Muller (1833),\nand the enormous progress of palaeontology and comparative anatomy\nbetween 1820 and 1860--provided this necessary foundation. Darwin was\nthe first to coordinate the ample results of these lines of research.\nWith no less comprehensiveness than discrimination he consolidated them\nas a basis of a modified theory of descent, and associated with them\nhis own theory of natural selection, which we take to be distinctive\nof \"Darwinism\" in the stricter sense. The illuminating truth of these\ncumulative arguments was so great in every branch of biology that,\nin spite of the most vehement opposition, the battle was won within a\nsingle decade, and Darwin secured the general admiration and recognition\nthat had been denied to his forerunner, Lamarck, up to the hour of his\ndeath (1829).\n\nBefore, however, we consider the momentous influence that Darwinism has\nhad in anthropology, we shall find it useful to glance at its history\nin the course of the last half century, and notice the various theories\nthat have contributed to its advance. The first attempt to give\nextensive expression to the reform of biology by Darwin's work will be\nfound in my \"Generelle Morphologie\" (1866) (\"Generelle Morphologie\nder Organismen\", 2 vols., Berlin, 1866.) which was followed by a more\npopular treatment of the subject in my \"Naturliche Schopfungsgeschichte\"\n(1868) (English translation; \"The History of Creation\", London,\n1876.), a compilation from the earlier work. In the first volume of the\n\"Generelle Morphologie\" I endeavoured to show the great importance\nof evolution in settling the fundamental questions of biological\nphilosophy, especially in regard to comparative anatomy. In the second\nvolume I dealt broadly with the principle of evolution, distinguishing\nontogeny and phylogeny as its two coordinate main branches, and\nassociating the two in the Biogenetic Law. The Law may be formulated\nthus: \"Ontogeny (embryology or the development of the individual) is a\nconcise and compressed recapitulation of phylogeny (the palaeontological\nor genealogical series) conditioned by laws of heredity and adaptation.\"\nThe \"Systematic introduction to general evolution,\" with which the\nsecond volume of the \"Generelle Morphologie\" opens, was the first\nattempt to draw up a natural system of organisms (in harmony with\nthe principles of Lamarck and Darwin) in the form of a hypothetical\npedigree, and was provisionally set forth in eight genealogical tables.\n\nIn the nineteenth chapter of the \"Generelle Morphologie\"--a part of\nwhich has been republished, without any alteration, after a lapse of\nforty years--I made a critical study of Lamarck's theory of descent and\nof Darwin's theory of selection, and endeavoured to bring the complex\nphenomena of heredity and adaptation under definite laws for the first\ntime. Heredity I divided into conservative and progressive: adaptation\ninto indirect (or potential) and direct (or actual). I then found\nit possible to give some explanation of the correlation of the two\nphysiological functions in the struggle for life (selection), and to\nindicate the important laws of divergence (or differentiation) and\ncomplexity (or division of labour), which are the direct and inevitable\noutcome of selection. Finally, I marked off dysteleology as the science\nof the aimless (vestigial, abortive, atrophied, and useless) organs\nand parts of the body. In all this I worked from a strictly monistic\nstandpoint, and sought to explain all biological phenomena on the\nmechanical and naturalistic lines that had long been recognised in the\nstudy of inorganic nature. Then (1866), as now, being convinced of the\nunity of nature, the fundamental identity of the agencies at work in the\ninorganic and the organic worlds, I discarded vitalism, teleology, and\nall hypotheses of a mystic character.\n\nIt was clear from the first that it was essential, in the monistic\nconception of evolution, to distinguish between the laws of conservative\nand progressive heredity. Conservative heredity maintains from\ngeneration to generation the enduring characters of the species. Each\norganism transmits to its descendants a part of the morphological\nand physiological qualities that it has received from its parents and\nancestors. On the other hand, progressive heredity brings new characters\nto the species--characters that were not found in preceding generations.\nEach organism may transmit to its offspring a part of the morphological\nand physiological features that it has itself acquired, by adaptation,\nin the course of its individual career, through the use or disuse of\nparticular organs, the influence of environment, climate, nutrition,\netc. At that time I gave the name of \"progressive heredity\" to\nthis inheritance of acquired characters, as a short and convenient\nexpression, but have since changed the term to \"transformative heredity\"\n(as distinguished from conservative). This term is preferable,\nas inherited regressive modifications (degeneration, retrograde\nmetamorphisis, etc.) come under the same head.\n\nTransformative heredity--or the transmission of acquired characters--is\none of the most important principles in evolutionary science. Unless\nwe admit it most of the facts of comparative anatomy and physiology are\ninexplicable. That was the conviction of Darwin no less than of Lamarck,\nof Spencer as well as Virchow, of Huxley as well as Gegenbaur, indeed of\nthe great majority of speculative biologists. This fundamental principle\nwas for the first time called in question and assailed in 1885 by\nAugust Weismann of Freiburg, the eminent zoologist to whom the theory\nof evolution owes a great deal of valuable support, and who has attained\ndistinction by his extension of the theory of selection. In explanation\nof the phenomena of heredity he introduced a new theory, the \"theory of\nthe continuity of the germ-plasm.\" According to him the living substance\nin all organisms consists of two quite distinct kinds of plasm, somatic\nand germinal. The permanent germ-plasm, or the active substance of the\ntwo germ-cells (egg-cell and sperm-cell), passes unchanged through a\nseries of generations, and is not affected by environmental influences.\nThe environment modifies only the soma-plasm, the organs and tissues\nof the body. The modifications that these parts undergo through the\ninfluence of the environment or their own activity (use and habit), do\nnot affect the germ-plasm, and cannot therefore be transmitted.\n\nThis theory of the continuity of the germ-plasm has been expounded by\nWeismann during the last twenty-four years in a number of able volumes,\nand is regarded by many biologists, such as Mr Francis Galton, Sir E.\nRay Lankester, and Professor J. Arthur Thomson (who has recently made\na thoroughgoing defence of it in his important work \"Heredity\" (London,\n1908.)), as the most striking advance in evolutionary science. On the\nother hand, the theory has been rejected by Herbert Spencer, Sir W.\nTurner, Gegenbaur, Kolliker, Hertwig, and many others. For my part I\nhave, with all respect for the distinguished Darwinian, contested\nthe theory from the first, because its whole foundation seems to me\nerroneous, and its deductions do not seem to be in accord with the main\nfacts of comparative morphology and physiology. Weismann's theory in its\nentirety is a finely conceived molecular hypothesis, but it is devoid of\nempirical basis. The notion of the absolute and permanent independence\nof the germ-plasm, as distinguished from the soma-plasm, is purely\nspeculative; as is also the theory of germinal selection. The\ndeterminants, ids, and idants, are purely hypothetical elements. The\nexperiments that have been devised to demonstrate their existence really\nprove nothing.\n\nIt seems to me quite improper to describe this hypothetical structure\nas \"Neodarwinism.\" Darwin was just as convinced as Lamarck of the\ntransmission of acquired characters and its great importance in the\nscheme of evolution. I had the good fortune to visit Darwin at Down\nthree times and discuss with him the main principles of his system, and\non each occasion we were fully agreed as to the incalculable importance\nof what I call transformative inheritance. It is only proper to point\nout that Weismann's theory of the germ-plasm is in express contradiction\nto the fundamental principles of Darwin and Lamarck. Nor is it more\nacceptable in what one may call its \"ultradarwinism\"--the idea that the\ntheory of selection explains everything in the evolution of the organic\nworld. This belief in the \"omnipotence of natural selection\" was not\nshared by Darwin himself. Assuredly, I regard it as of the utmost\nvalue, as the process of natural selection through the struggle for\nlife affords an explanation of the mechanical origin of the adapted\norganisation. It solves the great problem: how could the finely adapted\nstructure of the animal or plant body be formed unless it was built on a\npreconceived plan? It thus enables us to dispense with the teleology of\nthe metaphysician and the dualist, and to set aside the old mythological\nand poetic legends of creation. The idea had occurred in vague form to\nthe great Empedocles 2000 years before the time of Darwin, but it was\nreserved for modern research to give it ample expression. Nevertheless,\nnatural selection does not of itself give the solution of all our\nevolutionary problems. It has to be taken in conjunction with the\ntransformism of Lamarck, with which it is in complete harmony.\n\nThe monumental greatness of Charles Darwin, who surpasses every other\nstudent of science in the nineteenth century by the loftiness of his\nmonistic conception of nature and the progressive influence of his\nideas, is perhaps best seen in the fact that not one of his many\nsuccessors has succeeded in modifying his theory of descent in any\nessential point or in discovering an entirely new standpoint in the\ninterpretation of the organic world. Neither Nageli nor Weismann,\nneither De Vries nor Roux, has done this. Nageli, in his\n\"Mechanisch-Physiologische Theorie der Abstammungslehre\" (Munich,\n1884.), which is to a great extent in agreement with Weismann,\nconstructed a theory of the idioplasm, that represents it (like the\ngerm-plasm) as developing continuously in a definite direction from\ninternal causes. But his internal \"principle of progress\" is at the\nbottom just as teleological as the vital force of the Vitalists, and\nthe micellar structure of the idioplasm is just as hypothetical as the\n\"dominant\" structure of the germ-plasm. In 1889 Moritz Wagner sought to\nexplain the origin of species by migration and isolation, and on that\nbasis constructed a special \"migration-theory.\" This, however, is not\nout of harmony with the theory of selection. It merely elevates one\nsingle factor in the theory to a predominant position. Isolation is\nonly a special case of selection, as I had pointed out in the fifteenth\nchapter of my \"Natural history of creation\". The \"mutation-theory\" of De\nVries (\"Die Mutationstheorie\", Leipzig, 1903.), that would explain the\norigin of species by sudden and saltatory variations rather than by\ngradual modification, is regarded by many botanists as a great step\nin advance, but it is generally rejected by zoologists. It affords no\nexplanation of the facts of adaptation, and has no causal value.\n\nMuch more important than these theories is that of Wilhelm Roux (\"Der\nKampf der Theile im Organismus\", Leipzig, 1881.) of \"the struggle of\nparts within the organism, a supplementation of the theory of mechanical\nadaptation.\" He explains the functional autoformation of the purposive\nstructure by a combination of Darwin's principle of selection with\nLamarck's idea of transformative heredity, and applies the two\nin conjunction to the facts of histology. He lays stress on the\nsignificance of functional adaptation, which I had described in 1866,\nunder the head of cumulative adaptation, as the most important factor in\nevolution. Pointing out its influence in the cell-life of the tissues,\nhe puts \"cellular selection\" above \"personal selection,\" and shows how\nthe finest conceivable adaptations in the structure of the tissue may\nbe brought about quite mechanically, without preconceived plan. This\n\"mechanical teleology\" is a valuable extension of Darwin's monistic\nprinciple of selection to the whole field of cellular physiology and\nhistology, and is wholly destructive of dualistic vitalism.\n\nThe most important advance that evolution has made since Darwin and\nthe most valuable amplification of his theory of selection is, in my\nopinion, the work of Richard Semon: \"Die Mneme als erhaltendes Prinzip\nim Wechsel des organischen Geschehens\" (Leipzig, 1904.). He offers a\npsychological explanation of the facts of heredity by reducing them to a\nprocess of (unconscious) memory. The physiologist Ewald Hering had shown\nin 1870 that memory must be regarded as a general function of organic\nmatter, and that we are quite unable to explain the chief vital\nphenomena, especially those of reproduction and inheritance, unless\nwe admit this unconscious memory. In my essay \"Die Perigenesis der\nPlastidule\" (Berlin, 1876.) I elaborated this far-reaching idea, and\napplied the physical principle of transmitted motion to the plastidules,\nor active molecules of plasm. I concluded that \"heredity is the memory\nof the plastidules, and variability their power of comprehension.\" This\n\"provisional attempt to give a mechanical explanation of the elementary\nprocesses of evolution\" I afterwards extended by showing that\nsensitiveness is (as Carl Nageli, Ernst Mach, and Albrecht Rau express\nit) a general quality of matter. This form of panpsychism finds its\nsimplest expression in the \"trinity of substance.\"\n\nTo the two fundamental attributes that Spinoza ascribed to\nsubstance--Extension (matter as occupying space) and Cogitation\n(energy, force)--we now add the third fundamental quality of Psychoma\n(sensitiveness, soul). I further elaborated this trinitarian conception\nof substance in the nineteenth chapter of my \"Die Lebenswunder\" (1904)\n(\"Wonders of Life\", London, 1904.), and it seems to me well calculated\nto afford a monistic solution of many of the antitheses of philosophy.\n\nThis important Mneme-theory of Semon and the luminous physiological\nexperiments and observations associated with it not only throw\nconsiderable light on transformative inheritance, but provide a sound\nphysiological foundation for the biogenetic law. I had endeavoured\nto show in 1874, in the first chapter of my \"Anthropogenie\" (English\ntranslation; \"The Evolution of Man\", 2 volumes, London, 1879 and 1905.),\nthat this fundamental law of organic evolution holds good generally, and\nthat there is everywhere a direct causal connection between ontogeny\nand phylogeny. \"Phylogenesis is the mechanical cause of ontogenesis\"; in\nother words, \"The evolution of the stem or race is--in accordance with\nthe laws of heredity and adaptation--the real cause of all the changes\nthat appear, in a condensed form, in the development of the individual\norganism from the ovum, in either the embryo or the larva.\"\n\nIt is now fifty years since Charles Darwin pointed out, in the\nthirteenth chapter of his epoch-making \"Origin of Species\", the\nfundamental importance of embryology in connection with his theory of\ndescent:\n\n\"The leading facts in embryology, which are second to none in\nimportance, are explained on the principle of variations in the many\ndescendants from some one ancient progenitor, having appeared at a not\nvery early period of life, and having been inherited at a corresponding\nperiod.\" (\"Origin of Species\" (6th edition), page 396.)\n\nHe then shows that the striking resemblance of the embryos and larvae\nof closely related animals, which in the mature stage belong to widely\ndifferent species and genera, can only be explained by their descent\nfrom a common progenitor. Fritz Muller made a closer study of these\nimportant phenomena in the instructive instance of the Crustacean larva,\nas given in his able work \"Fur Darwin\" (1864). (English translation;\n\"Facts and Arguments for Darwin\", London, 1869.) I then, in 1872,\nextended the range so as to include all animals (with the exception\nof the unicellular Protozoa) and showed, by means of the theory of\nthe Gastraea, that all multicellular, tissue-forming animals--all\nthe Metazoa--develop in essentially the same way from the primary\ngerm-layers. I conceived the embryonic form, in which the whole\nstructure consists of only two layers of cells, and is known as the\ngastrula, to be the ontogenetic recapitulation, maintained by tenacious\nheredity, of a primitive common progenitor of all the Metazoa, the\nGastraea. At a later date (1895) Monticelli discovered that this\nconjectural ancestral form is still preserved in certain primitive\nCoelenterata--Pemmatodiscus, Kunstleria, and the nearly-related\nOrthonectida.\n\nThe general application of the biogenetic law to all classes of animals\nand plants has been proved in my \"Systematische Phylogenie\". (3 volumes,\nBerlin, 1894-96.) It has, however, been frequently challenged, both\nby botanists and zoologists, chiefly owing to the fact that many have\nfailed to distinguish its two essential elements, palingenesis and\ncenogenesis. As early as 1874 I had emphasised, in the first chapter\nof my \"Evolution of Man\", the importance of discriminating carefully\nbetween these two sets of phenomena:\n\n\"In the evolutionary appreciation of the facts of embryology we must\ntake particular care to distinguish sharply and clearly between\nthe primary, palingenetic evolutionary processes and the secondary,\ncenogenetic processes. The palingenetic phenomena, or embryonic\nRECAPITULATIONS, are due to heredity, to the transmission of characters\nfrom one generation to another. They enable us to draw direct inferences\nin regard to corresponding structures in the development of the species\n(e.g. the chorda or the branchial arches in all vertebrate embryos). The\ncenogenetic phenomena, on the other hand, or the embryonic VARIATIONS,\ncannot be traced to inheritance from a mature ancestor, but are due to\nthe adaptation of the embryo or the larva to certain conditions of\nits individual development (e.g. the amnion, the allantois, and the\nvitelline arteries in the embryos of the higher vertebrates). These\ncenogenetic phenomena are later additions; we must not infer from them\nthat there were corresponding processes in the ancestral history, and\nhence they are apt to mislead.\"\n\nThe fundamental importance of these facts of comparative anatomy,\natavism, and the rudimentary organs, was pointed out by Darwin in the\nfirst part of his classic work, \"The Descent of Man and Selection in\nRelation to Sex\" (1871). (\"Descent of Man\" (Popular Edition), page 927.)\nIn the \"General summary and conclusion\" (chapter XXI.) he was able\nto say, with perfect justice: \"He who is not content to look, like a\nsavage, at the phenomena of nature as disconnected, cannot any longer\nbelieve that man is the work of a separate act of creation. He will be\nforced to admit that the close resemblance of the embryo of man to that,\nfor instance, of a dog--the construction of his skull, limbs, and whole\nframe on the same plan with that of other mammals, independently of\nthe uses to which the parts may be put--the occasional reappearance of\nvarious structures, for instance of several muscles, which man does not\nnormally possess, but which are common to the Quadrumana--and a crowd of\nanalogous facts--all point in the plainest manner to the conclusion that\nman is the co-descendant with other mammals of a common progenitor.\"\n\nThese few lines of Darwin's have a greater scientific value than\nhundreds of those so-called \"anthropological treatises,\" which give\ndetailed descriptions of single organs, or mathematical tables with\nseries of numbers and what are claimed to be \"exact analyses,\" but are\ndevoid of synoptic conclusions and a philosophical spirit.\n\nCharles Darwin is not generally recognised as a great anthropologist,\nnor does the school of modern anthropologists regard him as a leading\nauthority. In Germany, especially, the great majority of the members of\nthe anthropological societies took up an attitude of hostility to him\nfrom the very beginning of the controversy in 1860. \"The Descent of Man\"\nwas not merely rejected, but even the discussion of it was forbidden on\nthe ground that it was \"unscientific.\"\n\nThe centre of this inveterate hostility for thirty years--especially\nafter 1877--was Rudolph Virchow of Berlin, the leading investigator in\npathological anatomy, who did so much for the reform of medicine by\nhis establishment of cellular pathology in 1858. As a prominent\nrepresentative of \"exact\" or \"descriptive\" anthropology, and lacking a\nbroad equipment in comparative anatomy and ontogeny, he was unable to\naccept the theory of descent. In earlier years, and especially during\nhis splendid period of activity at Wurzburg (1848-1856), he had been a\nconsistent free-thinker, and had in a number of able articles (collected\nin his \"Gesammelte Abhandlungen\") (\"Gesammelte Abhandlungen zur\nwissenschaftlichen Medizin\", Berlin, 1856.) upheld the unity of human\nnature, the inseparability of body and spirit. In later years at Berlin,\nwhere he was more occupied with political work and sociology (especially\nafter 1866), he abandoned the positive monistic position for one of\nagnosticism and scepticism, and made concessions to the dualistic dogma\nof a spiritual world apart from the material frame.\n\nIn the course of a Scientific Congress at Munich in 1877 the conflict\nof these antithetic views of nature came into sharp relief. At this\nmemorable Congress I had undertaken to deliver the first address\n(September 18th) on the subject of \"Modern evolution in relation to the\nwhole of science.\" I maintained that Darwin's theory not only solved\nthe great problem of the origin of species, but that its implications,\nespecially in regard to the nature of man, threw considerable light on\nthe whole of science, and on anthropology in particular. The discovery\nof the real origin of man by evolution from a long series of mammal\nancestors threw light on his place in nature in every aspect, as Huxley\nhad already shown in his excellent lectures of 1863. Just as all the\norgans and tissues of the human body had originated from those of the\nnearest related mammals, certain ape-like forms, so we were bound to\nconclude that his mental qualities also had been derived from those of\nhis extinct primate ancestor.\n\nThis monistic view of the origin and nature of man, which is now\nadmitted by nearly all who have the requisite acquaintance with\nbiology, and approach the subject without prejudice, encountered a sharp\nopposition at that time. The opposition found its strongest expression\nin an address that Virchow delivered at Munich four days afterwards\n(September 22nd), on \"The freedom of science in the modern State.\" He\nspoke of the theory of evolution as an unproved hypothesis, and declared\nthat it ought not to be taught in the schools, because it was dangerous\nto the State. \"We must not,\" he said, \"teach that man has descended from\nthe ape or any other animal.\" When Darwin, usually so lenient in his\njudgment, read the English translation of Virchow's speech, he expressed\nhis disapproval in strong terms. But the great authority that Virchow\nhad--an authority well founded in pathology and sociology--and his\nprestige as President of the German Anthropological Society, had the\neffect of preventing any member of the Society from raising serious\nopposition to him for thirty years. Numbers of journals and treatises\nrepeated his dogmatic statement: \"It is quite certain that man has\ndescended neither from the ape nor from any other animal.\" In this he\npersisted till his death in 1902. Since that time the whole position of\nGerman anthropology has changed. The question is no longer whether\nman was created by a distinct supernatural act or evolved from other\nmammals, but to which line of the animal hierarchy we must look for the\nactual series of ancestors. The interested reader will find an account\nof this \"battle of Munich\" (1877) in my three Berlin lectures (April,\n1905) (\"Der Kampf um die Entwickelungs-Gedanken\". (English translation;\n\"Last Words on Evolution\", London, 1906.))\n\nThe main points in our genealogical tree were clearly recognised by\nDarwin in the sixth chapter of the \"Descent of Man\". Lowly organised\nfishes, like the lancelet (Amphioxus), are descended from lower\ninvertebrates resembling the larvae of an existing Tunicate\n(Appendicularia). From these primitive fishes were evolved higher fishes\nof the ganoid type and others of the type of Lepidosiren (Dipneusta). It\nis a very small step from these to the Amphibia:\n\n\"In the class of mammals the steps are not difficult to conceive which\nled from the ancient Monotremata to the ancient Marsupials; and from\nthese to the early progenitors of the placental mammals. We may thus\nascend to the Lemuridae; and the interval is not very wide from these to\nthe Simiadae. The Simiadae then branched off into two great stems,\nthe New World and Old World monkeys; and from the latter, at a remote\nperiod, Man, the wonder and glory of the Universe, proceeded.\" (\"Descent\nof Man\" (Popular Edition), page 255.)\n\nIn these few lines Darwin clearly indicated the way in which we were\nto conceive our ancestral series within the vertebrates. It is fully\nconfirmed by all the arguments of comparative anatomy and embryology,\nof palaeontology and physiology; and all the research of the subsequent\nforty years has gone to establish it. The deep interest in geology which\nDarwin maintained throughout his life and his complete knowledge of\npalaeontology enabled him to grasp the fundamental importance of the\npalaeontological record more clearly than anthropologists and zoologists\nusually do.\n\nThere has been much debate in subsequent decades whether Darwin himself\nmaintained that man was descended from the ape, and many writers\nhave sought to deny it. But the lines I have quoted verbatim from the\nconclusion of the sixth chapter of the \"Descent of Man\" (1871) leave no\ndoubt that he was as firmly convinced of it as was his great\nprecursor Jean Lamarck in 1809. Moreover, Darwin adds, with particular\nexplicitness, in the \"general summary and conclusion\" (chapter XXI.) of\nthat standard work (\"Descent of Man\", page 930.):\n\n\"By considering the embryological structure of man--the homologies\nwhich he presents with the lower animals,--the rudiments which he\nretains,--and the reversions to which he is liable, we can partly recall\nin imagination the former condition of our early progenitors; and can\napproximately place them in their proper place in the zoological series.\nWe thus learn that man is descended from a hairy, tailed quadruped,\nprobably arboreal in its habits, and an inhabitant of the Old World.\nThis creature, if its whole structure had been examined by a naturalist,\nwould have been classed amongst the Quadrumana, as surely as the still\nmore ancient progenitor of the Old and New World monkeys.\"\n\nThese clear and definite lines leave no doubt that Darwin--so critical\nand cautious in regard to important conclusions--was quite as firmly\nconvinced of the descent of man from the apes (the Catarrhinae, in\nparticular) as Lamarck was in 1809 and Huxley in 1863.\n\nIt is to be noted particularly that, in these and other observations\non the subject, Darwin decidedly assumes the monophyletic origin of\nthe mammals, including man. It is my own conviction that this is of the\ngreatest importance. A number of difficult questions in regard to the\ndevelopment of man, in respect of anatomy, physiology, psychology,\nand embryology, are easily settled if we do not merely extend our\nprogonotaxis to our nearest relatives, the anthropoid apes and the\ntailed monkeys from which these have descended, but go further back and\nfind an ancestor in the group of the Lemuridae, and still further back\nto the Marsupials and Monotremata. The essential identity of all the\nMammals in point of anatomical structure and embryonic development--in\nspite of their astonishing differences in external appearance and habits\nof life--is so palpably significant that modern zoologists are agreed\nin the hypothesis that they have all sprung from a common root, and that\nthis root may be sought in the earlier Palaeozoic Amphibia.\n\nThe fundamental importance of this comparative morphology of the\nMammals, as a sound basis of scientific anthropology, was recognised\njust before the beginning of the nineteenth century, when Lamarck first\nemphasised (1794) the division of the animal kingdom into Vertebrates\nand Invertebrates. Even thirteen years earlier (1781), when Goethe made\na close study of the mammal skeleton in the Anatomical Institute at\nJena, he was intensely interested to find that the composition of the\nskull was the same in man as in the other mammals. His discovery of the\nos intermaxillare in man (1784), which was contradicted by most of\nthe anatomists of the time, and his ingenious \"vertebral theory of\nthe skull,\" were the splendid fruit of his morphological studies. They\nremind us how Germany's greatest philosopher and poet was for many years\nardently absorbed in the comparative anatomy of man and the mammals, and\nhow he divined that their wonderful identity in structure was no mere\nsuperficial resemblance, but pointed to a deep internal connection.\nIn my \"Generelle Morphologie\" (1866), in which I published the first\nattempts to construct phylogenetic trees, I have given a number of\nremarkable theses of Goethe, which may be called \"phyletic prophecies.\"\nThey justify us in regarding him as a precursor of Darwin.\n\nIn the ensuing forty years I have made many conscientious efforts to\npenetrate further along that line of anthropological research that was\nopened up by Goethe, Lamarck, and Darwin. I have brought together the\nmany valuable results that have constantly been reached in comparative\nanatomy, physiology, ontogeny, and palaeontology, and maintained\nthe effort to reform the classification of animals and plants in an\nevolutionary sense. The first rough drafts of pedigrees that were\npublished in the \"Generelle Morphologie\" have been improved time after\ntime in the ten editions of my \"Naturaliche Schopfungsgeschichte\"\n(1868-1902). (English translation; \"The History of Creation\", London,\n1876.) A sounder basis for my phyletic hypotheses, derived from a\ndiscriminating combination of the three great records--morphology,\nontogeny, and palaeontology--was provided in the three volumes of my\n\"Systematische Phylogenie\" (Berlin, 1894-96.) (1894 Protists and Plants,\n1895 Vertebrates, 1896 Invertebrates). In my \"Anthropogenie\" (Leipzig,\n1874, 5th edition 1905. English translation; \"The Evolution of\nMan\", London, 1905.) I endeavoured to employ all the known facts of\ncomparative ontogeny (embryology) for the purpose of completing my\nscheme of human phylogeny (evolution). I attempted to sketch the\nhistorical development of each organ of the body, beginning with the\nmost elementary structures in the germ-layers of the Gastraea. At the\nsame time I drew up a corrected statement of the most important steps in\nthe line of our ancestral series.\n\nAt the fourth International Congress of Zoology at Cambridge (August\n26th, 1898) I delivered an address on \"Our present knowledge of the\nDescent of Man.\" It was translated into English, enriched with many\nvaluable notes and additions, by my friend and pupil in earlier days Dr\nHans Gadow (Cambridge), and published under the title: \"The Last Link;\nour present knowledge of the Descent of Man\". (London, 1898.) The\ndetermination of the chief animal forms that occur in the line of our\nancestry is there restricted to thirty types, and these are distributed\nin six main groups.\n\nThe first half of this \"Progonotaxis hominis,\" which has no support\nfrom fossil evidence, comprises three groups: (i) Protista (unicellular\norganisms, 1-5: (ii) Invertebrate Metazoa (Coelenteria 6-8, Vermalia\n9-11): (iii) Monorrhine Vertebrates (Acrania 12-13, Cyclostoma 14-15).\nThe second half, which is based on fossil records, also comprises three\ngroups: (iv) Palaeozoic cold-blooded Craniota (Fishes 16-18, Amphibia\n19, Reptiles 20: (v) Mesozoic Mammals (Monotrema 21, Marsupialia 22,\nMallotheria 23): (vi) Cenozoic Primates (Lemuridae 24-25, Tailed Apes\n26-27, Anthropomorpha 28-30). An improved and enlarged edition of this\nhypothetic \"Progonotaxis hominis\" was published in 1908, in my essay\n\"Unsere Ahnenreihe\". (\"Festschrift zur 350-jahrigen Jubelfeier der\nThuringer Universitat Jena\". Jena, 1908.)\n\nIf I have succeeded in furthering, in some degree, by these\nanthropological works, the solution of the great problem of Man's place\nin nature, and particularly in helping to trace the definite stages in\nour ancestral series, I owe the success, not merely to the vast progress\nthat biology has made in the last half century, but largely to the\nluminous example of the great investigators who have applied themselves\nto the problem, with so much assiduity and genius, for a century and\na quarter--I mean Goethe and Lamarck, Gegenbaur and Huxley, but, above\nall, Charles Darwin. It was the great genius of Darwin that first\nbrought together the scattered material of biology and shaped it into\nthat symmetrical temple of scientific knowledge, the theory of descent.\nIt was Darwin who put the crown on the edifice by his theory of natural\nselection. Not until this broad inductive law was firmly established was\nit possible to vindicate the special conclusion, the descent of man from\na series of other Vertebrates. By his illuminating discovery Darwin\ndid more for anthropology than thousands of those writers, who are\nmore specifically titled anthropologists, have done by their technical\ntreatises. We may, indeed, say that it is not merely as an exact\nobserver and ingenious experimenter, but as a distinguished\nanthropologist and far-seeing thinker, that Darwin takes his place among\nthe greatest men of science of the nineteenth century.\n\nTo appreciate fully the immortal merit of Darwin in connection with\nanthropology, we must remember that not only did his chief work, \"The\nOrigin of Species\", which opened up a new era in natural history in\n1859, sustain the most virulent and widespread opposition for a lengthy\nperiod, but even thirty years later, when its principles were generally\nrecognised and adopted, the application of them to man was energetically\ncontested by many high scientific authorities. Even Alfred Russel\nWallace, who discovered the principle of natural selection independently\nin 1858, did not concede that it was applicable to the higher mental\nand moral qualities of man. Dr Wallace still holds a spiritualist and\ndualist view of the nature of man, contending that he is composed of a\nmaterial frame (descended from the apes) and an immortal immaterial soul\n(infused by a higher power). This dual conception, moreover, is still\npredominant in the wide circles of modern theology and metaphysics,\nand has the general and influential adherence of the more conservative\nclasses of society.\n\nIn strict contradiction to this mystical dualism, which is generally\nconnected with teleology and vitalism, Darwin always maintained the\ncomplete unity of human nature, and showed convincingly that the\npsychological side of man was developed, in the same way as the body,\nfrom the less advanced soul of the anthropoid ape, and, at a still more\nremote period, from the cerebral functions of the older vertebrates. The\neighth chapter of the \"Origin of Species\", which is devoted to instinct,\ncontains weighty evidence that the instincts of animals are subject,\nlike all other vital processes, to the general laws of historic\ndevelopment. The special instincts of particular species were formed\nby adaptation, and the modifications thus acquired were handed on to\nposterity by heredity; in their formation and preservation natural\nselection plays the same part as in the transformation of every other\nphysiological function. The higher moral qualities of civilised man\nhave been derived from the lower mental functions of the uncultivated\nbarbarians and savages, and these in turn from the social instincts\nof the mammals. This natural and monistic psychology of Darwin's was\nafterwards more fully developed by his friend George Romanes in his\nexcellent works \"Mental Evolution in Animals\" and \"Mental Evolution in\nMan\". (London, 1885; 1888.)\n\nMany valuable and most interesting contributions to this monistic\npsychology of man were made by Darwin in his fine work on \"The Descent\nof Man and Selection in Relation to Sex\", and again in his supplementary\nwork, \"The Expression of the Emotions in Man and Animals\". To understand\nthe historical development of Darwin's anthropology one must read his\nlife and the introduction to \"The Descent of Man\". From the moment that\nhe was convinced of the truth of the principle of descent--that is to\nsay, from his thirtieth year, in 1838--he recognised clearly that\nman could not be excluded from its range. He recognised as a logical\nnecessity the important conclusion that \"man is the co-descendant with\nother species of some ancient, lower, and extinct form.\" For many years\nhe gathered notes and arguments in support of this thesis, and for the\npurpose of showing the probable line of man's ancestry. But in the first\nedition of \"The Origin of Species\" (1859) he restricted himself to the\nsingle line, that by this work \"light would be thrown on the origin of\nman and his history.\" In the fifty years that have elapsed since that\ntime the science of the origin and nature of man has made astonishing\nprogress, and we are now fairly agreed in a monistic conception of\nnature that regards the whole universe, including man, as a wonderful\nunity, governed by unalterable and eternal laws. In my philosophical\nbook \"Die Weltratsel\" (1899) (\"The Riddle of the Universe\", London,\n1900.) and in the supplementary volume \"Die Lebenswunder\" (1904) \"The\nWonders of Life\", London, (1904.), I have endeavoured to show that this\npure monism is securely established, and that the admission of the\nall-powerful rule of the same principle of evolution throughout the\nuniverse compels us to formulate a single supreme law--the all-embracing\n\"Law of Substance,\" or the united laws of the constancy of matter and\nthe conservation of energy. We should never have reached this supreme\ngeneral conception if Charles Darwin--a \"monistic philosopher\" in\nthe true sense of the word--had not prepared the way by his theory of\ndescent by natural selection, and crowned the great work of his life by\nthe association of this theory with a naturalistic anthropology.\n\n\nIX. SOME PRIMITIVE THEORIES OF THE ORIGIN OF MAN.\n\nBy J.G. FRAZER. Fellow of Trinity College, Cambridge.\n\nOn a bright day in late autumn a good many years ago I had ascended the\nhill of Panopeus in Phocis to examine the ancient Greek fortifications\nwhich crest its brow. It was the first of November, but the weather was\nvery hot; and when my work among the ruins was done, I was glad to\nrest under the shade of a clump of fine holly-oaks, to inhale the sweet\nrefreshing perfume of the wild thyme which scented all the air, and\nto enjoy the distant prospects, rich in natural beauty, rich too in\nmemories of the legendary and historic past. To the south the finely-cut\npeak of Helicon peered over the low intervening hills. In the west\nloomed the mighty mass of Parnassus, its middle slopes darkened by\npine-woods like shadows of clouds brooding on the mountain-side; while\nat its skirts nestled the ivy-mantled walls of Daulis overhanging the\ndeep glen, whose romantic beauty accords so well with the loves and\nsorrows of Procne and Philomela, which Greek tradition associated\nwith the spot. Northwards, across the broad plain to which the hill\nof Panopeus descends, steep and bare, the eye rested on the gap in the\nhills through which the Cephissus winds his tortuous way to flow under\ngrey willows, at the foot of barren stony hills, till his turbid waters\nlose themselves, no longer in the vast reedy swamps of the now vanished\nCopaic Lake, but in the darkness of a cavern in the limestone rock.\nEastward, clinging to the slopes of the bleak range of which the hill\nof Panopeus forms part, were the ruins of Chaeronea, the birthplace of\nPlutarch; and out there in the plain was fought the disastrous battle\nwhich laid Greece at the feet of Macedonia. There, too, in a later age\nEast and West met in deadly conflict, when the Roman armies under Sulla\ndefeated the Asiatic hosts of Mithridates. Such was the landscape spread\nout before me on one of those farewell autumn days of almost pathetic\nsplendour, when the departing summer seems to linger fondly, as if loth\nto resign to winter the enchanted mountains of Greece. Next day the\nscene had changed: summer was gone. A grey November mist hung low on the\nhills which only yesterday had shone resplendent in the sun, and under\nits melancholy curtain the dead flat of the Chaeronean plain, a wide\ntreeless expanse shut in by desolate slopes, wore an aspect of chilly\nsadness befitting the battlefield where a nation's freedom was lost.\n\nBut crowded as the prospect from Panopeus is with memories of the past,\nthe place itself, now so still and deserted, was once the scene of an\nevent even more ancient and memorable, if Greek story-tellers can be\ntrusted. For here, they say, the sage Prometheus created our first\nparents by fashioning them, like a potter, out of clay. (Pausanias X.\n4.4. Compare Apollodorus, \"Bibliotheca\", I. 7. 1; Ovid, \"Metamorph.\"\nI. 82 sq.; Juvenal, \"Sat\". XIV. 35. According to another version of\nthe tale, this creation of mankind took place not at Panopeus, but\nat Iconium in Lycaonia. After the original race of mankind had been\ndestroyed in the great flood of Deucalion, the Greek Noah, Zeus\ncommanded Prometheus and Athena to create men afresh by moulding images\nout of clay, breathing the winds into them, and making them live. See\n\"Etymologicum Magnum\", s.v. \"'Ikonion\", pages 470 sq. It is said that\nPrometheus fashioned the animals as well as men, giving to each kind of\nbeast its proper nature. See Philemon, quoted by Stobaeus, \"Florilegium\"\nII. 27. The creation of man by Prometheus is figured on ancient works of\nart. See J. Toutain, \"Etudes de Mythologie et d'Histoire des Religions\nAntiques\" (Paris, 1909), page 190. According to Hesiod (\"Works and\nDays\", 60 sqq.) it was Hephaestus who at the bidding of Zeus moulded the\nfirst woman out of moist earth.) The very spot where he did so can still\nbe seen. It is a forlorn little glen or rather hollow behind the hill\nof Panopeus, below the ruined but still stately walls and towers which\ncrown the grey rocks of the summit. The glen, when I visited it that hot\nday after the long drought of summer, was quite dry; no water trickled\ndown its bushy sides, but in the bottom I found a reddish crumbling\nearth, a relic perhaps of the clay out of which the potter Prometheus\nmoulded the Greek Adam and Eve. In a volume dedicated to the honour of\none who has done more than any other in modern times to shape the ideas\nof mankind as to their origin it may not be out of place to recall this\ncrude Greek notion of the creation of the human race, and to compare or\ncontrast it with other rudimentary speculations of primitive peoples\non the same subject, if only for the sake of marking the interval which\ndivides the childhood from the maturity of science.\n\nThe simple notion that the first man and woman were modelled out of clay\nby a god or other superhuman being is found in the traditions of many\npeoples. This is the Hebrew belief recorded in Genesis: \"The Lord God\nformed man of the dust of the ground, and breathed into his nostrils the\nbreath of life; and man became a living soul.\" (Genesis ii.7.) To the\nHebrews this derivation of our species suggested itself all the more\nnaturally because in their language the word for \"ground\" (adamah) is\nin form the feminine of the word for man (adam). (S.R. Driver and\nW.H.Bennett, in their commentaries on Genesis ii. 7.) From various\nallusions in Babylonian literature it would seem that the Babylonians\nalso conceived man to have been moulded out of clay. (H. Zimmern, in E.\nSchrader's \"Die Keilinschriften und das Alte Testament\" 3 (Berlin, 1902),\npage 506.) According to Berosus, the Babylonian priest whose account of\ncreation has been preserved in a Greek version, the god Bel cut off his\nown head, and the other gods caught the flowing blood, mixed it with\nearth, and fashioned men out of the bloody paste; and that, they said,\nis why men are so wise, because their mortal clay is tempered with\ndivine blood. (Eusebius, \"Chronicon\", ed. A. Schoene, Vol. I. (Berlin,\n1875), col. 16.) In Egyptian mythology Khnoumou, the Father of the gods,\nis said to have moulded men out of clay. (G. Maspero, \"Histoire Ancienne\ndes Peuples de l'Orient Classique\", I. (Paris, 1895), page 128.) We\ncannot doubt that such crude conceptions of the origin of our race were\nhanded down to the civilised peoples of antiquity by their savage or\nbarbarous forefathers. Certainly stories of the same sort are known to\nbe current among savages and barbarians.\n\nThus the Australian blacks in the neighbourhood of Melbourne said that\nPund-jel, the creator, cut three large sheets of bark with his big\nknife. On one of these he placed some clay and worked it up with his\nknife into a proper consistence. He then laid a portion of the clay on\none of the other pieces of bark and shaped it into a human form; first\nhe made the feet, then the legs, then the trunk, the arms, and the head.\nThus he made a clay man on each of the two pieces of bark; and being\nwell pleased with them he danced round them for joy. Next he took\nstringy bark from the Eucalyptus tree, made hair of it, and stuck it\non the heads of his clay men. Then he looked at them again, was pleased\nwith his work, and again danced round them for joy. He then lay down\non them, blew his breath hard into their mouths, their noses, and their\nnavels; and presently they stirred, spoke, and rose up as full-grown\nmen. (R. Brough Smyth, \"The Aborigines of Victoria\" (Melbourne, 1878),\nI. 424. This and many of the following legends of creation have been\nalready cited by me in a note on Pausanias X. 4. 4 (\"Pausanias's\nDescription of Greece, translated with a Commentary\" (London, 1898),\nVol V. pages 220 sq.).) The Maoris of New Zealand say that Tiki made man\nafter his own image. He took red clay, kneaded it, like the Babylonian\nBel, with his own blood, fashioned it in human form, and gave the image\nbreath. As he had made man in his own likeness he called him Tiki-ahua\nor Tiki's likeness. (R. Taylor \"Te Ika A Maui, or New Zealand and\nits Inhabitants\", Second Edition (London, 1870), page 117. Compare E.\nShortland, \"Maori Religion and Mythology\" (London, 1882), pages 21 sq.)\nA very generally received tradition in Tahiti was that the first human\npair was made by Taaroa, the chief god. They say that after he had\nformed the world he created man out of red earth, which was also the\nfood of mankind until bread-fruit was produced. Further, some say that\none day Taaroa called for the man by name, and when he came he made him\nfall asleep. As he slept, the creator took out one of his bones (ivi)\nand made a woman of it, whom he gave to the man to be his wife, and the\npair became the progenitors of mankind. This narrative was taken down\nfrom the lips of the natives in the early years of the mission to\nTahiti. The missionary who records it observes: \"This always appeared\nto me a mere recital of the Mosaic account of creation, which they\nhad heard from some European, and I never placed any reliance on it,\nalthough they have repeatedly told me it was a tradition among them\nbefore any foreigner arrived. Some have also stated that the woman's\nname was Ivi, which would be by them pronounced as if written \"Eve\".\n\"Ivi\" is an aboriginal word, and not only signifies a bone, but also a\nwidow, and a victim slain in war. Notwithstanding the assertion of\nthe natives, I am disposed to think that \"Ivi\", or Eve, is the only\naboriginal part of the story, as far as it respects the mother of the\nhuman race. (W. Ellis, \"Polynesian Researches\", Second Edition (London,\n1832), I. 110 sq. \"Ivi\" or \"iwi\" is the regular word for \"bone\" in the\nvarious Polynesian languages. See E. Tregear, \"The Maori-Polynesian\nComparative Dictionary\" (Wellington, New Zealand, 1891), page 109.)\nHowever, the same tradition has been recorded in other parts of\nPolynesia besides Tahiti. Thus the natives of Fakaofo or Bowditch Island\nsay that the first man was produced out of a stone. After a time he\nbethought him of making a woman. So he gathered earth and moulded the\nfigure of a woman out of it, and having done so he took a rib out of his\nleft side and thrust it into the earthen figure, which thereupon started\nup a live woman. He called her Ivi (Eevee) or \"rib\" and took her to\nwife, and the whole human race sprang from this pair. (G. Turner,\n\"Samoa\" (London, 1884), pages 267 sq.) The Maoris also are reported to\nbelieve that the first woman was made out of the first man's ribs. (J.L.\nNicholas, \"Narrative of a Voyage to New Zealand\" (London, 1817), I.\n59, who writes \"and to add still more to this strange coincidence, the\ngeneral term for bone is 'Hevee'.\") This wide diffusion of the story\nin Polynesia raises a doubt whether it is merely, as Ellis thought, a\nrepetition of the Biblical narrative learned from Europeans. In Nui, or\nNetherland Island, it was the god Aulialia who made earthen models of\na man and woman, raised them up, and made them live. He called the man\nTepapa and the woman Tetata. (G. Turner, \"Samoa\", pages 300 sq.)\n\nIn the Pelew Islands they say that a brother and sister made men out of\nclay kneaded with the blood of various animals, and that the characters\nof these first men and of their descendants were determined by the\ncharacters of the animals whose blood had been kneaded with the\nprimordial clay; for instance, men who have rat's blood in them are\nthieves, men who have serpent's blood in them are sneaks, and men who\nhave cock's blood in them are brave. (J. Kubary, \"Die Religion der\nPelauer\", in A. Bastian's \"Allerlei aus Volks- und Menschenkunde\"\n(Berlin, 1888), I. 3, 56.) According to a Melanesian legend, told in\nMota, one of the Banks Islands, the hero Qat moulded men of clay, the\nred clay from the marshy river-side at Vanua Lava. At first he made men\nand pigs just alike, but his brothers remonstrated with him, so he\nbeat down the pigs to go on all fours and made men walk upright. Qat\nfashioned the first woman out of supple twigs, and when she smiled\nhe knew she was a living woman. (R.H. Codrington, \"The Melanesians\"\n(Oxford, 1891), page 158.) A somewhat different version of the\nMelanesian story is told at Lakona, in Santa Maria. There they say that\nQat and another spirit (\"vui\") called Marawa both made men. Qat made\nthem out of the wood of dracaena-trees. Six days he worked at them,\ncarving their limbs and fitting them together. Then he allowed them six\ndays to come to life. Three days he hid them away, and three days more\nhe worked to make them live. He set them up and danced to them and beat\nhis drum, and little by little they stirred, till at last they could\nstand all by themselves. Then Qat divided them into pairs and called\neach pair husband and wife. Marawa also made men out of a tree, but it\nwas a different tree, the tavisoviso. He likewise worked at them six\ndays, beat his drum, and made them live, just as Qat did. But when he\nsaw them move, he dug a pit and buried them in it for six days, and\nthen, when he scraped away the earth to see what they were doing, he\nfound them all rotten and stinking. That was the origin of death. (R.H.\nCodrington op. cit., pages 157 sq.)\n\nThe inhabitants of Noo-Hoo-roa, in the Kei Islands say that their\nancestors were fashioned out of clay by the supreme god, Dooadlera,\nwho breathed life into the clay figures. (C.M. Pleyte, \"Ethnographische\nBeschrijving der Kei-Eilanden\", \"Tijdschrift van het Nederlandsch\nAardrijkskundig Genootschap\", Tweede Serie X. (1893), page 564.) The\naborigines of Minahassa, in the north of Celebes, say that two beings\ncalled Wailan Wangko and Wangi were alone on an island, on which grew\na cocoa-nut tree. Said Wailan Wangko to Wangi, \"Remain on earth while\nI climb up the tree.\" Said Wangi to Wailan Wangko, \"Good.\" But then\na thought occurred to Wangi and he climbed up the tree to ask Wailan\nWangko why he, Wangi, should remain down there all alone. Said Wailan\nWangko to Wangi, \"Return and take earth and make two images, a man and a\nwoman.\" Wangi did so, and both images were men who could move but could\nnot speak. So Wangi climbed up the tree to ask Wailan Wangko, \"How now?\nThe two images are made, but they cannot speak.\" Said Wailan Wangko to\nWangi, \"Take this ginger and go and blow it on the skulls and the ears\nof these two images, that they may be able to speak; call the man Adam\nand the woman Ewa.\" (N. Graafland \"De Minahassa\" (Rotterdam, 1869), I.\npages 96 sq.) In this narrative the names of the man and woman betray\nEuropean influence, but the rest of the story may be aboriginal. The\nDyaks of Sakarran in British Borneo say that the first man was made by\ntwo large birds. At first they tried to make men out of trees, but\nin vain. Then they hewed them out of rocks, but the figures could not\nspeak. Then they moulded a man out of damp earth and infused into his\nveins the red gum of the kumpang-tree. After that they called to him and\nhe answered; they cut him and blood flowed from his wounds. (Horsburgh,\nquoted by H. Ling Roth, \"The Natives of Sarawak and of British North\nBorneo\" (London, 1896), I. pages 299 sq. Compare The Lord Bishop\nof Labuan, \"On the Wild Tribes of the North-West Coast of Borneo,\"\n\"Transactions of the Ethnological Society of London\", New Series, II.\n(1863), page 27.)\n\nThe Kumis of South-Eastern India related to Captain Lewin, the Deputy\nCommissioner of Hill Tracts, the following tradition of the creation of\nman. \"God made the world and the trees and the creeping things first,\nand after that he set to work to make one man and one woman, forming\ntheir bodies of clay; but each night, on the completion of his work,\nthere came a great snake, which, while God was sleeping, devoured the\ntwo images. This happened twice or thrice, and God was at his wit's end,\nfor he had to work all day, and could not finish the pair in less than\ntwelve hours; besides, if he did not sleep, he would be no good,\" said\nCaptain Lewin's informant. \"If he were not obliged to sleep, there would\nbe no death, nor would mankind be afflicted with illness. It is when\nhe rests that the snake carries us off to this day. Well, he was at his\nwit's end, so at last he got up early one morning and first made a dog\nand put life into it, and that night, when he had finished the images,\nhe set the dog to watch them, and when the snake came, the dog barked\nand frightened it away. This is the reason at this day that when a\nman is dying the dogs begin to howl; but I suppose God sleeps heavily\nnow-a-days, or the snake is bolder, for men die all the same.\" (Capt.\nT.H. Lewin, \"Wild Races of South-Eastern India\" (London, 1870),\npages 224-26.) The Khasis of Assam tell a similar tale. (A. Bastian,\n\"Volkerstamme am Brahmaputra und verwandtschaftliche Nachbarn\" (Berlin,\n1883), page 8; Major P.R.T. Gurdon, \"The Khasis\" (London, 1907), page\n106.)\n\nThe Ewe-speaking tribes of Togo-land, in West Africa, think that God\nstill makes men out of clay. When a little of the water with which he\nmoistens the clay remains over, he pours it on the ground and out of\nthat he makes the bad and disobedient people. When he wishes to make a\ngood man he makes him out of good clay; but when he wishes to make a\nbad man, he employs only bad clay for the purpose. In the beginning\nGod fashioned a man and set him on the earth; after that he fashioned\na woman. The two looked at each other and began to laugh, whereupon\nGod sent them into the world. (J. Spieth, \"Die Ewe-Stamme, Material zur\nKunde des Ewe-Volkes in Deutsch-Togo\" (Berlin, 1906), pages 828, 840.)\nThe Innuit or Esquimaux of Point Barrow, in Alaska, tell of a time when\nthere was no man in the land, till a spirit named \"a se lu\", who resided\nat Point Barrow, made a clay man, set him up on the shore to dry,\nbreathed into him and gave him life. (\"Report of the International\nExpedition to Point Barrow\" (Washington, 1885), page 47.) Other\nEsquimaux of Alaska relate how the Raven made the first woman out of\nclay to be a companion to the first man; he fastened water-grass to the\nback of the head to be hair, flapped his wings over the clay figure,\nand it arose, a beautiful young woman. (E.W. Nelson, \"The Eskimo about\nBering Strait\", \"Eighteenth Annual Report of the Bureau of American\nEthnology\", Part I. (Washington, 1899), page 454.) The Acagchemem\nIndians of California said that a powerful being called Chinigchinich\ncreated man out of clay which he found on the banks of a lake; male and\nfemale created he them, and the Indians of the present day are their\ndescendants. (Friar Geronimo Boscana, \"Chinigchinich\", appended to (A.\nRobinson's) \"Life in California\" (New York, 1846), page 247.) A priest\nof the Natchez Indians in Louisiana told Du Pratz \"that God had kneaded\nsome clay, such as that which potters use and had made it into a little\nman; and that after examining it, and finding it well formed, he blew up\nhis work, and forthwith that little man had life, grew, acted, walked,\nand found himself a man perfectly well shaped.\" As to the mode in which\nthe first woman was created, the priest had no information, but thought\nshe was probably made in the same way as the first man; so Du Pratz\ncorrected his imperfect notions by reference to Scripture. (M. Le Page\nDu Pratz, \"The History of Louisiana\" (London, 1774), page 330.) The\nMichoacans of Mexico said that the great god Tucapacha first made man\nand woman out of clay, but that when the couple went to bathe in a river\nthey absorbed so much water that the clay of which they were composed\nall fell to pieces. Then the creator went to work again and moulded them\nafresh out of ashes, and after that he essayed a third time and made\nthem of metal. This last attempt succeeded. The metal man and woman\nbathed in the river without falling to pieces, and by their union they\nbecame the progenitors of mankind. (A. de Herrera, \"General History of\nthe vast Continent and Islands of America\", translated into English by\nCapt. J. Stevens (London, 1725, 1726), III. 254; Brasseur de Bourbourg,\n\"Histoire des Nations Civilisees du Mexique et de l'Amerique-Centrale\"\n(Paris, 1857--1859), III. 80 sq; compare id. I. 54 sq.)\n\nAccording to a legend of the Peruvian Indians, which was told to a\nSpanish priest in Cuzco about half a century after the conquest, it was\nin Tiahuanaco that man was first created, or at least was created afresh\nafter the deluge. \"There (in Tiahuanaco),\" so runs the legend, \"the\nCreator began to raise up the people and nations that are in that\nregion, making one of each nation of clay, and painting the dresses that\neach one was to wear; those that were to wear their hair, with hair, and\nthose that were to be shorn, with hair cut. And to each nation was given\nthe language, that was to be spoken, and the songs to be sung, and the\nseeds and food that they were to sow. When the Creator had finished\npainting and making the said nations and figures of clay, he gave life\nand soul to each one, as well men as women, and ordered that they should\npass under the earth. Thence each nation came up in the places to which\nhe ordered them to go.\" (E.J. Payne, \"History of the New World called\nAmerica\", I. (Oxford, 1892), page 462.)\n\nThese examples suffice to prove that the theory of the creation of man\nout of dust or clay has been current among savages in many parts of\nthe world. But it is by no means the only explanation which the savage\nphilosopher has given of the beginnings of human life on earth. Struck\nby the resemblances which may be traced between himself and the beasts,\nhe has often supposed, like Darwin himself, that mankind has been\ndeveloped out of lower forms of animal life. For the simple savage has\nnone of that high notion of the transcendant dignity of man which makes\nso many superior persons shrink with horror from the suggestion that\nthey are distant cousins of the brutes. He on the contrary is not too\nproud to own his humble relations; indeed his difficulty often is\nto perceive the distinction between him and them. Questioned by a\nmissionary, a Bushman of more than average intelligence \"could not state\nany difference between a man and a brute--he did not know but a buffalo\nmight shoot with bows and arrows as well as man, if it had them.\"\n(Reverend John Campbell, \"Travels in South Africa\" (London, 1822, II.\npage 34.) When the Russians first landed on one of the Alaskan islands,\nthe natives took them for cuttle-fish \"on account of the buttons on\ntheir clothes.\" (I. Petroff, \"Report on the Population, Industries, and\nResources of Alaska\", page 145.) The Giliaks of the Amoor think that the\noutward form and size of an animal are only apparent; in substance every\nbeast is a real man, just like a Giliak himself, only endowed with an\nintelligence and strength, which often surpass those of mere ordinary\nhuman beings. (L. Sternberg, \"Die Religion der Giljaken\", \"Archiv fur\nReligionswissenschaft\", VIII. (1905), page 248.) The Borororos, an\nIndian tribe of Brazil, will have it that they are parrots of a gorgeous\nred plumage which live in their native forests. Accordingly they treat\nthe birds as their fellow-tribesmen, keeping them in captivity, refusing\nto eat their flesh, and mourning for them when they die. (K. von den\nSteinen, \"Unter den Naturvolkern Zentral-Brasiliens\" (Berlin, 1894),\npages 352 sq., 512.))\n\nThis sense of the close relationship of man to the lower creation is the\nessence of totemism, that curious system of superstition which unites\nby a mystic bond a group of human kinsfolk to a species of animals or\nplants. Where that system exists in full force, the members of a totem\nclan identify themselves with their totem animals in a way and to an\nextent which we find it hard even to imagine. For example, men of the\nCassowary clan in Mabuiag think that cassowaries are men or nearly so.\n\"Cassowary, he all same as relation, he belong same family,\" is the\naccount they give of their relationship with the long-legged bird.\nConversely they hold that they themselves are cassowaries for all\npractical purposes. They pride themselves on having long thin legs like\na cassowary. This reflection affords them peculiar satisfaction when\nthey go out to fight, or to run away, as the case may be; for at such\ntimes a Cassowary man will say to himself, \"My leg is long and thin, I\ncan run and not feel tired; my legs will go quickly and the grass will\nnot entangle them.\" Members of the Cassowary clan are reputed to be\npugnacious, because the cassowary is a bird of very uncertain temper and\ncan kick with extreme violence. (A.C. Haddon, \"The Ethnography of\nthe Western Tribe of Torres Straits\", \"Journal of the Anthropological\nInstitute\", XIX. (1890), page 393; \"Reports of the Cambridge\nAnthropological Expedition to Torres Straits\", V. (Cambridge, 1904),\npages 166, 184.) So among the Ojibways men of the Bear clan are reputed\nto be surly and pugnacious like bears, and men of the Crane clan to\nhave clear ringing voices like cranes. (W.W. Warren, \"History of the\nOjibways\", \"Collections of the Minnesota Historical Society\", V. (Saint\nPaul, Minn. 1885), pages 47, 49.) Hence the savage will often speak of\nhis totem animal as his father or his brother, and will neither kill it\nhimself nor allow others to do so, if he can help it. For example, if\nsomebody were to kill a bird in the presence of a native Australian who\nhad the bird for his totem, the black might say, \"What for you kill\nthat fellow? that my father!\" or \"That brother belonging to me you\nhave killed; why did you do it?\" (E. Palmer, \"Notes on some Australian\nTribes\", \"Journal of the Anthropological Institute\", XIII. (1884), page\n300.) Bechuanas of the Porcupine clan are greatly afflicted if anybody\nhurts or kills a porcupine in their presence. They say, \"They have\nkilled our brother, our master, one of ourselves, him whom we sing of\";\nand so saying they piously gather the quills of their murdered brother,\nspit on them, and rub their eyebrows with them. They think they would\ndie if they touched its flesh. In like manner Bechuanas of the Crocodile\nclan call the crocodile one of themselves, their master, their\nbrother; and they mark the ears of their cattle with a long slit like a\ncrocodile's mouth by way of a family crest. Similarly Bechuanas of the\nLion clan would not, like the members of other clans, partake of lion's\nflesh; for how, say they, could they eat their grandfather? If they are\nforced in self-defence to kill a lion, they do so with great regret and\nrub their eyes carefully with its skin, fearing to lose their sight if\nthey neglected this precaution. (T. Arbousset et F. Daumas, \"Relation\nd'un Voyage d'Exploration au Nord-Est de la Colonie du Cap de\nBonne-Esperance\" (Paris, 1842), pages 349 sq., 422-24.) A Mandingo\nporter has been known to offer the whole of his month's pay to save\nthe life of a python, because the python was his totem and he therefore\nregarded the reptile as his relation; he thought that if he allowed\nthe creature to be killed, the whole of his own family would perish,\nprobably through the vengeance to be taken by the reptile kinsfolk of\nthe murdered serpent. (M. le Docteur Tautain, \"Notes sur les Croyances\net Pratiques Religieuses des Banmanas\", \"Revue d'Ethnographie\",\nIII. (1885), pages 396 sq.; A. Rancon, \"Dans la Haute-Gambie, Voyage\nd'Exploration Scientifique\" (Paris, 1894), page 445.)\n\nSometimes, indeed, the savage goes further and identifies the revered\nanimal not merely with a kinsman but with himself; he imagines that one\nof his own more or less numerous souls, or at all events that a vital\npart of himself, is in the beast, so that if it is killed he must die.\nThus, the Balong tribe of the Cameroons, in West Africa, think that\nevery man has several souls, of which one is lodged in an elephant, a\nwild boar, a leopard, or what not. When any one comes home, feels ill,\nand says, \"I shall soon die,\" and is as good as his word, his friends\nare of opinion that one of his souls has been shot by a hunter in a wild\nboar or a leopard, for example, and that that is the real cause of his\ndeath. (J. Keller, \"Ueber das Land und Volk der Balong\", \"Deutsches\nKolonialblatt\", 1 October, 1895, page 484.) A Catholic missionary,\nsleeping in the hut of a chief of the Fan negroes, awoke in the middle\nof the night to see a huge black serpent of the most dangerous sort\nin the act of darting at him. He was about to shoot it when the chief\nstopped him, saying, \"In killing that serpent, it is me that you would\nhave killed. Fear nothing, the serpent is my elangela.\" (Father Trilles,\n\"Chez les Fang, leurs Moeurs, leur Langue, leur Religion\", \"Les Missions\nCatholiques\", XXX. (1898), page 322.) At Calabar there used to be some\nyears ago a huge old crocodile which was well known to contain the\nspirit of a chief who resided in the flesh at Duke Town. Sporting\nVice-Consuls, with a reckless disregard of human life, from time to time\nmade determined attempts to injure the animal, and once a peculiarly\nactive officer succeeded in hitting it. The chief was immediately laid\nup with a wound in his leg. He SAID that a dog had bitten him, but\nfew people perhaps were deceived by so flimsy a pretext. (Miss Mary H.\nKingsley, \"Travels in West Africa\" (London, 1897), pages 538 sq. As to\nthe external or bush souls of human beings, which in this part of Africa\nare supposed to be lodged in the bodies of animals, see Miss Mary H.\nKingsley op. cit. pages 459-461; R. Henshaw, \"Notes on the Efik belief\nin 'bush soul'\", \"Man\", VI.(1906), pages 121 sq.; J. Parkinson,\n\"Notes on the Asaba people (Ibos) of the Niger\", \"Journal of the\nAnthropological Institute\", XXXVI. (1906), pages 314 sq.) Once when Mr\nPartridge's canoe-men were about to catch fish near an Assiga town in\nSouthern Nigeria, the natives of the town objected, saying, \"Our\nsouls live in those fish, and if you kill them we shall die.\" (Charles\nPartridge, \"Cross River Natives\" (London, 1905), pages 225 sq.) On\nanother occasion, in the same region, an Englishman shot a hippopotamus\nnear a native village. The same night a woman died in the village,\nand her friends demanded and obtained from the marksman five pounds as\ncompensation for the murder of the woman, whose soul or second self had\nbeen in that hippopotamus. (C.H. Robinson, \"Hausaland\" (London, 1896),\npages 36 sq.) Similarly at Ndolo, in the Congo region, we hear of a\nchief whose life was bound up with a hippopotamus, but he prudently\nsuffered no one to fire at the animal. (\"Notes Analytiques sur les\nCollections Ethnographiques du Musee du Congo\", I. (Brussels, 1902-06),\npage 150.)\n\nAmongst people who thus fail to perceive any sharp line of distinction\nbetween beasts and men it is not surprising to meet with the belief that\nhuman beings are directly descended from animals. Such a belief is often\nfound among totemic tribes who imagine that their ancestors sprang from\ntheir totemic animals or plants; but it is by no means confined to\nthem. Thus, to take instances, some of the Californian Indians, in whose\nmythology the coyote or prairie-wolf is a leading personage, think that\nthey are descended from coyotes. At first they walked on all fours; then\nthey began to have some members of the human body, one finger, one toe,\none eye, one ear, and so on; then they got two fingers, two toes, two\neyes, two ears, and so forth; till at last, progressing from period to\nperiod, they became perfect human beings. The loss of their tails, which\nthey still deplore, was produced by the habit of sitting upright. (H.R.\nSchoolcraft, \"Indian Tribes of the United States\", IV. (Philadelphia,\n1856), pages 224 sq.; compare id. V. page 217. The descent of some, not\nall, Indians from coyotes is mentioned also by Friar Boscana, in (A.\nRobinson's) \"Life in California\" (New York, 1846), page 299.)\nSimilarly Darwin thought that \"the tail has disappeared in man and the\nanthropomorphous apes, owing to the terminal portion having been injured\nby friction during a long lapse of time; the basal and embedded portion\nhaving been reduced and modified, so as to become suitable to the erect\nor semi-erect position.\" (Charles Darwin, \"The Descent of Man\", Second\nEdition (London, 1879), page 60.) The Turtle clam of the Iroquois think\nthat they are descended from real mud turtles which used to live in a\npool. One hot summer the pool dried up, and the mud turtles set out to\nfind another. A very fat turtle, waddling after the rest in the heat,\nwas much incommoded by the weight of his shell, till by a great effort\nhe heaved it off altogether. After that he gradually developed into a\nman and became the progenitor of the Turtle clan. (E.A. Smith, \"Myths\nof the Iroquois\", \"Second Annual Report of the Bureau of Ethnology\"\n(Washington, 1883), page 77.) The Crawfish band of the Choctaws are\nin like manner descended from real crawfish, which used to live under\nground, only coming up occasionally through the mud to the surface. Once\na party of Choctaws smoked them out, taught them the Choctaw language,\ntaught them to walk on two legs, made them cut off their toe nails and\npluck the hair from their bodies, after which they adopted them into the\ntribe. But the rest of their kindred, the crawfish, are crawfish under\nground to this day. (Geo. Catlin, \"North American Indians\" 4 (London,\n1844), II. page 128.) The Osage Indians universally believed that they\nwere descended from a male snail and a female beaver. A flood swept the\nsnail down to the Missouri and left him high and dry on the bank, where\nthe sun ripened him into a man. He met and married a beaver maid, and\nfrom the pair the tribe of the Osages is descended. For a long time\nthese Indians retained a pious reverence for their animal ancestors and\nrefrained from hunting beavers, because in killing a beaver they killed\na brother of the Osages. But when white men came among them and offered\nhigh prices for beaver skins, the Osages yielded to the temptation and\ntook the lives of their furry brethren. (Lewis and Clarke, \"Travels to\nthe Source of the Missouri River\" (London, 1815), I. 12 (Vol. I. pages\n44 sq. of the London reprint, 1905).) The Carp clan of the Ootawak\nIndians are descended from the eggs of a carp which had been deposited\nby the fish on the banks of a stream and warmed by the sun. (\"Lettres\nEdifiantes et Curieuses\", Nouvelle Edition, VI. (Paris, 1781), page\n171.) The Crane clan of the Ojibways are sprung originally from a pair\nof cranes, which after long wanderings settled on the rapids at the\noutlet of Lake Superior, where they were changed by the Great Spirit\ninto a man and woman. (L.H. Morgan, \"Ancient Society\" (London, 1877),\npage 180.) The members of two Omaha clans were originally buffaloes and\nlived, oddly enough, under water, which they splashed about, making it\nmuddy. And at death all the members of these clans went back to their\nancestors the buffaloes. So when one of them lay adying, his friends\nused to wrap him up in a buffalo skin with the hair outside and say to\nhim, \"You came hither from the animals and you are going back thither.\nDo not face this way again. When you go, continue walking. (J. Owen\nDorsey, \"Omaha Sociology\", \"Third Annual Report of the Bureau of\nEthnology\" (Washington, 1884), pages 229, 233.) The Haida Indians of\nQueen Charlotte Islands believe that long ago the raven, who is the\nchief figure in the mythology of North-West America, took a cockle from\nthe beach and married it; the cockle gave birth to a female child, whom\nthe raven took to wife, and from their union the Indians were produced.\n(G.M. Dawson, \"Report on the Queen Charlotte Islands\" (Montreal,\n1880), pages 149B sq. (\"Geological Survey of Canada\"); F. Poole,\n\"Queen Charlotte Islands\", page 136.) The Delaware Indians called the\nrattle-snake their grandfather and would on no account destroy one of\nthese reptiles, believing that were they to do so the whole race of\nrattle-snakes would rise up and bite them. Under the influence of the\nwhite man, however, their respect for their grandfather the rattle-snake\ngradually died away, till at last they killed him without compunction\nor ceremony whenever they met him. The writer who records the old custom\nobserves that he had often reflected on the curious connection which\nappears to subsist in the mind of an Indian between man and the brute\ncreation; \"all animated nature,\" says he, \"in whatever degree, is in\ntheir eyes a great whole, from which they have not yet ventured to\nseparate themselves.\" (Rev. John Heckewelder, \"An Account of the\nHistory, Manners, and Customs, of the Indian Nations, who once inhabited\nPennsylvania and the Neighbouring States\", \"Transactions of the\nHistorical and Literary Committee of the American Philosophical\nSociety\", I. (Philadelphia, 1819), pages 245, 247, 248.)\n\nSome of the Indians of Peru boasted of being descended from the puma\nor American lion; hence they adored the lion as a god and appeared at\nfestivals like Hercules dressed in the skins of lions with the heads\nof the beasts fixed over their own. Others claimed to be sprung from\ncondors and attired themselves in great black and white wings, like\nthat enormous bird. (Garcilasso de la Vega, \"First Part of the Royal\nCommentaries of the Yncas\", Vol. I. page 323, Vol. II. page 156\n(Markham's translation).) The Wanika of East Africa look upon the hyaena\nas one of their ancestors or as associated in some way with their origin\nand destiny. The death of a hyaena is mourned by the whole people, and\nthe greatest funeral ceremonies which they perform are performed for\nthis brute. The wake held over a chief is as nothing compared to the\nwake held over a hyaena; one tribe only mourns the death of its chief,\nbut all the tribes unite to celebrate the obsequies of a hyaena.\n(Charles New, \"Life, Wanderings, and Labours in Eastern Africa\" (London,\n1873) page 122.) Some Malagasy families claim to be descended from the\nbabacoote (Lichanotus brevicaudatus), a large lemur of grave appearance\nand staid demeanour, which lives in the depth of the forest. When\nthey find one of these creatures dead, his human descendants bury it\nsolemnly, digging a grave for it, wrapping it in a shroud, and weeping\nand lamenting over its carcase. A doctor who had shot a babacoote was\naccused by the inhabitants of a Betsimisaraka village of having\nkilled \"one of their grandfathers in the forest,\" and to appease their\nindignation he had to promise not to skin the animal in the village\nbut in a solitary place where nobody could see him. (Father Abinal,\n\"Croyances fabuleuses des Malgaches\", \"Les Missions Catholiques\", XII.\n(1880), page 526; G.H. Smith, \"Some Betsimisaraka superstitions\", \"The\nAntananarivo Annual and Madagascar Magazine\", No. 10 (Antananarivo,\n1886), page 239; H.W. Little, \"Madagascar, its History and People\"\n(London, 1884), pages 321 sq; A. van Gennep, \"Tabou et Totemisme a\nMadagascar\" (Paris, 1904), pages 214 sqq.) Many of the Betsimisaraka\nbelieve that the curious nocturnal animal called the aye-aye (Cheiromys\nmadagascariensis) \"is the embodiment of their forefathers, and hence\nwill not touch it, much less do it an injury. It is said that when one\nis discovered dead in the forest, these people make a tomb for it and\nbury it with all the forms of a funeral. They think that if they attempt\nto entrap it, they will surely die in consequence.\" (G.A. Shaw, \"The\nAye-aye\", \"Antananarivo Annual and Madagascar Magazine\", Vol. II.\n(Antananarivo, 1896), pages 201, 203 (Reprint of the Second four\nNumbers). Compare A. van Gennep, \"Tabou et Totemisme a Madagascar\",\npages 223 sq.) Some Malagasy tribes believe themselves descended from\ncrocodiles and accordingly they deem the formidable reptiles their\nbrothers. If one of these scaly brothers so far forgets the ties of\nkinship as to devour a man, the chief of the tribe, or in his absence\nan old man familiar with the tribal customs, repairs at the head of the\npeople to the edge of the water, and summons the family of the culprit\nto deliver him up to the arm of justice. A hook is then baited and cast\ninto the river or lake. Next day the guilty brother or one of his family\nis dragged ashore, formally tried, sentenced to death, and executed. The\nclaims of justice being thus satisfied, the dead animal is lamented\nand buried like a kinsman; a mound is raised over his grave and a stone\nmarks the place of his head. (Father Abinal, \"Croyances fabuleuses des\nMalgaches\", \"Les Missions Catholiques\", XII. (1880), page 527; A. van\nGennep, \"Tabou et Totemisme a Madagascar\", pages 281 sq.)\n\nAmongst the Tshi-speaking tribes of the Gold Coast in West Africa the\nHorse-mackerel family traces its descent from a real horse-mackerel whom\nan ancestor of theirs once took to wife. She lived with him happily\nin human shape on shore till one day a second wife, whom the man had\nmarried, cruelly taunted her with being nothing but a fish. That hurt\nher so much that bidding her husband farewell she returned to her old\nhome in the sea, with her youngest child in her arms, and never came\nback again. But ever since the Horse-mackerel people have refrained from\neating horse-mackerels, because the lost wife and mother was a fish of\nthat sort. (A.B. Ellis, \"The Tshi-speaking Peoples of the Gold Coast\nof West Africa\" (London, 1887), pages 208-11. A similar tale is told by\nanother fish family who abstain from eating the fish (appei) from which\nthey take their name (A.B. Ellis op. cit. pages 211 sq.).) Some of the\nLand Dyaks of Borneo tell a similar tale to explain a similar custom.\n\"There is a fish which is taken in their rivers called a puttin, which\nthey would on no account touch, under the idea that if they did they\nwould be eating their relations. The tradition respecting it is, that a\nsolitary old man went out fishing and caught a puttin, which he dragged\nout of the water and laid down in his boat. On turning round, he found\nit had changed into a very pretty little girl. Conceiving the idea she\nwould make, what he had long wished for, a charming wife for his son,\nhe took her home and educated her until she was fit to be married. She\nconsented to be the son's wife cautioning her husband to use her well.\nSome time after their marriage, however, being out of temper, he struck\nher, when she screamed, and rushed away into the water; but not without\nleaving behind her a beautiful daughter, who became afterwards the\nmother of the race.\" (The Lord Bishop of Labuan, \"On the Wild Tribes\nof the North-West Coast of Borneo\", \"Transactions of the Ethnological\nSociety of London\", New Series II. (London, 1863), pages 26 sq. Such\nstories conform to a well-known type which may be called the Swan-Maiden\ntype of story, or Beauty and the Beast, or Cupid and Psyche. The\noccurrence of stories of this type among totemic peoples, such as the\nTshi-speaking negroes of the Gold Coast, who tell them to explain their\ntotemic taboos, suggests that all such tales may have originated in\ntotemism. I shall deal with this question elsewhere.)\n\nMembers of a clan in Mandailing, on the west coast of Sumatra, assert\nthat they are descended from a tiger, and at the present day, when a\ntiger is shot, the women of the clan are bound to offer betel to the\ndead beast. When members of this clan come upon the tracks of a tiger,\nthey must, as a mark of homage, enclose them with three little sticks.\nFurther, it is believed that the tiger will not attack or lacerate his\nkinsmen, the members of the clan. (H. Ris, \"De Onderafdeeling Klein\nMandailing Oeloe en Pahantan en hare Bevolking met uitzondering van\nde Oeloes\", \"Bijdragen tot de Tall- Land- en Volkenkunde van\nNederlansch-Indie, XLVI.\" (1896), page 473.) The Battas of Central\nSumatra are divided into a number of clans which have for their totems\nwhite buffaloes, goats, wild turtle-doves, dogs, cats, apes, tigers, and\nso forth; and one of the explanations which they give of their totems\nis that these creatures were their ancestors, and that their own souls\nafter death can transmigrate into the animals. (J.B. Neumann, \"Het\nPane en Bila-stroomgebied op het eiland Sumatra\", \"Tijdschrift van het\nNederlandsch Aardrijkskundig Genootschap\", Tweede Serie, III. Afdeeling,\nMeer uitgebreide Artikelen, No. 2 (Amsterdam, 1886), pages 311 sq.;\nid. ib. Tweede Serie, IV. Afdeeling, Meer uitgebreide Artikelen, No. 1\n(Amsterdam, 1887), pages 8 sq.) In Amboyna and the neighbouring islands\nthe inhabitants of some villages aver that they are descended from\ntrees, such as the Capellenia moluccana, which had been fertilised by\nthe Pandion Haliaetus. Others claim to be sprung from pigs, octopuses,\ncrocodiles, sharks, and eels. People will not burn the wood of the trees\nfrom which they trace their descent, nor eat the flesh of the animals\nwhich they regard as their ancestors. Sicknesses of all sorts are\nbelieved to result from disregarding these taboos. (J.G.F. Riedel, \"De\nsluik- en kroesharige rassen tusschen Selebes en Papua\" (The Hague,\n1886), pages 32, 61; G.W.W.C. Baron van Hoevell, \"Ambon en meer\nbepaaldelijk de Oeliasers\" (Dordrecht, 1875), page 152.) Similarly in\nCeram persons who think they are descended from crocodiles, serpents,\niguanas, and sharks will not eat the flesh of these animals. (J.G.F.\nRiedel op. cit. page 122.) Many other peoples of the Molucca Islands\nentertain similar beliefs and observe similar taboos. (J.G.F. Riedel\n\"De sluik- en kroesharige rassen tusschen Selebes en Papua\" (The Hague,\n1886), pages 253, 334, 341, 348, 412, 414, 432.) Again, in Ponape, one\nof the Caroline Islands, \"The different families suppose themselves to\nstand in a certain relation to animals, and especially to fishes, and\nbelieve in their descent from them. They actually name these animals\n'mothers'; the creatures are sacred to the family and may not be\ninjured. Great dances, accompanied with the offering of prayers, are\nperformed in their honour. Any person who killed such an animal would\nexpose himself to contempt and punishment, certainly also to the\nvengeance of the insulted deity.\" Blindness is commonly supposed to\nbe the consequence of such a sacrilege. (Dr Hahl, \"Mittheilungen\nuber Sitten und rechtliche Verhaltnisse auf Ponape\", \"Ethnologisches\nNotizblatt\", Vol. II. Heft 2 (Berlin, 1901), page 10.)\n\nSome of the aborigines of Western Australia believe that their ancestors\nwere swans, ducks, or various other species of water-fowl before they\nwere transformed into men. (Captain G. Grey, \"A Vocabulary of the\nDialects of South Western Australia\", Second Edition (London, 1840),\npages 29, 37, 61, 63, 66, 71.) The Dieri tribe of Central Australia, who\nare divided into totemic clans, explain their origin by the following\nlegend. They say that in the beginning the earth opened in the midst of\nPerigundi Lake, and the totems (murdus or madas) came trooping out one\nafter the other. Out came the crow, and the shell parakeet, and the emu,\nand all the rest. Being as yet imperfectly formed and without members\nor organs of sense, they laid themselves down on the sandhills which\nsurrounded the lake then just as they do now. It was a bright day and\nthe totems lay basking in the sunshine, till at last, refreshed and\ninvigorated by it, they stood up as human beings and dispersed in all\ndirections. That is why people of the same totem are now scattered all\nover the country. You may still see the island in the lake out of which\nthe totems came trooping long ago. (A.W. Howitt, \"Native Tribes of\nSouth-East Australia\" (London, 1904), pages 476, 779 sq.) Another\nDieri legend relates how Paralina, one of the Mura-Muras or mythical\npredecessors of the Dieri, perfected mankind. He was out hunting\nkangaroos, when he saw four incomplete beings cowering together. So he\nwent up to them, smoothed their bodies, stretched out their limbs, slit\nup their fingers and toes, formed their mouths, noses, and eyes, stuck\nears on them, and blew into their ears in order that they might hear.\nHaving perfected their organs and so produced mankind out of these\nrudimentary beings, he went about making men everywhere. (A.W. Howitt\nop. cit., pages 476, 780 sq.) Yet another Dieri tradition sets forth how\nthe Mura-Mura produced the race of man out of a species of small black\nlizards, which may still be met with under dry bark. To do this he\ndivided the feet of the lizards into fingers and toes, and, applying\nhis forefinger to the middle of their faces, created a nose; likewise he\ngave them human eyes, mouths and ears. He next set one of them upright,\nbut it fell down again because of its tail; so he cut off its tail and\nthe lizard then walked on its hind legs. That is the origin of mankind.\n(S. Gason, \"The Manners and Customs of the Dieyerie tribe of Australian\nAborigines\", \"Native Tribes of South Australia\" (Adelaide, 1879),\npage 260. This writer fell into the mistake of regarding the Mura-Mura\n(Mooramoora) as a Good-Spirit instead of as one of the mythical but more\nor less human predecessors of the Dieri in the country. See A.W. Howitt,\n\"Native Tribes of South-East Australia\", pages 475 sqq.)\n\nThe Arunta tribe of Central Australia similarly tell how in the\nbeginning mankind was developed out of various rudimentary forms of\nanimal life. They say that in those days two beings called Ungambikula,\nthat is, \"out of nothing,\" or \"self-existing,\" dwelt in the western sky.\nFrom their lofty abode they could see, far away to the east, a number\nof inapertwa creatures, that is, rudimentary human beings or incomplete\nmen, whom it was their mission to make into real men and women. For at\nthat time there were no real men and women; the rudimentary creatures\n(inapertwa) were of various shapes and dwelt in groups along the shore\nof the salt water which covered the country. These embryos, as we may\ncall them, had no distinct limbs or organs of sight, hearing, and smell;\nthey did not eat food, and they presented the appearance of human beings\nall doubled up into a rounded mass, in which only the outline of the\ndifferent parts of the body could be vaguely perceived. Coming down\nfrom their home in the western sky, armed with great stone knives, the\nUngambikula took hold of the embryos, one after the other. First of all\nthey released the arms from the bodies, then making four clefts at the\nend of each arm they fashioned hands and fingers; afterwards legs, feet,\nand toes were added in the same way. The figure could now stand; a nose\nwas then moulded and the nostrils bored with the fingers. A cut with the\nknife made the mouth, which was pulled open several times to render it\nflexible. A slit on each side of the face separated the upper and lower\neye-lids, disclosing the eyes, which already existed behind them; and\na few strokes more completed the body. Thus out of the rudimentary\ncreatures were formed men and women. These rudimentary creatures or\nembryos, we are told, \"were in reality stages in the transformation\nof various animals and plants into human beings, and thus they were\nnaturally, when made into human beings, intimately associated with the\nparticular animal or plant, as the case may be, of which they were the\ntransformations--in other words, each individual of necessity belonged\nto a totem, the name of which was of course that of the animal or plant\nof which he or she was a transformation.\" However, it is not said\nthat all the totemic clans of the Arunta were thus developed; no such\ntradition, for example, is told to explain the origin of the important\nWitchetty Grub clan. The clans which are positively known, or at least\nsaid, to have originated out of embryos in the way described are the\nPlum Tree, the Grass Seed, the Large Lizard, the Small Lizard, the\nAlexandra Parakeet, and the Small Rat clans. When the Ungambikula had\nthus fashioned people of these totems, they circumcised them all, except\nthe Plum Tree men, by means of a fire-stick. After that, having done the\nwork of creation or evolution, the Ungambikula turned themselves\ninto little lizards which bear a name meaning \"snappers-up of flies.\"\n(Baldwin Spencer and F.J. Gillen, \"Native Tribes of Central Australia\"\n(London, 1899), pages 388 sq.; compare id., \"Northern Tribes of Central\nAustralia\" (London, 1904), page 150.)\n\nThis Arunta tradition of the origin of man, as Messrs Spencer and\nGillen, who have recorded it, justly observe, \"is of considerable\ninterest; it is in the first place evidently a crude attempt to describe\nthe origin of human beings out of non-human creatures who were of\nvarious forms; some of them were representatives of animals, others of\nplants, but in all cases they are to be regarded as intermediate stages\nin the transition of an animal or plant ancestor into a human individual\nwho bore its name as that of his or her totem.\" (Baldwin Spencer and\nF.J. Gillen, \"Native Tribes of Central Australia\", pages 391 sq.) In a\nsense these speculations of the Arunta on their own origin may be said\nto combine the theory of creation with the theory of evolution; for\nwhile they represent men as developed out of much simpler forms of life,\nthey at the same time assume that this development was effected by the\nagency of two powerful beings, whom so far we may call creators. It is\nwell known that at a far higher stage of culture a crude form of\nthe evolutionary hypothesis was propounded by the Greek philosopher\nEmpedocles. He imagined that shapeless lumps of earth and water, thrown\nup by the subterranean fires, developed into monstrous animals, bulls\nwith the heads of men, men with the heads of bulls, and so forth; till\nat last, these hybrid forms being gradually eliminated, the various\nexisting species of animals and men were evolved. (E. Zeller, \"Die\nPhilosophie der Griechen\", I.4 (Leipsic, 1876), pages 718 sq.; H. Ritter\net L. Preller, \"Historia Philosophiae Graecae et Romanae ex fontium\nlocis contexta\" 5, pages 102 sq. H. Diels, \"Die Fragmente der\nVorsokratiker\" 2, I. (Berlin, 1906), pages 190 sqq. Compare Lucretius \"De\nrerum natura\", V. 837 sqq.) The theory of the civilised Greek of Sicily\nmay be set beside the similar theory of the savage Arunta of Central\nAustralia. Both represent gropings of the human mind in the dark abyss\nof the past; both were in a measure grotesque anticipations of the\nmodern theory of evolution.\n\nIn this essay I have made no attempt to illustrate all the many various\nand divergent views which primitive man has taken of his own origin. I\nhave confined myself to collecting examples of two radically different\nviews, which may be distinguished as the theory of creation and the\ntheory of evolution. According to the one, man was fashioned in his\nexisting shape by a god or other powerful being; according to the other\nhe was evolved by a natural process out of lower forms of animal life.\nRoughly speaking, these two theories still divide the civilised world\nbetween them. The partisans of each can appeal in support of their view\nto a large consensus of opinion; and if truth were to be decided by\nweighing the one consensus against the other, with \"Genesis\" in the\none scale and \"The Origin of Species\" in the other, it might perhaps be\nfound, when the scales were finally trimmed, that the balance hung very\neven between creation and evolution.\n\n\n\n\nX. THE INFLUENCE OF DARWIN ON THE STUDY OF ANIMAL EMBRYOLOGY. By A.\nSedgwick, M.A., F.R.S.\n\nProfessor of Zoology and Comparative Anatomy in the University of\nCambridge.\n\nThe publication of \"The Origin of Species\" ushered in a new era in the\nstudy of Embryology. Whereas, before the year 1859 the facts of anatomy\nand development were loosely held together by the theory of types, which\nowed its origin to the great anatomists of the preceding generation,\nto Cuvier, L. Agassiz, J. Muller, and R. Owen, they were now combined\ntogether into one organic whole by the theory of descent and by the\nhypothesis of recapitulation which was deduced from that theory. The\nview (First clearly enunciated by Fritz Muller in his well-known work,\n\"Fur Darwin\", Leipzig, 1864; (English Edition, \"Facts for Darwin\",\n1869).) that a knowledge of embryonic and larval histories would lay\nbare the secrets of race-history and enable the course of evolution\nto be traced, and so lead to the discovery of the natural system of\nclassification, gave a powerful stimulus to morphological study in\ngeneral and to embryological investigation in particular. In Darwin's\nwords: \"Embryology rises greatly in interest, when we look at the embryo\nas a picture, more or less obscured, of the progenitor, either in its\nadult or larval state, of all the members of the same great class.\"\n(\"Origin\" (6th edition), page 396.) In the period under consideration\nthe output of embryological work has been enormous. No group of the\nanimal kingdom has escaped exhaustive examination and no effort has been\nspared to obtain the embryos of isolated and out of the way forms, the\ndevelopment of which might have an important bearing upon questions\nof phylogeny and classification. Marine zoological stations have been\nestablished, expeditions have been sent to distant countries, and the\nmethods of investigation have been greatly improved. The result of this\nactivity has been that the main features of the developmental history\nof all the most important animals are now known and the curiosity as to\ndevelopmental processes, so greatly excited by the promulgation of the\nDarwinian theory, has to a considerable extent been satisfied.\n\nTo what extent have the results of this vast activity fulfilled the\nexpectations of the workers who have achieved them? The Darwin centenary\nis a fitting moment at which to take stock of our position. In this\ninquiry we shall leave out of consideration the immense and intensely\ninteresting additions to our knowledge of Natural History. These may be\nsaid to constitute a capital fund upon which philosophers, poets and\nmen of science will draw for many generations. The interest of Natural\nHistory existed long before Darwinian evolution was thought of and\nwill endure without any reference to philosophic speculations. She is\na mistress in whose face are beauties and in whose arms are delights\nelsewhere unattainable. She is and always has been pursued for her own\nsake without any reference to philosophy, science, or utility.\n\nDarwin's own views of the bearing of the facts of embryology upon\nquestions of wide scientific interest are perfectly clear. He writes\n(\"Origin\" (6th edition), page 395.):\n\n\"On the other hand it is highly probable that with many animals the\nembryonic or larval stages show us, more or less completely, the\ncondition of the progenitor of the whole group in its adult state. In\nthe great class of the Crustacea, forms wonderfully distinct from each\nother, namely, suctorial parasites, cirripedes, entomostraca, and even\nthe malacostraca, appear at first as larvae under the nauplius-form; and\nas these larvae live and feed in the open sea, and are not adapted for\nany peculiar habits of life, and from other reasons assigned by Fritz\nMuller, it is probable that at some very remote period an independent\nadult animal, resembling the Nauplius, existed, and subsequently\nproduced, along several divergent lines of descent, the above-named\ngreat Crustacean groups. So again it is probable, from what we know of\nthe embryos of mammals, birds, fishes, and reptiles, that these animals\nare the modified descendants of some ancient progenitor, which was\nfurnished in its adult state with branchiae, a swim-bladder, four\nfin-like limbs, and a long tail, all fitted for an aquatic life.\n\n\"As all the organic beings, extinct and recent, which have ever lived,\ncan be arranged within a few great classes; and as all within each\nclass have, according to our theory, been connected together by fine\ngradations, the best, and, if our collections were nearly perfect, the\nonly possible arrangement, would be genealogical; descent being the\nhidden bond of connexion which naturalists have been seeking under the\nterm of the Natural System. On this view we can understand how it is\nthat, in the eyes of most naturalists, the structure of the embryo is\neven more important for classification than that of the adult. In two or\nmore groups of animals, however much they may differ from each other\nin structure and habits in their adult condition, if they pass through\nclosely similar embryonic stages, we may feel assured that they all are\ndescended from one parent-form, and are therefore closely related.\nThus, community in embryonic structure reveals community of descent; but\ndissimilarity in embryonic development does not prove discommunity of\ndescent, for in one of two groups the developmental stages may have been\nsuppressed, or may have been so greatly modified through adaptation to\nnew habits of life, as to be no longer recognisable. Even in groups, in\nwhich the adults have been modified to an extreme degree, community of\norigin is often revealed by the structure of the larvae; we have seen,\nfor instance, that cirripedes, though externally so like shell-fish,\nare at once known by their larvae to belong to the great class of\ncrustaceans. As the embryo often shows us more or less plainly the\nstructure of the less modified and ancient progenitor of the group, we\ncan see why ancient and extinct forms so often resemble in their\nadult state the embryos of existing species of the same class. Agassiz\nbelieves this to be a universal law of nature; and we may hope hereafter\nto see the law proved true. It can, however, be proved true only in\nthose cases in which the ancient state of the progenitor of the group\nhas not been wholly obliterated, either by successive variations having\nsupervened at a very early period of growth, or by such variations\nhaving been inherited at an earlier stage than that at which they first\nappeared. It should also be borne in mind, that the law may be true,\nbut yet, owing to the geological record not extending far enough back\nin time, may remain for a long period, or for ever, incapable of\ndemonstration. The law will not strictly hold good in those cases in\nwhich an ancient form became adapted in its larval state to some special\nline of life, and transmitted the same larval state to a whole group of\ndescendants; for such larvae will not resemble any still more ancient\nform in its adult state.\"\n\nAs this passage shows, Darwin held that embryology was of interest\nbecause of the light it seems to throw upon ancestral history\n(phylogeny) and because of the help it would give in enabling us to\narrive at a natural system of classification. With regard to the latter\npoint, he quotes with approval the opinion that \"the structure of\nthe embryo is even more important for classification than that of the\nadult.\" What justification is there for this view? The phase of life\nchosen for the ordinary anatomical and physiological studies, namely,\nthe adult phase, is merely one of the large number of stages of\nstructure through which the organism passes. By far the greater number\nof these are included in what is specially called the developmental\nor (if we include larvae with embryos) embryonic period, for the\ndevelopmental changes are more numerous and take place with greater\nrapidity at the beginning of life than in its later periods. As each of\nthese stages is equal in value, for our present purpose, to the adult\nphase, it clearly follows that if there is anything in the view that\nthe anatomical study of organisms is of importance in determining their\nmutual relations, the study of the organism in its various embryonic\n(and larval) stages must have a greater importance than the study of the\nsingle and arbitrarily selected stage of life called the adult.\n\nBut a deeper reason than this has been assigned for the importance of\nembryology in classification. It has been asserted, and is implied by\nDarwin in the passage quoted, that the ancestral history is repeated\nin a condensed form in the embryonic, and that a study of the latter\nenables us to form a picture of the stages of structure through which\nthe organism has passed in its evolution. It enables us on this view to\nreconstruct the pedigrees of animals and so to form a genealogical tree\nwhich shall be the true expression of their natural relations.\n\nThe real question which we have to consider is to what extent the\nembryological studies of the last 50 years have confirmed or rendered\nprobable this \"theory of recapitulation.\" In the first place it must\nbe noted that the recapitulation theory is itself a deduction from the\ntheory of evolution. The facts of embryology, particularly of vertebrate\nembryology, and of larval history receive, it is argued, an explanation\non the view that the successive stages of development are, on the\nwhole, records of adult stages of structure which the species has passed\nthrough in its evolution. Whether this statement will bear a critical\nverbal examination I will not now pause to inquire, for it is more\nimportant to determine whether any independent facts can be alleged in\nfavour of the theory. If it could be shown, as was stated to be the case\nby L. Agassiz, that ancient and extinct forms of life present features\nof structure now only found in embryos, we should have a body of facts\nof the greatest importance in the present discussion. But as Huxley (See\nHuxley's \"Scientific Memoirs\", London, 1898, Vol. I. page 303: \"There is\nno real parallel between the successive forms assumed in the development\nof the life of the individual at present, and those which have appeared\nat different epochs in the past.\" See also his Address to the\nGeological Society of London (1862) 'On the Palaeontological Evidence of\nEvolution', ibid. Vol. II. page 512.) has shown and as the whole course\nof palaeontological and embryological investigation has demonstrated, no\nsuch statement can be made. The extinct forms of life are very similar\nto those now existing and there is nothing specially embryonic about\nthem. So that the facts, as we know them, lend no support to theory.\n\nBut there is another class of facts which have been alleged in favour\nof the theory, viz. the facts which have been included in the\ngeneralisation known as the Law of v. Baer. The law asserts that embryos\nof different species of animals of the same group are more alike\nthan the adults and that, the younger the embryo, the greater are the\nresemblances. If this law could be established it would undoubtedly be\na strong argument in favour of the \"recapitulation\" explanation of the\nfacts of embryology. But its truth has been seriously disputed. If it\nwere true we should expect to find that the embryos of closely similar\nspecies would be indistinguishable from one another, but this is\nnotoriously not the case. It is more difficult to meet the assertion\nwhen it is made in the form given above, for here we are dealing with\nmatters of opinion. For instance, no one would deny that the embryo of a\ndogfish is different from the embryo of a rabbit, but there is room for\ndifference of opinion when it is asserted that the difference is less\nthan the difference between an adult dogfish and an adult rabbit. It\nwould be perfectly true to say that the differences between the embryos\nconcern other organs more than do the differences between the adults,\nbut who is prepared to affirm that the presence of a cephalic coelom and\nof cranial segments, of external gills, of six gill slits, of the kidney\ntubes opening into the muscle-plate coelom, of an enormous yolk-sac, of\na neurenteric canal, and the absence of any trace of an amnion, of an\nallantois and of a primitive streak are not morphological facts of as\nhigh an import as those implied by the differences between the adults?\nThe generalisation undoubtedly had its origin in the fact that there is\nwhat may be called a family resemblance between embryos and larvae, but\nthis resemblance, which is by no means exact, is largely superficial and\ndoes not extend to anatomical detail.\n\nIt is useless to say, as Weismann has stated (\"The Evolution Theory\",\nby A. Weismann, English Translation, Vol. II. page 176, London, 1904.),\nthat \"it cannot be disputed that the rudiments [vestiges his translator\nmeans] of gill-arches and gill-clefts, which are peculiar to one stage\nof human ontogeny, give us every ground for concluding that we possessed\nfish-like ancestors.\" The question at issue is: did the pharyngeal\narches and clefts of mammalian embryos ever discharge a branchial\nfunction in an adult ancestor of the mammalia? We cannot therefore,\nwithout begging the question at issue in the grossest manner, apply to\nthem the terms \"gill-arches\" and \"gill-clefts\". That they are homologous\nwith the \"gill-arches\" and \"gill-clefts\" of fishes is true; but there\nis no evidence to show that they ever discharged a branchial function.\nUntil such evidence is forthcoming, it is beside the point to say that\nit \"cannot be disputed\" that they are evidence of a piscine ancestry.\n\nIt must, therefore, be admitted that one outcome of the progress of\nembryological and palaeontological research for the last 50 years is\nnegative. The recapitulation theory originated as a deduction from the\nevolution theory and as a deduction it still remains.\n\nLet us before leaving the subject apply another test. If the evolution\ntheory and the recapitulation theory are both true, how is it that\nliving birds are not only without teeth but have no rudiments of teeth\nat any stage of their existence? How is it that the missing digits in\nbirds and mammals, the missing or reduced limb of snakes and whales, the\nreduced mandibulo-hyoid cleft of elasmobranch fishes are not present or\nrelatively more highly developed in the embryo than in the adult? How\nis it that when a marked variation, such as an extra digit, or a reduced\nlimb, or an extra segment, makes its appearance, it is not confined to\nthe adult but can be seen all through the development? All the clear\nevidence we can get tends to show that marked variations, whether of\nreduction or increase, of organs are manifest during the whole of the\ndevelopment of the organ and do not merely affect the adult. And on\nreflection we see that it could hardly be otherwise. All such evidence\nis distinctly at variance with the theory of recapitulation, at least\nas applied to embryos. In the case of larvae of course the case will be\ndifferent, for in them the organs are functional, and reduction in the\nadult will not be accompanied by reduction in the larva unless a change\nin the conditions of life of the larva enables it to occur.\n\nIf after 50 years of research and close examination of the facts of\nembryology the recapitulation theory is still without satisfactory\nproof, it seems desirable to take a wider sweep and to inquire whether\nthe facts of embryology cannot be included in a larger category.\n\nAs has been pointed out by Huxley, development and life are\nco-extensive, and it is impossible to point to any period in the life of\nan organism when the developmental changes cease. It is true that these\nchanges take place more rapidly at the commencement of life, but they\nare never wholly absent, and those which occur in the later or so-called\nadult stages of life do not differ in their essence, however much they\nmay differ in their degree, from those which occur during the embryonic\nand larval periods. This consideration at once brings the changes of\nthe embryonic period into the same category as those of the adult and\nsuggests that an explanation which will account for the one will account\nfor the other. What then is the problem we are dealing with? Surely\nit is this: Why does an organism as soon as it is established at the\nfertilisation of the ovum enter upon a cycle of transformations which\nnever cease until death puts an end to them? In other words what is\nthe meaning of that cycle of changes which all organisms present in a\ngreater or less degree and which constitute the very essence of life?\nIt is impossible to give an answer to this question so long as we remain\nwithin the precincts of Biology--and it is not my present purpose to\npenetrate beyond those precincts into the realms of philosophy. We have\nto do with an ultimate biological fact, with a fundamental property of\nliving matter, which governs and includes all its other properties. How\nmay this property be stated? Thus: it is a property of living matter\nto react in a remarkable way to external forces without undergoing\ndestruction. The life-cycle, of which the embryonic and larval periods\nare a part, consists of the orderly interaction between the organism\nand its environment. The action of the environment produces certain\nmorphological changes in the organism. These changes enable the organism\nto come into relation with new external forces, to move into what\nis practically a new environment, which in its turn produces further\nstructural changes in the organism. These in their turn enable, indeed\nnecessitate, the organism to move again into a new environment, and so\nthe process continues until the structural changes are of such a nature\nthat the organism is unable to adapt itself to the environment in which\nit finds itself. The essential condition of success in this process is\nthat the organism should always shift into the environment to which its\nnew structure is suited--any failure in this leading to the impairment\nof the organism. In most cases the shifting of the environment is a\nvery gradual process (whether consisting in the very slight and gradual\nalteration in the relation of the embryo as a whole to the egg-shell or\nuterine wall, or in the relations of its parts to each other, or in\nthe successive phases of adult life), and the morphological changes in\nconnection with each step of it are but slight. But in some cases jumps\nare made such as we find in the phenomena known as hatching, birth, and\nmetamorphosis.\n\nThis property of reacting to the environment without undergoing\ndestruction is, as has been stated, a fundamental property of organisms.\nIt is impossible to conceive of any matter, to which the term living\ncould be applied, being without it. And with this property of reacting\nto the environment goes the further property of undergoing a change\nwhich alters the relation of the organism to the old environment\nand places it in a new environment. If this reasoning is correct, it\nnecessarily follows that this property must have been possessed by\nliving matter at its first appearance on the earth. In other words\nliving matter must always have presented a life-cycle, and the question\narises what kind of modification has that cycle undergone? Has it\nincreased or diminished in duration and complexity since organisms first\nappeared on the earth? The current view is that the cycle was at first\nvery short and that it has increased in length by the evolutionary\ncreation of new adult phases, that these new phases are in addition to\nthose already existing and that each of them as it appears takes\nover from the preceding adult phase the functional condition of the\nreproductive organs. According to the same view the old adult phases are\nnot obliterated but persist in a more or less modified form as larval\nstages. It is further supposed that as the life-history lengthens at one\nend by the addition of new adult phases, it is shortened at the other by\nthe abbreviation of embryonic development and by the absorption of some\nof the early larval stages into the embryonic period; but on the whole\nthe lengthening process has exceeded that of shortening, so that the\nwhole life-history has, with the progress of evolution, become longer\nand more complicated.\n\nNow there can be no doubt that the life-history of organisms has been\nshortened in the way above suggested, for cases are known in which this\ncan practically be seen to occur at the present day. But the process\nof lengthening by the creation of new stages at the other end of the\nlife-cycle is more difficult to conceive and moreover there is no\nevidence for its having occurred. This, indeed, may have occurred, as\nis suggested below, but the evidence we have seems to indicate\nthat evolutionary modification has proceeded by ALTERING and not by\nSUPERSEDING: that is to say that each stage in the life-history, as we\nsee it to-day, has proceeded from a corresponding stage in a former era\nby the modification of that stage and not by the creation of a new one.\nLet me, at the risk of repetition, explain my meaning more fully by\ntaking a concrete illustration. The mandibulo-hyoid cleft (spiracle)\nof the elasmobranch fishes, the lateral digits of the pig's foot, the\nhind-limbs of whales, the enlarged digit of the ostrich's foot\nare supposed to be organs which have been recently modified.\nThis modification is not confined to the final adult stage of the\nlife-history but characterises them throughout the whole of their\ndevelopment. A stage with a reduced spiracle does not proceed in\ndevelopment from a preceding stage in which the spiracle shows no\nreduction: it is reduced at its first appearance. The same statement may\nbe made of organs which have entirely disappeared in the adult, such as\nbird's teeth and snake's fore-limbs: the adult stage in which they have\ndisappeared is not preceded by embryonic stages in which the teeth and\nlimbs or rudiments of them are present. In fact the evidence indicates\nthat adult variations of any part are accompanied by precedent\nvariations in the same direction in the embryo. The evidence seems to\nshow, not that a stage is added on at the end of the life-history, but\nonly that some of the stages in the life-history are modified. Indeed,\non the wider view of development taken in this essay, a view which makes\nit coincident with life, one would not expect often to find, even if new\nstages are added in the course of evolution, that they are added at the\nend of the series when the organism has passed through its reproductive\nperiod. It is possible of course that new stages have been intercalated\nin the course of the life-history, though it is difficult to see\nhow this has occurred. It is much more likely, if we may judge from\navailable evidence, that every stage has had its counterpart in\nthe ancestral form from which it has been derived by descent with\nmodification. Just as the adult phase of the living form differs, owing\nto evolutionary modification, from the adult phase of the ancestor from\nwhich it has proceeded, so each larval phase will differ for the same\nreason from the corresponding larval phase in the life-history of the\nancestor. Inasmuch as the organism is variable at every stage of its\nindependent existence and is exposed to the action of natural selection\nthere is no reason why it should escape modification at any stage.\n\nIf there is any truth in these considerations it would seem to follow\nthat at the dawn of life the life-cycle must have been, either in posse\nor in esse, at least as long as it is at the present time, and that\nthe peculiarity of passing through a series of stages in which new\ncharacters are successively evolved is a primordial quality of living\nmatter.\n\nBefore leaving this part of the subject, it is necessary to touch upon\nanother aspect of it. What are these variations in structure which\nsucceed one another in the life-history of an organism? I am conscious\nthat I am here on the threshold of a chamber which contains the clue to\nsome of our difficulties, and that I cannot enter it. Looked at from\none point of view they belong to the class of genetic variations, which\ndepend upon the structure or constitution of the protoplasm; but instead\nof appearing in different zygotes (A zygote is a fertilised ovum, i.e. a\nnew organism resulting from the fusion of an ovum and a spermatozoon.),\nthey are present in the same zygote though at different times in its\nlife-history. They are of the same order as the mutational variations\nof the modern biologist upon which the appearance of a new character\ndepends. What is a genetic or mutational variation? It is a genetic\ncharacter which was not present in either of the parents. But these\n\"growth variations\" were present in the parents, and in this they differ\nfrom mutational variations. But what are genetic characters? They are\ncharacters which must appear if any development occurs. They are usually\ncontrasted with \"acquired characters,\" using the expression \"acquired\ncharacter\" in the Lamarckian sense. But strictly speaking they ARE\nacquired characters, for the zygote at first has none of the characters\nwhich it subsequently acquires, but only the power of acquiring them\nin response to the action of the environment. But the characters so\nacquired are not what we technically understand and what Lamarck meant\nby \"acquired characters.\" They are genetic characters, as defined above.\nWhat then are Lamarck's \"acquired characters\"? They are variations in\ngenetic characters caused in a particular way. There are, in fact,\ntwo kinds of variation in genetic characters depending on the mode\nof causation. Firstly, there are those variations consequent upon a\nvariation in the constitution of the protoplasm of a particular zygote,\nand independent of the environment in which the organism develops,\nsave in so far as this simply calls them forth: these are the so-called\ngenetic or mutational variations. Secondly, there are those variations\nwhich occur in zygotes of similar germinal constitution and which are\ncaused solely by differences in the environment to which the individuals\nare respectively exposed: these are the \"acquired characters\" of Lamarck\nand of authors generally. In consequence of this double sense in which\nthe term \"acquired characters\" may be used, great confusion may and\ndoes occur. If the protoplasm be compared to a machine, and the external\nconditions to the hand that works the machine, then it may be said that,\nas the machine can only work in one way, it can only produce one kind\nof result (genetic character), but the particular form or quality\n(Lamarckian \"acquired character\") of the result will depend upon the\nhand that works the machine (environment), just as the quality of the\nsound produced by a fiddle depends entirely upon the hand which plays\nupon it. It would be improper to apply the term \"mutation\" to those\ngenetic characters which are not new characters or new variants of old\ncharacters, but such genetic characters are of the same nature as\nthose characters to which the term mutation has been applied. It may be\nnoticed in passing that it is very questionable if the modern biologist\nhas acted in the real interests of science in applying the term mutation\nin the sense in which he has applied it. The genetic characters of\norganisms come from one of two sources: either they are old characters\nand are due to the action of what we call inheritance or they are new\nand are due to what we call variation. If the term mutation is applied\nto the actual alteration of the machinery of the protoplasm, no\nobjection can be felt to its use; but if it be applied, as it is, to the\nproduct of the action of the altered machine, viz. to the new genetic\ncharacter, it leads to confusion. Inheritance is the persistence of the\nstructure of the machine; characters are the products of the working of\nthe machine; variation in genetic characters is due to the alteration\n(mutation) in the arrangement of the machinery, while variation in\nacquired characters (Lamarckian) is due to differences in the mode of\nworking the machinery. The machinery when it starts (in the new zygote)\nhas the power of grinding out certain results, which we call the\ncharacters of the organism. These appear at successive intervals\nof time, and the orderly manifestation of them is what we call the\nlife-history of the organism. This brings us back to the question with\nwhich we started this discussion, viz. what is the relation of these\nvariations in structure, which successively appear in an organism and\nconstitute its life-history, to the mutational variations which appear\nin different organisms of the same brood or species. The question is\nbrought home to us when we ask what is a bud-sport, such as a nectarine\nappearing on a peach-tree? From one point of view, it is simply a\nmutation appearing in asexual reproduction; from another it is one of\nthese successional characters (\"growth variations\") which constitute\nthe life-history of the zygote, for it appears in the same zygote which\nfirst produces a peach. Here our analogy of a machine which only works\nin one way seems to fail us, for these bud-sports do not appear in all\nparts of the organism, only in certain buds or parts of it, so that one\npart of the zygotic machine would appear to work differently to another.\nTo discuss this question further would take us too far from our subject.\nSuffice it to say that we cannot answer it, any more than we can this\nfurther question of burning interest at the present day, viz. to\nwhat extent and in what manner is the machine itself altered by the\nparticular way in which it is worked. In connection with this question\nwe can only submit one consideration: the zygotic machine can, by\nits nature, only work once, so that any alteration in it can only be\nascertained by studying the replicas of it which are produced in the\nreproductive organs.\n\nIt is a peculiarity that the result which we call the ripening of the\ngenerative organs nearly always appears among the final products of the\naction of the zygotic machine. It is remarkable that this should be\nthe case. What is the reason of it? The late appearance of functional\nreproductive organs is almost a universal law, and the explanation of it\nis suggested by expressing the law in another way, viz. that the machine\nis almost always so constituted that it ceases to work efficiently\nsoon after the reproductive organs have sufficiently discharged their\nfunction. Why this should occur we cannot explain: it is an ultimate\nfact of nature, and cannot be included in any wider category. The\nperiod during which the reproductive organs can act may be short as\nin ephemerids or long as in man and trees, and there is no reason to\nsuppose that their action damages the vital machinery, though sometimes,\nas in the case of annual plants (Metschnikoff), it may incidentally\ndo so; but, long or short, the cessation of their actions is always\na prelude to the end. When they and their action are impaired, the\norganism ceases to react with precision to the environment, and the\norganism as a whole undergoes retrogressive changes.\n\nIt has been pointed out above that there is reason to believe that at\nthe dawn of life the life-cycle was, EITHER IN ESSE OR IN POSSE, at\nleast as long as it is at the present time. The qualification implied by\nthe words in italics is necessary, for it is clearly possible that the\nexternal conditions then existing were not suitable for the production\nof all the stages of the potential life-history, and that what we\ncall organic evolution has consisted in a gradual evolution of new\nenvironments to which the organism's innate capacity of change has\nenabled it to adapt itself. We have warrant for this possibility in the\ncase of the Axolotl and in other similar cases of neoteny. And these\ncases further bring home to us the fact, to which I have already\nreferred, that the full development of the functional reproductive\norgans is nearly always associated with the final stages of the\nlife-history.\n\nOn this view of the succession of characters in the life-history of\norganisms, how shall we explain the undoubted fact that the development\nof buds hardly ever presents any phenomena corresponding to the\nembryonic and larval changes? The reason is clearly this, that budding\nusually occurs after the embryonic stage is past; when the characters of\nembryonic life have been worked out by the machine. When it takes place\nat an early stage in embryonic life, as it does in cases of so-called\nembryonic fission, the product shows, either partly or entirely,\nphenomena similar to those of embryonic development. The only case known\nto me in which budding by the adult is accompanied by morphological\nfeatures similar to those displayed by embryos is furnished by the\nbudding of the medusiform spore-sacs of hydrozoon polyps. But this case\nis exceptional, for here we have to do with an attempt, which fails, to\nform a free-swimming organism, the medusa; and the vestiges which appear\nin the buds are the umbrella-cavity, marginal tentacles, circular canal,\netc., of the medusa arrested in development.\n\nBut the question still remains, are there no cases in which, as implied\nby the recapitulation theory, variations in any organ are confined to\nthe period in which the organ is functional and do not affect it in the\nembryonic stages? The teeth of the whalebone whales may be cited as\na case in which this is said to occur; but here the teeth are only\nimperfectly developed in the embryo and are soon absorbed. They have\nbeen affected by the change which has produced their disappearance in\nthe adult, but not to complete extinction. Nor are they now likely to be\nextinguished, for having become exclusively embryonic they are largely\nprotected from the action of natural selection. This consideration\nbrings up a most important aspect of the question, so far as\ndisappearing organs are concerned. Every organ is laid down at a certain\nperiod in the embryo and undergoes a certain course of growth until\nit obtains full functional development. When for any cause reduction\nbegins, it is affected at all stages of its growth, unless it has\nfunctional importance in the larva, and in some cases its life is\nshortened at one or both ends. In cases, as in that of the whale's\nteeth, in which it entirely disappears in the adult, the latter part\nof its life is cut off; in others, the beginning of its life may\nbe deferred. This happens, for instance, with the spiracle of many\nElasmobranchs, which makes its appearance after the hyobranchial cleft,\nnot before it as it should do, being anterior to it in position, and\nas it does in the Amniota in which it shows no reduction in size as\ncompared with the other pharyngeal clefts. In those Elasmobranchs\nin which it is absent in the adult but present in the embryo (e.g.\nCarcharias) its life is shortened at both ends. Many more instances\nof organs, of which the beginning and end have been cut off, might be\nmentioned; e.g. the muscle-plate coelom of Aves, the primitive streak\nand the neurenteric canal of amniote blastoderms. In yet other cases in\nwhich the reduced organ is almost on the verge of disappearance, it\nmay appear for a moment and disappear more than once in the course of\ndevelopment. As an instance of this striking phenomenon I may mention\nthe neurenteric canal of avine embryos, and the anterior neuropore of\nAscidians. Lastly the reduced organ may disappear in the developing\nstages before it does so in the adult. As an instance of this may be\nmentioned the mandibular palp of those Crustacea with zoaea larvae. This\nstructure disappears in the larva only to reappear in a reduced form in\nlater stages. In all these cases we are dealing with an organ which, we\nimagine, attained a fuller functional development at some previous stage\nin race-history, but in most of them we have no proof that it did so. It\nmay be, and the possibility must not be lost sight of, that these organs\nnever were anything else than functionless and that though they have\nbeen got rid of in the adult by elimination in the course of time, they\nhave been able to persist in embryonic stages which are protected from\nthe full action of natural selection. There is no reason to suppose that\nliving matter at its first appearance differed from non-living matter\nin possessing only properties conducive to its well-being and prolonged\nexistence. No one thinks that the properties of the various forms of\ninorganic matter are all strictly related to external conditions.\nOf what use to the diamond is its high specific gravity and high\nrefrangibility, and to gold of its yellow colour and great weight? These\nsubstances continue to exist in virtue of other properties than these.\nIt is impossible to suppose that the properties of living matter at\nits first appearance were all useful to it, for even now after aeons of\nelimination we find that it possesses many useless organs and that\nmany of its relations to the external world are capable of considerable\nimprovement.\n\nIn writing this essay I have purposely refrained from taking a definite\nposition with regard to the problems touched. My desire has been\nto write a chapter showing the influence of Darwin's work so far as\nEmbryology is concerned, and the various points which come up for\nconsideration in discussing his views. Darwin was the last man who would\nhave claimed finality for any of his doctrines, but he might fairly have\nclaimed to have set going a process of intellectual fermentation which\nis still very far from completion.\n\n\n\n\nXI. THE PALAEONTOLOGICAL RECORD. By W.B. Scott.\n\nProfessor of Geology in the University of Princeton, U.S.A.\n\n\nI. ANIMALS.\n\nTo no branch of science did the publication of \"The Origin of Species\"\nprove to be a more vivifying and transforming influence than to\nPalaeontology. This science had suffered, and to some extent, still\nsuffers from its rather anomalous position between geology and biology,\neach of which makes claim to its territory, and it was held in strict\nbondage to the Linnean and Cuvierian dogma that species were immutable\nentities. There is, however, reason to maintain that this strict bondage\nto a dogma now abandoned, was not without its good side, and served the\npurpose of keeping the infant science in leading-strings until it was\nable to walk alone, and preventing a flood of premature generalisations\nand speculations.\n\nAs Zittel has said: \"Two directions were from the first apparent\nin palaeontological research--a stratigraphical and a biological.\nStratigraphers wished from palaeontology mainly confirmation regarding\nthe true order or relative age of zones of rock-deposits in the field.\nBiologists had, theoretically at least, the more genuine interest in\nfossil organisms as individual forms of life.\" (Zittel, \"History of\nGeology and Palaeontology\", page 363, London, 1901.) The geological\nor stratigraphical direction of the science was given by the work of\nWilliam Smith, \"the father of historical geology,\" in the closing decade\nof the eighteenth century. Smith was the first to make a systematic use\nof fossils in determining the order of succession of the rocks which\nmake up the accessible crust of the earth, and this use has continued,\nwithout essential change, to the present day. It is true that the\ntheory of evolution has greatly modified our conceptions concerning the\nintroduction of new species and the manner in which palaeontological\ndata are to be interpreted in terms of stratigraphy, but, broadly\nspeaking, the method remains fundamentally the same as that introduced\nby Smith.\n\nThe biological direction of palaeontology was due to Cuvier and his\nassociates, who first showed that fossils were not merely varieties\nof existing organisms, but belonged to extinct species and genera,\nan altogether revolutionary conception, which startled the scientific\nworld. Cuvier made careful studies, especially of fossil vertebrates,\nfrom the standpoint of zoology and was thus the founder of palaeontology\nas a biological science. His great work on \"Ossements Fossiles\" (Paris,\n1821) has never been surpassed as a masterpiece of the comparative\nmethod of anatomical investigation, and has furnished to the\npalaeontologist the indispensable implements of research.\n\nOn the other hand, Cuvier's theoretical views regarding the history\nof the earth and its successive faunas and floras are such as no one\nbelieves to-day. He held that the earth had been repeatedly devastated\nby great cataclysms, which destroyed every living thing, necessitating\nan entirely new creation, thus regarding the geological periods as\nsharply demarcated and strictly contemporaneous for the whole earth,\nand each species of animal and plant as confined to a single period.\nCuvier's immense authority and his commanding personality dominated\nscientific thought for more than a generation and marked out the line\nwhich the development of palaeontology was to follow. The work was\nenthusiastically taken up by many very able men in the various European\ncountries and in the United States, but, controlled as it was by the\nbelief in the fixity of species, it remained almost entirely descriptive\nand consisted in the description and classification of the different\ngroups of fossil organisms. As already intimated, this narrowness of\nview had its compensations, for it deferred generalisations until some\nadequate foundations for these had been laid.\n\nDominant as it was, Cuvier's authority was slowly undermined by the\nprogress of knowledge and the way was prepared for the introduction of\nmore rational conceptions. The theory of \"Catastrophism\" was attacked by\nseveral geologists, most effectively by Sir Charles Lyell, who greatly\namplified the principles enunciated by Hutton and Playfair in the\npreceding century, and inaugurated a new era in geology. Lyell's\nuniformitarian views of the earth's history and of the agencies which\nhad wrought its changes, had undoubted effect in educating men's minds\nfor the acceptance of essentially similar views regarding the organic\nworld. In palaeontology too the doctrine of the immutability of species,\nthough vehemently maintained and reasserted, was gradually weakening. In\nreviewing long series of fossils, relations were observed which pointed\nto genetic connections and yet were interpreted as purely ideal.\nAgassiz, for example, who never accepted the evolutionary theory, drew\nattention to facts which could be satisfactorily interpreted only in\nterms of that theory. Among the fossils he indicated \"progressive,\"\n\"synthetic,\" \"prophetic,\" and \"embryonic\" types, and pointed out the\nparallelism which obtains between the geological succession of ancient\nanimals and the ontogenetic development of recent forms. In Darwin's\nwords: \"This view accords admirably well with our theory.\" (\"Origin of\nSpecies\" (6th edition), page 310.) Of similar import were Owen's views\non \"generalised types\" and \"archetypes.\"\n\nThe appearance of \"The Origin of Species\" in 1859 revolutionised all\nthe biological sciences. From the very nature of the case, Darwin\nwas compelled to give careful consideration to the palaeontological\nevidence; indeed, it was the palaeontology and modern distribution of\nanimals in South America which first led him to reflect upon the great\nproblem. In his own words: \"I had been deeply impressed by discovering\nin the Pampean formation great fossil animals covered with armour\nlike that on the existing armadillos; secondly, by the manner in which\nclosely allied animals replace one another in proceeding southward over\nthe Continent; and thirdly, by the South American character of most of\nthe productions of the Galapagos archipelago, and more especially by\nthe manner in which they differ slightly on each island of the group.\"\n(\"Life and Letters of Charles Darwin\", I. page 82.) In the famous tenth\nand eleventh chapters of the \"Origin\", the palaeontological evidence\nis examined at length and the imperfection of the geological record is\nstrongly emphasised. The conclusion is reached, that, in view of this\nextreme imperfection, palaeontology could not reasonably be expected to\nyield complete and convincing proof of the evolutionary theory. \"I look\nat the geological record as a history of the world imperfectly kept,\nand written in a changing dialect; of this history we possess the last\nvolume alone, relating only to two or three countries. Of this volume,\nonly here and there a short chapter has been preserved; and of each\npage, only here and there a few lines.\" (\"Origin of Species\", page 289.)\nYet, aside from these inevitable difficulties, he concludes, that \"the\nother great leading facts in palaeontology agree admirably with the\ntheory of descent with modification through variation and natural\nselection.\" (Ibid. page 313.)\n\nDarwin's theory gave an entirely new significance and importance to\npalaeontology. Cuvier's conception of the science had been a limited,\nthough a lofty one. \"How glorious it would be if we could arrange the\norganised products of the universe in their chronological order!... The\nchronological succession of organised forms, the exact determination\nof those types which appeared first, the simultaneous origin of certain\nspecies and their gradual decay, would perhaps teach us as much\nabout the mysteries of organisation as we can possibly learn through\nexperiments with living organisms.\" (Zittel op. cit. page 140.) This,\nhowever, was rather the expression of a hope for the distant future than\nan account of what was attainable, and in practice the science remained\nalmost purely descriptive, until Darwin gave it a new standpoint, new\nproblems and an altogether fresh interest and charm. The revolution\nthus accomplished is comparable only to that produced by the Copernican\nastronomy.\n\nFrom the first it was obvious that one of the most searching tests\nof the evolutionary theory would be given by the advance of\npalaeontological discovery. However imperfect the geological record\nmight be, its ascertained facts would necessarily be consistent, under\nany reasonable interpretation, with the demands of a true theory;\notherwise the theory would eventually be overwhelmed by the mass of\nirreconcilable data. A very great stimulus was thus given to geological\ninvestigation and to the exploration of new lands. In the last forty\nyears, the examination of North and South America, of Africa and Asia\nhas brought to light many chapters in the history of life, which are\nastonishingly full and complete. The flood of new material continues to\naccumulate at such a rate that it is impossible to keep abreast of it,\nand the very wealth of the collections is a source of difficulty and\nembarrassment. In modern palaeontology phylogenetic questions and\nproblems occupy a foremost place and, as a result of the labours of many\neminent investigators in many lands, it may be said that this science\nhas proved to be one of the most solid supports of Darwin's theory.\nTrue, there are very many unsolved problems, and the discouraged worker\nis often tempted to believe that the fossils raise more questions than\nthey answer. Yet, on the other hand, the whole trend of the evidence\nis so strongly in favour of the evolutionary doctrine, that no other\ninterpretation seems at all rational.\n\nTo present any adequate account of the palaeontological record from the\nevolutionary standpoint, would require a large volume and a singularly\nunequal, broken and disjointed history it would be. Here the record is\nscanty, interrupted, even unintelligible, while there it is crowded with\nembarrassing wealth of material, but too often these full chapters are\nseparated by such stretches of unrecorded time, that it is difficult to\nconnect them. It will be more profitable to present a few illustrative\nexamples than to attempt an outline of the whole history.\n\nAt the outset, the reader should be cautioned not to expect too\nmuch, for the task of determining phylogenies fairly bristles with\ndifficulties and encounters many unanswered questions. Even when the\nevidence seems to be as copious and as complete as could be wished,\ndifferent observers will put different interpretations upon it, as in\nthe notorious case of the Steinheim shells. (In the Miocene beds of\nSteinheim, Wurtemberg, occur countless fresh-water shells, which show\nnumerous lines of modification, but these have been very differently\ninterpreted by different writers.) The ludicrous discrepances which\noften appear between the phylogenetic \"trees\" of various writers have\ncast an undue discredit upon the science and have led many zoologists\nto ignore palaeontology altogether as unworthy of serious attention. One\nprincipal cause of these discrepant and often contradictory results is\nour ignorance concerning the exact modes of developmental change.\nWhat one writer postulates as almost axiomatic, another will reject as\nimpossible and absurd. Few will be found to agree as to how far a given\nresemblance is offset by a given unlikeness, and so long as the question\nis one of weighing evidence and balancing probabilities, complete\nharmony is not to be looked for. These formidable difficulties confront\nus even in attempting to work out from abundant material a brief chapter\nin the phylogenetic history of some small and clearly limited group,\nand they become disproportionately greater, when we extend our view over\nvast periods of time and undertake to determine the mutual relationships\nof classes and types. If the evidence were complete and available, we\nshould hardly be able to unravel its infinite complexity, or to find\na clue through the mazes of the labyrinth. \"Our ideas of the course of\ndescent must of necessity be diagrammatic.\" (D.H. Scott, \"Studies in\nFossil Botany\", page 524. London, 1900.)\n\nSome of the most complete and convincing examples of descent with\nmodification are to be found among the mammals, and nowhere more\nabundantly than in North America, where the series of continental\nformations, running through the whole Tertiary period, is remarkably\nfull. Most of these formations contain a marvellous wealth of mammalian\nremains and in an unusual state of preservation. The oldest Eocene\n(Paleocene) has yielded a mammalian fauna which is still of prevailingly\nMesozoic character, and contains but few forms which can be regarded\nas ancestral to those of later times. The succeeding fauna of the lower\nEocene proper (Wasatch stage) is radically different and, while a few\nforms continue over from the Paleocene, the majority are evidently\nrecent immigrants from some region not yet identified. From the Wasatch\nonward, the development of many phyla may be traced in almost unbroken\ncontinuity, though from time to time the record is somewhat obscured by\nmigrations from the Old World and South America. As a rule, however, it\nis easy to distinguish between the immigrant and the indigenous elements\nof the fauna.\n\nFrom their gregarious habits and individual abundance, the history of\nmany hoofed animals is preserved with especial clearness. So well known\nas to have become a commonplace, is the phylogeny of the horses, which,\ncontrary to all that would have been expected, ran the greater part of\nits course in North America. So far as it has yet been traced, the line\nbegins in the lower Eocene with the genus Eohippus, a little creature\nnot much larger than a cat, which has a short neck, relatively short\nlimbs, and in particular, short feet, with four functional digits and\na splint-like rudiment in the fore-foot, three functional digits and\na rudiment in the hind-foot. The forearm bones (ulna and radius) are\ncomplete and separate, as are also the bones of the lower leg (fibula\nand tibia). The skull has a short face, with the orbit, or eye-socket,\nincompletely enclosed with bone, and the brain-case is slender and\nof small capacity. The teeth are short-crowned, the incisors without\n\"mark,\" or enamel pit, on the cutting edge; the premolars are all\nsmaller and simpler than the molars. The pattern of the upper molars is\nso entirely different from that seen in the modern horses that, without\nthe intermediate connecting steps, no one would have ventured to derive\nthe later from the earlier plan. This pattern is quadritubercular, with\nfour principal, conical cusps arranged in two transverse pairs, forming\na square, and two minute cuspules between each transverse pair, a tooth\nwhich is much more pig-like than horse-like. In the lower molars the\ncusps have already united to form two crescents, one behind the other,\nforming a pattern which is extremely common in the early representatives\nof many different families, both of the Perissodactyla and the\nArtiodactyla. In spite of the manifold differences in all parts of the\nskeleton between Eohippus and the recent horses, the former has stamped\nupon it an equine character which is unmistakable, though it can hardly\nbe expressed in words.\n\nEach one of the different Eocene and Oligocene horizons has its\ncharacteristic genus of horses, showing a slow, steady progress in a\ndefinite direction, all parts of the structure participating in the\nadvance. It is not necessary to follow each of these successive steps\nof change, but it should be emphasised that the changes are gradual and\nuninterrupted. The genus Mesohippus, of the middle Oligocene, may be\nselected as a kind of half-way stage in the long progression. Comparing\nMesohippus with Eohippus, we observe that the former is much larger,\nsome species attaining the size of a sheep, and has a relatively longer\nneck, longer limbs and much more elongate feet, which are tridactyl, and\nthe middle toe is so enlarged that it bears most of the weight, while\nthe lateral digits are very much more slender. The fore-arm bones have\nbegun to co-ossify and the ulna is greatly reduced, while the fibula,\nthough still complete, is hardly more than a thread of bone. The skull\nhas a longer face and a nearly enclosed orbit, and the brain-case is\nfuller and more capacious, the internal cast of which shows that the\nbrain was richly convoluted. The teeth are still very short-crowned,\nbut the upper incisors plainly show the beginning of the \"mark\"; the\npremolars have assumed the molar form, and the upper molars, though\nplainly derived from those of Eohippus, have made a long stride toward\nthe horse pattern, in that the separate cusps have united to form a\ncontinuous outer wall and two transverse crests.\n\nIn the lower Miocene the interesting genus Desmatippus shows a further\nadvance in the development of the teeth, which are beginning to assume\nthe long-crowned shape, delaying the formation of roots; a thin layer\nof cement covers the crowns, and the transverse crests of the upper\ngrinding teeth display an incipient degree of their modern complexity.\nThis tooth-pattern is strictly intermediate between the recent type\nand the ancient type seen in Mesohippus and its predecessors. The\nupper Miocene genera, Protohippus and Hipparion are, to all intents and\npurposes, modern in character, but their smaller size, tridactyl feet\nand somewhat shorter-crowned teeth are reminiscences of their ancestry.\n\nFrom time to time, when a land-connection between North America and\nEurasia was established, some of the successive equine genera migrated\nto the Old World, but they do not seem to have gained a permanent\nfooting there until the end of the Miocene or beginning of the Pliocene,\neventually diversifying into the horses, asses, and zebras of Africa,\nAsia and Europe. At about the same period, the family extended its range\nto South America and there gave rise to a number of species and genera,\nsome of them extremely peculiar. For some unknown reason, all the horse\ntribe had become extinct in the western hemisphere before the European\ndiscovery, but not until after the native race of man had peopled the\ncontinents.\n\nIn addition to the main stem of equine descent, briefly considered\nin the foregoing paragraphs, several side-branches were given off at\nsuccessive levels of the stem. Most of these branches were short-lived,\nbut some of them flourished for a considerable period and ramified into\nmany species.\n\nApparently related to the horses and derived from the same root-stock is\nthe family of the Palaeotheres, confined to the Eocene and Oligocene of\nEurope, dying out without descendants. In the earlier attempts to work\nout the history of the horses, as in the famous essay of Kowalevsky\n(\"Sur l'Anchitherium aurelianense Cuv. et sur l'histoire paleontologique\ndes Chevaux\", \"Mem. de l'Acad. Imp. des Sc. de St Petersbourg\", XX. no.\n5, 1873.), the Palaeotheres were placed in the direct line, because\nthe number of adequately known Eocene mammals was then so small, that\nCuvier's types were forced into various incongruous positions, to serve\nas ancestors for unrelated series.\n\nThe American family of the Titanotheres may also be distantly related\nto the horses, but passed through an entirely different course of\ndevelopment. From the lower Eocene to the lower sub-stage of the middle\nOligocene the series is complete, beginning with small and rather\nlightly built animals. Gradually the stature and massiveness increase,\na transverse pair of nasal horns make their appearance and, as\nthese increase in size, the canine tusks and incisors diminish\ncorrespondingly. Already in the oldest known genus the number of digits\nhad been reduced to four in the fore-foot and three in the hind, but\nthere the reduction stops, for the increasing body-weight made necessary\nthe development of broad and heavy feet. The final members of the\nseries comprise only large, almost elephantine animals, with immensely\ndeveloped and very various nasal horns, huge and massive heads, and\naltogether a grotesque appearance. The growth of the brain did not\nat all keep pace with the increase of the head and body, and the\nludicrously small brain may will have been one of the factors which\ndetermined the startlingly sudden disappearance and extinction of the\ngroup.\n\nLess completely known, but of unusual interest, is the genealogy of the\nrhinoceros family, which probably, though not certainly, was likewise\nof American origin. The group in North America at least, comprised three\ndivisions, or sub-families, of very different proportions, appearance\nand habits, representing three divergent lines from the same stem.\nThough the relationship between the three lines seems hardly open\nto question, yet the form ancestral to all of them has not yet been\nidentified. This is because of our still very incomplete knowledge\nof several perissodactyl genera of the Eocene, any one of which may\neventually prove to be the ancestor sought for.\n\nThe first sub-family is the entirely extinct group of Hyracodonts, which\nmay be traced in successive modifications through the upper Eocene,\nlower and middle Oligocene, then disappearing altogether. As yet, the\nhyracodonts have been found only in North America, and the last genus of\nthe series, Hyracodon, was a cursorial animal. Very briefly stated,\nthe modifications consist in a gradual increase in size, with greater\nslenderness of proportions, accompanied by elongation of the neck,\nlimbs, and feet, which become tridactyl and very narrow. The grinding\nteeth have assumed the rhinoceros-like pattern and the premolars\nresemble the molars in form; on the other hand, the front teeth,\nincisors and canines, have become very small and are useless as weapons.\nAs the animal had no horns, it was quite defenceless and must have found\nits safety in its swift running, for Hyracodon displays many superficial\nresemblances to the contemporary Oligocene horses, and was evidently\nadapted for speed. It may well have been the competition of the horses\nwhich led to the extinction of these cursorial rhinoceroses.\n\nThe second sub-family, that of the Amynodonts, followed a totally\ndifferent course of development, becoming short-legged and short-footed,\nmassive animals, the proportions of which suggest aquatic habits; they\nretained four digits in the front foot. The animal was well provided\nwith weapons in the large canine tusks, but was without horns. Some\nmembers of this group extended their range to the Old World, but they\nall died out in the middle Oligocene, leaving no successors.\n\nThe sub-family of the true rhinoceroses cannot yet be certainly traced\nfarther back than to the base of the middle Oligocene, though some\nfragmentary remains found in the lower Oligocene are probably also\nreferable to it. The most ancient and most primitive member of\nthis series yet discovered, the genus Trigonias, is unmistakably a\nrhinoceros, yet much less massive, having more the proportions of a\ntapir; it had four toes in the front foot, three in the hind, and had a\nfull complement of teeth, except for the lower canines, though the upper\ncanines are about to disappear, and the peculiar modification of the\nincisors, characteristic of the true rhinoceroses, is already apparent;\nthe skull is hornless. Representatives of this sub-family continue\nthrough the Oligocene and Miocene of North America, becoming rare and\nlocalised in the Pliocene and then disappearing altogether. In the Old\nWorld, on the other hand, where the line appeared almost as early as it\ndid in America, this group underwent a great expansion and ramification,\ngiving rise not only to the Asiatic and African forms, but also to\nseveral extinct series.\n\nTurning now to the Artiodactyla, we find still another group of mammals,\nthat of the camels and llamas, which has long vanished from North\nAmerica, yet took its rise and ran the greater part of its course in\nthat continent. From the lower Eocene onward the history of this series\nis substantially complete, though much remains to be learned concerning\nthe earlier members of the family. The story is very like that of the\nhorses, to which in many respects it runs curiously parallel. Beginning\nwith very small, five-toed animals, we observe in the successive genera\na gradual transformation in all parts of the skeleton, an elongation of\nthe neck, limbs and feet, a reduction of the digits from five to two,\nand eventually the coalescence of the remaining two digits into a\n\"cannon-bone.\" The grinding teeth, by equally gradual steps, take on\nthe ruminant pattern. In the upper Miocene the line divides into the two\nbranches of the camels and llamas, the former migrating to Eurasia\nand the latter to South America, though representatives of both lines\npersisted in North America until a very late period. Interesting\nside-branches of this line have also been found, one of which ended in\nthe upper Miocene in animals which had almost the proportions of the\ngiraffes and must have resembled them in appearance.\n\nThe American Tertiary has yielded several other groups of ruminant-like\nanimals, some of which form beautifully complete evolutionary series,\nbut space forbids more than this passing mention of them.\n\nIt was in Europe that the Artiodactyla had their principal development,\nand the upper Eocene, Oligocene and Miocene are crowded with such an\noverwhelming number and variety of forms that it is hardly possible to\nmarshal them in orderly array and determine their mutual relationships.\nYet in this chaotic exuberance of life, certain important facts stand\nout clearly, among these none is of greater interest and importance than\nthe genealogy of the true Ruminants, or Pecora, which may be traced from\nthe upper Eocene onward. The steps of modification and change are very\nsimilar to those through which the camel phylum passed in North America,\nbut it is instructive to note that, despite their many resemblances, the\ntwo series can be connected only in their far distant beginnings. The\npecoran stock became vastly more expanded and diversified than did\nthe camel line and was evidently more plastic and adaptable, spreading\neventually over all the continents except Australia, and forming to-day\none of the dominant types of mammals, while the camels are on the\ndecline and not far from extinction. The Pecora successively ramified\ninto the deer, antelopes, sheep, goats and oxen, and did not reach\nNorth America till the Miocene, when they were already far advanced in\nspecialisation. To this invasion of the Pecora, or true ruminants, it\nseems probable that the decline and eventual disappearance of the camels\nis to be ascribed.\n\nRecent discoveries in Egypt have thrown much light upon a problem which\nlong baffled the palaeontologist, namely, the origin of the elephants.\n(C.W. Andrews, \"On the Evolution of the Proboscidea\", \"Phil. Trans. Roy.\nSoc.\" London, Vol. 196, 1904, page 99.) Early representatives of this\norder, Mastodons, had appeared almost simultaneously (in the geological\nsense of that word) in the upper Miocene of Europe and North America,\nbut in neither continent was any more ancient type known which\ncould plausibly be regarded as ancestral to them. Evidently, these\nproblematical animals had reached the northern continents by migrating\nfrom some other region, but no one could say where that region lay. The\nEocene and Oligocene beds of the Fayoum show us that the region sought\nfor is Africa, and that the elephants form just such a series of gradual\nmodifications as we have found among other hoofed animals. The later\nsteps of the transformation, by which the mastodons lost their lower\ntusks, and their relatively small and simple grinding teeth acquired the\ngreat size and highly complex structure of the true elephants, may be\nfollowed in the uppermost Miocene and Pliocene fossils of India and\nsouthern Europe.\n\nEgypt has also of late furnished some very welcome material which\ncontributes to the solution of another unsolved problem which had quite\neluded research, the origin of the whales. The toothed-whales may be\ntraced back in several more or less parallel lines as far as the\nlower Miocene, but their predecessors in the Oligocene are still so\nincompletely known that safe conclusions can hardly be drawn from\nthem. In the middle Eocene of Egypt, however, has been found a\nsmall, whale-like animal (Protocetus), which shows what the ancestral\ntoothed-whale was like, and at the same time seems to connect these\nthoroughly marine mammals with land-animals. Though already entirely\nadapted to an aquatic mode of life, the teeth, skull and backbone of\nProtocetus display so many differences from those of the later\nwhales and so many approximations to those of primitive, carnivorous\nland-mammals, as, in a large degree, to bridge over the gap between the\ntwo groups. Thus one of the most puzzling of palaeontological questions\nis in a fair way to receive a satisfactory answer. The origin of the\nwhalebone-whales and their relations to the toothed-whales cannot yet be\ndetermined, since the necessary fossils have not been discovered.\n\nAmong the carnivorous mammals, phylogenetic series are not so clear and\ndistinct as among the hoofed animals, chiefly because the carnivores are\nindividually much less abundant, and well-preserved skeletons are among\nthe prizes of the collector. Nevertheless, much has already been learned\nconcerning the mutual relations of the carnivorous families, and several\nphylogenetic series, notably that of the dogs, are quite complete. It\nhas been made extremely probable that the primitive dogs of the Eocene\nrepresent the central stock, from which nearly or quite all the other\nfamilies branched off, though the origin and descent of the cats have\nnot yet been determined.\n\nIt should be clearly understood that the foregoing account of mammalian\ndescent is merely a selection of a few representative cases and might be\nalmost indefinitely extended. Nothing has been said, for example, of\nthe wonderful museum of ancient mammalian life which is entombed in the\nrocks of South America, especially of Patagonia, and which opens a\nworld so entirely different from that of the northern continents,\nyet exemplifying the same laws of \"descent with modification.\" Very\nbeautiful phylogenetic series have already been established among these\nmost interesting and marvellously preserved fossils, but lack of space\nforbids a consideration of them.\n\nThe origin of the mammalia, as a class, offers a problem of which\npalaeontology can as yet present no definitive solution. Many\nmorphologists regard the early amphibia as the ancestral group from\nwhich the mammals were derived, while most palaeontologists believe\nthat the mammals are descended from the reptiles. The most ancient known\nmammals, those from the upper Triassic of Europe and North America, are\nso extremely rare and so very imperfectly known, that they give little\nhelp in determining the descent of the class, but, on the other\nhand, certain reptilian orders of the Permian period, especially\nwell represented in South Africa, display so many and such close\napproximations to mammalian structure, as strongly to suggest a genetic\nrelationship. It is difficult to believe that all those likenesses\nshould have been independently acquired and are without phylogenetic\nsignificance.\n\nBirds are comparatively rare as fossils and we should therefore look in\nvain among them for any such long and closely knit series as the\nmammals display in abundance. Nevertheless, a few extremely fortunate\ndiscoveries have made it practically certain that birds are descended\nfrom reptiles, of which they represent a highly specialised branch. The\nmost ancient representative of this class is the extraordinary genus\nArchaeopteryx from the upper Jurassic of Bavaria, which, though\nan unmistakable bird, retains so many reptilian structures and\ncharacteristics as to make its derivation plain. Not to linger over\nanatomical minutiae, it may suffice to mention the absence of a horny\nbeak, which is replaced by numerous true teeth, and the long lizard-like\ntail, which is made up of numerous distinct vertebrae, each with a pair\nof quill-like feathers attached to it. Birds with teeth are also found\nin the Cretaceous, though in most other respects the birds of that\nperiod had attained a substantially modern structure. Concerning\nthe interrelations of the various orders and families of birds,\npalaeontology has as yet little to tell us.\n\nThe life of the Mesozoic era was characterised by an astonishing number\nand variety of reptiles, which were adapted to every mode of life,\nand dominated the air, the sea and the land, and many of which were\nof colossal proportions. Owing to the conditions of preservation which\nobtained during the Mesozoic period, the history of the reptiles is a\nbroken and interrupted one, so that we can make out many short series,\nrather than any one of considerable length. While the relations of\nseveral reptilian orders can be satisfactorily determined, others still\nbaffle us entirely, making their first known appearance in a fully\ndifferentiated state. We can trace the descent of the sea-dragons, the\nIchthyosaurs and Plesiosaurs, from terrestrial ancestors, but the most\nancient turtles yet discovered show us no closer approximation to any\nother order than do the recent turtles; and the oldest known Pterosaurs,\nthe flying dragons of the Jurassic, are already fully differentiated.\nThere is, however, no ground for discouragement in this, for the\nprogress of discovery has been so rapid of late years, and our knowledge\nof Mesozoic life has increased with such leaps and bounds, that there is\nevery reason to expect a solution of many of the outstanding problems in\nthe near future.\n\nPassing over the lower vertebrates, for lack of space to give them\nany adequate consideration, we may briefly take up the record of\ninvertebrate life. From the overwhelming mass of material it is\ndifficult to make a representative selection and even more difficult\nto state the facts intelligibly without the use of unduly technical\nlanguage and without the aid of illustrations.\n\nSeveral groups of the Mollusca, or shell-fish, yield very full and\nconvincing evidence of their descent from earlier and simpler forms,\nand of these none is of greater interest than the Ammonites, an extinct\norder of the cephalopoda. The nearest living ally of the ammonites is\nthe pearly nautilus, the other existing cephalopods, such as the squids,\ncuttle-fish, octopus, etc., are much more distantly related. Like the\nnautilus, the ammonites all possess a coiled and chambered shell, but\ntheir especial characteristic is the complexity of the \"sutures.\" By\nsutures is meant the edges of the transverse partitions, or septa, where\nthese join the shell-wall, and their complexity in the fully developed\ngenera is extraordinary, forming patterns like the most elaborate\noak-leaf embroidery, while in the nautiloids the sutures form simple\ncurves. In the rocks of the Mesozoic era, wherever conditions of\npreservation are favourable, these beautiful shells are stored in\ncountless multitudes, of an incredible variety of form, size and\nornamentation, as is shown by the fact that nearly 5000 species have\nalready been described. The ammonites are particularly well adapted for\nphylogenetic studies, because, by removing the successive whorls of the\ncoiled shell, the individual development may be followed back in inverse\norder, to the microscopic \"protoconch,\" or embryonic shell, which lies\nconcealed in the middle of the coil. Thus the valuable aid of embryology\nis obtained in determining relationships.\n\nThe descent of the ammonites, taken as a group, is simple and clear;\nthey arose as a branch of the nautiloids in the lower Devonian, the\nshells known as goniatites having zigzag, angulated sutures. Late in\nthe succeeding Carboniferous period appear shells with a truly ammonoid\ncomplexity of sutures, and in the Permian their number and variety\ncause them to form a striking element of the marine faunas. It is in the\nMesozoic era, however, that these shells attain their full development;\nincreasing enormously in the Triassic, they culminate in the Jurassic\nin the number of families, genera and species, in the complexity of\nthe sutures, and in the variety of shell-ornamentation. A slow decline\nbegins in the Cretaceous, ending in the complete extinction of the whole\ngroup at the end of that period. As a final phase in the history of the\nammonites, there appear many so-called \"abnormal\" genera, in which the\nshell is irregularly coiled, or more or less uncoiled, in some forms\nbecoming actually straight. It is interesting to observe that some of\nthese genera are not natural groups, but are \"polyphyletic,\" i.e.\nare each derived from several distinct ancestral genera, which have\nundergone a similar kind of degeneration.\n\nIn the huge assembly of ammonites it is not yet possible to arrange all\nthe forms in a truly natural classification, which shall express the\nvarious interrelations of the genera, yet several beautiful series have\nalready been determined. In these series the individual development\nof the later general shows transitory stages which are permanent in\nantecedent genera. To give a mere catalogue of names without figures\nwould not make these series more intelligible.\n\nThe Brachiopoda, or \"lamp-shells,\" are a phylum of which comparatively\nfew survive to the present day; their shells have a superficial likeness\nto those of the bivalved Mollusca, but are not homologous with the\nlatter, and the phylum is really very distinct from the molluscs. While\ngreatly reduced now, these animals were incredibly abundant throughout\nthe Palaeozoic era, great masses of limestone being often composed\nalmost exclusively of their shells, and their variety is in keeping with\ntheir individual abundance. As in the case of the ammonites, the problem\nis to arrange this great multitude of forms in an orderly array that\nshall express the ramifications of the group according to a genetic\nsystem. For many brachiopods, both recent and fossil, the individual\ndevelopment, or ontogeny, has been worked out and has proved to be\nof great assistance in the problems of classification and phylogeny.\nAlready very encouraging progress has been made in the solution of these\nproblems. All brachiopods form first a tiny, embryonic shell, called\nthe protegulum, which is believed to represent the ancestral form of the\nwhole group, and in the more advanced genera the developmental stages\nclearly indicate the ancestral genera of the series, the succession\nof adult forms in time corresponding to the order of the ontogenetic\nstages. The transformation of the delicate calcareous supports of the\narms, often exquisitely preserved, are extremely interesting. Many of\nthe Palaeozoic genera had these supports coiled like a pair of spiral\nsprings, and it has been shown that these genera were derived from types\nin which the supports were simply shelly loops.\n\nThe long extinct class of crustacea known as the Trilobites are likewise\nvery favourable subjects for phylogenetic studies. So far as the known\nrecord can inform us, the trilobites are exclusively Palaeozoic in\ndistribution, but their course must have begun long before that era, as\nis shown by the number of distinct types among the genera of the\nlower Cambrian. The group reached the acme of abundance and relative\nimportance in the Cambrian and Ordovician; then followed a long, slow\ndecline, ending in complete and final disappearance before the end of\nthe Permian. The newly-hatched and tiny trilobite larva, known as\nthe protaspis, is very near to the primitive larval form of all the\ncrustacea. By the aid of the correlated ontogenetic stages and the\nsuccession of the adult forms in the rocks, many phylogenetic series\nhave been established and a basis for the natural arrangement of the\nwhole class has been laid.\n\nVery instructive series may also be observed among the Echinoderms and,\nwhat is very rare, we are able in this sub-kingdom to demonstrate the\nderivation of one class from another. Indeed, there is much reason to\nbelieve that the extinct class Cystidea of the Cambrian is the ancestral\ngroup, from which all the other Echinoderms, star-fishes, brittle-stars,\nsea-urchins, feather-stars, etc., are descended.\n\nThe foregoing sketch of the palaeontological record is, of necessity,\nextremely meagre, and does not represent even an outline of the\nevidence, but merely a few illustrative examples, selected almost\nat random from an immense body of material. However, it will perhaps\nsuffice to show that the geological record is not so hopelessly\nincomplete as Darwin believed it to be. Since \"The Origin of Species\"\nwas written, our knowledge of that record has been enormously extended\nand we now possess, no complete volumes, it is true, but some remarkably\nfull and illuminating chapters. The main significance of the whole lies\nin the fact, that JUST IN PROPORTION TO THE COMPLETENESS OF THE RECORD\nIS THE UNEQUIVOCAL CHARACTER OF ITS TESTIMONY TO THE TRUTH OF THE\nEVOLUTIONARY THEORY.\n\nThe test of a true, as distinguished from a false, theory is the manner\nin which newly discovered and unanticipated facts arrange themselves\nunder it. No more striking illustration of this can be found than in the\ncontrasted fates of Cuvier's theory and of that of Darwin. Even before\nCuvier's death his views had been undermined and the progress of\ndiscovery soon laid them in irreparable ruin, while the activity of\nhalf-a-century in many different lines of inquiry has established the\ntheory of evolution upon a foundation of ever growing solidity. It is\nDarwin's imperishable glory that he prescribed the lines along which all\nthe biological sciences were to advance to conquests not dreamed of when\nhe wrote.\n\n\n\n\nXII. THE PALAEONTOLOGICAL RECORD. By D.H. Scott, F.R.S.\n\nPresident of the Linnean Society.\n\n\nII. PLANTS.\n\nThere are several points of view from which the subject of the present\nessay may be regarded. We may consider the fossil record of plants\nin its bearing: I. on the truth of the doctrine of Evolution; II. on\nPhylogeny, or the course of Evolution; III. on the theory of Natural\nSelection. The remarks which follow, illustrating certain aspects only\nof an extensive subject, may conveniently be grouped under these three\nheadings.\n\nI. THE TRUTH OF EVOLUTION.\n\nWhen \"The Origin of Species\" was written, it was necessary to show that\nthe Geological Record was favourable to, or at least consistent with,\nthe Theory of Descent. The point is argued, closely and fully, in\nChapter X. \"On the Imperfection of the Geological Record,\" and Chapter\nXI. \"On the Geological Succession of Organic Beings\"; there is, however,\nlittle about plants in these chapters. At the present time the truth\nof Evolution is no longer seriously disputed, though there are writers,\nlike Reinke, who insist, and rightly so, that the doctrine is still\nonly a belief, rather than an established fact of science. (J. Reinke,\n\"Kritische Abstammungslehre\", \"Wiesner-Festschrift\", page 11, Vienna,\n1908.) Evidently, then, however little the Theory of Descent may be\nquestioned in our own day, it is desirable to assure ourselves how the\ncase stands, and in particular how far the evidence from fossil plants\nhas grown stronger with time.\n\nAs regards direct evidence for the derivation of one species from\nanother, there has probably been little advance since Darwin wrote, at\nleast so we must infer from the emphasis laid on the discontinuity\nof successive fossil species by great systematic authorities like\nGrand'Eury and Zeiller in their most recent writings. We must either\nadopt the mutationist views of those authors (referred to in the last\nsection of this essay) or must still rely on Darwin's explanation of the\nabsence of numerous intermediate varieties. The attempts which have been\nmade to trace, in the Tertiary rocks, the evolution of recent species,\ncannot, owing to the imperfect character of the evidence, be regarded as\nwholly satisfactory.\n\nWhen we come to groups of a somewhat higher order we have an interesting\nhistory of the evolution of a recent family in the work, not yet\ncompleted, of Kidston and Gwynne-Vaughan on the fossil Osmundaceae.\n(\"Trans. Royal Soc. Edinburgh\", Vol. 45, Part III. 1907, Vol. 46, Part\nII. 1908, Vol. 46, Part III. 1909.) The authors are able, mainly on\nanatomical evidence, to trace back this now limited group of Ferns,\nthrough the Tertiary and Mesozoic to the Permian, and to show, with\ngreat probability, how their structure has been derived from that of\nearly Palaeozoic types.\n\nThe history of the Ginkgoaceae, now represented only by the isolated\nmaidenhair tree, scarcely known in a wild state, offers another striking\nexample of a family which can be traced with certainty to the older\nMesozoic and perhaps further back still. (See Seward and Gowan, \"The\nMaidenhair Tree (Gingko biloba)\", \"Annals of Botany\", Vol. XIV. 1900,\npage 109; also A. Sprecher \"Le Ginkgo biloba\", L., Geneva, 1907.)\n\nOn the wider question of the derivation of the great groups of plants,\na very considerable advance has been made, and, so far as the higher\nplants are concerned, we are now able to form a far better conception\nthan before of the probable course of evolution. This is a matter\nof phylogeny, and the facts will be considered under that head; our\nimmediate point is that the new knowledge of the relations between the\nclasses of plants in question materially strengthens the case for the\ntheory of descent. The discoveries of the last few years throw light\nespecially on the relation of the Angiosperms to the Gymnosperms,\non that of the Seed-plants generally to the Ferns, and on the\ninterrelations between the various classes of the higher Cryptogams.\n\nThat the fossil record has not done still more for Evolution is due to\nthe fact that it begins too late--a point on which Darwin laid stress\n(\"Origin of Species\" (6th edition), page 286.) and which has more\nrecently been elaborated by Poulton. (\"Essays on Evolution\", pages 46\net seq., Oxford, 1908.) An immense proportion of the whole evolutionary\nhistory lies behind the lowest fossiliferous rocks, and the case is\nworse for plants than for animals, as the record for the former begins,\nfor all practical purposes, much higher up in the rocks.\n\nIt may be well here to call attention to a question, often overlooked,\nwhich has lately been revived by Reinke. (Reinke, loc. cit. page 13.) As\nall admit, we know nothing of the origin of life; consequently, for all\nwe can tell, it is as probable that life began, on this planet, with\nmany living things, as with one. If the first organic beings were many,\nthey may have been heterogeneous, or at least exposed to different\nconditions, from their origin; in either case there would have been a\nnumber of distinct series from the beginning, and if so we should not\nbe justified in assuming that all organisms are related to one another.\nThere may conceivably be several of the original lines of descent still\nsurviving, or represented among extinct forms--to reverse the remark\nof a distinguished botanist, there may be several Vegetable Kingdoms!\nHowever improbable this may sound, the possibility is one to be borne in\nmind.\n\nThat all VASCULAR plants really belong to one stock seems certain, and\nhere the palaeontological record has materially strengthened the\ncase for a monophyletic history. The Bryophyta are not likely to be\nabsolutely distinct, for their sexual organs, and the stomata of the\nMosses strongly suggest community of descent with the higher plants; if\nthis be so it no doubt establishes a certain presumption in favour of\na common origin for plants generally, for the gap between \"Mosses and\nFerns\" has been regarded as the widest in the Vegetable Kingdom. The\ndirect evidence of consanguinity is however much weaker when we come to\nthe Algae, and it is conceivable (even if improbable) that the higher\nplants may have had a distinct ancestry (now wholly lost) from the\nbeginning. The question had been raised in Darwin's time, and he\nreferred to it in these words: \"No doubt it is possible, as Mr G.H.\nLewes has urged, that at the first commencement of life many different\nforms were evolved; but if so, we may conclude that only a very few\nhave left modified descendants.\" (\"Origin of Species\", page 425.) This\nquestion, though it deserves attention, does not immediately affect the\nsubject of the palaeontological record of plants, for there can be no\nreasonable doubt as to the interrelationship of those groups on which\nthe record at present throws light.\n\nThe past history of plants by no means shows a regular progression from\nthe simple to the complex, but often the contrary. This apparent anomaly\nis due to two causes.\n\n1. The palaeobotanical record is essentially the story of the successive\nascendancy of a series of dominant families, each of which attained\nits maximum, in organisation as well as in extent, and then sank into\ncomparative obscurity, giving place to other families, which under new\nconditions were better able to take a leading place. As each family ran\nits downward course, either its members underwent an actual reduction in\nstructure as they became relegated to herbaceous or perhaps aquatic life\n(this may have happened with the Horsetails and with Isoetes if derived\nfrom Lepidodendreae), or the higher branches of the family were crowded\nout altogether and only the \"poor relations\" were able to maintain their\nposition by evading the competition of the ascendant races; this is also\nillustrated by the history of the Lycopod phylum. In either case there\nwould result a lowering of the type of organisation within the group.\n\n2. The course of real progress is often from the complex to the simple.\nIf, as we shall find some grounds for believing, the Angiosperms came\nfrom a type with a flower resembling in its complexity that of Mesozoic\n\"Cycads,\" almost the whole evolution of the flower in the highest\nplants has been a process of reduction. The stamen, in particular, has\nundoubtedly become extremely simplified during evolution; in the most\nprimitive known seed-plants it was a highly compound leaf or pinna; its\nreduction has gone on in the Conifers and modern Cycads, as well as in\nthe Angiosperms, though in different ways and to a varying extent.\n\nThe seed offers another striking example; the Palaeozoic seeds (if we\nleave the seed-like organs of certain Lycopods out of consideration)\nwere always, so far as we know, highly complex structures, with\nan elaborate vascular system, a pollen-chamber, and often a\nmuch-differentiated testa. In the present day such seeds exist only in a\nfew Gymnosperms which retain their ancient characters--in all the higher\nSpermophytes the structure is very much simplified, and this holds good\neven in the Coniferae, where there is no countervailing complication of\novary and stigma.\n\nReduction, in fact, is not always, or even generally, the same thing as\ndegeneration. Simplification of parts is one of the most usual means of\nadvance for the organism as a whole. A large proportion of the higher\nplants are microphyllous in comparison with the highly megaphyllous\nfern-like forms from which they appear to have been derived.\n\nDarwin treated the general question of advance in organisation with much\ncaution, saying: \"The geological record... does not extend far enough\nback, to show with unmistakeable clearness that within the known history\nof the world organisation has largely advanced.\" (\"Origin of Species\",\npage 308.) Further on (Ibid. page 309.) he gives two standards by which\nadvance may be measured: \"We ought not solely to compare the highest\nmembers of a class at any two periods... but we ought to compare all the\nmembers, high and low, at the two periods.\" Judged by either standard\nthe Horsetails and Club Mosses of the Carboniferous were higher than\nthose of our own day, and the same is true of the Mesozoic Cycads. There\nis a general advance in the succession of classes, but not within each\nclass.\n\nDarwin's argument that \"the inhabitants of the world at each successive\nperiod in its history have beaten their predecessors in the race for\nlife, and are, in so far, higher in the scale\" (\"Origin of Species\",\npage 315.) is unanswerable, but we must remember that \"higher in the\nscale\" only means \"better adapted to the existing conditions.\" Darwin\npoints out (Ibid. page 279.) that species have remained unchanged for\nlong periods, probably longer than the periods of modification, and only\nunderwent change when the conditions of their life were altered. Higher\norganisation, judged by the test of success, is thus purely relative to\nthe changing conditions, a fact of which we have a striking illustration\nin the sudden incoming of the Angiosperms with all their wonderful\nfloral adaptations to fertilisation by the higher families of Insects.\n\nII. PHYLOGENY.\n\nThe question of phylogeny is really inseparable from that of the truth\nof the doctrine of evolution, for we cannot have historical evidence\nthat evolution has actually taken place without at the same time having\nevidence of the course it has followed.\n\nAs already pointed out, the progress hitherto made has been rather in\nthe way of joining up the great classes of plants than in tracing the\ndescent of particular species or genera of the recent flora. There\nappears to be a difference in this respect from the Animal record,\nwhich tells us so much about the descent of living species, such as the\nelephant or the horse. The reason for this difference is no doubt to be\nfound in the fact that the later part of the palaeontological record\nis the most satisfactory in the case of animals and the least so in the\ncase of plants. The Tertiary plant-remains, in the great majority of\ninstances, are impressions of leaves, the conclusions to be drawn from\nwhich are highly precarious; until the whole subject of Angiospermous\npalaeobotany has been reinvestigated, it would be rash to venture on\nany statements as to the descent of the families of Dicotyledons or\nMonocotyledons.\n\nOur attention will be concentrated on the following questions, all\nrelating to the phylogeny of main groups of plants: i. The Origin of the\nAngiosperms. ii. The Origin of the Seed-plants. iii. The Origin of the\ndifferent classes of the Higher Cryptogamia.\n\ni. THE ORIGIN OF THE ANGIOSPERMS.\n\nThe first of these questions has long been the great crux of botanical\nphylogeny, and until quite recently no light had been thrown upon the\ndifficulty. The Angiosperms are the Flowering Plants, par excellence,\nand form, beyond comparison, the dominant sub-kingdom in the flora of\nour own age, including, apart from a few Conifers and Ferns, all the\nmost familiar plants of our fields and gardens, and practically all\nplants of service to man. All recent work has tended to separate the\nAngiosperms more widely from the other seed-plants now living, the\nGymnosperms. Vast as is the range of organisation presented by the great\nmodern sub-kingdom, embracing forms adapted to every environment, there\nis yet a marked uniformity in certain points of structure, as in the\ndevelopment of the embryo-sac and its contents, the pollination\nthrough the intervention of a stigma, the strange phenomenon of double\nfertilisation (One sperm fertilising the egg, while the other unites\nwith the embryo-sac nucleus, itself the product of a nuclear fusion, to\ngive rise to a nutritive tissue, the endosperm.), the structure of\nthe stamens, and the arrangement of the parts of the flower. All these\npoints are common to Monocotyledons and Dicotyledons, and separate the\nAngiosperms collectively from all other plants.\n\nIn geological history the Angiosperms first appear in the Lower\nCretaceous, and by Upper Cretaceous times had already swamped all other\nvegetation and seized the dominant position which they still hold. Thus\nthey are isolated structurally from the rest of the Vegetable Kingdom,\nwhile historically they suddenly appear, almost in full force, and\napparently without intermediaries with other groups. To quote Darwin's\nvigorous words: \"The rapid development, as far as we can judge, of\nall the higher plants within recent geological times is an abominable\nmystery.\" (\"More Letters of Charles Darwin\", Vol. II. page 20, letter\nto J.D. Hooker, 1879.) A couple of years later he made a bold suggestion\n(which he only called an \"idle thought\") to meet this difficulty. He\nsays: \"I have been so astonished at the apparently sudden coming in of\nthe higher phanerogams, that I have sometimes fancied that development\nmight have slowly gone on for an immense period in some isolated\ncontinent or large island, perhaps near the South Pole.\" (Ibid, page\n26, letter to Hooker, 1881.) This idea of an Angiospermous invasion from\nsome lost southern land has sometimes been revived since, but has not,\nso far as the writer is aware, been supported by evidence. Light on the\nproblem has come from a different direction.\n\nThe immense development of plants with the habit of Cycads, during the\nMesozoic Period up to the Lower Cretaceous, has long been known. The\nexisting Order Cycadaceae is a small family, with 9 genera and perhaps\n100 species, occurring in the tropical and sub-tropical zones of both\nthe Old and New World, but nowhere forming a dominant feature in the\nvegetation. Some few attain the stature of small trees, while in the\nmajority the stem is short, though often living to a great age. The\nlarge pinnate or rarely bipinnate leaves give the Cycads a superficial\nresemblance in habit to Palms. Recent Cycads are dioecious; throughout\nthe family the male fructification is in the form of a cone, each scale\nof the cone representing a stamen, and bearing on its lower surface\nnumerous pollen-sacs, grouped in sori like the sporangia of Ferns. In\nall the genera, except Cycas itself, the female fructifications are\nlikewise cones, each carpel bearing two ovules on its margin. In Cycas,\nhowever, no female cone is produced, but the leaf-like carpels, bearing\nfrom two to six ovules each, are borne directly on the main stem of the\nplant in rosettes alternating with those of the ordinary leaves--the\nmost primitive arrangement known in any living seed-plant. The\nwhole Order is relatively primitive, as shown most strikingly in its\ncryptogamic mode of fertilisation, by means of spermatozoids, which it\nshares with the maidenhair tree alone, among recent seed-plants.\n\nIn all the older Mesozoic rocks, from the Trias to the Lower Cretaceous,\nplants of the Cycad class (Cycadophyta, to use Nathorst's comprehensive\nname) are extraordinarily abundant in all parts of the world; in\nfact they were almost as prominent in the flora of those ages as the\nDicotyledons are in that of our own day. In habit and to a great extent\nin anatomy, the Mesozoic Cycadophyta for the most part much resemble the\nrecent Cycadaceae. But, strange to say, it is only in the rarest\ncases that the fructification has proved to be of the simple type\ncharacteristic of the recent family; the vast majority of the abundant\nfertile specimens yielded by the Mesozoic rocks possess a type of\nreproductive apparatus far more elaborate than anything known in\nCycadaceae or other Gymnosperms. The predominant Mesozoic family,\ncharacterised by this advanced reproductive organisation, is known\nas the Bennettiteae; in habit these plants resembled the more stunted\nCycads of the recent flora, but differed from them in the presence of\nnumerous lateral fructifications, like large buds, borne on the stem\namong the crowded bases of the leaves. The organisation of these\nfructifications was first worked out on European specimens by\nCarruthers, Solms-Laubach, Lignier and others, but these observers had\nonly more or less ripe fruits to deal with; the complete structure of\nthe flower has only been elucidated within the last few years by the\nresearches of Wieland on the magnificent American material, derived from\nthe Upper Jurassic and Lower Cretaceous beds of Maryland, Dakota and\nWyoming. (G.R. Wieland, \"American Fossil Cycads\", Carnegie Institution,\nWashington, 1906.) The word \"flower\" is used deliberately, for reasons\nwhich will be apparent from the following brief description, based on\nWieland's observations.\n\nThe fructification is attached to the stem by a thick stalk, which,\nin its upper part, bears a large number of spirally arranged bracts,\nforming collectively a kind of perianth and completely enclosing the\nessential organs of reproduction. The latter consist of a whorl of\nstamens, of extremely elaborate structure, surrounding a central cone\nor receptacle bearing numerous ovules. The stamens resemble the fertile\nfronds of a fern; they are of a compound, pinnate form, and bear\nvery large numbers of pollen-sacs, each of which is itself a compound\nstructure consisting of a number of compartments in which the pollen\nwas formed. In their lower part the stamens are fused together by their\nstalks, like the \"monadelphous\" stamens of a mallow. The numerous ovules\nborne on the central receptacle are stalked, and are intermixed with\nsterile scales; the latter are expanded at their outer ends, which are\nunited to form a kind of pericarp or ovary-wall, only interrupted by the\nprotruding micropyles of the ovules. There is thus an approach to\nthe closed pistil of an Angiosperm, but it is evident that the ovules\nreceived the pollen directly. The whole fructification is of large size;\nin the case of Cycadeoidea dacotensis, one of the species investigated\nby Wieland, the total length, in the bud condition, is about 12 cm.,\nhalf of which belongs to the peduncle.\n\nThe general arrangement of the organs is manifestly the same as in a\ntypical Angiospermous flower, with a central pistil, a surrounding whorl\nof stamens and an enveloping perianth; there is, as we have seen, some\napproach to the closed ovary of an Angiosperm; another point, first\ndiscovered nearly 20 years ago by Solms-Laubach in his investigation of\na British species, is that the seed was practically \"exalbuminous,\" its\ncavity being filled by the large, dicotyledonous embryo, whereas in all\nknown Gymnosperms a large part of the sac is occupied by a nutritive\ntissue, the prothallus or endosperm; here also we have a condition only\nmet with elsewhere among the higher Flowering Plants.\n\nTaking all the characters into account, the indications of affinity\nbetween the Mesozoic Cycadophyta and the Angiosperms appear extremely\nsignificant, as was recognised by Wieland when he first discovered the\nhermaphrodite nature of the Bennettitean flower. The Angiosperm\nwith which he specially compared the fossil type was the Tulip tree\n(Liriodendron) and certainly there is a remarkable analogy with\nthe Magnoliaceous flowers, and with those of related orders such as\nRanunculaceae and the Water-lilies. It cannot, of course, be maintained\nthat the Bennettiteae, or any other Mesozoic Cycadophyta at present\nknown, were on the direct line of descent of the Angiosperms, for there\nare some important points of difference, as, for example, in the great\ncomplexity of the stamens, and in the fact that the ovary-wall\nor pericarp was not formed by the carpels themselves, but by the\naccompanying sterile scale-leaves. Botanists, since the discovery of the\nbisexual flowers of the Bennettiteae, have expressed different views as\nto the nearness of their relation to the higher Flowering Plants, but\nthe points of agreement are so many that it is difficult to resist the\nconviction that a real relation exists, and that the ancestry of the\nAngiosperms, so long shrouded in complete obscurity, is to be sought\namong the great plexus of Cycad-like plants which dominated the flora\nof the world in Mesozoic times. (On this subject see, in addition\nto Wieland's great work above cited, F.W. Oliver, \"Pteridosperms\nand Angiosperms\", \"New Phytologist\", Vol. V. 1906; D.H. Scott,\n\"The Flowering Plants of the Mesozoic Age in the Light of Recent\nDiscoveries\", \"Journal R. Microscop. Soc.\" 1907, and especially E.A.N.\nArber and J. Parkin, \"On the Origin of Angiosperms\", \"Journal Linn.\nSoc.\" (Bot.) Vol. XXXVIII. page 29, 1907.)\n\nThe great complexity of the Bennettitean flower, the earliest known\nfructification to which the word \"flower\" can be applied without forcing\nthe sense, renders it probable, as Wieland and others have pointed\nout, that the evolution of the flower in Angiosperms has consisted\nessentially in a process of reduction, and that the simplest forms\nof flower are not to be regarded as the most primitive. The older\nmorphologists generally took the view that such simple flowers were to\nbe explained as reductions from a more perfect type, and this opinion,\nthough abandoned by many later writers, appears likely to be true when\nwe consider the elaboration of floral structure attained among the\nMesozoic Cycadophyta, which preceded the Angiosperms in evolution.\n\nIf, as now seems probable, the Angiosperms were derived from ancestors\nallied to the Cycads, it would naturally follow that the Dicotyledons\nwere first evolved, for their structure has most in common with that of\nthe Cycadophyta. We should then have to regard the Monocotyledons as\na side-line, diverging probably at a very early stage from the main\ndicotyledonous stock, a view which many botanists have maintained,\nof late, on other grounds. (See especially Ethel Sargant, \"The\nReconstruction of a Race of Primitive Angiosperms\", \"Annals of Botany\",\nVol. XXII. page 121, 1908.) So far, however, as the palaeontological\nrecord shows, the Monocotyledons were little if at all later in their\nappearance than the Dicotyledons, though always subordinate in numbers.\nThe typical and beautifully preserved Palm-wood from Cretaceous rocks\nis striking evidence of the early evolution of a characteristic\nmonocotyledonous family. It must be admitted that the whole question of\nthe evolution of Monocotyledons remains to be solved.\n\nAccepting, provisionally, the theory of the cycadophytic origin of\nAngiosperms, it is interesting to see to what further conclusions we\nare led. The Bennettiteae, at any rate, were still at the gymnospermous\nlevel as regards their pollination, for the exposed micropyles of the\novules were in a position to receive the pollen directly, without the\nintervention of a stigma. It is thus indicated that the Angiosperms\nsprang from a gymnospermous source, and that the two great phyla of\nSeed-plants have not been distinct from the first, though no doubt the\ngreat majority of known Gymnosperms, especially the Coniferae, represent\nbranch-lines of their own.\n\nThe stamens of the Bennettiteae are arranged precisely as in an\nangiospermous flower, but in form and structure they are like the\nfertile fronds of a Fern, in fact the compound pollen-sacs, or synangia\nas they are technically called, almost exactly agree with the spore-sacs\nof a particular family of Ferns--the Marattiaceae, a limited group,\nnow mainly tropical, which was probably more prominent in the later\nPalaeozoic times than at present. The scaly hairs, or ramenta, which\nclothe every part of the plant, are also like those of Ferns.\n\nIt is not likely that the characters in which the Bennettiteae resemble\nthe Ferns came to them directly from ancestors belonging to that class;\nan extensive group of Seed-plants, the Pteridospermeae, existed in\nPalaeozoic times and bear evident marks of affinity with the Fern\nphylum. The fern-like characters so remarkably persistent in the highly\norganised Cycadophyta of the Mesozoic were in all likelihood derived\nthrough the Pteridosperms, plants which show an unmistakable approach to\nthe cycadophytic type.\n\nThe family Bennettiteae thus presents an extraordinary association\nof characters, exhibiting, side by side, features which belong to the\nAngiosperms, the Gymnosperms and the Ferns.\n\nii. ORIGIN OF SEED-PLANTS.\n\nThe general relation of the gymnospermous Seed-plants to the Higher\nCryptogamia was cleared up, independently of fossil evidence, by the\nbrilliant researches of Hofmeister, dating from the middle of the\npast century. (W. Hofmeister, \"On the Germination, Development and\nFructification of the Higher Cryptogamia\", Ray Society, London, 1862.\nThe original German treatise appeared in 1851.) He showed that \"the\nembryo-sac of the Coniferae may be looked upon as a spore remaining\nenclosed in its sporangium; the prothallium which it forms does not come\nto the light.\" (Ibid. page 438.) He thus determined the homologies on\nthe female side. Recognising, as some previous observers had already\ndone, that the microspores of those Cryptogams in which two kinds of\nspore are developed, are equivalent to the pollen-grains of the higher\nplants, he further pointed out that fertilisation \"in the Rhizocarpeae\nand Selaginellae takes place by free spermatozoa, and in the Coniferae\nby a pollen-tube, in the interior of which spermatozoa are probably\nformed\"--a remarkable instance of prescience, for though spermatozoids\nhave not been found in the Conifers proper, they were demonstrated\nin the allied groups Cycadaceae and Ginkgo, in 1896, by the Japanese\nbotanists Ikeno and Hirase. A new link was thus established between the\nGymnosperms and the Cryptogams.\n\nIt remained uncertain, however, from which line of Cryptogams the\ngymnospermous Seed-plants had sprung. The great point of morphological\ncomparison was the presence of two kinds of spore, and this was known to\noccur in the recent Lycopods and Water-ferns (Rhizocarpeae) and was\nalso found in fossil representatives of the third phylum, that of the\nHorsetails. As a matter of fact all the three great Cryptogamic classes\nhave found champions to maintain their claim to the ancestry of the\nSeed-plants, and in every case fossil evidence was called in. For a long\ntime the Lycopods were the favourites, while the Ferns found the least\nsupport. The writer remembers, however, in the year 1881, hearing the\nlate Prof. Sachs maintain, in a lecture to his class, that the descent\nof the Cycads could be traced, not merely from Ferns, but from a\ndefinite family of Ferns, the Marattiaceae, a view which, though in a\nsomewhat crude form, anticipated more modern ideas.\n\nWilliamson appears to have been the first to recognise the presence, in\nthe Carboniferous flora, of plants combining the characters of Ferns and\nCycads. (See especially his \"Organisation of the Fossil Plants of the\nCoal-Measures\", Part XIII. \"Phil. Trans. Royal Soc.\" 1887 B. page 299.)\nThis conclusion was first reached in the case of the genera Heterangium\nand Lyginodendron, plants, which with a wholly fern-like habit, were\nfound to unite an anatomical structure holding the balance between\nthat of Ferns and Cycads, Heterangium inclining more to the former\nand Lyginodendron to the latter. Later researches placed Williamson's\noriginal suggestion on a firmer basis, and clearly proved the\nintermediate nature of these genera, and of a number of others, so far\nas their vegetative organs were concerned. This stage in our knowledge\nwas marked by the institution of the class Cycadofilices by Potonie in\n1897.\n\nNothing, however, was known of the organs of reproduction of the\nCycadofilices, until F.W. Oliver, in 1903, identified a fossil seed,\nLagenostoma Lomaxi, as belonging to Lyginodendron, the identification\ndepending, in the first instance, on the recognition of an identical\nform of gland, of very characteristic structure, on the vegetative\norgans of Lyginodendron and on the cupule enveloping the seed. This\nevidence was supported by the discovery of a close anatomical agreement\nin other respects, as well as by constant association between the seed\nand the plant. (F.W. Oliver and D.H. Scott, \"On the Structure of the\nPalaeozoic Seed, Lagenostoma Lomaxi, etc.\" \"Phil. Trans. Royal Soc.\"\nVol. 197 B. 1904.) The structure of the seed of Lyginodendron, proved to\nbe of the same general type as that of the Cycads, as shown especially\nby the presence of a pollen-chamber or special cavity for the reception\nof the pollen-grains, an organ only known in the Cycads and Ginkgo among\nrecent plants.\n\nWithin a few months after the discovery of the seed of Lyginodendron,\nKidston found the large, nut-like seed of a Neuropteris, another\nfern-like Carboniferous plant, in actual connection with the pinnules\nof the frond, and since then seeds have been observed on the frond in\nspecies of Aneimites and Pecopteris, and a vast body of evidence, direct\nor indirect, has accumulated, showing that a large proportion of the\nPalaeozoic plants formerly classed as Ferns were in reality reproduced\nby seeds of the same type as those of recent Cycadaceae. (A summary\nof the evidence will be found in the writer's article \"On the present\nposition of Palaeozoic Botany\", \"Progressus Rei Botanicae\", 1907, page\n139, and \"Studies in Fossil Botany\", Vol. II. (2nd edition) London,\n1909.) At the same time, the anatomical structure, where it is open to\ninvestigation, confirms the suggestion given by the habit, and shows\nthat these early seed-bearing plants had a real affinity with Ferns.\nThis conclusion received strong corroboration when Kidston, in 1905,\ndiscovered the male organs of Lyginodendron, and showed that they were\nidentical with a fructification of the genus Crossotheca, hitherto\nregarded as belonging to Marattiaceous Ferns. (Kidston, \"On the\nMicrosporangia of the Pteridospermeae, etc.\" \"Phil. Trans. Royal Soc.\"\nVol. 198, B. 1906.)\n\nThe general conclusion which follows from the various observations\nalluded to, is that in Palaeozoic times there was a great body of plants\n(including, as it appears, a large majority of the fossils previously\nregarded as Ferns) which had attained the rank of Spermophyta,\nbearing seeds of a Cycadean type on fronds scarcely differing from the\nvegetative foliage, and in other respects, namely anatomy, habit and the\nstructure of the pollen-bearing organs, retaining many of the characters\nof Ferns. From this extensive class of plants, to which the name\nPteridospermeae has been given, it can scarcely be doubted that the\nabundant Cycadophyta, of the succeeding Mesozoic period, were derived.\nThis conclusion is of far-reaching significance, for we have already\nfound reason to think that the Angiosperms themselves sprang, in\nlater times, from the Cycadophytic stock; it thus appears that the\nFern-phylum, taken in a broad sense, ultimately represents the source\nfrom which the main line of descent of the Phanerogams took its rise.\n\nIt must further be borne in mind that in the Palaeozoic period there\nexisted another group of seed-bearing plants, the Cordaiteae, far more\nadvanced than the Pteridospermeae, and in many respects approaching the\nConiferae, which themselves begin to appear in the latest Palaeozoic\nrocks. The Cordaiteae, while wholly different in habit from the\ncontemporary fern-like Seed-plants, show unmistakable signs of a common\norigin with them. Not only is there a whole series of forms\nconnecting the anatomical structure of the Cordaiteae with that of the\nLyginodendreae among Pteridosperms, but a still more important point is\nthat the seeds of the Cordaiteae, which have long been known, are of\nthe same Cycadean type as those of the Pteridosperms, so that it is not\nalways possible, as yet, to discriminate between the seeds of the two\ngroups. These facts indicate that the same fern-like stock which gave\nrise to the Cycadophyta and through them, as appears probable, to the\nAngiosperms, was also the source of the Cordaiteae, which in their turn\nshow manifest affinity with some at least of the Coniferae. Unless the\nlatter are an artificial group, a view which does not commend itself to\nthe writer, it would appear probable that the Gymnosperms generally,\nas well as the Angiosperms, were derived from an ancient race of\nCryptogams, most nearly related to the Ferns. (Some botanists, however,\nbelieve that the Coniferae, or some of them, are probably more nearly\nrelated to the Lycopods. See Seward and Ford, \"The Araucarieae, Recent\nand Extinct\", \"Phil. Trans. Royal Soc.\" Vol. 198 B. 1906.)\n\nIt may be mentioned here that the small gymnospermous group Gnetales\n(including the extraordinary West African plant Welwitschia) which were\nformerly regarded by some authorities as akin to the Equisetales, have\nrecently been referred, on better grounds, to a common origin with the\nAngiosperms, from the Mesozoic Cycadophyta.\n\nThe tendency, therefore, of modern work on the palaeontological record\nof the Seed-plants has been to exalt the importance of the Fern-phylum,\nwhich, on present evidence, appears to be that from which the great\nmajority, possibly the whole, of the Spermophyta have been derived.\n\nOne word of caution, however, is necessary. The Seed-plants are of\nenormous antiquity; both the Pteridosperms and the more highly organised\nfamily Cordaiteae, go back as far in geological history (namely to the\nDevonian) as the Ferns themselves or any other Vascular Cryptogams. It\nmust therefore be understood that in speaking of the derivation of the\nSpermophyta from the Fern-phylum, we refer to that phylum at a very\nearly stage, probably earlier than the most ancient period to which\nour record of land-plants extends. The affinity between the oldest\nSeed-plants and the Ferns, in the widest sense, seems established, but\nthe common stock from which they actually arose is still unknown; though\nno doubt nearer to the Ferns than to any other group, it must have\ndiffered widely from the Ferns as we now know them, or perhaps even from\nany which the fossil record has yet revealed to us.\n\niii. THE ORIGIN OF THE HIGHER CRYPTOGAMIA.\n\nThe Sub-kingdom of the higher Spore-plants, the Cryptogamia possessing a\nvascular system, was more prominent in early geological periods than at\npresent. It is true that the dominance of the Pteridophyta in Palaeozoic\ntimes has been much exaggerated owing to the assumption that everything\nwhich looked like a Fern really was a Fern. But, allowing for the fact,\nnow established, that most of the Palaeozoic fern-like plants were\nalready Spermophyta, there remains a vast mass of Cryptogamic forms\nof that period, and the familiar statement that they formed the main\nconstituent of the Coal-forests still holds good. The three\nclasses, Ferns (Filicales), Horsetails (Equisetales) and Club-mosses\n(Lycopodiales), under which we now group the Vascular Cryptogams, all\nextend back in geological history as far as we have any record of the\nflora of the land; in the Palaeozoic, however, a fourth class, the\nSphenophyllales, was present.\n\nAs regards the early history of the Ferns, which are of special interest\nfrom their relation to the Seed-plants, it is impossible to speak quite\npositively, owing to the difficulty of discriminating between true\nfossil Ferns and the Pteridosperms which so closely simulated them.\nThe difficulty especially affects the question of the position of\nMarattiaceous Ferns in the Palaeozoic Floras. This family, now so\nrestricted, was until recently believed to have been one of the\nmost important groups of Palaeozoic plants, especially during later\nCarboniferous and Permian times. Evidence both from anatomy and from\nsporangial characters appeared to establish this conclusion. Of late,\nhowever, doubts have arisen, owing to the discovery that some\nsupposed members of the Marattiaceae bore seeds, and that a form of\nfructification previously referred to that family (Crossotheca) was\nreally the pollen-bearing apparatus of a Pteridosperm (Lyginodendron).\nThe question presents much difficulty; though it seems certain that our\nideas of the extent of the family in Palaeozoic times will have to be\nrestricted, there is still a decided balance of evidence in favour\nof the view that a considerable body of Marattiaceous Ferns actually\nexisted. The plants in question were of large size (often arborescent)\nand highly organised--they represent, in fact, one of the highest\ndevelopments of the Fern-stock, rather than a primitive type of the\nclass.\n\nThere was, however, in the Palaeozoic period, a considerable group of\ncomparatively simple Ferns (for which Arber has proposed the collective\nname Primofilices); the best known of these are referred to the family\nBotryopterideae, consisting of plants of small or moderate dimensions,\nwith, on the whole, a simple anatomical structure, in certain cases\nactually simpler than that of any recent Ferns. On the other hand the\nsporangia of these plants were usually borne on special fertile fronds,\na mark of rather high differentiation. This group goes back to the\nDevonian and includes some of the earliest types of Fern with which we\nare acquainted. It is probable that the Primofilices (though not the\nparticular family Botryopterideae) represent the stock from which the\nvarious families of modern Ferns, already developed in the Mesozoic\nperiod, may have sprung.\n\nNone of the early Ferns show any clear approach to other classes of\nVascular Cryptogams; so far as the fossil record affords any evidence,\nFerns have always been plants with relatively large and usually compound\nleaves. There is no indication of their derivation from a microphyllous\nancestry, though, as we shall see, there is some slight evidence for the\nconverse hypothesis. Whatever the origin of the Ferns may have been it\nis hidden in the older rocks.\n\nIt has, however, been held that certain other Cryptogamic phyla had\na common origin with the Ferns. The Equisetales are at present a\nwell-defined group; even in the rich Palaeozoic floras the habit,\nanatomy and reproductive characters usually render the members of this\nclass unmistakable, in spite of the great development and stature which\nthey then attained. It is interesting, however, to find that in the\noldest known representatives of the Equisetales the leaves were highly\ndeveloped and dichotomously divided, thus differing greatly from the\nmere scale-leaves of the recent Horsetails, or even from the simple\nlinear leaves of the later Calamites. The early members of the class, in\ntheir forked leaves, and in anatomical characters, show an approximation\nto the Sphenophyllales, which are chiefly represented by the large genus\nSphenophyllum, ranging through the Palaeozoic from the Middle Devonian\nonwards. These were plants with rather slender, ribbed stems, bearing\nwhorls of wedge-shaped or deeply forked leaves, six being the typical\nnumber in each whorl. From their weak habit it has been conjectured,\nwith much probability, that they may have been climbing plants, like the\nscrambling Bedstraws of our hedgerows. The anatomy of the stem is simple\nand root-like; the cones are remarkable for the fact that each scale or\nsporophyll is a double structure, consisting of a lower, usually sterile\nlobe and one or more upper lobes bearing the sporangia; in one species\nboth parts of the sporophyll were fertile. Sphenophyllum was evidently\nmuch specialised; the only other known genus is based on an isolated\ncone, Cheirostrobus, of Lower Carboniferous age, with an extraordinarily\ncomplex structure. In this genus especially, but also in the entire\ngroup, there is an evident relation to the Equisetales; hence it is of\ngreat interest that Nathorst has described, from the Devonian of Bear\nIsland in the Arctic regions, a new genus Pseudobornia, consisting of\nlarge plants, remarkable for their highly compound leaves which,\nwhen found detached, were taken for the fronds of a Fern. The whorled\narrangement of the leaves, and the habit of the plant, suggest\naffinities either with the Equisetales or the Sphenophyllales; Nathorst\nmakes the genus the type of a new class, the Pseudoborniales. (A.G.\nNathorst, \"Zur Oberdevonischen Flora der Baren-Insel\", \"Kongl. Svenska\nVetenskaps-Akademiens Handlingar\" Bd. 36, No. 3, Stockholm, 1902.)\n\nThe available data, though still very fragmentary, certainly suggest\nthat both Equisetales and Sphenophyllales may have sprung from a\ncommon stock having certain fern-like characters. On the other hand the\nSphenophylls, and especially the peculiar genus Cheirostrobus, have in\ntheir anatomy a good deal in common with the Lycopods, and of late years\nthey have been regarded as the derivatives of a stock common to\nthat class and the Equisetales. At any rate the characters of the\nSphenophyllales and of the new group Pseudoborniales suggest the\nexistence, at a very early period, of a synthetic race of plants,\ncombining the characters of various phyla of the Vascular Cryptogams.\nIt may further be mentioned that the Psilotaceae, an isolated epiphytic\nfamily hitherto referred to the Lycopods, have been regarded by several\nrecent authors as the last survivors of the Sphenophyllales, which they\nresemble both in their anatomy and in the position of their sporangia.\n\nThe Lycopods, so far as their early history is known, are remarkable\nrather for their high development in Palaeozoic times than for any\nindications of a more primitive ancestry. In the recent Flora, two\nof the four living genera (Excluding Psilotaceae.) (Selaginella and\nIsoetes) have spores of two kinds, while the other two (Lycopodium and\nPhylloglossum) are homosporous. Curiously enough, no certain instance\nof a homosporous Palaeozoic Lycopod has yet been discovered, though\nwell-preserved fructifications are numerous. Wherever the facts have\nbeen definitely ascertained, we find two kinds of spore, differentiated\nquite as sharply as in any living members of the group. Some of the\nPalaeozoic Lycopods, in fact, went further, and produced bodies of the\nnature of seeds, some of which were actually regarded, for many\nyears, as the seeds of Gymnosperms. This specially advanced form of\nfructification goes back at least as far as the Lower Carboniferous,\nwhile the oldest known genus of Lycopods, Bothrodendron, which is found\nin the Devonian, though not seed-bearing, was typically heterosporous,\nif we may judge from the Coal-measure species. No doubt homosporous\nLycopods existed, but the great prevalence of the higher mode of\nreproduction in days which to us appear ancient, shows how long a course\nof evolution must have already been passed through before the oldest\nknown members of the group came into being. The other characters of\nthe Palaeozoic Lycopods tell the same tale; most of them attained\nthe stature of trees, with a corresponding elaboration of anatomical\nstructure, and even the herbaceous forms show no special simplicity.\nIt appears from recent work that herbaceous Lycopods, indistinguishable\nfrom our recent Selaginellas, already existed in the time of the\nCoal-measures, while one herbaceous form (Miadesmia) is known to have\nborne seeds.\n\nThe utmost that can be said for primitiveness of character in Palaeozoic\nLycopods is that the anatomy of the stem, in its primary ground-plan, as\ndistinguished from its secondary growth, was simpler than that of most\nLycopodiums and Selaginellas at the present day. There are also some\npeculiarities in the underground organs (Stigmaria) which suggest the\npossibility of a somewhat imperfect differentiation between root and\nstem, but precisely parallel difficulties are met with in the case of\nthe living Selaginellas, and in some degree in species of Lycopodium.\n\nIn spite of their high development in past ages the Lycopods, recent\nand fossil, constitute, on the whole, a homogeneous group, and there is\nlittle at present to connect them with other phyla. Anatomically some\nrelation to the Sphenophylls is indicated, and perhaps the recent\nPsilotaceae give some support to this connection, for while their\nnearest alliance appears to be with the Sphenophylls, they approach the\nLycopods in anatomy, habit, and mode of branching.\n\nThe typically microphyllous character of the Lycopods, and the simple\nrelation between sporangium and sporophyll which obtains throughout the\nclass, have led various botanists to regard them as the most primitive\nphylum of the Vascular Cryptogams. There is nothing in the fossil record\nto disprove this view, but neither is there anything to support it, for\nthis class so far as we know is no more ancient than the megaphyllous\nCryptogams, and its earliest representatives show no special simplicity.\nIf the indications of affinity with Sphenophylls are of any value\nthe Lycopods are open to suspicion of reduction from a megaphyllous\nancestry, but there is no direct palaeontological evidence for such a\nhistory.\n\nThe general conclusions to which we are led by a consideration of the\nfossil record of the Vascular Cryptogams are still very hypothetical,\nbut may be provisionally stated as follows:\n\nThe Ferns go back to the earliest known period. In Mesozoic times\npractically all the existing families had appeared; in the Palaeozoic\nthe class was less extensive than formerly believed, a majority of the\nsupposed Ferns of that age having proved to be seed-bearing plants. The\noldest authentic representatives of the Ferns were megaphyllous plants,\nbroadly speaking, of the same type as those of later epochs, though\ndiffering much in detail. As far back as the record extends they show no\nsign of becoming merged with other phyla in any synthetic group.\n\nThe Equisetales likewise have a long history, and manifestly attained\ntheir greatest development in Palaeozoic times. Their oldest forms show\nan approach to the extinct class Sphenophyllales, which connects them\nto some extent, by anatomical characters, with the Lycopods. At the\nsame time the oldest Equisetales show a somewhat megaphyllous character,\nwhich was more marked in the Devonian Pseudoborniales. Some remote\naffinity with the Ferns (which has also been upheld on other grounds)\nmay thus be indicated. It is possible that in the Sphenophyllales we\nmay have the much-modified representatives of a very ancient synthetic\ngroup.\n\nThe Lycopods likewise attained their maximum in the Palaeozoic, and\nshow, on the whole, a greater elaboration of structure in their early\nforms than at any later period, while at the same time maintaining a\nconsiderable degree of uniformity in morphological characters throughout\ntheir history. The Sphenophyllales are the only other class with which\nthey show any relation; if such a connection existed, the common point\nof origin must lie exceedingly far back.\n\nThe fossil record, as at present known, cannot, in the nature of things,\nthrow any direct light on what is perhaps the most disputed question in\nthe morphology of plants--the origin of the alternating generations of\nthe higher Cryptogams and the Spermophyta. At the earliest period\nto which terrestrial plants have been traced back all the groups of\nVascular Cryptogams were in a highly advanced stage of evolution, while\ninnumerable Seed-plants--presumably the descendants of Cryptogamic\nancestors--were already flourishing. On the other hand we know\npractically nothing of Palaeozoic Bryophyta, and the evidence even for\ntheir existence at that period cannot be termed conclusive. While\nthere are thus no palaeontological grounds for the hypothesis that the\nVascular plants came of a Bryophytic stock, the question of their actual\norigin remains unsolved.\n\nIII. NATURAL SELECTION.\n\nHitherto we have considered the palaeontological record of plants in\nrelation to Evolution. The question remains, whether the record\nthrows any light on the theory of which Darwin and Wallace were the\nauthors--that of Natural Selection. The subject is clearly one which\nmust be investigated by other methods than those of the palaeontologist;\nstill there are certain important points involved, on which the\npalaeontological record appears to bear.\n\nOne of these points is the supposed distinction between morphological\nand adaptive characters, on which Nageli, in particular, laid so much\nstress. The question is a difficult one; it was discussed by Darwin\n(\"Origin of Species\" (6th edition), pages 170-176.), who, while\nshowing that the apparent distinction is in part to be explained by our\nimperfect knowledge of function, recognised the existence of important\nmorphological characters which are not adaptations. The following\npassage expresses his conclusion. \"Thus, as I am inclined to believe,\nmorphological differences, which we consider as important--such as\nthe arrangement of the leaves, the divisions of the flower or of the\novarium, the position of the ovules, etc.--first appeared in many cases\nas fluctuating variations, which sooner or later became constant through\nthe nature of the organism and of the surrounding conditions, as well\nas through the inter-crossing of distinct individuals, but not through\nnatural selection; for as these morphological characters do not affect\nthe welfare of the species, any slight deviations in them could not have\nbeen governed or accumulated through this latter agency.\" (Ibid. page\n176.)\n\nThis is a sufficiently liberal concession; Nageli, however, went much\nfurther when he said: \"I do not know among plants a morphological\nmodification which can be explained on utilitarian principles.\" (See\n\"More Letters\", Vol. II. page 375 (footnote).) If this were true the\nfield of Natural Selection would be so seriously restricted, as to leave\nthe theory only a very limited importance.\n\nIt can be shown, as the writer believes, that many typical\n\"morphological characters,\" on which the distinction between great\nclasses of plants is based, were adaptive in origin, and even that their\nconstancy is due to their functional importance. Only one or two cases\nwill be mentioned, where the fossil evidence affects the question.\n\nThe pollen-tube is one of the most important morphological characters of\nthe Spermophyta as now existing--in fact the name Siphonogama is used\nby Engler in his classification, as expressing a peculiarly constant\ncharacter of the Seed-plants. Yet the pollen-tube is a manifest\nadaptation, following on the adoption of the seed-habit, and serving\nfirst to bring the spermatozoids with greater precision to their\ngoal, and ultimately to relieve them of the necessity for independent\nmovement. The pollen-tube is constant because it has proved to be\nindispensable.\n\nIn the Palaeozoic Seed-plants there are a number of instances in which\nthe pollen-grains, contained in the pollen-chamber of a seed, are so\nbeautifully preserved that the presence of a group of cells within the\ngrain can be demonstrated; sometimes we can even see how the cell-walls\nbroke down to emit the sperms, and quite lately it is said that the\nsperms themselves have been recognised. (F.W. Oliver, \"On Physostoma\nelegans, an archaic type of seed from the Palaeozoic Rocks\", \"Annals of\nBotany\", January, 1909. See also the earlier papers there cited.) In\nno case, however, is there as yet any satisfactory evidence for\nthe formation of a pollen-tube; it is probable that in these early\nSeed-plants the pollen-grains remained at about the evolutionary level\nof the microspores in Pilularia or Selaginella, and discharged their\nspermatozoids directly, leaving them to find their own way to the\nfemale cells. It thus appears that there were once Spermophyta without\npollen-tubes. The pollen-tube method ultimately prevailed, becoming a\nconstant \"morphological character,\" for no other reason than because,\nunder the new conditions, it provided a more perfect mechanism for the\naccomplishment of the act of fertilisation. We have still, in the Cycads\nand Ginkgo, the transitional case, where the tube remains short, serves\nmainly as an anchor and water-reservoir, but yet is able, by its slight\ngrowth, to give the spermatozoids a \"lift\" in the right direction. In\nother Seed-plants the sperms are mere passengers, carried all the way by\nthe pollen-tube; this fact has alone rendered the Angiospermous method\nof fertilisation through a stigma possible.\n\nWe may next take the seed itself--the very type of a morphological\ncharacter. Our fossil record does not go far enough back to tell us the\norigin of the seed in the Cycadophyta and Pteridosperms (the main line\nof its development) but some interesting sidelights may be obtained from\nthe Lycopod phylum. In two Palaeozoic genera, as we have seen, seed-like\norgans are known to have been developed, resembling true seeds in the\npresence of an integument and of a single functional embryo-sac, as well\nas in some other points. We will call these organs \"seeds\" for the sake\nof shortness. In one genus (Lepidocarpon) the seeds were borne on a cone\nindistinguishable from that of the ordinary cryptogamic Lepidodendreae,\nthe typical Lycopods of the period, while the seed itself retained\nmuch of the detailed structure of the sporangium of that family. In the\nsecond genus, Miadesmia, the seed-bearing plant was herbaceous, and much\nlike a recent Selaginella. (See Margaret Benson, \"Miadesmia membranacea,\na new Palaeozoic Lycopod with a seed-like structure\", \"Phil. Trans.\nRoyal Soc. Vol.\" 199, B. 1908.) The seeds of the two genera are\ndifferently constructed, and evidently had an independent origin. Here,\nthen, we have seeds arising casually, as it were, at different points\namong plants which otherwise retain all the characters of their\ncryptogamic fellows; the seed is not yet a morphological character of\nimportance. To suppose that in these isolated cases the seed sprang into\nbeing in obedience to a Law of Advance (\"Vervollkommungsprincip\"),\nfrom which other contemporary Lycopods were exempt, involves us in\nunnecessary mysticism. On the other hand it is not difficult to see how\nthese seeds may have arisen, as adaptive structures, under the influence\nof Natural Selection. The seed-like structure afforded protection to the\nprothallus, and may have enabled the embryo to be launched on the world\nin greater security. There was further, as we may suppose, a gain in\ncertainty of fertilisation. As the writer has pointed out elsewhere,\nthe chances against the necessary association of the small male with the\nlarge female spores must have been enormously great when the cones were\nborne high up on tall trees. The same difficulty may have existed in the\ncase of the herbaceous Miadesmia, if, as Miss Benson conjectures, it was\nan epiphyte. One way of solving the problem was for pollination to take\nplace while the megaspore was still on the parent plant, and this is\njust what the formation of an ovule or seed was likely to secure.\n\nThe seeds of the Pteridosperms, unlike those of the Lycopod stock,\nhave not yet been found in statu nascendi--in all known cases they were\nalready highly developed organs and far removed from the cryptogamic\nsporangium. But in two respects we find that these seeds, or some\nof them, had not yet realised their possibilities. In the seed\nof Lyginodendron and other cases the micropyle, or orifice of the\nintegument, was not the passage through which the pollen entered; the\nopen neck of the pollen-chamber protruded through the micropyle and\nitself received the pollen. We have met with an analogous case, at a\nmore advanced stage of evolution, in the Bennettiteae, where the wall\nof the gynaecium, though otherwise closed, did not provide a stigma to\ncatch the pollen, but allowed the micropyles of the ovules to protrude\nand receive the pollen in the old gymnospermous fashion. The integument\nin the one case and the pistil in the other had not yet assumed all\nthe functions to which the organ ultimately became adapted. Again, no\nPalaeozoic seed has yet been found to contain an embryo, though the\npreservation is often good enough for it to have been recognised if\npresent. It is probable that the nursing of the embryo had not yet come\nto be one of the functions of the seed, and that the whole embryonic\ndevelopment was relegated to the germination stage.\n\nIn these two points, the reception of the pollen by the micropyle and\nthe nursing of the embryo, it appears that many Palaeozoic seeds\nwere imperfect, as compared with the typical seeds of later times.\nAs evolution went on, one function was superadded on another, and\nit appears impossible to resist the conclusion that the whole\ndifferentiation of the seed was a process of adaptation, and\nconsequently governed by Natural Selection, just as much as the\nspecialisation of the rostellum in an Orchid, or of the pappus in a\nComposite.\n\nDid space allow, other examples might be added. We may venture to\nmaintain that the glimpses which the fossil record allows us into early\nstages in the evolution of organs now of high systematic importance,\nby no means justify the belief in any essential distinction between\nmorphological and adaptive characters.\n\nAnother point, closely connected with Darwin's theory, on which the\nfossil history of plants has been supposed to have some bearing, is\nthe question of Mutation, as opposed to indefinite variation. Arber and\nParkin, in their interesting memoir on the Origin of Angiosperms,\nhave suggested calling in Mutation to explain the apparently sudden\ntransition from the cycadean to the angiospermous type of foliage, in\nlate Mesozoic times, though they express themselves with much caution,\nand point out \"a distinct danger that Mutation may become the last\nresort of the phylogenetically destitute\"!\n\nThe distinguished French palaeobotanists, Grand'Eury (C. Grand'Eury,\n\"Sur les mutations de quelques Plantes fossiles du Terrain houiller\".\n\"Comptes Rendus\", CXLII. page 25, 1906.) and Zeiller (R. Zeiller\n\"Les Vegetaux fossiles et leurs Enchainements\", \"Revue du Mois\", III.\nFebruary, 1907.), are of opinion, to quote the words of the latter\nwriter, that the facts of fossil Botany are in agreement with the sudden\nappearance of new forms, differing by marked characters from those that\nhave given them birth; he adds that these results give more amplitude\nto this idea of Mutation, extending it to groups of a higher order,\nand even revealing the existence of discontinuous series between the\nsuccessive terms of which we yet recognise bonds of filiation. (Loc.\ncit. page 23.)\n\nIf Zeiller's opinion should be confirmed, it would no doubt be a serious\nblow to the Darwinian theory. As Darwin said: \"Under a scientific point\nof view, and as leading to further investigation, but little advantage\nis gained by believing that new forms are suddenly developed in an\ninexplicable manner from old and widely different forms, over the old\nbelief in the creation of species from the dust of the earth.\" (\"Origin\nof Species\", page 424.)\n\nIt most however be pointed out, that such mutations as Zeiller, and to\nsome extent Arber and Parkin, appear to have in view, bridging the gulf\nbetween different Orders and Classes, bear no relation to any mutations\nwhich have been actually observed, such as the comparatively small\nchanges, of sub-specific value, described by De Vries in the type-case\nof Oenothera Lamarckiana. The results of palaeobotanical research have\nundoubtedly tended to fill up gaps in the Natural System of plants--that\nmany such gaps still persist is not surprising; their presence may well\nserve as an incentive to further research but does not, as it seems\nto the writer, justify the assumption of changes in the past, wholly\nwithout analogy among living organisms.\n\nAs regards the succession of species, there are no greater authorities\nthan Grand'Eury and Zeiller, and great weight must be attached to their\nopinion that the evidence from continuous deposits favours a somewhat\nsudden change from one specific form to another. At the same time\nit will be well to bear in mind that the subject of the \"absence of\nnumerous intermediate varieties in any single formation\" was fully\ndiscussed by Darwin. (\"Origin of Species\", pages 275-282, and page\n312.); the explanation which he gave may go a long way to account for\nthe facts which recent writers have regarded as favouring the theory of\nsaltatory mutation.\n\nThe rapid sketch given in the present essay can do no more than call\nattention to a few salient points, in which the palaeontological records\nof plants has an evident bearing on the Darwinian theory. At the present\nday the whole subject of palaeobotany is a study in evolution, and\nderives its chief inspiration from the ideas of Darwin and Wallace. In\nreturn it contributes something to the verification of their teaching;\nthe recent progress of the subject, in spite of the immense difficulties\nwhich still remain, has added fresh force to Darwin's statement that\n\"the great leading facts in palaeontology agree admirably with the\ntheory of descent with modification through variation and natural\nselection.\" (Ibid. page 313.)\n\n\n\n\nXIII. THE INFLUENCE OF ENVIRONMENT ON THE FORMS OF PLANTS. By Georg\nKlebs, PH.D.\n\nProfessor of Botany in the University of Heidelberg.\n\n\nThe dependence of plants on their environment became the object of\nscientific research when the phenomena of life were first investigated\nand physiology took its place as a special branch of science. This\noccurred in the course of the eighteenth century as the result of the\npioneer work of Hales, Duhamel, Ingenhousz, Senebier and others. In\nthe nineteenth century, particularly in the second half, physiology\nexperienced an unprecedented development in that it began to concern\nitself with the experimental study of nutrition and growth, and with\nthe phenomena associated with stimulus and movement; on the other hand,\nphysiology neglected phenomena connected with the production of form, a\ndepartment of knowledge which was the province of morphology, a purely\ndescriptive science. It was in the middle of the last century that the\ngrowth of comparative morphology and the study of phases of development\nreached their highest point.\n\nThe forms of plants appeared to be the expression of their inscrutable\ninner nature; the stages passed through in the development of the\nindividual were regarded as the outcome of purely internal and hidden\nlaws. The feasibility of experimental inquiry seemed therefore remote.\nMeanwhile, the recognition of the great importance of such a causal\nmorphology emerged from the researches of the physiologists of that\ntime, more especially from those of Hofmeister (Hofmeister, \"Allgemeine\nMorphologie\", Leipzig, 1868, page 579.), and afterwards from the work of\nSachs. (Sachs, \"Stoff und Form der Pflanzenorgane\", Vol. I. 1880; Vol.\nII. 1882. \"Gesammelte Abhandlungen uber Pflanzen-Physiologie\", II.\nLeipzig, 1893.) Hofmeister, in speaking of this line of inquiry,\ndescribed it as \"the most pressing and immediate aim of the investigator\nto discover to what extent external forces acting on the organism are of\nimportance in determining its form.\" This advance was the outcome of the\ninfluence of that potent force in biology which was created by Darwin's\n\"Origin of Species\" (1859).\n\nThe significance of the splendid conception of the transformation of\nspecies was first recognised and discussed by Lamarck (1809); as an\nexplanation of transformation he at once seized upon the idea--an\nintelligible view--that the external world is the determining factor.\nLamarck (Lamarck, \"Philosophie zoologique\", pages 223-227. Paris, 1809.)\nendeavoured, more especially, to demonstrate from the behaviour\nof plants that changes in environment induce change in form which\neventually leads to the production of new species. In the case of\nanimals, Lamarck adopted the teleological view that alterations in the\nenvironment first lead to alterations in the needs of the organisms,\nwhich, as the result of a kind of conscious effort of will, induce\nuseful modifications and even the development of new organs. His work\nhas not exercised any influence on the progress of science: Darwin\nhimself confessed in regard to Lamarck's work--\"I got not a fact or idea\nfrom it.\" (\"Life and Letters\", Vol. II. page 215.)\n\nOn a mass of incomparably richer and more essential data Darwin\nbased his view of the descent of organisms and gained for it general\nacceptance; as an explanation of modification he elaborated the\ningeniously conceived selection theory. The question of special interest\nin this connection, namely what is the importance of the influence\nof the environment, Darwin always answered with some hesitation and\ncaution, indeed with a certain amount of indecision.\n\nThe fundamental principle underlying his theory is that of general\nvariability as a whole, the nature and extent of which, especially\nin cultivated organisms, are fully dealt with in his well-known book.\n(Darwin, \"The variation of Animals and Plants under domestication\",\n2 vols., edition 1, 1868; edition 2, 1875; popular edition 1905.) In\nregard to the question as to the cause of variability Darwin adopts a\nconsistently mechanical view. He says: \"These several considerations\nalone render it probable that variability of every kind is directly or\nindirectly caused by changed conditions of life. Or, to put the case\nunder another point of view, if it were possible to expose all the\nindividuals of a species during many generations to absolutely uniform\nconditions of life, there would be no variability.\" (\"The variation of\nAnimals and Plants\" (2nd edition), Vol. II. page 242.) Darwin did not\ndraw further conclusions from this general principle.\n\nVariations produced in organisms by the environment are distinguished by\nDarwin as \"the definite\" and \"the indefinite.\" (Ibid. II. page 260. See\nalso \"Origin of Species\" (6th edition), page 6.) The first occur \"when\nall or nearly all the offspring of an individual exposed to certain\nconditions during several generations are modified in the same manner.\"\nIndefinite variation is much more general and a more important factor in\nthe production of new species; as a result of this, single individuals\nare distinguished from one another by \"slight\" differences, first in\none then in another character. There may also occur, though this is very\nrare, more marked modifications, \"variations which seem to us in our\nignorance to arise spontaneously.\" (\"Origin of Species\" (6th edition),\npage 421.) The selection theory demands the further postulate that such\nchanges, \"whether extremely slight or strongly marked,\" are inherited.\nDarwin was no nearer to an experimental proof of this assumption than to\nthe discovery of the actual cause of variability. It was not until the\nlater years of his life that Darwin was occupied with the \"perplexing\nproblem... what causes almost every cultivated plant to vary\" (\"Life\nand Letters\", Vol. III. page 342.): he began to make experiments on the\ninfluence of the soil, but these were soon given up.\n\nIn the course of the violent controversy which was the outcome of\nDarwin's work the fundamental principles of his teaching were not\nadvanced by any decisive observations. Among the supporters and\nopponents, Nageli (Nageli, \"Theorie der Abstammungslehre\", Munich, 1884;\ncf. Chapter III.) was one of the few who sought to obtain proofs by\nexperimental methods. His extensive cultural experiments with alpine\nHieracia led him to form the opinion that the changes which are induced\nby an alteration in the food-supply, in climate or in habitat, are not\ninherited and are therefore of no importance from the point of view of\nthe production of species. And yet Nageli did attribute an important\ninfluence to the external world; he believed that adaptations of plants\narise as reactions to continuous stimuli, which supply a need and are\ntherefore useful. These opinions, which recall the teleological\naspect of Lamarckism, are entirely unsupported by proof. While other\nfar-reaching attempts at an explanation of the theory of descent were\nformulated both in Nageli's time and afterwards, some in support of,\nothers in opposition to Darwin, the necessity of investigating, from\ndifferent standpoints, the underlying causes, variability and heredity,\nwas more and more realised. To this category belong the statistical\ninvestigations undertaken by Quetelet and Galton, the researches into\nhybridisation, to which an impetus was given by the re-discovery of\nthe Mendelian law of segregation, as also by the culture experiments\non mutating species following the work of de Vries, and lastly the\nconsideration of the question how far variation and heredity are\ngoverned by external influences. These latter problems, which\nare concerned in general with the causes of form-production and\nform-modification, may be treated in a short summary which falls under\ntwo heads, one having reference to the conditions of form-production in\nsingle species, the other being concerned with the conditions governing\nthe transformation of species.\n\nI. THE INFLUENCE OF EXTERNAL CONDITIONS ON FORM-PRODUCTION IN SINGLE\nSPECIES.\n\nThe members of plants, which we express by the terms stem, leaf, flower,\netc. are capable of modification within certain limits; since Lamarck's\ntime this power of modification has been brought more or less into\nrelation with the environment. We are concerned not only with the\nquestion of experimental demonstration of this relationship, but, more\ngenerally, with an examination of the origin of forms, the sequences of\nstages in development that are governed by recognisable causes. We have\nto consider the general problem; to study the conditions of all typical\nas well as of atypic forms, in other words, to found a physiology of\nform.\n\nIf we survey the endless variety of plant-forms and consider the highly\ncomplex and still little known processes in the interior of cells, and\nif we remember that the whole of this branch of investigation came into\nexistence only a few decades ago, we are able to grasp the fact that\na satisfactory explanation of the factors determining form cannot be\ndiscovered all at once. The goal is still far away. We are not concerned\nnow with the controversial question, whether, on the whole, the\nfundamental processes in the development of form can be recognised by\nphysiological means. A belief in the possibility of this can in any case\ndo no harm. What we may and must attempt is this--to discover points\nof attack on one side or another, which may enable us by means of\nexperimental methods to come into closer touch with these elusive\nand difficult problems. While we are forced to admit that there is at\npresent much that is insoluble there remains an inexhaustible supply of\nproblems capable of solution.\n\nThe object of our investigations is the species; but as regards the\nquestion, what is a species, science of to-day takes up a position\ndifferent from that of Darwin. For him it was the Linnean species which\nillustrates variation: we now know, thanks to the work of Jordan,\nde Bary, and particularly to that of de Vries (de Vries, \"Die\nMutationstheorie\", Leipzig, 1901, Vol. I. page 33.), that the Linnean\nspecies consists of a large or small number of entities, elementary\nspecies. In experimental investigation it is essential that observations\nbe made on a pure species, or, as Johannsen (Johannsen, \"Ueber\nErblichkeit in Populationen und reinen Linien\", Jena, 1903.) says, on\na pure \"line.\" What has long been recognised as necessary in the\ninvestigation of fungi, bacteria and algae must also be insisted on in\nthe case of flowering plants; we must start with a single individual\nwhich is reproduced vegetatively or by strict self-fertilisation.\nIn dioecious plants we must aim at the reproduction of brothers and\nsisters.\n\nWe may at the outset take it for granted that a pure species remains the\nsame under similar external conditions; it varies as these vary. IT IS\nCHARACTERISTIC OF A SPECIES THAT IT ALWAYS EXHIBITS A CONSTANT RELATION\nTO A PARTICULAR ENVIRONMENT. In the case of two different species, e.g.\nthe hay and anthrax bacilli or two varieties of Campanula with blue and\nwhite flowers respectively, a similar environment produces a constant\ndifference. The cause of this is a mystery.\n\nAccording to the modern standpoint, the living cell is a complex\nchemico-physical system which is regarded as a dynamical system of\nequilibrium, a conception suggested by Herbert Spencer and which has\nacquired a constantly increasing importance in the light of modern\ndevelopments in physical chemistry. The various chemical compounds,\nproteids, carbohydrates, fats, the whole series of different ferments,\netc. occur in the cell in a definite physical arrangement. The two\nsystems of two species must as a matter of fact possess a constant\ndifference, which it is necessary to define by a special term. We say,\ntherefore, that the SPECIFIC STRUCTURE is different.\n\nBy way of illustrating this provisionally, we may assume that the\nproteids of the two species possess a constant chemical difference. This\nconception of specific structure is specially important in its bearing\non a further treatment of the subject. In the original cell, eventually\nalso in every cell of a plant, the characters which afterwards\nbecome apparent must exist somewhere; they are integral parts of the\ncapabilities or potentialities of specific structure. Thus not only the\ncharacters which are exhibited under ordinary conditions in nature, but\nalso many others which become apparent only under special conditions (In\nthis connection I leave out of account, as before, the idea of material\ncarriers of heredity which since the publication of Darwin's Pangenesis\nhypothesis has been frequently suggested. See my remarks in \"Variationen\nder Bluten\", \"Pringsheim's Jahrb. Wiss. Bot.\" 1905, page 298; also\nDetto, \"Biol. Centralbl.\" 1907, page 81, \"Die Erklarbarkeit der\nOntogenese durch materielle Anlagen\".), are to be included as such\npotentialities in cells; the conception of specific structure includes\nthe WHOLE OF THE POTENTIALITIES OF A SPECIES; specific structure\ncomprises that which we must always assume without being able to explain\nit.\n\nA relatively simple substance, such as oxalate of lime, is known under\na great number of different crystalline forms belonging to different\nsystems (Compare Kohl's work on \"Anatomisch-phys. Untersuchungen uber\nKalksalze\", etc. Marburg, 1889.); these may occur as single crystals,\nconcretions or as concentric sphaerites. The power to assume this\nvariety of form is in some way inherent in the molecular structure,\nthough we cannot, even in this case, explain the necessary connection\nbetween structure and crystalline form. These potentialities can only\nbecome operative under the influence of external conditions; their\nstimulation into activity depends on the degree of concentration of the\nvarious solutions, on the nature of the particular calcium salt, on the\nacid or alkaline reactions. Broadly speaking, the plant cell behaves in\na similar way. The manifestation of each form, which is inherent as a\npotentiality in the specific structure, is ultimately to be referred to\nexternal conditions.\n\nAn insight into this connection is, however, rendered exceedingly\ndifficult, often quite impossible, because the environment never\ndirectly calls into action the potentialities. Its influence is exerted\non what we may call the inner world of the organism, the importance of\nwhich increases with the degree of differentiation. The production of\nform in every plant depends upon processes in the interior of the cells,\nand the nature of these determines which among the possible characters\nis to be brought to light. In no single case are we acquainted with the\ninternal process responsible for the production of a particular\nform. All possible factors may play a part, such as osmotic pressure,\npermeability of the protoplasm, the degree of concentration of the\nvarious chemical substances, etc.; all these factors should be included\nin the category of INTERNAL CONDITIONS. This inner world appears the\nmore hidden from our ken because it is always represented by a certain\ndefinite state, whether we are dealing with a single cell or with a\nsmall group of cells. These have been produced from pre-existing cells\nand they in turn from others; the problem is constantly pushed back\nthrough a succession of generations until it becomes identified with\nthat of the origin of species.\n\nA way, however, is opened for investigation; experience teaches us that\nthis inner world is not a constant factor: on the contrary, it appears\nto be very variable. The dependence of VARIABLE INTERNAL on VARIABLE\nEXTERNAL conditions gives us the key with which research may open the\ndoor. In the lower plants this dependence is at once apparent, each cell\nis directly subject to external influences. In the higher plants with\ntheir different organs, these influences were transmitted to cells in\ncourse of development along exceedingly complex lines. In the case of\nthe growing-point of a bud, which is capable of producing a complete\nplant, direct influences play a much less important part than those\nexerted through other organs, particularly through the roots and leaves,\nwhich are essential in nutrition. These correlations, as we may call\nthem, are of the greatest importance as aids to an understanding of\nform-production. When a bud is produced on a particular part of a plant,\nit undergoes definite internal modifications induced by the influence of\nother organs, the activity of which is governed by the environment, and\nas the result of this it develops along a certain direction; it may,\nfor example, become a flower. The particular direction of development\nis determined before the rudiment is differentiated and is exerted so\nstrongly that further development ensues without interruption, even\nthough the external conditions vary considerably and exert a positively\ninimical influence: this produces the impression that development\nproceeds entirely independently of the outer world. The widespread\nbelief that such independence exists is very premature and at all events\nunproven.\n\nThe state of the young rudiment is the outcome of previous influences of\nthe external world communicated through other organs. Experiments show\nthat in certain cases, if the efficiency of roots and leaves as organs\nconcerned with nutrition is interfered with, the production of flowers\nis affected, and their characters, which are normally very constant,\nundergo far-reaching modifications. To find the right moment at which to\nmake the necessary alteration in the environment is indeed difficult\nand in many cases not yet possible. This is especially the case with\nfertilised eggs, which in a higher degree than buds have acquired,\nthrough parental influences, an apparently fixed internal organisation,\nand this seems to have pre-determined their development. It is, however,\nhighly probable that it will be possible, by influencing the parents,\nto alter the internal organisation and to switch off development on to\nother lines.\n\nHaving made these general observations I will now cite a few of the many\nfacts at our disposal, in order to illustrate the methods and aim of the\nexperimental methods of research. As a matter of convenience I will deal\nseparately with modification of development and with modification of\nsingle organs.\n\nI. EFFECT OF ENVIRONMENT UPON THE COURSE OF DEVELOPMENT.\n\nEvery plant, whether an alga or a flowering plant passes, under natural\nconditions, through a series of developmental stages characteristic of\neach species, and these consist in a regular sequence of definite\nforms. It is impossible to form an opinion from mere observation and\ndescription as to what inner changes are essential for the production of\nthe several forms. We must endeavour to influence the inner factors by\nknown external conditions in such a way that the individual stages in\ndevelopment are separately controlled and the order of their sequence\ndetermined at will by experimental treatment. Such control over the\ncourse of development may be gained with special certainty in the case\nof the lower organisms.\n\nWith these it is practicable to control the principal conditions of\ncultivation and to vary them in various ways. By this means it has been\ndemonstrated that each developmental stage depends upon special external\nconditions, and in cases where our knowledge is sufficient, a particular\nstage may be obtained at will. In the Green Algae (See Klebs, \"Die\nBedingung der Fortpflanzung... \", Jena, 1896; also \"Jahrb. fur\nWiss. Bot.\" 1898 and 1900; \"Probleme der Entwickelung, III.\" \"Biol.\nCentralbl.\" 1904, page 452.), as in the case of Fungi, we may classify\nthe stages of development into purely vegetative growth (growth,\ncell-division, branching), asexual reproduction (formation of zoospores,\nconidia) and sexual processes (formation of male and female sexual\norgans). By modifying the external conditions it is possible to induce\nalgae or fungi (Vaucheria, Saprolegnia) to grow continuously for\nseveral years or, in the course of a few days, to die after an enormous\nproduction of asexual or sexual cells. In some instances even an almost\ncomplete stoppage of growth may be caused, reproductive cells being\nscarcely formed before the organism is again compelled to resort to\nreproduction. Thus the sequence of the different stages in development\ncan be modified as we may desire.\n\nThe result of a more thorough investigation of the determining\nconditions appears to produce at first sight a confused impression\nof all sorts of possibilities. Even closely allied species exhibit\ndifferences in regard to the connection between their development and\nexternal conditions. It is especially noteworthy that the same form in\ndevelopment may be produced as the result of very different alterations\nin the environment. At the same time we can undoubtedly detect a certain\nunity in the multiplicity of the individual phenomena.\n\nIf we compare the factors essential for the different stages in\ndevelopment, we see that the question always resolves itself into one\nof modification of similar conditions common to all life-processes. We\nshould rather have inferred that there exist specific external stimuli\nfor each developmental stage, for instance, certain chemical agencies.\nExperiments hitherto made support the conclusion that QUANTITATIVE\nalterations in the general conditions of life produce different types of\ndevelopment. An alga or a fungus grows so long as all the conditions\nof nutrition remain at a certain optimum for growth. In order to bring\nabout asexual reproduction, e.g. the formation of zoospores, it is\nsometimes necessary to increase the degree of intensity of external\nfactors; sometimes, on the other hand, these must be reduced in\nintensity. In the case of many algae a decrease in light-intensity or\nin the amount of salts in the culture solution, or in the temperature,\ninduces asexual reproduction, while in others, on the contrary, an\nincrease in regard to each of these factors is required to produce\nthe same result. This holds good for the quantitative variations which\ninduce sexual reproduction in algae. The controlling factor is found to\nbe a reduction in the supply of nutritive salts and the exposure of the\nplants to prolonged illumination or, better still, an increase in the\nintensity of the light, the efficiency of illumination depending on the\nconsequent formation of organic substances such as carbohydrates.\n\nThe quantitative alterations of external conditions may be spoken of as\nreleasing stimuli. They produce, in the complex equilibrium of the cell,\nquantitative modifications in the arrangement and distribution of mass,\nby means of which other chemical processes are at once set in motion,\nand finally a new condition of equilibrium is attained. But the\ncommonly expressed view that the environment can as a rule act only as\na releasing agent is incorrect, because it overlooks an essential point.\nThe power of a cell to receive stimuli is only acquired as the result\nof previous nutrition, which has produced a definite condition of\nconcentration of different substances. Quantities are in this case\nthe determining factors. The distribution of quantities is especially\nimportant in the sexual reproduction of algae, for which a vigorous\nproduction of the materials formed during carbon-assimilation appears to\nbe essential.\n\nIn the Flowering plants, on the other hand, for reasons already\nmentioned, the whole problem is more complicated. Investigations on\nchanges in the course of development of fertilised eggs have hitherto\nbeen unsuccessful; the difficulty of influencing egg-cells deeply\nimmersed in tissue constitutes a serious obstacle. Other parts of plants\nare, however, convenient objects of experiment; e.g. the growing apices\nof buds which serve as cuttings for reproductive purposes, or buds on\ntubers, runners, rhizomes, etc. A growing apex consists of cells capable\nof division in which, as in egg-cells, a complete series of latent\npossibilities of development is embodied. Which of these possibilities\nbecomes effective depends upon the action of the outer world transmitted\nby organs concerned with nutrition.\n\nOf the different stages which a flowering plant passes through in the\ncourse of its development we will deal only with one in order to show\nthat, in spite of its great complexity, the problem is, in essentials,\nequally open to attack in the higher plants and in the simplest\norganisms. The most important stage in the life of a flowering plant\nis the transition from purely vegetative growth to sexual\nreproduction--that is, the production of flowers. In certain cases it\ncan be demonstrated that there is no internal cause, dependent simply\non the specific structure, which compels a plant to produce its flowers\nafter a definite period of vegetative growth. (Klebs, \"Willkurliche\nEntwickelungsanderungen\", Jena 1903; see also \"Probleme der\nEntwickelung\", I. II. \"Centralbl.\" 1904.)\n\nOne extreme case, that of exceptionally early flowering, has been\nobserved in nature and more often in cultivation. A number of plants\nunder certain conditions are able to flower soon after germination.\n(Cf. numerous records of this kind by Diels, \"Jugendformen und Bluten\",\nBerlin, 1906.) This shortening of the period of development is exhibited\nin the most striking form in trees, as in the oak (Mobius, \"Beitrage zur\nLehre von der Fortpflanzung\", Jena, 1897, page 89.), flowering seedlings\nof which have been observed from one to three years old, whereas\nnormally the tree does not flower until it is sixty or eighty years old.\n\nAnother extreme case is represented by prolonged vegetative growth\nleading to the complete suppression of flower-production. This result\nmay be obtained with several plants, such as Glechoma, the sugar beet,\nDigitalis, and others, if they are kept during the winter in a warm,\ndamp atmosphere, and in rich soil; in the following spring or summer\nthey fail to flower. (Klebs, \"Willkurliche Aenderungen\", etc. Jena,\n1903, page 130.) Theoretically, however, experiments are of greater\nimportance in which the production of flowers is inhibited by\nvery favourable conditions of nutrition (Klebs, \"Ueber kunstliche\nMetamorphosen\", Stuttgart, 1906, page 115) (\"Abh. Naturf. Ges. Halle\",\nXXV.) occurring at the normal flowering period. Even in the case of\nplants of Sempervivum several years old, which, as is shown by control\nexperiments on precisely similar plants, are on the point of flowering,\nflowering is rendered impossible if they are forced to very vigorous\ngrowth by an abundant supply of water and salts in the spring.\nFlowering, however, occurs, if such plants are cultivated in relatively\ndry sandy soil and in the presence of strong light. Careful researches\ninto the conditions of growth have led, in the cases Sempervivum, to\nthe following results: (1) With a strong light and vigorous\ncarbon-assimilation a considerably increased supply of water and\nnutritive salts produces active vegetative growth. (2) With a vigorous\ncarbon-assimilation in strong light, and a decrease in the supply of\nwater and salts active flower-production is induced. (3) If an average\nsupply of water and salts is given both processes are possible;\nthe intensity of carbon-assimilation determines which of the two is\nmanifested. A diminution in the production of organic substances,\nparticularly of carbohydrates, induces vegetative growth. This can\nbe effected by culture in feeble light or in light deprived of the\nyellow-red rays: on the other hand, flower-production follows an\nincrease in light-intensity. These results are essentially in agreement\nwith well-known observations on cultivated plants, according to which,\nthe application of much moisture, after a plentiful supply of manure\ncomposed of inorganic salts, hinders the flower-production of many\nvegetables, while a decrease in the supply of water and salts favours\nflowering.\n\nii. INFLUENCE OF THE ENVIRONMENT ON THE FORM OF SINGLE ORGANS. (A\nconsiderable number of observations bearing on this question are given\nby Goebel in his \"Experimentelle Morphologie der Pflanzen\", Leipzig,\n1908. It is not possible to deal here with the alteration in anatomical\nstructure; cf. Kuster, \"Pathologische Pflanzenanatomie\", Jena, 1903.)\n\nIf we look closely into the development of a flowering plant, we notice\nthat in a given species differently formed organs occur in definite\npositions. In a potato plant colourless runners are formed from the\nbase of the main stem which grow underground and produce tubers at their\ntips: from a higher level foliage shoots arise nearer the apex. External\nappearances suggest that both the place of origin and the form of these\norgans were predetermined in the egg-cell or in the tuber. But it was\nshown experimentally by the well-known investigator Knight (Knight,\n\"Selection from the Physiological and Horticultural Papers\", London,\n1841.) that tubers may be developed on the aerial stem in place of\nfoliage shoots. These observations were considerably extended by\nVochting. (Vochting, \"Ueber die Bildung der Knollen\", Cassel, 1887; see\nalso \"Bot. Zeit.\" 1902, 87.) In one kind of potato, germinating tubers\nwere induced to form foliage shoots under the influence of a higher\ntemperature; at a lower temperature they formed tuber-bearing shoots.\nMany other examples of the conversion of foliage-shoots into runners and\nrhizomes, or vice versa, have been described by Goebel and others. As in\nthe asexual reproduction of algae quantitative alteration in the amount\nof moisture, light, temperature, etc. determines whether this or that\nform of shoot is produced. If the primordia of these organs are exposed\nto altered conditions of nutrition at a sufficiently early stage a\ncomplete substitution of one organ for another is effected. If the\nrudiment has reached a certain stage in development before it is exposed\nto these influences, extraordinary intermediate forms are obtained,\nbearing the characters of both organs.\n\nThe study of regeneration following injury is of greater importance as\nregards the problem of the development and place of origin of organs.\n(Reference may be made to the full summary of results given by Goebel in\nhis \"Experimentelle Morphologie\", Leipzig and Berlin, 1908, Section IV.)\nOnly in relatively very rare cases is there a complete re-formation\nof the injured organ itself, as e.g. in the growing-apex. Much more\ncommonly injury leads to the development of complementary formations, it\nmay be the rejuvenescence of a hitherto dormant rudiment, or it may be\nthe formation of such ab initio. In all organs, stems, roots, leaves,\nas well as inflorescences, this kind of regeneration, which occurs in\na great variety of ways according to the species, may be observed on\ndetached pieces of the plant. Cases are also known, such, for example,\nas the leaves of many plants which readily form roots but not shoots,\nwhere a complete regeneration does not occur.\n\nThe widely spread power of reacting to wounding affords a very valuable\nmeans of inducing a fresh development of buds and roots on places\nwhere they do not occur in normal circumstances. Injury creates special\nconditions, but little is known as yet in regard to alterations directly\nproduced in this way. Where the injury consists in the separation of\nan organ from its normal connections, the factors concerned are more\ncomprehensible. A detached leaf, e.g., is at once cut off from a supply\nof water and salts, and is deprived of the means of getting rid of\norganic substances which it produces; the result is a considerable\nalteration in the degree of concentration. No experimental investigation\non these lines has yet been made. Our ignorance has often led to the\nview that we are dealing with a force whose specific quality is the\nrestitution of the parts lost by operation; the proof, therefore,\nthat in certain cases a similar production of new roots or buds may\nbe induced without previous injury and simply by a change in external\nconditions assumes an importance. (Klebs, \"Willkurliche Entwickelung\",\npage 100; also, \"Probleme der Entwickelung\", \"Biol. Centralbl.\" 1904,\npage 610.)\n\nA specially striking phenomenon of regeneration, exhibited also by\nuninjured plants, is afforded by polarity, which was discovered by\nVochting. (See the classic work of Vochting, \"Ueber Organbildung im\nPflanzenreich\", I. Bonn, 1888; also \"Bot. Zeit.\" 1906, page 101; cf.\nGoebel, \"Experimentelle Morphologie\", Leipzig and Berlin, 1908, Section\nV, Polaritat.) It is found, for example, that roots are formed from the\nbase of a detached piece of stem and shoots from the apex. Within\nthe limits of this essay it is impossible to go into this difficult\nquestion; it is, however, important from the point of view of our\ngeneral survey to emphasise the fact that the physiological distinctions\nbetween base and apex of pieces of stem are only of a quantitative\nkind, that is, they consist in the inhibition of certain phenomena or\nin favouring them. As a matter of fact roots may be produced from the\napices of willows and cuttings of other plants; the distinction is thus\nobliterated under the influence of environment. The fixed polarity of\ncuttings from full grown stems cannot be destroyed; it is the expression\nof previous development. Vochting speaks of polarity as a fixed\ninherited character. This is an unconvincing conclusion, as nothing can\nbe deduced from our present knowledge as to the causes which led up to\npolarity. We know that the fertilised egg, like the embryo, is fixed at\none end by which it hangs freely in the embryo-sac and afterwards in\nthe endosperm. From the first, therefore, the two ends have different\nnatures, and these are revealed in the differentiation into root-apex\nand stem-apex. A definite direction in the flow of food-substances\nis correlated with this arrangement, and this eventually leads to a\npolarity in the tissues. This view requires experimental proof, which in\nthe case of the egg-cells of flowering plants hardly appears possible;\nbut it derives considerable support from the fact that in herbaceous\nplants, e.g. Sempervivum (Klebs, \"Variationen der Bluten\", \"Jahrb. Wiss.\nBot.\" 1905, page 260.), rosettes or flower-shoots are formed in response\nto external conditions at the base, in the middle, or at the apex of the\nstem, so that polarity as it occurs under normal conditions cannot be\nthe result of unalterable hereditary factors. On the other hand, the\nlower plants should furnish decisive evidence on this question, and\nthe experiments of Stahl, Winkler, Kniep, and others indicate the right\nmethod of attacking the problem.\n\nThe relation of leaf-form to environment has often been investigated and\nis well known. The leaves of bog and water plants (Cf.Goebel, loc.\ncit. chapter II.; also Gluck, \"Untersuchungen uber Wasser- und\nSumpfgewachse\", Jena, Vols. I.-II. 1905-06.) afford the most striking\nexamples of modifications: according as they are grown in water, moist\nor dry air, the form of the species characteristic of the particular\nhabitat is produced, since the stems are also modified. To the same\ngroup of phenomena belongs the modification of the forms of leaves and\nstems in plants on transplantation from the plains to the mountains\n(Bonnier, \"Recherches sur l'Anatomie experimentale des Vegetaux\",\nCorbeil, 1895.) or vice versa. Such variations are by no means isolated\nexamples. All plants exhibit a definite alteration in form as the result\nof prolonged cultivation in moist or dry air, in strong or feeble\nlight, or in darkness, or in salt solutions of different composition and\nstrength.\n\nEvery individual which is exposed to definite combinations of external\nfactors exhibits eventually the same type of modification. This is the\ntype of variation which Darwin termed \"definite.\" It is easy to realise\nthat indefinite or fluctuating variations belong essentially to the same\nclass of phenomena; both are reactions to changes in environment. In the\nproduction of individual variations two different influences undoubtedly\ncooperate. One set of variations is caused by different external\nconditions, during the production, either of sexual cells or of\nvegetative primordia; another set is the result of varying external\nconditions during the development of the embryo into an adult plant. The\ntwo sets of influences cannot as yet be sharply differentiated. If,\nfor purposes of vegetative reproduction, we select pieces of the\nsame parent-plant of a pure species, the second type of variation\npredominates. Individual fluctuations depend essentially in such cases\non small variations in environment during development.\n\nThese relations must be borne in mind if we wish to understand the\nresults of statistical methods. Since the work of Quetelet, Galton, and\nothers the statistical examination of individual differences in animals\nand plants has become a special science, which is primarily based on the\nconsideration that the application of the theory of probability renders\npossible mathematical statement and control of the results. The facts\nshow that any character, size of leaf, length of stem, the number of\nmembers in a flower, etc. do not vary haphazard but in a very regular\nmanner. In most cases it is found that there is a value which occurs\nmost commonly, the average or medium value, from which the larger and\nsmaller deviations, the so-called plus and minus variations fall away in\na continuous series and end in a limiting value. In the simpler cases\na falling off occurs equally on both sides of the curve; the curve\nconstructed from such data agrees very closely with the Gaussian curve\nof error. In more complicated cases irregular curves of different kinds\nare obtained which may be calculated on certain suppositions.\n\nThe regular fluctuations about a mean according to the rule of\nprobability is often attributed to some law underlying variability. (de\nVries, \"Mutationstheorie\", Vol. I. page 35, Leipzig, 1901.) But there is\nno such law which compels a plant to vary in a particular manner. Every\nexperimental investigation shows, as we have already remarked, that\nthe fluctuation of characters depends on fluctuation in the external\nfactors. The applicability of the method of probability follows from\nthe fact that the numerous individuals of a species are influenced by\na limited number of variable conditions. (Klebs, \"Willkurl. Ent.\" Jena,\n1903, page 141.) As each of these conditions includes within certain\nlimits all possible values and exhibits all possible combinations, it\nfollows that, according to the rules of probability, there must be\na mean value, about which the larger and smaller deviations are\ndistributed. Any character will be found to have the mean value which\ncorresponds with that combination of determining factors which occurs\nmost frequently. Deviations towards plus and minus values will be\ncorrespondingly produced by rarer conditions.\n\nA conclusion of fundamental importance may be drawn from this\nconception, which is, to a certain extent, supported by experimental\ninvestigation. (Klebs, \"Studien uber Variation\", \"Arch. fur Entw.\"\n1907.) There is no normal curve for a particular CHARACTER, there is\nonly a curve for the varying combinations of conditions occurring in\nnature or under cultivation. Under other conditions entirely different\ncurves may be obtained with other variants as a mean value. If, for\nexample, under ordinary conditions the number 10 is the most frequent\nvariant for the stamens of Sedum spectabile, in special circumstances\n(red light) this is replaced by the number 5. The more accurately we\nknow the conditions for a particular form or number, and are able to\nreproduce it by experiment, the nearer we are to achieving our aim of\nrendering a particular variation impossible or of making it dominant.\n\nIn addition to the individual variations of a species, more pronounced\nfluctuations occur relatively rarely and sporadically which are spoken\nof as \"single variations,\" or if specially striking as abnormalities\nor monstrosities. These forms have long attracted the attention of\nmorphologists; a large number of observations of this kind are given\nin the handbooks of Masters (Masters, \"Vegetable Teratology\", London,\n1869.) and Penzig (Penzig, \"Pflanzen-Teratologie\", Vols I. and II. Genua,\n1890-94.) These variations, which used to be regarded as curiosities,\nhave now assumed considerable importance in connection with the causes\nof form-development. They also possess special interest in relation to\nthe question of heredity, a subject which does not at present concern\nus, as such deviations from normal development undoubtedly arise as\nindividual variations induced by the influence of environment.\n\nAbnormal developments of all kinds in stems, leaves, and flowers, may\nbe produced by parasites, insects, or fungi. They may also be induced\nby injury, as Blaringhem (Blaringhem, \"Mutation et traumatismes\", Paris,\n1907.) has more particularly demonstrated, which, by cutting away the\nleading shoots of branches in an early stage of development, caused\nfasciation, torsion, anomalous flowers, etc. The experiments of\nBlaringhem point to the probability that disturbances in the conditions\nof food-supply consequent on injury are the cause of the production of\nmonstrosities. This is certainly the case in my experiments with species\nof Sempervivum (Klebs, \"Kunstliche Metamorphosen\", Stuttgart, 1906.);\nindividuals, which at first formed normal flowers, produced a great\nvariety of abnormalities as the result of changes in nutrition, we\nmay call to mind the fact that the formation of inflorescences occurs\nnormally when a vigorous production of organic compounds, such as\nstarch, sugar, etc. follows a diminution in the supply of mineral\nsalts. On the other hand, the development of inflorescences is entirely\nsuppressed if, at a suitable moment before the actual foundations have\nbeen laid, water and mineral salts are supplied to the roots. If, during\nthe week when the inflorescence has just been laid down and is growing\nvery slowly, the supply of water and salts is increased, the internal\nconditions of the cells are essentially changed. At a later stage, after\nthe elongation of the inflorescence, rosettes of leaves are produced\ninstead of flowers, and structures intermediate between the two kinds of\norgans; a number of peculiar plant-forms are thus obtained (Cf. Lotsy,\n\"Vorlesungen uber Deszendenztheorien\", Vol. II. pl. 3, Jena, 1908.)\nAbnormalities in the greatest variety are produced in flowers by varying\nthe time at which the stimulus is applied, and by the cooperation\nof other factors such as temperature, darkness, etc. In number and\narrangement the several floral members vary within wide limits;\nsepals, petals, stamens, and carpels are altered in form and colour, a\ntransformation of stamens to carpels and from carpels to stamens occurs\nin varying degrees. The majority of the deviations observed had not\npreviously been seen either under natural conditions or in cultivation;\nthey were first brought to light through the influence of external\nfactors.\n\nSuch transformations of flowers become apparent at a time, which is\nseparated by about two months from the period at which the particular\ncause began to act. There is, therefore, no close connection between\nthe appearance of the modifications and the external conditions which\nprevail at the moment. When we are ignorant of the causes which are\noperative so long before the results are seen, we gain the impression\nthat such variations as occur are spontaneous or autonomous expressions\nof the inner nature of the plant. It is much more likely that, as in\nSempervivum, they were originally produced by an external stimulus which\nhad previously reached the sexual cells or the young embryo. In any case\nabnormalities of this kind appear to be of a special type as compared\nwith ordinary fluctuating variations. Darwin pointed out this\ndifference; Bateson (Bateson, \"Materials for the study of Variation\",\nLondon, 1894, page 5.) has attempted to make the distinction sharper, at\nthe same time emphasising its importance in heredity.\n\nBateson applies the term CONTINUOUS to small variations connected with\none another by transitional stages, while those which are more striking\nand characterised from the first by a certain completeness, he names\nDISCONTINUOUS. He drew attention to a great difficulty which stands in\nthe way of Lamarck's hypothesis, as also of Darwin's view. \"According to\nboth theories, specific diversity of form is consequent upon diversity\nof environment, and diversity of environment is thus the ultimate\nmeasure of diversity of specific form. Here then we meet the difficulty\nthat diverse environments often shade into each other insensibly and\nform a continuous series, whereas the Specific Forms of life which\nare subject to them on the whole form a Discontinuous Series.\"\nThis difficulty is, however, not of fundamental importance as well\nauthenticated facts have been adduced showing that by alteration of the\nenvironment discontinuous variations, such as alterations in the number\nand form of members of a flower, may be produced. We can as yet no more\nexplain how this happens than we can explain the existence of continuous\nvariations. We can only assert that both kinds of variation arise\nin response to quantitative alterations in external conditions. The\nquestion as to which kind of variation is produced depends on the\ngreater or less degree of alteration; it is correlated with the state of\nthe particular cells at the moment.\n\nIn this short sketch it is only possible to deal superficially with a\nsmall part of the subject. It has been clearly shown that in view of the\ngeneral dependence of development on the factors of the environment\na number of problems are ready for experimental treatment. One must,\nhowever, not forget that the science of the physiology of form has not\nprogressed beyond its initial stages. Just now our first duty is to\ndemonstrate the dependence on external factors in as many forms of\nplants as possible, in order to obtain a more thorough control of all\nthe different plant-forms. The problem is not only to produce at will\n(and independently of their normal mode of life) forms which occur\nin nature, but also to stimulate into operation potentialities which\nnecessarily lie dormant under the conditions which prevail in nature.\nThe constitution of a species is much richer in possibilities of\ndevelopment than would appear to be the case under normal conditions. It\nremains for man to stimulate into activity all the potentialities.\n\nBut the control of plant-form is only a preliminary step--the foundation\nstones on which to erect a coherent scientific structure. We must\ndiscover what are the internal processes in the cell produced by\nexternal factors, which as a necessary consequence result in the\nappearance of a definite form. We are here brought into contact with the\nmost obscure problem of life. Progress can only be made pari passu with\nprogress in physics and chemistry, and with the growth of our knowledge\nof nutrition, growth, etc.\n\nLet us take one of the simplest cases--an alteration in form. A\ncylindrical cell of the alga Stigeoclonium assumes, as Livingstone\n(Livingstone, \"On the nature of the stimulus which causes the change\nof form, etc.\" \"Botanical Gazette\", XXX. 1900; also XXXII. 1901.) has\nshown, a spherical form when the osmotic pressure of the culture fluid\nis increased; or a spore of Mucor, which, in a sugar solution grows\ninto a branched filament, in the presence of a small quantity of acid\n(hydrogen ions) becomes a comparatively large sphere. (Ritter, \"Ueber\nKugelhefe, etc.\" \"Ber. bot. Gesell.\" Berlin, XXV. page 255, 1907.)\nIn both cases there has undoubtedly been an alteration in the osmotic\npressure of the cell-sap, but this does not suffice to explain the\nalteration in form, since the unknown alterations, which are induced in\nthe protoplasm, must in their turn influence the cell-membrane. In\nthe case of the very much more complex alterations in form, such as we\nencounter in the course of development of plants, there do not appear\nto be any clues which lead us to a deeper insight into the phenomena.\nNevertheless we continue the attempt, seeking with the help of any\navailable hypothesis for points of attack, which may enable us to\nacquire a more complete mastery of physiological methods. To quote a\nsingle example; I may put the question, what internal changes produce a\ntransition from vegetative growth to sexual reproduction?\n\nThe facts, which are as clearly established from the lower as for the\nhigher plants, teach us that quantitative alteration in the environment\nproduces such a transition. This suggests the conclusion that\nquantitative internal changes in the cells, and with them disturbances\nin the degree of concentration, are induced, through which the chemical\nreactions are led in the direction of sexual reproduction. An increase\nin the production of organic substances in the presence of light,\nchiefly of the carbohydrates, with a simultaneous decrease in the amount\nof inorganic salts and water, are the cause of the disturbance and\nat the same time of the alteration in the direction of development.\nPossibly indeed mineral salts as such are not in question, but only in\nthe form of other organic combinations, particularly proteid material,\nso that we are concerned with an alteration in the relation of the\ncarbohydrates and proteids. The difficulties of such researches are very\ngreat because the methods are not yet sufficiently exact to demonstrate\nthe frequently small quantitative differences in chemical composition.\nQuestions relating to the enzymes, which are of the greatest importance\nin all these life-processes, are especially complicated. In any case\nit is the necessary result of such an hypothesis that we must employ\nchemical methods of investigation in dealing with problems connected\nwith the physiology of form.\n\nII. INFLUENCE OF ENVIRONMENT ON THE TRANSFORMATION OF SPECIES.\n\nThe study of the physiology of form-development in a pure species has\nalready yielded results and makes slow but sure progress. The physiology\nof the possibility of the transformation of one species into another is\nbased, as yet, rather on pious hope than on accomplished fact. From\nthe first it appeared to be hopeless to investigate physiologically\nthe origin of Linnean species and at the same time that of the natural\nsystem, an aim which Darwin had before him in his enduring work. The\nhistorical sequence of events, of which an organism is the expression,\ncan only be treated hypothetically with the help of facts supplied\nby comparative morphology, the history of development, geographical\ndistribution, and palaeontology. (See Lotsy, \"Vorlesungen\" (Jena, I.\n1906, II. 1908), for summary of the facts.) A glance at the controversy\nwhich is going on today in regard to different hypotheses shows that\nthe same material may lead different investigators to form entirely\ndifferent opinions. Our ultimate aim is to find a solution of the\nproblem as to the cause of the origin of species. Indeed such\nattempts are now being made: they are justified by the fact that under\ncultivation new and permanent strains are produced; the fundamental\nimportance of this was first grasped by Darwin. New points of view in\nregard to these lines of inquiry have been adopted by H. de Vries\nwho has succeeded in obtaining from Oenothera Lamarckiana a number of\nconstant \"elementary\" species. Even if it is demonstrated that he was\nsimply dealing with the complex splitting up of a hybrid (Bateson,\n\"Reports to the Evolution Committee of the Royal Society\", London, 1902;\ncf. also Lotsy, \"Vorlesungen\", Vol. I. page 234.), the facts adduced in\nno sense lose their very great value.\n\nWe must look at the problem in its simplest form; we find it in every\ncase where a new race differs essentially from the original type in a\nsingle character only; for example, in the colour of the flowers or in\nthe petalody of the stamens (doubling of flowers). In this connection\nwe must keep in view the fact that every visible character in a plant is\nthe resultant of the cooperation of specific structure, with its various\npotentialities, and the influence of the environment. We know, that in\na pure species all characters vary, that a blue-flowering Campanula or\na red Sempervivum can be converted by experiment into white-flowering\nforms, that a transformation of stamens into petals may be caused by\nfungi or by the influence of changed conditions of nutrition, or\nthat plants in dry and poor soil become dwarfed. But so far as the\nexperiments justify a conclusion, it would appear that such alterations\nare not inherited by the offspring. Like all other variations they\nappear only so long as special conditions prevail in the surroundings.\n\nIt has been shown that the case is quite different as regards the\nwhite-flowering, double or dwarf races, because these retain their\ncharacters when cultivated under practically identical conditions, and\nside by side with the blue, single-flowering or tall races. The problem\nmay therefore be stated thus: how can a character, which appears in the\none case only under the strictly limited conditions of the experiment,\nin other cases become apparent under the very much wider conditions of\nordinary cultivation? If a character appears, in these circumstances,\nin the case of all individuals, we then speak of constant races. In such\nsimple cases the essential point is not the creation of a new character\nbut rather an ALTERATION OF THIS CHARACTER IN ACCORDANCE WITH THE\nENVIRONMENT. In the examples mentioned the modified character in the\nsimple varieties (or a number of characters in elementary species)\nappears more or less suddenly and is constant in the above sense. The\nresult is what de Vries has termed a Mutation. In this connection we\nmust bear in mind the fact that no difference, recognisable externally,\nneed exist between individual variation and mutation. Even the most\nminute quantitative difference between two plants may be of specific\nvalue if it is preserved under similar external conditions during many\nsuccessive generations. We do not know how this happens. We may state\nthe problem in other terms; by saying that the specific structure must\nbe altered. It is possible, to some extent, to explain this sudden\nalteration, if we regard it as a chemical alteration of structure either\nin the specific qualities of the proteids or of the unknown carriers\nof life. In the case of many organic compounds their morphological\ncharacters (the physical condition, crystalline form, etc.) are at once\nchanged by alteration of atomic relations or by incorporation of new\nradicals. (For instance ethylchloride (C2H5Cl) is a gas at 21 deg\nC., ethylenechloride (C2H4Cl2) a fluid boiling at 84 deg C., beta\ntrichlorethane (C2H3Cl3) a fluid boiling at 113 deg C.,\nperchlorethane (C2Cl6) a crystalline substance. Klebs, (\"Willkurliche\nEntwickelungsanderungen\" page 158.) Much more important, however, would\nbe an answer to the question, whether an individual variation can be\nconverted experimentally into an inherited character--a mutation in de\nVries's sense.\n\nIn all circumstances we may recognise as a guiding principle the\nassumption adopted by Lamarck, Darwin, and many others, that the\ninheritance of any one character, or in more general terms, the\ntransformation of one species into another, is, in the last instance,\nto be referred to a change in the environment. From a causal-mechanical\npoint of view it is not a priori conceivable that one species can\never become changed into another so long as external conditions remain\nconstant. The inner structure of a species must be essentially altered\nby external influences. Two methods of experimental research may be\nadopted, the effect of crossing distinct species and, secondly, the\neffect of definite factors of the environment.\n\nThe subject of hybridisation is dealt with in another part of this\nessay. It is enough to refer here to the most important fact, that as\nthe result of combinations of characters of different species new and\nconstant forms are produced. Further, Tschermack, Bateson and others\nhave demonstrated the possibility that hitherto unknown inheritable\ncharacters may be produced by hybridisation.\n\nThe other method of producing constant races by the influence of special\nexternal conditions has often been employed. The sporeless races of\nBacteria and Yeasts (Cf. Detto, \"Die Theorie der direkten Anpassung... \",\npages 98 et seq., Jena, 1904; see also Lotsy, \"Vorlesungen\", II. pages\n636 et seq., where other similar cases are described.) are well known,\nin which an internal alteration of the cells is induced by the influence\nof poison or higher temperature, so that the power of producing spores\neven under normal conditions appears to be lost. A similar state of\nthings is found in some races which under certain definite conditions\nlose their colour or their virulence. Among the phanerogams the\ninvestigations of Schubler on cereals afford parallel cases, in which\nthe influence of a northern climate produces individuals which ripen\ntheir seeds early; these seeds produce plants which seed early in\nsouthern countries. Analogous results were obtained by Cieslar in his\nexperiments; seeds of conifers from the Alps when planted in the plains\nproduced plants of slow growth and small diameter.\n\nAll these observations are of considerable interest theoretically; they\nshow that the action of environment certainly induces such internal\nchanges, and that these are transmitted to the next generation. But as\nregards the main question, whether constant races may be obtained by\nthis means, the experiments cannot as yet supply a definite answer. In\nphanerogams, the influence very soon dies out in succeeding generations;\nin the case of bacteria, in which it is only a question of the loss of\na character it is relatively easy for this to reappear. It is not\nimpossible, that in all such cases there is a material hanging-on of\ncertain internal conditions, in consequence of which the modification\nof the character persists for a time in the descendants, although the\noriginal external conditions are no longer present.\n\nThus a slow dying-out of the effect of a stimulus was seen in my\nexperiments on Veronica chamaedrys. (Klebs, \"Kunstliche Metamorphosen\",\nStuttgart, 1906, page 132.) During the cultivation of an artificially\nmodified inflorescence I obtained a race showing modifications in\ndifferent directions, among which twisting was especially conspicuous.\nThis plant, however, does not behave as the twisted race of Dipsacus\nisolated by de Vries (de Vries, \"Mutationstheorie\", Vol. II. Leipzig,\n1903, page 573.), which produced each year a definite percentage of\ntwisted individuals. In the vegetative reproduction of this Veronica the\ntorsion appeared in the first, also in the second and third year, but\nwith diminishing intensity. In spite of good cultivation this character\nhas apparently now disappeared; it disappeared still more quickly in\nseedlings. In another character of the same Veronica chamaedrys the\ninfluence of the environment was stronger. The transformation of the\ninflorescences to foliage-shoots formed the starting-point; it occurred\nonly under narrowly defined conditions, namely on cultivation as a\ncutting in moist air and on removal of all other leaf-buds. In the\nmajority (7/10) of the plants obtained from the transformed shoots, the\nmodification appeared in the following year without any interference.\nOf the three plants which were under observation several years the first\nlost the character in a short time, while the two others still retain\nit, after vegetative propagation, in varying degrees. The same character\noccurs also in some of the seedlings; but anything approaching a\nconstant race has not been produced.\n\nAnother means of producing new races has been attempted by Blaringhem.\n(Blaringhem, \"Mutation et Traumatisme\", Paris, 1907.) On removing at\nan early stage the main shoots of different plants he observed various\nabnormalities in the newly formed basal shoots. From the seeds of such\nplants he obtained races, a large percentage of which exhibited these\nabnormalities. Starting from a male Maize plant with a fasciated\ninflorescence, on which a proportion of the flowers had become male,\na new race was bred in which hermaphrodite flowers were frequently\nproduced. In the same way Blaringhem obtained, among other similar\nresults, a race of barley with branched ears. These races, however,\nbehaved in essentials like those which have been demonstrated by de\nVries to be inconstant, e.g. Trifolium pratense quinquefolium and\nothers. The abnormality appears in a proportion of the individuals\nand only under very special conditions. It must be remembered too that\nBlaringhem worked with old cultivated plants, which from the first had\nbeen disposed to split into a great variety of races. It is possible,\nbut difficult to prove, that injury contributed to this result.\n\nA third method has been adopted by MacDougal (MacDougal, \"Heredity and\nOrigin of species\", \"Monist\", 1906; \"Report of department of botanical\nresearch\", \"Fifth Year-book of the Carnegie Institution of Washington\",\npage 119, 1907.) who injected strong (10 percent) sugar solution or weak\nsolutions of calcium nitrate and zinc sulphate into young carpels of\ndifferent plants. From the seeds of a plant of Raimannia odorata the\ncarpels of which had been thus treated he obtained several plants\ndistinguished from the parent-forms by the absence of hairs and by\ndistinct forms of leaves. Further examination showed that he had here to\ndo with a new elementary species. MacDougal also obtained a more or less\ndistinct mutant of Oenothera biennis. We cannot as yet form an opinion\nas to how far the effect is due to the wound or to the injection of\nfluid as such, or to its chemical properties. This, however, is not so\nessential as to decide whether the mutant stands in any relation to the\ninfluence of external factors. It is at any rate very important that\nthis kind of investigation should be carried further.\n\nIf it could be shown that new and inherited races were obtained by\nMacDougal's method, it would be safe to conclude that the same end might\nbe gained by altering the conditions of the food-stuff conducted to the\nsexual cells. New races or elementary species, however, arise without\nwounding or injection. This at once raises the much discussed question,\nhow far garden-cultivation has led to the creation of new races?\nContrary to the opinion expressed by Darwin and others, de Vries\n(\"Mutationstheorie\", Vol. I. pages 412 et seq.) tried to show that\ngarden-races have been produced only from spontaneous types which occur\nin a wild state or from sub-races, which the breeder has accidentally\ndiscovered but not originated. In a small number of cases only has de\nVries adduced definite proof. On the other side we have the work of\nKorschinsky (Korschinsky, \"Heterogenesis und Evolution\", \"Flora\", 1901.)\nwhich shows that whole series of garden-races have made their appearance\nonly after years of cultivation. In the majority of races we are\nentirely ignorant of their origin.\n\nIt is, however, a fact that if a plant is removed from natural\nconditions into cultivation, a well-marked variation occurs. The\nwell-known plant-breeder L. de Vilmorin (L. de Vilmorin, \"Notices sur\nl'amelioration des plantes\", Paris, 1886, page 36.), speaking from his\nown experience, states that a plant is induced to \"affoler,\" that is\nto exhibit all possible variations from which the breeder may make a\nfurther selection only after cultivation for several generations. The\neffect of cultivation was particularly striking in Veronica chamaedrys\n(Klebs, \"Kunstliche Metamorphosen\", Stuttgart, 1906, page 152.) which,\nin spite of its wide distribution in nature, varies very little. After a\nfew years of cultivation this \"good\" and constant species becomes highly\nvariable. The specimens on which the experiments were made were three\nmodified inflorescence cuttings, the parent-plants of which certainly\nexhibited no striking abnormalities. In a short time many hitherto\nlatent potentialities became apparent, so that characters, never\npreviously observed, or at least very rarely, were exhibited, such\nas scattered leaf-arrangement, torsion, terminal or branched\ninflorescences, the conversion of the inflorescence into foliage-shoots,\nevery conceivable alteration in the colour of flowers, the assumption of\na green colour by parts of the flowers, the proliferation of flowers.\n\nAll this points to some disturbance in the species resulting from\nmethods of cultivation. It has, however, not yet been possible to\nproduce constant races with any one of these modified characters. But\nvariations appeared among the seedlings, some of which, e.g. yellow\nvariegation, were not inheritable, while others have proved constant.\nThis holds good, so far as we know at present, for a small rose-coloured\nform which is to be reckoned as a mutation. Thus the prospect of\nproducing new races by cultivation appears to be full of promise.\n\nSo long as the view is held that good nourishment, i.e. a plentiful\nsupply of water and salts, constitutes the essential characteristic of\ngarden-cultivation, we can hardly conceive that new mutations can be\nthus produced. But perhaps the view here put forward in regard to the\nproduction of form throws new light on this puzzling problem.\n\nGood manuring is in the highest degree favourable to vegetative growth,\nbut is in no way equally favourable to the formation of flowers. The\nconstantly repeated expression, good or favourable nourishment, is not\nonly vague but misleading, because circumstances favourable to growth\ndiffer from those which promote reproduction; for the production of\nevery form there are certain favourable conditions of nourishment, which\nmay be defined for each species. Experience shows that, within definite\nand often very wide limits, it does not depend upon the ABSOLUTE AMOUNT\nof the various food substances, but upon their respective degrees of\nconcentration. As we have already stated, the production of flowers\nfollows a relative increase in the amount of carbohydrates formed in\nthe presence of light, as compared with the inorganic salts on which\nthe formation of albuminous substances depends. (Klebs, \"Kunstliche\nMetamorphosen\", page 117.) The various modifications of flowers are due\nto the fact that a relatively too strong solution of salts is supplied\nto the rudiments of these organs. As a general rule every plant\nform depends upon a certain relation between the different chemical\nsubstances in the cells and is modified by an alteration of that\nrelation.\n\nDuring long cultivation under conditions which vary in very different\ndegrees, such as moisture, the amount of salts, light intensity,\ntemperature, oxygen, it is possible that sudden and special disturbances\nin the relations of the cell substances have a directive influence on\nthe inner organisation of the sexual cells, so that not only inconstant\nbut also constant varieties will be formed.\n\nDefinite proof in support of this view has not yet been furnished, and\nwe must admit that the question as to the cause of heredity remains,\nfundamentally, as far from solution as it was in Darwin's time. As the\nresult of the work of many investigators, particularly de Vries,\nthe problem is constantly becoming clearer and more definite. The\npenetration into this most difficult and therefore most interesting\nproblem of life and the creation by experiment of new races or\nelementary species are no longer beyond the region of possibility.\n\n\n\n\nXIV. EXPERIMENTAL STUDY OF THE INFLUENCE OF ENVIRONMENT ON ANIMALS.\nBy Jacques Loeb, M.D. Professor of Physiology in the University of\nCalifornia.\n\n\nI. INTRODUCTORY REMARKS.\n\nWhat the biologist calls the natural environment of an animal is from a\nphysical point of view a rather rigid combination of definite forces. It\nis obvious that by a purposeful and systematic variation of these and\nby the application of other forces in the laboratory, results must be\nobtainable which do not appear in the natural environment. This is the\nreasoning underlying the modern development of the study of the effects\nof environment upon animal life. It was perhaps not the least important\nof Darwin's services to science that the boldness of his conceptions\ngave to the experimental biologist courage to enter upon the attempt of\ncontrolling at will the life-phenomena of animals, and of bringing about\neffects which cannot be expected in Nature.\n\nThe systematic physico-chemical analysis of the effect of outside\nforces upon the form and reactions of animals is also our only means of\nunravelling the mechanism of heredity beyond the scope of the Mendelian\nlaw. The manner in which a germ-cell can force upon the adult certain\ncharacters will not be understood until we succeed in varying\nand controlling hereditary characteristics; and this can only be\naccomplished on the basis of a systematic study of the effects of\nchemical and physical forces upon living matter.\n\nOwing to limitation of space this sketch is necessarily very incomplete,\nand it must not be inferred that studies which are not mentioned here\nwere considered to be of minor importance. All the writer could hope to\ndo was to bring together a few instances of the experimental analysis of\nthe effect of environment, which indicate the nature and extent of our\ncontrol over life-phenomena and which also have some relation to the\nwork of Darwin. In the selection of these instances preference is given\nto those problems which are not too technical for the general reader.\n\nThe forces, the influence of which we shall discuss, are in succession\nchemical agencies, temperature, light, and gravitation. We shall also\ntreat separately the effect of these forces upon form and instinctive\nreactions.\n\n\nII. THE EFFECTS OF CHEMICAL AGENCIES.\n\n(a) HETEROGENEOUS HYBRIDISATION.\n\nIt was held until recently that hybridisation is not possible except\nbetween closely related species and that even among these a successful\nhybridisation cannot always be counted upon. This view was well\nsupported by experience. It is, for instance, well known that the\nmajority of marine animals lay their unfertilised eggs in the ocean and\nthat the males shed their sperm also into the sea-water. The numerical\nexcess of the spermatozoa over the ova in the sea-water is the only\nguarantee that the eggs are fertilised, for the spermatozoa are\ncarried to the eggs by chance and are not attracted by the latter. This\nstatement is the result of numerous experiments by various authors,\nand is contrary to common belief. As a rule all or the majority of\nindividuals of a species in a given region spawn on the same day, and\nwhen this occurs the sea-water constitutes a veritable suspension of\nsperm. It has been shown by experiment that in fresh sea-water the sperm\nmay live and retain its fertilising power for several days. It is thus\nunavoidable that at certain periods more than one kind of spermatozoon\nis suspended in the sea-water and it is a matter of surprise that the\nmost heterogeneous hybridisations do not constantly occur. The reason\nfor this becomes obvious if we bring together mature eggs and equally\nmature and active sperm of a different family. When this is done no egg\nis, as a rule, fertilised. The eggs of a sea-urchin can be fertilised by\nsperm of their own species, or, though in smaller numbers, by the sperm\nof other species of sea-urchins, but not by the sperm of other groups of\nechinoderms, e.g. starfish, brittle-stars, holothurians or crinoids, and\nstill less by the sperm of more distant groups of animals. The consensus\nof opinion seemed to be that the spermatozoon must enter the egg\nthrough a narrow opening or canal, the so-called micropyle, and that\nthe micropyle allowed only the spermatozoa of the same or of a closely\nrelated species to enter the egg.\n\nIt seemed to the writer that the cause of this limitation of\nhybridisation might be of another kind and that by a change in the\nconstitution of the sea-water it might be possible to bring about\nheterogenous hybridisations, which in normal sea-water are impossible.\nThis assumption proved correct. Sea-water has a faintly alkaline\nreaction (in terms of the physical chemist its concentration of hydroxyl\nions is about (10 to the power minus six)N at Pacific Grove, California,\nand about (10 to the power minus 5)N at Woods Hole, Massachusetts).\nIf we slightly raise the alkalinity of the sea-water by adding to it a\nsmall but definite quantity of sodium hydroxide or some other alkali,\nthe eggs of the sea-urchin can be fertilised with the sperm of widely\ndifferent groups of animals, possibly with the sperm of any marine\nanimal which sheds it into the ocean. In 1903 it was shown that if we\nadd from about 0.5 to 0.8 cubic centimetre N/10 sodium hydroxide to\n50 cubic centimetres of sea-water, the eggs of Strongylocentrotus\npurpuratus (a sea-urchin which is found on the coast of California)\ncan be fertilised in large quantities by the sperm of various kinds of\nstarfish, brittle-stars and holothurians; while in normal sea-water or\nwith less sodium hydroxide not a single egg of the same female could\nbe fertilised with the starfish sperm which proved effective in the\nhyper-alkaline sea-water. The sperm of the various forms of starfish was\nnot equally effective for these hybridisations; the sperm of Asterias\nochracea and A. capitata gave the best results, since it was possible to\nfertilise 50 per cent or more of the sea-urchin eggs, while the sperm of\nPycnopodia and Asterina fertilised only 2 per cent of the same eggs.\n\nGodlewski used the same method for the hybridisation of the sea-urchin\neggs with the sperm of a crinoid (Antedon rosacea). Kupelwieser\nafterwards obtained results which seemed to indicate the possibility of\nfertilising the eggs of Strongylocentrotus with the sperm of a mollusc\n(Mytilus.) Recently, the writer succeeded in fertilising the\neggs of Strongylocentrotus franciscanus with the sperm of a\nmollusc--Chlorostoma. This result could only be obtained in sea-water\nthe alkalinity of which had been increased (through the addition of\n0.8 cubic centimetre N/10 sodium hydroxide to 50 cubic centimetres\nof sea-water). We thus see that by increasing the alkalinity of the\nsea-water it is possible to effect heterogeneous hybridisations which\nare at present impossible in the natural environment of these animals.\n\nIt is, however, conceivable that in former periods of the earth's\nhistory such heterogeneous hybridisations were possible. It is known\nthat in solutions like sea-water the degree of alkalinity must increase\nwhen the amount of carbon-dioxide in the atmosphere is diminished. If it\nbe true, as Arrhenius assumes, that the Ice age was caused or preceded\nby a diminution in the amount of carbon-dioxide in the air, such a\ndiminution must also have resulted in an increase of the alkalinity\nof the sea-water, and one result of such an increase must have been to\nrender possible heterogeneous hybridisations in the ocean which in the\npresent state of alkalinity are practically excluded.\n\nBut granted that such hybridisations were possible, would they have\ninfluenced the character of the fauna? In other words, are the hybrids\nbetween sea-urchin and starfish, or better still, between sea-urchin and\nmollusc, capable of development, and if so, what is their character?\nThe first experiment made it appear doubtful whether these heterogeneous\nhybrids could live. The sea-urchin eggs which were fertilised in the\nlaboratory by the spermatozoa of the starfish, as a rule, died earlier\nthan those of the pure breeds. But more recent results indicate that\nthis was due merely to deficiencies in the technique of the earlier\nexperiments. The writer has recently obtained hybrid larvae between the\nsea-urchin egg and the sperm of a mollusc (Chlorostoma) which, in the\nlaboratory, developed as well and lived as long as the pure breeds of\nthe sea-urchin, and there was nothing to indicate any difference in the\nvitality of the two breeds.\n\nSo far as the question of heredity is concerned, all the experiments on\nheterogeneous hybridisation of the egg of the sea-urchin with the sperm\nof starfish, brittle-stars, crinoids and molluscs, have led to the same\nresult, namely, that the larvae have purely maternal characteristics and\ndiffer in no way from the pure breed of the form from which the egg\nis taken. By way of illustration it may be said that the larvae of the\nsea-urchin reach on the third day or earlier (according to species\nand temperature) the so-called pluteus stage, in which they possess a\ntypical skeleton; while neither the larvae of the starfish nor those\nof the mollusc form a skeleton at the corresponding stage. It was,\ntherefore, a matter of some interest to find out whether or not the\nlarvae produced by the fertilisation of the sea-urchin egg with the\nsperm of starfish or mollusc would form the normal and typical pluteus\nskeleton. This was invariably the case in the experiments of Godlewski,\nKupelwieser, Hagedoorn, and the writer. These hybrid larvae were\nexclusively maternal in character.\n\nIt might be argued that in the case of heterogeneous hybridisation the\nsperm-nucleus does not fuse with the egg-nucleus, and that, therefore,\nthe spermatozoon cannot transmit its hereditary substances to the\nlarvae. But these objections are refuted by Godlewski's experiments,\nin which he showed definitely that if the egg of the sea-urchin is\nfertilised with the sperm of a crinoid the fusion of the egg-nucleus\nand sperm-nucleus takes place in the normal way. It remains for further\nexperiments to decide what the character of the adult hybrids would be.\n\n(b). ARTIFICIAL PARTHENOGENESIS.\n\nPossibly in no other field of Biology has our ability to control\nlife-phenomena by outside conditions been proved to such an extent as\nin the domain of fertilisation. The reader knows that the eggs of the\noverwhelming majority of animals cannot develop unless a spermatozoon\nenters them. In this case a living agency is the cause of development\nand the problem arises whether it is possible to accomplish the same\nresult through the application of well-known physico-chemical agencies.\nThis is, indeed, true, and during the last ten years living larvae\nhave been produced by chemical agencies from the unfertilised eggs\nof sea-urchins, starfish, holothurians and a number of annelids and\nmolluscs; in fact this holds true in regard to the eggs of practically\nall forms of animals with which such experiments have been tried long\nenough. In each form the method of procedure is somewhat different and\na long series of experiments is often required before the successful\nmethod is found.\n\nThe facts of Artificial Parthenogenesis, as the chemical fertilisation\nof the egg is called, have, perhaps, some bearing on the problem of\nevolution. If we wish to form a mental image of the process of evolution\nwe have to reckon with the possibility that parthenogenetic propagation\nmay have preceded sexual reproduction. This suggests also the\npossibility that at that period outside forces may have supplied\nthe conditions for the development of the egg which at present the\nspermatozoon has to supply. For this, if for no other reason, a brief\nconsideration of the means of artificial parthenogenesis may be of\ninterest to the student of evolution.\n\nIt seemed necessary in these experiments to imitate as completely as\npossible by chemical agencies the effects of the spermatozoon upon\nthe egg. When a spermatozoon enters the egg of a sea-urchin or certain\nstarfish or annelids, the immediate effect is a characteristic change of\nthe surface of the egg, namely the formation of the so-called membrane\nof fertilisation. The writer found that we can produce this membrane in\nthe unfertilised egg by certain acids, especially the monobasic acids\nof the fatty series, e.g. formic, acetic, propionic, butyric, etc.\nCarbon-dioxide is also very efficient in this direction. It was also\nfound that the higher acids are more efficient than the lower ones,\nand it is possible that the spermatozoon induces membrane-formation by\ncarrying into the egg a higher fatty acid, namely oleic acid or one of\nits salts or esters.\n\nThe physico-chemical process which underlies the formation of the\nmembrane seems to be the cause of the development of the egg. In all\ncases in which the unfertilised egg has been treated in such a way as\nto cause it to form a membrane it begins to develop. For the eggs of\ncertain animals membrane-formation is all that is required to induce a\ncomplete development of the unfertilised egg, e.g. in the starfish and\ncertain annelids. For the eggs of other animals a second treatment is\nnecessary, presumably to overcome some of the injurious effects of\nacid treatment. Thus the unfertilised eggs of the sea-urchin\nStrongylocentrotus purpuratus of the Californian coast begin to develop\nwhen membrane-formation has been induced by treatment with a fatty acid,\ne.g. butyric acid; but the development soon ceases and the eggs\nperish in the early stages of segmentation, or after the first nuclear\ndivision. But if we treat the same eggs, after membrane-formation, for\nfrom 35 to 55 minutes (at 15 deg C.) with sea-water the concentration\n(osmotic pressure) of which has been raised through the addition of a\ndefinite amount of some salt or sugar, the eggs will segment and develop\nnormally, when transferred back to normal sea-water. If care is taken,\npractically all the eggs can be caused to develop into plutei, the\nmajority of which may be perfectly normal and may live as long as larvae\nproduced from eggs fertilised with sperm.\n\nIt is obvious that the sea-urchin egg is injured in the process of\nmembrane-formation and that the subsequent treatment with a hypertonic\nsolution only acts as a remedy. The nature of this injury became clear\nwhen it was discovered that all the agencies which cause haemolysis,\ni.e. the destruction of the red blood corpuscles, also cause\nmembrane-formation in unfertilised eggs, e.g. fatty acids or ether,\nalcohols or chloroform, etc., or saponin, solanin, digitalin, bile\nsalts and alkali. It thus happens that the phenomena of artificial\nparthenogenesis are linked together with the phenomena of haemolysis\nwhich at present play so important a role in the study of immunity. The\ndifference between cytolysis (or haemolysis) and fertilisation seems to\nbe this, that the latter is caused by a superficial or slight cytolysis\nof the egg, while if the cytolytic agencies have time to act on the\nwhole egg the latter is completely destroyed. If we put unfertilised\neggs of a sea-urchin into sea-water which contains a trace of saponin we\nnotice that, after a few minutes, all the eggs form the typical\nmembrane of fertilisation. If the eggs are then taken out of the saponin\nsolution, freed from all traces of saponin by repeated washing in normal\nsea-water, and transferred to the hypertonic sea-water for from 35 to\n55 minutes, they develop into larvae. If, however, they are left in\nthe sea-water containing the saponin they undergo, a few minutes after\nmembrane-formation, the disintegration known in pathology as CYTOLYSIS.\nMembrane-formation is, therefore, caused by a superficial or incomplete\ncytolysis. The writer believes that the subsequent treatment of the egg\nwith hypertonic sea-water is needed only to overcome the destructive\neffects of this partial cytolysis. The full reasons for this belief\ncannot be given in a short essay.\n\nMany pathologists assume that haemolysis or cytolysis is due to a\nliquefaction of certain fatty or fat-like compounds, the so-called\nlipoids, in the cell. If this view is correct, it would be necessary to\nascribe the fertilisation of the egg to the same process.\n\nThe analogy between haemolysis and fertilisation throws, possibly,\nsome light on a curious observation. It is well known that the blood\ncorpuscles, as a rule, undergo cytolysis if injected into the blood of\nan animal which belongs to a different family. The writer found last\nyear that the blood of mammals, e.g. the rabbit, pig, and cattle, causes\nthe egg of Strongylocentrotus to form a typical fertilisation-membrane.\nIf such eggs are afterwards treated for a short period with hypertonic\nsea-water they develop into normal larvae (plutei). Some substance\ncontained in the blood causes, presumably, a superficial cytolysis of\nthe egg and thus starts its development.\n\nWe can also cause the development of the sea-urchin egg without\nmembrane-formation. The early experiments of the writer were done in\nthis way and many experimenters still use such methods. It is probable\nthat in this case the mechanism of fertilisation is essentially the same\nas in the case where the membrane-formation is brought about, with\nthis difference only, that the cytolytic effect is less when no\nfertilisation-membrane is formed. This inference is corroborated by\nobservations on the fertilisation of the sea-urchin egg with ox blood.\nIt very frequently happens that not all of the eggs form membranes in\nthis process. Those eggs which form membranes begin to develop, but\nperish if they are not treated with hypertonic sea-water. Some of the\nother eggs, however, which do not form membranes, develop directly into\nnormal larvae without any treatment with hypertonic sea-water, provided\nthey are exposed to the blood for only a few minutes. Presumably some\nblood enters the eggs and causes the cytolytic effects in a less degree\nthan is necessary for membrane-formation, but in a sufficient degree to\ncause their development. The slightness of the cytolytic effect allows\nthe egg to develop without treatment with hypertonic sea-water.\n\nSince the entrance of the spermatozoon causes that degree of cytolysis\nwhich leads to membrane-formation, it is probable that, in addition to\nthe cytolytic or membrane-forming substance (presumably a higher fatty\nacid), it carries another substance into the egg which counteracts the\ndeleterious cytolytic effects underlying membrane-formation.\n\nThe question may be raised whether the larvae produced by artificial\nparthenogenesis can reach the mature stage. This question may be\nanswered in the affirmative, since Delage has succeeded in raising\nseveral parthenogenetic sea-urchin larvae beyond the metamorphosis into\nthe adult stage and since in all the experiments made by the writer\nthe parthenogenetic plutei lived as long as the plutei produced from\nfertilised eggs.\n\n(c). ON THE PRODUCTION OF TWINS FROM ONE EGG THROUGH A CHANGE IN THE\nCHEMICAL CONSTITUTION OF THE SEA-WATER.\n\nThe reader is probably familiar with the fact that there exist two\ndifferent types of human twins. In the one type the twins differ as much\nas two children of the same parents born at different periods; they\nmay or may not have the same sex. In the second type the twins have\ninvariably the same sex and resemble each other most closely. Twins\nof the latter type are produced from the same egg, while twins of the\nformer type are produced from two different eggs.\n\nThe experiments of Driesch and others have taught us that twins\noriginate from one egg in this manner, namely, that the first two cells\ninto which the egg divides after fertilisation become separated from\neach other. This separation can be brought about by a change in the\nchemical constitution of the sea-water. Herbst observed that if the\nfertilised eggs of the sea-urchin are put into sea-water which is freed\nfrom calcium, the cells into which the egg divides have a tendency\nto fall apart. Driesch afterwards noticed that eggs of the sea-urchin\ntreated with sea-water which is free from lime have a tendency to give\nrise to twins. The writer has recently found that twins can be produced\nnot only by the absence of lime, but also through the absence of sodium\nor of potassium; in other words, through the absence of one or two of\nthe three important metals in the sea-water. There is, however, a second\ncondition, namely, that the solution used for the production of twins\nmust have a neutral or at least not an alkaline reaction.\n\nThe procedure for the production of twins in the sea-urchin egg consists\nsimply in this:--the eggs are fertilised as usual in normal sea-water\nand then, after repeated washing in a neutral solution of sodium\nchloride (of the concentration of the sea-water), are placed in a\nneutral mixture of potassium chloride and calcium chloride, or of sodium\nchloride and potassium chloride, or of sodium chloride and calcium\nchloride, or of sodium chloride and magnesium chloride. The eggs must\nremain in this solution until half an hour or an hour after they have\nreached the two-cell stage. They are then transferred into normal\nsea-water and allowed to develop. From 50 to 90 per cent of the eggs of\nStrongylocentrotus purpuratus treated in this manner may develop into\ntwins. These twins may remain separate or grow partially together and\nform double monsters, or heal together so completely that only slight or\neven no imperfections indicate that the individual started its career\nas a pair of twins. It is also possible to control the tendency of such\ntwins to grow together by a change in the constitution of the sea-water.\nIf we use as a twin-producing solution a mixture of sodium, magnesium\nand potassium chlorides (in the proportion in which these salts exist in\nthe sea-water) the tendency of the twins to grow together is much\nmore pronounced than if we use simply a mixture of sodium chloride and\nmagnesium chloride.\n\nThe mechanism of the origin of twins, as the result of altering the\ncomposition of the sea-water, is revealed by observation of the first\nsegmentation of the egg in these solutions. This cell-division is\nmodified in a way which leads to a separation of the first two cells.\nIf the egg is afterwards transferred back into normal sea-water, each\nof these two cells develops into an independent embryo. Since normal\nsea-water contains all three metals, sodium, calcium, and potassium, and\nsince it has besides an alkaline reaction, we perceive the reason why\ntwins are not normally produced from one egg. These experiments suggest\nthe possibility of a chemical cause for the origin of twins from one egg\nor of double monstrosities in mammals. If, for some reason, the liquids\nwhich surround the human egg a short time before and after the first\ncell-division are slightly acid, and at the same time lacking in one\nof the three important metals, the conditions for the separation of the\nfirst two cells and the formation of identical twins are provided.\n\nIn conclusion it may be pointed out that the reverse result, namely,\nthe fusion of normally double organs, can also be brought about\nexperimentally through a change in the chemical constitution of the\nsea-water. Stockard succeeded in causing the eyes of fish embryos\n(Fundulus heteroclitus) to fuse into a single cyclopean eye through the\naddition of magnesium chloride to the sea-water. When he added about 6\ngrams of magnesium chloride to 100 cubic centimetres of sea-water and\nplaced the fertilised eggs in the mixture, about 50 per cent of the\neggs gave rise to one-eyed embryos. \"When the embryos were studied the\none-eyed condition was found to result from the union or fusion of the\n'anlagen' of the two eyes. Cases were observed which showed various\ndegrees in this fusion; it appeared as though the optic vessels were\nformed too far forward and ventral, so that their antero-ventro-median\nsurfaces fused. This produces one large optic cup, which in all cases\ngives more or less evidence of its double nature.\" (Stockard, \"Archiv f.\nEntwickelungsmechanik\", Vol. 23, page 249, 1907.)\n\nWe have confined ourselves to a discussion of rather simple effects of\nthe change in the constitution of the sea-water upon development. It\nis a priori obvious, however, that an unlimited number of pathological\nvariations might be produced by a variation in the concentration and\nconstitution of the sea-water, and experience confirms this statement.\nAs an example we may mention the abnormalities observed by Herbst in the\ndevelopment of sea-urchins through the addition of lithium to sea-water.\nIt is, however, as yet impossible to connect in a rational way the\neffects produced in this and similar cases with the cause which produced\nthem; and it is also impossible to define in a simple way the character\nof the change produced.\n\nIII. THE INFLUENCE OF TEMPERATURE.\n\n(a) THE INFLUENCE OF TEMPERATURE UPON THE DENSITY OF PELAGIC ORGANISMS\nAND THE DURATION OF LIFE.\n\nIt has often been noticed by explorers who have had a chance to compare\nthe faunas in different climates that in polar seas such species as\nthrive at all in those regions occur, as a rule, in much greater density\nthan they do in the moderate or warmer regions of the ocean. This refers\nto those members of the fauna which live at or near the surface, since\nthey alone lend themselves to a statistical comparison. In his account\nof the Valdivia expedition, Chun (Chun, \"Aus den Tiefen des Weltmeeres\",\npage 225, Jena, 1903.) calls especial attention to this quantitative\ndifference in the surface fauna and flora of different regions. \"In the\nicy water of the Antarctic, the temperature of which is below 0 deg C.,\nwe find an astonishingly rich animal and plant life. The same condition\nwith which we are familiar in the Arctic seas is repeated here, namely,\nthat the quantity of plankton material exceeds that of the temperate and\nwarm seas.\" And again, in regard to the pelagic fauna in the region of\nthe Kerguelen Islands, he states: \"The ocean is alive with transparent\njelly fish, Ctenophores (Bolina and Callianira) and of Siphonophore\ncolonies of the genus Agalma.\"\n\nThe paradoxical character of this general observation lies in the fact\nthat a low temperature retards development, and hence should be\nexpected to have the opposite effect from that mentioned by Chun. Recent\ninvestigations have led to the result that life-phenomena are affected\nby temperature in the same sense as the velocity of chemical reactions.\nIn the case of the latter van't Hoff had shown that a decrease in\ntemperature by 10 degrees reduces their velocity to one half or less,\nand the same has been found for the influence of temperature on the\nvelocity of physiological processes. Thus Snyder and T.B. Robertson\nfound that the rate of heartbeat in the tortoise and in Daphnia is\nreduced to about one-half if the temperature is lowered 10 deg C., and\nMaxwell, Keith Lucas, and Snyder found the same influence of temperature\nfor the rate with which an impulse travels in the nerve. Peter observed\nthat the rate of development in a sea-urchin's egg is reduced to less\nthan one-half if the temperature (within certain limits) is reduced by\n10 degrees. The same effect of temperature upon the rate of development\nholds for the egg of the frog, as Cohen and Peter calculated from\nthe experiments of O. Hertwig. The writer found the same\ntemperature-coefficient for the rate of maturation of the egg of a\nmollusc (Lottia).\n\nAll these facts prove that the velocity of development of animal life\nin Arctic regions, where the temperature is near the freezing point of\nwater, must be from two to three times smaller than in regions where the\ntemperature of the ocean is about 10 deg C. and from four to nine times\nsmaller than in seas the temperature of which is about 20 deg C. It is,\ntherefore, exactly the reverse of what we should expect when authors\nstate that the density of organisms at or near the surface of the ocean\nin polar regions is greater than in more temperate regions.\n\nThe writer believes that this paradox finds its explanation in\nexperiments which he has recently made on the influence of temperature\non the duration of life of cold-blooded marine animals. The experiments\nwere made on the fertilised and unfertilised eggs of the sea-urchin, and\nyielded the result that for the lowering of temperature by 1 deg C.\nthe duration of life was about doubled. Lowering the temperature by 10\ndegrees therefore prolongs the life of the organism 2 to the power 10,\ni.e. over a thousand times, and a lowering by 20 degrees prolongs it\nabout one million times. Since this prolongation of life is far\nin excess of the retardation of development through a lowering of\ntemperature, it is obvious that, in spite of the retardation of\ndevelopment in Arctic seas, animal life must be denser there than in\ntemperate or tropical seas. The excessive increase of the duration of\nlife at the poles will necessitate the simultaneous existence of more\nsuccessive generations of the same species in these regions than in the\ntemperate or tropical regions.\n\nThe writer is inclined to believe that these results have some bearing\nupon a problem which plays an important role in theories of evolution,\nnamely, the cause of natural death. It has been stated that the\nprocesses of differentiation and development lead also to the natural\ndeath of the individual. If we express this in chemical terms it means\nthat the chemical processes which underlie development also determine\nnatural death. Physical chemistry has taught us to identify two chemical\nprocesses even if only certain of their features are known. One of\nthese means of identification is the temperature coefficient. When two\nchemical processes are identical, their velocity must be reduced by\nthe same amount if the temperature is lowered to the same extent.\nThe temperature coefficient for the duration of life of cold-blooded\norganisms seems, however, to differ enormously from the temperature\ncoefficient for their rate of development. For a difference in\ntemperature of 10 deg C. the duration of life is altered five hundred\ntimes as much as the rate of development; and, for a change of 20 deg\nC., it is altered more than a hundred thousand times as much. From this\nwe may conclude that, at least for the sea-urchin eggs and embryo,\nthe chemical processes which determine natural death are certainly not\nidentical with the processes which underlie their development. T.B.\nRobertson has also arrived at the conclusion, for quite different\nreasons, that the process of senile decay is essentially different from\nthat of growth and development.\n\n(b) CHANGES IN THE COLOUR OF BUTTERFLIES PRODUCED THROUGH THE INFLUENCE\nOF TEMPERATURE.\n\nThe experiments of Dorfmeister, Weismann, Merrifield, Standfuss,\nand Fischer, on seasonal dimorphism and the aberration of colour in\nbutterflies have so often been discussed in biological literature that\na short reference to them will suffice. By seasonal dimorphism is meant\nthe fact that species may appear at different seasons of the year in a\nsomewhat different form or colour. Vanessa prorsa is the summer form,\nVanessa levana the winter form of the same species. By keeping the pupae\nof Vanessa prorsa several weeks at a temperature of from 0 deg to 1 deg\nWeismann succeeded in obtaining from the summer chrysalids specimens\nwhich resembled the winter variety, Vanessa levana.\n\nIf we wish to get a clear understanding of the causes of variation in\nthe colour and pattern of butterflies, we must direct our attention to\nthe experiments of Fischer, who worked with more extreme temperatures\nthan his predecessors, and found that almost identical aberrations\nof colour could be produced by both extremely high and extremely low\ntemperatures. This can be clearly seen from the following tabulated\nresults of his observations. At the head of each column the reader\nfinds the temperature to which Fischer submitted the pupae, and in the\nvertical column below are found the varieties that were produced. In the\nvertical column A are given the normal forms:\n\n(Temperatures in deg C.)\n\n  0 to -20     0 to +10    A.           +35 to +37    +36 to +41  +42 to +46\n                          (Normal forms)\n\n  ichnusoides  polaris     urticae      ichnusa       polaris     ichnusoides\n    (nigrita)                                                       (nigrita)\n\n  antigone     fischeri    io             -           fischeri    antigone\n    (iokaste)                                                       (iokaste)\n\n  testudo      dixeyi      polychloros  erythromelas  dixeyi      testudo\n\n  hygiaea      artemis     antiopa      epione        artemis     hygiaea\n\n  elymi        wiskotti    cardui         -           wiskotti    elymi\n\n  klymene      merrifieldi atalanta       -           merrifieldi klymene\n\n  weismanni    porima      prorsa         -           porima      weismanni\n\nThe reader will notice that the aberrations produced at a very low\ntemperature (from 0 to -20 deg C.) are absolutely identical with\nthe aberrations produced by exposing the pupae to extremely high\ntemperatures (42 to 46 deg C.). Moreover the aberrations produced by a\nmoderately low temperature (from 0 to 10 deg C.) are identical with the\naberrations produced by a moderately high temperature (36 to 41 deg C.)\n\nFrom these observations Fischer concludes that it is erroneous to speak\nof a specific effect of high and of low temperatures, but that there\nmust be a common cause for the aberration found at the high as well\nas at the low temperature limits. This cause he seems to find in the\ninhibiting effects of extreme temperatures upon development.\n\nIf we try to analyse such results as Fischer's from a physico-chemical\npoint of view, we must realise that what we call life consists of a\nseries of chemical reactions, which are connected in a catenary way;\ninasmuch as one reaction or group of reactions (a) (e.g. hydrolyses)\ncauses or furnishes the material for a second reaction or group\nof reactions (b) (e.g. oxydations). We know that the temperature\ncoefficient for physiological processes varies slightly at various parts\nof the scale; as a rule it is higher near 0 and lower near 30 deg. But\nwe know also that the temperature coefficients do not vary equally from\nthe various physiological processes. It is, therefore, to be expected\nthat the temperature coefficients for the group of reactions of the type\n(a) will not be identical through the whole scale with the temperature\ncoefficients for the reactions of the type (b). If therefore a certain\nsubstance is formed at the normal temperature of the animal in such\nquantities as are needed for the catenary reaction (b), it is not to be\nexpected that this same perfect balance will be maintained for extremely\nhigh or extremely low temperatures; it is more probable that one group\nof reactions will exceed the other and thus produce aberrant chemical\neffects, which may underlie the colour aberrations observed by Fischer\nand other experimenters.\n\nIt is important to notice that Fischer was also able to produce\naberrations through the application of narcotics. Wolfgang Ostwald has\nproduced experimentally, through variation of temperature, dimorphism of\nform in Daphnia. Lack of space precludes an account of these important\nexperiments, as of so many others.\n\nIV. THE EFFECTS OF LIGHT.\n\nAt the present day nobody seriously questions the statement that the\naction of light upon organisms is primarily one of a chemical character.\nWhile this chemical action is of the utmost importance for organisms,\nthe nutrition of which depends upon the action of chlorophyll, it\nbecomes of less importance for organisms devoid of chlorophyll.\nNevertheless, we find animals in which the formation of organs by\nregeneration is not possible unless they are exposed to light. An\nobservation made by the writer on the regeneration of polyps in a\nhydroid, Eudendrium racemosum, at Woods Hole, may be mentioned as an\ninstance of this. If the stem of this hydroid, which is usually covered\nwith polyps, is put into an aquarium the polyps soon fall off. If the\nstems are kept in an aquarium where light strikes them during the day, a\nregeneration of numerous polyps takes place in a few days. If, however,\nthe stems of Eudendrium are kept permanently in the dark, no polyps are\nformed even after an interval of some weeks; but they are formed in a\nfew days after the same stems have been transferred from the dark to\nthe light. Diffused daylight suffices for this effect. Goldfarb, who\nrepeated these experiments, states that an exposure of comparatively\nshort duration is sufficient for this effect, it is possible that the\nlight favours the formation of substances which are a prerequisite for\nthe origin of polyps and their growth.\n\nOf much greater significance than this observation are the facts which\nshow that a large number of animals assume, to some extent, the\ncolour of the ground on which they are placed. Pouchet found through\nexperiments upon crustaceans and fish that this influence of the ground\non the colour of animals is produced through the medium of the eyes.\nIf the eyes are removed or the animals made blind in another way these\nphenomena cease. The second general fact found by Pouchet was that the\nvariation in the colour of the animal is brought about through an action\nof the nerves on the pigment-cells of the skin; the nerve-action being\ninduced through the agency of the eye.\n\nThe mechanism and the conditions for the change in colouration were made\nclear through the beautiful investigations of Keeble and Gamble, on\nthe colour-change in crustaceans. According to these authors the\npigment-cells can, as a rule, be considered as consisting of a central\nbody from which a system of more or less complicated ramifications or\nprocesses spreads out in all directions. As a rule, the centre of the\ncell contains one or more different pigments which under the influence\nof nerves can spread out separately or together into the ramifications.\nThese phenomena of spreading and retraction of the pigments into or from\nthe ramifications of the pigment-cells form on the whole the basis for\nthe colour changes under the influence of environment. Thus Keeble\nand Gamble observed that Macromysis flexuosa appears transparent and\ncolourless or grey on sandy ground. On a dark ground their colour\nbecomes darker. These animals have two pigments in their chromatophores,\na brown pigment and a whitish or yellow pigment; the former is much more\nplentiful than the latter. When the animal appears transparent all the\npigment is contained in the centre of the cells, while the ramifications\nare free from pigment. When the animal appears brown both pigments are\nspread out into the ramifications. In the condition of maximal spreading\nthe animals appear black.\n\nThis is a comparatively simple case. Much more complicated conditions\nwere found by Keeble and Gamble in other crustaceans, e.g. in Hippolyte\ncranchii, but the influence of the surroundings upon the colouration of\nthis form was also satisfactorily analysed by these authors.\n\nWhile many animals show transitory changes in colour under the influence\nof their surroundings, in a few cases permanent changes can be produced.\nThe best examples of this are those which were observed by Poulton\nin the chrysalids of various butterflies, especially the small\ntortoise-shell. These experiments are so well known that a short\nreference to them will suffice. Poulton (Poulton, E.B., \"Colours of\nAnimals\" (The International Scientific Series), London, 1890, page 121.)\nfound that in gilt or white surroundings the pupae became light coloured\nand there was often an immense development of the golden spots, \"so that\nin many cases the whole surface of the pupae glittered with an apparent\nmetallic lustre. So remarkable was the appearance that a physicist to\nwhom I showed the chrysalids, suggested that I had played a trick and\nhad covered them with goldleaf.\" When black surroundings were used \"the\npupae were as a rule extremely dark, with only the smallest trace, and\noften no trace at all, of the golden spots which are so conspicuous in\nthe lighter form.\" The susceptibility of the animal to this influence of\nits surroundings was found to be greatest during a definite period when\nthe caterpillar undergoes the metamorphosis into the chrysalis stage.\nAs far as the writer is aware, no physico-chemical explanation, except\npossibly Wiener's suggestion of colour-photography by mechanical colour\nadaptation, has ever been offered for the results of the type of those\nobserved by Poulton.\n\n\nV. EFFECTS OF GRAVITATION.\n\n(a) EXPERIMENTS ON THE EGG OF THE FROG.\n\nGravitation can only indirectly affect life-phenomena; namely, when we\nhave in a cell two different non-miscible liquids (or a liquid and a\nsolid) of different specific gravity, so that a change in the position\nof the cell or the organ may give results which can be traced to a\nchange in the position of the two substances. This is very nicely\nillustrated by the frog's egg, which has two layers of very viscous\nprotoplasm one of which is black and one white. The dark one occupies\nnormally the upper position in the egg and may therefore be assumed to\npossess a smaller specific gravity than the white substance. When\nthe egg is turned with the white pole upwards a tendency of the white\nprotoplasm to flow down again manifests itself. It is, however, possible\nto prevent or retard this rotation of the highly viscous protoplasm, by\ncompressing the eggs between horizontal glass plates. Such compression\nexperiments may lead to rather interesting results, as O. Schultze first\npointed out. Pflueger had already shown that the first plane of division\nin a fertilised frog's egg is vertical and Roux established the fact\nthat the first plane of division is identical with the plane of symmetry\nof the later embryo. Schultze found that if the frog's egg is turned\nupside down at the time of its first division and kept in this abnormal\nposition, through compression between two glass plates for about 20\nhours, a small number of eggs may give rise to twins. It is possible,\nin this case, that the tendency of the black part of the egg to rotate\nupwards along the surface of the egg leads to a separation of its first\ncells, such a separation leading to the formation of twins.\n\nT.H. Morgan made an interesting additional observation. He destroyed\none half of the egg after the first segmentation and found that the\nhalf which remained alive gave rise to only one half of an embryo, thus\nconfirming an older observation of Roux. When, however, Morgan put the\negg upside down after the destruction of one of the first two cells, and\ncompressed the eggs between two glass plates, the surviving half of the\negg gave rise to a perfect embryo of half size (and not to a half embryo\nof normal size as before.) Obviously in this case the tendency of the\nprotoplasm to flow back to its normal position was partially successful\nand led to a partial or complete separation of the living from the dead\nhalf; whereby the former was enabled to form a whole embryo, which, of\ncourse, possessed only half the size of an embryo originating from a\nwhole egg.\n\n(b) EXPERIMENTS ON HYDROIDS.\n\nA striking influence of gravitation can be observed in a hydroid,\nAntennularia antennina, from the bay of Naples. This hydroid consists of\na long straight main stem which grows vertically upwards and which has\nat regular intervals very fine and short bristle-like lateral branches,\non the upper side of which the polyps grow. The main stem is negatively\ngeotropic, i.e. its apex continues to grow vertically upwards when we\nput it obliquely into the aquarium, while the roots grow vertically\ndownwards. The writer observed that when the stem is put horizontally\ninto the water the short lateral branches on the lower side give rise to\nan altogether different kind of organ, namely, to roots, and these roots\ngrow indefinitely in length and attach themselves to solid bodies; while\nif the stem had remained in its normal position no further growth\nwould have occurred in the lateral branches. From the upper side of the\nhorizontal stem new stems grow out, mostly directly from the original\nstem, occasionally also from the short lateral branches. It is thus\npossible to force upon this hydroid an arrangement of organs which is\naltogether different from the hereditary arrangement. The writer\nhad called the change in the hereditary arrangement of organs or the\ntransformation of organs by external forces HETEROMORPHOSIS. We cannot\nnow go any further into this subject, which should, however, prove of\ninterest in relation to the problem of heredity.\n\nIf it is correct to apply inferences drawn from the observation on the\nfrog's egg to the behaviour of Antennularia, one might conclude that the\ncells of Antennularia also contain non-miscible substances of different\nspecific gravity, and that wherever the specifically lighter substance\ncomes in contact with the sea-water (or gets near the surface of the\ncell) the growth of a stem is favoured; while contact with the sea-water\nof the specifically heavier of the substances, will favour the formation\nof roots.\n\nVI. THE EXPERIMENTAL CONTROL OF ANIMAL INSTINCTS.\n\n(a) EXPERIMENTS ON THE MECHANISM OF HELIOTROPIC REACTIONS IN ANIMALS.\n\nSince the instinctive reactions of animals are as hereditary as\ntheir morphological character, a discussion of experiments on the\nphysico-chemical character of the instinctive reactions of animals\nshould not be entirely omitted from this sketch. It is obvious that such\nexperiments must begin with the simplest type of instincts, if they are\nexpected to lead to any results; and it is also obvious that only such\nanimals must be selected for this purpose, the reactions of which are\nnot complicated by associative memory, or, as it may preferably be\ntermed, associative hysteresis.\n\nThe simplest type of instincts is represented by the purposeful motions\nof animals to or from a source of energy, e.g. light; and it is with\nsome of these that we intend to deal here. When we expose winged aphides\n(after they have flown away from the plant), or young caterpillars of\nPorthesia chrysorrhoea (when they are aroused from their winter sleep)\nor marine or freshwater copepods and many other animals, to diffused\ndaylight falling in from a window, we notice a tendency among these\nanimals to move towards the source of light. If the animals are\nnaturally sensitive, or if they are rendered sensitive through the\nagencies which we shall mention later, and if the light is strong\nenough, they move towards the source of light in as straight a line as\nthe imperfections and peculiarities of their locomotor apparatus will\npermit. It is also obvious that we are here dealing with a forced\nreaction in which the animals have no more choice in the direction\nof their motion than have the iron filings in their arrangement in a\nmagnetic field. This can be proved very nicely in the case of starving\ncaterpillars of Porthesia. The writer put such caterpillars into a glass\ntube the axis of which was at right angles to the plane of the window:\nthe caterpillars went to the window side of the tube and remained there,\neven if leaves of their food-plant were put into the tube directly\nbehind them. Under such conditions the animals actually died from\nstarvation, the light preventing them from turning to the food, which\nthey eagerly ate when the light allowed them to do so. One cannot say\nthat these animals, which we call positively helioptropic, are attracted\nby the light, since it can be shown that they go towards the source\nof the light even if in so doing they move from places of a higher to\nplaces of a lower degree of illumination.\n\nThe writer has advanced the following theory of these instinctive\nreactions. Animals of the type of those mentioned are automatically\norientated by the light in such a way that symmetrical elements of their\nretina (or skin) are struck by the rays of light at the same angle.\nIn this case the intensity of light is the same for both retinae or\nsymmetrical parts of the skin.\n\nThis automatic orientation is determined by two factors, first a\npeculiar photo-sensitiveness of the retina (or skin), and second\na peculiar nervous connection between the retina and the muscular\napparatus. In symmetrically built heliotropic animals in which the\nsymmetrical muscles participate equally in locomotion, the symmetrical\nmuscles work with equal energy as long as the photo-chemical processes\nin both eyes are identical. If, however, one eye is struck by stronger\nlight than the other, the symmetrical muscles will work unequally and\nin positively heliotropic animals those muscles will work with greater\nenergy which bring the plane of symmetry back into the direction of the\nrays of light and the head towards the source of light. As soon as both\neyes are struck by the rays of light at the same angle, there is no more\nreason for the animal to deviate from this direction and it will move in\na straight line. All this holds good on the supposition that the animals\nare exposed to only one source of light and are very sensitive to light.\n\nAdditional proof for the correctness of this theory was furnished\nthrough the experiments of G.H. Parker and S.J. Holmes. The former\nworked on a butterfly, Vanessa antiope, the latter on other arthropods.\nAll the animals were in a marked degree positively heliotropic. These\nauthors found that if one cornea is blackened in such an animal, it\nmoves continually in a circle when it is exposed to a source of light,\nand in these motions the eye which is not covered with paint is directed\ntowards the centre of the circle. The animal behaves, therefore, as if\nthe darkened eye were in the shade.\n\n(b) THE PRODUCTION OF POSITIVE HELIOTROPISM BY ACIDS AND OTHER MEANS AND\nTHE PERIODIC DEPTH-MIGRATIONS OF PELAGIC ANIMALS.\n\nWhen we observe a dense mass of copepods collected from a freshwater\npond, we notice that some have a tendency to go to the light while\nothers go in the opposite direction and many, if not the majority,\nare indifferent to light. It is an easy matter to make the negatively\nheliotropic or the indifferent copepods almost instantly positively\nheliotropic by adding a small but definite amount of carbon-dioxide\nin the form of carbonated water to the water in which the animals are\ncontained. If the animals are contained in 50 cubic centimetres of water\nit suffices to add from three to six cubic centimetres of carbonated\nwater to make all the copepods energetically positively heliotropic.\nThis heliotropism lasts about half an hour (probably until all the\ncarbon-dioxide has again diffused into the air.) Similar results may be\nobtained with any other acid.\n\nThe same experiments may be made with another freshwater crustacean,\nnamely Daphnia, with this difference, however, that it is as a rule\nnecessary to lower the temperature of the water also. If the water\ncontaining the Daphniae is cooled and at the same time carbon-dioxide\nadded, the animals which were before indifferent to light now become\nmost strikingly positively heliotropic. Marine copepods can be made\npositively heliotropic by the lowering of the temperature alone, or by a\nsudden increase in the concentration of the sea-water.\n\nThese data have a bearing upon the depth-migrations of pelagic animals,\nas was pointed out years ago by Theo. T. Groom and the writer. It is\nwell known that many animals living near the surface of the ocean or\nfreshwater lakes, have a tendency to migrate upwards towards evening and\ndownwards in the morning and during the day. These periodic motions are\ndetermined to a large extent, if not exclusively, by the heliotropism\nof these animals. Since the consumption of carbon-dioxide by the green\nplants ceases towards evening, the tension of this gas in the water must\nrise and this must have the effect of inducing positive heliotropism or\nincreasing its intensity. At the same time the temperature of the\nwater near the surface is lowered and this also increases the positive\nheliotropism in the organisms.\n\nThe faint light from the sky is sufficient to cause animals which are in\na high degree positively heliotropic to move vertically upwards towards\nthe light, as experiments with such pelagic animals, e.g. copepods, have\nshown. When, in the morning, the absorption of carbon-dioxide by the\ngreen algae begins again and the temperature of the water rises, the\nanimals lose their positive heliotropism, and slowly sink down or become\nnegatively heliotropic and migrate actively downwards.\n\nThese experiments have also a bearing upon the problem of the\ninheritance of instincts. The character which is transmitted in this\ncase is not the tendency to migrate periodically upwards and downwards,\nbut the positive heliotropism. The tendency to migrate is the outcome of\nthe fact that periodically varying external conditions induce a periodic\nchange in the sense and intensity of the heliotropism of these animals.\nIt is of course immaterial for the result, whether the carbon-dioxide or\nany other acid diffuse into the animal from the outside or whether they\nare produced inside in the tissue cells of the animals. Davenport and\nCannon found that Daphniae, which at the beginning of the experiment,\nreact sluggishly to light react much more quickly after they have been\nmade to go to the light a few times. The writer is inclined to attribute\nthis result to the effect of acids, e.g. carbon-dioxide, produced in the\nanimals themselves in consequence of their motion. A similar effect of\nthe acids was shown by A.D. Waller in the case of the response of nerve\nto stimuli.\n\nThe writer observed many years ago that winged male and female ants\nare positively helioptropic and that their heliotropic sensitiveness\nincreases and reaches its maximum towards the period of nuptial flight.\nSince the workers show no heliotropism it looks as if an internal\nsecretion from the sexual glands were the cause of their heliotropic\nsensitiveness. V. Kellogg has observed that bees also become intensely\npositively heliotropic at the period of their wedding flight, in fact so\nmuch so that by letting light fall into the observation hive from above,\nthe bees are prevented from leaving the hive through the exit at the\nlower end.\n\nWe notice also the reverse phenomenon, namely, that chemical changes\nproduced in the animal destroy its heliotropism. The caterpillars of\nPorthesia chrysorrhoea are very strongly positively heliotropic when\nthey are first aroused from their winter sleep. This heliotropic\nsensitiveness lasts only as long as they are not fed. If they are kept\npermanently without food they remain permanently positively heliotropic\nuntil they die from starvation. It is to be inferred that as soon as\nthese animals take up food, a substance or substances are formed\nin their bodies which diminish or annihilate their heliotropic\nsensitiveness.\n\nThe heliotropism of animals is identical with the heliotropism of\nplants. The writer has shown that the experiments on the effect of acids\non the heliotropism of copepods can be repeated with the same result in\nVolvox. It is therefore erroneous to try to explain these heliotropic\nreactions of animals on the basis of peculiarities (e.g. vision) which\nare not found in plants.\n\nWe may briefly discuss the question of the transmission through the sex\ncells of such instincts as are based upon heliotropism. This problem\nreduces itself simply to that of the method whereby the gametes transmit\nheliotropism to the larvae or to the adult. The writer has expressed the\nidea that all that is necessary for this transmission is the presence in\nthe eyes (or in the skin) of the animal of a photo-sensitive substance.\nFor the transmission of this the gametes need not contain anything more\nthan a catalyser or ferment for the synthesis of the photo-sensitive\nsubstance in the body of the animal. What has been said in regard to\nanimal heliotropism might, if space permitted, be extended, mutatis\nmutandis, to geotropism and stereotropism.\n\n(c) THE TROPIC REACTIONS OF CERTAIN TISSUE-CELLS AND THE MORPHOGENETIC\nEFFECTS OF THESE REACTIONS.\n\nSince plant-cells show heliotropic reactions identical with those\nof animals, it is not surprising that certain tissue-cells also show\nreactions which belong to the class of tropisms. These reactions of\ntissue-cells are of special interest by reason of their bearing upon the\ninheritance of morphological characters. An example of this is found in\nthe tiger-like marking of the yolk-sac of the embryo of Fundulus and in\nthe marking of the young fish itself. The writer found that the former\nis entirely, and the latter at least in part, due to the creeping of the\nchromatophores upon the blood-vessels. The chromatophores are at first\nscattered irregularly over the yolk-sac and show their characteristic\nramifications. There is at that time no definite relation between\nblood-vessels and chromatophores. As soon as a ramification of a\nchromatophore comes in contact with a blood-vessel the whole mass of the\nchromatophore creeps gradually on the blood-vessel and forms a complete\nsheath around the vessel, until finally all the chromatophores form a\nsheath around the vessels and no more pigment cells are found in the\nmeshes between the vessels. Nobody who has not actually watched the\nprocess of the creeping of the chromatophores upon the blood-vessels\nwould anticipate that the tiger-like colouration of the yolk-sac in the\nlater stages of the development was brought about in this way. Similar\nfacts can be observed in regard to the first marking of the embryo\nitself. The writer is inclined to believe that we are here dealing with\na case of chemotropism, and that the oxygen of the blood may be the\ncause of the spreading of the chromatophores around the blood-vessels.\nCertain observations seem to indicate the possibility that in the adult\nthe chromatophores have, in some forms at least, a more rigid structure\nand are prevented from acting in the way indicated. It seems to the\nwriter that such observations as those made on Fundulus might simplify\nthe problem of the hereditary transmission of certain markings.\n\nDriesch has found that a tropism underlies the arrangement of the\nskeleton in the pluteus larvae of the sea-urchin. The position of this\nskeleton is predetermined by the arrangement of the mesenchyme cells,\nand Driesch has shown that these cells migrate actively to the place\nof their destination, possibly led there under the influence of certain\nchemical substances. When Driesch scattered these cells mechanically\nbefore their migration, they nevertheless reached their destination.\n\nIn the developing eggs of insects the nuclei, together with some\ncytoplasm, migrate to the periphery of the egg. Herbst pointed out that\nthis might be a case of chemotropism, caused by the oxygen surrounding\nthe egg. The writer has expressed the opinion that the formation of\nthe blastula may be caused generally by a tropic reaction of the\nblastomeres, the latter being forced by an outside influence to creep to\nthe surface of the egg.\n\nThese examples may suffice to indicate that the arrangement of definite\ngroups of cells and the morphological effects resulting therefrom may\nbe determined by forces lying outside the cells. Since these forces are\nubiquitous and constant it appears as if we were dealing exclusively\nwith the influence of a gamete; while in reality all that it is\nnecessary for the gamete to transmit is a certain form of irritability.\n\n(d) FACTORS WHICH DETERMINE PLACE AND TIME FOR THE DEPOSITION OF EGGS.\n\nFor the preservation of species the instinct of animals to lay their\neggs in places in which the young larvae find their food and can develop\nis of paramount importance. A simple example of this instinct is the\nfact that the common fly lays its eggs on putrid material which serves\nas food for the young larvae. When a piece of meat and of fat of the\nsame animal are placed side by side, the fly will deposit its eggs upon\nthe meat on which the larvae can grow, and not upon the fat, on which\nthey would starve. Here we are dealing with the effect of a volatile\nnitrogenous substance which reflexly causes the peristaltic motions for\nthe laying of the egg in the female fly.\n\nKammerer has investigated the conditions for the laying of eggs in two\nforms of salamanders, e.g. Salamandra atra and S. maculosa. In both\nforms the eggs are fertilised in the body and begin to develop in the\nuterus. Since there is room only for a few larvae in the uterus, a large\nnumber of eggs perish and this number is the greater the longer the\nperiod of gestation. It thus happens that when the animals retain their\neggs a long time, very few young ones are born; and these are in a\nrather advanced stage of development, owing to the long time which\nelapsed since they were fertilised. When the animal lays its eggs\ncomparatively soon after copulation, many eggs (from 12 to 72) are\nproduced and the larvae are of course in an early stage of development.\nIn the early stage the larvae possess gills and can therefore live in\nwater, while in later stages they have no gills and breathe through\ntheir lungs. Kammerer showed that both forms of Salamandra can be\ninduced to lay their eggs early or late, according to the physical\nconditions surrounding them. If they are kept in water or in proximity\nto water and in a moist atmosphere they have a tendency to lay their\neggs earlier and a comparatively high temperature enhances the tendency\nto shorten the period of gestation. If the salamanders are kept in\ncomparative dryness they show a tendency to lay their eggs rather late\nand a low temperature enhances this tendency.\n\nSince Salamandra atra is found in rather dry alpine regions with a\nrelatively low temperature and Salamandra maculosa in lower regions with\nplenty of water and a higher temperature, the fact that S. atra bears\nyoung which are already developed and beyond the stage of aquatic life,\nwhile S. maculosa bears young ones in an earlier stage, has been termed\nadaptation. Kammerer's experiments, however, show that we are dealing\nwith the direct effects of definite outside forces. While we may speak\nof adaptation when all or some of the variables which determine a\nreaction are unknown, it is obviously in the interest of further\nscientific progress to connect cause and effect directly whenever our\nknowledge allows us to do so.\n\nVII. CONCLUDING REMARKS.\n\nThe discovery of De Vries, that new species may arise by mutation and\nthe wide if not universal applicability of Mendel's Law to phenomena of\nheredity, as shown especially by Bateson and his pupils, must, for\nthe time being, if not permanently, serve as a basis for theories of\nevolution. These discoveries place before the experimental biologist the\ndefinite task of producing mutations by physico-chemical means. It\nis true that certain authors claim to have succeeded in this, but\nthe writer wishes to apologise to these authors for his inability to\nconvince himself of the validity of their claims at the present moment.\nHe thinks that only continued breeding of these apparent mutants through\nseveral generations can afford convincing evidence that we are here\ndealing with mutants rather than with merely pathological variations.\n\nWhat was said in regard to the production of new species by\nphysico-chemical means may be repeated with still more justification\nin regard to the second problem of transformation, namely the making\nof living from inanimate matter. The purely morphological imitations\nof bacteria or cells which physicists have now and then proclaimed as\nartificially produced living beings; or the plays on words by which,\ne.g. the regeneration of broken crystals and the regeneration of lost\nlimbs by a crustacean were declared identical, will not appeal to the\nbiologist. We know that growth and development in animals and plants are\ndetermined by definite although complicated series of catenary chemical\nreactions, which result in the synthesis of a DEFINITE compound or group\nof compounds, namely, NUCLEINS.\n\nThe nucleins have the peculiarity of acting as ferments or enzymes\nfor their own synthesis. Thus a given type of nucleus will continue to\nsynthesise other nuclein of its own kind. This determines the continuity\nof a species; since each species has, probably, its own specific nuclein\nor nuclear material. But it also shows us that whoever claims to have\nsucceeded in making living matter from inanimate will have to prove that\nhe has succeeded in producing nuclein material which acts as a ferment\nfor its own synthesis and thus reproduces itself. Nobody has thus far\nsucceeded in this, although nothing warrants us in taking it for granted\nthat this task is beyond the power of science.\n\n\n\n\nXV. THE VALUE OF COLOUR IN THE STRUGGLE FOR LIFE. By E.B. Poulton.\n\nHope Professor of Zoology in the University of Oxford.\n\n\nINTRODUCTION.\n\nThe following pages have been written almost entirely from the\nhistorical stand-point. Their principal object has been to give some\naccount of the impressions produced on the mind of Darwin and his great\ncompeer Wallace by various difficult problems suggested by the colours\nof living nature. In order to render the brief summary of Darwin's\nthoughts and opinions on the subject in any way complete, it was found\nnecessary to say again much that has often been said before. No attempt\nhas been made to display as a whole the vast contribution of Wallace;\nbut certain of its features are incidentally revealed in passages quoted\nfrom Darwin's letters. It is assumed that the reader is familiar with\nthe well-known theories of Protective Resemblance, Warning Colours, and\nMimicry both Batesian and Mullerian. It would have been superfluous to\nexplain these on the present occasion; for a far more detailed account\nthan could have been attempted in these pages has recently appeared.\n(Poulton, \"Essays on Evolution\" Oxford, 1908, pages 293-382.) Among the\nolder records I have made a point of bringing together the principal\nobservations scattered through the note-books and collections of W.J.\nBurchell. These have never hitherto found a place in any memoir dealing\nwith the significance of the colours of animals.\n\nINCIDENTAL COLOURS.\n\nDarwin fully recognised that the colours of living beings are not\nnecessarily of value as colours, but that they may be an incidental\nresult of chemical or physical structure. Thus he wrote to T. Meehan,\nOct. 9, 1874: \"I am glad that you are attending to the colours of\ndioecious flowers; but it is well to remember that their colours may be\nas unimportant to them as those of a gall, or, indeed, as the colour\nof an amethyst or ruby is to these gems.\" (\"More Letters of Charles\nDarwin\", Vol. I. pages 354, 355. See also the admirable account of\nincidental colours in \"Descent of Man\" (2nd edition), 1874, pages 261,\n262.)\n\nIncidental colours remain as available assets of the organism ready to\nbe turned to account by natural selection. It is a probable speculation\nthat all pigmentary colours were originally incidental; but now and for\nimmense periods of time the visible tints of animals have been modified\nand arranged so as to assist in the struggle with other organisms or in\ncourtship. The dominant colouring of plants, on the other hand, is\nan essential element in the paramount physiological activity of\nchlorophyll. In exceptional instances, however, the shapes and visible\ncolours of plants may be modified in order to promote concealment.\n\nTELEOLOGY AND ADAPTATION.\n\nIn the department of Biology which forms the subject of this essay,\nthe adaptation of means to an end is probably more evident than in\nany other; and it is therefore of interest to compare, in a brief\nintroductory section, the older with the newer teleological views.\n\nThe distinctive feature of Natural Selection as contrasted with other\nattempts to explain the process of Evolution is the part played by the\nstruggle for existence. All naturalists in all ages must have known\nsomething of the operations of \"Nature red in tooth and claw\"; but it\nwas left for this great theory to suggest that vast extermination is\na necessary condition of progress, and even of maintaining the ground\nalready gained.\n\nRealising that fitness is the outcome of this fierce struggle, thus\nturned to account for the first time, we are sometimes led to associate\nthe recognition of adaptation itself too exclusively with Natural\nSelection. Adaptation had been studied with the warmest enthusiasm\nnearly forty years before this great theory was given to the scientific\nworld, and it is difficult now to realise the impetus which the works\nof Paley gave to the study of Natural History. That they did inspire the\nnaturalists of the early part of the last century is clearly shown in\nthe following passages.\n\nIn the year 1824 the Ashmolean Museum at Oxford was intrusted to the\ncare of J.S. Duncan of New College. He was succeeded in this office by\nhis brother, P.B. Duncan, of the same College, author of a History of\nthe Museum, which shows very clearly the influence of Paley upon the\nstudy of nature, and the dominant position given to his teachings:\n\"Happily at this time (1824) a taste for the study of natural history\nhad been excited in the University by Dr Paley's very interesting\nwork on Natural Theology, and the very popular lectures of Dr Kidd on\nComparative Anatomy, and Dr Buckland on Geology.\" In the arrangement of\nthe contents of the Museum the illustration of Paley's work was given\nthe foremost place by J.S. Duncan: \"The first division proposes to\nfamiliarize the eye to those relations of all natural objects which form\nthe basis of argument in Dr Paley's Natural Theology; to induce a mental\nhabit of associating the view of natural phenomena with the conviction\nthat they are the media of Divine manifestation; and by such association\nto give proper dignity to every branch of natural science.\" (From\n\"History and Arrangement of the Ashmolean Museum\" by P.B. Duncan: see\npages vi, vii of \"A Catalogue of the Ashmolean Museum\", Oxford, 1836.)\n\nThe great naturalist, W.J. Burchell, in his classical work shows the\nsame recognition of adaptation in nature at a still earlier date.\nUpon the subject of collections he wrote (\"Travels in the Interior of\nSouthern Africa\", London, Vol. I. 1822, page 505. The references to\nBurchell's observations in the present essay are adapted from\nthe author's article in \"Report of the British and South African\nAssociations\", 1905, Vol. III. pages 57-110.): \"It must not be supposed\nthat these charms (the pleasures of Nature) are produced by the mere\ndiscovery of new objects: it is the harmony with which they have been\nadapted by the Creator to each other, and to the situations in which\nthey are found, which delights the observer in countries where Art has\nnot yet introduced her discords.\" The remainder of the passage is so\nadmirable that I venture to quote it: \"To him who is satisfied with\namassing collections of curious objects, simply for the pleasure of\npossessing them, such objects can afford, at best, but a childish\ngratification, faint and fleeting; while he who extends his view beyond\nthe narrow field of nomenclature, beholds a boundless expanse, the\nexploring of which is worthy of the philosopher, and of the best talents\nof a reasonable being.\"\n\nOn September 14, 1811, Burchell was at Zand Valley (Vlei), or Sand Pool,\na few miles south-west of the site of Prieska, on the Orange River. Here\nhe found a Mesembryanthemum (M. turbiniforme, now M. truncatum) and also\na \"Gryllus\" (Acridian), closely resembling the pebbles with which their\nlocality was strewn. He says of both of these, \"The intention of Nature,\nin these instances, seems to have been the same as when she gave to the\nChameleon the power of accommodating its color, in a certain degree,\nto that of the object nearest to it, in order to compensate for the\ndeficiency of its locomotive powers. By their form and colour, this\ninsect may pass unobserved by those birds, which otherwise would soon\nextirpate a species so little able to elude its pursuers, and this juicy\nlittle Mesembryanthemum may generally escape the notice of cattle and\nwild animals.\" (Loc. cit. pages 310, 311. See Sir William Thiselton-Dyer\n\"Morphological Notes\", XI.; \"Protective Adaptations\", I.; \"Annals of\nBotany\", Vol. XX. page 124. In plates VII., VIII. and IX. accompanying\nthis article the author represents the species observed by Burchell,\ntogether with others in which analogous adaptations exist. He writes:\n\"Burchell was clearly on the track on which Darwin reached the goal.\nBut the time had not come for emancipation from the old teleology. This,\nhowever, in no respect detracts from the merit or value of his work.\nFor, as Huxley has pointed out (\"Life and Letters of Thomas Henry\nHuxley\", London, 1900, I. page 457), the facts of the old teleology are\nimmediately transferable to Darwinism, which simply supplies them with a\nnatural in place of a supernatural explanation.\") Burchell here seems\nto miss, at least in part, the meaning of the relationship between the\nquiescence of the Acridian and its cryptic colouring. Quiescence is an\nessential element in the protective resemblance to a stone--probably\neven more indispensable than the details of the form and colouring.\nAlthough Burchell appears to overlook this point he fully recognised the\ncommunity between protection by concealment and more aggressive modes\nof defence; for, in the passage of which a part is quoted above, he\nspecially refers to some earlier remarks on page 226 of his Vol. I. We\nhere find that even when the oxen were resting by the Juk rivier (Yoke\nriver), on July 19, 1811, Burchell observed \"Geranium spinosum, with\na fleshy stem and large white flowers...; and a succulent species of\nPelargonium... so defended by the old panicles, grown to hard woody\nthorns, that no cattle could browze upon it.\" He goes on to say, \"In\nthis arid country, where every juicy vegetable would soon be eaten up by\nthe wild animals, the Great Creating Power, with all-provident wisdom,\nhas given to such plants either an acrid or poisonous juice, or sharp\nthorns, to preserve the species from annihilation... \" All these modes\nof defence, especially adapted to a desert environment, have since\nbeen generally recognised, and it is very interesting to place beside\nBurchell's statement the following passage from a letter written by\nDarwin, Aug. 7, 1868, to G.H. Lewes; \"That Natural Selection would tend\nto produce the most formidable thorns will be admitted by every one\nwho has observed the distribution in South America and Africa (vide\nLivingstone) of thorn-bearing plants, for they always appear where the\nbushes grow isolated and are exposed to the attacks of mammals. Even\nin England it has been noticed that all spine-bearing and sting-bearing\nplants are palatable to quadrupeds, when the thorns are crushed.\" (\"More\nLetters\", I. page 308.)\n\nADAPTATION AND NATURAL SELECTION.\n\nI have preferred to show the influence of the older teleology upon\nNatural History by quotations from a single great and insufficiently\nappreciated naturalist. It might have been seen equally well in the\npages of Kirby and Spence and those of many other writers. If the older\nnaturalists who thought and spoke with Burchell of \"the intention\nof Nature\" and the adaptation of beings \"to each other, and to\nthe situations in which they are found,\" could have conceived the\npossibility of evolution, they must have been led, as Darwin was, by the\nsame considerations to Natural Selection. This was impossible for them,\nbecause the philosophy which they followed contemplated the phenomena of\nadaptation as part of a static immutable system. Darwin, convinced that\nthe system is dynamic and mutable, was prevented by these very phenomena\nfrom accepting anything short of the crowning interpretation offered by\nNatural Selection. (\"I had always been much struck by such adaptations\n(e.g. woodpecker and tree-frog for climbing, seeds for dispersal),\nand until these could be explained it seemed to me almost useless\nto endeavour to prove by indirect evidence that species have been\nmodified.\" \"Autobiography\" in \"Life and Letters of Charles Darwin\", Vol.\nI. page 82. The same thought is repeated again and again in Darwin's\nletters to his friends. It is forcibly urged in the Introduction to\nthe \"Origin\" (1859), page 3.) And the birth of Darwin's unalterable\nconviction that adaptation is of dominant importance in the organic\nworld,--a conviction confirmed and ever again confirmed by his\nexperience as a naturalist--may probably be traced to the influence of\nthe great theologian. Thus Darwin, speaking of his Undergraduate days,\ntells us in his \"Autobiography\" that the logic of Paley's \"Evidences\nof Christianity\" and \"Moral Philosophy\" gave him as much delight as did\nEuclid.\n\n\"The careful study of these works, without attempting to learn any part\nby rote, was the only part of the academical course which, as I then\nfelt and as I still believe, was of the least use to me in the education\nof my mind. I did not at that time trouble myself about Paley's\npremises; and taking these on trust, I was charmed and convinced by the\nlong line of argumentation.\" (\"Life and Letters\", I. page 47.)\n\nWhen Darwin came to write the \"Origin\" he quoted in relation to Natural\nSelection one of Paley's conclusions. \"No organ will be formed, as Paley\nhas remarked, for the purpose of causing pain or for doing an injury to\nits possessor.\" (\"Origin of Species\" (1st edition) 1859, page 201.)\n\nThe study of adaptation always had for Darwin, as it has for many,\na peculiar charm. His words, written Nov. 28, 1880, to Sir W.\nThiselton-Dyer, are by no means inapplicable to-day: \"Many of the\nGermans are very contemptuous about making out use of organs; but they\nmay sneer the souls out of their bodies, and I for one shall think it\nthe most interesting part of natural history.\" (\"More Letters\" II. page\n428.)\n\nPROTECTIVE AND AGGRESSIVE RESEMBLANCE: PROCRYPTIC AND ANTICRYPTIC\nCOLOURING.\n\nColouring for the purpose of concealment is sometimes included under the\nhead Mimicry, a classification adopted by H.W. Bates in his classical\npaper. Such an arrangement is inconvenient, and I have followed Wallace\nin keeping the two categories distinct.\n\nThe visible colours of animals are far more commonly adapted for\nProtective Resemblance than for any other purpose. The concealment of\nanimals by their colours, shapes and attitudes, must have been well\nknown from the period at which human beings first began to take an\nintelligent interest in Nature. An interesting early record is that of\nSamuel Felton, who (Dec. 2, 1763) figured and gave some account of an\nAcridian (Phyllotettix) from Jamaica. Of this insect he says \"THE THORAX\nis like a leaf that is raised perpendicularly from the body.\" (\"Phil.\nTrans. Roy. Soc.\" Vol. LIV. Tab. VI. page 55.)\n\nBoth Protective and Aggressive Resemblances were appreciated and clearly\nexplained by Erasmus Darwin in 1794: \"The colours of many animals seem\nadapted to their purposes of concealing themselves either to avoid\ndanger, or to spring upon their prey.\" (\"Zoonomia\", Vol. I. page 509,\nLondon, 1794.)\n\nProtective Resemblance of a very marked and beautiful kind is found\nin certain plants, inhabitants of desert areas. Examples observed by\nBurchell almost exactly a hundred years ago have already been mentioned.\nIn addition to the resemblance to stones Burchell observed, although\nhe did not publish the fact, a South African plant concealed by its\nlikeness to the dung of birds. (Sir William Thiselton-Dyer has suggested\nthe same method of concealment (\"Annals of Botany\", Vol. XX. page 123).\nReferring to Anacampseros papyracea, figured on plate IX., the author\nsays of its adaptive resemblance: \"At the risk of suggesting one perhaps\nsomewhat far-fetched, I must confess that the aspect of the plant always\ncalls to my mind the dejecta of some bird, and the more so owing to the\nwhitening of the branches towards the tips\" (loc. cit. page 126). The\nstudent of insects, who is so familiar with this very form of protective\nresemblance in larvae, and even perfect insects, will not be inclined to\nconsider the suggestion far-fetched.) The observation is recorded in\none of the manuscript journals kept by the great explorer during his\njourney. I owe the opportunity of studying it to the kindness of Mr\nFrancis A. Burchell of the Rhodes University College, Grahamstown. The\nfollowing account is given under the date July 5, 1812, when Burchell\nwas at the Makkwarin River, about half-way between the Kuruman River and\nLitakun the old capital of the Bachapins (Bechuanas): \"I found a curious\nlittle Crassula (not in flower) so snow white, that I should never has\n(have) distinguished it from the white limestones... It was an inch high\nand a little branchy,... and was at first mistaken for the dung of birds\nof the passerine order. I have often had occasion to remark that in\nstony place(s) there grow many small succulent plants and abound insects\n(chiefly Grylli) which have exactly the same colour as the ground and\nmust for ever escape observation unless a person sit on the ground and\nobserve very attentively.\"\n\nThe cryptic resemblances of animals impressed Darwin and Wallace in\nvery different degrees, probably in part due to the fact that Wallace's\ntropical experiences were so largely derived from the insect world, in\npart to the importance assigned by Darwin to Sexual Selection \"a\nsubject which had always greatly interested me,\" as he says in his\n\"Autobiography\", (\"Life and Letters\", Vol. I. page 94.) There is no\nreference to Cryptic Resemblance in Darwin's section of the Joint Essay,\nalthough he gives an excellent short account of Sexual Selection (see\npage 295). Wallace's section on the other hand contains the following\nstatement: \"Even the peculiar colours of many animals, especially\ninsects, so closely resembling the soil or the leaves or the trunks on\nwhich they habitually reside, are explained on the same principle; for\nthough in the course of ages varieties of many tints may have occurred,\nYET THOSE RACES HAVING COLOURS BEST ADAPTED TO CONCEALMENT FROM THEIR\nENEMIES WOULD INEVITABLY SURVIVE THE LONGEST.\" (\"Journ. Proc. Linn.\nSoc.\" Vol. III. 1859, page 61. The italics are Wallace's.)\n\nIt would occupy too much space to attempt any discussion of the\ndifference between the views of these two naturalists, but it is clear\nthat Darwin, although fully believing in the efficiency of protective\nresemblance and replying to St George Mivart's contention that Natural\nSelection was incompetent to produce it (\"Origin\" (6th edition) London,\n1872, pages 181, 182; see also page 66.), never entirely agreed with\nWallace's estimate of its importance. Thus the following extract from a\nletter to Sir Joseph Hooker, May 21, 1868, refers to Wallace: \"I find\nI must (and I always distrust myself when I differ from him) separate\nrather widely from him all about birds' nests and protection; he is\nriding that hobby to death.\" (\"More Letters\", I. page 304.) It is clear\nfrom the account given in \"The Descent of Man\", (London, 1874, pages\n452-458. See also \"Life and Letters\", III. pages 123-125, and \"More\nLetters\", II. pages 59-63, 72-74, 76-78, 84-90, 92, 93.), that the\ndivergence was due to the fact that Darwin ascribed more importance\nto Sexual Selection than did Wallace, and Wallace more importance to\nProtective Resemblance than Darwin. Thus Darwin wrote to Wallace,\nOct. 12 and 13, 1867: \"By the way, I cannot but think that you push\nprotection too far in some cases, as with the stripes on the tiger.\"\n(\"More Letters\", I. page 283.) Here too Darwin was preferring the\nexplanation offered by Sexual Selection (\"Descent of Man\" (2nd edition)\n1874, pages 545, 546.), a preference which, considering the relation of\nthe colouring of the lion and tiger to their respective environments,\nfew naturalists will be found to share. It is also shown that Darwin\ncontemplated the possibility of cryptic colours such as those of\nPatagonian animals being due to sexual selection influenced by the\naspect of surrounding nature.\n\nNearly a year later Darwin in his letter of May 5, 1868?, expressed\nhis agreement with Wallace's views: \"Expect that I should put sexual\nselection as an equal, or perhaps as even a more important agent in\ngiving colour than Natural Selection for protection.\" (\"More Letters\",\nII. pages 77, 78.) The conclusion expressed in the above quoted passage\nis opposed by the extraordinary development of Protective Resemblance in\nthe immature stages of animals, especially insects.\n\nIt must not be supposed, however, that Darwin ascribed an unimportant\nrole to Cryptic Resemblances, and as observations accumulated he came to\nrecognise their efficiency in fresh groups of the animal kingdom. Thus\nhe wrote to Wallace, May 5, 1867: \"Haeckel has recently well shown that\nthe transparency and absence of colour in the lower oceanic animals,\nbelonging to the most different classes, may be well accounted for on\nthe principle of protection.\" (\"More Letters\", II. page 62. See also\n\"Descent of Man\", page 261.) Darwin also admitted the justice of\nProfessor E.S. Morse's contention that the shells of molluscs are often\nadaptively coloured. (\"More Letters\", II. page 95.) But he looked\nupon cryptic colouring and also mimicry as more especially Wallace's\ndepartments, and sent to him and to Professor Meldola observations and\nnotes bearing upon these subjects. Thus the following letter given to me\nby Dr A.R. Wallace and now, by kind permission, published for the first\ntime, accompanied a photograph of the chrysalis of Papilio sarpedon\nchoredon, Feld., suspended from a leaf of its food-plant:\n\nJuly 9th, Down, Beckenham, Kent.\n\nMy Dear Wallace,\n\nDr G. Krefft has sent me the enclosed from Sydney. A nurseryman saw a\ncaterpillar feeding on a plant and covered the whole up, but when he\nsearched for the cocoon (pupa), was long before he could find it, so\ngood was its imitation in colour and form to the leaf to which it was\nattached. I hope that the world goes well with you. Do not trouble\nyourself by acknowledging this.\n\nEver yours\n\nCh. Darwin.\n\nAnother deeply interesting letter of Darwin's bearing upon protective\nresemblance, has only recently been shown to me by my friend Professor\nE.B. Wilson, the great American Cytologist. With his kind consent and\nthat of Mr Francis Darwin, this letter, written four months before\nDarwin's death on April 19, 1882, is reproduced here (The letter is\naddressed: \"Edmund B. Wilson, Esq., Assistant in Biology, John Hopkins\nUniversity, Baltimore Md, U. States.\"):\n\nDecember 21, 1881.\n\nDear Sir,\n\nI thank you much for having taken so much trouble in describing fully\nyour interesting and curious case of mimickry.\n\nI am in the habit of looking through many scientific Journals, and\nthough my memory is now not nearly so good as it was, I feel pretty sure\nthat no such case as yours has been described (amongst the nudibranch)\nmolluscs. You perhaps know the case of a fish allied to Hippocampus,\n(described some years ago by Dr Gunther in \"Proc. Zoolog. Socy.\") which\nclings by its tail to sea-weeds, and is covered with waving filaments\nso as itself to look like a piece of the same sea-weed. The parallelism\nbetween your and Dr Gunther's case makes both of them the more\ninteresting; considering how far a fish and a mollusc stand apart. It\nwould be difficult for anyone to explain such cases by the direct\naction of the environment.--I am glad that you intend to make further\nobservations on this mollusc, and I hope that you will give a figure and\nif possible a coloured figure.\n\nWith all good wishes from an old brother naturalist,\n\nI remain, Dear Sir,\n\nYours faithfully,\n\nCharles Darwin.\n\nProfessor E.B. Wilson has kindly given the following account of the\ncircumstances under which he had written to Darwin: \"The case to which\nDarwin's letter refers is that of the nudibranch mollusc Scyllaea,\nwhich lives on the floating Sargassum and shows a really astonishing\nresemblance to the plant, having leaf-shaped processes very closely\nsimilar to the fronds of the sea-weed both in shape and in colour. The\nconcealment of the animal may be judged from the fact that we found\nthe animal quite by accident on a piece of Sargassum that had been in a\nglass jar in the laboratory for some time and had been closely examined\nin the search for hydroids and the like without disclosing the presence\nupon it of two large specimens of the Scyllaea (the animal, as I recall\nit, is about two inches long). It was first detected by its movements\nalone, by someone (I think a casual visitor to the laboratory) who was\nlooking closely at the Sargassum and exclaimed 'Why, the sea-weed is\nmoving its leaves'! We found the example in the summer of 1880 or 1881\nat Beaufort, N.C., where the Johns Hopkins laboratory was located for\nthe time being. It must have been seen by many others, before or since.\n\n\"I wrote and sent to Darwin a short description of the case at the\nsuggestion of Brooks, with whom I was at the time a student. I was, of\ncourse, entirely unknown to Darwin (or to anyone else) and to me the\nprincipal interest of Darwin's letter is the evidence that it gives of\nhis extraordinary kindness and friendliness towards an obscure youngster\nwho had of course absolutely no claim upon his time or attention. The\nlittle incident made an indelible impression upon my memory and taught\nme a lesson that was worth learning.\"\n\nVARIABLE PROTECTIVE RESEMBLANCE.\n\nThe wonderful power of rapid colour adjustment possessed by the\ncuttle-fish was observed by Darwin in 1832 at St Jago, Cape de Verd\nIslands, the first place visited during the voyage of the \"Beagle\".\nFrom Rio he wrote to Henslow, giving the following account of his\nobservations, May 18, 1832: \"I took several specimens of an Octopus\nwhich possessed a most marvellous power of changing its colours,\nequalling any chameleon, and evidently accommodating the changes to the\ncolour of the ground which it passed over. Yellowish green, dark brown,\nand red, were the prevailing colours; this fact appears to be new, as\nfar as I can find out.\" (\"Life and Letters\", I. pages 235, 236. See\nalso Darwin's \"Journal of Researches\", 1876, pages 6-8, where a far more\ndetailed account is given together with a reference to \"Encycl. of Anat.\nand Physiol.\")\n\nDarwin was well aware of the power of individual colour adjustment,\nnow known to be possessed by large numbers of lepidopterous pupae and\nlarvae. An excellent example was brought to his notice by C.V. Riley\n(\"More Letters\" II, pages 385, 386.), while the most striking of the\nearly results obtained with the pupae of butterflies--those of Mrs M.E.\nBarber upon Papilio nireus--was communicated by him to the Entomological\nSociety of London. (\"Trans. Ent. Soc. Lond.\" 1874, page 519. See also\n\"More Letters\", II. page 403.)\n\nIt is also necessary to direct attention to C.W. Beebe's (\"Zoologica:\nN.Y. Zool. Soc.\" Vol. I. No. 1, Sept. 25, 1907: \"Geographic variation\nin birds with especial reference to the effects of humidity\".) recent\ndiscovery that the pigmentation of the plumage of certain birds is\nincreased by confinement in a superhumid atmosphere. In Scardafella\ninca, on which the most complete series of experiments was made, the\nchanges took place only at the moults, whether normal and annual or\nartificially induced at shorter periods. There was a corresponding\nincrease in the choroidal pigment of the eye. At a certain advanced\nstage of feather pigmentation a brilliant iridescent bronze or green\ntint made its appearance on those areas where iridescence most often\noccurs in allied genera. Thus in birds no less than in insects,\ncharacters previously regarded as of taxonomic value, can be evoked or\nwithheld by the forces of the environment.\n\nWARNING OR APOSEMATIC COLOURS.\n\nFrom Darwin's description of the colours and habits it is evident that\nhe observed, in 1833, an excellent example of warning colouring in a\nlittle South American toad (Phryniscus nigricans). He described it in a\nletter to Henslow, written from Monte Video, Nov. 24, 1832: \"As for\none little toad, I hope it may be new, that it may be christened\n'diabolicus.' Milton must allude to this very individual when he talks\nof 'squat like a toad'; its colours are by Werner (\"Nomenclature of\nColours\", 1821) ink black, vermilion red and buff orange.\" (\"More\nLetters\", I. page 12.) In the \"Journal of Researches\" (1876, page 97.)\nits colours are described as follows: \"If we imagine, first, that it had\nbeen steeped in the blackest ink, and then, when dry, allowed to crawl\nover a board, freshly painted with the brightest vermilion, so as to\ncolour the soles of its feet and parts of its stomach, a good idea\nof its appearance will be gained.\" \"Instead of being nocturnal in its\nhabits, as other toads are, and living in damp obscure recesses, it\ncrawls during the heat of the day about the dry sand-hillocks and\narid plains,... \" The appearance and habits recall T. Belt's well-known\ndescription of the conspicuous little Nicaraguan frog which he found to\nbe distasteful to a duck. (\"The Naturalist in Nicaragua\" (2nd edition)\nLondon, 1888, page 321.)\n\nThe recognition of the Warning Colours of caterpillars is due in the\nfirst instance to Darwin, who, reflecting on Sexual Selection, was\npuzzled by the splendid colours of sexually immature organisms. He\napplied to Wallace \"who has an innate genius for solving difficulties.\"\n(\"Descent of Man\", page 325. On this and the following page an excellent\naccount of the discovery will be found, as well as in Wallace's \"Natural\nSelection\", London, 1875, pages 117-122.) Darwin's original letter\nexists (\"Life and Letters\", III. pages 93, 94.), and in it we are\ntold that he had taken the advice given by Bates: \"You had better ask\nWallace.\" After some consideration Wallace replied that he believed the\ncolours of conspicuous caterpillars and perfect insects were a warning\nof distastefulness and that such forms would be refused by birds.\nDarwin's reply (\"Life and Letters\", III. pages 94, 95.) is extremely\ninteresting both for its enthusiasm at the brilliancy of the hypothesis\nand its caution in acceptance without full confirmation:\n\n\"Bates was quite right; you are the man to apply to in a difficulty. I\nnever heard anything more ingenious than your suggestion, and I hope you\nmay be able to prove it true. That is a splendid fact about the white\nmoths (A single white moth which was rejected by young turkeys, while\nother moths were greedily devoured: \"Natural Selection\", 1875, page\n78.); it warms one's very blood to see a theory thus almost proved to be\ntrue.\"\n\nTwo years later the hypothesis was proved to hold for caterpillars of\nmany kinds by J. Jenner Weir and A.G. Butler, whose observations have\nsince been abundantly confirmed by many naturalists. Darwin wrote to\nWeir, May 13, 1869: \"Your verification of Wallace's suggestion seems\nto me to amount to quite a discovery.\" (\"More Letters\", II. page 71\n(footnote).)\n\nRECOGNITION OR EPISEMATIC CHARACTERS.\n\nThis principle does not appear to have been in any way foreseen by\nDarwin, although he draws special attention to several elements of\npattern which would now be interpreted by many naturalists as epismes.\nHe believed that the markings in question interfered with the cryptic\neffect, and came to the conclusion that, even when common to both sexes,\nthey \"are the result of sexual selection primarily applied to the male.\"\n(\"Descent of Man\", page 544.) The most familiar of all recognition\ncharacters was carefully explained by him, although here too explained\nas an ornamental feature now equally transmitted to both sexes: \"The\nhare on her form is a familiar instance of concealment through colour;\nyet this principle partly fails in a closely-allied species, the rabbit,\nfor when running to its burrow, it is made conspicuous to the sportsman,\nand no doubt to all beasts of prey, by its upturned white tail.\"\n(\"Descent of Man\", page 542.)\n\nThe analogous episematic use of the bright colours of flowers to attract\ninsects for effecting cross-fertilisation and of fruits to attract\nvertebrates for effecting dispersal is very clearly explained in the\n\"Origin\". (Edition 1872, page 161. For a good example of Darwin's\ncaution in dealing with exceptions see the allusion to brightly coloured\nfruit in \"More Letters\", II. page 348.)\n\nIt is not, at this point, necessary to treat sematic characters at\nany greater length. They will form the subject of a large part of\nthe following section, where the models of Batesian (Pseudaposematic)\nmimicry are considered as well as the Mullerian (Synaposematic)\ncombinations of Warning Colours.\n\nMIMICRY,--BATESIAN OR PSEUDAPOSEMATIC, MULLERIAN OR SYNAPOSEMATIC.\n\nThe existence of superficial resemblances between animals of various\ndegrees of affinity must have been observed for hundreds of years.\nAmong the early examples, the best known to me have been found in\nthe manuscript note-books and collections of W.J. Burchell, the great\ntraveller in Africa (1810-15) and Brazil (1825-30). The most interesting\nof his records on this subject are brought together in the following\nparagraphs.\n\nConspicuous among well-defended insects are the dark steely or\niridescent greenish blue fossorial wasps or sand-wasps, Sphex and the\nallied genera. Many Longicorn beetles mimic these in colour, slender\nshape of body and limbs, rapid movements, and the readiness with which\nthey take to flight. On Dec. 21, 1812, Burchell captured one such beetle\n(Promeces viridis) at Kosi Fountain on the journey from the source\nof the Kuruman River to Klaarwater. It is correctly placed among the\nLongicorns in his catalogue, but opposite to its number is the comment\n\"Sphex! totus purpureus.\"\n\nIn our own country the black-and-yellow colouring of many stinging\ninsects, especially the ordinary wasps, affords perhaps the commonest\nmodel for mimicry. It is reproduced with more or less accuracy on moths,\nflies and beetles. Among the latter it is again a Longicorn which offers\none of the best-known, although by no means one of the most perfect,\nexamples. The appearance of the well-known \"wasp-beetle\" (Clytus\narietis) in the living state is sufficiently suggestive to prevent\nthe great majority of people from touching it. In Burchell's Brazilian\ncollection there is a nearly allied species (Neoclytus curvatus) which\nappears to be somewhat less wasp-like than the British beetle. The\nspecimen bears the number \"1188,\" and the date March 27, 1827, when\nBurchell was collecting in the neighbourhood of San Paulo. Turning to\nthe corresponding number in the Brazilian note-book we find this\nrecord: \"It runs rapidly like an ichneumon or wasp, of which it has the\nappearance.\"\n\nThe formidable, well-defended ants are as freely mimicked by other\ninsects as the sand-wasps, ordinary wasps and bees. Thus on February\n17, 1901, Guy A.K. Marshall captured, near Salisbury, Mashonaland,\nthree similar species of ants (Hymenoptera) with a bug (Hemiptera) and\na Locustid (Orthoptera), the two latter mimicking the former. All the\ninsects, seven in number, were caught on a single plant, a small bushy\nvetch. (\"Trans. Ent. Soc. Lond.\" 1902, page 535, plate XIX. figs.\n53-59.)\n\nThis is an interesting recent example from South Africa, and large\nnumbers of others might be added--the observations of many naturalists\nin many lands; but nearly all of them known since that general awakening\nof interest in the subject which was inspired by the great hypotheses\nof H.W. Bates and Fritz Muller. We find, however, that Burchell had\nmore than once recorded the mimetic resemblance to ants. An extremely\nant-like bug (the larva of a species of Alydus) in his Brazilian\ncollection is labelled \"1141,\" with the date December 8, 1826, when\nBurchell was at the Rio das Pedras, Cubatao, near Santos. In the\nnote-book the record is as follows: \"1141 Cimex. I collected this for a\nFormica.\"\n\nSome of the chief mimics of ants are the active little hunting spiders\nbelonging to the family Attidae. Examples have been brought forward\nduring many recent years, especially by my friends Dr and Mrs Peckham,\nof Milwaukee, the great authorities on this group of Araneae. Here too\nwe find an observation of the mimetic resemblance recorded by Burchell,\nand one which adds in the most interesting manner to our knowledge\nof the subject. A fragment, all that is now left, of an Attid spider,\ncaptured on June 30, 1828, at Goyaz, Brazil, bears the following note,\nin this case on the specimen and not in the note-book: \"Black... runs and\nseems like an ant with large extended jaws.\" My friend Mr R.I. Pocock,\nto whom I have submitted the specimen, tells me that it is not one of\nthe group of species hitherto regarded as ant-like, and he adds, \"It is\nmost interesting that Burchell should have noticed the resemblance to an\nant in its movements. This suggests that the perfect imitation in shape,\nas well as in movement, seen in many species was started in forms of an\nappropriate size and colour by the mimicry of movement alone.\" Up to the\npresent time Burchell is the only naturalist who has observed an example\nwhich still exhibits this ancestral stage in the evolution of mimetic\nlikeness.\n\nFollowing the teachings of his day, Burchell was driven to believe that\nit was part of the fixed and inexorable scheme of things that these\nstrange superficial resemblances existed. Thus, when he found other\nexamples of Hemipterous mimics, including one (Luteva macrophthalma)\nwith \"exactly the manners of a Mantis,\" he added the sentence, \"In the\ngenus Cimex (Linn.) are to be found the outward resemblances of insects\nof many other genera and orders\" (February 15, 1829). Of another\nBrazilian bug, which is not to be found in his collection, and cannot\ntherefore be precisely identified, he wrote: \"Cimex... Nature seems\nto have intended it to imitate a Sphex, both in colour and the rapid\npalpitating and movement of the antennae\" (November 15, 1826). At the\nsame time it is impossible not to feel the conviction that Burchell felt\nthe advantage of a likeness to stinging insects and to aggressive ants,\njust as he recognised the benefits conferred on desert plants by spines\nand by concealment. Such an interpretation of mimicry was perfectly\nconsistent with the theological doctrines of his day. (See Kirby and\nSpence, \"An Introduction to Entomology\" (1st edition), London, Vol. II.\n1817, page 223.)\n\nThe last note I have selected from Burchell's manuscript refers to one\nof the chief mimics of the highly protected Lycid beetles. The whole\nassemblage of African insects with a Lycoid colouring forms a most\nimportant combination and one which has an interesting bearing upon the\ntheories of Bates and Fritz Muller. This most wonderful set of\nmimetic forms, described in 1902 by Guy A.K. Marshall, is composed\nof flower-haunting beetles belonging to the family Lycidae, and the\nheterogeneous group of varied insects which mimic their conspicuous and\nsimple scheme of colouring. The Lycid beetles, forming the centre or\n\"models\" of the whole company, are orange-brown in front for about\ntwo-thirds of the exposed surface, black behind for the remaining third.\nThey are undoubtedly protected by qualities which make them excessively\nunpalatable to the bulk of insect-eating animals. Some experimental\nproof of this has been obtained by Mr Guy Marshall. What are the forms\nwhich surround them? According to the hypothesis of Bates they would be,\nat any rate mainly, palatable hard-pressed insects which only hold their\nown in the struggle for life by a fraudulent imitation of the trade-mark\nof the successful and powerful Lycidae. According to Fritz Muller's\nhypothesis we should expect that the mimickers would be highly\nprotected, successful and abundant species, which (metaphorically\nspeaking) have found it to their advantage to possess an advertisement,\na danger-signal, in common with each other, and in common with the\nbeetles in the centre of the group.\n\nHow far does the constitution of this wonderful combination--the largest\nand most complicated as yet known in all the world--convey to us the\nidea of mimicry working along the lines supposed by Bates or those\nsuggested by Muller? Figures 1 to 52 of Mr Marshall's coloured plate\n(\"Trans. Ent. Soc. Lond.\" 1902, plate XVIII. See also page 517, where\nthe group is analysed.) represent a set of forty-two or forty-three\nspecies or forms of insects captured in Mashonaland, and all except two\nin the neighbourhood of Salisbury. The combination includes six species\nof Lycidae; nine beetles of five groups all specially protected by\nnauseous qualities, Telephoridae, Melyridae, Phytophaga, Lagriidae,\nCantharidae; six Longicorn beetles; one Coprid beetle; eight stinging\nHymenoptera; three or four parasitic Hymenoptera (Braconidae, a group\nmuch mimicked and shown by some experiments to be distasteful); five\nbugs (Hemiptera, a largely unpalatable group); three moths (Arctiidae\nand Zygaenidae, distasteful families); one fly. In fact the whole\ncombination, except perhaps one Phytophagous, one Coprid and the\nLongicorn beetles, and the fly, fall under the hypothesis of Muller\nand not under that of Bates. And it is very doubtful whether these\nexceptions will be sustained: indeed the suspicion of unpalatability\nalready besets the Longicorns and is always on the heels,--I should say\nthe hind tarsi--of a Phytophagous beetle.\n\nThis most remarkable group which illustrates so well the problem of\nmimicry and the alternative hypotheses proposed for its solution, was,\nas I have said, first described in 1902. Among the most perfect of\nthe mimetic resemblances in it is that between the Longicorn beetle,\nAmphidesmus analis, and the Lycidae. It was with the utmost astonishment\nand pleasure that I found this very resemblance had almost certainly\nbeen observed by Burchell. A specimen of the Amphidesmus exists in his\ncollection and it bears \"651.\" Turning to the same number in the\nAfrican Catalogue we find that the beetle is correctly placed among the\nLongicorns, that it was captured at Uitenhage on Nov. 18, 1813, and that\nit was found associated with Lycid beetles in flowers (\"consocians cum\nLycis 78-87 in floribus\"). Looking up Nos. 78-87 in the collection and\ncatalogue, three species of Lycidae are found, all captured on Nov. 18,\n1813, at Uitenhage. Burchell recognised the wide difference in affinity,\nshown by the distance between the respective numbers; for his catalogue\nis arranged to represent relationships. He observed, what students of\nmimicry are only just beginning to note and record, the coincidence\nbetween model and mimic in time and space and in habits. We are\njustified in concluding that he observed the close superficial likeness\nalthough he does not in this case expressly allude to it.\n\nOne of the most interesting among the early observations of superficial\nresemblance between forms remote in the scale of classification was made\nby Darwin himself, as described in the following passage from his letter\nto Henslow, written from Monte Video, Aug. 15, 1832: \"Amongst the lower\nanimals nothing has so much interested me as finding two species of\nelegantly coloured true Planaria inhabiting the dewy forest! The false\nrelation they bear to snails is the most extraordinary thing of the kind\nI have ever seen.\" (\"More Letters\", I. page 9.)\n\nMany years later, in 1867, he wrote to Fritz Muller suggesting that the\nresemblance of a soberly coloured British Planarian to a slug might be\ndue to mimicry. (\"Life and Letters\", III. page 71.)\n\nThe most interesting copy of Bates's classical memoir on Mimicry\n(\"Contributions to an Insect Fauna of the Amazon Valley\". \"Trans. Linn.\nSoc.\" Vol. XXIII. 1862, page 495.), read before the Linnean Society in\n1861, is that given by him to the man who has done most to support and\nextend the theory. My kind friend has given that copy to me; it bears\nthe inscription:\n\n\"Mr A.R. Wallace from his old travelling companion the Author.\"\n\nOnly a year and a half after the publication of the \"Origin\", we find\nthat Darwin wrote to Bates on the subject which was to provide such\nstriking evidence of the truth of Natural Selection: \"I am glad to hear\nthat you have specially attended to 'mimetic' analogies--a most curious\nsubject; I hope you publish on it. I have for a long time wished to\nknow whether what Dr Collingwood asserts is true--that the most striking\ncases generally occur between insects inhabiting the same country.\" (The\nletter is dated April 4, 1861. \"More Letters\", I. page 183.)\n\nThe next letter, written about six months later, reveals the remarkable\nfact that the illustrious naturalist who had anticipated Edward Forbes\nin the explanation of arctic forms on alpine heights (\"I was forestalled\nin only one important point, which my vanity has always made me regret,\nnamely, the explanation by means of the Glacial period of the presence\nof the same species of plants and of some few animals on distant\nmountain summits and in the arctic regions. This view pleased me so much\nthat I wrote it out in extenso, and I believe that it was read by Hooker\nsome years before E. Forbes published his celebrated memoir on the\nsubject. In the very few points in which we differed, I still think\nthat I was in the right. I have never, of course, alluded in print to\nmy having independently worked out this view.\" \"Autobiography, Life and\nLetters\", I. page 88.), had also anticipated H.W. Bates in the theory\nof Mimicry: \"What a capital paper yours will be on mimetic resemblances!\nYou will make quite a new subject of it. I had thought of such cases\nas a difficulty; and once, when corresponding with Dr Collingwood, I\nthought of your explanation; but I drove it from my mind, for I felt\nthat I had not knowledge to judge one way or the other.\" (The letter is\ndated Sept. 25, 1861: \"More Letters\", I. page 197.)\n\nBates read his paper before the Linnean Society, Nov. 21, 1861, and\nDarwin's impressions on hearing it were conveyed in a letter to\nthe author dated Dec. 3: \"Under a general point of view, I am quite\nconvinced (Hooker and Huxley took the same view some months ago) that\na philosophic view of nature can solely be driven into naturalists by\ntreating special subjects as you have done. Under a special point of\nview, I think you have solved one of the most perplexing problems which\ncould be given to solve.\" (\"Life and Letters\", II. page 378.) The memoir\nappeared in the following year, and after reading it Darwin wrote\nas follows, Nov. 20, 1862: \"... In my opinion it is one of the most\nremarkable and admirable papers I ever read in my life... I am rejoiced\nthat I passed over the whole subject in the \"Origin\", for I should have\nmade a precious mess of it. You have most clearly stated and solved a\nwonderful problem... Your paper is too good to be largely appreciated by\nthe mob of naturalists without souls; but, rely on it, that it will\nhave LASTING value, and I cordially congratulate you on your first great\nwork. You will find, I should think, that Wallace will fully appreciate\nit.\" (\"Life and Letters\", II. pages 391-393.) Four days later, Nov. 24,\nDarwin wrote to Hooker on the same subject: \"I have now finished his\npaper...' it seems to me admirable. To my mind the act of segregation of\nvarieties into species was never so plainly brought forward, and there\nare heaps of capital miscellaneous observations.\" (\"More Letters\", I.\npage 214.)\n\nDarwin was here referring to the tendency of similar varieties of the\nsame species to pair together, and on Nov. 25 he wrote to Bates asking\nfor fuller information on this subject. (\"More Letters\", I. page 215.\nSee also parts of Darwin's letter to Bates in \"Life and Letters\", II.\npage 392.) If Bates's opinion were well founded, sexual selection would\nbear a most important part in the establishment of such species. (See\nPoulton, \"Essays on Evolution\", 1908, pages 65, 85-88.) It must be\nadmitted, however, that the evidence is as yet quite insufficient to\nestablish this conclusion. It is interesting to observe how Darwin\nat once fixed on the part of Bates's memoir which seemed to bear upon\nsexual selection. A review of Bates's theory of Mimicry was contributed\nby Darwin to the \"Natural History Review\" (New Ser. Vol. III. 1863, page\n219.) and an account of it is to be found in the \"Origin\" (Edition\n1872, pages 375-378.) and in \"The Descent of Man\". (Edition 1874, pages\n323-325.)\n\nDarwin continually writes of the value of hypothesis as the inspiration\nof inquiry. We find an example in his letter to Bates, Nov. 22, 1860:\n\"I have an old belief that a good observer really means a good theorist,\nand I fully expect to find your observations most valuable.\" (\"More\nLetters\", I. page 176.) Darwin's letter refers to many problems upon\nwhich Bates had theorised and observed, but as regards Mimicry itself\nthe hypothesis was thought out after the return of the letter from the\nAmazons, when he no longer had the opportunity of testing it by the\nobservation of living Nature. It is by no means improbable that, had\nhe been able to apply this test, Bates would have recognised that his\ndivision of butterfly resemblances into two classes,--one due to\nthe theory of mimicry, the other to the influence of local\nconditions,--could not be sustained.\n\nFritz Muller's contributions to the problem of Mimicry were all made\nin S.E. Brazil, and numbers of them were communicated, with other\nobservations on natural history, to Darwin, and by him sent to Professor\nR. Meldola who published many of the facts. Darwin's letters to Meldola\n(Poulton, \"Charles Darwin and the theory of Natural Selection\", London,\n1896, pages 199-218.) contain abundant proofs of his interest in\nMuller's work upon Mimicry. One deeply interesting letter (Loc. cit.\npages 201, 202.) dated Jan. 23, 1872, proves that Fritz Muller before\nhe originated the theory of Common Warning Colours (Synaposematic\nResemblance or Mullerian Mimicry), which will ever be associated with\nhis name, had conceived the idea of the production of mimetic likeness\nby sexual selection.\n\nDarwin's letter to Meldola shows that he was by no means inclined to\ndismiss the suggestion as worthless, although he considered it daring.\n\"You will also see in this letter a strange speculation, which I should\nnot dare to publish, about the appreciation of certain colours being\ndeveloped in those species which frequently behold other forms similarly\nornamented. I do not feel at all sure that this view is as incredible as\nit may at first appear. Similar ideas have passed through my mind\nwhen considering the dull colours of all the organisms which inhabit\ndull-coloured regions, such as Patagonia and the Galapagos Is.\" A little\nlater, on April 5, he wrote to Professor August Weismann on the same\nsubject: \"It may be suspected that even the habit of viewing differently\ncoloured surrounding objects would influence their taste, and\nFritz Muller even goes so far as to believe that the sight of gaudy\nbutterflies might influence the taste of distinct species.\" (\"Life and\nLetters\", III. page 157.)\n\nThis remarkable suggestion affords interesting evidence that F. Muller\nwas not satisfied with the sufficiency of Bates's theory. Nor is\nthis surprising when we think of the numbers of abundant conspicuous\nbutterflies which he saw exhibiting mimetic likenesses. The common\ninstances in his locality, and indeed everywhere in tropical America,\nwere anything but the hard-pressed struggling forms assumed by the\ntheory of Bates. They belonged to the groups which were themselves\nmimicked by other butterflies. Fritz Muller's suggestion also shows\nthat he did not accept Bates's alternative explanation of a superficial\nlikeness between models themselves, based on some unknown influence of\nlocal physico-chemical forces. At the same time Muller's own suggestion\nwas subject to this apparently fatal objection, that the sexual\nselection he invoked would tend to produce resemblances in the males\nrather than the females, while it is well known that when the sexes\ndiffer the females are almost invariably more perfectly mimetic than the\nmales and in a high proportion of cases are mimetic while the males are\nnon-mimetic.\n\nThe difficulty was met several years later by Fritz Muller's well-known\ntheory, published in 1879 (\"Kosmos\", May 1879, page 100.), and\nimmediately translated by Meldola and brought before the Entomological\nSociety. (\"Proc. Ent. Soc. Lond.\" 1879, page xx.) Darwin's letter to\nMeldola dated June 6, 1879, shows \"that the first introduction of this\nnew and most suggestive hypothesis into this country was due to the\ndirect influence of Darwin himself, who brought it before the notice\nof the one man who was likely to appreciate it at its true value and to\nfind the means for its presentation to English naturalists.\" (\"Charles\nDarwin and the Theory of Natural Selection\", page 214.) Of the\nhypothesis itself Darwin wrote \"F. Muller's view of the mutual\nprotection was quite new to me.\" (Ibid. page 213.) The hypothesis of\nMullerian mimicry was at first strongly opposed. Bates himself could\nnever make up his mind to accept it. As the Fellows were walking out\nof the meeting at which Professor Meldola explained the hypothesis, an\neminent entomologist, now deceased, was heard to say to Bates: \"It's a\ncase of save me from my friends!\" The new ideas encountered and still\nencounter to a great extent the difficulty that the theory of Bates had\nso completely penetrated the literature of natural history. The present\nwriter has observed that naturalists who have not thoroughly absorbed\nthe older hypothesis are usually far more impressed by the newer\none than are those whose allegiance has already been rendered. The\nacceptance of Natural Selection itself was at first hindered by\nsimilar causes, as Darwin clearly recognised: \"If you argue about the\nnon-acceptance of Natural Selection, it seems to me a very striking fact\nthat the Newtonian theory of gravitation, which seems to every one now\nso certain and plain, was rejected by a man so extraordinarily able as\nLeibnitz. The truth will not penetrate a preoccupied mind.\" (To Sir J.\nHooker, July 28, 1868, \"More Letters\", I. page 305. See also the letter\nto A.R. Wallace, April 30, 1868, in \"More Letters\" II. page 77, lines\n6-8 from top.)\n\nThere are many naturalists, especially students of insects, who appear\nto entertain an inveterate hostility to any theory of mimicry. Some of\nthem are eager investigators in the fascinating field of geographical\ndistribution, so essential for the study of Mimicry itself. The changes\nof pattern undergone by a species of Erebia as we follow it over\ndifferent parts of the mountain ranges of Europe is indeed a most\ninteresting inquiry, but not more so than the differences between e.g.\nthe Acraea johnstoni of S.E. Rhodesia and of Kilimanjaro. A naturalist\nwho is interested by the Erebia should be equally interested by the\nAcraea; and so he would be if the student of mimicry did not also\nrecord that the characteristics which distinguish the northern from\nthe southern individuals of the African species correspond with the\npresence, in the north but not in the south, of certain entirely\ndifferent butterflies. That this additional information should so\ngreatly weaken, in certain minds, the appeal of a favourite study, is a\npsychological problem of no little interest. This curious antagonism is\nI believe confined to a few students of insects. Those naturalists who,\nstanding rather farther off, are able to see the bearings of the subject\nmore clearly, will usually admit the general support yielded by an\never-growing mass of observations to the theories of Mimicry propounded\nby H.W. Bates and Fritz Muller. In like manner natural selection itself\nwas in the early days often best understood and most readily accepted by\nthose who were not naturalists. Thus Darwin wrote to D.T. Ansted, Oct.\n27, 1860: \"I am often in despair in making the generality of NATURALISTS\neven comprehend me. Intelligent men who are not naturalists and have not\na bigoted idea of the term species, show more clearness of mind.\" (\"More\nLetters\", I. page 175.)\n\nEven before the \"Origin\" appeared Darwin anticipated the first results\nupon the mind of naturalists. He wrote to Asa Gray, Dec. 21, 1859: \"I\nhave made up my mind to be well abused; but I think it of importance\nthat my notions should be read by intelligent men, accustomed to\nscientific argument, though NOT naturalists. It may seem absurd, but\nI think such men will drag after them those naturalists who have too\nfirmly fixed in their heads that a species is an entity.\" (\"Life and\nLetters\" II. page 245.)\n\nMimicry was not only one of the first great departments of zoological\nknowledge to be studied under the inspiration of natural Selection,\nit is still and will always remain one of the most interesting\nand important of subjects in relation to this theory as well as to\nevolution. In mimicry we investigate the effect of environment in its\nsimplest form: we trace the effects of the pattern of a single species\nupon that of another far removed from it in the scale of classification.\nWhen there is reason to believe that the model is an invader from\nanother region and has only recently become an element in the\nenvironment of the species native to its second home, the problem gains\na special interest and fascination. Although we are chiefly dealing with\nthe fleeting and changeable element of colour we expect to find and we\ndo find evidence of a comparatively rapid evolution. The invasion of\na fresh model is for certain species an unusually sudden change in the\nforces of the environment and in some instances we have grounds for the\nbelief that the mimetic response has not been long delayed.\n\nMIMICRY AND SEX.\n\nEver since Wallace's classical memoir on mimicry in the Malayan\nSwallowtail butterflies, those naturalists who have written on the\nsubject have followed his interpretation of the marked prevalence of\nmimetic resemblance in the female sex as compared with the male. They\nhave believed with Wallace that the greater dangers of the female, with\nslower flight and often alighting for oviposition, have been in part\nmet by the high development of this special mode of protection. The fact\ncannot be doubted. It is extremely common for a non-mimetic male to be\naccompanied by a beautifully mimetic female and often by two or three\ndifferent forms of female, each mimicking a different model. The male\nof a polymorphic mimetic female is, in fact, usually non-mimetic (e.g.\nPapilio dardanus = merope), or if a mimic (e.g. the Nymphaline genus\nEuripus), resembles a very different model. On the other hand a\nnon-mimetic female accompanied by a mimetic male is excessively rare. An\nexample is afforded by the Oriental Nymphaline, Cethosia, in which the\nmales of some species are rough mimics of the brown Danaines. In some\nof the orb-weaving spiders the males mimic ants, while the much larger\nfemales are non-mimetic. When both sexes mimic, it is very common in\nbutterflies and is also known in moths, for the females to be better and\noften far better mimics than the males.\n\nAlthough still believing that Wallace's hypothesis in large part\naccounts for the facts briefly summarised above, the present writer has\nrecently been led to doubt whether it offers a complete explanation.\nMimicry in the male, even though less beneficial to the species than\nmimicry in the female, would still surely be advantageous. Why then is\nit so often entirely restricted to the female? While the attempt to find\nan answer to this question was haunting me, I re-read a letter\nwritten by Darwin to Wallace, April 15, 1868, containing the following\nsentences: \"When female butterflies are more brilliant than their males\nyou believe that they have in most cases, or in all cases, been rendered\nbrilliant so as to mimic some other species, and thus escape danger. But\ncan you account for the males not having been rendered equally brilliant\nand equally protected? Although it may be most for the welfare of\nthe species that the female should be protected, yet it would be some\nadvantage, certainly no disadvantage, for the unfortunate male to enjoy\nan equal immunity from danger. For my part, I should say that the female\nalone had happened to vary in the right manner, and that the beneficial\nvariations had been transmitted to the same sex alone. Believing in\nthis, I can see no improbability (but from analogy of domestic animals\na strong probability) that variations leading to beauty must often have\noccurred in the males alone, and been transmitted to that sex alone.\nThus I should account in many cases for the greater beauty of the male\nover the female, without the need of the protective principle.\" (\"More\nLetters\", II. pages 73, 74. On the same subject--\"the gay-coloured\nfemales of Pieris\" (Perrhybris (Mylothris) pyrrha of Brazil), Darwin\nwrote to Wallace, May 5, 1868, as follows: \"I believe I quite follow you\nin believing that the colours are wholly due to mimicry; and I further\nbelieve that the male is not brilliant from not having received through\ninheritance colour from the female, and from not himself having varied;\nin short, that he has not been influenced by selection.\" It should be\nnoted that the male of this species does exhibit a mimetic pattern on\nthe under surface. \"More Letters\" II. page 78.)\n\nThe consideration of the facts of mimicry thus led Darwin to the\nconclusion that the female happens to vary in the right manner more\ncommonly than the male, while the secondary sexual characters of males\nsupported the conviction \"that from some unknown cause such characters\n(viz. new characters arising in one sex and transmitted to it alone)\napparently appear oftener in the male than in the female.\" (Letter from\nDarwin to Wallace, May 5, 1867, \"More Letters\", II. Page 61.)\n\nComparing these conflicting arguments we are led to believe that the\nfirst is the stronger. Mimicry in the male would be no disadvantage but\nan advantage, and when it appears would be and is taken advantage of\nby selection. The secondary sexual characters of males would be no\nadvantage but a disadvantage to females, and, as Wallace thinks, are\nwithheld from this sex by selection. It is indeed possible that mimicry\nhas been hindered and often prevented from passing to the males by\nsexual selection. We know that Darwin was much impressed (\"Descent of\nMan\", page 325.) by Thomas Belt's daring and brilliant suggestion that\nthe white patches which exist, although ordinarily concealed, on the\nwings of mimetic males of certain Pierinae (Dismorphia), have been\npreserved by preferential mating. He supposed this result to have been\nbrought about by the females exhibiting a deep-seated preference for\nmales that displayed the chief ancestral colour, inherited from periods\nbefore any mimetic pattern had been evolved in the species. But it has\nalways appeared to me that Belt's deeply interesting suggestion requires\nmuch solid evidence and repeated confirmation before it can be accepted\nas a valid interpretation of the facts. In the present state of our\nknowledge, at any rate of insects and especially of Lepidoptera, it is\nprobable that the female is more apt to vary than the male and that an\nimportant element in the interpretation of prevalent female mimicry is\nprovided by this fact.\n\nIn order adequately to discuss the question of mimicry and sex it would\nbe necessary to analyse the whole of the facts, so far as they are known\nin butterflies. On the present occasion it is only possible to state the\ninferences which have been drawn from general impressions,--inferences\nwhich it is believed will be sustained by future inquiry.\n\n(1) Mimicry may occasionally arise in one sex because the differences\nwhich distinguish it from the other sex happen to be such as to afford a\nstarting-point for the resemblance. Here the male is at no disadvantage\nas compared with the female, and the rarity of mimicry in the male\nalone (e.g. Cethosia) is evidence that the great predominance of female\nmimicry is not to be thus explained.\n\n(2) The tendency of the female to dimorphism and polymorphism has been\nof great importance in determining this predominance. Thus if the female\nappear in two different forms and the male in only one it will be twice\nas probable that she will happen to possess a sufficient foundation for\nthe evolution of mimicry.\n\n(3) The appearance of melanic or partially melanic forms in the female\nhas been of very great service, providing as it does a change of\nground-colour. Thus the mimicry of the black generally red-marked\nAmerican \"Aristolochia swallowtails\" (Pharmacophagus) by the females of\nPapilio swallowtails was probably begun in this way.\n\n(4) It is probably incorrect to assume with Haase that mimicry always\narose in the female and was later acquired by the male. Both sexes of\nthe third section of swallowtails (Cosmodesmus) mimic Pharmacophagus in\nAmerica, far more perfectly than do the females of Papilio. But this is\nnot due to Cosmodesmus presenting us with a later stage of history begun\nin Papilio; for in Africa Cosmodesmus is still mimetic (of Danainae) in\nboth sexes although the resemblances attained are imperfect, while\nmany African species of Papilio have non-mimetic males with beautifully\nmimetic females. The explanation is probably to be sought in the fact\nthat the females of Papilio are more variable and more often tend to\nbecome dimorphic than those of Cosmodesmus, while the latter group has\nmore often happened to possess a sufficient foundation for the origin of\nthe resemblance in patterns which, from the start, were common to male\nand female.\n\n(5) In very variable species with sexes alike, mimicry can be rapidly\nevolved in both sexes out of very small beginnings. Thus the reddish\nmarks which are common in many individuals of Limenitis arthemis were\nalmost certainly the starting-point for the evolution of the beautifully\nmimetic L. archippus. Nevertheless in such cases, although there is\nno reason to suspect any greater variability, the female is commonly a\nsomewhat better mimic than the male and often a very much better mimic.\nWallace's principle seems here to supply the obvious interpretation.\n\n(6) When the difference between the patterns of the model and presumed\nancestor of the mimic is very great, the female is often alone mimetic;\nwhen the difference is comparatively small, both sexes are commonly\nmimetic. The Nymphaline genus Hypolimnas is a good example. In\nHypolimnas itself the females mimic Danainae with patterns very\ndifferent from those preserved by the non-mimetic males: in the\nsub-genus Euralia, both sexes resemble the black and white Ethiopian\nDanaines with patterns not very dissimilar from that which we infer to\nhave existed in the non-mimetic ancestor.\n\n(7) Although a melanic form or other large variation may be of the\nutmost importance in facilitating the start of a mimetic likeness, it is\nimpossible to explain the evolution of any detailed resemblance in\nthis manner. And even the large colour variation itself may well be\nthe expression of a minute and \"continuous\" change in the chemical and\nphysical constitution of pigments.\n\nSEXUAL SELECTION (EPIGAMIC CHARACTERS).\n\nWe do not know the date at which the idea of Sexual Selection arose in\nDarwin's mind, but it was probably not many years after the sudden flash\nof insight which, in October 1838, gave to him the theory of Natural\nSelection. An excellent account of Sexual Selection occupies the\nconcluding paragraph of Part I. of Darwin's Section of the Joint Essay\non Natural Selection, read July 1st, 1858, before the Linnean Society.\n(\"Journ. Proc. Linn. Soc.\" Vol. III. 1859, page 50.) The principles are\nso clearly and sufficiently stated in these brief sentences that it\nis appropriate to quote the whole: \"Besides this natural means of\nselection, by which those individuals are preserved, whether in their\negg, or larval, or mature state, which are best adapted to the place\nthey fill in nature, there is a second agency at work in most unisexual\nanimals, tending to produce the same effect, namely, the struggle of the\nmales for the females. These struggles are generally decided by the law\nof battle, but in the case of birds, apparently, by the charms of their\nsong, by their beauty or their power of courtship, as in the dancing\nrock-thrush of Guiana. The most vigorous and healthy males, implying\nperfect adaptation, must generally gain the victory in their contests.\nThis kind of selection, however, is less rigorous than the other; it\ndoes not require the death of the less successful, but gives to them\nfewer descendants. The struggle falls, moreover, at a time of year when\nfood is generally abundant, and perhaps the effect chiefly produced\nwould be the modification of the secondary sexual characters, which are\nnot related to the power of obtaining food, or to defence from enemies,\nbut to fighting with or rivalling other males. The result of this\nstruggle amongst the males may be compared in some respects to that\nproduced by those agriculturists who pay less attention to the careful\nselection of all their young animals, and more to the occasional use of\na choice mate.\"\n\nA full exposition of Sexual Selection appeared in the \"The Descent of\nMan\" in 1871, and in the greatly augmented second edition, in 1874.\nIt has been remarked that the two subjects, \"The Descent of Man and\nSelection in Relation to Sex\", seem to fuse somewhat imperfectly into\nthe single work of which they form the title. The reason for their\nassociation is clearly shown in a letter to Wallace, dated May 28, 1864:\n\"... I suspect that a sort of sexual selection has been the most powerful\nmeans of changing the races of man.\" (\"More Letters\", II. page 33.)\n\nDarwin, as we know from his Autobiography (\"Life and Letters\", I. page\n94.), was always greatly interested in this hypothesis, and it has been\nshown in the preceding pages that he was inclined to look favourably\nupon it as an interpretation of many appearances usually explained by\nNatural Selection. Hence Sexual Selection, incidentally discussed in\nother sections of the present essay, need not be considered at any\nlength, in the section specially allotted to it.\n\nAlthough so interested in the subject and notwithstanding his conviction\nthat the hypothesis was sound, Darwin was quite aware that it was\nprobably the most vulnerable part of the \"Origin\". Thus he wrote to H.W.\nBates, April 4, 1861: \"If I had to cut up myself in a review I would\nhave (worried?) and quizzed sexual selection; therefore, though I am\nfully convinced that it is largely true, you may imagine how pleased I\nam at what you say on your belief.\" (\"More Letters\", I. page 183.)\n\nThe existence of sound-producing organs in the males of insects was,\nDarwin considered, the strongest evidence in favour of the operation\nof sexual selection in this group. (\"Life and Letters\", III. pages 94,\n138.) Such a conclusion has received strong support in recent years by\nthe numerous careful observations of Dr F.A. Dixey (\"Proc. Ent. Soc.\nLond.\" 1904, page lvi; 1905, pages xxxvii, liv; 1906, page ii.) and Dr\nG.B. Longstaff (\"Proc. Ent. Soc. Lond.\" 1905, page xxxv; \"Trans. Ent.\nSoc. Lond.\" 1905, page 136; 1908, page 607.) on the scents of male\nbutterflies. The experience of these naturalists abundantly confirms and\nextends the account given by Fritz Muller (\"Jen. Zeit.\" Vol. XI. 1877,\npage 99; \"Trans. Ent. Soc. Lond.\" 1878, page 211.) of the scents\nof certain Brazilian butterflies. It is a remarkable fact that the\napparently epigamic scents of male butterflies should be pleasing to\nman while the apparently aposematic scents in both sexes of species with\nwarning colours should be displeasing to him. But the former is far more\nsurprising than the latter. It is not perhaps astonishing that a scent\nwhich is ex hypothesi unpleasant to an insect-eating Vertebrate should\nbe displeasing to the human sense; but it is certainly wonderful that an\nodour which is ex hypothesi agreeable to a female butterfly should also\nbe agreeable to man.\n\nEntirely new light upon the seasonal appearance of epigamic characters\nis shed by the recent researches of C.W. Beebe (\"The American\nNaturalist\", Vol. XLII. No. 493, Jan. 1908, page 34.), who caused the\nscarlet tanager (Piranga erythromelas) and the bobolink (Dolichonyx\noryzivorus) to retain their breeding plumage through the whole year by\nmeans of fattening food, dim illumination, and reduced activity. Gradual\nrestoration to the light and the addition of meal-worms to the diet\ninvariably brought back the spring song, even in the middle of winter.\nA sudden alteration of temperature, either higher or lower, caused the\nbirds nearly to stop feeding, and one tanager lost weight rapidly and in\ntwo weeks moulted into the olive-green winter plumage. After a year, and\nat the beginning of the normal breeding season, \"individual tanagers\nand bobolinks were gradually brought under normal conditions and\nactivities,\" and in every case moulted from nuptial plumage to nuptial\nplumage. \"The dull colours of the winter season had been skipped.\" The\nauthor justly claims to have established \"that the sequence of plumage\nin these birds is not in any way predestined through inheritance...,\nbut that it may be interrupted by certain factors in the environmental\ncomplex.\"\n\n\n\n\nXVI. GEOGRAPHICAL DISTRIBUTION OF PLANTS. By Sir William Thiselton-Dyer,\nK.C.M.G., C.I.E. Sc.D., F.R.S.\n\nThe publication of \"The Origin of Species\" placed the study of Botanical\nGeography on an entirely new basis. It is only necessary to study the\nmonumental \"Geographie Botanique raisonnee\" of Alphonse De Candolle,\npublished four years earlier (1855), to realise how profound and\nfar-reaching was the change. After a masterly and exhaustive discussion\nof all available data De Candolle in his final conclusions could only\narrive at a deadlock. It is sufficient to quote a few sentences:--\n\n\"L'opinion de Lamarck est aujourd'hui abandonee par tous les\nnaturalistes qui ont etudie sagement les modifications possibles des\netres organises...\n\n\"Et si l'on s'ecarte des exagerations de Lamarck, si l'on suppose un\npremier type de chaque genre, de chaque famille tout au moins, on se\ntrouve encore a l'egard de l'origine de ces types en presence de la\ngrande question de la creation.\n\n\"Le seul parti a prendre est donc d'envisager les etres organises comme\nexistant depuis certaines epoques, avec leurs qualites particulieres.\"\n(Vol. II. page 1107.)\n\nReviewing the position fourteen years afterwards, Bentham\nremarked:--\"These views, generally received by the great majority of\nnaturalists at the time De Candolle wrote, and still maintained by a\nfew, must, if adhered to, check all further enquiry into any connection\nof facts with causes,\" and he added, \"there is little doubt but that if\nDe Candolle were to revise his work, he would follow the example of\nso many other eminent naturalists, and... insist that the present\ngeographical distribution of plants was in most instances a derivative\none, altered from a very different former distribution.\" (\"Pres. Addr.\"\n(1869) \"Proc. Linn. Soc.\" 1868-69, page lxviii.)\n\nWriting to Asa Gray in 1856, Darwin gave a brief preliminary account\nof his ideas as to the origin of species, and said that geographical\ndistribution must be one of the tests of their validity. (\"Life and\nLetters\", II. page 78.) What is of supreme interest is that it was also\ntheir starting-point. He tells us:--\"When I visited, during the voyage\nof H.M.S. \"Beagle\", the Galapagos Archipelago,... I fancied myself\nbrought near to the very act of creation. I often asked myself how these\nmany peculiar animals and plants had been produced: the simplest answer\nseemed to be that the inhabitants of the several islands had descended\nfrom each other, undergoing modification in the course of their\ndescent.\" (\"The Variation of Animals and Plants\" (2nd edition), 1890, I.\npages 9, 10.) We need not be surprised then, that in writing in 1845\nto Sir Joseph Hooker, he speaks of \"that grand subject, that almost\nkeystone of the laws of creation, Geographical Distribution.\" (\"Life and\nLetters\", I. page 336.)\n\nYet De Candolle was, as Bentham saw, unconsciously feeling his way,\nlike Lyell, towards evolution, without being able to grasp it. They both\nstrove to explain phenomena by means of agencies which they saw actually\nat work. If De Candolle gave up the ultimate problem as insoluble:--\"La\ncreation ou premiere formation des etres organises echappe, par sa\nnature et par son anciennete, a nos moyens d'observation\" (Loc. cit.\npage 1106.), he steadily endeavoured to minimise its scope. At least\nhalf of his great work is devoted to the researches by which he\nextricated himself from a belief in species having had a multiple\norigin, the view which had been held by successive naturalists from\nGmelin to Agassiz. To account for the obvious fact that species\nconstantly occupy dissevered areas, De Candolle made a minute study of\ntheir means of transport. This was found to dispose of the vast majority\nof cases, and the remainder he accounted for by geographical change.\n(Loc. cit. page 1116.)\n\nBut Darwin strenuously objected to invoking geographical change as a\nsolution of every difficulty. He had apparently long satisfied himself\nas to the \"permanence of continents and great oceans.\" Dana, he tells us\n\"was, I believe, the first man who maintained\" this (\"Life and Letters\",\nIII. page 247. Dana says:--\"The continents and oceans had their general\noutline or form defined in earliest time,\" \"Manual of Geology\", revised\nedition. Philadelphia, 1869, page 732. I have no access to an earlier\nedition.), but he had himself probably arrived at it independently.\nModern physical research tends to confirm it. The earth's centre of\ngravity, as pointed out by Pratt from the existence of the Pacific\nOcean, does not coincide with its centre of figure, and it has been\nconjectured that the Pacific Ocean dates its origin from the separation\nof the moon from the earth.\n\nThe conjecture appears to be unnecessary. Love shows that \"the force\nthat keeps the Pacific Ocean on one side of the earth is gravity,\ndirected more towards the centre of gravity than the centre of the\nfigure.\" (\"Report of the 77th Meeting of the British Association\"\n(Leicester, 1907), London, 1908, page 431.) I can only summarise the\nconclusions of a technical but masterly discussion. \"The broad general\nfeatures of the distribution of continent and ocean can be regarded\nas the consequences of simple causes of a dynamical character,\" and\nfinally, \"As regards the contour of the great ocean basins, we seem\nto be justified in saying that the earth is approximately an oblate\nspheroid, but more nearly an ellipsoid with three unequal axes, having\nits surface furrowed according to the formula for a certain spherical\nharmonic of the third degree\" (Ibid. page 436.), and he shows that this\nfurrowed surface must be produced \"if the density is greater in one\nhemispheroid than in the other, so that the position of the centre of\ngravity is eccentric.\" (Ibid. page 431.) Such a modelling of the earth's\nsurface can only be referred to a primitive period of plasticity. If\nthe furrows account for the great ocean basins, the disposition of the\ncontinents seems equally to follow. Sir George Darwin has pointed out\nthat they necessarily \"arise from a supposed primitive viscosity or\nplasticity of the earth's mass. For during this course of evolution the\nearth's mass must have suffered a screwing motion, so that the polar\nregions have travelled a little from west to east relatively to the\nequator. This affords a possible explanation of the north and south\ntrend of our great continents.\" (\"Encycl. Brit.\" (9th edition), Vol.\nXXIII. \"Tides\", page 379.)\n\nIt would be trespassing on the province of the geologist to pursue the\nsubject at any length. But as Wallace (\"Island Life\" (2nd edition),\n1895, page 103.), who has admirably vindicated Darwin's position, points\nout, the \"question of the permanence of our continents... lies at the\nroot of all our inquiries into the great changes of the earth and its\ninhabitants.\" But he proceeds: \"The very same evidence which has been\nadduced to prove the GENERAL stability and permanence of our continental\nareas also goes to prove that they have been subjected to wonderful\nand repeated changes in DETAIL.\" (Loc. cit. page 101.) Darwin of course\nwould have admitted this, for with a happy expression he insisted\nto Lyell (1856) that \"the skeletons, at least, of our continents are\nancient.\" (\"More Letters\", II. page 135.) It is impossible not to\nadmire the courage and tenacity with which he carried on the conflict\nsingle-handed. But he failed to convince Lyell. For we still find\nhim maintaining in the last edition of the \"Principles\": \"Continents\ntherefore, although permanent for whole geological epochs, shift their\npositions entirely in the course of ages.\" (Lyell's \"Principles of\nGeology\" (11th edition), London, 1872, I. page 258.)\n\nEvidence, however, steadily accumulates in Darwin's support. His\nposition still remains inexpugnable that it is not permissible to invoke\ngeographical change to explain difficulties in distribution without\nvalid geological and physical support. Writing to Mellard Reade, who in\n1878 had said, \"While believing that the ocean-depths are of enormous\nage, it is impossible to reject other evidences that they have once\nbeen land,\" he pointed out \"the statement from the 'Challenger' that all\nsediment is deposited within one or two hundred miles from the shores.\"\n(\"More Letters\", II. page 146.) The following year Sir Archibald Geikie\n(\"Geographical Evolution\", \"Proc. R. Geogr. Soc.\" 1879, page 427.)\ninformed the Royal Geographical Society that \"No part of the results\nobtained by the 'Challenger' expedition has a profounder interest for\ngeologists and geographers than the proof which they furnish that the\nfloor of the ocean basins has no real analogy among the sedimentary\nformations which form most of the framework of the land.\"\n\nNor has Darwin's earlier argument ever been upset. \"The fact which\nI pointed out many years ago, that all oceanic islands are volcanic\n(except St Paul's, and now that is viewed by some as the nucleus of an\nancient volcano), seem to me a strong argument that no continent ever\noccupied the great oceans.\" (\"More Letters\", II. page 146.)\n\nDr Guppy, who devoted several years to geological and botanical\ninvestigations in the Pacific, found himself forced to similar\nconclusions. \"It may be at once observed,\" he says, \"that my belief in\nthe general principle that islands have always been islands has not\nbeen shaken,\" and he entirely rejects \"the hypothesis of a Pacific\ncontinent.\" He comes back, in full view of the problems on the spot,\nto the position from which, as has been seen, Darwin started: \"If the\ndistribution of a particular group of plants or animals does not seem to\naccord with the present arrangement of the land, it is by far the safest\nplan, even after exhausting all likely modes of explanation, not to\ninvoke the intervention of geographical changes; and I scarcely think\nthat our knowledge of any one group of organisms is ever sufficiently\nprecise to justify a recourse to hypothetical alterations in the present\nrelations of land and sea.\" (\"Observations of a Naturalist in the\nPacific between 1896 and 1899\", London, 1903, I. page 380.) Wallace\nclinches the matter when he finds \"almost the whole of the vast areas of\nthe Atlantic, Pacific, Indian, and Southern Oceans, without a solitary\nrelic of the great islands or continents supposed to have sunk beneath\ntheir waves.\" (\"Island Life\", page 105.)\n\nWriting to Wallace (1876), Darwin warmly approves the former's \"protest\nagainst sinking imaginary continents in a quite reckless manner, as\nwas stated by Forbes, followed, alas, by Hooker, and caricatured by\nWollaston and (Andrew) Murray.\" (\"Life and Letters\", III. page 230.)\nThe transport question thus became of enormously enhanced importance. We\nneed not be surprised then at his writing to Lyell in 1856:--\"I cannot\navoid thinking that Forbes's 'Atlantis' was an ill-service to science,\nas checking a close study of means of dissemination\" (Ibid. II. page\n78.), and Darwin spared no pains to extend our knowledge of them. He\nimplores Hooker, ten years later, to \"admit how little is known on the\nsubject,\" and summarises with some satisfaction what he had himself\nachieved:--\"Remember how recently you and others thought that salt\nwater would soon kill seeds... Remember that no one knew that seeds would\nremain for many hours in the crops of birds and retain their vitality;\nthat fish eat seeds, and that when the fish are devoured by birds the\nseeds can germinate, etc. Remember that every year many birds are blown\nto Madeira and to the Bermudas. Remember that dust is blown 1000 miles\nacross the Atlantic.\" (\"More Letters\", I. page 483.)\n\nIt has always been the fashion to minimise Darwin's conclusions, and\nthese have not escaped objection. The advocatus diaboli has a useful\nfunction in science. But in attacking Darwin his brief is generally\nfound to be founded on a slender basis of facts. Thus Winge and Knud\nAndersen have examined many thousands of migratory birds and found \"that\ntheir crops and stomachs were always empty. They never observed any\nseeds adhering to the feathers, beaks or feet of the birds.\" (R.F.\nScharff, \"European Animals\", page 64, London, 1907.) The most\nconsiderable investigation of the problem of Plant Dispersal since\nDarwin is that of Guppy. He gives a striking illustration of how easily\nan observer may be led into error by relying on negative evidence.\n\n\"When Ekstam published, in 1895, the results of his observations on the\nplants of Nova Zembla, he observed that he possessed no data to show\nwhether swimming and wading birds fed on berries; and he attached all\nimportance to dispersal by winds. On subsequently visiting Spitzbergen\nhe must have been at first inclined, therefore, to the opinion\nof Nathorst, who, having found only a solitary species of bird (a\nsnow-sparrow) in that region, naturally concluded that birds had been\nof no importance as agents in the plant-stocking. However, Ekstam's\nopportunities were greater, and he tells us that in the craws of six\nspecimens of Lagopus hyperboreus shot in Spitzbergen in August he found\nrepresented almost 25 per cent. of the usual phanerogamic flora of that\nregion in the form of fruits, seeds, bulbils, flower-buds, leaf-buds,\netc... \"\n\n\"The result of Ekstam's observations in Spitzbergen was to lead him to\nattach a very considerable importance in plant dispersal to the agency\nof birds; and when in explanation of the Scandinavian elements in the\nSpitzbergen flora he had to choose between a former land connection and\nthe agency of birds, he preferred the bird.\" (Guppy, op. cit. II. pages\n511, 512.)\n\nDarwin objected to \"continental extensions\" on geological grounds,\nbut he also objected to Lyell that they do not \"account for all the\nphenomena of distribution on islands\" (\"Life and Letters\", II. page\n77.), such for example as the absence of Acacias and Banksias in New\nZealand. He agreed with De Candolle that \"it is poor work putting\ntogether the merely POSSIBLE means of distribution.\" But he also\nagreed with him that they were the only practicable door of escape from\nmultiple origins. If they would not work then \"every one who believes\nin single centres will have to admit continental extensions\" (Ibid. II.\npage 82.), and that he regarded as a mere counsel of despair:--\"to make\ncontinents, as easily as a cook does pancakes.\" (Ibid. II. page 74.)\n\nThe question of multiple origins however presented itself in another\nshape where the solution was much more difficult. The problem, as\nstated by Darwin, is this:--\"The identity of many plants and animals,\non mountain-summits, separated from each other by hundreds of miles of\nlowlands... without the apparent possibility of their having migrated\nfrom one point to the other.\" He continues, \"even as long ago as 1747,\nsuch facts led Gmelin to conclude that the same species must have been\nindependently created at several distinct points; and we might have\nremained in this same belief, had not Agassiz and others called vivid\nattention to the Glacial period, which affords... a simple explanation of\nthe facts.\" (\"Origin of Species\" (6th edition) page 330.)\n\nThe \"simple explanation\" was substantially given by E. Forbes in 1846.\nIt is scarcely too much to say that it belongs to the same class of\nfertile and far-reaching ideas as \"natural selection\" itself. It is\nan extraordinary instance, if one were wanted at all, of Darwin's\nmagnanimity and intense modesty that though he had arrived at the theory\nhimself, he acquiesced in Forbes receiving the well-merited credit.\n\"I have never,\" he says, \"of course alluded in print to my having\nindependently worked out this view.\" But he would have been more than\nhuman if he had not added:--\"I was forestalled in... one important point,\nwhich my vanity has always made me regret.\" (\"Life and Letters\", I. page\n88.)\n\nDarwin, however, by applying the theory to trans-tropical migration,\nwent far beyond Forbes. The first enunciation to this is apparently\ncontained in a letter to Asa Gray in 1858. The whole is too long\nto quote, but the pith is contained in one paragraph. \"There is a\nconsiderable body of geological evidence that during the Glacial epoch\nthe whole world was colder; I inferred that,... from erratic boulder\nphenomena carefully observed by me on both the east and west coast of\nSouth America. Now I am so bold as to believe that at the height of\nthe Glacial epoch, AND WHEN ALL TROPICAL PRODUCTIONS MUST HAVE BEEN\nCONSIDERABLY DISTRESSED, several temperate forms slowly travelled into\nthe heart of the Tropics, and even reached the southern hemisphere; and\nsome few southern forms penetrated in a reverse direction northward.\"\n(\"Life and Letters\", II. page 136.) Here again it is clear that though\nhe credits Agassiz with having called vivid attention to the Glacial\nperiod, he had himself much earlier grasped the idea of periods of\nrefrigeration.\n\nPutting aside the fact, which has only been made known to us since\nDarwin's death, that he had anticipated Forbes, it is clear that he gave\nthe theory a generality of which the latter had no conception. This is\npointed out by Hooker in his classical paper \"On the Distribution of\nArctic Plants\" (1860). \"The theory of a southern migration of northern\ntypes being due to the cold epochs preceding and during the glacial,\noriginated, I believe, with the late Edward Forbes; the extended one,\nof the trans-tropical migration, is Mr Darwin's.\" (\"Linn. Trans.\"\nXXIII. page 253. The attempt appears to have been made to claim for Heer\npriority in what I may term for short the arctic-alpine theory (Scharff,\n\"European Animals\", page 128). I find no suggestion of his having hit\nupon it in his correspondence with Darwin or Hooker. Nor am I aware\nof any reference to his having done so in his later publications. I\nam indebted to his biographer, Professor Schroter, of Zurich, for an\nexamination of his earlier papers with an equally negative result.)\nAssuming that local races have derived from a common ancestor, Hooker's\ngreat paper placed the fact of the migration on an impregnable basis.\nAnd, as he pointed out, Darwin has shown that \"such an explanation meets\nthe difficulty of accounting for the restriction of so many American and\nAsiatic arctic types to their own peculiar longitudinal zones, and for\nwhat is a far greater difficulty, the representation of the same arctic\ngenera by most closely allied species in different longitudes.\"\n\nThe facts of botanical geography were vital to Darwin's argument. He\nhad to show that they admitted of explanation without assuming multiple\norigins for species, which would be fatal to the theory of Descent. He\nhad therefore to strengthen and extend De Candolle's work as to means\nof transport. He refused to supplement them by hypothetical geographical\nchanges for which there was no independent evidence: this was simply to\nattempt to explain ignotum per ignotius. He found a real and, as it has\nturned out, a far-reaching solution in climatic change due to cosmical\ncauses which compelled the migration of species as a condition of their\nexistence. The logical force of the argument consists in dispensing with\nany violent assumption, and in showing that the principle of descent is\nadequate to explain the ascertained facts.\n\nIt does not, I think, detract from the merit of Darwin's conclusions\nthat the tendency of modern research has been to show that the effects\nof the Glacial period were less simple, more localised and less\ngeneral than he perhaps supposed. He admitted that \"equatorial\nrefrigeration... must have been small.\" (\"More Letters\", I. page 177.) It\nmay prove possible to dispense with it altogether. One cannot but regret\nthat as he wrote to Bates:--\"the sketch in the 'Origin' gives a very\nmeagre account of my fuller MS. essay on this subject.\" (Loc. cit.)\nWallace fully accepted \"the effect of the Glacial epoch in bringing\nabout the present distribution of Alpine and Arctic plants in the\nNORTHERN HEMISPHERE,\" but rejected \"the lowering of the temperature of\nthe tropical regions during the Glacial period\" in order to account for\ntheir presence in the SOUTHERN hemisphere. (\"More Letters\", II. page 25\n(footnote 1).) The divergence however does not lie very deep. Wallace\nattaches more importance to ordinary means of transport. \"If plants can\npass in considerable numbers and variety over wide seas and oceans, it\nmust be yet more easy for them to traverse continuous areas of land,\nwherever mountain-chains offer suitable stations.\" (\"Island Life\" (2nd\nedition), London, 1895, page 512.) And he argues that such periodical\nchanges of climate, of which the Glacial period may be taken as a type,\nwould facilitate if not stimulate the process. (Loc. cit. page 518.)\n\nIt is interesting to remark that Darwin drew from the facts of plant\ndistribution one of his most ingenious arguments in support of this\ntheory. (See \"More Letters\", I. page 424.) He tells us, \"I was led to\nanticipate that the species of the larger genera in each country would\noftener present varieties, than the species of the smaller genera.\"\n(\"Origin\", page 44.) He argues \"where, if we may use the expression, the\nmanufactory of species has been active, we ought generally to find the\nmanufactory still in action.\" (Ibid. page 45.) This proved to be the\ncase. But the labour imposed upon him in the study was immense. He\ntabulated local floras \"belting the whole northern hemisphere\" (\"More\nLetters\", I. page 107.), besides voluminous works such as De Candolle's\n\"Prodromus\". The results scarcely fill a couple of pages. This is a good\nillustration of the enormous pains which he took to base any statement\non a secure foundation of evidence, and for this the world, till the\npublication of his letters, could not do him justice. He was a great\nadmirer of Herbert Spencer, whose \"prodigality of original thought\"\nastonished him. \"But,\" he says, \"the reflection constantly recurred to\nme that each suggestion, to be of real value to service, would require\nyears of work.\" (Ibid. II. page 235.)\n\nAt last the ground was cleared and we are led to the final conclusion.\n\"If the difficulties be not insuperable in admitting that in the long\ncourse of time all the individuals of the same species belonging to\nthe same genus, have proceeded from some one source; then all the grand\nleading facts of geographical distribution are explicable on the\ntheory of migration, together with subsequent modification and the\nmultiplication of new forms.\" (\"Origin\", page 360.) In this single\nsentence Darwin has stated a theory which, as his son F. Darwin has said\nwith justice, has \"revolutionized botanical geography.\" (\"The Botanical\nWork of Darwin\", \"Ann. Bot.\" 1899, page xi.) It explains how physical\nbarriers separate and form botanical regions; how allied species become\nconcentrated in the same areas; how, under similar physical conditions,\nplants may be essentially dissimilar, showing that descent and not the\nsurroundings is the controlling factor; how insular floras have acquired\ntheir peculiarities; in short how the most various and apparently\nuncorrelated problems fall easily and inevitably into line.\n\nThe argument from plant distribution was in fact irresistible. A proof,\nif one were wanted, was the immediate conversion of what Hooker called\n\"the stern keen intellect\" (\"More Letters\", I. page 134.) of Bentham, by\ngeneral consent the leading botanical systematist at the time. It is a\nstriking historical fact that a paper of his own had been set down for\nreading at the Linnean Society on the same day as Darwin's, but had to\ngive way. In this he advocated the fixity of species. He withdrew it\nafter hearing Darwin's. We can hardly realise now the momentous effect\non the scientific thought of the day of the announcement of the new\ntheory. Years afterwards (1882) Bentham, notwithstanding his habitual\nrestraint, could not write of it without emotion. \"I was forced, however\nreluctantly, to give up my long-cherished convictions, the results of\nmuch labour and study.\" The revelation came without preparation. Darwin,\nhe wrote, \"never made any communications to me in relation to his\nviews and labours.\" But, he adds, \"I... fully adopted his theories and\nconclusions, notwithstanding the severe pain and disappointment they\nat first occasioned me.\" (\"Life and Letters\", II. page 294.) Scientific\nhistory can have few incidents more worthy. I do not know what is most\nstriking in the story, the pathos or the moral dignity of Bentham's\nattitude.\n\nDarwin necessarily restricted himself in the \"Origin\" to establishing\nthe general principles which would account for the facts of\ndistribution, as a part of his larger argument, without attempting\nto illustrate them in particular cases. This he appears to have\ncontemplated doing in a separate work. But writing to Hooker in 1868\nhe said:--\"I shall to the day of my death keep up my full interest\nin Geographical Distribution, but I doubt whether I shall ever have\nstrength to come in any fuller detail than in the \"Origin\" to this grand\nsubject.\" (\"More Letters\", II. page 7.) This must be always a matter for\nregret. But we may gather some indication of his later speculations from\nthe letters, the careful publication of which by F. Darwin has rendered\na service to science, the value of which it is difficult to exaggerate.\nThey admit us to the workshop, where we see a great theory, as it were,\nin the making. The later ideas that they contain were not it is true\npublic property at the time. But they were communicated to the leading\nbiologists of the day and indirectly have had a large influence.\n\nIf Darwin laid the foundation, the present fabric of Botanical Geography\nmust be credited to Hooker. It was a happy partnership. The far-seeing,\ngeneralising power of the one was supplied with data and checked in\nconclusions by the vast detailed knowledge of the other. It may be\npermitted to quote Darwin's generous acknowledgment when writing the\n\"Origin\":--\"I never did pick any one's pocket, but whilst writing my\npresent chapter I keep on feeling (even when differing most from you)\njust as if I were stealing from you, so much do I owe to your writings\nand conversation, so much more than mere acknowledgements show.\" (\"Life\nand Letters\", II. page 148 (footnote).) Fourteen years before he had\nwritten to Hooker: \"I know I shall live to see you the first authority\nin Europe on... Geographical Distribution.\" (Ibid. I. page 336.) We owe\nit to Hooker that no one now undertakes the flora of a country without\nindicating the range of the species it contains. Bentham tells us:\n\"After De Candolle, independently of the great works of Darwin... the\nfirst important addition to the science of geographical botany was that\nmade by Hooker in his \"Introductory Essay to the Flora of Tasmania\",\nwhich, though contemporaneous only with the \"Origin of Species\", was\ndrawn up with a general knowledge of his friend's observations and\nviews.\" (Pres. Addr. (1869), \"Proc. Linn. Soc.\" 1868-69, page lxxiv.) It\ncannot be doubted that this and the great memoir on the \"Distribution of\nArctic Plants\" were only less epoch-making than the \"Origin\" itself, and\nmust have supplied a powerful support to the general theory of organic\nevolution.\n\nDarwin always asserted his \"entire ignorance of Botany.\" (\"More\nLetters\", I. page 400.) But this was only part of his constant\nhalf-humorous self-depreciation. He had been a pupil of Henslow, and it\nis evident that he had a good working knowledge of systematic botany. He\ncould find his way about in the literature and always cites the names of\nplants with scrupulous accuracy. It was because he felt the want of\nsuch a work for his own researches that he urged the preparation of\nthe \"Index Kewensis\", and undertook to defray the expense. It has been\nthought singular that he should have been elected a \"correspondant\"\nof the Academie des Sciences in the section of Botany, but it is not\nsurprising that his work in Geographical Botany made the botanists\nanxious to claim him. His heart went with them. \"It has always pleased\nme,\" he tells us, \"to exalt plants in the scale of organised beings.\"\n(\"Life and Letters\", I. page 98.) And he declares that he finds \"any\nproposition more easily tested in botanical works (Ibid. II. page 99.)\nthan in zoological.\"\n\nIn the \"Introductory Essay\" Hooker dwelt on the \"continuous current of\nvegetation from Scandinavia to Tasmania\" (\"Introductory Essay to the\nFlora of Tasmania\", London, 1859. Reprinted from the \"Botany of the\nAntarctic Expedition\", Part III., \"Flora of Tasmania\", Vol I. page\nciii.), but finds little evidence of one in the reverse direction.\n\"In the New World, Arctic, Scandinavian, and North American genera and\nspecies are continuously extended from the north to the south temperate\nand even Antarctic zones; but scarcely one Antarctic species, or even\ngenus advances north beyond the Gulf of Mexico\" (page civ.). Hooker\nconsidered that this negatived \"the idea that the Southern and Northern\nFloras have had common origin within comparatively modern geological\nepochs.\" (Loc. cit.) This is no doubt a correct conclusion. But it is\ndifficult to explain on Darwin's view alone, of alternating cold in the\ntwo hemispheres, the preponderant migration from the north to the south.\nHe suggests, therefore, that it \"is due to the greater extent of land\nin the north and to the northern forms... having... been advanced through\nnatural selection and competition to a higher stage of perfection or\ndominating power.\" (\"Origin of Species\" (6th edition), page 340; cf.\nalso \"Life and Letters\", II. page 142.) The present state of the Flora\nof New Zealand affords a striking illustration of the correctness of\nthis view. It is poor in species, numbering only some 1400, of which\nthree-fourths are endemic. They seem however quite unable to resist the\ninvasion of new comers and already 600 species of foreign origin have\nsucceeded in establishing themselves.\n\nIf we accept the general configuration of the earth's surface as\npermanent a continuous and progressive dispersal of species from the\ncentre to the circumference, i.e. southwards, seems inevitable. If an\nobserver were placed above a point in St George's Channel from which\none half of the globe was visible he would see the greatest possible\nquantity of land spread out in a sort of stellate figure. The maritime\nsupremacy of the English race has perhaps flowed from the central\nposition of its home. That such a disposition would facilitate a\ncentrifugal migration of land organisms is at any rate obvious, and\nfluctuating conditions of climate operating from the pole would supply\nan effective means of propulsion. As these became more rigorous animals\nat any rate would move southwards to escape them. It would be equally\nthe case with plants if no insuperable obstacle interposed. This implies\na mobility in plants, notwithstanding what we know of means of transport\nwhich is at first sight paradoxical. Bentham has stated this in a\nstriking way: \"Fixed and immovable as is the individual plant, there is\nno class in which the race is endowed with greater facilities for the\nwidest dispersion... Plants cast away their offspring in a dormant state,\nready to be carried to any distance by those external agencies which we\nmay deem fortuitous, but without which many a race might perish from the\nexhaustion of the limited spot of soil in which it is rooted.\" (Pres.\nAddr.(1869), \"Proc. Linn. Soc.\" 1868-69, pages lxvi, lxvii.)\n\nI have quoted this passage from Bentham because it emphasises a point\nwhich Darwin for his purpose did not find it necessary to dwell upon,\nthough he no doubt assumed it. Dispersal to a distance is, so to speak,\nan accidental incident in the life of a species. Lepidium Draba, a\nnative of South-eastern Europe, owes its prevalence in the Isle of\nThanet to the disastrous Walcheren expedition; the straw-stuffing of the\nmattresses of the fever-stricken soldiers who were landed there was used\nby a farmer for manure. Sir Joseph Hooker (\"Royal Institution Lecture\",\nApril 12, 1878.) tells us that landing on Lord Auckland's Island, which\nwas uninhabited, \"the first evidence I met with of its having been\npreviously visited by man was the English chickweed; and this I traced\nto a mound that marked the grave of a British sailor, and that was\ncovered with the plant, doubtless the offspring of seed that had adhered\nto the spade or mattock with which the grave had been dug.\"\n\nSome migration from the spot where the individuals of a species\nhave germinated is an essential provision against extinction. Their\ndescendants otherwise would be liable to suppression by more vigorous\ncompetitors. But they would eventually be extinguished inevitably,\nas pointed out by Bentham, by the exhaustion of at any rate some one\nnecessary constituent of the soil. Gilbert showed by actual analysis\nthat the production of a \"fairy ring\" is simply due to the using up\nby the fungi of the available nitrogen in the enclosed area which\ncontinually enlarges as they seek a fresh supply on the outside margin.\nAnyone who cultivates a garden can easily verify the fact that every\nplant has some adaptation for varying degrees of seed-dispersal. It\ncannot be doubted that slow but persistent terrestrial migration has\nplayed an enormous part in bringing about existing plant-distribution,\nor that climatic changes would intensify the effect because they would\nforce the abandonment of a former area and the occupation of a new one.\nWe are compelled to admit that as an incident of the Glacial period a\nwhole flora may have moved down and up a mountain side, while only some\nof its constituent species would be able to take advantage of means of\nlong-distance transport.\n\nI have dwelt on the importance of what I may call short-distance\ndispersal as a necessary condition of plant life, because I think it\nsuggests the solution of a difficulty which leads Guppy to a conclusion\nwith which I am unable to agree. But the work which he has done taken as\na whole appears to me so admirable that I do so with the utmost respect.\nHe points out, as Bentham had already done, that long-distance dispersal\nis fortuitous. And being so it cannot have been provided for by\nprevious adaptation. He says (Guppy, op. cit. II. page 99.): \"It is not\nconceivable that an organism can be adapted to conditions outside\nits environment.\" To this we must agree; but, it may be asked, do the\ngeneral means of plant dispersal violate so obvious a principle? He\nproceeds: \"The great variety of the modes of dispersal of seeds is in\nitself an indication that the dispersing agencies avail themselves in a\nhap-hazard fashion of characters and capacities that have been developed\nin other connections.\" (Loc. cit. page 102.) \"Their utility in these\nrespects is an accident in the plant's life.\" (Loc. cit. page 100.) He\nattributes this utility to a \"determining agency,\" an influence which\nconstantly reappears in various shapes in the literature of Evolution\nand is ultra-scientific in the sense that it bars the way to the search\nfor material causes. He goes so far as to doubt whether fleshy fruits\nare an adaptation for the dispersal of their contained seeds. (Loc. cit.\npage 102.) Writing as I am from a hillside which is covered by hawthorn\nbushes sown by birds, I confess I can feel little doubt on the subject\nmyself. The essential fact which Guppy brings out is that long-distance\nunlike short-distance dispersal is not universal and purposeful, but\nselective and in that sense accidental. But it is not difficult to see\nhow under favouring conditions one must merge into the other.\n\nGuppy has raised one novel point which can only be briefly referred to\nbut which is of extreme interest. There are grounds for thinking that\nflowers and insects have mutually reacted upon one another in their\nevolution. Guppy suggests that something of the same kind may be true\nof birds. I must content myself with the quotation of a single sentence.\n\"With the secular drying of the globe and the consequent differentiation\nof climate is to be connected the suspension to a great extent of the\nagency of birds as plant dispersers in later ages, not only in the\nPacific Islands but all over the tropics. The changes of climate, birds\nand plants have gone on together, the range of the bird being controlled\nby the climate, and the distribution of the plant being largely\ndependent on the bird.\" (Loc.cit. II. page 221.)\n\nDarwin was clearly prepared to go further than Hooker in accounting for\nthe southern flora by dispersion from the north. Thus he says: \"We must,\nI suppose, admit that every yard of land has been successively covered\nwith a beech-forest between the Caucasus and Japan.\" (\"More Letters\",\nII. page 9.) Hooker accounted for the dissevered condition of the\nsouthern flora by geographical change, but this Darwin could not admit.\nHe suggested to Hooker that the Australian and Cape floras might have\nhad a point of connection through Abyssinia (Ibid. I. page 447.), an\nidea which was promptly snuffed out. Similarly he remarked to Bentham\n(1869): \"I suppose you think that the Restiaceae, Proteaceae, etc., etc.\nonce extended over the whole world, leaving fragments in the south.\"\n(Ibid. I. page 380.) Eventually he conjectured \"that there must have\nbeen a Tertiary Antarctic continent, from which various forms radiated\nto the southern extremities of our present continents.\" (\"Life and\nLetters\", III. page 231.) But characteristically he could not admit any\nland connections and trusted to \"floating ice for transporting seed.\"\n(\"More Letters\", I. page 116.) I am far from saying that this theory is\nnot deserving of serious attention, though there seems to be no positive\nevidence to support it, and it immediately raises the difficulty how did\nsuch a continent come to be stocked?\n\nWe must, however, agree with Hooker that the common origin of the\nnorthern and southern floras must be referred to a remote past. That\nDarwin had this in his mind at the time of the publication of the\n\"Origin\" is clear from a letter to Hooker. \"The view which I should have\nlooked at as perhaps most probable (though it hardly differs from yours)\nis that the whole world during the Secondary ages was inhabited by\nmarsupials, araucarias (Mem.--Fossil wood of this nature in South\nAmerica), Banksia, etc.; and that these were supplanted and exterminated\nin the greater area of the north, but were left alive in the south.\"\n(Ibid. I. page 453.) Remembering that Araucaria, unlike Banksia, belongs\nto the earlier Jurassic not to the angiospermous flora, this view is a\ngerminal idea of the widest generality.\n\nThe extraordinary congestion in species of the peninsulas of the Old\nWorld points to the long-continued action of a migration southwards.\nEach is in fact a cul-de-sac into which they have poured and from which\nthere is no escape. On the other hand the high degree of specialisation\nin the southern floras and the little power the species possess of\nholding their own in competition or in adaptation to new conditions\npoint to long-continued isolation. \"An island... will prevent free\nimmigration and competition, hence a greater number of ancient forms\nwill survive.\" (Ibid. I. page 481.) But variability is itself subject to\nvariation. The nemesis of a high degree of protected specialisation is\nthe loss of adaptability. (See Lyell, \"The Geological Evidences of the\nAntiquity of Man\", London, 1863, page 446.) It is probable that many\nelements of the southern flora are doomed: there is, for example, reason\nto think that the singular Stapelieae of S. Africa are a disappearing\ngroup. The tree Lobelias which linger in the mountains of Central\nAfrica, in Tropical America and in the Sandwich Islands have the aspect\nof extreme antiquity. I may add a further striking illustration from\nProfessor Seward: \"The tall, graceful fronds of Matonia pectinata,\nforming miniature forests on the slopes of Mount Ophir and other\ndistricts in the Malay Peninsula in association with Dipteris conjugata\nand Dipteris lobbiana, represent a phase of Mesozoic life which survives\n'Like a dim picture of the drowned past.'\" (\"Report of the 73rd Meeting\nof the British Assoc.\" (Southport, 1903), London, 1904, page 844.)\n\nThe Matonineae are ferns with an unusually complex vascular system and\nwere abundant \"in the northern hemisphere during the earlier part of the\nMesozoic era.\"\n\nIt was fortunate for science that Wallace took up the task which his\ncolleague had abandoned. Writing to him on the publication of his\n\"Geographical Distribution of Animals\" Darwin said: \"I feel sure\nthat you have laid a broad and safe foundation for all future work on\nDistribution. How interesting it will be to see hereafter plants treated\nin strict relation to your views.\" (\"More Letters\", II. page 12.) This\nhope was fulfilled in \"Island Life\". I may quote a passage from it which\nadmirably summarises the contrast between the northern and the southern\nfloras.\n\n\"Instead of the enormous northern area, in which highly organised\nand dominant groups of plants have been developed gifted with\ngreat colonising and aggressive powers, we have in the south three\ncomparatively small and detached areas, in which rich floras have\nbeen developed with SPECIAL adaptations to soil, climate, and organic\nenvironment, but comparatively impotent and inferior beyond their own\ndomain.\" (Wallace, \"Island Life\", pages 527, 528.)\n\nIt will be noticed that in the summary I have attempted to give of the\nhistory of the subject, efforts have been concentrated on bringing into\nrelation the temperate floras of the northern and southern hemispheres,\nbut no account has been taken of the rich tropical vegetation which\nbelts the world and little to account for the original starting-point\nof existing vegetation generally. It must be remembered on the one hand\nthat our detailed knowledge of the floras of the tropics is still very\nincomplete and far inferior to that of temperate regions; on the other\nhand palaeontological discoveries have put the problem in an entirely\nnew light. Well might Darwin, writing to Heer in 1875, say: \"Many\nas have been the wonderful discoveries in Geology during the last\nhalf-century, I think none have exceeded in interest your results with\nrespect to the plants which formerly existed in the arctic regions.\"\n(\"More Letters\", II. page 240.)\n\nAs early as 1848 Debey had described from the Upper Cretaceous rocks of\nAix-la-Chapelle Flowering plants of as high a degree of development\nas those now existing. The fact was commented upon by Hooker (\"Introd.\nEssay to the Flora of Tasmania\", page xx.), but its full significance\nseems to have been scarcely appreciated. For it implied not merely that\ntheir evolution must have taken place but the foundations of existing\ndistribution must have been laid in a preceding age. We now know\nfrom the discoveries of the last fifty years that the remains of the\nNeocomian flora occur over an area extending through 30 deg of latitude.\nThe conclusion is irresistible that within this was its centre of\ndistribution and probably of origin.\n\nDarwin was immensely impressed with the outburst on the world of a\nfully fledged angiospermous vegetation. He warmly approved the brilliant\ntheory of Saporta that this happened \"as soon (as) flower-frequenting\ninsects were developed and favoured intercrossing.\" (\"More Letters\", II.\npage 21.) Writing to him in 1877 he says: \"Your idea that dicotyledonous\nplants were not developed in force until sucking insects had been\nevolved seems to me a splendid one. I am surprised that the idea never\noccurred to me, but this is always the case when one first hears a\nnew and simple explanation of some mysterious phenomenon.\" (\"Life\nand Letters\", III. page 285. Substantially the same idea had\noccurred earlier to F.W.A. Miquel. Remarking that \"sucking insects\n(Haustellata)... perform in nature the important duty of maintaining the\nexistence of the vegetable kingdom, at least as far as the higher orders\nare concerned,\" he points our that \"the appearance in great numbers of\nhaustellate insects occurs at and after the Cretaceous epoch, when\nthe plants with pollen and closed carpels (Angiosperms) are found, and\nacquire little by little the preponderance in the vegetable kingdom.\"\n\"Archives Neerlandaises\", III. (1868). English translation in \"Journ. of\nBot.\" 1869, page 101.)\n\nEven with this help the abruptness still remains an almost insoluble\nproblem, though a forecast of floral structure is now recognised in some\nJurassic and Lower Cretaceous plants. But the gap between this and the\nstructural complexity and diversity of angiosperms is enormous. Darwin\nthought that the evolution might have been accomplished during a period\nof prolonged isolation. Writing to Hooker (1881) he says: \"Nothing is\nmore extraordinary in the history of the Vegetable Kingdom, as it seems\nto me, than the APPARENTLY very sudden or abrupt development of the\nhigher plants. I have sometimes speculated whether there did not exist\nsomewhere during long ages an extremely isolated continent, perhaps near\nthe South Pole.\" (\"Life and Letters\", III. page 248.)\n\nThe present trend of evidence is, however, all in favour of a northern\norigin for flowering plants, and we can only appeal to the imperfection\nof the geological record as a last resource to extricate us from the\ndifficulty of tracing the process. But Darwin's instinct that at some\ntime or other the southern hemisphere had played an important part in\nthe evolution of the vegetable kingdom did not mislead him. Nothing\nprobably would have given him greater satisfaction than the masterly\nsummary in which Seward has brought together the evidence for the origin\nof the Glossopteris flora in Gondwana land.\n\n\"A vast continental area, of which remnants are preserved in Australia,\nSouth Africa and South America... A tract of enormous extent occupying\nan area, part of which has since given place to a southern ocean, while\ndetached masses persist as portions of more modern continents, which\nhave enabled us to read in their fossil plants and ice-scratched\nboulders the records of a lost continent, in which the Mesozoic\nvegetation of the northern continent had its birth.\" (\"Encycl. Brit.\"\n(10th edition 1902), Vol. XXXI. (\"Palaeobotany; Mesozoic\"), page 422.)\nDarwin would probably have demurred on physical grounds to the extent\nof the continent, and preferred to account for the transoceanic\ndistribution of its flora by the same means which must have accomplished\nit on land.\n\nIt must in fairness be added that Guppy's later views give some support\nto the conjectural existence of the \"lost continent.\" \"The distribution\nof the genus Dammara\" (Agathis) led him to modify his earlier\nconclusions. He tells us:--\"In my volume on the geology of Vanua Levu\nit was shown that the Tertiary period was an age of submergence in the\nWestern Pacific, and a disbelief in any previous continental condition\nwas expressed. My later view is more in accordance with that of\nWichmann, who, on geological grounds, contended that the islands of the\nWestern Pacific were in a continental condition during the Palaeozoic\nand Mesozoic periods, and that their submergence and subsequent\nemergence took place in Tertiary times.\" (Guppy, op. cit. II. page 304.)\n\nThe weight of the geological evidence I am unable to scrutinise. But\nthough I must admit the possibility of some unconscious bias in my\nown mind on the subject, I am impressed with the fact that the known\ndistribution of the Glossopteris flora in the southern hemisphere is\nprecisely paralleled by that of Proteaceae and Restiaceae in it at the\npresent time. It is not unreasonable to suppose that both phenomena,\nso similar, may admit of the same explanation. I confess it would not\nsurprise me if fresh discoveries in the distribution of the Glossopteris\nflora were to point to the possibility of its also having migrated\nsouthwards from a centre of origin in the northern hemisphere.\n\nDarwin, however, remained sceptical \"about the travelling of plants\nfrom the north EXCEPT DURING THE TERTIARY PERIOD.\" But he added, \"such\nspeculations seem to me hardly scientific, seeing how little we know\nof the old floras.\" (\"Life and Letters\", III. page 247.) That in later\ngeological times the south has been the grave of the weakened offspring\nof the aggressive north can hardly be doubted. But if we look to the\nGlossopteris flora for the ancestry of Angiosperms during the Secondary\nperiod, Darwin's prevision might be justified, though he has given us no\nclue as to how he arrived at it.\n\nIt may be true that technically Darwin was not a botanist. But in two\npages of the \"Origin\" he has given us a masterly explanation of \"the\nrelationship, with very little identity, between the productions of\nNorth America and Europe.\" (Pages 333, 334.) He showed that this could\nbe accounted for by their migration southwards from a common area, and\nhe told Wallace that he \"doubted much whether the now called Palaearctic\nand Neartic regions ought to be separated.\" (\"Life and Letters\", III.\npage 230.) Catkin-bearing deciduous trees had long been seen to justify\nDarwin's doubt: oaks, chestnuts, beeches, hazels, hornbeams, birches,\nalders, willows and poplars are common both to the Old and New World.\nNewton found that the separate regions could not be sustained for birds,\nand he is now usually followed in uniting them as the Holartic. One\nfeels inclined to say in reading the two pages, as Lord Kelvin did to\na correspondent who asked for some further development of one of his\npapers, It is all there. We have only to apply the principle to previous\ngeological ages to understand why the flora of the Southern United\nStates preserves a Cretaceous facies. Applying it still further we can\nunderstand why, when the northern hemisphere gradually cooled through\nthe Tertiary period, the plants of the Eocene \"suggest a comparison of\nthe climate and forests with those of the Malay Archipelago and Tropical\nAmerica.\" (Clement Reid, \"Encycl. Brit.\" (10th edition), Vol. XXXI.\n(\"Palaeobotany; Tertiary\"), page 435.) Writing to Asa Gray in 1856\nwith respect to the United States flora, Darwin said that \"nothing has\nsurprised me more than the greater generic and specific affinity with\nEast Asia than with West America.\" (\"More Letters\", I. page 434.) The\nrecent discoveries of a Tulip tree and a Sassafras in China afford fresh\nillustrations. A few years later Asa Gray found the explanation in\nboth areas being centres of preservation of the Cretaceous flora from\na common origin. It is interesting to note that the paper in which this\nwas enunciated at once established his reputation.\n\nIn Europe the latitudinal range of the great mountain chains gave the\nMiocene flora no chance of escape during the Glacial period, and the\nMediterranean appears to have equally intercepted the flow of alpine\nplants to the Atlas. (John Ball in Appendix G, page 438, in \"Journal of\na Tour in Morocco and the Great Atlas\", J.D. Hooker and J. Ball, London,\n1878.) In Southern Europe the myrtle, the laurel, the fig and the\ndwarf-palm are the sole representatives of as many great tropical\nfamilies. Another great tropical family, the Gesneraceae has left single\nrepresentatives from the Pyrenees to the Balkans; and in the former\na diminutive yam still lingers. These are only illustrations of the\nevidence which constantly accumulates and which finds no rational\nexplanation except that which Darwin has given to it.\n\nThe theory of southward migration is the key to the interpretation of\nthe geographical distribution of plants. It derived enormous support\nfrom the researches of Heer and has now become an accepted commonplace.\nSaporta in 1888 described the vegetable kingdom as \"emigrant pour suivre\nune direction determinee et marcher du nord au sud, a la recherche\nde regions et de stations plus favorables, mieux appropriees aux\nadaptations acquises, a meme que la temperature terrestre perd ses\nconditions premieres.\" (\"Origine Paleontologique des arbres\", Paris,\n1888, page 28.) If, as is so often the case, the theory now seems to be\na priori inevitable, the historian of science will not omit to record\nthat the first germ sprang from the brain of Darwin.\n\nIn attempting this sketch of Darwin's influence on Geographical\nDistribution, I have found it impossible to treat it from an external\npoint of view. His interest in it was unflagging; all I could say became\nnecessarily a record of that interest and could not be detached from it.\nHe was in more or less intimate touch with everyone who was working\nat it. In reading the letters we move amongst great names. With an\nextraordinary charm of persuasive correspondence he was constantly\nsuggesting, criticising and stimulating. It is hardly an exaggeration\nto say that from the quiet of his study at Down he was founding and\ndirecting a wide-world school.\n\nPOSTSCRIPTUM.\n\nSince this essay was put in type Dr Ernst's striking account of the \"New\nFlora of the Volcanic Island of Krakatau\" (Cambridge, 1909.) has reached\nme. All botanists must feel a debt of gratitude to Prof. Seward for\nhis admirable translation of a memoir which in its original form\nis practically unprocurable and to the liberality of the Cambridge\nUniversity Press for its publication. In the preceding pages I have\ntraced the laborious research by which the methods of Plant Dispersal\nwere established by Darwin. In the island of Krakatau nature has\nsupplied a crucial experiment which, if it had occurred earlier, would\nhave at once secured conviction of their efficiency. A quarter of a\ncentury ago every trace of organic life in the island was \"destroyed\nand buried under a thick covering of glowing stones.\" Now, it is \"again\ncovered with a mantle of green, the growth being in places so\nluxuriant that it is necessary to cut one's way laboriously through the\nvegetation.\" (Op. cit. page 4.) Ernst traces minutely how this has been\nbrought about by the combined action of wind, birds and sea currents,\nas means of transport. The process will continue, and he concludes:--\"At\nlast after a long interval the vegetation on the desolated island will\nagain acquire that wealth of variety and luxuriance which we see in the\nfullest development which Nature has reached in the primaeval forest\nin the tropics.\" (Op. cit. page 72.) The possibility of such a result\nrevealed itself to the insight of Darwin with little encouragement or\nsupport from contemporary opinion.\n\nOne of the most remarkable facts established by Ernst is that this has\nnot been accomplished by the transport of seeds alone. \"Tree stems and\nbranches played an important part in the colonisation of Krakatau by\nplants and animals. Large piles of floating trees, stems, branches and\nbamboos are met with everywhere on the beach above high-water mark and\noften carried a considerable distance inland. Some of the animals on the\nisland, such as the fat Iguana (Varanus salvator) which suns itself in\nthe beds of streams, may have travelled on floating wood, possibly also\nthe ancestors of the numerous ants, but certainly plants.\" (Op. cit.\npage 56.) Darwin actually had a prevision of this. Writing to Hooker he\nsays:--\"Would it not be a prodigy if an unstocked island did not in the\ncourse of ages receive colonists from coasts whence the currents flow,\ntrees are drifted and birds are driven by gales?\" (\"More Letters\", I.\npage 483.) And ten years earlier:--\"I must believe in the... whole\nplant or branch being washed into the sea; with floods and slips and\nearthquakes; this must continually be happening.\" (\"Life and Letters\",\nII. pages 56, 57.) If we give to \"continually\" a cosmic measure, can the\nfact be doubted? All this, in the light of our present knowledge, is too\nobvious to us to admit of discussion. But it seems to me nothing less\nthan pathetic to see how in the teeth of the obsession as to continental\nextension, Darwin fought single-handed for what we now know to be the\ntruth.\n\nGuppy's heart failed him when he had to deal with the isolated case of\nAgathis which alone seemed inexplicable by known means of transport. But\nwhen we remember that it is a relic of the pre-Angiospermous flora, and\nis of Araucarian ancestry, it cannot be said that the impossibility,\nin so prolonged a history, of the bodily transference of cone-bearing\nbranches or even of trees, compels us as a last resort to fall back on\ncontinental extension to account for its existing distribution.\n\nWhen Darwin was in the Galapagos Archipelago, he tells us that he\nfancied himself \"brought near to the very act of creation.\" He saw\nhow new species might arise from a common stock. Krakatau shows us an\nearlier stage and how by simple agencies, continually at work, that\nstock might be supplied. It also shows us how the mixed and casual\nelements of a new colony enter into competition for the ground and\nbecome mutually adjusted. The study of Plant Distribution from a\nDarwinian standpoint has opened up a new field of research in Ecology.\nThe means of transport supply the materials for a flora, but their\nultimate fate depends on their equipment for the \"struggle for\nexistence.\" The whole subject can no longer be regarded as a mere\nstatistical inquiry which has seemed doubtless to many of somewhat arid\ninterest. The fate of every element of the earth's vegetation has sooner\nor later depended on its ability to travel and to hold its own under\nnew conditions. And the means by which it has secured success is an\neach case a biological problem which demands and will reward the most\nattentive study. This is the lesson which Darwin has bequeathed to us.\nIt is summed up in the concluding paragraph of the \"Origin\" (\"Origin of\nSpecies\" (6th edition), page 429.):--\"It is interesting to contemplate a\ntangled bank, clothed with many plants of many kinds, with birds singing\non the bushes, with various insects flitting about, and with worms\ncrawling through the damp earth, and to reflect that these elaborately\nconstructed forms, so different from each other, and dependent upon\neach other in so complex a manner, have all been produced by laws acting\naround us.\"\n\n\n\n\nXVII. GEOGRAPHICAL DISTRIBUTION OF ANIMALS. By Hans Gadow, M.A., Ph.D.,\nF.R.S.\n\nStrickland Curator and Lecturer on Zoology in the University of\nCambridge.\n\n\nThe first general ideas about geographical distribution may be found\nin some of the brilliant speculations contained in Buffon's \"Histoire\nNaturelle\". The first special treatise on the subject was however\nwritten in 1777 by E.A.W. Zimmermann, Professor of Natural Science\nat Brunswick, whose large volume, \"Specimen Zoologiae Geographicae\nQuadrupedum\"..., deals in a statistical way with the mammals; important\nfeatures of the large accompanying map of the world are the ranges\nof mountains and the names of hundreds of genera indicating their\ngeographical range. In a second work he laid special stress on\ndomesticated animals with reference to the spreading of the various\nraces of Mankind.\n\nIn the following year appeared the \"Philosophia Entomologica\" by J.C.\nFabricius, who was the first to divide the world into eight regions. In\n1803 G.R. Treviranus (\"Biologie oder Philosophie der lebenden Natur\",\nVol. II. Gottingen, 1803.) devoted a long chapter of his great work on\n\"Biologie\" to a philosophical and coherent treatment of the distribution\nof the whole animal kingdom. Remarkable progress was made in 1810 by F.\nTiedemann (\"Anatomie und Naturgeschichte der Vogel\". Heidelberg, 1810.)\nof Heidelberg. Few, if any, of the many subsequent Ornithologists seem\nto have appreciated, or known of, the ingenious way in which Tiedemann\nmarshalled his statistics in order to arrive at general conclusions.\nThere are, for instance, long lists of birds arranged in accordance\nwith their occurrence in one or more continents: by correlating the\ndistribution of the birds with their food he concludes \"that the\ncountries of the East Indian flora have no vegetable feeders in common\nwith America,\" and \"that it is probably due to the great peculiarity of\nthe African flora that Africa has few phytophagous kinds in common with\nother countries, whilst zoophagous birds have a far more independent,\noften cosmopolitan, distribution.\" There are also remarkable chapters\non the influence of environment, distribution, and migration, upon the\nstructure of the Birds! In short, this anatomist dealt with some of the\nfundamental causes of distribution.\n\nWhilst Tiedemann restricted himself to Birds, A. Desmoulins in 1822\nwrote a short but most suggestive paper on the Vertebrata, omitting\nthe birds; he combated the view recently proposed by the entomologist\nLatreille that temperature was the main factor in distribution. Some of\nhis ten main conclusions show a peculiar mixture of evolutionary ideas\ncoupled with the conception of the stability of species: whilst each\nspecies must have started from but one creative centre, there may be\nseveral \"analogous centres of creation\" so far as genera and families\nare concerned. Countries with different faunas, but lying within the\nsame climatic zones, are proof of the effective and permanent existence\nof barriers preventing an exchange between the original creative\ncentres.\n\nThe first book dealing with the \"geography and classification\" of the\nwhole animal kingdom was written by W. Swainson (\"A Treatise on\nthe Geography and Classification of Animals\", Lardner's \"Cabinet\nCyclopaedia\" London, 1835.) in 1835. He saw in the five races of Man\nthe clue to the mapping of the world into as many \"true zoological\ndivisions,\" and he reconciled the five continents with his mystical\nquinary circles.\n\nLyell's \"Principles of Geology\" should have marked a new epoch, since\nin his \"Elements\" he treats of the past history of the globe and the\ndistribution of animals in time, and in his \"Principles\" of their\ndistribution in space in connection with the actual changes undergone by\nthe surface of the world. But as the sub-title of his great work \"Modern\nchanges of the Earth and its inhabitants\" indicates, he restricted\nhimself to comparatively minor changes, and, emphatically believing\nin the permanency of the great oceans, his numerous and careful\ninterpretations of the effect of the geological changes upon the\ndispersal of animals did after all advance the problem but little.\n\nHitherto the marine faunas had been neglected. This was remedied by E.\nForbes, who established nine homozoic zones, based mainly on the study\nof the mollusca, the determining factors being to a great extent\nthe isotherms of the sea, whilst the 25 provinces were given by the\nconfiguration of the land. He was followed by J.D. Dana, who, taking\nprincipally the Crustacea as a basis, and as leading factors the mean\ntemperatures of the coldest and of the warmest months, established\nfive latitudinal zones. By using these as divisors into an American,\nAfro-European, Oriental, Arctic and Antarctic realm, most of which were\nlimited by an eastern and western land-boundary, he arrived at about\nthreescore provinces.\n\nIn 1853 appeared L.K. Schmarda's (\"Die geographische Verbreitung der\nThiere\", Wien, 1853.) two volumes, embracing the whole subject. Various\ncentres of creation being, according to him, still traceable, he formed\nthe hypothesis that these centres were originally islands, which later\nbecame enlarged and joined together to form the great continents, so\nthat the original faunas could overlap and mix whilst still remaining\npure at their respective centres. After devoting many chapters to the\npossible physical causes and modes of dispersal, he divided the land\ninto 21 realms which he shortly characterises, e.g. Australia as the\nonly country inhabited by marsupials, monotremes and meliphagous birds.\nTen main marine divisions were diagnosed in a similar way. Although some\nof these realms were not badly selected from the point of view of being\napplicable to more than one class of animals, they were obviously too\nnumerous for general purposes, and this drawback was overcome, in 1857,\nby P.L. Sclater. (\"On the general Geographical Distribution of the\nmembers of the class Aves\", \"Proc. Linn. Soc.\" (Zoology II. 1858, pages\n130-145.)) Starting with the idea, that \"each species must have been\ncreated within and over the geographical area, which it now occupies,\"\nhe concluded \"that the most natural primary ontological divisions of the\nEarth's surface\" were those six regions, which since their adoption\nby Wallace in his epoch-making work, have become classical. Broadly\nspeaking, these six regions are equivalent to the great masses of land;\nthey are convenient terms for geographical facts, especially since the\nPalaearctic region expresses the unity of Europe with the bulk of Asia.\nSclater further brigaded the regions of the Old World as Palaeogaea and\nthe two Americas as Neogaea, a fundamental mistake, justifiable to a\ncertain extent only since he based his regions mainly upon the present\ndistribution of the Passerine birds.\n\nUnfortunately these six regions are not of equal value. The Indian\ncountries and the Ethiopian region (Africa south of the Sahara) are\nobviously nothing but the tropical, southern continuations or appendages\nof one greater complex. Further, the great eastern mass of land is so\nintimately connected with North America that this continent has much\nmore in common with Europe and Asia than with South America. Therefore,\ninstead of dividing the world longitudinally as Sclater had done,\nHuxley, in 1868 (\"On the classification and distribution of the\nAlectoromorphae and Heteromorphae\", \"Proc. Zool. Soc.\" 1868, page\n294.), gave weighty reasons for dividing it transversely. Accordingly\nhe established two primary divisions, Arctogaea or the North world in\na wider sense, comprising Sclater's Indian, African, Palaearctic and\nNeartic regions; and Notogaea, the Southern world, which he divided\ninto (1) Austro-Columbia (an unfortunate substitute for the neotropical\nregion), (2) Australasia, and (3) New Zealand, the number of big regions\nthus being reduced to three but for the separation of New Zealand upon\nrather negative characters. Sclater was the first to accept these four\ngreat regions and showed, in 1874 (\"The geographical distribution of\nMammals\", \"Manchester Science Lectures\", 1874.), that they were well\nborne out by the present distribution of the Mammals.\n\nAlthough applicable to various other groups of animals, for instance to\nthe tailless Amphibia and to Birds (Huxley himself had been led to found\nhis two fundamental divisions on the distribution of the Gallinaceous\nbirds), the combination of South America with Australia was gradually\nfound to be too sweeping a measure. The obvious and satisfactory\nsolution was provided by W.T. Blanford (Anniversary address (Geological\nSociety, 1889), \"Proc. Geol. Soc.\" 1889-90, page 67; \"Quart. Journ.\"\nXLVI 1890.), who in 1890 recognised three main divisions, namely\nAustralian, South American, and the rest, for which the already existing\nterms (although used partly in a new sense, as proposed by an anonymous\nwriter in \"Natural Science\", III. page 289) \"Notogaea,\" \"Neogaea\" and\n\"Arctogaea\" have been gladly accepted by a number of English writers.\n\nAfter this historical survey of the search for larger and largest or\nfundamental centres of animal creation, which resulted in the mapping\nof the world into zoological regions and realms of after all doubtful\nvalue, we have to return to the year 1858. The eleventh and twelfth\nchapters of \"The Origin of Species\" (1859), dealing with \"Geographical\nDistribution,\" are based upon a great amount of observation, experiment\nand reading. As Darwin's main problem was the origin of species,\nnature's way of making species by gradual changes from others previously\nexisting, he had to dispose of the view, held universally, of the\nindependent creation of each species and at the same time to insist upon\na single centre of creation for each species; and in order to emphasise\nhis main point, the theory of descent, he had to disallow convergent, or\nas they were then called, analogous forms. To appreciate the difficulty\nof his position we have to take the standpoint of fifty years ago, when\nthe immutability of the species was an axiom and each was supposed to\nhave been created within or over the geographical area which it now\noccupies. If he once admitted that a species could arise from many\nindividuals instead of from one pair, there was no way of shutting the\ndoor against the possibility that these individuals may have been so\nnumerous that they occupied a very large district, even so large that\nit had become as discontinuous as the distribution of many a species\nactually is. Such a concession would at once be taken as an admission of\nmultiple, independent, origin instead of descent in Darwin's sense.\n\nFor the so-called multiple, independently repeated creation of species\nas an explanation of their very wide and often quite discontinuous\ndistribution, he substituted colonisation from the nearest and readiest\nsource together with subsequent modification and better adaptation to\ntheir new home.\n\nHe was the first seriously to call attention to the many accidental\nmeans, \"which more properly should be called occasional means of\ndistribution,\" especially to oceanic islands. His specific, even\nindividual, centres of creation made migrations all the more necessary,\nbut their extent was sadly baulked by the prevailing dogma of the\npermanency of the oceans. Any number of small changes (\"many islands\nhaving existed as halting places, of which not a wreck now remains\"\n(\"The Origin of Species\" (1st edition), page 396.).) were conceded\nfreely, but few, if any, great enough to permit migration of truly\nterrestrial creatures. The only means of getting across the gaps was by\nthe principle of the \"flotsam and jetsam,\" a theory which Darwin took\nover from Lyell and further elaborated so as to make it applicable to\nmany kinds of plants and animals, but sadly deficient, often grotesque,\nin the case of most terrestrial creatures.\n\nAnother very fertile source was Darwin's strong insistence upon the\ngreat influence which the last glacial epoch must have had upon the\ndistribution of animals and plants. Why was the migration of northern\ncreatures southwards of far-reaching and most significant importance?\nMore northerners have established themselves in southern lands than\nvice versa, because there is such a great mass of land in the north\nand greater continents imply greater intensity of selection. \"The\nproductions of real islands have everywhere largely yielded to\ncontinental forms.\" (Ibid. page 380.)... \"The Alpine forms have almost\neverywhere largely yielded to the more dominant forms generated in the\nlarger areas and more efficient workshops of the North.\"\n\nLet us now pass in rapid survey the influence of the publication of \"The\nOrigin of Species\" upon the study of Geographical Distribution in its\nwider sense.\n\nHitherto the following thought ran through the minds of most writers:\nWherever we examine two or more widely separated countries their\nrespective faunas are very different, but where two faunas can come into\ncontact with each other, they intermingle. Consequently these faunas\nrepresent centres of creation, whence the component creatures have\nspread peripherally so far as existing boundaries allowed them to do so.\nThis is of course the fundamental idea of \"regions.\" There is not one\nof the numerous writers who considered the possibility that these\nintermediate belts might represent not a mixture of species but\ntransitional forms, the result of changes undergone by the most\nperipheral migrants in adaptation to their new surroundings. The usual\nstandpoint was also that of Pucheran (\"Note sur l'equateur zoologique\",\n\"Rev. et Mag. de Zoologie\", 1855; also several other papers, ibid. 1865,\n1866, and 1867.) in 1855. But what a change within the next ten years!\nPucheran explains the agreement in coloration between the desert and\nits fauna as \"une harmonie post-etablie\"; the Sahara, formerly a marine\nbasin, was peopled by immigrants from the neighbouring countries, and\nthese new animals adapted themselves to the new environment. He also\ndiscusses, among other similar questions, the Isthmus of Panama with\nregard to its having once been a strait. From the same author may be\nquoted the following passage as a strong proof of the new influence:\n\"By the radiation of the contemporaneous faunas, each from one centre,\nwhence as the various parts of the world successively were formed and\nbecame habitable, they spread and became modified according to the local\nphysical conditions.\"\n\nThe \"multiple\" origin of each species as advocated by Sclater and\nMurray, although giving the species a broader basis, suffered from the\nsame difficulties. There was only one alternative to the old\northodox view of independent creation, namely the bold acceptance of\nland-connections to an extent for which geological and palaeontological\nscience was not yet ripe. Those who shrank from either view, gave up\nthe problem as mysterious and beyond the human intellect. This was the\nexpressed opinion of men like Swainson, Lyell and Humboldt. Only Darwin\nhad the courage to say that the problem was not insoluble. If we admit\n\"that in the long course of time the individuals of the same species,\nand likewise of allied species, have proceeded from some one source;\nthen I think all the grand leading facts of geographical distribution\nare explicable on the theory of migration... together with subsequent\nmodification and the multiplication of new forms.\" We can thus\nunderstand how it is that in some countries the inhabitants \"are linked\nto the extinct beings which formerly inhabited the same continent.\"\nWe can see why two areas, having nearly the same physical conditions,\nshould often be inhabited by very different forms of life,... and \"we can\nsee why in two areas, however distant from each other, there should be a\ncorrelation, in the presence of identical species... and of distinct but\nrepresentative species.\" (\"The Origin of Species\" (1st edition), pages\n408, 409.)\n\nDarwin's reluctance to assume great geological changes, such as a\nland-connection of Europe with North America, is easily explained by the\nfact that he restricted himself to the distribution of the present and\ncomparatively recent species. \"I do not believe that it will ever be\nproved that within the recent period continents which are now quite\nseparate, have been continuously, or almost continuously, united with\neach other, and with the many existing oceanic islands.\" (Ibid. page\n357.) Again, \"believing... that our continents have long remained in\nnearly the same relative position, though subjected to large, but\npartial oscillations of level,\" that means to say within the period of\nexisting species, or \"within the recent period.\" (Ibid. page. 370.) The\ndifficulty was to a great extent one of his own making. Whilst almost\neverybody else believed in the immutability of the species, which\nimplies an enormous age, logically since the dawn of creation, to him\nthe actually existing species as the latest results of evolution, were\nnecessarily something very new, so young that only the very latest of\nthe geological epochs could have affected them. It has since come to\nour knowledge that a great number of terrestrial \"recent\" species, even\nthose of the higher classes of Vertebrates, date much farther back than\nhad been thought possible. Many of them reach well into the Miocene, a\ntime since which the world seems to have assumed the main outlines of\nthe present continents.\n\nIn the year 1866 appeared A. Murray's work on the \"Geographical\nDistribution of Mammals\", a book which has perhaps received less\nrecognition than it deserves. His treatment of the general introductory\nquestions marks a considerable advance of our problem, although, and\npartly because, he did not entirely agree with Darwin's views as laid\ndown in the first edition of \"The Origin of Species\", which after all\nwas the great impulse given to Murray's work. Like Forbes he did not\nshrink from assuming enormous changes in the configuration of the\ncontinents and oceans because the theory of descent, with its necessary\npostulate of great migrations, required them. He stated, for instance,\n\"that a Miocene Atlantis sufficiently explains the common distribution\nof animals and plants in Europe and America up to the glacial epoch.\"\nAnd next he considers how, and by what changes, the rehabilitation and\ndistribution of these lands themselves were effected subsequent to\nthat period. Further, he deserves credit for having cleared up a\nmisunderstanding of the idea of specific centres of creation. Whilst for\ninstance Schmarda assumed without hesitation that the same species,\nif occurring at places separated by great distances, or apparently\ninsurmountable barriers, had been there created independently (multiple\ncentres), Lyell and Darwin held that each species had only one single\ncentre, and with this view most of us agree, but their starting point\nwas to them represented by one individual, or rather one single pair.\nAccording to Murray, on the other hand, this centre of a species is\nformed by all the individuals of a species, all of which equally undergo\nthose changes which new conditions may impose upon them. In this respect\na new species has a multiple origin, but this in a sense very different\nfrom that which was upheld by L. Agassiz. As Murray himself puts it: \"To\nmy multiple origin, communication and direct derivation is essential.\nThe species is compounded of many influences brought together through\nmany individuals, and distilled by Nature into one species; and, being\nonce established it may roam and spread wherever it finds the conditions\nof life not materially different from those of its original centre.\"\n(Murray, \"The Geographical Distribution of Mammals\", page 14. London,\n1866.) This declaration fairly agrees with more modern views, and\nit must be borne in mind that the application of the single-centre\nprinciple to the genera, families and larger groups in the search for\ndescent inevitably leads to one creative centre for the whole animal\nkingdom, a condition as unwarrantable as the myth of Adam and Eve being\nthe first representatives of Mankind.\n\nIt looks as if it had required almost ten years for \"The Origin\nof Species\" to show its full effect, since the year 1868 marks the\npublication of Haeckel's \"Naturliche Schoepfungsgeschichte\" in addition\nto other great works. The terms \"Oecology\" (the relation of organisms\nto their environment) and \"Chorology\" (their distribution in space) had\nbeen given us in his \"Generelle Morphologie\" in 1866. The fourteenth\nchapter of the \"History of Creation\" is devoted to the distribution of\norganisms, their chorology, with the emphatic assertion that \"not\nuntil Darwin can chorology be spoken of as a separate science, since\nhe supplied the acting causes for the elucidation of the hitherto\naccumulated mass of facts.\" A map (a \"hypothetical sketch\") shows the\nmonophyletic origin and the routes of distribution of Man.\n\nNatural Selection may be all-mighty, all-sufficient, but it requires\ntime, so much that the countless aeons required for the evolution of the\npresent fauna were soon felt to be one of the most serious drawbacks of\nthe theory. Therefore every help to ease and shorten this process should\nhave been welcomed. In 1868 M. Wagner (The first to formulate clearly\nthe fundamental idea of a theory of migration and its importance in\nthe origin of new species was L. von Buch, who in his \"Physikalische\nBeschreibung der Canarischen Inseln\", written in 1825, wrote as follows:\n\"Upon the continents the individuals of the genera by spreading far,\nform, through differences of the locality, food and soil, varieties\nwhich finally become constant as new species, since owing to the\ndistances they could never be crossed with other varieties and thus\nbe brought back to the main type. Next they may again, perhaps upon\ndifferent roads, return to the old home where they find the old\ntype likewise changed, both having become so different that they can\ninterbreed no longer. Not so upon islands, where the individuals shut\nup in narrow valleys or within narrow districts, can always meet one\nanother and thereby destroy every new attempt towards the fixing of a\nnew variety.\" Clearly von Buch explains here why island types remain\nfixed, and why these types themselves have become so different from\ntheir continental congeners.--Actually von Buch is aware of a most\nimportant point, the difference in the process of development which\nexists between a new species b, which is the result of an ancestral\nspecies a having itself changed into b and thereby vanished itself, and\na new species c which arose through separation out of the same ancestral\na, which itself persists as such unaltered. Von Buch's prophetic view\nseems to have escaped Lyell's and even Wagner's notice.) came to the\nrescue with his \"Darwin'sche Theorie und das Migrations-Gesetz der\nOrganismen\". (Leipzig, 1868.) He shows that migration, i.e. change of\nlocality, implies new environmental conditions (never mind whether\nthese be new stimuli to variation, or only acting as their selectors or\ncensors), and moreover secures separation from the original stock and\nthus eliminates or lessens the reactionary dangers of panmixia. Darwin\naccepted Wagner's theory as \"advantageous.\" Through the heated polemics\nof the more ardent selectionists Wagner's theory came to grow into an\nalternative instead of a help to the theory of selectional evolution.\nSeparation is now rightly considered a most important factor by modern\nstudents of geographical distribution.\n\nFor the same year, 1868, we have to mention Huxley, whose Arctogaea and\nNotogaea are nothing less than the reconstructed main masses of land\nof the Mesozoic period. Beyond doubt the configuration of land at that\nremote period has left recognisable traces in the present continents,\nbut whether they can account for the distribution of such a much later\ngroup as the Gallinaceous birds is more than questionable. In any case\nhe took for his text a large natural group of birds, cosmopolitan as\na whole, but with a striking distribution. The Peristeropodes, or\npigeon-footed division, are restricted to the Australian and Neotropical\nregions, in distinction to the Alectoropodes (with the hallux inserted\nat a level above the front toes) which inhabit the whole of the\nArctogaea, only a few members having spread into the South World.\nFurther, as Asia alone has its Pheasants and allies, so is Africa\ncharacterised by its Guinea-fowls and relations, America has the Turkey\nas an endemic genus, and the Grouse tribe in a wider sense has its\ncentre in the holarctic region: a splendid object lesson of descent,\nworld-wide spreading and subsequent differentiation. Huxley, by the way,\nwas the first--at least in private talk--to state that it will be for\nthe morphologist, the well-trained anatomist, to give the casting vote\nin questions of geographical distribution, since he alone can determine\nwhether we have to deal with homologous, or analogous, convergent,\nrepresentative forms.\n\nIt seems late to introduce Wallace's name in 1876, the year of the\npublication of his standard work. (\"The Geographical Distribution of\nAnimals\", 2 vols. London, 1876.) We cannot do better than quote the\nauthor's own words, expressing the hope that his \"book should bear a\nsimilar relation to the eleventh and twelfth chapters of the \"Origin of\nSpecies\" as Darwin's \"Animals and Plants under Domestication\" does to\nthe first chapter of that work,\" and to add that he has amply succeeded.\nPleading for a few primary centres he accepts Sclater's six regions and\ndoes not follow Huxley's courageous changes which Sclater himself had\naccepted in 1874. Holding the view of the permanence of the oceans he\naccounts for the colonisation of outlying islands by further elaborating\nthe views of Lyell and Darwin, especially in his fascinating \"Island\nLife\", with remarkable chapters on the Ice Age, Climate and Time and\nother fundamental factors. His method of arriving at the degree\nof relationship of the faunas of the various regions is eminently\nstatistical. Long lists of genera determine by their numbers the\naffinity and hence the source of colonisation. In order to make sure\nof his material he performed the laborious task of evolving a new\nclassification of the host of Passerine birds. This statistical method\nhas been followed by many authors, who, relying more upon quantity than\nquality, have obscured the fact that the key to the present distribution\nlies in the past changes of the earth's surface. However, with Wallace\nbegins the modern study of the geographical distribution of animals and\nthe sudden interest taken in this subject by an ever widening circle of\nenthusiasts far beyond the professional brotherhood.\n\nA considerable literature has since grown up, almost bewildering in its\nrange, diversity of aims and style of procedure. It is a chaos, with\nmany paths leading into the maze, but as yet very few take us to a\nposition commanding a view of the whole intricate terrain with its\nimpenetrable tangle and pitfalls.\n\nOne line of research, not initiated but greatly influenced by Wallace's\nworks, became so prominent as to almost constitute a period which may\nbe characterised as that of the search by specialists for either the\njustification or the amending of his regions. As class after class of\nanimals was brought up to reveal the secret of the true regions, some\nauthors saw in their different results nothing but the faultiness of\npreviously established regions; others looked upon eventual agreements\nas their final corroboration, especially when for instance such diverse\ngroups as mammals and scorpions could, with some ingenuity, be made to\nharmonise. But the obvious result of all these efforts was the growing\nknowledge that almost every class seemed to follow principles of its\nown. The regions tallied neither in extent nor in numbers, although\nmost of them gravitated more and more towards three centres, namely\nAustralia, South America and the rest of the world. Still zoologists\npersisted in the search, and the various modes and capabilities of\ndispersal of the respective groups were thought sufficient explanation\nof the divergent results in trying to bring the mapping of the world\nunder one scheme.\n\nContemporary literature is full of devices for the mechanical dispersal\nof animals. Marine currents, warm and cold, were favoured all the\nmore since they showed the probable original homes of the creatures in\nquestion. If these could not stand sea-water, they floated upon logs or\nicebergs, or they were blown across by storms; fishes were lifted over\nbarriers by waterspouts, and there is on record even an hypothetical\nland tortoise, full of eggs, which colonised an oceanic island after a\nperilous sea voyage upon a tree trunk. Accidents will happen, and beyond\ndoubt many freaks of discontinuous distribution have to be accounted\nfor by some such means. But whilst sufficient for the scanty settlers of\ntrue oceanic islands, they cannot be held seriously to account for the\nrich fauna of a large continent, over which palaeontology shows us that\nthe immigrants have passed like waves. It should also be borne in mind\nthat there is a great difference between flotsam and jetsam. A current\nis an extension of the same medium and the animals in it may suffer no\nchange during even a long voyage, since they may be brought from one\nlitoral to another where they will still be in the same or but slightly\naltered environment. But the jetsam is in the position of a passenger\nwho has been carried off by the wrong train. Almost every year some\nAmerican land birds arrive at our western coasts and none of them have\ngained a permanent footing although such visits must have taken place\nsince prehistoric times. It was therefore argued that only those groups\nof animals should be used for locating and defining regions which were\nabsolutely bound to the soil. This method likewise gave results not\nreconcilable with each other, even when the distribution of fossils\nwas taken into account, but it pointed to the absolute necessity of\nsearching for former land-connections regardless of their extent and the\npresent depths to which they may have sunk.\n\nThat the key to the present distribution lies in the past had been felt\nlong ago, but at last it was appreciated that the various classes of\nanimals and plants have appeared in successive geological epochs and\nalso at many places remote from each other. The key to the distribution\nof any group lies in the configuration of land and water of that epoch\nin which it made its first appearance. Although this sounds like a\nplatitude, it has frequently been ignored. If, for argument's sake,\nAmphibia were evolved somewhere upon the great southern land-mass of\nCarboniferous times (supposed by some to have stretched from South\nAmerica across Africa to Australia), the distribution of this developing\nclass must have proceeded upon lines altogether different from that of\nthe mammals which dated perhaps from lower Triassic times, when the old\nsouth continental belt was already broken up. The broad lines of this\ndistribution could never coincide with that of the other, older class,\nno matter whether the original mammalian centre was in the Afro-Indian,\nAustralian, or Brazilian portion. If all the various groups of animals\nhad come into existence at the same time and at the same place, then it\nwould be possible, with sufficient geological data, to construct a map\nshowing the generalised results applicable to the whole animal kingdom.\nBut the premises are wrong. Whatever regions we may seek to establish\napplicable to all classes, we are necessarily mixing up several\nprinciples, namely geological, historical, i.e. evolutionary, with\npresent day statistical facts. We might as well attempt one compound\npicture representing a chick's growth into an adult bird and a child's\ngrowth into manhood.\n\nIn short there are no general regions, not even for each class\nseparately, unless this class be one which is confined to a\ncomparatively short geological period. Most of the great classes have\nfar too long a history and have evolved many successive main groups.\nLet us take the mammals. Marsupials live now in Australia and in both\nAmericas, because they already existed in Mesozoic times; Ungulata\nexisted at one time or other all over the world except in Australia,\nbecause they are post-Cretaceous; Insectivores, although as old as any\nPlacentalia, are cosmopolitan excepting South America and Australia;\nStags and Bears, as examples of comparatively recent Arctogaeans, are\nfound everywhere with the exception of Ethiopia and Australia. Each of\nthese groups teaches a valuable historical lesson, but when these are\ncombined into the establishment of a few mammalian \"realms,\" they mean\nnothing but statistical majorities. If there is one at all, Australia is\nsuch a realm backed against the rest of the world, but as certainly it\nis not a mammalian creative centre!\n\nWell then, if the idea of generally applicable regions is a mare's nest,\nas was the search for the Holy Grail, what is the object of the study\nof geographical distribution? It is nothing less than the history of the\nevolution of life in space and time in the widest sense. The attempt to\naccount for the present distribution of any group of organisms involves\nthe aid of every branch of science. It bids fair to become a history of\nthe world. It started in a mild, statistical way, restricting itself to\nthe present fauna and flora and to the present configuration of land\nand water. Next came Oceanography concerned with the depths of the seas,\ntheir currents and temperatures; then enquiries into climatic changes,\nculminating in irreconcilable astronomical hypotheses as to glacial\nepochs; theories about changes of the level of the seas, mainly from the\npoint of view of the physicist and astronomer. Then came more and more\nto the front the importance of the geological record, hand in hand with\nthe palaeontological data and the search for the natural affinities, the\ngenetic system of the organisms. Now and then it almost seems as if the\nbiologists had done their share by supplying the problems and that the\nphysicists and geologists would settle them, but in reality it is not\nso. The biologists not only set the problems, they alone can check the\noffered solutions. The mere fact of palms having flourished in Miocene\nSpitzbergen led to an hypothetical shifting of the axis of the world\nrather than to the assumption, by way of explanation, that the palms\nthemselves might have changed their nature. One of the most valuable\naids in geological research, often the only means for reconstructing the\nface of the earth in by-gone periods, is afforded by fossils, but only\nthe morphologist can pronounce as to their trustworthiness as witnesses,\nbecause of the danger of mistaking analogous for homologous forms. This\ndifficulty applies equally to living groups, and it is so important that\na few instances may not be amiss.\n\nThere is undeniable similarity between the faunas of Madagascar and\nSouth America. This was supported by the Centetidae and Dendrobatidae,\ntwo entire \"families,\" as also by other facts. The value of the\nInsectivores, Solenodon in Cuba, Centetes in Madagascar, has been much\nlessened by their recognition as an extremely ancient group and as a\ncase of convergence, but if they are no longer put into the same\nfamily, this amendment is really to a great extent due to their widely\ndiscontinuous distribution. The only systematic difference of the\nDendrobatidae from the Ranidae is the absence of teeth, morphologically\na very unimportant character, and it is now agreed, on the strength of\ntheir distribution, that these little arboreal, conspicuously coloured\nfrogs, Dendrobates in South America, Mantella in Madagascar, do not form\na natural group, although a third genus, Cardioglossa in West Africa,\nseems also to belong to them. If these creatures lived all on the\nsame continent, we should unhesitatingly look upon them as forming a\nwell-defined, natural little group. On the other hand the Aglossa, with\ntheir three very divergent genera, namely Pipa in South America, Xenopus\nand Hymenochirus in Africa, are so well characterised as one ancient\ngroup that we use their distribution unhesitatingly as a hint of a\nformer connection between the two continents. We are indeed arguing in\nvicious circles. The Ratitae as such are absolutely worthless since they\nare a most heterogeneous assembly, and there are untold groups, of\nthe artificiality of which many a zoo-geographer had not the slightest\nsuspicion when he took his statistical material, the genera and\nfamilies, from some systematic catalogues or similar lists. A lamentable\ninstance is that of certain flightless Rails, recently extinct or\nsub-fossil, on the isalnds of Mauritius, Rodriguez and Chatham. Being\nflightless they have been used in support of a former huge Antarctic\ncontinent, instead of ruling them out of court as Rails which, each in\nits island, have lost the power of flight, a process which must have\ntaken place so recently that it is difficult, upon morphological\ngrounds, to justify their separation into Aphanapteryx in Mauritius,\nErythromachus in Rodriguez and Diaphorapteryx on Chatham Island.\nMorphologically they may well form but one genus, since they have sprung\nfrom the same stock and have developed upon the same lines; they are\ntherefore monogenetic: but since we know that they have become what they\nare independently of each other (now unlike any other Rails), they are\npolygenetic and therefore could not form one genus in the old Darwinian\nsense. Further, they are not a case of convergence, since their ancestry\nis not divergent but leads into the same stratum.\n\nTHE RECONSTRUCTION OF THE GEOGRAPHY OF SUCCESSIVE EPOCHS.\n\nA promising method is the study by the specialist of a large, widely\ndistributed group of animals from an evolutionary point of view.\nGood examples of this method are afforded by A.E. Ortmann's (\"The\ngeographical distribution of Freshwater Decapods and its bearing upon\nancient geography\", \"Proc. Amer. Phil. Soc.\" Vol. 41, 1902.) exhaustive\npaper and by A.W. Grabau's \"Phylogeny of Fusus and its Allies\"\n(\"Smithsonian Misc. Coll.\" 44, 1904.) After many important groups of\nanimals have been treated in this way--as yet sparingly attempted--the\nresults as to hypothetical land-connections etc. are sure to be\ncorrective and supplementary, and their problems will be solved, since\nthey are not imaginary.\n\nThe same problems are attacked, in the reverse way, by starting with the\nwhole fauna of a country and thence, so to speak, letting the research\nradiate. Some groups will be considered as autochthonous, others as\nimmigrants, and the directions followed by them will be inquired into;\nthe search may lead far and in various directions, and by comparison of\nresults, by making compound maps, certain routes will assume definite\nshape, and if they lead across straits and seas they are warrants to\nsearch for land-connections in the past. (A fair sample of this method\nis C.H. Eigenmann's \"The Freshwater Fishes of South and Middle America\",\n\"Popular Science Monthly\", Vol. 68, 1906.) There are now not a few maps\npurporting to show the outlines of land and water at various epochs.\nMany of these attempts do not tally with each other, owing to the\nlamentable deficiencies of geological and fossil data, but the bolder\nthe hypothetical outlines are drawn, the better, and this is preferable\nto the insertion of bays and similar detail which give such maps a\nfallacious look of certainty where none exists. Moreover it must be\nborne in mind that, when we draw a broad continental belt across an\nocean, this belt need never have existed in its entirety at any one\ntime. The features of dispersal, intended to be explained by it, would\nbe accomplished just as well by an unknown number of islands which have\njoined into larger complexes while elsewhere they subsided again:\nlike pontoon-bridges which may be opened anywhere, or like a series\nof superimposed dissolving views of land and sea-scapes. Hence the\nreconstructed maps of Europe, the only continent tolerably known, show\na considerable number of islands in puzzling changes, while elsewhere,\ne.g. in Asia, we have to be satisfied with sweeping generalisations.\n\nAt present about half-a-dozen big connections are engaging our\nattention, leaving as comparatively settled the extent and the duration\nof such minor \"bridges\" as that between Africa and Madagascar, Tasmania\nand Australia, the Antilles and Central America, Europe and North\nAfrica. (Not a few of those who are fascinated by, and satisfied with,\nthe statistical aspect of distribution still have a strong dislike to\nthe use of \"bridges\" if these lead over deep seas, and they get\nover present discontinuous occurrences by a former \"universal or\nsub-universal distribution\" of their groups.) This is indeed an easy\nmethod of cutting the knot, but in reality they shunt the question only\na stage or two back, never troubling to explain how their groups managed\nto attain to that sub-universal range; or do they still suppose that the\nwhole world was originally one paradise where everything lived side by\nside, until sin and strife and glacial epochs left nothing but scattered\nsurvivors?\n\nThe permanence of the great ocean-basins had become a dogma since it\nwas found that a universal elevation of the land to the extent of 100\nfathoms would produce but little changes, and when it was shown that\neven the 1000 fathom-line followed the great masses of land rather\nclosely, and still leaving the great basins (although transgression\nof the sea to the same extent would change the map of the world beyond\nrecognition), by general consent one mile was allowed as the utmost\nspeculative limit of subsidence. Naturally two or three miles, the\naverage depth of the oceans, seems enormous, and yet such a difference\nin level is as nothing in comparison with the size of the Earth. On\na clay model globe ten feet in diameter an ocean bed three miles deep\nwould scarcely be detected, and the highest mountains would be smaller\nthan the unavoidable grains in the glazed surface of our model. There\nare but few countries which have not be submerged at some time or\nother.\n\nCONNECTION OF SOUTH EASTERN ASIA WITH AUSTRALIA. Neumayr's\nSino-Australian continent during mid-Mesozoic times was probably a\nmuch changing Archipelago, with final separations subsequent to the\nCretaceous period. Henceforth Australasia was left to its own fate, but\nfor a possible connection with the antarctic continent.\n\nAFRICA, MADAGASCAR, INDIA. The \"Lemuria\" of Sclater and Haeckel cannot\nhave been more than a broad bridge in Jurassic times; whether it was\never available for the Lemurs themselves must depend upon the time of\nits duration, the more recent the better, but it is difficult to show\nthat it lasted into the Miocene.\n\nAFRICA AND SOUTH AMERICA. Since the opposite coasts show an entire\nabsence of marine fossils and deposits during the Mesozoic period,\nwhilst further north and south such are known to exist and are mostly\nidentical on either side, Neumayr suggested the existence of a great\nAfro-Son American mass of land during the Jurassic epoch. Such land\nis almost a necessity and is supported by many facts; it would easily\nexplain the distribution of numerous groups of terrestrial creatures.\nMoreover to the north of this hypothetical land, somewhere across\nfrom the Antilles and Guiana to North Africa and South Western Europe,\nexisted an almost identical fauna of Corals and Molluscs, indicating\neither a coast-line or a series of islands interrupted by shallow seas,\njust as one would expect if, and when, a Brazil-Ethiopian mass of land\nwere breaking up. Lastly from Central America to the Mediterranean\nstretches one of the Tertiary tectonic lines of the geologists. Here\nalso the great question is how long this continent lasted. Apparently\nthe South Atlantic began to encroach from the south so that by the\nlater Cretaceous epoch the land was reduced to a comparatively narrow\nBrazil-West Africa, remnants of which persisted certainly into the early\nTertiary, until the South Atlantic joined across the equator with the\nAtlantic portion of the \"Thetys,\" leaving what remained of South America\nisolated from the rest of the world.\n\nANTARCTIC CONNECTIONS. Patagonia and Argentina seem to have joined\nAntartica during the Cretaceous epoch, and this South Georgian bridge\nhad broken down again by mid-Tertiary times when South America became\nconsolidated. The Antarctic continent, presuming that it existed, seems\nalso to have been joined, by way of Tasmania, with Australia,\nalso during the Cretaceous epoch, and it is assumed that the great\nAustralia-Antarctic-Patagonian land was severed first to the south of\nTasmania and then at the South Georgian bridge. No connection, and\nthis is important, is indicated between Antarctica and either Africa or\nMadagascar.\n\nSo far we have followed what may be called the vicissitudes of the great\nPermo-Carboniferous Gondwana land in its fullest imaginary extent,\nan enormous equatorial and south temperate belt from South America to\nAfrica, South India and Australia, which seems to have provided the\nfoundation of the present Southern continents, two of which temporarily\njoined Antarctica, of which however we know nothing except that it\nexists now.\n\nLet us next consider the Arctic and periarctic lands. Unfortunately very\nlittle is known about the region within the arctic circle. If it was all\nland, or more likely great changing archipelagoes, faunistic exchange\nbetween North America, Europe and Siberia would present no difficulties,\nbut there is one connection which engages much attention, namely a land\nwhere now lies the North temperate and Northern part of the Atlantic\nocean. How far south did it ever extend and what is the latest date of\na direct practicable communication, say from North Western Europe\nto Greenland? Connections, perhaps often interrupted, e.g. between\nGreenland and Labrador, at another time between Greenland and\nScandinavia, seem to have existed at least since the Permo-Carboniferous\nepoch. If they existed also in late Cretaceous and in Tertiary times,\nthey would of course easily explain exchanges which we know to have\nrepeatedly taken place between America and Europe, but they are not\nproved thereby, since most of these exchanges can almost as easily\nhave occurred across the polar regions, and others still more easily by\nrepeated junction of Siberia with Alaska.\n\nLet us now describe a hypothetical case based on the supposition of\nconnecting bridges. Not to work in a circle, we select an important\ngroup which has not served as a basis for the reconstruction of bridges;\nand it must be a group which we feel justified in assuming to be old\nenough to have availed itself of ancient land-connections.\n\nThe occurrence of one species of Peripatus in the whole of Australia,\nTasmania and New Zealand (the latter being joined to Australia by way of\nNew Britain in Cretaceous times but not later) puts the genus back\ninto this epoch, no unsatisfactory assumption to the morphologist. The\napparent absence of Peripatus in Madagascar indicates that it did not\ncome from the east into Africa, that it was neither Afro-Indian, nor\nAfro-Australian; nor can it have started in South America. We therefore\nassume as its creative centre Australia or Malaya in the Cretaceous\nepoch, whence its occurrence in Sumatra, Malay Peninsula, New Britain,\nNew Zealand and Australia is easily explained. Then extension across\nAntarctica to Patagonia and Chile, whence it could spread into the rest\nof South America as this became consolidated in early Tertiary times.\nFor getting to the Antilles and into Mexico it would have to wait until\nthe Miocene, but long before that time it could arrive in Africa, there\nsurviving as a Congolese and a Cape species. This story is unsupported\nby a single fossil. Peripatus may have been \"sub-universal\" all over\ngreater Gondwana land in Carboniferous times, and then its absence from\nMadagascar would be difficult to explain, but the migrations suggested\nabove amount to little considering that the distance from Tasmania to\nSouth America could be covered in far less time than that represented by\nthe whole of the Eocene epoch alone.\n\nThere is yet another field, essentially the domain of geographical\ndistribution, the cultivation of which promises fair to throw much light\nupon Nature's way of making species. This is the study of the organisms\nwith regard to their environment. Instead of revealing pedigrees or\nof showing how and when the creatures got to a certain locality, it\ninvestigates how they behaved to meet the ever changing conditions of\ntheir habitats. There is a facies, characteristic of, and often peculiar\nto, the fauna of tropical moist forests, another of deserts, of high\nmountains, of underground life and so forth; these same facies are\nstamped upon whole associations of animals and plants, although these\nmay be--and in widely separated countries generally are--drawn from\ntotally different families of their respective orders. It does not go to\nthe root of the matter to say that these facies have been brought about\nby the extermination of all the others which did not happen to fit into\ntheir particular environment. One might almost say that tropical moist\nforests must have arboreal frogs and that these are made out of whatever\nsuitable material happened to be available; in Australia and South\nAmerica Hylidae, in Africa Ranidae, since there Hylas are absent. The\ndeserts must have lizards capable of standing the glare, the great\nchanges of temperature, of running over or burrowing into the loose\nsand. When as in America Iguanids are available, some of these are thus\nmodified, while in Africa and Asia the Agamids are drawn upon. Both in\nthe Damara and in the Transcaspian deserts, a Gecko has been turned into\na runner upon sand!\n\nWe cannot assume that at various epochs deserts, and at others moist\nforests were continuous all over the world. The different facies and\nassociations were developed at various times and places. Are we to\nsuppose that, wherever tropical forests came into existence, amongst\nthe stock of humivagous lizards were always some which presented those\nnascent variations which made them keep step with the similarly nascent\nforests, the overwhelming rest being eliminated? This principle would\nimply that the same stratum of lizards always had variations ready to\nfit any changed environment, forests and deserts, rocks and swamps.\nThe study of Ecology indicates a different procedure, a great, almost\nboundless plasticity of the organism, not in the sense of an exuberant\nmoulding force, but of a readiness to be moulded, and of this the\n\"variations\" are the visible outcome. In most cases identical facies\nare produced by heterogeneous convergences and these may seem to be but\nsuperficial, affecting only what some authors are pleased to call the\nphysiological characters; but environment presumably affects first those\nparts by which the organism comes into contact with it most directly,\nand if the internal structures remain unchanged, it is not because these\nare less easily modified but because they are not directly affected.\nWhen they are affected, they too change deeply enough.\n\nThat the plasticity should react so quickly--indeed this very quickness\nseems to have initiated our mistaking the variations called forth for\nsomething performed--and to the point, is itself the outcome of the long\ntraining which protoplasm has undergone since its creation.\n\nIn Nature's workshop he does not succeed who has ready an arsenal of\ntools for every conceivable emergency, but he who can make a tool at the\nspur of the moment. The ordeal of the practical test is Charles Darwin's\nglorious conception of Natural Selection.\n\n\n\n\nXVIII. DARWIN AND GEOLOGY. By J.W. Judd, C.B., LL.D., F.R.S.\n\n\n(Mr Francis Darwin has related how his father occasionally came up from\nDown to spend a few days with his brother Erasmus in London, and,\nafter his brother's death, with his daughter, Mrs Litchfield. On these\noccasions, it was his habit to arrange meetings with Huxley, to talk\nover zoological questions, with Hooker, to discuss botanical problems,\nand with Lyell to hold conversations on geology. After the death of\nLyell, Darwin, knowing my close intimacy with his friend during his\nlater years, used to ask me to meet him when he came to town, and \"talk\ngeology.\" The \"talks\" took place sometimes at Jermyn Street Museum, at\nother times in the Royal College of Science, South Kensington; but\nmore frequently, after having lunch with him, at his brother's or his\ndaughter's house. On several occasions, however, I had the pleasure of\nvisiting him at Down. In the postscript of a letter (of April 15, 1880)\narranging one of these visits, he writes: \"Since poor, dear Lyell's\ndeath, I rarely have the pleasure of geological talk with anyone.\")\n\nIn one of the very interesting conversations which I had with Charles\nDarwin during the last seven years of his life, he asked me in a very\npointed manner if I were able to recall the circumstances, accidental or\notherwise, which had led me to devote myself to geological studies. He\ninformed me that he was making similar inquiries of other friends, and I\ngathered from what he said that he contemplated at that time a study\nof the causes producing SCIENTIFIC BIAS in individual minds. I have\nno means of knowing how far this project ever assumed anything like\nconcrete form, but certain it is that Darwin himself often indulged\nin the processes of mental introspection and analysis; and he has\nthus fortunately left us--in his fragments of autobiography and in his\ncorrespondence--the materials from which may be reconstructed a fairly\ncomplete history of his own mental development.\n\nThere are two perfectly distinct inquiries which we have to undertake\nin connection with the development of Darwin's ideas on the subject of\nevolution:\n\nFIRST. How, when, and under what conditions was Darwin led to a\nconviction that species were not immutable, but were derived from\npre-existing forms?\n\nSECONDLY. By what lines of reasoning and research was he brought to\nregard \"natural selection\" as a vera causa in the process of evolution?\n\nIt is the first of these inquiries which specially interests the\ngeologist; though geology undoubtedly played a part--and by no means an\ninsignificant part--in respect to the second inquiry.\n\nWhen, indeed, the history comes to be written of that great revolution\nof thought in the nineteenth century, by which the doctrine of\nevolution, from being the dream of poets and visionaries, gradually grew\nto be the accepted creed of naturalists, the paramount influence exerted\nby the infant science of geology--and especially that resulting from\nthe publication of Lyell's epoch-making work, the \"Principles of\nGeology\"--cannot fail to be regarded as one of the leading factors.\nHerbert Spencer in his \"Autobiography\" bears testimony to the effect\nproduced on his mind by the recently published \"Principles\", when, at\nthe age of twenty, he had already begun to speculate on the subject\nof evolution (Herbert Spencer's \"Autobiography\", London, 1904, Vol. I.\npages 175-177.); and Alfred Russel Wallace is scarcely less emphatic\nconcerning the part played by Lyell's teaching in his scientific\neducation. (See \"My Life; a record of Events and Opinions\", London,\n1905, Vol. I. page 355, etc. Also his review of Lyell's \"Principles\"\nin \"Quarterly Review\" (Vol. 126), 1869, pages 359-394. See also \"The\nDarwin-Wallace Celebration by the Linnean Society\" (1909), page 118.)\nHuxley wrote in 1887 \"I owe more than I can tell to the careful study\nof the \"Principles of Geology\" in my young days.\" (\"Science and Pseudo\nScience\"; \"Collected Essays\", London, 1902, Vol. V. page 101.) As for\nCharles Darwin, he never tired--either in his published writings, his\nprivate correspondence or his most intimate conversations--of ascribing\nthe awakening of his enthusiasm and the direction of his energies\ntowards the elucidation of the problem of development to the \"Principles\nof Geology\" and the personal influence of its author. Huxley has well\nexpressed what the author of the \"Origin of Species\" so constantly\ninsisted upon, in the statements \"Darwin's greatest work is the outcome\nof the unflinching application to Biology of the leading idea and the\nmethod applied in the \"Principles\" to Geology (\"Proc. Roy. Soc.\" Vol.\nXLIV. (1888), page viii.; \"Collected Essays\" II. page 268, 1902.), and\n\"Lyell, for others, as for myself, was the chief agent in smoothing the\nroad for Darwin.\" (\"Life and Letters of Charles Darwin\" II. page 190.)\n\nWe propose therefore to consider, first, what Darwin owed to geology and\nits cultivators, and in the second place how he was able in the end so\nfully to pay a great debt which he never failed to acknowledge. Thanks\nto the invaluable materials contained in the \"Life and Letters of\nCharles Darwin\" (3 vols.) published by Mr Francis Darwin in 1887; and to\n\"More Letters of Charles Darwin\" (2 vols.) issued by the same author,\nin conjunction with Professor A.C. Seward, in 1903, we are permitted to\nfollow the various movements in Darwin's mind, and are able to record\nthe story almost entirely in his own words. (The first of these works\nis indicated in the following pages by the letters \"L.L.\"; the second by\n\"M.L.\")\n\nFrom the point of view of the geologist, Darwin's life naturally divides\nitself into four periods. In the first, covering twenty-two years,\nvarious influences were at work militating, now for and now against,\nhis adoption of a geological career; in the second period--the five\nmemorable years of the voyage of the \"Beagle\"--the ardent sportsman with\nsome natural-history tastes, gradually became the most enthusiastic and\nenlightened of geologists; in the third period, lasting ten years, the\nvaluable geological recruit devoted nearly all his energies and time\nto geological study and discussion and to preparing for publication the\nnumerous observations made by him during the voyage; the fourth period,\nwhich covers the latter half of his life, found Darwin gradually drawn\nmore and more from geological to biological studies, though always\nretaining the deepest interest in the progress and fortunes of his \"old\nlove.\" But geologists gladly recognise the fact that Darwin immeasurably\nbetter served their science by this biological work, than he could\npossibly have done by confining himself to purely geological questions.\n\nFrom his earliest childhood, Darwin was a collector, though up to the\ntime when, at eight years of age, he went to a preparatory school,\nseals, franks and similar trifles appear to have been the only objects\nof his quest. But a stone, which one of his schoolfellows at that time\ngave to him, seems to have attracted his attention and set him seeking\nfor pebbles and minerals; as the result of this newly acquired taste, he\nsays (writing in 1838) \"I distinctly recollect the desire I had of being\nable to know something about every pebble in front of the hall door--it\nwas my earliest and only geological aspiration at that time.\" (\"M.L.\"\nI. page 3.) He further suspects that while at Mr Case's school \"I do\nnot remember any mental pursuits except those of collecting stones,\"\netc... \"I was born a naturalist.\" (\"M.L.\" I. page 4.)\n\nThe court-yard in front of the hall door at the Mount House, Darwin's\nbirthplace and the home of his childhood, is surrounded by beds or\nrockeries on which lie a number of pebbles. Some of these pebbles (in\nquite recent times as I am informed) have been collected to form a\n\"cobbled\" space in front of the gate in the outer wall, which fronts the\nhall door; and a similar \"cobbled area,\" there is reason to believe, may\nhave existed in Darwin's childhood before the door itself. The pebbles,\nwhich were obtained from a neighbouring gravel-pit, being derived from\nthe glacial drift, exhibit very striking differences in colour and form.\nIt was probably this circumstance which awakened in the child his\nlove of observation and speculation. It is certainly remarkable that\n\"aspirations\" of the kind should have arisen in the mind of a child of 9\nor 10!\n\nWhen he went to Shrewsbury School, he relates \"I continued collecting\nminerals with much zeal, but quite unscientifically,--all that I cared\nabout was a new-NAMED mineral, and I hardly attempted to classify them.\"\n(\"L.L.\" I. page 34.)\n\nThere has stood from very early times in Darwin's native town of\nShrewsbury, a very notable boulder which has probably marked a boundary\nand is known as the \"Bell-stone\"--giving its name to a house and street.\nDarwin tells us in his \"Autobiography\" that while he was at Shrewsbury\nSchool at the age of 13 or 14 \"an old Mr Cotton in Shropshire, who knew\na good deal about rocks\" pointed out to me \"... the 'bell-stone'; he told\nme that there was no rock of the same kind nearer than Cumberland or\nScotland, and he solemnly assured me that the world would come to an end\nbefore anyone would be able to explain how this stone came where it\nnow lay\"! Darwin adds \"This produced a deep impression on me, and I\nmeditated over this wonderful stone.\" (\"L.L.\" I. page 41.)\n\nThe \"bell-stone\" has now, owing to the necessities of building, been\nremoved a short distance from its original site, and is carefully\npreserved within the walls of a bank. It is a block of irregular shape 3\nfeet long and 2 feet wide, and about 1 foot thick, weighing probably not\nless than one-third of a ton. By the courtesy of the directors of the\nNational Provincial Bank of England, I have been able to make a minute\nexamination of it, and Professors Bonney and Watts, with Mr Harker and\nMr Fearnsides have given me their valuable assistance. The rock is a\nmuch altered andesite and was probably derived from the Arenig district\nin North Wales, or possibly from a point nearer the Welsh Border. (I\nam greatly indebted to the Managers of the Bank at Shrewsbury for kind\nassistance in the examination of this interesting memorial: and Mr\nH.T. Beddoes, the Curator of the Shrewsbury Museum, has given me some\narchaeological information concerning the stone. Mr Richard Cotton was\na good local naturalist, a Fellow both of the Geological and Linnean\nSocieties; and to the officers of these societies I am indebted for\ninformation concerning him. He died in 1839, and although he does not\nappear to have published any scientific papers, he did far more for\nscience by influencing the career of the school boy!) It was of course\nbrought to where Shrewsbury now stands by the agency of a glacier--as\nDarwin afterwards learnt.\n\nWe can well believe from the perusal of these reminiscences that,\nat this time, Darwin's mind was, as he himself says, \"prepared for a\nphilosophical treatment of the subject\" of Geology. (\"L.L.\" I. page 41.)\nWhen at the age of 16, however, he was entered as a medical student at\nEdinburgh University, he not only did not get any encouragement of\nhis scientific tastes, but was positively repelled by the ordinary\ninstruction given there. Dr Hope's lectures on Chemistry, it is true,\ninterested the boy, who with his brother Erasmus had made a laboratory\nin the toolhouse, and was nicknamed \"Gas\" by his schoolfellows, while\nundergoing solemn and public reprimand from Dr Butler at Shrewsbury\nSchool for thus wasting his time. (\"L.L.\" I. page 35.) But most of\nthe other Edinburgh lectures were \"intolerably dull,\" \"as dull as the\nprofessors\" themselves, \"something fearful to remember.\" In after life\nthe memory of these lectures was like a nightmare to him. He speaks in\n1840 of Jameson's lectures as something \"I... for my sins experienced!\"\n(\"L.L.\" I. page 340.) Darwin especially signalises these lectures on\nGeology and Zoology, which he attended in his second year, as being\nworst of all \"incredibly dull. The sole effect they produced on me was\nthe determination never so long as I lived to read a book on Geology, or\nin any way to study the science!\" (\"L.L.\" I. page 41.)\n\nThe misfortune was that Edinburgh at that time had become the cockpit in\nwhich the barren conflict between \"Neptunism\" and \"Plutonism\" was being\nwaged with blind fury and theological bitterness. Jameson and his\npupils, on the one hand, and the friends and disciples of Hutton, on the\nother, went to the wildest extremes in opposing each other's peculiar\ntenets. Darwin tells us that he actually heard Jameson \"in a field\nlecture at Salisbury Craigs, discoursing on a trap-dyke, with\namygdaloidal margins and the strata indurated on each side, with\nvolcanic rocks all around us, say that it was a fissure filled with\nsediment from above, adding with a sneer that there were men who\nmaintained that it had been injected from beneath in a molten\ncondition.\" (\"L.L.\" I. pages 41-42.) \"When I think of this lecture,\"\nadded Darwin, \"I do not wonder that I determined never to attend to\nGeology.\" (This was written in 1876 and Darwin had in the summer of 1839\nrevisited and carefully studied the locality (\"L.L.\" I. page 290.) It is\nprobable that most of Jameson's teaching was of the same controversial\nand unilluminating character as this field-lecture at Salisbury Craigs.\n\nThere can be no doubt that, while at Edinburgh, Darwin must have become\nacquainted with the doctrines of the Huttonian School. Though so young,\nhe mixed freely with the scientific society of the city, Macgillivray,\nGrant, Leonard Horner, Coldstream, Ainsworth and others being among\nhis acquaintances, while he attended and even read papers at the local\nscientific societies. It is to be feared, however, that what Darwin\nwould hear most of, as characteristic of the Huttonian teaching, would\nbe assertions that chalk-flints were intrusions of molten silica, that\nfossil wood and other petrifactions had been impregnated with fused\nmaterials, that heat--but never water--was always the agent by which\nthe induration and crystallisation of rock-materials (even siliceous\nconglomerate, limestone and rock-salt) had been effected! These\nextravagant \"anti-Wernerian\" views the young student might well regard\nas not one whit less absurd and repellant than the doctrine of the\n\"aqueous precipitation\" of basalt. There is no evidence that Darwin,\neven if he ever heard of them, was in any way impressed, in his early\ncareer, by the suggestive passages in Hutton and Playfair, to which\nLyell afterwards called attention, and which foreshadowed the main\nprinciples of Uniformitarianism.\n\nAs a matter of fact, I believe that the influence of Hutton and Playfair\nin the development of a philosophical theory of geology has been very\ngreatly exaggerated by later writers on the subject. Just as Wells\nand Matthew anticipated the views of Darwin on Natural Selection,\nbut without producing any real influence on the course of biological\nthought, so Hutton and Playfair adumbrated doctrines which only became\nthe basis of vivifying theory in the hands of Lyell. Alfred Russel\nWallace has very justly remarked that when Lyell wrote the \"Principles\nof Geology\", \"the doctrines of Hutton and Playfair, so much in advance\nof their age, seemed to be utterly forgotten.\" (\"Quarterly Review\", Vol.\nCXXVI. (1869), page 363.) In proof of this it is only necessary to\npoint to the works of the great masters of English geology, who preceded\nLyell, in which the works of Hutton and his followers are scarcely ever\nmentioned. This is true even of the \"Researches in Theoretical Geology\"\nand the other works of the sagacious De la Beche. (Of the strength\nand persistence of the prejudice felt against Lyell's views by his\ncontemporaries, I had a striking illustration some little time after\nLyell's death. One of the old geologists who in the early years of the\ncentury had done really good work in connection with the Geological\nSociety expressed a hope that I was not \"one of those who had been\ncarried away by poor Lyell's fads.\" My surprise was indeed great when\nfurther conversation showed me that the whole of the \"Principles\" were\nincluded in the \"fads\"!) Darwin himself possessed a copy of Playfair's\n\"Illustrations of the Huttonian Theory\", and occasionally quotes it;\nbut I have met with only one reference to Hutton, and that a somewhat\nenigmatical one, in all Darwin's writings. In a letter to Lyell in 1841,\nwhen his mind was much exercised concerning glacial questions, he says\n\"What a grand new feature all this ice work is in Geology! How old\nHutton would have stared!\" (\"M.L.\" II. page 149.)\n\nAs a consequence of the influences brought to bear on his mind during\nhis two years' residence in Edinburgh, Darwin, who had entered that\nUniversity with strong geological aspirations, left it and proceeded to\nCambridge with a pronounced distaste for the whole subject. The result\nof this was that, during his career as an under-graduate, he neglected\nall the opportunities for geological study. During that important period\nof life, when he was between eighteen and twenty years of age, Darwin\nspent his time in riding, shooting and beetle-hunting, pursuits which\nwere undoubtedly an admirable preparation for his future work as an\nexplorer; but in none of his letters of this period does he even mention\ngeology. He says, however, \"I was so sickened with lectures at\nEdinburgh that I did not even attend Sedgwick's eloquent and interesting\nlectures.\" (\"L.L.\" I. page 48.)\n\nIt was only after passing his examination, and when he went up to spend\ntwo extra terms at Cambridge, that geology again began to attract his\nattention. The reading of Sir John Herschel's \"Introduction to the Study\nof Natural Philosophy\", and of Humboldt's \"Personal Narrative\", a\ncopy of which last had been given to him by his good friend and mentor\nHenslow, roused his dormant enthusiasm for science, and awakened in his\nmind a passionate desire for travel. And it was from Henslow, whom\nhe had accompanied in his excursions, but without imbibing any marked\ntaste, at that time, for botany, that the advice came to think of and to\n\"begin the study of geology.\" (\"L.L.\" I. page 56.) This was in 1831, and\nin the summer vacation of that year we find him back again at Shrewsbury\n\"working like a tiger\" at geology and endeavouring to make a map\nand section of Shropshire--work which he says was not \"as easy as I\nexpected.\" (\"L.L.\" I. page 189.) No better field for geological studies\ncould possibly be found than Darwin's native county.\n\nWriting to Henslow at this time, and referring to a form of the\ninstrument devised by his friend, Darwin says: \"I am very glad to say I\nthink the clinometer will answer admirably. I put all the tables in my\nbedroom at every conceivable angle and direction. I will venture to say\nthat I have measured them as accurately as any geologist going could\ndo.\" But he adds: \"I have been working at so many things that I have\nnot got on much with geology. I suspect the first expedition I take,\nclinometer and hammer in hand, will send me back very little wiser and\na good deal more puzzled than when I started.\" (\"L.L.\" I. page 189.)\nValuable aid was, however, at hand, for at this time Sedgwick, to whom\nDarwin had been introduced by the ever-helpful Henslow, was making one\nof his expeditions into Wales, and consented to accept the young student\nas his companion during the geological tour. (\"L.L.\" I. page 56.) We\nfind Darwin looking forward to this privilege with the keenest interest.\n(\"L.L.\" I. page 189.)\n\nWhen at the beginning of August (1831), Sedgwick arrived at his father's\nhouse in Shrewsbury, where he spent a night, Darwin began to receive his\nfirst and only instruction as a field-geologist. The journey they took\ntogether led them through Llangollen, Conway, Bangor, and Capel Curig,\nat which latter place they parted after spending many hours in examining\nthe rocks at Cwm Idwal with extreme care, seeking for fossils but\nwithout success. Sedgwick's mode of instruction was admirable--he from\ntime to time sent the pupil off on a line parallel to his own, \"telling\nme to bring back specimens of the rocks and to mark the stratification\non a map.\" (\"L.L.\" I. page 57.) On his return to Shrewsbury, Darwin\nwrote to Henslow, \"My trip with Sedgwick answered most perfectly,\"\n(\"L.L.\" I. page 195.), and in the following year he wrote again from\nSouth America to the same friend, \"Tell Professor Sedgwick he does not\nknow how much I am indebted to him for the Welsh expedition; it has\ngiven me an interest in Geology which I would not give up for any\nconsideration. I do not think I ever spent a more delightful three weeks\nthan pounding the north-west mountains.\" (\"L.L.\" I. pages 237-8.)\n\nIt would be a mistake, however, to suppose that at this time Darwin\nhad acquired anything like the affection for geological study, which\nhe afterwards developed. After parting with Sedgwick, he walked in a\nstraight line by compass and map across the mountains to Barmouth to\nvisit a reading party there, but taking care to return to Shropshire\nbefore September 1st, in order to be ready for the shooting. For as\nhe candidly tells us, \"I should have thought myself mad to give up the\nfirst days of partridge-shooting for geology or any other science!\"\n(\"L.L.\" I. page 58.)\n\nAny regret we may be disposed to feel that Darwin did not use his\nopportunities at Edinburgh and Cambridge to obtain systematic and\npractical instruction in mineralogy and geology, will be mitigated,\nhowever, when we reflect on the danger which he would run of being\nindoctrinated with the crude \"catastrophic\" views of geology, which were\nat that time prevalent in all the centres of learning.\n\nWriting to Henslow in the summer of 1831, Darwin says \"As yet I have\nonly indulged in hypotheses, but they are such powerful ones that I\nsuppose, if they were put into action but for one day, the world would\ncome to an end.\" (\"L.L.\" I. page 189.)\n\nMay we not read in this passage an indication that the self-taught\ngeologist had, even at this early stage, begun to feel a distrust for\nthe prevalent catastrophism, and that his mind was becoming a field in\nwhich the seeds which Lyell was afterwards to sow would \"fall on good\nground\"?\n\nThe second period of Darwin's geological career--the five years spent\nby him on board the \"Beagle\"--was the one in which by far the most\nimportant stage in his mental development was accomplished. He left\nEngland a healthy, vigorous and enthusiastic collector; he returned five\nyears later with unique experiences, the germs of great ideas, and\na knowledge which placed him at once in the foremost ranks of the\ngeologists of that day. Huxley has well said that \"Darwin found on board\nthe \"Beagle\" that which neither the pedagogues of Shrewsbury, nor the\nprofessoriate of Edinburgh, nor the tutors of Cambridge had managed\nto give him.\" (\"Proc. Roy. Soc.\" Vol. XLIV. (1888), page IX.) Darwin\nhimself wrote, referring to the date at which the voyage was expected to\nbegin: \"My second life will then commence, and it shall be as a birthday\nfor the rest of my life.\" (\"L.L.\" I. page 214.); and looking back on the\nvoyage after forty years, he wrote; \"The voyage of the 'Beagle' has been\nby far the most important event in my life, and has determined my whole\ncareer;... I have always felt that I owe to the voyage the first real\ntraining or education of my mind; I was led to attend closely to several\nbranches of natural history, and thus my powers of observation were\nimproved, though they were always fairly developed.\" (\"L.L.\" I. page\n61.)\n\nReferring to these general studies in natural history, however, Darwin\nadds a very significant remark: \"The investigation of the geology of\nthe places visited was far more important, as reasoning here comes into\nplay. On first examining a new district nothing can appear more hopeless\nthan the chaos of rocks; but by recording the stratification and nature\nof the rocks and fossils at many points, always reasoning and predicting\nwhat will be found elsewhere, light soon begins to dawn on the district,\nand the structure of the whole becomes more or less intelligible.\"\n(\"L.L.\" I. page 62.)\n\nThe famous voyage began amid doubts, discouragements and\ndisappointments. Fearful of heart-disease, sad at parting from home\nand friends, depressed by sea-sickness, the young explorer, after being\ntwice driven back by baffling winds, reached the great object of\nhis ambition, the island of Teneriffe, only to find that, owing to\nquarantine regulations, landing was out of the question.\n\nBut soon this inauspicious opening of the voyage was forgotten. Henslow\nhad advised his pupil to take with him the first volume of Lyell's\n\"Principles of Geology\", then just published--but cautioned him (as\nnearly all the leaders in geological science at that day would certainly\nhave done) \"on no account to accept the views therein advocated.\"\n(\"L.L.\" I. page 73.) It is probable that the days of waiting, discomfort\nand sea-sickness at the beginning of the voyage were relieved by the\nreading of this volume. For he says that when he landed, three weeks\nafter setting sail from Plymouth, in St Jago, the largest of the Cape de\nVerde Islands, the volume had already been \"studied attentively; and\nthe book was of the highest service to me in many ways... \" His first\noriginal geological work, he declares, \"showed me clearly the wonderful\nsuperiority of Lyell's manner of treating geology, compared with that\nof any other author, whose works I had with me or ever afterwards read.\"\n(\"L.L.\" I. page 62.)\n\nAt St Jago Darwin first experienced the joy of making new discoveries,\nand his delight was unbounded. Writing to his father he says,\n\"Geologising in a volcanic country is most delightful; besides the\ninterest attached to itself, it leads you into most beautiful and\nretired spots.\" (\"L.L.\" I. page 228.) To Henslow he wrote of St Jago:\n\"Here we spent three most delightful weeks... St Jago is singularly\nbarren, and produces few plants or insects, so that my hammer was my\nusual companion, and in its company most delightful hours I spent.\" \"The\ngeology was pre-eminently interesting, and I believe quite new; there\nare some facts on a large scale of upraised coast (which is an excellent\nepoch for all the volcanic rocks to date from), that would interest Mr\nLyell.\" (\"L.L.\" I. page 235.) After more than forty years the memory of\nthis, his first geological work, seems as fresh as ever, and he wrote in\n1876, \"The geology of St Jago is very striking, yet simple: a stream\nof lava formerly flowed over the bed of the sea, formed of triturated\nrecent shells and corals, which it has baked into a hard white rock.\nSince then the whole island has been upheaved. But the line of white\nrock revealed to me a new and important fact, namely, that there had\nbeen afterwards subsidence round the craters, which had since been in\naction, and had poured forth lava.\" (\"L.L.\" I. page 65.)\n\nIt was at this time, probably, that Darwin made his first attempt at\ndrawing a sketch-map and section to illustrate the observations he had\nmade (see his \"Volcanic Islands\", pages 1 and 9). His first important\ngeological discovery, that of the subsidence of strata around volcanic\nvents (which has since been confirmed by Mr Heaphy in New Zealand and\nother authors) awakened an intense enthusiasm, and he writes: \"It then\nfirst dawned on me that I might perhaps write a book on the geology of\nthe various countries visited, and this made me thrill with delight.\nThat was a memorable hour to me, and how distinctly I can call to mind\nthe low cliff of lava beneath which I rested, with the sun glaring hot,\na few strange desert plants growing near, and with living corals in the\ntidal pools at my feet.\" (\"L.L.\" I. page 66.)\n\nBut it was when the \"Beagle\", after touching at St Paul's rock and\nTristan d'Acunha (for a sufficient time only to collect specimens),\nreached the shores of South America, that Darwin's real work began; and\nhe was able, while the marine surveys were in progress, to make many\nextensive journeys on land. His letters at this time show that geology\nhad become his chief delight, and such exclamations as \"Geology carries\nthe day,\" \"I find in Geology a never failing interest,\" etc. abound in\nhis correspondence.\n\nDarwin's time was divided between the study of the great deposits of red\nmud--the Pampean formation--with its interesting fossil bones and shells\naffording proofs of slow and constant movements of the land, and the\nunderlying masses of metamorphic and plutonic rocks. Writing to Henslow\nin March, 1834, he says: \"I am quite charmed with Geology, but, like\nthe wise animal between two bundles of hay, I do not know which to\nlike best; the old crystalline groups of rocks, or the softer and\nfossiliferous beds. When puzzling about stratification, etc., I\nfeel inclined to cry 'a fig for your big oysters, and your bigger\nmegatheriums.' But then when digging out some fine bones, I wonder how\nany man can tire his arms with hammering granite.\" (\"L.L.\" I. page\n249.) We are told by Darwin that he loved to reason about and attempt to\npredict the nature of the rocks in each new district before he arrived\nat it.\n\nThis love of guessing as to the geology of a district he was about to\nvisit is amusingly expressed by him in a letter (of May, 1832) to his\ncousin and old college-friend, Fox. After alluding to the beetles he\nhad been collecting--a taste his friend had in common with himself--he\nwrites of geology that \"It is like the pleasure of gambling. Speculating\non first arriving, what the rocks may be, I often mentally cry out 3 to\n1 tertiary against primitive; but the latter have hitherto won all the\nbets.\" (\"L.L.\" I. page 233.)\n\nNot the least important of the educational results of the voyage to\nDarwin was the acquirement by him of those habits of industry and method\nwhich enabled him in after life to accomplish so much--in spite of\nconstant failures of health. From the outset, he daily undertook\nand resolutely accomplished, in spite of sea-sickness and other\ndistractions, four important tasks. In the first place he regularly\nwrote up the pages of his Journal, in which, paying great attention to\nliterary style and composition, he recorded only matters that would be\nof general interest, such as remarks on scenery and vegetation, on the\npeculiarities and habits of animals, and on the characters, avocations\nand political institutions of the various races of men with whom he was\nbrought in contact. It was the freshness of these observations that gave\nhis \"Narrative\" so much charm. Only in those cases in which his ideas\nhad become fully crystallised, did he attempt to deal with scientific\nmatters in this journal. His second task was to write in voluminous\nnote-books facts concerning animals and plants, collected on sea or\nland, which could not be well made out from specimens preserved in\nspirit; but he tells us that, owing to want of skill in dissecting and\ndrawing, much of the time spent in this work was entirely thrown away,\n\"a great pile of MS. which I made during the voyage has proved almost\nuseless.\" (\"L.L.\" I. page 62.) Huxley confirmed this judgment on his\nbiological work, declaring that \"all his zeal and industry resulted, for\nthe most part, in a vast accumulation of useless manuscript.\" (\"Proc.\nRoy. Soc.\" Vol. XLIV. (1888), page IX.) Darwin's third task was of a\nvery different character and of infinitely greater value. It consisted\nin writing notes of his journeys on land--the notes being devoted to\nthe geology of the districts visited by him. These formed the basis, not\nonly of a number of geological papers published on his return, but also\nof the three important volumes forming \"The Geology of the voyage of the\n'Beagle'\". On July 24th, 1834, when little more than half of the voyage\nhad been completed, Darwin wrote to Henslow, \"My notes are becoming\nbulky. I have about 600 small quarto pages full; about half of this is\nGeology.\" (\"M.L.\" I. page 14.) The last, and certainly not the least\nimportant of all his duties, consisted in numbering, cataloguing, and\npacking his specimens for despatch to Henslow, who had undertaken the\ncare of them. In his letters he often expresses the greatest solicitude\nlest the value of these specimens should be impaired by the removal of\nthe numbers corresponding to his manuscript lists. Science owes much\nto Henslow's patient care of the collections sent to him by Darwin. The\nlatter wrote in Henslow's biography, \"During the five years' voyage,\nhe regularly corresponded with me and guided my efforts; he received,\nopened, and took care of all the specimens sent home in many large\nboxes.\" (\"Life of Henslow\", by L. Jenyns (Blomefield), London, 1862,\npage 53.)\n\nDarwin's geological specimens are now very appropriately lodged for the\nmost part in the Sedgwick Museum, Cambridge, his original Catalogue with\nsubsequent annotations being preserved with them. From an examination of\nthese catalogues and specimens we are able to form a fair notion of\nthe work done by Darwin in his little cabin in the \"Beagle\", in the\nintervals between his land journeys.\n\nBesides writing up his notes, it is evident that he was able to\naccomplish a considerable amount of study of his specimens, before they\nwere packed up for despatch to Henslow. Besides hand-magnifiers and\na microscope, Darwin had an equipment for blowpipe-analysis, a\ncontact-goniometer and magnet; and these were in constant use by him.\nHis small library of reference (now included in the Collection of books\nplaced by Mr F. Darwin in the Botany School at Cambridge (\"Catalogue\nof the Library of Charles Darwin now in the Botany School, Cambridge\".\nCompiled by H.W. Rutherford; with an introduction by Francis Darwin.\nCambridge, 1908.)) appears to have been admirably selected, and in all\nprobability contained (in addition to a good many works relating to\nSouth America) a fair number of excellent books of reference. Among\nthose relating to mineralogy, he possessed the manuals of Phillips,\nAlexander Brongniart, Beudant, von Kobell and Jameson: all the\n\"Cristallographie\" of Brochant de Villers and, for blowpipe work, Dr\nChildren's translation of the book of Berzelius on the subject. In\naddition to these, he had Henry's \"Experimental Chemistry\" and Ure's\n\"Dictionary\" (of Chemistry). A work, he evidently often employed, was P.\nSyme's book on \"Werner's Nomenclature of Colours\"; while, for Petrology,\nhe used Macculloch's \"Geological Classification of Rocks\". How\ndiligently and well he employed his instruments and books is shown by\nthe valuable observations recorded in the annotated Catalogues drawn up\non board ship.\n\nThese catalogues have on the right-hand pages numbers and descriptions\nof the specimens, and on the opposite pages notes on the specimens--the\nresult of experiments made at the time and written in a very small hand.\nOf the subsequently made pencil notes, I shall have to speak later.\n(I am greatly indebted to my friend Mr A. Harker, F.R.S., for his\nassistance in examining these specimens and catalogues. He has also\narranged the specimens in the Sedgwick Museum, so as to make reference\nto them easy. The specimens from Ascension and a few others are however\nin the Museum at Jermyn Street.)\n\nIt is a question of great interest to determine the period and the\noccasion of Darwin's first awakening to the great problem of the\ntransmutation of species. He tells us himself that his grandfather's\n\"Zoonomia\" had been read by him \"but without producing any effect,\" and\nthat his friend Grant's rhapsodies on Lamarck and his views on evolution\nonly gave rise to \"astonishment.\" (\"L.L.\" I. page 38.)\n\nHuxley, who had probably never seen the privately printed volume of\nletters to Henslow, expressed the opinion that Darwin could not have\nperceived the important bearing of his discovery of bones in the Pampean\nFormation, until they had been studied in England, and their analogies\npronounced upon by competent comparative anatomists. And this seemed to\nbe confirmed by Darwin's own entry in his pocket-book for 1837, \"In\nJuly opened first notebook on Transmutation of Species. Had been greatly\nstruck from about the month of previous March on character of South\nAmerican fossils... \" (\"L.L.\" I. page 276.)\n\nThe second volume of Lyell's \"Principles of Geology\" was published in\nJanuary, 1832, and Darwin's copy (like that of the other two volumes,\nin a sadly dilapidated condition from constant use) has in it the\ninscription, \"Charles Darwin, Monte Video. Nov. 1832.\" As everyone\nknows, Darwin in dedicating the second edition of his Journal of the\nVoyage to Lyell declared, \"the chief part of whatever scientific merit\nthis journal and the other works of the author may possess, has been\nderived from studying the well-known and admirable 'Principles of\nGeology'\".\n\nIn the first chapter of this second volume of the \"Principles\", Lyell\ninsists on the importance of the species question to the geologist,\nbut goes on to point out the difficulty of accepting the only\nserious attempt at a transmutation theory which had up to that time\nappeared--that of Lamarck. In subsequent chapters he discusses the\nquestions of the modification and variability of species, of hybridity,\nand of the geographical distribution of plants and animals. He then\ngives vivid pictures of the struggle for existence, ever going\non between various species, and of the causes which lead to their\nextinction--not by overwhelming catastrophes, but by the silent and\nalmost unobserved action of natural causes. This leads him to consider\ntheories with regard to the introduction of new species, and, rejecting\nthe fanciful notions of \"centres or foci of creation,\" he argues\nstrongly in favour of the view, as most reconcileable with observed\nfacts, that \"each species may have had its origin in a single pair, or\nindividual, where an individual was sufficient, and species may have\nbeen created in succession at such times and in such places as to enable\nthem to multiply and endure for an appointed period, and occupy an\nappointed space on the globe.\" (\"Principles of Geology\", Vol. II. (1st\nedition 1832), page 124. We now know, as has been so well pointed out\nby Huxley, that Lyell, as early as 1827, was prepared to accept the\ndoctrine of the transmutation of species. In that year he wrote to\nMantell, \"What changes species may really undergo! How impossible will\nit be to distinguish and lay down a line, beyond which some of the\nso-called extinct species may have never passed into recent ones\"\n(Lyell's \"Life and Letters\" Vol. I. page 168). To Sir John Herschel in\n1836, he wrote, \"In regard to the origination of new species, I am\nvery glad to find that you think it probable that it may be carried on\nthrough the intervention of intermediate causes. I left this rather to\nbe inferred, not thinking it worth while to offend a certain class of\npersons by embodying in words what would only be a speculation\" (Ibid.\npage 467). He expressed the same views to Whewell in 1837 (Ibid. Vol.\nII. page 5.), and to Sedgwick (Ibid. Vol. II. page 36) to whom he says,\nof \"the theory, that the creation of new species is going on at the\npresent day\"--\"I really entertain it,\" but \"I have studiously avoided\nlaying the doctrine down dogmatically as capable of proof\" (see Huxley\nin \"L.L.\" II. pages 190-195.))\n\nAfter pointing out how impossible it would be for a naturalist to prove\nthat a newly DISCOVERED species was really newly CREATED (Mr F. Darwin\nhas pointed out that his father (like Lyell) often used the term\n\"Creation\" in speaking of the origin of new species (\"L.L.\" II. chapter\n1.)), Lyell argued that no satisfactory evidence OF THE WAY in which\nthese new forms were created, had as yet been discovered, but that he\nentertained the hope of a possible solution of the problem being found\nin the study of the geological record.\n\nIt is not difficult, in reading these chapters of Lyell's great work,\nto realise what an effect they would have on the mind of Darwin, as\nnew facts were collected and fresh observations concerning extinct and\nrecent forms were made in his travels. We are not surprised to find him\nwriting home, \"I am become a zealous disciple of Mr Lyell's views, as\nknown in his admirable book. Geologising in South America, I am tempted\nto carry parts to a greater extent even than he does.\" (\"L.L.\" I. page\n263.)\n\nLyell's anticipation that the study of the geological record might\nafford a clue to the discovery of how new species originate was\nremarkably fulfilled, within a few months, by Darwin's discovery of\nfossil bones in the red Pampean mud.\n\nIt is very true that, as Huxley remarked, Darwin's knowledge of\ncomparative anatomy must have been, at that time, slight; but that he\nrecognised the remarkable resemblances between the extinct and existing\nmammals of South America is proved beyond all question by a passage in\nhis letter to Henslow, written November 24th, 1832: \"I have been very\nlucky with fossil bones; I have fragments of at least six\ndistinct animals... I found a large surface of osseous polygonal\nplates... Immediately I saw them I thought they must belong to an\nenormous armadillo, living species of which genus are so abundant here,\"\nand he goes on to say that he has \"the lower jaw of some large animal\nwhich, from the molar teeth, I should think belonged to the Edentata.\"\n(\"M.L.\" I. pages 11, 12. See \"Extracts of Letters addressed to Prof.\nHenslow by C. Darwin\" (1835), page 7.)\n\nHaving found this important clue, Darwin followed it up with\ncharacteristic perseverance. In his quest for more fossil bones he was\nindefatigable. Mr Francis Darwin tells us, \"I have often heard him speak\nof the despair with which he had to break off the projecting extremity\nof a huge, partly excavated bone, when the boat waiting for him would\nwait no longer.\" (\"L.L.\" I. page 276 (footnote).) Writing to Haeckel in\n1864, Darwin says: \"I shall never forget my astonishment when I dug\nout a gigantic piece of armour, like that of the living armadillo.\"\n(Haeckel, \"History of Creation\", Vol. I. page 134, London, 1876.)\n\nIn a letter to Henslow in 1834 Darwin says: \"I have just got scent\nof some fossil bones... what they may be I do not know, but if gold or\ngalloping will get them they shall be mine.\" (\"M.L.\" I. page 15.)\n\nDarwin also showed his sense of the importance of the discovery of these\nbones by his solicitude about their safe arrival and custody. From the\nFalkland Isles (March, 1834), he writes to Henslow: \"I have been alarmed\nby your expression 'cleaning all the bones' as I am afraid the printed\nnumbers will be lost: the reason I am so anxious they should not be, is,\nthat a part were found in a gravel with recent shells, but others in a\nvery different bed. Now with these latter there were bones of an Agouti,\na genus of animals, I believe, peculiar to America, and it would\nbe curious to prove that some one of the genus co-existed with the\nMegatherium: such and many other points depend on the numbers being\ncarefully preserved.\" (\"Extracts from Letters etc.\", pages 13-14.) In\nthe abstract of the notes read to the Geological Society in 1835, we\nread: \"In the gravel of Patagonia he (Darwin) also found many bones of\nthe Megatherium and of five or six other species of quadrupeds, among\nwhich he has detected the bones of a species of Agouti. He also met with\nseveral examples of the polygonal plates, etc.\" (\"Proc. Geol. Soc.\" Vol.\nII. pages 211-212.)\n\nDarwin's own recollections entirely bear out the conclusion that he\nfully recognised, WHILE IN SOUTH AMERICA, the wonderful significance\nof the resemblances between the extinct and recent mammalian faunas. He\nwrote in his \"Autobiography\": \"During the voyage of the 'Beagle' I had\nbeen deeply impressed by discovering in the Pampean formation\ngreat fossil animals covered with armour like that on the existing\narmadillos.\" (\"L.L.\" I. page 82.)\n\nThe impression made on Darwin's mind by the discovery of these fossil\nbones, was doubtless deepened as, in his progress southward from Brazil\nto Patagonia, he found similar species of Edentate animals everywhere\nreplacing one another among the living forms, while, whenever fossils\noccurred, they also were seen to belong to the same remarkable group of\nanimals. (While Darwin was making these observations in South America,\na similar generalisation to that at which he arrived was being reached,\nquite independently and almost simultaneously, with respect to the\nfossil and recent mammals of Australia. In the year 1831, Clift gave\nto Jameson a list of bones occurring in the caves and breccias of\nAustralia, and in publishing this list the latter referred to the fact\nthat the forms belonged to marsupials, similar to those of the\nexisting Australian fauna. But he also stated that, as a skull had been\nidentified (doubtless erroneously) as having belonged to a hippopotamus,\nother mammals than marsupials must have spread over the island in late\nTertiary times. It is not necessary to point out that this paper was\nquite unknown to Darwin while in South America. Lyell first noticed it\nin the third edition of his \"Principles\", which was published in May,\n1834 (see \"Edinb. New Phil. Journ.\" Vol. X. (1831), pages 394-6, and\nLyell's \"Principles\" (3rd edition), Vol. III. page 421). Darwin referred\nto this discovery in 1839 (see his \"Journal\", page 210.))\n\nThat the passage in Darwin's pocket-book for 1837 can only refer to an\nAWAKENING of Darwin's interest in the subject--probably resulting from\na sight of the bones when they were being unpacked--I think there\ncannot be the smallest doubt; AND WE MAY THEREFORE CONFIDENTLY FIX UPON\nNOVEMBER, 1832, AS THE DATE AT WHICH DARWIN COMMENCED THAT LONG SERIES\nOF OBSERVATIONS AND REASONINGS WHICH EVENTUALLY CULMINATED IN THE\nPREPARATION OF THE \"ORIGIN OF SPECIES\". Equally certain is it, that it\nwas his geological work that led Darwin into those paths of research\nwhich in the end conducted him to his great discoveries. I quite agree\nwith the view expressed by Mr F. Darwin and Professor Seward, that\nDarwin, like Lyell, \"thought it 'almost useless' to try to prove the\ntruth of evolution until the cause of change was discovered\" (\"M.L.\"\nI. page 38.), and that possibly he may at times have vacillated in his\nopinions, but I believe there is evidence that, from the date mentioned,\nthe \"species question\" was always more or less present in Darwin's mind.\n(Although we admit with Huxley that Darwin's training in comparative\nanatomy was very small, yet it may be remembered that he was a medical\nstudent for two years, and, if he hated the lectures, he enjoyed the\nsociety of naturalists. He had with him in the little \"Beagle\" library a\nfair number of zoological books, including works on Osteology by Cuvier,\nDesmarest and Lesson, as well as two French Encyclopaedias of Natural\nHistory. As a sportsman, he would obtain specimens of recent mammals in\nSouth America, and would thus have opportunities of studying their teeth\nand general anatomy. Keen observer, as he undoubtedly was, we need not\nthen be surprised that he was able to make out the resemblances between\nthe recent and fossil forms.)\n\nIt is clear that, as time went on, Darwin became more and more absorbed\nin his geological work. One very significant fact was that the once\nardent sportsman, when he found that shooting the necessary game and\nzoological specimens interfered with his work with the hammer, gave up\nhis gun to his servant. (\"L.L.\" I. page 63.) There is clear evidence\nthat Darwin gradually became aware how futile were his attempts to add\nto zoological knowledge by dissection and drawing, while he felt ever\nincreasing satisfaction with his geological work.\n\nThe voyage fortunately extended to a much longer period (five years)\nthan the two originally intended, but after being absent nearly three\nyears, Darwin wrote to his sister in November, 1834, \"Hurrah! hurrah!\nit is fixed that the 'Beagle' shall not go one mile south of Cape\nTres Montes (about 200 miles south of Chiloe), and from that point to\nValparaiso will be finished in about five months. We shall examine the\nChonos Archipelago, entirely unknown, and the curious inland sea behind\nChiloe. For me it is glorious. Cape Tres Montes is the most southern\npoint where there is much geological interest, as there the modern beds\nend. The Captain then talks of crossing the Pacific; but I think we\nshall persuade him to finish the coast of Peru, where the climate\nis delightful, the country hideously sterile, but abounding with the\nhighest interest to the geologist... I have long been grieved and most\nsorry at the interminable length of the voyage (though I never would\nhave quitted it)... I could not make up my mind to return. I could not\ngive up all the geological castles in the air I had been building up for\nthe last two years.\" (\"L.L.\" I. pages 257-58.)\n\nIn April, 1835, he wrote to another sister: \"I returned a week ago from\nmy excursion across the Andes to Mendoza. Since leaving England I have\nnever made so successful a journey... how deeply I have enjoyed it; it\nwas something more than enjoyment; I cannot express the delight which I\nfelt at such a famous winding-up of all my geology in South America. I\nliterally could hardly sleep at nights for thinking over my day's work.\nThe scenery was so new, and so majestic; everything at an elevation\nof 12,000 feet bears so different an aspect from that in the lower\ncountry... To a geologist, also, there are such manifest proofs of\nexcessive violence; the strata of the highest pinnacles are tossed about\nlike the crust of a broken pie.\" (\"L.L.\" I. pages 259-60.)\n\nDarwin anticipated with intense pleasure his visit to the Galapagos\nIslands. On July 12th, 1835, he wrote to Henslow: \"In a few days' time\nthe \"Beagle\" will sail for the Galapagos Islands. I look forward with\njoy and interest to this, both as being somewhat nearer to England and\nfor the sake of having a good look at an active volcano. Although\nwe have seen lava in abundance, I have never yet beheld the crater.\"\n(\"M.L.\" I. page 26.) He could little anticipate, as he wrote these\nlines, the important aid in the solution of the \"species question\" that\nwould ever after make his visit to the Galapagos Islands so memorable.\nIn 1832, as we have seen, the great discovery of the relations of living\nto extinct mammals in the same area had dawned upon his mind; in 1835\nhe was to find a second key for opening up the great mystery, by\nrecognising the variations of similar types in adjoining islands among\nthe Galapagos.\n\nThe final chapter in the second volume of the \"Principles\" had aroused\nin Darwin's mind a desire to study coral-reefs, which was gratified\nduring his voyage across the Pacific and Indian Oceans. His theory on\nthe subject was suggested about the end of 1834 or the beginning of\n1835, as he himself tells us, before he had seen a coral-reef,\nand resulted from his work during two years in which he had \"been\nincessantly attending to the effects on the shores of South America of\nthe intermittent elevation of the land, together with denudation and the\ndeposition of sediment.\" (\"L.L.\" I. page 70.)\n\nOn arriving at the Cape of Good Hope in July, 1836, Darwin was greatly\ngratified by hearing that Sedgwick had spoken to his father in high\nterms of praise concerning the work done by him in South America.\nReferring to the news from home, when he reached Bahia once more, on the\nreturn voyage (August, 1836), he says: \"The desert, volcanic rocks, and\nwild sea of Ascension... suddenly wore a pleasing aspect, and I set to\nwork with a good-will at my old work of Geology.\" (\"L.L.\" I. page 265.)\nWriting fifty years later, he says: \"I clambered over the mountains of\nAscension with a bounding step and made the volcanic rocks resound under\nmy geological hammer!\" (\"L.L.\" I. page 66.)\n\nThat his determination was now fixed to devote his own labours to the\ntask of working out the geological results of the voyage, and that\nhe was prepared to leave to more practised hands the study of his\nbiological collections, is clear from the letters he sent home at this\ntime. From St Helena he wrote to Henslow asking that he would propose\nhim as a Fellow of the Geological Society; and his Certificate, in\nHenslow's handwriting, is dated September 8th, 1836, being signed from\npersonal knowledge by Henslow and Sedgwick. He was proposed on November\n2nd and elected November 30th, being formally admitted to the Society\nby Lyell, who was then President, on January 4th, 1837, on which date he\nalso read his first paper. Darwin did not become a Fellow of the Linnean\nSociety till eighteen years later (in 1854).\n\nAn estimate of the value and importance of Darwin's geological\ndiscoveries during the voyage of the \"Beagle\" can best be made when\nconsidering the various memoirs and books in which the author\ndescribed them. He was too cautious to allow himself to write his first\nimpressions in his Journal, and wisely waited till he could study his\nspecimens under better conditions and with help from others on his\nreturn. The extracts published from his correspondence with Henslow and\nothers, while he was still abroad, showed, nevertheless, how great was\nthe mass of observation, how suggestive and pregnant with results were\nthe reasonings of the young geologist.\n\nTwo sets of these extracts from Darwin's letters to Henslow were\nprinted while he was still abroad. The first of these was the series of\n\"Geological Notes made during a survey of the East and West Coasts of\nSouth America, in the years 1832, 1833, 1834 and 1835, with an account\nof a transverse section of the Cordilleras of the Andes between\nValparaiso and Mendoza\". Professor Sedgwick, who read these notes to\nthe Geological Society on November 18th, 1835, stated that \"they were\nextracted from a series of letters (addressed to Professor Henslow),\ncontaining a great mass of information connected with almost every\nbranch of natural history,\" and that he (Sedgwick) had made a selection\nof the remarks which he thought would be more especially interesting to\nthe Geological Society. An abstract of three pages was published in the\n\"Proceedings of the Geological Society\" (Vol. II. pages 210-12.), but so\nunknown was the author at this time that he was described as F. Darwin,\nEsq., of St John's College, Cambridge! Almost simultaneously (on\nNovember 16th, 1835) a second set of extracts from these letters--this\ntime of a general character--were read to the Philosophical Society at\nCambridge, and these excited so much interest that they were privately\nprinted in pamphlet form for circulation among the members.\n\nMany expeditions and \"scientific missions\" have been despatched to\nvarious parts of the world since the return of the \"Beagle\" in 1836, but\nit is doubtful whether any, even the most richly endowed of them, has\nbrought back such stores of new information and fresh discoveries as\ndid that little \"ten-gun brig\"--certainly no cabin or laboratory was the\nbirth-place of ideas of such fruitful character as was that narrow end\nof a chart-room, where the solitary naturalist could climb into his\nhammock and indulge in meditation.\n\nThe third and most active portion of Darwin's career as a geologist was\nthe period which followed his return to England at the end of 1836. His\nimmediate admission to the Geological Society, at the beginning of 1837,\ncoincided with an important crisis in the history of geological science.\n\nThe band of enthusiasts who nearly thirty years before had inaugurated\nthe Geological Society--weary of the fruitless conflicts between\n\"Neptunists\" and \"Plutonists\"--had determined to eschew theory and\nconfine their labours to the collection of facts, their publications to\nthe careful record of observations. Greenough, the actual founder of the\nSociety, was an ardent Wernerian, and nearly all his fellow-workers had\ncome, more or less directly, under the Wernerian teaching. Macculloch\nalone gave valuable support to the Huttonian doctrines, so far as they\nrelated to the influence of igneous activity--but the most important\nportion of the now celebrated \"Theory of the Earth\"--that dealing with\nthe competency of existing agencies to account for changes in past\ngeological times--was ignored by all alike. Macculloch's influence on\nthe development of geology, which might have had far-reaching effects,\nwas to a great extent neutralised by his peculiarities of mind and\ntemper; and, after a stormy and troublous career, he retired from the\nsociety in 1832. In all the writings of the great pioneers in English\ngeology, Hutton and his splendid generalisation are scarcely ever\nreferred to. The great doctrines of Uniformitarianism, which he had\nforeshadowed, were completely ignored, and only his extravagances of\n\"anti-Wernerianism\" seem to have been remembered.\n\nWhen between 1830 and 1832, Lyell, taking up the almost forgotten ideas\nof Hutton, von Hoff and Prevost, published that bold challenge to\nthe Catastrophists--the \"Principles of Geology\"--he was met with the\nstrongest opposition, not only from the outside world, which was amused\nby his \"absurdities\" and shocked by his \"impiety\"--but not less from\nhis fellow-workers and friends in the Geological Society. For Lyell's\nnumerous original observations, and his diligent collection of facts his\ncontemporaries had nothing but admiration, and they cheerfully admitted\nhim to the highest offices in the society, but they met his reasonings\non geological theory with vehement opposition and his conclusions with\ncoldness and contempt.\n\nThere is, indeed, a very striking parallelism between the reception of\nthe \"Principles of Geology\" by Lyell's contemporaries and the manner in\nwhich the \"Origin of Species\" was met a quarter of a century later, as\nis so vividly described by Huxley. (\"L.L.\" II. pages 179-204.) Among\nLyell's fellow-geologists, two only--G. Poulett Scrope and John Herschel\n(Both Lyell and Darwin fully realised the value of the support of these\ntwo friends. Scrope in his appreciative reviews of the \"Principles\"\njustly pointed out what was the weakest point, the inadequate\nrecognition of sub-aerial as compared with marine denudation. Darwin\nalso admitted that Scrope had to a great extent forestalled him in his\ntheory of Foliation. Herschel from the first insisted that the leading\nidea of the \"Principles\" must be applied to organic as well as to\ninorganic nature and must explain the appearance of new species (see\nLyell's \"Life and Letters\", Vol. I. page 467). Darwin tells us that\nHerschel's \"Introduction to the Study of Natural Philosophy\" with\nHumboldt's \"Personal Narrative\" \"stirred up in me a burning zeal\" in\nhis undergraduate days. I once heard Lyell exclaim with fervour \"If\never there was a heaven-born genius it was John Herschel!\")--declared\nthemselves from the first his strong supporters. Scrope in two\nluminous articles in the \"Quarterly Review\" did for Lyell what Huxley\naccomplished for Darwin in his famous review in the \"Times\"; but Scrope\nunfortunately was at that time immersed in the stormy sea of politics,\nand devoted his great powers of exposition to the preparation of\nfugitive pamphlets. Herschel, like Scrope, was unable to support\nLyell at the Geological Society, owing to his absence on the important\nastronomical mission to the Cape.\n\nIt thus came about that, in the frequent conflicts of opinion within the\nwalls of the Geological Society, Lyell had to bear the brunt of battle\nfor Uniformitarianism quite alone, and it is to be feared that he found\nhimself sadly overmatched when opposed by the eloquence of Sedgwick, the\nsarcasm of Buckland, and the dead weight of incredulity on the part of\nGreenough, Conybeare, Murchison and other members of the band of pioneer\nworkers. As time went on there is evidence that the opposition of De la\nBeche and Whewell somewhat relaxed; the brilliant \"Paddy\" Fitton (as his\nfriends called him) was sometimes found in alliance with Lyell, but was\ncharacteristically apt to turn his weapon, as occasion served, on friend\nor foe alike; the amiable John Phillips \"sat upon the fence.\" Only when\na new generation arose--including Jukes, Ramsay, Forbes and Hooker--did\nLyell find his teachings received with anything like favour.\n\nWe can well understand, then, how Lyell would welcome such a recruit as\nyoung Darwin--a man who had declared himself more Lyellian than Lyell,\nand who brought to his support facts and observations gleaned from so\nwide a field.\n\nThe first meeting of Lyell and Darwin was characteristic of the two men.\nDarwin at once explained to Lyell that, with respect to the origin of\ncoral-reefs, he had arrived at views directly opposed to those published\nby \"his master.\" To give up his own theory, cost Lyell, as he told\nHerschel, a \"pang at first,\" but he was at once convinced of the\nimmeasurable superiority of Darwin's theory. I have heard members\nof Lyell's family tell of the state of wild excitement and sustained\nenthusiasm, which lasted for days with Lyell after this interview, and\nhis letters to Herschel, Whewell and others show his pleasure at the new\nlight thrown upon the subject and his impatience to have the matter laid\nbefore the Geological Society.\n\nWriting forty years afterwards, Darwin, speaking of the time of the\nreturn of the \"Beagle\", says: \"I saw a great deal of Lyell. One of his\nchief characteristics was his sympathy with the work of others, and\nI was as much astonished as delighted at the interest which he\nshowed when, on my return to England, I explained to him my views on\ncoral-reefs. This encouraged me greatly, and his advice and example had\nmuch influence on me.\" (\"L.L.\" I. page 68.) Darwin further states that\nhe saw more of Lyell at this time than of any other scientific man, and\nat his request sent his first communication to the Geological Society.\n(\"L.L.\" I. page 67.)\n\n\"Mr Lonsdale\" (the able curator of the Geological Society), Darwin wrote\nto Henslow, \"with whom I had much interesting conversation,\" \"gave me a\nmost cordial reception,\" and he adds, \"If I was not much more inclined\nfor geology than the other branches of Natural History, I am sure Mr\nLyell's and Lonsdale's kindness ought to fix me. You cannot conceive\nanything more thoroughly good-natured than the heart-and-soul manner in\nwhich he put himself in my place and thought what would be best to do.\"\n(\"L.L.\" I. page 275.)\n\nWithin a few days of Darwin's arrival in London we find Lyell writing to\nOwen as follows:\n\n\"Mrs Lyell and I expect a few friends here on Saturday next, 29th\n(October), to an early tea party at eight o'clock, and it will give us\ngreat pleasure if you can join it. Among others you will meet Mr Charles\nDarwin, whom I believe you have seen, just returned from South America,\nwhere he has laboured for zoologists as well as for hammer-bearers.\nI have also asked your friend Broderip.\" (\"The Life of Richard Owen\",\nLondon, 1894, Vol. I. page 102.) It would probably be on this occasion\nthat the services of Owen were secured for the work on the fossil bones\nsent home by Darwin.\n\nOn November 2nd, we find Lyell introducing Darwin as his guest at the\nGeological Society Club; on December 14th, Lyell and Stokes proposed\nDarwin as a member of the Club; between that date and May 3rd of the\nfollowing year, when his election to the Club took place, he was several\ntimes dining as a guest.\n\nOn January 4th, 1837, as we have already seen, Darwin was formally\nadmitted to the Geological Society, and on the same evening he read\nhis first paper (I have already pointed out that the notes read at the\nGeological Society on Nov. 18, 1835 were extracts made by Sedgwick from\nletters sent to Henslow, and not a paper sent home for publication by\nDarwin.) before the Society, \"Observations of proofs of recent elevation\non the coast of Chili, made during the Survey of H.M.S. \"Beagle\",\ncommanded by Captain FitzRoy, R.N.\" By C. Darwin, F.G.S. This paper was\npreceded by one on the same subject by Mr A. Caldcleugh, and the reading\nof a letter and other communications from the Foreign Office also\nrelating to the earthquakes in Chili.\n\nAt the meeting of the Council of the Geological Society on February 1st,\nDarwin was nominated as a member of the new Council, and he was elected\non February 17th.\n\nThe meeting of the Geological Society on April 19th was devoted to the\nreading by Owen of his paper on Toxodon, perhaps the most remarkable\nof the fossil mammals found by Darwin in South America; and at the\nnext meeting, on May 3rd, Darwin himself read \"A Sketch of the Deposits\ncontaining extinct Mammalia in the neighbourhood of the Plata\". The\nnext following meeting, on May 17th, was devoted to Darwin's Coral-reef\npaper, entitled \"On certain areas of elevation and subsidence in\nthe Pacific and Indian Oceans, as deduced from the study of Coral\nFormations\". Neither of these three early papers of Darwin were\npublished in the Transactions of the Geological Society, but the\nminutes of the Council show that they were \"withdrawn by the author by\npermission of the Council.\"\n\nDarwin's activity during this session led to some rather alarming\neffects upon his health, and he was induced to take a holiday in\nStaffordshire and the Isle of Wight. He was not idle, however, for a\nremark of his uncle, Mr Wedgwood, led him to make those interesting\nobservations on the work done by earthworms, that resulted in his\npreparing a short memoir on the subject, and this paper, \"On the\nFormation of Mould\", was read at the Society on November 1st, 1837,\nbeing the first of Darwin's papers published in full; it appeared in\nVol. V. of the \"Geological Transactions\", pages 505-510.\n\nDuring this session, Darwin attended nearly all the Council meetings,\nand took such an active part in the work of the Society that it is not\nsurprising to find that he was now requested to accept the position of\nSecretary. After some hesitation, in which he urged his inexperience\nand want of knowledge of foreign languages, he consented to accept the\nappointment. (\"L.L.\" I. page 285.)\n\nAt the anniversary meeting on February 16th, 1838, the Wollaston Medal\nwas given to Owen in recognition of his services in describing the\nfossil mammals sent home by Darwin. In his address, the President,\nProfessor Whewell, dwelt at length on the great value of the papers\nwhich Darwin had laid before the Society during the preceding session.\n\nOn March 7th, Darwin read before the Society the most important perhaps\nof all his geological papers, \"On the Connexion of certain Volcanic\nPhenomena in South America, and on the Formation of Mountain-Chains and\nVolcanoes as the effect of Continental Elevations\". In this paper he\nboldly attacked the tenets of the Catastrophists. It is evident that\nDarwin at this time, taking advantage of the temporary improvement in\nhis health, was throwing himself into the breach of Uniformitarianism\nwith the greatest ardour. Lyell wrote to Sedgwick on April 21st, 1837,\n\"Darwin is a glorious addition to any society of geologists, and is\nworking hard and making way, both in his book and in our discussions.\"\n(\"The Life and Letters of the Reverend Adam Sedgwick\", Vol. I. page 484,\nCambridge, 1890.)\n\nWe have unfortunately few records of the animated debates which took\nplace at this time between the old and new schools of geologists. I have\noften heard Lyell tell how Lockhart would bring down a party of friends\nfrom the Athenaeum Club to Somerset House on Geological nights, not, as\nhe carefully explained, that \"he cared for geology, but because he liked\nto while the fellows fight.\" But it fortunately happens that a few days\nafter this last of Darwin's great field-days, at the Geological Society,\nLyell, in a friendly letter to his father-in-law, Leonard Horner, wrote\na very lively account of the proceedings while his impressions were\nstill fresh; and this gives us an excellent idea of the character of\nthese discussions.\n\nNeither Sedgwick nor Buckland were present on this occasion, but we can\nimagine how they would have chastised their two \"erring pupils\"--more\nin sorrow than in anger--had they been there. Greenough, too, was\nabsent--possibly unwilling to countenance even by his presence such\noutrageous doctrines.\n\nDarwin, after describing the great earthquakes which he had experienced\nin South America, and the evidence of their connection with volcanic\noutbursts, proceeded to show that earthquakes originated in fractures,\ngradually formed in the earth's crust, and were accompanied by movements\nof the land on either side of the fracture. In conclusion he boldly\nadvanced the view \"that continental elevations, and the action of\nvolcanoes, are phenomena now in progress, caused by some great but slow\nchange in the interior of the earth; and, therefore, that it might\nbe anticipated, that the formation of mountain chains is likewise in\nprogress: and at a rate which may be judged of by either actions, but\nmost clearly by the growth of volcanoes.\" (\"Proc. Geol. Soc.\" Vol. II.\npages 654-60.)\n\nLyell's account (\"Life, Letters and Journals of Sir Charles Lyell,\nBart.\", edited by his sister-in-law, Mrs Lyell, Vol. II. pages 40,\n41 (Letter to Leonard Horner, 1838), 2 vols. London, 1881.) of the\ndiscussion was as follows: \"In support of my heretical notions,\" Darwin\n\"opened upon De la Beche, Phillips and others his whole battery of the\nearthquakes and volcanoes of the Andes, and argued that spaces at least\na thousand miles long were simultaneously subject to earthquakes and\nvolcanic eruptions, and that the elevation of the Pampas, Patagonia,\netc., all depended on a common cause; also that the greater the\ncontortions of strata in a mountain chain, the smaller must have been\neach separate and individual movement of that long series which was\nnecessary to upheave the chain. Had they been more violent, he\ncontended that the subterraneous fluid matter would have gushed out and\noverflowed, and the strata would have been blown up and annihilated. (It\nis interesting to compare this with what Darwin wrote to Henslow\nseven years earlier.) He therefore introduces a cooling of one small\nunderground injection, and then the pumping in of other lava, or\nporphyry, or granite, into the previously consolidated and first-formed\nmass of igneous rock. (Ideas somewhat similar to this suggestion have\nrecently been revived by Dr See (\"Proc. Am. Phil. Soc.\" Vol. XLVII.\n1908, page 262.).) When he had done his description of the reiterated\nstrokes of his volcanic pump, De la Beche gave us a long oration about\nthe impossibility of strata of the Alps, etc., remaining flexible\nfor such a time as they must have done, if they were to be tilted,\nconvoluted, or overturned by gradual small shoves. He never, however,\nexplained his theory of original flexibility, and therefore I am as\nunable as ever to comprehend why flexiblility is a quality so limited in\ntime.\n\n\"Phillips then got up and pronounced a panegyric upon the \"Principles\nof Geology\", and although he still differed, thought the actual cause\ndoctrine had been so well put, that it had advanced the science and\nformed a date or era, and that for centuries the two opposite doctrines\nwould divide geologists, some contending for greater pristine forces,\nothers satisfied, like Lyell and Darwin, with the same intensity as\nnature now employs.\n\n\"Fitton quizzed Phillips a little for the warmth of his eulogy, saying\nthat he (Fitton) and others, who had Mr Lyell always with them, were in\nthe habit of admiring and quarrelling with him every day, as one\nmight do with a sister or cousin, whom one would only kiss and embrace\nfervently after a long absence. This seemed to be Mr Phillips' case,\ncoming up occasionally from the provinces. Fitton then finished this\ndrollery by charging me with not having done justice to Hutton, who he\nsaid was for gradual elevation.\n\n\"I replied, that most of the critics had attacked me for overrating\nHutton, and that Playfair understood him as I did.\n\n\"Whewell concluded by considering Hopkins' mathematical calculations, to\nwhich Darwin had often referred. He also said that we ought not to try\nand make out what Hutton would have taught and thought, if he had known\nthe facts which we now know.\"\n\nIt may be necessary to point out, in explanation of the above narrative,\nthat while it was perfectly clear from Hutton's rather obscure and\ninvolved writings that he advocated slow and gradual change on\nthe earth's surface, his frequent references to violent action and\nearthquakes led many--including Playfair, Lyell and Whewell--to believe\nthat he held the changes going on in the earth's interior to be of\na catastrophic nature. Fitton, however, maintained that Hutton was\nconsistently uniformitarian. Before the idea of the actual \"flowing\" of\nsolid bodies under intense pressure had been grasped by geologists,\nDe la Beche, like Playfair before him, maintained that the bending\nand folding of rocks must have been effected before their complete\nconsolidation.\n\nIn concluding his account of this memorable discussion, Lyell adds: \"I\nwas much struck with the different tone in which my gradual causes\nwas treated by all, even including De la Beche, from that which they\nexperienced in the same room four years ago, when Buckland, De la\nBeche(?), Sedgwick, Whewell, and some others treated them with as much\nridicule as was consistent with politeness in my presence.\"\n\nThis important paper was, in spite of its theoretical character,\npublished in full in the \"Transactions of the Geological Society\" (Ser.\n2, Vol. V. pages 601-630). It did not however appear till 1840, and\npossibly some changes may have been made in it during the long interval\nbetween reading and printing. During the year 1839, Darwin continued his\nregular attendance at the Council meetings, but there is no record of\nany discussions in which he may have taken part, and he contributed\nno papers himself to the Society. At the beginning of 1840, he was\nre-elected for the third time as Secretary, but the results of failing\nhealth are indicated by the circumstance that, only at one meeting early\nin the session, was he able to attend the Council. At the beginning of\nthe next session (Feb. 1841) Bunbury succeeded him as Secretary,\nDarwin still remaining on the Council. It may be regarded as a striking\nindication of the esteem in which he was held by his fellow geologists,\nthat Darwin remained on the Council for 14 consecutive years down to\n1849, though his attendances were in some years very few. In 1843 and\n1844 he was a Vice-president, but after his retirement at the beginning\nof 1850, he never again accepted re-nomination. He continued, however,\nto contribute papers to the Society, as we shall see, down to the end of\n1862.\n\nAlthough Darwin early became a member of the Geological Dining Club, it\nis to be feared that he scarcely found himself in a congenial atmosphere\nat those somewhat hilarious gatherings, where the hardy wielders of the\nhammer not only drank port--and plenty of it--but wound up their\nmeal with a mixture of Scotch ale and soda water, a drink which, as\nreminiscent of the \"field,\" was regarded as especially appropriate to\ngeologists. Even after the meetings, which followed the dinners,\nthey reassembled for suppers, at which geological dainties, like\n\"pterodactyle pie\" figured in the bill of fare, and fines of bumpers\nwere inflicted on those who talked the \"ologies.\"\n\nAfter being present at a fair number of meetings in 1837 and 1838,\nDarwin's attendances at the Club fell off to two in 1839, and by 1841\nhe had ceased to be a member. In a letter to Lyell on Dec. 2nd, 1841,\nLeonard Horner wrote that the day before \"At the Council, I had the\nsatisfaction of seeing Darwin again in his place and looking well. He\ntried the last evening meeting, but found it too much, but I hope before\nthe end of the season he will find himself equal to that also. I hail\nDarwin's recovery as a vast gain to science.\" Darwin's probably last\nattendance, this time as a guest, was in 1851, when Horner again\nwrote to Lyell, \"Charles Darwin was at the Geological Society's Club\nyesterday, where he had not been for ten years--remarkably well, and\ngrown quite stout.\" (\"Memoirs of Leonard Horner\" (privately printed),\nVol. II. pages 39 and 195.)\n\nIt may be interesting to note that at the somewhat less lively dining\nClub--the Philosophical--in the founding of which his friends Lyell and\nHooker had taken so active a part, Darwin found himself more at home,\nand he was a frequent attendant--in spite of his residence being at\nDown--from 1853 to 1864. He even made contributions on scientific\nquestions after these dinners. In a letter to Hooker he states that he\nwas deeply interested in the reforms of the Royal Society, which the\nClub was founded to promote. He says also that he had arranged to come\nto town every Club day \"and then my head, I think, will allow me on an\naverage to go to every other meeting. But it is grievous how often any\nchange knocks me up.\" (\"L.L.\" II. pages 42, 43.)\n\nOf the years 1837 and 1838 Darwin himself says they were \"the most\nactive ones which I ever spent, though I was occasionally unwell, and\nso lost some time... I also went a little into society.\" (\"L.L.\" I. pages\n67, 68.) But of the four years from 1839 to 1842 he has to confess sadly\n\"I did less scientific work, though I worked as hard as I could, than\nduring any other equal length of time in my life. This was owing to\nfrequently recurring unwellness, and to one long and serious illness.\"\n(\"L.L.\" I. page 69.)\n\nDarwin's work at the Geological Society did not by any means engage the\nwhole of his energies, during the active years 1837 and 1838. In June of\nthe latter year, leaving town in somewhat bad health, he found himself\nat Edinburgh again, and engaged in examining the Salisbury Craigs, in a\nvery different spirit to that excited by Jameson's discourse. (\"L.L.\"\nI. page 290.) Proceeding to the Highlands he then had eight days of hard\nwork at the famous \"Parallel Roads of Glen Roy\", being favoured with\nglorious weather.\n\nHe says of the writing of the paper on the subject--the only memoir\ncontributed by Darwin to the Royal Society, to which he had been\nrecently elected--that it was \"one of the most difficult and instructive\ntasks I was ever engaged on.\" The paper extends to 40 quarto pages\nand is illustrated by two plates. Though it is full of the records\nof careful observation and acute reasoning, yet the theory of marine\nbeaches which he propounded was, as he candidly admitted in after years\n(\"M.L.\" II page 188.), altogether wrong. The alternative lake-theory he\nfound himself unable to accept at the time, for he could not understand\nhow barriers could be formed at successive levels across the valleys;\nand until the following year, when the existence of great glaciers\nin the district was proved by the researches of Agassiz, Buckland and\nothers, the difficulty appeared to him an insuperable one. Although\nDarwin said of this paper in after years that it \"was a great failure\nand I am ashamed of it\"--yet he retained his interest in the question\never afterwards, and he says \"my error has been a good lesson to me\nnever to trust in science to the principle of exclusion.\" (\"M.L.\" II.\npages 171-93.)\n\nAlthough Darwin had not realised in 1838 that large parts of the British\nIslands had been occupied by great glaciers, he had by no means failed\nwhile in South America to recognise the importance of ice-action. His\nobservations, as recorded in his Journal, on glaciers coming down to\nthe sea-level, on the west coast of South America, in a latitude\ncorresponding to a much lower one than that of the British Islands,\nprofoundly interested geologists; and the same work contains many\nvaluable notes on the boulders and unstratified beds in South America in\nwhich they were included.\n\nBut in 1840 Agassiz read his startling paper on the evidence of the\nformer existence of glaciers in the British Islands, and this was\nfollowed by Buckland's memoir on the same subject. On April 14, 1841,\nDarwin contributed to the Geological Society his important paper \"On the\nDistribution of Erratic Boulders and the Contemporaneous Unstratified\nDeposits of South America\", a paper full of suggestiveness for those\nstudying the glacial deposits of this country. It was published in the\n\"Transactions\" in 1842.\n\nThe description of traces of glacial action in North Wales, by Buckland,\nappears to have greatly excited the interest of Darwin. With Sedgwick he\nhad, in 1831, worked at the stratigraphy of that district, but neither\nof them had noticed the very interesting surface features. (\"L.L.\" I.\npage 58.) Darwin was able to make a journey to North Wales in June,\n1842 (alas! it was his last effort in field-geology) and as a result\nhe published his most able and convincing paper on the subject in the\nSeptember number of the \"Philosophical Magazine\" for 1842. Thus the\nmystery of the bell-stone was at last solved and Darwin, writing many\nyears afterwards, said \"I felt the keenest delight when I first read of\nthe action of icebergs in transporting boulders, and I gloried in the\nprogress of Geology.\" (\"L.L.\" I. page 41.) To the \"Geographical Journal\"\nhe had sent in 1839 a note \"On a Rock seen on an Iceberg in 16 deg S.\nLatitude.\" For the subject of ice-action, indeed, Darwin retained the\ngreatest interest to the end of his life. (\"M.L.\" II. pages 148-71.)\n\nIn 1846, Darwin read two papers to the Geological Society \"On the\ndust which falls on vessels in the Atlantic, and On the Geology of the\nFalkland Islands\"; in 1848 he contributed a note on the transport of\nboulders from lower to higher levels; and in 1862 another note on the\nthickness of the Pampean formation, as shown by recent borings at Buenos\nAyres. An account of the \"British Fossil Lepadidae\" read in 1850, was\nwithdrawn by him.\n\nAt the end of 1836 Darwin had settled himself in lodgings in Fitzwilliam\nStreet, Cambridge, and devoted three months to the work of unpacking his\nspecimens and studying his collection of rocks. The pencilled notes on\nthe Manuscript Catalogue in the Sedgwick Museum enable us to realise\nhis mode of work, and the diligence with which it was carried on. The\nletters M and H, indicate the assistance he received from time to\ntime from Professor Miller, the crystallographer, and from his friend\nHenslow. Miller not only measured many of the crystals submitted to him,\nbut evidently taught Darwin to use the reflecting goniometer himself\nwith considerable success. The \"book of measurements\" in which the\nrecords were kept, appears to have been lost, but the pencilled notes\nin the catalogue show how thoroughly the work was done. The letter R\nattached to some of the numbers in the catalogue evidently refers to the\nfact that they were submitted to Mr Trenham Reeks (who analysed some of\nhis specimens) at the Geological Survey quarters in Craig's Court. This\nwas at a later date when Darwin was writing the \"Volcanic Islands\" and\n\"South America\".\n\nIt was about the month of March, 1837, that Darwin completed this work\nupon his rocks, and also the unpacking and distribution of his fossil\nbones and other specimens. We have seen that November, 1832, must\ncertainly be regarded as the date when he FIRST realised the important\nfact that the fossil mammals of the Pampean formation were all closely\nrelated to the existing forms in South America; while October, 1835,\nwas, as undoubtedly, the date when the study of the birds and other\nforms of life in the several islands of the Galapagos Islands gave\nhim his SECOND impulse towards abandoning the prevalent view of the\nimmutability of species. When then in his pocket-book for 1837 Darwin\nwrote the often quoted passage: \"In July opened first note-book on\nTransmutation of Species. Had been greatly struck from about the month\nof previous March on character of South American fossils, and species on\nGalapagos Archipelago. These facts (especially latter), origin of all my\nviews\" (\"L.L.\" I. page 276.), it is clear that he must refer, not to\nhis first inception of the idea of evolution, but to the flood of\nrecollections, the reawakening of his interest in the subject, which\ncould not fail to result from the sight of his specimens and the\nreference to his notes.\n\nExcept during the summer vacation, when he was visiting his father and\nuncle, and with the latter making his first observations upon the work\nof earthworms, Darwin was busy with his arrangements for the publication\nof the five volumes of the \"Zoology of the 'Beagle'\" and in getting the\nnecessary financial aid from the government for the preparation of the\nplates. He was at the same time preparing his \"Journal\" for publication.\nDuring the years 1837 to 1843, Darwin worked intermittently on the\nvolumes of Zoology, all of which he edited, while he wrote introductions\nto those by Owen and Waterhouse and supplied notes to the others.\n\nAlthough Darwin says of his Journal that the preparation of the book\n\"was not hard work, as my MS. Journal had been written with care.\" Yet\nfrom the time that he settled at 36, Great Marlborough Street in March,\n1837, to the following November he was occupied with this book. He tells\nus that the account of his scientific observations was added at this\ntime. The work was not published till March, 1839, when it appeared\nas the third volume of the \"Narrative of the Surveying Voyages of H.M.\nShips 'Adventure' and 'Beagle' between the years 1826 and 1836\". The\nbook was probably a long time in the press, for there are no less than\n20 pages of addenda in small print. Even in this, its first form, the\nwork is remarkable for its freshness and charm, and excited a great\namount of attention and interest. In addition to matters treated of in\ngreater detail in his other works, there are many geological notes of\nextreme value in this volume, such as his account of lightning tubes, of\nthe organisms found in dust, and of the obsidian bombs of Australia.\n\nHaving thus got out of hand a number of preliminary duties, Darwin was\nready to set to work upon the three volumes which were designed by him\nto constitute \"The Geology of the Voyage of the 'Beagle'\". The first of\nthese was to be on \"The Structure and Distribution of Coral-reefs\". He\ncommenced the writing of the book on October 5, 1838, and the last proof\nwas corrected on May 6, 1842. Allowing for the frequent interruptions\nthrough illness, Darwin estimated that it cost him twenty months of hard\nwork.\n\nDarwin has related how his theory of Coral-reefs which was begun in a\nmore \"deductive spirit\" than any of his other work, for in 1834 or 1835\nit \"was thought out on the west coast of South America, before I had\nseen a true coral-reef.\" (\"L.L.\" I. page 70.) The final chapter in\nLyell's second volume of the \"Principles\" was devoted to the subject\nof Coral-reefs, and a theory was suggested to account for the peculiar\nphenomena of \"atolls.\" Darwin at once saw the difficulty of accepting\nthe view that the numerous and diverse atolls all represent submerged\nvolcanic craters. His own work had for two years been devoted to the\nevidence of land movements over great areas in South America, and thus\nhe was led to announce his theory of subsidence to account for barrier\nand encircling reefs as well as atolls.\n\nFortunately, during his voyage across the Pacific and Indian Oceans, in\nhis visit to Australia and his twelve days' hard work at Keeling Island,\nhe had opportunities for putting his theory to the test of observation.\n\nOn his return to England, Darwin appears to have been greatly surprised\nat the amount of interest that his new theory excited. Urged by Lyell,\nhe read to the Geological Society a paper on the subject, as we have\nseen, with as little delay as possible, but this paper was \"withdrawn by\npermission of the Council.\" An abstract of three pages however appeared\nin the \"Proceedings of the Geological Society\". (Vol. II. pages 552-554\n(May 31, 1837).) A full account of the observations and the theory was\ngiven in the \"Journal\" (1839) in the 40 pages devoted to Keeling\nIsland in particular and to Coral formations generally. (\"Journal\" (1st\nedition), pages 439-69.)\n\nIt will be readily understood what an amount of labour the book on\nCoral reefs cost Darwin when we reflect on the number of charts, sailing\ndirections, narratives of voyages and other works which, with the\nfriendly assistance of the authorities at the Admiralty, he had\nto consult before he could draw up his sketch of the nature and\ndistribution of the reefs, and this was necessary before the theory, in\nall its important bearings, could be clearly enunciated. Very pleasing\nis it to read how Darwin, although arriving at a different conclusion to\nLyell, shows, by quoting a very suggestive passage in the \"Principles\"\n(1st edition Vol. II. page 296.), how the latter only just missed the\ntrue solution. This passage is cited, both in the \"Journal\" and the\nvolume on Coral-reefs. Lyell, as we have seen, received the new theory\nnot merely ungrudgingly, but with the utmost enthusiasm.\n\nIn 1849 Darwin was gratified by receiving the support of Dana, after his\nprolonged investigation in connection with the U.S. Exploring Expedition\n(\"M.L.\" II. pages 226-8.), and in 1874 he prepared a second edition of\nhis book, in which some objections which had been raised to the theory\nwere answered. A third edition, edited by Professor Bonney, appeared in\n1880, and a fourth (a reprint of the first edition, with introduction by\nmyself) in 1890.\n\nAlthough Professor Semper, in his account of the Pelew Islands, had\nsuggested difficulties in the acceptance of Darwin's theory, it was\nnot till after the return of the \"Challenger\" expedition in 1875 that a\nrival theory was propounded, and somewhat heated discussions were raised\nas to the respective merits of the two theories. While geologists have,\nnearly without exception, strongly supported Darwin's views, the notes\nof dissent have come almost entirely from zoologists. At the height\nof the controversy unfounded charges of unfairness were made against\nDarwin's supporters and the authorities of the Geological Society, but\nthis unpleasant subject has been disposed of, once for all, by Huxley.\n(\"Essays upon some Controverted Questions\", London, 1892, pages 314-328\nand 623-625.)\n\nDarwin's final and very characteristic utterance on the coral-reef\ncontroversy is found in a letter which he wrote to Professor Alexander\nAgassiz, May 5th, 1881: less than a year before his death: \"If I am\nwrong, the sooner I am knocked on the head and annihilated so much the\nbetter. It still seems to me a marvellous thing that there should not\nhave been much, and long-continued, subsidence in the beds of the great\noceans. I wish that some doubly rich millionaire would take it into his\nhead to have borings made in some of the Pacific and Indian atolls, and\nbring home cores for slicing from a depth of 500 or 600 feet.\" (\"L.L.\"\nIII. page 184.)\n\nThough the \"doubly rich millionaire\" has not been forthcoming, the\nenergy, in England, of Professor Sollas, and in New South Wales of\nProfessor Anderson Stuart served to set on foot a project, which, aided\nat first by the British Association for the Advancement of Science, and\nafterwards taken up jointly by the Royal Society, the New South\nWales Government, and the Admiralty, has led to the most definite and\nconclusive results.\n\nThe Committee appointed by the Royal Society to carry out the\nundertaking included representatives of all the views that had been\nput forward on the subject. The place for the experiment was, with the\nconsent of every member of the Committee, selected by the late Admiral\nSir W.J. Wharton--who was not himself an adherent of Darwin's views--and\nno one has ventured to suggest that his selection, the splendid atoll of\nFunafuti, was not a most judicious one.\n\nBy the pluck and perseverance of Professor Sollas in the preliminary\nexpedition, and of Professor T. Edgeworth David and his pupils, in\nsubsequent investigations of the island, the rather difficult piece\nof work was brought to a highly satisfactory conclusion. The New South\nWales Government lent boring apparatus and workmen, and the Admiralty\ncarried the expedition to its destination in a surveying ship which,\nunder Captain (now Admiral) A. Mostyn Field, made the most complete\nsurvey of the atoll and its surrounding seas that has ever been\nundertaken in the case of a coral formation.\n\nAfter some failures and many interruptions, the boring was carried to\nthe depth of 1114 feet, and the cores obtained were sent to England.\nHere the examination of the materials was fortunately undertaken by\na zoologist of the highest repute, Dr G.J. Hinde--who has a wide\nexperience in the study of organisms by sections--and he was aided at\nall points by specialists in the British Museum of Natural History\nand by other naturalists. Nor were the chemical and other problems\nneglected.\n\nThe verdict arrived at, after this most exhaustive study of a series of\ncores obtained from depths twice as great as that thought necessary by\nDarwin, was as follows:--\"The whole of the cores are found to be built\nup of those organisms which are seen forming coral-reefs near the\nsurface of the ocean--many of them evidently in situ; and not the\nslightest indication could be detected, by chemical or microscopic\nmeans, which suggested the proximity of non-calcareous rocks, even in\nthe lowest portions brought up.\"\n\nBut this was not all. Professor David succeeded in obtaining the aid\nof a very skilful engineer from Australia, while the Admiralty allowed\nCommander F.C.D. Sturdee to take a surveying ship into the lagoon\nfor further investigations. By very ingenious methods, and with great\nperseverance, two borings were put down in the midst of the lagoon to\nthe depth of nearly 200 feet. The bottom of the lagoon, at the depth of\n101 1/2 feet from sea-level, was found to be covered with remains of the\ncalcareous, green sea-weed Halimeda, mingled with many foraminifera; but\nat a depth of 163 feet from the surface of the lagoon the boring tools\nencountered great masses of coral, which were proved from the fragments\nbrought up to belong to species that live within AT MOST 120 feet from\nthe surface of the ocean, as admitted by all zoologists. (\"The Atoll\nof Funafuti; Report of the Coral Reef Committee of the Royal Society\",\nLondon, 1904.)\n\nDarwin's theory, as is well known, is based on the fact that the\ntemperature of the ocean at any considerable depth does not permit of\nthe existence and luxuriant growth of the organisms that form the reefs.\nHe himself estimated this limit of depth to be from 120 to 130 feet;\nDana, as an extreme, 150 feet; while the recent very prolonged and\nsuccessful investigations of Professor Alexander Agassiz in the Pacific\nand Indian Oceans lead him also to assign a limiting depth of 150 feet;\nthe EFFECTIVE, REEF-FORMING CORALS, however, flourishing at a much\nsmaller depth. Mr Stanley Gardiner gives for the most important\nreef-forming corals depths between 30 and 90 feet, while a few are found\nas low as 120 feet or even 180 feet.\n\nIt will thus be seen that the verdict of Funafuti is clearly and\nunmistakeably in favour of Darwin's theory. It is true that some\nzoologists find a difficulty in realising a slow sinking of parts of the\nocean floor, and have suggested new and alternative explanations: but\ngeologists generally, accepting the proofs of slow upheaval in\nsome areas--as shown by the admirable researches of Alexander\nAgassiz--consider that it is absolutely necessary to admit that this\nelevation is balanced by subsidence in other areas. If atolls and\nbarrier-reefs did not exist we should indeed be at a great loss to frame\na theory to account for their absence.\n\nAfter finishing his book on Coral-reefs, Darwin made his summer\nexcursion to North Wales, and prepared his important memoir on the\nglaciers of that district: but by October (1842) we find him fairly\nsettled at work upon the second volume of his \"Geology of the\n'Beagle'--Geological Observations on the Volcanic Islands, visited\nduring the Voyage of H.M.S. 'Beagle'\". The whole of the year 1843 was\ndevoted to this work, but he tells his friend Fox that he could \"manage\nonly a couple of hours per day, and that not very regularly.\" (\"L.L.\" I.\npage 321.) Darwin's work on the various volcanic islands examined by\nhim had given him the most intense pleasure, but the work of writing\nthe book by the aid of his notes and specimens he found \"uphill\nwork,\" especially as he feared the book would not be read, \"even by\ngeologists.\" (Loc. cit.)\n\nAs a matter of fact the work is full of the most interesting\nobservations and valuable suggestions, and the three editions (or\nreprints) which have appeared have proved a most valuable addition to\ngeological literature. It is not necessary to refer to the novel and\noften very striking discoveries described in this well-known work. The\nsubsidence beneath volcanic vents, the enormous denudation of volcanic\ncones reducing them to \"basal wrecks,\" the effects of solfatarric action\nand the formation of various minerals in the cavities of rocks--all\nof these subjects find admirable illustration from his graphic\ndescriptions. One of the most important discussions in this volume is\nthat dealing with the \"lamination\" of lavas as especially well seen in\nthe rocks of Ascension. Like Scrope, Darwin recognised the close analogy\nbetween the structure of these rocks and those of metamorphic origin--a\nsubject which he followed out in the volume \"Geological Observations on\nSouth America\".\n\nOf course in these days, since the application of the microscope to the\nstudy of rocks in thin sections, Darwin's nomenclature and descriptions\nof the petrological characters of the lavas appear to us somewhat crude.\nBut it happened that the \"Challenger\" visited most of the volcanic\nislands described by Darwin, and the specimens brought home were\nexamined by the eminent petrologist Professor Renard. Renard was so\nstruck with the work done by Darwin, under disadvantageous conditions,\nthat he undertook a translation of Darwin's work into French, and I\ncannot better indicate the manner in which the book is regarded by\ngeologists than by quoting a passage from Renard's preface. Referring\nto his own work in studying the rocks brought home by the \"Challenger\"\n(Renard's descriptions of these rocks are contained in the \"Challenger\nReports\". Mr Harker is supplementing these descriptions by a series of\npetrological memoirs on Darwin's specimens, the first of which appeared\nin the \"Geological Magazine\" for March, 1907.), he says:\n\n\"Je dus, en me livrant a ces recherches, suivre ligne par ligne les\ndivers chapitres des \"Observations geologiques\" consacrees aux iles de\nl'Atlantique, oblige que j'etais de comparer d'une maniere suivie les\nresultats auxquels j'etais conduit avec ceux de Darwin, qui servaient\nde controle a mes constatations. Je ne tardai pas a eprouver une vive\nadmiration pour ce chercheur qui, sans autre appareil que la loupe,\nsans autre reaction que quelques essais pyrognostiques, plus rarement\nquelques mesures au goniometre, parvenait a discerner la nature des\nagregats mineralogiques les plue complexes et les plus varies. Ce\ncoup d'oeil qui savait embrasser de si vastes horizons, penetre ici\nprofondement tous les details lithologiques. Avec quelle surete\net quelle exactitude la structure et la composition des roches ne\nsont'elles pas determinees, l'origne de ces masses minerales deduite et\nconfirmee par l'etude comparee des manifestations volcaniques d'autres\nregions; avec quelle science les relations entre les faits qu'il\ndecouvre et ceux signales ailleurs par ses devanciers ne sont'elles pas\netablies, et comme voici ebranlees les hypotheses regnantes, admises\nsans preuves, celles, par exemple, des crateres de soulevement et de la\ndifferenciation radicale des phenomenes plutoniques et volcaniques!\nCe qui acheve de donner a ce livre un incomparable merite, ce sont les\nidees nouvelles qui s'y trouvent en germe et jetees la comme au\nhasard ainsi qu'un superflu d'abondance intellectuelle inepuisable.\"\n(\"Observations Geologiques sur les Iles Volcaniques... \", Paris, 1902,\npages vi., vii.)\n\nWhile engaged in his study of banded lavas, Darwin was struck with the\nanalogy of their structure with that of glacier ice, and a note on the\nsubject, in the form of a letter addressed to Professor J.D. Forbes, was\npublished in the \"Proceedings of the Royal Society of Edinburgh\". (Vol.\nII. (1844-5), pages 17, 18.)\n\nFrom April, 1832, to September, 1835, Darwin had been occupied in\nexamining the coast or making inland journeys in the interior of the\nSouth American continent. Thus while eighteen months were devoted, at\nthe beginning and end of the voyage to the study of volcanic islands\nand coral-reefs, no less than three and a half years were given to South\nAmerican geology. The heavy task of dealing with the notes and specimens\naccumulated during that long period was left by Darwin to the last.\nFinishing the \"Volcanic Islands\" on February 14th, 1844, he, in July of\nthe same year, commenced the preparation of two important works which\nengaged him till near the end of the year 1846. The first was his\n\"Geological Observations on South America\", the second a recast of his\n\"Journal\", published under the short title of \"A Naturalist's Voyage\nround the World\".\n\nThe first of these works contains an immense amount of information\ncollected by the author under great difficulties and not unfrequently\nat considerable risk to life and health. No sooner had Darwin landed\nin South America than two sets of phenomena powerfully arrested his\nattention. The first of these was the occurrence of great masses of red\nmud containing bones and shells, which afforded striking evidence that\nthe whole continent had shared in a series of slow and gradual but\noften interrupted movements. The second related to the great masses of\ncrystalline rocks which, underlying the muds, cover so great a part of\nthe continent. Darwin, almost as soon as he landed, was struck by\nthe circumstance that the direction, as shown by his compass, of\nthe prominent features of these great crystalline rock-masses--their\ncleavage, master-joints, foliation and pegmatite veins--was the same as\nthe orientation described by Humboldt (whose works he had so carefully\nstudied) on the west of the same great continent.\n\nThe first five chapters of the book on South America were devoted to\nformations of recent date and to the evidence collected on the east and\nwest coasts of the continent in regard to those grand earth-movements,\nsome of which could be shown to have been accompanied by\nearthquake-shocks. The fossil bones, which had given him the first hint\nconcerning the mutability of species, had by this time been studied and\ndescribed by comparative anatomists, and Darwin was able to elaborate\nmuch more fully the important conclusion that the existing fauna of\nSouth America has a close analogy with that of the period immediately\npreceding our own.\n\nThe remaining three chapters of the book dealt with the metamorphic and\nplutonic rocks, and in them Darwin announced his important conclusions\nconcerning the relations of cleavage and foliation, and on the close\nanalogy of the latter structure with the banding found in rock-masses\nof igneous origin. With respect to the first of these conclusions, he\nreceived the powerful support of Daniel Sharpe, who in the years\n1852 and 1854 published two papers on the structure of the Scottish\nHighlands, supplying striking confirmation of the correctness of\nDarwin's views. Although Darwin's and Sharpe's conclusions were\ncontested by Murchison and other geologists, they are now universally\naccepted. In his theory concerning the origin of foliation, Darwin had\nbeen to some extent anticipated by Scrope, but he supplied many facts\nand illustrations leading to the gradual acceptance of a doctrine which,\nwhen first enunciated, was treated with neglect, if not with contempt.\n\nThe whole of this volume on South American geology is crowded with the\nrecords of patient observations and suggestions of the greatest value;\nbut, as Darwin himself saw, it was a book for the working geologist and\n\"caviare to the general.\" Its author, indeed, frequently expressed\nhis sense of the \"dryness\" of the book; he even says \"I long hesitated\nwhether I would publish it or not,\" and he wrote to Leonard Horner \"I am\nastonished that you should have had the courage to go right through my\nbook.\" (\"M.L.\" II. page 221.)\n\nFortunately the second book, on which Darwin was engaged at this time,\nwas of a very different character. His \"Journal\", almost as he had\nwritten it on board ship, with facts and observations fresh in his mind,\nhad been published in 1839 and attracted much attention. In 1845, he\nsays, \"I took much pains in correcting a new edition,\" and the work\nwhich was commenced in April, 1845, was not finished till August of\nthat year. The volume contains a history of the voyage with \"a sketch\nof those observations in Natural History and Geology, which I think will\npossess some interest for the general reader.\" It is not necessary\nto speak of the merits of this scientific classic. It became a\ngreat favourite with the general public--having passed through many\neditions--it was, moreover, translated into a number of different\nlanguages. Darwin was much gratified by these evidences of popularity,\nand naively remarks in his \"Autobiography\", \"The success of this my\nfirst literary child tickles my vanity more than that of any of my other\nbooks\" (\"L.L.\" I. page 80.)--and this was written after the \"Origin of\nSpecies\" had become famous!\n\nIn Darwin's letters there are many evidences that his labours during\nthese ten years devoted to the working out of the geological results\nof the voyage often made many demands on his patience and indomitable\ncourage. Most geologists have experience of the contrast between the\npleasures felt when wielding the hammer in the field, and the duller\nlabour of plying the pen in the study. But in Darwin's case, innumerable\ninterruptions from sickness and other causes, and the oft-deferred hope\nof reaching the end of his task were not the only causes operating to\nmake the work irksome. The great project, which was destined to become\nthe crowning achievement of his life, was now gradually assuming more\ndefinite shape, and absorbing more of his time and energies.\n\nNevertheless, during all this period, Darwin so far regarded his\ngeological pursuits as his PROPER \"work,\" that attention to other\nmatters was always spoken of by him as \"indulging in idleness.\" If at\nthe end of this period the world had sustained the great misfortune of\nlosing Darwin by death before the age of forty--and several times that\nevent seemed only too probable--he might have been remembered only as\na very able geologist of most advanced views, and a traveller who had\nwritten a scientific narrative of more than ordinary excellence!\n\nThe completion of the \"Geology of the 'Beagle'\" and the preparation of\na revised narrative of the voyage mark the termination of that period of\nfifteen years of Darwin's life during which geological studies were\nhis principal occupation. Henceforth, though his interest in geological\nquestions remained ever keen, biological problems engaged more and more\nof his attention to the partial exclusion of geology.\n\nThe eight years from October, 1846, to October, 1854, were mainly\ndevoted to the preparation of his two important monographs on the recent\nand fossil Cirripedia. Apart from the value of his description of the\nfossil forms, this work of Darwin's had an important influence on the\nprogress of geological science. Up to that time a practice had prevailed\nfor the student of a particular geological formation to take up the\ndescription of the plant and animal remains in it--often without\nhaving anything more than a rudimentary knowledge of the living forms\ncorresponding to them. Darwin in his monograph gave a very admirable\nillustration of the enormous advantage to be gained--alike for biology\nand geology--by undertaking the study of the living and fossil forms\nof a natural group of organisms in connection with one another. Of the\nadvantage of these eight years of work to Darwin himself, in preparing\nfor the great task lying before him, Huxley has expressed a very strong\nopinion indeed. (\"L.L.\" II. pages 247-48.)\n\nBut during these eight years of \"species work,\" Darwin found\nopportunities for not a few excursions into the field of geology. He\noccasionally attended the Geological Society, and, as we have already\nseen, read several papers there during this period. His friend, Dr\nHooker, then acting as botanist to the Geological Survey, was engaged\nin studying the Carboniferous flora, and many discussions on Palaezoic\nplants and on the origin of coal took place at this period. On this last\nsubject he felt the deepest interest and told Hooker, \"I shall never\nrest easy in Down churchyard without the problem be solved by some one\nbefore I die.\" (\"M.L.\" I. pages 63, 64.)\n\nAs at all times, conversations and letters with Lyell on every branch of\ngeological science continued with unabated vigour, and in spite of the\nabsorbing character of the work on the Cirripedes, time was found for\nall. In 1849 his friend Herschel induced him to supply a chapter of\nforty pages on Geology to the Admiralty \"Manual of Scientific Inquiry\"\nwhich he was editing. This is Darwin's single contribution to books of\nan \"educational\" kind. It is remarkable for its clearness and simplicity\nand attention to minute details. It may be read by the student of\nDarwin's life with much interest, for the directions he gives to an\nexplorer are without doubt those which he, as a self-taught geologist,\nproved to be serviceable during his life on the \"Beagle\".\n\nOn the completion of the Cirripede volumes, in 1854, Darwin was able to\ngrapple with the immense pile of MS. notes which he had accumulated\non the species question. The first sketch of 35 pages (1842), had been\nenlarged in 1844 into one of 230 pages ([The first draft of the \"Origin\"\nis being prepared for Press by Mr Francis Darwin and will be published\nby the Cambridge University Press this year (1909). A.C.S.]); but in\n1856 was commenced the work (never to be completed) which was designed\non a scale three or four times more extensive than that on which the\n\"Origin of Species\" was in the end written.\n\nIn drawing up those two masterly chapters of the \"Origin\", \"On\nthe Imperfection of the Geological Record,\" and \"On the Geological\nSuccession of Organic Beings\", Darwin had need of all the experience and\nknowledge he had been gathering during thirty years, the first half\nof which had been almost wholly devoted to geological study. The most\nenlightened geologists of the day found much that was new, and still\nmore that was startling from the manner of its presentation, in these\nwonderful essays. Of Darwin's own sense of the importance of the\ngeological evidence in any presentation of his theory a striking proof\nwill be found in a passage of the touching letter to his wife, enjoining\nthe publication of his sketch of 1844. \"In case of my sudden death,\"\nhe wrote, \"... the editor must be a geologist as well as a naturalist.\"\n(\"L.L.\" II. pages 16, 17.)\n\nIn spite of the numerous and valuable palaeontological discoveries made\nsince the publication of \"The Origin of Species\", the importance of the\nfirst of these two geological chapters is as great as ever. It still\nremains true that \"Those who believe that the geological record is in\nany degree perfect, will at once reject the theory\"--as indeed they must\nreject any theory of evolution. The striking passage with which Darwin\nconcludes this chapter--in which he compares the record of the rocks\nto the much mutilated volumes of a human history--remains as apt an\nillustration as it did when first written.\n\nAnd the second geological chapter, on the Succession of Organic\nBeings--though it has been strengthened in a thousand ways, by the\ndiscoveries concerning the pedigrees of the horse, the elephant and\nmany other aberrant types, though new light has been thrown even on the\norigin of great groups like the mammals, and the gymnosperms, though\nnot a few fresh links have been discovered in the chains of evidence,\nconcerning the order of appearance of new forms of life--we would\nnot wish to have re-written. Only the same line of argument could be\nadopted, though with innumerable fresh illustrations. Those who reject\nthe reasonings of this chapter, neither would they be persuaded if a\nlong and complete succession of \"ancestral forms\" could rise from the\ndead and pass in procession before them.\n\nAmong the geological discussions, which so frequently occupied Darwin's\nattention during the later years of his life, there was one concerning\nwhich his attitude seemed somewhat remarkable--I allude to his views\non \"the permanence of Continents and Ocean-basins.\" In a letter to Mr\nMellard Reade, written at the end of 1880, he wrote: \"On the whole, I\nlean to the side that the continents have since Cambrian times occupied\napproximately their present positions. But, as I have said, the question\nseems a difficult one, and the more it is discussed the better.\" (\"M.L.\"\nII. page 147.) Since this was written, the important contribution to the\nsubject by the late Dr W.T. Blanford (himself, like Darwin, a naturalist\nand geologist) has appeared in an address to the Geological Society in\n1890; and many discoveries, like that of Dr Woolnough in Fiji, have\nled to considerable qualifications of the generalisation that all the\nislands in the great ocean are wholly of volcanic or coral origin.\n\nI remember once expressing surprise to Darwin that, after the views\nwhich he had originated concerning the existence of areas of elevation\nand others of subsidence in the Pacific Ocean, and in face of the\nadmitted difficulty of accounting for the distribution of certain\nterrestrial animals and plants, if the land and sea areas had been\npermanent in position, he still maintained that theory. Looking at me\nwith a whimsical smile, he said: \"I have seen many of my old friends\nmake fools of themselves, by putting forward new theoretical views or\nrevising old ones, AFTER THEY WERE SIXTY YEARS OF AGE; so, long ago,\nI determined that on reaching that age I would write nothing more of a\nspeculative character.\"\n\nThough Darwin's letters and conversations on geology during these later\nyears were the chief manifestations of the interest he preserved in his\n\"old love,\" as he continued to call it, yet in the sunset of that active\nlife a gleam of the old enthusiasm for geology broke forth once more.\nThere can be no doubt that Darwin's inability to occupy himself with\nfield-work proved an insuperable difficulty to any attempt on his part\nto resume active geological research. But, as is shown by the series of\ncharming volumes on plant-life, Darwin had found compensation in making\npatient and persevering experiment take the place of enterprising and\nexact observation; and there was one direction in which he could indulge\nthe \"old love\" by employment of the new faculty.\n\nWe have seen that the earliest memoir written by Darwin, which was\npublished in full, was a paper \"On the Formation of Mould\" which was\nread at the Geological Society on November 1st, 1837, but did not appear\nin the \"Transactions\" of the Society till 1840, where it occupied four\nand a half quarto pages, including some supplementary matter, obtained\nlater, and a woodcut. This little paper was confined to observations\nmade in his uncle's fields in Staffordshire, where burnt clay, cinders,\nand sand were found to be buried under a layer of black earth, evidently\nbrought from below by earthworms, and to a recital of similar facts from\nScotland obtained through the agency of Lyell. The subsequent history\nof Darwin's work on this question affords a striking example of the\ntenacity of purpose with which he continued his enquiries on any subject\nthat interested him.\n\nIn 1842, as soon as he was settled at Down, he began a series of\nobservations on a foot-path and in his fields, that continued with\nintermissions during his whole life, and he extended his enquiries from\ntime to time to the neighbouring parks of Knole and Holwood. In 1844\nwe find him making a communication to the \"Gardener's Chronicle\" on the\nsubject. About 1870, his attention to the question was stimulated by the\ncircumstance that his niece (Miss L. Wedgwood) undertook to collect and\nweigh the worm-casts thrown up, during a whole year, on measured\nsquares selected for the purpose, at Leith Hill Place. He also obtained\ninformation from Professor Ramsay concerning observations made by him on\na pavement near his house in 1871. Darwin at this time began to realise\nthe great importance of the action of worms to the archaeologist. At\nan earlier date he appears to have obtained some information concerning\narticles found buried on the battle-field of Shrewsbury, and the old\nRoman town of Uriconium, near his early home; between 1871 and 1878 Mr\n(afterwards Lord) Farrer carried on a series of investigations at the\nRoman Villa discovered on his land at Abinger; Darwin's son William\nexamined for his father the evidence at Beaulieu Abbey, Brading,\nStonehenge and other localities in the neighbourhood of his home; his\nsons Francis and Horace were enlisted to make similar enquiries at\nChideock and Silchester; while Francis Galton contributed facts noticed\nin his walks in Hyde Park. By correspondence with Fritz Muller and Dr\nErnst, Darwin obtained information concerning the worm-casts found in\nSouth America; from Dr Kreft those of Australia; and from Mr Scott\nand Dr (afterwards Sir George) King, those of India; the last-named\ncorrespondent also supplied him with much valuable information obtained\nin the South of Europe. Help too was obtained from the memoirs on\nEarthworms published by Perrier in 1874 and van Hensen in 1877, while\nProfessor Ray Lankester supplied important facts with regard to their\nanatomy.\n\nWhen therefore the series of interesting monographs on plant-life had\nbeen completed, Darwin set to work in bringing the information that he\nhad gradually accumulated during forty-four years to bear on the subject\nof his early paper. He also utilised the skill and ingenuity he had\nacquired in botanical work to aid in the elucidation of many of the\ndifficulties that presented themselves. I well remember a visit which\nI paid to Down at this period. At the side of the little study stood\nflower-pots containing earth with worms, and, without interrupting\nour conversation, Darwin would from time to time lift the glass plate\ncovering a pot to watch what was going on. Occasionally, with a humorous\nsmile, he would murmur something about a book in another room, and slip\naway; returning shortly, without the book but with unmistakeable signs\nof having visited the snuff-jar outside. After working about a year at\nthe worms, he was able at the end of 1881 to publish the charming little\nbook--\"The Formation of Vegetable Mould through the Action of Worms,\nwith Observations on their Habits\". This was the last of his books, and\nits reception by reviewers and the public alike afforded the patient old\nworker no little gratification. Darwin's scientific career, which had\nbegun with geological research, most appropriately ended with a return\nto it.\n\nIt has been impossible to sketch the origin and influence of Darwin's\ngeological work without, at almost every step, referring to the part\nplayed by Lyell and the \"Principles of Geology\". Haeckel, in the\nchapters on Lyell and Darwin in his \"History of Creation\", and Huxley in\nhis striking essay \"On the Reception of the Origin of Species\" (\"L.L.\"\nII. pages 179-204.) have both strongly insisted on the fact that the\n\"Origin\" of Darwin was a necessary corollary to the \"Principles\" of\nLyell.\n\nIt is true that, in an earlier essay, Huxley had spoken of the doctrine\nof Uniformitarianism as being, in a certain sense, opposed to that of\nEvolution (Huxley's Address to the Geological Society, 1869. \"Collected\nEssays\", Vol. VIII. page 305, London, 1896.); but in his later years he\ntook up a very different and more logical position, and maintained\nthat \"Consistent uniformitarianism postulates evolution as much in the\norganic as in the inorganic world. The origin of a new species by other\nthan ordinary agencies would be a vastly greater 'catastrophe' than\nany of those which Lyell success fully eliminated from sober geological\nspeculation.\" (\"L.L.\" II. page 190.)\n\nHuxley's admiration for the \"Principles of Geology\", and his conviction\nof the greatness of the revolution of thought brought about by Lyell,\nwas almost as marked as in the case of Darwin himself. (See his Essay\non \"Science and Pseudo Science\". \"Collected Essays\", Vol. V. page 90,\nLondon, 1902.) He felt, however, as many others have done, that in one\nrespect the very success of Lyell's masterpiece has been the reason why\nits originality and influence have not been so fully recognised as they\ndeserved to be. Written as the book was before its author had arrived at\nthe age of thirty, no less than eleven editions of the \"Principles\"\nwere called for in his lifetime. With the most scrupulous care, Lyell,\ndevoting all his time and energies to the task of collecting and sifting\nall evidence bearing on the subjects of his work, revised and re-revised\nit; and as in each edition, eliminations, modifications, corrections,\nand additions were made, the book, while it increased in value as a\nstorehouse of facts, lost much of its freshness, vigour and charm as a\npiece of connected reasoning.\n\nDarwin undoubtedly realised this when he wrote concerning the\n\"Principles\", \"the first edition, my old true love, which I never\ndeserted for the later editions.\" (\"M.L.\" II. page 222.) Huxley once\ntold me that when, in later life, he read the first edition, he was both\nsurprised and delighted, feeling as if it were a new book to him. (I\nhave before me a letter which illustrates this feeling on Huxley's\npart. He had lamented to me that he did not possess a copy of the first\nedition of the \"Principles\", when, shortly afterwards, I picked up a\ndilapidated copy on a bookstall; this I had bound and sent to my old\nteacher and colleague. His reply is characteristic:\n\nOctober 8, 1884.\n\nMy Dear Judd,\n\nYou could not have made me a more agreeable present than the copy of the\nfirst edition of Lyell, which I find on my table. I have never been able\nto meet with the book, and your copy is, as the old woman said of her\nBible, \"the best of books in the best of bindings.\"\n\nEver yours sincerely,\n\nT.H. Huxley.\n\n(I cannot refrain from relating an incident which very strikingly\nexemplifies the affection for one another felt by Lyell and Huxley. In\nhis last illness, when confined to his bed, Lyell heard that Huxley was\nto lecture at the Royal Institution on the \"Results of the 'Challenger'\nexpedition\": he begged me to attend the lecture and bring him an account\nof it. Happening to mention this to Huxley, he at once undertook to\ngo to Lyell in my place, and he did so on the morning following his\nlecture. I shall never forget the look of gratitude on the face of the\ninvalid when he told me, shortly afterwards, how Huxley had sat by his\nbedside and \"repeated the whole lecture to him.\")\n\nDarwin's generous nature seems often to have made him experience a fear\nlest he should do less than justice to his \"dear old master,\" and to the\ninfluence that the \"Principles of Geology\" had in moulding his mind. In\n1845 he wrote to Lyell, \"I have long wished, not so much for your sake,\nas for my own feelings of honesty, to acknowledge more plainly than by\nmere reference, how much I geologically owe you. Those authors, however,\nwho like you, educate people's minds as well as teach them special\nfacts, can never, I should think, have full justice done them except by\nposterity, for the mind thus insensibly improved can hardly perceive\nits own upward ascent.\" (\"L.L.\" I. pages 337-8.) In another letter, to\nLeonard Horner, he says: \"I always feel as if my books came half out of\nLyell's brain, and that I never acknowledge this sufficiently.\" (\"M.L.\"\nII. page 117.) Darwin's own most favourite book, the \"Narrative of the\nVoyage\", was dedicated to Lyell in glowing terms; and in the \"Origin of\nSpecies\" he wrote of \"Lyell's grand work on the \"Principles of\nGeology\", which the future historian will recognise as having produced a\nrevolution in Natural Science.\" \"What glorious good that work has done\"\nhe fervently exclaims on another occasion. (\"L.L.\" I. page 342.)\n\nTo the very end of his life, as all who were in the habit of talking\nwith Darwin can testify, this sense of his indebtedness to Lyell\nremained with him. In his \"Autobiography\", written in 1876, the year\nafter Lyell's death, he spoke in the warmest terms of the value to him\nof the \"Principles\" while on the voyage and of the aid afforded to him\nby Lyell on his return to England. (\"L.L.\" I. page 62.) But the year\nbefore his own death, Darwin felt constrained to return to the subject\nand to place on record a final appreciation--one as honourable to the\nwriter as it is to his lost friend:\n\n\"I saw more of Lyell than of any other man, both before and after\nmy marriage. His mind was characterised, as it appeared to me, by\nclearness, caution, sound judgment, and a good deal of originality. When\nI made any remark to him on Geology, he never rested until he saw the\nwhole case clearly, and often made me see it more clearly than I had\ndone before. He would advance all possible objections to my suggestion,\nand even after these were exhausted would remain long dubious. A second\ncharacteristic was his hearty sympathy with the work of other scientific\nmen... His delight in science was ardent, and he felt the\nkeenest interest in the future progress of mankind. He was very\nkind-hearted... His candour was highly remarkable. He exhibited this by\nbecoming a convert to the Descent theory, though he had gained much fame\nby opposing Lamarck's views, and this after he had grown old.\"\n\n\"THE SCIENCE OF GEOLOGY IS ENORMOUSLY INDEBTED TO LYELL--MORE SO, AS I\nBELIEVE, THAN TO ANY OTHER MAN WHO EVER LIVED.\" (\"L.L.\" I. pages 71-2\n(the italics are mine.))\n\nThose who knew Lyell intimately will recognise the truth of the portrait\ndrawn by his dearest friend, and I believe that posterity will endorse\nDarwin's deliberate verdict concerning the value of his labours.\n\nIt was my own good fortune, to be brought into close contact with these\ntwo great men during the later years of their life, and I may perhaps be\npermitted to put on record the impressions made upon me during friendly\nintercourse with both.\n\nIn some respects, there was an extraordinary resemblance in their modes\nand habits of thought, between Lyell and Darwin; and this likeness was\nalso seen in their modesty, their deference to the opinion of younger\nmen, their enthusiasm for science, their freedom from petty jealousies\nand their righteous indignation for what was mean and unworthy in\nothers. But yet there was a difference. Both Lyell and Darwin were\ncautious, but perhaps Lyell carried his caution to the verge of\ntimidity. I think Darwin possessed, and Lyell lacked, what I can only\ndescribe by the theological term, \"faith--the substance of things hoped\nfor, the evidence of things not seen.\" Both had been constrained to feel\nthat the immutability of species could not be maintained. Both,\ntoo, recognised the fact that it would be useless to proclaim this\nconviction, unless prepared with a satisfactory alternative to what\nHuxley called \"the Miltonic hypothesis.\" But Darwin's conviction was so\nfar vital and operative that it sustained him while working unceasingly\nfor twenty-two years in collecting evidence bearing on the question,\ntill at last he was in the position of being able to justify that\nconviction to others.\n\nAnd yet Lyell's attitude--and that of Hooker, which was very\nsimilar--proved of inestimable service to science, as Darwin often\nacknowledged. One of the greatest merits of the \"Origin of Species\" is\nthat so many difficulties and objections are anticipated and fairly met;\nand this was to a great extent the result of the persistent and very\ncandid--if always friendly--criticism of Lyell and Hooker.\n\nI think the divergence of mental attitude in Lyell and Darwin must\nbe attributed to a difference in temperament, the evidence of which\nsometimes appears in a very striking manner in their correspondence.\nThus in 1838, while they were in the thick of the fight with\nthe Catastrophists of the Geological Society, Lyell wrote\ncharacteristically: \"I really find, when bringing up my Preliminary\nEssays in \"Principles\" to the science of the present day, so far as I\nknow it, that the great outline, and even most of the details, stand\nso uninjured, and in many cases they are so much strengthened by new\ndiscoveries, especially by yours, that we may begin to hope that\nthe great principles there insisted on will stand the test of new\ndiscoveries.\" (Lyell's \"Life, Letters and Journals\", Vol. II. page 44.)\nTo which the more youthful and impetuous Darwin replies: \"BEGIN TO HOPE:\nwhy the POSSIBILITY of a doubt has never crossed my mind for many a day.\nThis may be very unphilosophical, but my geological salvation is staked\non it... it makes me quite indignant that you should talk of HOPING.\"\n(\"L.L.\" I. page 296.)\n\nIt was not only Darwin's \"geological salvation\" that was at stake, when\nhe surrendered himself to his enthusiasm for an idea. To his firm faith\nin the doctrine of continuity we owe the \"Origin of Species\"; and while\nDarwin became the \"Paul\" of evolution, Lyell long remained the \"doubting\nThomas.\"\n\nMany must have felt like H.C. Watson when he wrote: \"How could Sir\nC. Lyell... for thirty years read, write, and think, on the subject of\nspecies AND THEIR SUCCESSION, and yet constantly look down the wrong\nroad!\" (\"L.L.\" II. page 227.) Huxley attributed this hesitation of Lyell\nto his \"profound antipathy\" to the doctrine of the \"pithecoid origin of\nman.\" (\"L.L.\" II. page 193.) Without denying that this had considerable\ninfluence (and those who knew Lyell and his great devotion to his wife\nand her memory, are aware that he and she felt much stronger convictions\nconcerning such subjects as the immortality of the soul than Darwin\nwas able to confess to) yet I think Darwin had divined the real\ncharacteristics of his friend's mind, when he wrote: \"He would advance\nall possible objections... AND EVEN AFTER THESE WERE EXHAUSTED, WOULD\nREMAIN LONG DUBIOUS.\"\n\nVery touching indeed was the friendship maintained to the end between\nthese two leaders of thought--free as their intercourse was from any\nsmallest trace of self-seeking or jealousy. When in 1874 I spent some\ntime with Lyell in his Forfarshire home, a communication from Darwin was\nalways an event which made a \"red-letter day,\" as Lyell used to say;\nand he gave me many indications in his conversation of how strongly he\nrelied upon the opinion of Darwin--more indeed than on the judgment\nof any other man--this confidence not being confined to questions of\nscience, but extending to those of morals, politics, and religion.\n\nI have heard those who knew Lyell only slightly, speak of his manners\nas cold and reserved. His complete absorption in his scientific work,\ncoupled with extreme short-sightedness, almost in the end amounting to\nblindness, may have permitted those having but a casual acquaintance\nwith him to accept such a view. But those privileged to know him\nintimately recognised the nobleness of his character and can realise\nthe justice and force of Hooker's words when he heard of his death: \"My\nloved, my best friend, for well nigh forty years of my life. The most\ngenerous sharer of my own and my family's hopes, joys and sorrows, whose\naffection for me was truly that of a father and brother combined.\"\n\nBut the strongest of all testimonies to the grandeur of Lyell's\ncharacter is the lifelong devotion to him of such a man as Darwin.\nBefore the two met, we find Darwin constantly writing of facts and\nobservations that he thinks \"will interest Mr Lyell\"; and when they came\ntogether the mutual esteem rapidly ripened into the warmest affection.\nBoth having the advantage of a moderate independence, permitting of an\nentire devotion of their lives to scientific research, they had much in\ncommon, and the elder man--who had already achieved both scientific and\nliterary distinction--was able to give good advice and friendly help\nto the younger one. The warmth of their friendship comes out very\nstrikingly in their correspondence. When Darwin first conceived the idea\nof writing a book on the \"species question,\" soon after his return from\nthe voyage, it was \"by following the example of Lyell in Geology\" that\nhe hoped to succeed (\"L.L.\" I. page 83.); when in 1844, Darwin had\nfinished his first sketch of the work, and, fearing that his life might\nnot be spared to complete his great undertaking, committed the care of\nit in a touching letter to his wife, it was his friend Lyell whom he\nnamed as her adviser and the possible editor of the book (\"L.L.\" II.\npages 17-18.); it was Lyell who, in 1856, induced Darwin to lay the\nfoundations of a treatise (\"L.L.\" I. page 84.) for which the author\nhimself selected the \"Principles\" as his model; and when the dilemma\narose from the receipt of Wallace's essay, it was to Lyell jointly with\nHooker that Darwin turned, not in vain, for advice and help.\n\nDuring the later years of his life, I never heard Darwin allude to his\nlost friend--and he did so very often--without coupling his name\nwith some term of affection. For a brief period, it is true, Lyell's\nexcessive caution when the \"Origin\" was published, seemed to try even\nthe patience of Darwin; but when \"the master\" was at last able to\ndeclare himself fully convinced, he was the occasion of more rejoicing\non the part of Darwin, than any other convert to his views. The latter\nwas never tired of talking of Lyell's \"magnanimity\" and asserted that,\n\"To have maintained in the position of a master, one side of a question\nfor thirty years, and then deliberately give it up, is a fact to which I\nmuch doubt whether the records of science offer a parallel.\" (\"L.L.\" II.\npages 229-30.)\n\nOf Darwin himself, I can safely affirm that I never knew anyone who\nhad met him, even for the briefest period, who was not charmed by his\npersonality. Who could forget the hearty hand-grip at meeting, the\ngentle and lingering pressure of the palm at parting, and above all\nthat winning smile which transformed his countenance--so as to make\nportraits, and even photographs, seem ever afterwards unsatisfying!\nLooking back, one is indeed tempted to forget the profoundness of the\nphilosopher, in recollection of the loveableness of the man.\n\n\n\n\nXIX. DARWIN'S WORK ON THE MOVEMENTS OF PLANTS. By Francis Darwin,\n\nHonorary Fellow of Christ's College, Cambridge.\n\n\nMy father's interest in plants was of two kinds, which may be roughly\ndistinguished as EVOLUTIONARY and PHYSIOLOGICAL. Thus in his purely\nevolutionary work, for instance in \"The Origin of Species\" and in his\nbook on \"Variation under Domestication\", plants as well as animals\nserved as material for his generalisations. He was largely dependent\non the work of others for the facts used in the evolutionary work, and\ndespised himself for belonging to the \"blessed gang\" of compilers. And\nhe correspondingly rejoiced in the employment of his wonderful power of\nobservation in the physiological problems which occupied so much of his\nlater life. But inasmuch as he felt evolution to be his life's work, he\nregarded himself as something of an idler in observing climbing plants,\ninsectivorous plants, orchids, etc. In this physiological work he was\nto a large extent urged on by his passionate desire to understand the\nmachinery of all living things. But though it is true that he worked\nat physiological problems in the naturalist's spirit of curiosity, yet\nthere was always present to him the bearing of his facts on the problem\nof evolution. His interests, physiological and evolutionary, were indeed\nso interwoven that they cannot be sharply separated. Thus his original\ninterest in the fertilisation of flowers was evolutionary. \"I was\nled\" (\"Life and Letters\", I. page 90.), he says, \"to attend to the\ncross-fertilisation of flowers by the aid of insects, from having come\nto the conclusion in my speculations on the origin of species, that\ncrossing played an important part in keeping specific forms constant.\"\nIn the same way the value of his experimental work on heterostyled\nplants crystalised out in his mind into the conclusion that the product\nof illegitimate unions are equivalent to hybrids--a conclusion of the\ngreatest interest from an evolutionary point of view. And again his work\n\"Cross and Self Fertilisation\" may be condensed to a point of view\nof great importance in reference to the meaning and origin of sexual\nreproduction. (See Professor Goebel's article in the present volume.)\n\nThe whole of his physiological work may be looked at as an illustration\nof the potency of his theory as an \"instrument for the extension of the\nrealm of natural knowledge.\" (Huxley in Darwin's \"Life and Letters.\" II.\npage 204.)\n\nHis doctrine of natural selection gave, as is well known, an impulse\nto the investigation of the use of organs--and thus created the great\nschool of what is known in Germany as Biology--a department of science\nfor which no English word exists except the rather vague term Natural\nHistory. This was especially the case in floral biology, and it is\ninteresting to see with what hesitation he at first expressed the value\nof his book on Orchids (\"Life and Letters\", III. page 254.), \"It will\nperhaps serve to illustrate how Natural History may be worked under the\nbelief of the modification of species\" (1861). And in 1862 he speaks\n(Loc. cit.) more definitely of the relation of his work to natural\nselection: \"I can show the meaning of some of the apparently meaningless\nridges (and) horns; who will now venture to say that this or that\nstructure is useless?\" It is the fashion now to minimise the value of\nthis class of work, and we even find it said by a modern writer that to\ninquire into the ends subserved by organs is not a scientific problem.\nThose who take this view surely forget that the structure of all living\nthings is, as a whole, adaptive, and that a knowledge of how the\npresent forms come to be what they are includes a knowledge of why\nthey survived. They forget that the SUMMATION of variations on which\ndivergence depends is under the rule of the environment considered as\na selective force. They forget that the scientific study of the\ninterdependence of organisms is only possible through a knowledge of the\nmachinery of the units. And that, therefore, the investigation of such\nwidely interesting subjects as extinction and distribution must include\na knowledge of function. It is only those who follow this line of\nwork who get to see the importance of minute points of structure and\nunderstand as my father did even in 1842, as shown in his sketch of the\n\"Origin\" (Now being prepared for publication.), that every grain of sand\ncounts for something in the balance. Much that is confidently stated\nabout the uselessness of different organs would never have been\nwritten if the naturalist spirit were commoner nowadays. This spirit\nis strikingly shown in my father's work on the movements of plants. The\ncircumstance that botanists had not, as a class, realised the interest\nof the subject accounts for the fact that he was able to gather such a\nrich harvest of results from such a familiar object as a twining plant.\nThe subject had been investigated by H. von Mohl, Palm, and Dutrochet,\nbut they failed not only to master the problem but (which here concerns\nus) to give the absorbing interest of Darwin's book to what they\ndiscovered.\n\nHis work on climbing plants was his first sustained piece of work on the\nphysiology of movement, and he remarks in 1864: \"This has been new sort\nof work for me.\" (\"Life and Letters\", III. page 315. He had, however,\nmade a beginning on the movements of Drosera.) He goes on to remark with\nsomething of surprise, \"I have been pleased to find what a capital guide\nfor observations a full conviction of the change of species is.\"\n\nIt was this point of view that enabled him to develop a broad conception\nof the power of climbing as an adaptation by means of which plants are\nenabled to reach the light. Instead of being compelled to construct a\nstem of sufficient strength to stand alone, they succeed in the struggle\nby making use of other plants as supports. He showed that the great\nclass of tendril- and root-climbers which do not depend on twining round\na pole, like a scarlet-runner, but on attaching themselves as they grow\nupwards, effect an economy. Thus a Phaseolus has to manufacture a stem\nthree feet in length to reach a height of two feet above the ground,\nwhereas a pea \"which had ascended to the same height by the aid of its\ntendrils, was but little longer than the height reached.\" (\"Climbing\nPlants\" (2nd edition 1875), page 193.)\n\nThus he was led on to the belief that TWINING is the more ancient form\nof climbing, and that tendril-climbers have been developed from twiners.\nIn accordance with this view we find LEAF-CLIMBERS, which may be looked\non as incipient tendril-bearers, occurring in the same genera with\nsimple twiners. (Loc. cit. page 195.) He called attention to the case\nof Maurandia semperflorens in which the young flower-stalks revolve\nspontaneously and are sensitive to a touch, but neither of these\nqualities is of any perceptible value to the species. This forced him to\nbelieve that in other young plants the rudiments of the faculty needed\nfor twining would be found--a prophecy which he made good in his \"Power\nof Movement\" many years later.\n\nIn \"Climbing Plants\" he did little more than point out the remarkable\nfact that the habit of climbing is widely scattered through the\nvegetable kingdom. Thus climbers are to be found in 35 out of the 59\nPhanerogamic Alliances of Lindley, so that \"the conclusion is forced\non our minds that the capacity of revolving (If a twining plant, e.g.\na hop, is observed before it has begun to ascend a pole, it will\nbe noticed that, owing to the curvature of the stem, the tip is not\nvertical but hangs over in a roughly horizontal position. If such a\nshoot is watched it will be found that if, for instance, it points\nto the north at a given hour, it will be found after a short interval\npointing north-east, then east, and after about two hours it will once\nmore be looking northward. The curvature of the stem depends on one side\ngrowing quicker than the opposite side, and the revolving movement,\ni.e. circumnutation, depends on the region of quickest growth creeping\ngradually round the stem from south through west to south again. Other\nplants, e.g. Phaseolus, revolve in the opposite direction.), on which\nmost climbers depend, is inherent, though undeveloped, in almost every\nplant in the vegetable kingdom.\" (\"Climbing Plants\", page 205.)\n\nIn the \"Origin\" (Edition I. page 427, Edition VI. page 374.) Darwin\nspeaks of the \"apparent paradox, that the very same characters are\nanalogical when one class or order is compared with another, but give\ntrue affinities when the members of the same class or order are compared\none with another.\" In this way we might perhaps say that the climbing\nof an ivy and a hop are analogical; the resemblance depending on the\nadaptive result rather than on community of blood; whereas the relation\nbetween a leaf-climber and a true tendril-bearer reveals descent. This\nparticular resemblance was one in which my father took especial delight.\nHe has described an interesting case occurring in the Fumariaceae.\n(\"Climbing Plants\", page 195.) \"The terminal leaflets of the\nleaf-climbing Fumaria officinalis are not smaller than the other\nleaflets; those of the leaf-climbing Adlumia cirrhosa are greatly\nreduced; those of Corydalis claviculata (a plant which may be\nindifferently called a leaf-climber or a tendril-bearer) are either\nreduced to microscopical dimensions or have their blades wholly aborted,\nso that this plant is actually in a state of transition; and finally in\nthe Dicentra the tendrils are perfectly characterized.\"\n\nIt is a remarkable fact that the quality which, broadly speaking, forms\nthe basis of the climbing habit (namely revolving nutation, otherwise\nknown as circumnutation) subserves two distinct ends. One of these is\nthe finding of a support, and this is common to twiners and tendrils.\nHere the value ends as far as tendril-climbers are concerned, but in\ntwiners Darwin believed that the act of climbing round a support is a\ncontinuation of the revolving movement (circumnutation). If we imagine a\nman swinging a rope round his head and if we suppose the rope to strike\na vertical post, the free end will twine round it. This may serve as\na rough model of twining as explained in the \"Movements and Habits\nof Climbing Plants\". It is on these points--the nature of revolving\nnutation and the mechanism of twining--that modern physiologists differ\nfrom Darwin. (See the discussion in Pfeffer's \"The Physiology of Plants\"\nEng. Tr. (Oxford, 1906), III. page 34, where the literature is given.\nAlso Jost, \"Vorlesungen uber Pflanzenphysiologie\", page 562, Jena,\n1904.)\n\nTheir criticism originated in observations made on a revolving shoot\nwhich is removed from the action of gravity by keeping the plant slowly\nrotating about a horizontal axis by means of the instrument known as a\nklinostat. Under these conditions circumnutation becomes irregular or\nceases altogether. When the same experiment is made with a plant which\nhas twined spirally up a stick, the process of climbing is checked and\nthe last few turns become loosened or actually untwisted. From this\nit has been argued that Darwin was wrong in his description of\ncircumnutation as an automatic change in the region of quickest growth.\nWhen the free end of a revolving shoot points towards the north there\nis no doubt that the south side has been elongating more than the north;\nafter a time it is plain from the shoot hanging over to the east that\nthe west side of the plant has grown most, and so on. This rhythmic\nchange of the position of the region of greatest growth Darwin ascribes\nto an unknown internal regulating power. Some modern physiologists,\nhowever, attempt to explain the revolving movement as due to a\nparticular form of sensitiveness to gravitation which it is not\nnecessary to discuss in detail in this place. It is sufficient for my\npurpose to point out that Darwin's explanation of circumnutation is\nnot universally accepted. Personally I believe that circumnutation is\nautomatic--is primarily due to internal stimuli. It is however in some\nway connected with gravitational sensitiveness, since the movement\nnormally occurs round a vertical line. It is not unnatural that,\nwhen the plant has no external stimulus by which the vertical can be\nrecognised, the revolving movement should be upset.\n\nVery much the same may be said of the act of twining, namely that most\nphysiologists refuse to accept Darwin's view (above referred to) that\ntwining is the direct result of circumnutation. Everyone must allow\nthat the two phenomena are in some way connected, since a plant\nwhich circumnutates clockwise, i.e. with the sun, twines in the same\ndirection, and vice versa. It must also be granted that geotropism has a\nbearing on the problem, since all plants twine upwards, and cannot twine\nalong a horizontal support. But how these two factors are combined, and\nwhether any (and if so what) other factors contribute, we cannot say.\nIf we give up Darwin's explanation, we must at the same time say with\nPfeffer that \"the causes of twining are... unknown.\" (\"The Physiology of\nPlants\", Eng. Tr. (Oxford, 1906), III. page 37.)\n\nLet us leave this difficult question and consider some other points made\nout in the progress of the work on climbing plants. One result of what\nhe called his \"niggling\" (\"Life and Letters\", III. page 312.) work on\ntendrils was the discovery of the delicacy of their sense of touch, and\nthe rapidity of their movement. Thus in a passion-flower tendril, a bit\nof platinum wire weighing 1.2 mg. produced curvature (\"Climbing\nPlants\", page 171.), as did a loop of cotton weighing 2 mg. Pfeffer\n(\"Untersuchungen a.d. Bot. Inst. z. Tubingen\", Bd. I. 1881-85, page\n506.), however, subsequently found much greater sensitiveness: thus\nthe tendril of Sicyos angulatus reacted to 0.00025 mg., but this only\noccurred when the delicate rider of cottonwool fibre was disturbed by\nthe wind. The same author expanded and explained in a most interesting\nway the meaning of Darwin's observation that tendrils are not stimulated\nto movement by drops of water resting on them. Pfeffer showed that\nDIRTY water containing minute particles of clay in suspension acts as a\nstimulus. He also showed that gelatine acts like pure water; if a smooth\nglass rod is coated with a 10 per cent solution of gelatine and is then\napplied to a tendril, no movement occurs in spite of the fact that the\ngelatine is solid when cold. Pfeffer (\"Physiology\", Eng. Tr. III.\npage 52. Pfeffer has pointed out the resemblance between the contact\nirritability of plants and the human sense of touch. Our skin is not\nsensitive to uniform pressure such as is produced when the finger\nis dipped into mercury (Tubingen \"Untersuchungen\", I. page 504.)\ngeneralises the result in the statement that the tendril has a special\nform of irritability and only reacts to \"differences of pressure or\nvariations of pressure in contiguous... regions.\" Darwin was especially\ninterested in such cases of specialised irritability. For instance in\nMay, 1864, he wrote to Asa Gray (\"Life and Letters\", III. page 314.)\ndescribing the tendrils of Bignonia capreolata, which \"abhor a simple\nstick, do not much relish rough bark, but delight in wool or moss.\"\nHe received, from Gray, information as to the natural habitat of the\nspecies, and finally concluded that the tendrils \"are specially adapted\nto climb trees clothed with lichens, mosses, or other such productions.\"\n(\"Climbing Plants\", page 102.)\n\nTendrils were not the only instance discovered by Darwin of delicacy\nof touch in plants. In 1860 he had already begun to observe Sundew\n(Drosera), and was full of astonishment at its behaviour. He wrote to\nSir Joseph Hooker (\"Life and Letters\", III. page 319.): \"I have been\nworking like a madman at Drosera. Here is a fact for you which is\ncertain as you stand where you are, though you won't believe it, that a\nbit of hair 1/78000 of one grain in weight placed on gland, will cause\nONE of the gland-bearing hairs of Drosera to curve inwards.\" Here again\nPfeffer (Pfeffer in \"Untersuchungen a. d. Bot. Inst. z. Tubingen\",\nI. page 491.) has, as in so many cases, added important facts to my\nfather's observations. He showed that if the leaf of Drosera is entirely\nfreed from such vibrations as would reach it if observed on an ordinary\ntable, it does not react to small weights, so that in fact it was the\nvibration of the minute fragment of hair on the gland that produced\nmovement. We may fancifully see an adaptation to the capture of\ninsects--to the dancing of a gnat's foot on the sensitive surface.\n\nDarwin was fond of telling how when he demonstrated the sensitiveness\nof Drosera to Mr Huxley and (I think) to Sir John Burdon Sanderson, he\ncould perceive (in spite of their courtesy) that they thought the whole\nthing a delusion. And the story ended with his triumph when Mr Huxley\ncried out, \"It IS moving.\"\n\nDarwin's work on tendrils has led to some interesting investigations on\nthe mechanisms by which plants perceive stimuli. Thus Pfeffer (Tubingen\n\"Untersuchungen\" I. page 524.) showed that certain epidermic cells\noccurring in tendrils are probably organs of touch. In these cells the\nprotoplasm burrows as it were into cavities in the thickness of the\nexternal cell-walls and thus comes close to the surface, being separated\nfrom an object touching the tendril merely by a very thin layer of\ncell-wall substance. Haberlandt (\"Physiologische Pflanzenanatomie\",\nEdition III. Leipzig, 1904. \"Sinnesorgane im Pflanzenreich\", Leipzig,\n1901, and other publications.) has greatly extended our knowledge of\nvegetable structure in relation to mechanical stimulation. He defines a\nsense-organ as a contrivance by which the DEFORMATION or forcible change\nof form in the protoplasm--on which mechanical stimulation depends--is\nrendered rapid and considerable in amplitude (\"Sinnesorgane\", page 10).\nHe has shown that in certain papillose and bristle-like contrivances,\nplants possess such sense-organs; and moreover that these contrivances\nshow a remarkable similarity to corresponding sense-organs in animals.\n\nHaberlandt and Nemec (\"Ber. d. Deutschen bot. Gesellschaft\", XVIII.\n1900. See F. Darwin, Presidential Address to Section K, British\nAssociation, 1904.) published independently and simultaneously a\ntheory of the mechanism by which plants are orientated in relation\nto gravitation. And here again we find an arrangement identical in\nprinciple with that by which certain animals recognise the vertical,\nnamely the pressure of free particles on the irritable wall of a cavity.\nIn the higher plants, Nemec and Haberlandt believe that special loose\nand freely movable starch-grains play the part of the otoliths or\nstatoliths of the crustacea, while the protoplasm lining the cells in\nwhich they are contained corresponds to the sensitive membrane lining\nthe otocyst of the animal. What is of special interest in our present\nconnection is that according to this ingenious theory (The original\nconception was due to Noll (\"Heterogene Induction\", Leipzig, 1892), but\nhis view differed in essential points from those here given.) the\nsense of verticality in a plant is a form of contact-irritability. The\nvertical position is distinguished from the horizontal by the fact that,\nin the latter case, the loose starch-grains rest on the lateral walls\nof the cells instead of on the terminal walls as occurs in the normal\nupright position. It should be added that the statolith theory is\nstill sub judice; personally I cannot doubt that it is in the main a\nsatisfactory explanation of the facts.\n\nWith regard to the RAPIDITY of the reaction of tendrils, Darwin records\n(\"Climbing Plants\", page 155. Others have observed movement after about\n6\".) that a Passion-Flower tendril moved distinctly within 25 seconds of\nstimulation. It was this fact, more than any other, that made him doubt\nthe current explanation, viz. that the movement is due to unequal\ngrowth on the two sides of the tendril. The interesting work of Fitting\n(Pringsheim's \"Jahrb.\" XXXVIII. 1903, page 545.) has shown, however,\nthat the primary cause is not (as Darwin supposed) contraction on the\nconcave, but an astonishingly rapid increase in growth-rate on the\nconvex side.\n\nOn the last page of \"Climbing Plants\" Darwin wrote: \"It has often been\nvaguely asserted that plants are distinguished from animals by not\nhaving the power of movement. It should rather be said that plants\nacquire and display this power only when it is of some advantage to\nthem.\"\n\nHe gradually came to realise the vividness and variety of vegetable\nlife, and that a plant like an animal has capacities of behaving in\ndifferent ways under different circumstances, in a manner that may be\ncompared to the instinctive movements of animals. This point of view is\nexpressed in well-known passages in the \"Power of Movement\". (\"The Power\nof Movement in Plants\", 1880, pages 571-3.) \"It is impossible not to be\nstruck with the resemblance between the... movements of plants and many\nof the actions performed unconsciously by the lower animals.\" And\nagain, \"It is hardly an exaggeration to say that the tip of the\nradicle... having the power of directing the movements of the adjoining\nparts, acts like the brain of one of the lower animals; the brain being\nseated within the anterior end of the body, receiving impressions from\nthe sense-organs, and directing the several movements.\"\n\nThe conception of a region of perception distinct from a region of\nmovement is perhaps the most fruitful outcome of his work on the\nmovements of plants. But many years before its publication, viz. in\n1861, he had made out the wonderful fact that in the Orchid Catasetum\n(\"Life and Letters\", III. page 268.) the projecting organs or antennae\nare sensitive to a touch, and transmit an influence \"for more than one\ninch INSTANTANEOUSLY,\" which leads to the explosion or violent ejection\nof the pollinia. And as we have already seen a similar transmission of\na stimulus was discovered by him in Sundew in 1860, so that in 1862 he\ncould write to Hooker (\"Life and Letters\", III. page 321.): \"I cannot\navoid the conclusion, that Drosera possesses matter at least in some\ndegree analogous in constitution and function to nervous matter.\" I\npropose in what follows to give some account of the observations on\nthe transmission of stimuli given in the \"Power of Movement\". It is\nimpossible within the space at my command to give anything like a\ncomplete account of the matter, and I must necessarily omit all mention\nof much interesting work. One well-known experiment consisted in putting\nopaque caps on the tips of seedling grasses (e.g. oat and canary-grass)\nand then exposing them to light from one side. The difference, in the\namount of curvature towards the light, between the blinded and\nunblinded specimens, was so great that it was concluded that the\nlight-sensitiveness resided exclusively in the tip. The experiment\nundoubtedly proves that the sensitiveness is much greater in the tip\nthan elsewhere, and that there is a transmission of stimulus from the\ntip to the region of curvature. But Rothert (Rothert, Cohn's \"Beitrage\",\nVII. 1894.) has conclusively proved that the basal part where the\ncurvature occurs is also DIRECTLY sensitive to light. He has shown,\nhowever, that in other grasses (Setaria, Panicum) the cotyledon is the\nonly part which is sensitive, while the hypocotyl, where the movement\noccurs, is not directly sensitive.\n\nIt was however the question of the localisation of the gravitational\nsense in the tip of the seedling root or radicle that aroused most\nattention, and it was on this question that a controversy arose which\nhas continued to the present day.\n\nThe experiment on which Darwin's conclusion was based consisted simply\nin cutting off the tip, and then comparing the behaviour of roots so\ntreated with that of normal specimens. An uninjured root when placed\nhorizontally regains the vertical by means of a sharp downward\ncurve; not so a decapitated root which continues to grow more or less\nhorizontally. It was argued that this depends on the loss of an organ\nspecialised for the perception of gravity, and residing in the tip of\nthe root; and the experiment (together with certain important variants)\nwas claimed as evidence of the existence of such an organ.\n\nIt was at once objected that the amputation of the tip might check\ncurvature by interfering with longitudinal growth, on the distribution\nof which curvature depends. This objection was met by showing that an\ninjury, e.g. splitting the root longitudinally (See F. Darwin, \"Linnean\nSoc. Journal (Bot).\" XIX. 1882, page 218.), which does not remove the\ntip, but seriously checks growth, does not prevent geotropism. This\nwas of some interest in another and more general way, in showing that\ncurvature and longitudinal growth must be placed in different categories\nas regards the conditions on which they depend.\n\nAnother objection of a much more serious kind was that the amputation\nof the tip acts as a shock. It was shown by Rothert (See his excellent\nsummary of the subject in \"Flora\" 1894 (Erganzungsband), page 199.) that\nthe removal of a small part of the cotyledon of Setaria prevents the\nplant curving towards the light, and here there is no question of\nremoving the sense-organ since the greater part of the sensitive\ncotyledon is intact. In view of this result it was impossible to rely on\nthe amputations performed on roots as above described.\n\nAt this juncture a new and brilliant method originated in Pfeffer's\nlaboratory. (See Pfeffer, \"Annals of Botany\", VIII. 1894, page 317, and\nCzapek, Pringsheim's \"Jahrb.\" XXVII. 1895, page 243.) Pfeffer and Czapek\nshowed that it is possible to bend the root of a lupine so that, for\ninstance, the supposed sense-organ at the tip is vertical while the\nmotile region is horizontal. If the motile region is directly sensitive\nto gravity the root ought to curve downwards, but this did not occur: on\nthe contrary it continued to grow horizontally. This is precisely what\nshould happen if Darwin's theory is the right one: for if the tip is\nkept vertical, the sense-organ is in its normal position and receives no\nstimulus from gravitation, and therefore can obviously transmit none to\nthe region of curvature. Unfortunately this method did not convince the\nbotanical world because some of those who repeated Czapek's experiment\nfailed to get his results.\n\nCzapek (\"Berichte d. Deutsch. bot. Ges.\" XV. 1897, page 516, and\nnumerous subsequent papers. English readers should consult Czapek in the\n\"Annals of Botany\", XIX. 1905, page 75.) has devised another interesting\nmethod which throws light on the problem. He shows that roots, which\nhave been placed in a horizontal position and have therefore been\ngeotropically stimulated, can be distinguished by a chemical test from\nvertical, i.e. unstimulated roots. The chemical change in the root can\nbe detected before any curvature has occurred and must therefore be a\nsymptom of stimulation, not of movement. It is particularly interesting\nto find that the change in the root, on which Czapek's test depends,\ntakes place in the tip, i.e. in the region which Darwin held to be the\ncentre for gravitational sensitiveness.\n\nIn 1899 I devised a method (F. Darwin, \"Annals of Botany\", XIII. 1899,\npage 567.) by which I sought to prove that the cotyledon of Setaria is\nnot only the organ for light-perception, but also for gravitation. If\na seedling is supported horizontally by pushing the apical part\n(cotyledon) into a horizontal tube, the cotyledon will, according to\nmy supposition, be stimulated gravitationally and a stimulus will be\ntransmitted to the basal part of the stem (hypocotyl) causing it to\nbend. But this curvature merely raises the basal end of the seedling,\nthe sensitive cotyledon remains horizontal, imprisoned in its tube; it\nwill therefore be continually stimulated and will continue to transmit\ninfluences to the bending region, which should therefore curl up into a\nhelix or corkscrew-like form,--and this is precisely what occurred.\n\nI have referred to this work principally because the same method was\napplied to roots by Massart (Massart, \"Mem. Couronnes Acad. R. Belg.\"\nLXII. 1902.) and myself (F. Darwin, \"Linnean Soc. Journ.\" XXXV. 1902,\npage 266.) with a similar though less striking result. Although these\nresearches confirmed Darwin's work on roots, much stress cannot be laid\non them as there are several objections to them, and they are not easily\nrepeated.\n\nThe method which--as far as we can judge at present--seems likely\nto solve the problem of the root-tip is most ingenious and is due to\nPiccard. (Pringsheim's \"Jahrb.\" XL. 1904, page 94.)\n\nAndrew Knight's celebrated experiment showed that roots react to\ncentrifugal force precisely as they do to gravity. So that if a bean\nroot is fixed to a wheel revolving rapidly on a horizontal axis, it\ntends to curve away from the centre in the line of a radius of the\nwheel. In ordinary demonstrations of Knight's experiment the seed is\ngenerally fixed so that the root is at right angles to a radius, and as\nfar as convenient from the centre of rotation. Piccard's experiment is\narranged differently. (A seed is depicted below a horizontal dotted\nline AA, projecting a root upwards.) The root is oblique to the axis\nof rotation, and the extreme tip projects beyond that axis. Line AA\nrepresents the axis of rotation, T is the tip of the root just above the\nline AA, and B is the region just below line AA in which curvature takes\nplace. If the motile region B is directly sensitive to gravitation (and\nis the only part which is sensitive) the root will curve (down and away\nfrom the vertical) away from the axis of rotation, just as in Knight's\nexperiment. But if the tip T is alone sensitive to gravitation the\nresult will be exactly reversed, the stimulus originating in T and\nconveyed to B will produce curvature (up towards the vertical). We may\nthink of the line AA as a plane dividing two worlds. In the lower one\ngravity is of the earthly type and is shown by bodies falling and roots\ncurving downwards: in the upper world bodies fall upwards and roots\ncurve in the same direction. The seedling is in the lower world, but its\ntip containing the supposed sense-organ is in the strange world where\nroots curve upwards. By observing whether the root bends up or down we\ncan decide whether the impulse to bend originates in the tip or in the\nmotile region.\n\nPiccard's results showed that both curvatures occurred and he\nconcluded that the sensitive region is not confined to the tip. (Czapek\n(Pringsheim's \"Jahrb.\" XXXV. 1900, page 362) had previously given\nreasons for believing that, in the root, there is no sharp line of\nseparation between the regions of perception and movement.)\n\nHaberlandt (Pringsheim's \"Jahrb.\" XLV. 1908, page 575.) has recently\nrepeated the experiment with the advantage of better apparatus and more\nexperience in dealing with plants, and has found as Piccard did that\nboth the tip and the curving region are sensitive to gravity, but with\nthe important addition that the sensitiveness of the tip is much greater\nthan that of the motile region. The case is in fact similar to that of\nthe oat and canary-grass. In both instances my father and I were wrong\nin assuming that the sensitiveness is confined to the tip, yet there\nis a concentration of irritability in that region and transmission of\nstimulus is as true for geotropism as it is for heliotropism. Thus after\nnearly thirty years the controversy of the root-tip has apparently ended\nsomewhat after the fashion of the quarrels at the \"Rainbow\" in\n\"Silas Marner\"--\"you're both right and you're both wrong.\" But the\n\"brain-function\" of the root-tip at which eminent people laughed in\nearly days turns out to be an important part of the truth. (By using\nPiccard's method I have succeeded in showing that the gravitational\nsensitiveness of the cotyledon of Sorghum is certainly much greater than\nthe sensitiveness of the hypocotyl--if indeed any such sensitiveness\nexists. See Wiesner's \"Festschrift\", Vienna, 1908.)\n\nAnother observation of Darwin's has given rise to much controversy.\n(\"Power of Movement\", page 133.) If a minute piece of card is fixed\nobliquely to the tip of a root some influence is transmitted to the\nregion of curvature and the root bends away from the side to which\nthe card was attached. It was thought at the time that this proved the\nroot-tip to be sensitive to contact, but this is not necessarily the\ncase. It seems possible that the curvature is a reaction to the injury\ncaused by the alcoholic solution of shellac with which the cards were\ncemented to the tip. This agrees with the fact given in the \"Power of\nMovement\" that injuring the root-tip on one side, by cutting or burning\nit, induced a similar curvature. On the other hand it was shown that\ncurvature could be produced in roots by cementing cards, not to the\nnaked surface of the root-tip, but to pieces of gold-beaters skin\napplied to the root; gold-beaters skin being by itself almost without\neffect. But it must be allowed that, as regards touch, it is not clear\nhow the addition of shellac and card can increase the degree of contact.\nThere is however some evidence that very close contact from a solid\nbody, such as a curved fragment of glass, produces curvature: and this\nmay conceivably be the explanation of the effect of gold-beaters skin\ncovered with shellac. But on the whole it is perhaps safer to classify\nthe shellac experiments with the results of undoubted injury rather than\nwith those of contact.\n\nAnother subject on which a good deal of labour was expended is the sleep\nof leaves, or as Darwin called it their NYCTITROPIC movement. He showed\nfor the first time how widely spread this phenomenon is, and attempted\nto give an explanation of the use to the plant of the power of sleeping.\nHis theory was that by becoming more or less vertical at night the\nleaves escape the chilling effect of radiation. Our method of testing\nthis view was to fix some of the leaves of a sleeping plant so that they\nremained horizontal at night and therefore fully exposed to radiation,\nwhile their fellows were partly protected by assuming the nocturnal\nposition. The experiments showed clearly that the horizontal leaves were\nmore injured than the sleeping, i.e. more or less vertical, ones. It may\nbe objected that the danger from cold is very slight in warm countries\nwhere sleeping plants abound. But it is quite possible that a lowering\nof the temperature which produces no visible injury may nevertheless\nbe hurtful by checking the nutritive processes (e.g. translocation of\ncarbohydrates), which go on at night. Stahl (\"Bot. Zeitung\", 1897, page\n81.) however has ingeniously suggested that the exposure of the leaves\nto radiation is not DIRECTLY hurtful because it lowers the temperature\nof the leaf, but INDIRECTLY because it leads to the deposition of dew on\nthe leaf-surface. He gives reasons for believing that dew-covered leaves\nare unable to transpire efficiently, and that the absorption of mineral\nfood-material is correspondingly checked. Stahl's theory is in no way\ndestructive of Darwin's, and it is possible that nyctitropic leaves are\nadapted to avoid the indirect as well as the direct results of cooling\nby radiation.\n\nIn what has been said I have attempted to give an idea of some of the\ndiscoveries brought before the world in the \"Power of Movement\" (In 1881\nProfessor Wiesner published his \"Das Bewegungsvermogen der Pflanzen\",\na book devoted to the criticism of \"The Power of Movement in Plants\". A\nletter to Wiesner, published in \"Life and Letters\", III. page 336, shows\nDarwin's warm appreciation of his critic's work, and of the spirit in\nwhich it is written.) and of the subsequent history of the problems.\nWe must now pass on to a consideration of the central thesis of the\nbook,--the relation of circumnutation to the adaptive curvatures of\nplants.\n\nDarwin's view is plainly stated on pages 3-4 of the \"Power of Movement\".\nSpeaking of circumnutation he says, \"In this universally present\nmovement we have the basis or groundwork for the acquirement, according\nto the requirements of the plant, of the most diversified movements.\"\nHe then points out that curvatures such as those towards the light or\ntowards the centre of the earth can be shown to be exaggerations of\ncircumnutation in the given directions. He finally points out that\nthe difficulty of conceiving how the capacities of bending in definite\ndirections were acquired is diminished by his conception. \"We know that\nthere is always movement in progress, and its amplitude, or direction,\nor both, have only to be modified for the good of the plant in relation\nwith internal or external stimuli.\"\n\nIt may at once be allowed that the view here given has not been accepted\nby physiologists. The bare fact that circumnutation is a general\nproperty of plants (other than climbing species) is not generally\nrejected. But the botanical world is no nearer to believing in the\ntheory of reaction built on it.\n\nIf we compare the movements of plants with those of the lower animals we\nfind a certain resemblance between the two. According to Jennings (H.S.\nJennings, \"The Behavior of the Lower Animals\". Columbia U. Press, N.Y.\n1906.) a Paramoecium constantly tends to swerve towards the aboral side\nof its body owing to certain peculiarities in the set and power of\nits cilia. But the tendency to swim in a circle, thus produced, is\nneutralised by the rotation of the creature about its longitudinal\naxis. Thus the direction of the swerves IN RELATION TO THE PATH of the\norganism is always changing, with the result that the creature moves in\nwhat approximates to a straight line, being however actually a spiral\nabout the general line of progress. This method of motion is strikingly\nlike the circumnutation of a plant, the apex of which also describes a\nspiral about the general line of growth. A rooted plant obviously cannot\nrotate on its axis, but the regular series of curvatures of which its\ngrowth consists correspond to the aberrations of Paramoecium distributed\nregularly about its course by means of rotation. (In my address to the\nBiological Section of the British Association at Cardiff (1891) I\nhave attempted to show the connection between circumnutation and\nRECTIPETALITY, i.e. the innate capacity of growing in a straight line.)\nJust as a plant changes its direction of growth by an exaggeration of\none of the curvature-elements of which circumnutation consists, so\ndoes a Paramoecium change its course by the accentuation of one of\nthe deviations of which its path is built. Jennings has shown that the\ninfusoria, etc., react to stimuli by what is known as the \"method of\ntrial.\" If an organism swims into a region where the temperature is too\nhigh or where an injurious substance is present, it changes its course.\nIt then moves forward again, and if it is fortunate enough to escape the\ninfluence, it continues to swim in the given direction. If however its\nchange of direction leads it further into the heated or poisonous region\nit repeats the movement until it emerges from its difficulties. Jennings\nfinds in the movements of the lower organisms an analogue with what\nis known as pain in conscious organisms. There is certainly this much\nresemblance that a number of quite different sub-injurious agencies\nproduce in the lower organisms a form of reaction by the help of which\nthey, in a partly fortuitous way, escape from the threatening element\nin their environment. The higher animals are stimulated in a parallel\nmanner to vague and originally purposeless movements, one of which\nremoves the discomfort under which they suffer, and the organism finally\nlearns to perform the appropriate movement without going through the\ntentative series of actions.\n\nI am tempted to recognise in circumnutation a similar groundwork of\ntentative movements out of which the adaptive ones were originally\nselected by a process rudely representative of learning by experience.\n\nIt is, however, simpler to confine ourselves to the assumption that\nthose plants have survived which have acquired through unknown causes\nthe power of reacting in appropriate ways to the external stimuli of\nlight, gravity, etc. It is quite possible to conceive this occurring in\nplants which have no power of circumnutating--and, as already pointed\nout, physiologists do as a fact neglect circumnutation as a factor in\nthe evolution of movements. Whatever may be the fate of Darwin's theory\nof circumnutation there is no doubt that the research he carried out\nin support of, and by the light of, this hypothesis has had a powerful\ninfluence in guiding the modern theories of the behaviour of plants.\nPfeffer (\"The Physiology of Plants\", Eng. Tr. III. page 11.), who more\nthan any one man has impressed on the world a rational view of the\nreactions of plants, has acknowledged in generous words the great value\nof Darwin's work in the same direction. The older view was that, for\ninstance, curvature towards the light is the direct mechanical result of\nthe difference of illumination on the lighted and shaded surfaces of the\nplant. This has been proved to be an incorrect explanation of the\nfact, and Darwin by his work on the transmission of stimuli has greatly\ncontributed to the current belief that stimuli act indirectly. Thus we\nnow believe that in a root and a stem the mechanism for the perception\nof gravitation is identical, but the resulting movements are different\nbecause the motor-irritabilities are dissimilar in the two cases. We\nmust come back, in fact, to Darwin's comparison of plants to animals.\nIn both there is perceptive machinery by which they are made delicately\nalive to their environment, in both the existing survivors are those\nwhose internal constitution has enabled them to respond in a beneficial\nway to the disturbance originating in their sense-organs.\n\n\n\n\nXX. THE BIOLOGY OF FLOWERS. By K. Goebel, Ph.D.\n\nProfessor of Botany in the University of Munich.\n\n\nThere is scarcely any subject to which Darwin devoted so much time and\nwork as to his researches into the biology of flowers, or, in other\nwords, to the consideration of the question to what extent the\nstructural and physiological characters of flowers are correlated with\ntheir function of producing fruits and seeds. We know from his own words\nwhat fascination these studies possessed for him. We repeatedly find,\nfor example, in his letters expressions such as this:--\"Nothing in my\nlife has ever interested me more than the fertilisation of such plants\nas Primula and Lythrum, or again Anacamptis or Listera.\" (\"More Letters\nof Charles Darwin\", Vol. II. page 419.)\n\nExpressions of this kind coming from a man whose theories exerted an\nepoch-making influence, would be unintelligible if his researches into\nthe biology of flowers had been concerned only with records of isolated\nfacts, however interesting these might be. We may at once take it\nfor granted that the investigations were undertaken with the view of\nfollowing up important problems of general interest, problems which are\nbriefly dealt with in this essay.\n\nDarwin published the results of his researches in several papers and in\nthree larger works, (i) \"On the various contrivances by which British\nand Foreign Orchids are fertilised by insects\" (First edition, London,\n1862; second edition, 1877; popular edition, 1904.) (ii) \"The effects of\nCross and Self fertilisation in the vegetable kingdom\" (First edition,\n1876; second edition, 1878). (iii) \"The different forms of Flowers on\nplants of the same species\" (First edition, 1877; second edition, 1880).\n\nAlthough the influence of his work is considered later, we may here\npoint out that it was almost without a parallel; not only does it\ninclude a mass of purely scientific observations, but it awakened\ninterest in very wide circles, as is shown by the fact that we find the\nresults of Darwin's investigations in floral biology universally quoted\nin school books; they are even willingly accepted by those who, as\nregards other questions, are opposed to Darwin's views.\n\nThe works which we have mentioned are, however, not only of special\ninterest because of the facts they contribute, but because of the MANNER\nin which the facts are expressed. A superficial reader seeking merely\nfor catch-words will, for instance, probably find the book on cross and\nself-fertilisation rather dry because of the numerous details which\nit contains: it is, indeed, not easy to compress into a few words the\ngeneral conclusions of this volume. But on closer examination, we cannot\nbe sufficiently grateful to the author for the exactness and objectivity\nwith which he enables us to participate in the scheme of his researches.\nHe never tries to persuade us, but only to convince us that his\nconclusions are based on facts; he always gives prominence to such facts\nas appear to be in opposition to his opinions,--a feature of his work in\naccordance with a maxim which he laid down:--\"It is a golden rule,\nwhich I try to follow, to put every fact which is opposed to one's\npreconceived opinion in the strongest light.\" (\"More Letters\", Vol. II.\npage 324.)\n\nThe result of this method of presentation is that the works mentioned\nabove represent a collection of most valuable documents even for those\nwho feel impelled to draw from the data other conclusions than those of\nthe author. Each investigation is the outcome of a definite question, a\n\"preconceived opinion,\" which is either supported by the facts or\nmust be abandoned. \"How odd it is that anyone should not see that all\nobservation must be for or against some view if it is to be of any\nservice!\" (Ibid. Vol. I. page 195.)\n\nThe points of view which Darwin had before him were principally the\nfollowing. In the first place the proof that a large number of the\npeculiarities in the structure of flowers are not useless, but of the\ngreatest significance in pollination must be of considerable importance\nfor the interpretation of adaptations; \"The use of each trifling detail\nof structure is far from a barren search to those who believe in natural\nselection.\" (\"Fertilisation of Orchids\" (1st edition), page 351; (2nd\nedition 1904) page 286.) Further, if these structural relations are\nshown to be useful, they may have been acquired because from the many\nvariations which have occurred along different lines, those have been\npreserved by natural selection \"which are beneficial to the organism\nunder the complex and ever-varying conditions of life.\" (Ibid. page\n351.) But in the case of flowers there is not only the question of\nadaptation to fertilisation to be considered. Darwin, indeed,\nsoon formed the opinion which he has expressed in the following\nsentence,--\"From my own observations on plants, guided to a certain\nextent by the experience of the breeders of animals, I became convinced\nmany years ago that it is a general law of nature that flowers are\nadapted to be crossed, at least occasionally, by pollen from a distinct\nplant.\" (\"Cross and Self fertilisation\" (1st edition), page 6.)\n\nThe experience of animal breeders pointed to the conclusion that\ncontinual in-breeding is injurious. If this is correct, it raises the\nquestion whether the same conclusion holds for plants. As most flowers\nare hermaphrodite, plants afford much more favourable material than\nanimals for an experimental solution of the question, what results\nfollow from the union of nearly related sexual cells as compared with\nthose obtained by the introduction of new blood. The answer to this\nquestion must, moreover, possess the greatest significance for the\ncorrect understanding of sexual reproduction in general.\n\nWe see, therefore, that the problems which Darwin had before him in his\nresearches into the biology of flowers were of the greatest importance,\nand at the same time that the point of view from which he attacked the\nproblems was essentially a teleological one.\n\nWe may next inquire in what condition he found the biology of flowers at\nthe time of his first researches, which were undertaken about the year\n1838. In his autobiography he writes,--\"During the summer of 1839,\nand, I believe, during the previous summer, I was led to attend to the\ncross-fertilisation of flowers by the aid of insects, from having come\nto the conclusion in my speculations on the origin of species, that\ncrossing played an important part in keeping specific forms constant.\"\n(\"The Life and Letters of Charles Darwin\", Vol. I. page 90, London,\n1888.) In 1841 he became acquainted with Sprengel's work: his researches\ninto the biology of flowers were thus continued for about forty years.\n\nIt is obvious that there could only be a biology of flowers after it had\nbeen demonstrated that the formation of seeds and fruit in the flower\nis dependent on pollination and subsequent fertilisation. This proof\nwas supplied at the end of the seventeenth century by R.J. Camerarius\n(1665-1721). He showed that normally seeds and fruits are developed only\nwhen the pollen reaches the stigma. The manner in which this happens was\nfirst thoroughly investigated by J.G. Kolreuter (1733-1806 (Kolreuter,\n\"Vorlaufige Nachricht von einigen das Geschlecht der Planzen\nbetreffenden Versuchen und Beobachtungen\", Leipzig, 1761; with three\nsupplements, 1763-66. Also, \"Mem. de l'acad. St Petersbourg\", Vol. XV.\n1809.)), the same observer to whom we owe the earliest experiments in\nhybridisation of real scientific interest. Kolreuter mentioned that\npollen may be carried from one flower to another partly by wind and\npartly by insects. But he held the view, and that was, indeed, the\nnatural assumption, that self-fertilisation usually occurs in a flower,\nin other words that the pollen of a flower reaches the stigma of\nthe same flower. He demonstrated, however, certain cases in which\ncross-pollination occurs, that is in which the pollen of another flower\nof the same species is conveyed to the stigma. He was familiar with the\nphenomenon, exhibited by numerous flowers, to which Sprengel afterwards\napplied the term Dichogamy, expressing the fact that the anthers and\nstigmas of a flower often ripen at different times, a peculiarity\nwhich is now recognised as one of the commonest means of ensuring\ncross-pollination.\n\nWith far greater thoroughness and with astonishing power of observation\nC.K. Sprengel (1750-1816) investigated the conditions of pollination of\nflowers. Darwin was introduced by that eminent botanist Robert Brown to\nSprengel's then but little appreciated work,--\"Das entdeckte Geheimniss\nder Natur im Bau und in der Befruchtung der Blumen\" (Berlin, 1793); this\nis by no means the least service to Botany rendered by Robert Brown.\n\nSprengel proceeded from a naive teleological point of view. He firmly\nbelieved \"that the wise Author of nature had not created a single hair\nwithout a definite purpose.\" He succeeded in demonstrating a number of\nbeautiful adaptations in flowers for ensuring pollination; but his work\nexercised but little influence on his contemporaries and indeed for a\nlong time after his death. It was through Darwin that Sprengel's work\nfirst achieved a well deserved though belated fame. Even such botanists\nas concerned themselves with researches into the biology of flowers\nappear to have formerly attached much less value to Sprengel's work\nthan it has received since Darwin's time. In illustration of this we may\nquote C.F. Gartner whose name is rightly held in the highest esteem as\nthat of one of the most eminent hybridologists. In his work \"Versuche\nund Beobachtungen uder die Befruchtungsorgane der vollkommeneren\nGewachse und uber die naturliche und kunstliche Befruchtung durch den\neigenen Pollen\" he also deals with flower-pollination. He recognised the\naction of the wind, but he believed, in spite of the fact that he\nboth knew and quoted Kolreuter and Sprengel, that while insects assist\npollination, they do so only occasionally, and he held that insects are\nresponsible for the conveyance of pollen; thorough investigations\nwould show \"that a very small proportion of the plants included in this\ncategory require this assistance in their native habitat.\" (Gartner,\n\"Versucher und Beobachtungen... \", page 335, Stuttgart, 1844.) In the\nmajority of plants self-pollination occurs.\n\nSeeing that even investigators who had worked for several decades at\nfertilisation-phenomena had not advanced the biology of flowers beyond\nthe initial stage, we cannot be surprised that other botanists followed\nto even a less extent the lines laid down by Kolreuter and Sprengel.\nThis was in part the result of Sprengel's supernatural teleology and in\npart due to the fact that his book appeared at a time when other lines\nof inquiry exerted a dominating influence.\n\nAt the hands of Linnaeus systematic botany reached a vigorous\ndevelopment, and at the beginning of the nineteenth century the anatomy\nand physiology of plants grew from small beginnings to a flourishing\nbranch of science. Those who concerned themselves with flowers\nendeavoured to investigate their development and structure or the most\nminute phenomena connected with fertilisation and the formation of the\nembryo. No room was left for the extension of the biology of flowers on\nthe lines marked out by Kolreuter and Sprengel. Darwin was the first to\ngive new life and a deeper significance to this subject, chiefly\nbecause he took as his starting-point the above-mentioned problems, the\nimportance of which is at once admitted by all naturalists.\n\nThe further development of floral biology by Darwin is in the first\nplace closely connected with the book on the fertilisation of Orchids.\nIt is noteworthy that the title includes the sentence,--\"and on the good\neffects of intercrossing.\"\n\nThe purpose of the book is clearly stated in the introduction:--\"The\nobject of the following work is to show that the contrivances by which\nOrchids are fertilised, are as varied and almost as perfect as any of\nthe most beautiful adaptations in the animal kingdom; and, secondly,\nto show that these contrivances have for their main object the\nfertilisation of each flower by the pollen of another flower.\"\n(\"Fertilisation of Orchids\", page 1.) Orchids constituted a particularly\nsuitable family for such researches. Their flowers exhibit a striking\nwealth of forms; the question, therefore, whether the great variety\nin floral structure bears any relation to fertilisation (In the older\nbotanical literature the word fertilisation is usually employed in cases\nwhere POLLINATION is really in question: as Darwin used it in this sense\nit is so used here.) must in this case possess special interest.\n\nDarwin succeeded in showing that in most of the orchids examined\nself-fertilisation is either an impossibility, or, under natural\nconditions, occurs only exceptionally. On the other hand these plants\npresent a series of extraordinarily beautiful and remarkable adaptations\nwhich ensure the transference of pollen by insects from one flower to\nanother. It is impossible to describe adequately in a few words the\nwealth of facts contained in the Orchid book. A few examples may,\nhowever, be quoted in illustration of the delicacy of the observations\nand of the perspicuity employed in interpreting the facts.\n\nThe majority of orchids differ from other seed plants (with the\nexception of the Asclepiads) in having no dust-like pollen. The pollen,\nor more correctly, the pollen-tetrads, remain fastened together as\nclub-shaped pollinia usually borne on a slender pedicel. At the base of\nthe pedicel is a small viscid disc by which the pollinium is attached\nto the head or proboscis of one of the insects which visit the flower.\nDarwin demonstrated that in Orchis and other flowers the pedicel of\nthe pollinium, after its removal from the anther, undergoes a curving\nmovement. If the pollinium was originally vertical, after a time it\nassumed a horizontal position. In the latter position, if the insect\nvisited another flower, the pollinium would exactly hit the sticky\nstigmatic surface and thus effect fertilisation. The relation between\nthe behaviour of the viscid disc and the secretion of nectar by the\nflower is especially remarkable. The flowers possess a spur which in\nsome species (e.g. Gymnadenia conopsea, Platanthera bifolia, etc.)\ncontains honey (nectar), which serves as an attractive bait for insects,\nbut in others (e.g. our native species of Orchis) the spur is empty.\nDarwin held the opinion, confirmed by later investigations, that in the\ncase of flowers without honey the insects must penetrate the wall of the\nnectarless spurs in order to obtain a nectar-like substance. The glands\nbehave differently in the nectar-bearing and in the nectarless flowers.\nIn the former they are so sticky that they at once adhere to the body of\nthe insect; in the nectarless flowers firm adherence only occurs after\nthe viscid disc has hardened. It is, therefore, adaptively of value\nthat the insects should be detained longer in the nectarless flowers (by\nhaving to bore into the spur),--than in flowers in which the nectar is\nfreely exposed. \"If this relation, on the one hand, between the viscid\nmatter requiring some little time to set hard, and the nectar being so\nlodged that moths are delayed in getting it; and, on the other hand,\nbetween the viscid matter being at first as viscid as ever it will\nbecome, and the nectar lying all ready for rapid suction, be accidental,\nit is a fortunate accident for the plant. If not accidental, and I\ncannot believe it to be accidental, what a singular case of adaptation!\"\n(\"Fertilisation of Orchids\" (1st edition), page 53.)\n\nAmong exotic orchids Catasetum is particularly remarkable. One and the\nsame species bears different forms of flowers. The species known as\nCatasetum tridentatum has pollinia with very large viscid discs;\non touching one of the two filaments (antennae) which occur on the\ngynostemium of the flower the pollinia are shot out to a fairly long\ndistance (as far as 1 metre) and in such manner that they alight on the\nback of the insect, where they are held. The antennae have, moreover,\nacquired an importance, from the point of view of the physiology of\nstimulation, as stimulus-perceiving organs. Darwin had shown that it is\nonly a touch on the antennae that causes the explosion, while contact,\nblows, wounding, etc. on other places produce no effect. This form of\nflower proved to be the male. The second form, formerly regarded as\na distinct species and named Monachanthus viridis, is shown to be the\nfemale flower. The anthers have only rudimentary pollinia and do not\nopen; there are no antennae, but on the other hand numerous seeds\nare produced. Another type of flower, known as Myanthus barbatus, was\nregarded by Darwin as a third form: this was afterwards recognised\nby Rolfe (Rolfe, R.A. \"On the sexual forms of Catasetum with special\nreference to the researches of Darwin and others,\" \"Journ. Linn. Soc.\"\nVol. XXVII. (Botany), 1891, pages 206-225.) as the male flower\nof another species, Catasetum barbatum Link, an identification in\naccordance with the discovery made by Cruger in Trinidad that it always\nremains sterile.\n\nDarwin had noticed that the flowers of Catasetum do not secrete nectar,\nand he conjectured that in place of it the insects gnaw a tissue in\nthe cavity of the labellum which has a \"slightly sweet, pleasant and\nnutritious taste.\" This conjecture as well as other conclusions drawn by\nDarwin from Catasetum have been confirmed by Cruger--assuredly the best\nproof of the acumen with which the wonderful floral structure of this\n\"most remarkable of the Orchids\" was interpretated far from its native\nhabitat.\n\nAs is shown by what we have said about Catasetum, other problems in\naddition to those concerned with fertilisation are dealt with in the\nOrchid book. This is especially the case in regard to flower morphology.\nThe scope of flower morphology cannot be more clearly and better\nexpressed than by these words: \"He will see how curiously a flower may\nbe moulded out of many separate organs--how perfect the cohesion of\nprimordially distinct parts may become,--how organs may be used for\npurposes widely different from their proper function,--how other organs\nmay be entirely suppressed, or leave mere useless emblems of their\nformer existence.\" (\"Fertilisation of Orchids\", page 289.)\n\nIn attempting, from this point of view, to refer the floral structure\nof orchids to their original form, Darwin employed a much more thorough\nmethod than that of Robert Brown and others. The result of this was the\nproduction of a considerable literature, especially in France, along\nthe lines suggested by Darwin's work. This is the so-called anatomical\nmethod, which seeks to draw conclusions as to the morphology of the\nflower from the course of the vascular bundles in the several parts. (He\nwrote in one of his letters, \"... the destiny of the whole human race is\nas nothing to the course of vessels of orchids\" (\"More Letters\", Vol.\nII. page 275.) Although the interpretation of the orchid flower given\nby Darwin has not proved satisfactory in one particular point--the\ncomposition of the labellum--the general results have received universal\nassent, namely \"that all Orchids owe what they have in common to descent\nfrom some monocotyledonous plant, which, like so many other plants of\nthe same division, possessed fifteen organs arranged alternately three\nwithin three in five whorls.\" (\"Fertilisation of Orchids\" (1st edition),\npage 307.) The alterations which their original form has undergone have\npersisted so far as they were found to be of use.\n\nWe see also that the remarkable adaptations of which we have given some\nexamples are directed towards cross-fertilisation. In only a few of\nthe orchids investigated by Darwin--other similar cases have since been\ndescribed--was self-fertilisation found to occur regularly or usually.\nThe former is the case in the Bee Ophrys (Ophrys apifera), the mechanism\nof which greatly surprised Darwin. He once remarked to a friend that one\nof the things that made him wish to live a few thousand years was his\ndesire to see the extinction of the Bee Ophrys, an end to which he\nbelieved its self-fertilising habit was leading. (\"Life and Letters\",\nVol. III. page 276 (footnote).) But, he wrote, \"the safest conclusion,\nas it seems to me, is, that under certain unknown circumstances, and\nperhaps at very long intervals of time, one individual of the Bee Ophrys\nis crossed by another.\" (\"Fertilisation of Orchids\" page 71.)\n\nIf, on the one hand, we remember how much more sure self-fertilisation\nwould be than cross-fertilisation, and, on the other hand, if we call to\nmind the numerous contrivances for cross-fertilisation, the\nconclusion is naturally reached that \"it is an astonishing fact that\nself-fertilisation should not have been an habitual occurrence. It\napparently demonstrates to us that there must be something injurious in\nthe process. Nature thus tells us, in the most emphatic manner, that she\nabhors perpetual self-fertilisation... For may we not further infer as\nprobable, in accordance with the belief of the vast majority of the\nbreeders of our domestic productions, that marriage between near\nrelations is likewise in some way injurious, that some unknown great\ngood is derived from the union of individuals which have been kept\ndistinct for many generations?\" (Ibid., page 359.)\n\nThis view was supported by observations on plants of other families,\ne.g. Papilionaceae; it could, however, in the absence of experimental\nproof, be regarded only as a \"working hypothesis.\"\n\nAll adaptations to cross-pollination might also be of use simply because\nthey made pollination possible when for any reason self-pollination had\nbecome difficult or impossible. Cross-pollination would, therefore, be\nof use, not as such, but merely as a means of pollination in general;\nit would to some extent serve as a remedy for a method unsuitable in\nitself, such as a modification standing in the way of self-pollination,\nand on the other hand as a means of increasing the chance of pollination\nin the case of flowers in which self-pollination was possible, but which\nmight, in accidental circumstances, be prevented. It was, therefore,\nvery important to obtain experimental proof of the conclusion to which\nDarwin was led by the belief of the majority of breeders and by the\nevidence of the widespread occurrence of cross-pollination and of the\nremarkable adaptations thereto.\n\nThis was supplied by the researches which are described in the two other\nworks named above. The researches on which the conclusions rest had, in\npart at least, been previously published in separate papers: this is the\ncase as regards the heterostyled plants. The discoveries which Darwin\nmade in the course of his investigations of these plants belong to the\nmost brilliant in biological science.\n\nThe case of Primula is now well known. C.K. Sprengel and others were\nfamiliar with the remarkable fact that different individuals of the\nEuropean species of Primula bear differently constructed flowers; some\nplants possess flowers in which the styles project beyond the stamens\nattached to the corolla-tube (long-styled form), while in others the\nstamens are inserted above the stigma which is borne on a short style\n(short-styled form). It has been shown by Breitenbach that both forms of\nflower may occur on the same plant, though this happens very rarely. An\nanalogous case is occasionally met with in hybrids, which bear flowers\nof different colour on the same plant (e.g. Dianthus caryophyllus).\nDarwin showed that the external differences are correlated with others\nin the structure of the stigma and in the nature of the pollen.\nThe long-styled flowers have a spherical stigma provided with large\nstigmatic papillae; the pollen grains are oblong and smaller than those\nof the short-styled flowers. The number of the seeds produced is smaller\nand the ovules larger, probably also fewer in number. The short-styled\nflowers have a smooth compressed stigma and a corolla of somewhat\ndifferent form; they produce a greater number of seeds.\n\nThese different forms of flowers were regarded as merely a case of\nvariation, until Darwin showed \"that these heterostyled plants are\nadapted for reciprocal fertilisation; so that the two or three forms,\nthough all are hermaphrodites, are related to one another almost\nlike the males and females of ordinary unisexual animals.\" (\"Forms\nof Flowers\" (1st edition), page 2.) We have here an example of\nhermaphrodite flowers which are sexually different. There are essential\ndifferences in the manner in which fertilisation occurs. This may\nbe effected in four different ways; there are two legitimate and two\nillegitimate types of fertilisation. The fertilisation is legitimate\nif pollen from the long-styled flowers reaches the stigma of the\nshort-styled form or if pollen of the short-styled flowers is brought\nto the stigma of the long-styled flower, that is the organs of the\nsame length of the two different kinds of flower react on one\nanother. Illegitimate fertilisation is represented by the two kinds of\nself-fertilisation, also by cross-fertilisation, in which the pollen of\nthe long-styled form reaches the stigma of the same type of flower and,\nsimilarly, by cross-pollination in the case of the short-styled flowers.\n\nThe applicability of the terms legitimate and illegitimate depends, on\nthe one hand, upon the fact that insects which visit the different forms\nof flowers pollinate them in the manner suggested; the pollen of the\nshort-styled flowers adhere to that part of the insect's body which\ntouches the stigma of the long-styled flower and vice versa. On the\nother hand, it is based also on the fact that experiment shows that\nartificial pollination produces a very different result according as\nthis is legitimate or illegitimate; only the legitimate union ensures\ncomplete fertility, the plants thus produced being stronger than those\nwhich are produced illegitimately.\n\nIf we take 100 as the number of flowers which produce seeds as the\nresult of legitimate fertilisation, we obtain the following numbers from\nillegitimate fertilisation:\n\nPrimula officinalis (P. veris) (Cowslip)... 69 Primula elatior\n(Oxlip).................... 27 Primula acaulis (P. vulgaris)\n(Primrose)... 60\n\nFurther, the plants produced by the illegitimate method of fertilisation\nshowed, e.g. in P. officinalis, a decrease in fertility in later\ngenerations, sterile pollen and in the open a feebler growth. (Under\nvery favourable conditions (in a greenhouse) the fertility of the plants\nof the fourth generation increases--a point, which in view of various\ntheoretical questions, deserves further investigation.) They behave in\nfact precisely in the same way as hybrids between species of different\ngenera. This result is important, \"for we thus learn that the difficulty\nin sexually uniting two organic forms and the sterility of their\noffspring, afford no sure criterion of so-called specific distinctness\"\n(\"Forms of Flowers\", page 242): the relative or absolute sterility\nof the illegitimate unions and that of their illegitimate descendants\ndepend exclusively on the nature of the sexual elements and on their\ninability to combine in a particular manner. This functional difference\nof sexual cells is characteristic of the behaviour of hybrids as of the\nillegitimate unions of heterostyled plants. The agreement becomes\neven closer if we regard the Primula plants bearing different forms of\nflowers not as belonging to a systematic entity or \"species,\" but as\nincluding several elementary species. The legitimately produced plants\nare thus true hybrids (When Darwin wrote in reference to the different\nforms of heterostyled plants, \"which all belong to the same species\nas certainly as do the two sexes of the same species\" (\"Cross and\nSelf fertilisation\", page 466), he adopted the term species in a\ncomprehensive sense. The recent researches of Bateson and Gregory (\"On\nthe inheritance of Heterostylism in Primula\"; \"Proc. Roy. Soc.\" Ser. B,\nVol. LXXVI. 1905, page 581) appear to me also to support the view that\nthe results of illegitimate crossing of heterostyled Primulas correspond\nwith those of hybridisation. The fact that legitimate pollen effects\nfertilisation, even if illegitimate pollen reaches the stigma a short\ntime previously, also points to this conclusion. Self-pollination in the\ncase of the short-styled form, for example, is not excluded. In spite\nof this, the numerical proportion of the two forms obtained in the open\nremains approximately the same as when the pollination was exclusively\nlegitimate, presumably because legitimate pollen is prepotent.), with\nwhich their behaviour in other respects, as Darwin showed, presents so\nclose an agreement. This view receives support also from the fact that\ndescendants of a flower fertilised illegitimately by pollen from another\nplant with the same form of flower belong, with few exceptions, to the\nsame type as that of their parents. The two forms of flower, however,\nbehave differently in this respect. Among 162 seedlings of the\nlong-styled illegitimately pollinated plants of Primula officinalis,\nincluding five generations, there were 156 long-styled and only six\nshort-styled forms, while as the result of legitimate fertilisation\nnearly half of the offspring were long-styled and half short-styled. The\nshort-styled illegitimately pollinated form gave five long-styled\nand nine short-styled; the cause of this difference requires further\nexplanation. The significance of heterostyly, whether or not we now\nregard it as an arrangement for the normal production of hybrids, is\ncomprehensively expressed by Darwin: \"We may feel sure that plants have\nbeen rendered heterostyled to ensure cross-fertilisation, for we now\nknow that a cross between the distinct individuals of the same species\nis highly important for the vigour and fertility of the offspring.\"\n(\"Forms of Flowers\", page 258.) If we remember how important the\ninterpretation of heterostyly has become in all general problems as,\nfor example, those connected with the conditions of the formation of\nhybrids, a fact which was formerly overlooked, we can appreciate how\nDarwin was able to say in his autobiography: \"I do not think anything in\nmy scientific life has given me so much satisfaction as making out the\nmeaning of the structure of these plants.\" (\"Life and Letters\", Vol. I.\npage 91.)\n\nThe remarkable conditions represented in plants with three kinds of\nflowers, such as Lythrum and Oxalis, agree in essentials with those\nin Primula. These cannot be considered in detail here; it need only be\nnoted that the investigation of these cases was still more laborious.\nIn order to establish the relative fertility of the different unions in\nLythrum salicaria 223 different fertilisations were made, each flower\nbeing deprived of its male organs and then dusted with the appropriate\npollen.\n\nIn the book containing the account of heterostyled plants other\nspecies are dealt with which, in addition to flowers opening normally\n(chasmogamous), also possess flowers which remain closed but are capable\nof producing fruit. These cleistogamous flowers afford a striking\nexample of habitual self-pollination, and H. von Mohl drew special\nattention to them as such shortly after the appearance of Darwin's\nOrchid book. If it were only a question of producing seed in the\nsimplest way, cleistogamous flowers would be the most conveniently\nconstructed. The corolla and frequently other parts of the flower are\nreduced; the development of the seed may, therefore, be accomplished\nwith a smaller expenditure of building material than in chasmogamous\nflowers; there is also no loss of pollen, and thus a smaller amount\nsuffices for fertilisation.\n\nAlmost all these plants, as Darwin pointed out, have also chasmogamous\nflowers which render cross-fertilisation possible. His view that\ncleistogamous flowers are derived from originally chasmogamous flowers\nhas been confirmed by more recent researches. Conditions of nutrition in\nthe broader sense are the factors which determine whether chasmogamous\nor cleistogamous flowers are produced, assuming, of course, that the\nplants in question have the power of developing both forms of flower.\nThe former may fail to appear for some time, but are eventually\ndeveloped under favourable conditions of nourishment. The belief of many\nauthors that there are plants with only cleistogamous flowers cannot\ntherefore be accepted as authoritative without thorough experimental\nproof, as we are concerned with extra-european plants for which it is\noften difficult to provide appropriate conditions in cultivation.\n\nDarwin sees in cleistogamous flowers an adaptation to a good supply of\nseeds with a small expenditure of material, while chasmogamous flowers\nof the same species are usually cross-fertilised and \"their offspring\nwill thus be invigorated, as we may infer from a wide-spread analogy.\"\n(\"Forms of Flowers\" (1st edition), page 341.) Direct proof in support of\nthis has hitherto been supplied in a few cases only; we shall often\nfind that the example set by Darwin in solving such problems as these by\nlaborious experiment has unfortunately been little imitated.\n\nAnother chapter of this book treats of the distribution of the sexes in\npolygamous, dioecious, and gyno-dioecious plants (the last term, now in\ncommon use, we owe to Darwin). It contains a number of important facts\nand discussions and has inspired the experimental researches of Correns\nand others.\n\nThe most important of Darwin's work on floral biology is, however, that\non cross and self-fertilisation, chiefly because it states the results\nof experimental investigations extending over many years. Only\nsuch experiments, as we have pointed out, could determine whether\ncross-fertilisation is in itself beneficial, and self-fertilisation\non the other hand injurious; a conclusion which a merely comparative\nexamination of pollination-mechanisms renders in the highest degree\nprobable. Later floral biologists have unfortunately almost entirely\nconfined themselves to observations on floral mechanisms. But there is\nlittle more to be gained by this kind of work than an assumption\nlong ago made by C.K. Sprengel that \"very many flowers have the sexes\nseparate and probably at least as many hermaphrodite flowers are\ndichogamous; it would thus appear that Nature was unwilling that any\nflower should be fertilised by its own pollen.\"\n\nIt was an accidental observation which inspired Darwin's experiments on\nthe effect of cross and self-fertilisation. Plants of Linaria vulgaris\nwere grown in two adjacent beds; in the one were plants produced by\ncross-fertilisation, that is, from seeds obtained after fertilisation\nby pollen of another plant of the same species; in the other grew plants\nproduced by self-fertilisation, that is from seed produced as the result\nof pollination of the same flower. The first were obviously superior to\nthe latter.\n\nDarwin was surprised by this observation, as he had expected a\nprejudicial influence of self-fertilisation to manifest itself after\na series of generations: \"I always supposed until lately that no\nevil effects would be visible until after several generations of\nself-fertilisation, but now I see that one generation sometimes suffices\nand the existence of dimorphic plants and all the wonderful contrivances\nof orchids are quite intelligible to me.\" (\"More Letters\", Vol. II. page\n373.)\n\nThe observations on Linaria and the investigations of the results of\nlegitimate and illegitimate fertilisation in heterostyled plants were\napparently the beginning of a long series of experiments. These were\nconcerned with plants of different families and led to results which are\nof fundamental importance for a true explanation of sexual reproduction.\n\nThe experiments were so arranged that plants were shielded from\ninsect-visits by a net. Some flowers were then pollinated with their own\npollen, others with pollen from another plant of the same species. The\nseeds were germinated on moist sand; two seedlings of the same age, one\nfrom a cross and the other from a self-fertilised flower, were selected\nand planted on opposite sides of the same pot. They grew therefore under\nidentical external conditions; it was thus possible to compare their\npeculiarities such as height, weight, fruiting capacity, etc. In other\ncases the seedlings were placed near to one another in the open and in\nthis way their capacity of resisting unfavourable external conditions\nwas tested. The experiments were in some cases continued to the tenth\ngeneration and the flowers were crossed in different ways. We see,\ntherefore, that this book also represents an enormous amount of most\ncareful and patient original work.\n\nThe general result obtained is that plants produced as the result of\ncross-fertilisation are superior, in the majority of cases, to those\nproduced as the result of self-fertilisation, in height, resistance to\nexternal injurious influences, and in seed-production.\n\nIpomoea purpurea may be quoted as an example. If we express the result\nof cross-fertilisation by 100, we obtain the following numbers for the\nfertilised plants.\n\n     Generation.   Height.    Number of seeds.\n\n     1             100: 76   100: 64\n     2             100: 79   -\n     3             100: 68   100: 94\n     4             100: 86   100: 94\n     5             100: 75   100: 89\n     6             100: 72   -\n     7             100: 81   -\n     8             100: 85   -\n     9             100: 79   100: 26 (Number of capsules)\n     10            100: 54   -\n\n\nTaking the average, the ratio as regards growth is 100:77. The\nconsiderable superiority of the crossed plants is apparent in the first\ngeneration and is not increased in the following generations; but there\nis some fluctuation about the average ratio. The numbers representing\nthe fertility of crossed and self-fertilised plants are more difficult\nto compare with accuracy; the superiority of the crossed plants is\nchiefly explained by the fact that they produce a much larger number\nof capsules, not because there are on the average more seeds in each\ncapsule. The ratio of the capsules was, e.g. in the third generation,\n100:38, that of the seeds in the capsules 100:94. It is also especially\nnoteworthy that in the self-fertilised plants the anthers were smaller\nand contained a smaller amount of pollen, and in the eighth generation\nthe reduced fertility showed itself in a form which is often found in\nhybrids, that is the first flowers were sterile. (Complete sterility was\nnot found in any of the plants investigated by Darwin. Others appear\nto be more sensitive; Cluer found Zea Mais \"almost sterile\" after three\ngenerations of self-fertilisation. (Cf. Fruwirth, \"Die Zuchtung der\nLandwirtschaftlichen Kulturpflanzen\", Berlin, 1904, II. page 6.))\n\nThe superiority of crossed individuals is not exhibited in the same\nway in all plants. For example in Eschscholzia californica the crossed\nseedlings do not exceed the self-fertilised in height and vigour,\nbut the crossing considerably increases the plant's capacity for\nflower-production, and the seedlings from such a mother-plant are more\nfertile.\n\nThe conception implied by the term crossing requires a closer analysis.\nAs in the majority of plants, a large number of flowers are in bloom\nat the same time on one and the same plant, it follows that insects\nvisiting the flowers often carry pollen from one flower to another of\nthe same stock. Has this method, which is spoken of as Geitonogamy, the\nsame influence as crossing with pollen from another plant? The results\nof Darwin's experiments with different plants (Ipomoea purpurea,\nDigitalis purpurea, Mimulus luteus, Pelargonium, Origanum) were not in\ncomplete agreement; but on the whole they pointed to the conclusion that\nGeitonogamy shows no superiority over self-fertilisation (Autogamy).\n(Similarly crossing in the case of flowers of Pelargonium zonale, which\nbelong to plants raised from cuttings from the same parent, shows no\nsuperiority over self-fertilisation.) Darwin, however, considered it\npossible that this may sometimes be the case. \"The sexual elements\nin the flowers on the same plant can rarely have been differentiated,\nthough this is possible, as flower-buds are in one sense distinct\nindividuals, sometimes varying and differing from one another in\nstructure or constitution.\" (\"Cross and Self fertilisation\" (1st\nedition), page 444.)\n\nAs regards the importance of this question from the point of view of\nthe significance of cross-fertilisation in general, it may be noted\nthat later observers have definitely discovered a difference between the\nresults of autogamy and geitonogamy. Gilley and Fruwirth found that in\nBrassica Napus, the length and weight of the fruits as also the total\nweight of the seeds in a single fruit were less in the case of autogamy\nthan in geitonogamy. With Sinapis alba a better crop of seeds was\nobtained after geitonogamy, and in the Sugar Beet the average weight\nof a fruit in the case of a self-fertilised plant was 0.009 gr., from\ngeitonogamy 0.012 gr., and on cross-fertilisation 0.013 gr.\n\nOn the whole, however, the results of geitonogamy show that the\nfavourable effects of cross-fertilisation do not depend simply on the\nfact that the pollen of one flower is conveyed to the stigma of another.\nBut the plants which are crossed must in some way be different.\nIf plants of Ipomoea purpurea (and Mimulus luteus) which have been\nself-fertilised for seven generations and grown under the same\nconditions of cultivation are crossed together, the plants so crossed\nwould not be superior to the self-fertilised; on the other hand crossing\nwith a fresh stock at once proves very advantageous. The favourable\neffect of crossing is only apparent, therefore, if the parent plants\nare grown under different conditions or if they belong to different\nvarieties. \"It is really wonderful what an effect pollen from a distinct\nseedling plant, which has been exposed to different conditions of life,\nhas on the offspring in comparison with pollen from the same flower or\nfrom a distinct individual, but which has been long subjected to the\nsame conditions. The subject bears on the very principle of life, which\nseems almost to require changes in the conditions.\" (\"More Letters\",\nVol. II. page 406.)\n\nThe fertility--measured by the number or weight of the seeds produced\nby an equal number of plants--noticed under different conditions of\nfertilisation may be quoted in illustration.\n\n\n                                  On crossing   On crossing    On self-\n                                  with a fresh  plants of the  fertilisation\n                                  stock         same stock\n  Mimuleus luteus\n   (First and ninth generation)       100             4              3\n\n  Eschscholzia californica\n   (second generation)                100            45             40\n\n  Dianthus caryophyllus\n   (third and fourth generation)      100            45             33\n\n  Petunia violacea                    100            54             46\n\n\nCrossing under very similar conditions shows, therefore, that the\ndifference between the sexual cells is smaller and thus the result of\ncrossing is only slightly superior to that given by self-fertilisation.\nIs, then, the favourable result of crossing with a foreign stock to be\nattributed to the fact that this belongs to another systematic entity\nor to the fact that the plants, though belonging to the same entity\nwere exposed to different conditions? This is a point on which further\nresearches must be taken into account, especially since the analysis of\nthe systematic entities has been much more thorough than formerly. (In\nthe case of garden plants, as Darwin to a large extent claimed, it\nis not easy to say whether two individuals really belong to the same\nvariety, as they are usually of hybrid origin. In some instances\n(Petunia, Iberis) the fresh stock employed by Darwin possessed flowers\ndiffering in colour from those of the plant crossed with it.) We\nknow that most of Linneaus's species are compound species, frequently\nconsisting of a very large number of smaller or elementary species\nformerly included under the comprehensive term varieties. Hybridisation\nhas in most cases affected our garden and cultivated plants so that they\ndo not represent pure species but a mixture of species.\n\nBut this consideration has no essential bearing on Darwin's point of\nview, according to which the nature of the sexual cells is influenced by\nexternal conditions. Even individuals growing close to one another are\nonly apparently exposed to identical conditions. Their sexual cells may\ntherefore be differently influenced and thus give favourable results\non crossing, as \"the benefits which so generally follow from a cross\nbetween two plants apparently depend on the two differing somewhat in\nconstitution or character.\" As a matter of fact we are familiar with a\nlarge number of cases in which the condition of the reproductive organs\nis influenced by external conditions. Darwin has himself demonstrated\nthis for self-sterile plants, that is plants in which self-fertilisation\nproduces no result. This self-sterility is affected by climatic\nconditions: thus in Brazil Eschscholzia californica is absolutely\nsterile to the pollen of its own flowers; the descendants of Brazilian\nplants in Darwin's cultures were partially self-fertile in one\ngeneration and in a second generation still more so. If one has any\ndoubt in this case whether it is a question of the condition of\nthe style and stigma, which possibly prevents the entrance of the\npollen-tube or even its development, rather than that of the actual\nsexual cells, in other cases there is no doubt that an influence is\nexerted on the latter.\n\nJanczewski (Janczewski, \"Sur les antheres steriles des Groseilliers\",\n\"Bull. de l'acad. des sciences de Cracovie\", June, 1908.) has recently\nshown that species of Ribes cultivated under unnatural conditions\nfrequently produce a mixed (i.e. partly useless) or completely sterile\npollen, precisely as happens with hybrids. There are, therefore,\nsubstantial reasons for the conclusion that conditions of life exert an\ninfluence on the sexual cells. \"Thus the proposition that the benefit\nfrom cross-fertilisation depends on the plants which are crossed\nhaving been subjected during previous generations to somewhat different\nconditions, or to their having varied from some unknown cause as if they\nhad been thus subjected, is securely fortified on all sides.\" (\"Cross\nand Self fertilisation\" (1st edition), page 444.)\n\nWe thus obtain an insight into the significance of sexuality. If an\noccasional and slight alteration in the conditions under which plants\nand animals live is beneficial (Reasons for this are given by Darwin\nin \"Variation under Domestication\" (2nd edition), Vol. II. page\n127.), crossing between organisms which have been exposed to different\nconditions becomes still more advantageous. The entire constitution\nis in this way influenced from the beginning, at a time when the whole\norganisation is in a highly plastic state. The total life-energy, so\nto speak, is increased, a gain which is not produced by asexual\nreproduction or by the union of sexual cells of plants which have lived\nunder the same or only slightly different conditions. All the\nwonderful arrangements for cross-fertilisation now appear to be useful\nadaptations. Darwin was, however, far from giving undue prominence to\nthis point of view, though this has been to some extent done by others.\nHe particularly emphasised the following consideration:--\"But we should\nalways keep in mind that two somewhat opposed ends have to be gained;\nthe first and more important one being the production of seeds by\nany means, and the second, cross-fertilisation.\" (\"Cross and Self\nfertilisation\" (1st edition), page 371.) Just as in some orchids and\ncleistogamic flowers self-pollination regularly occurs, so it may also\noccur in other cases. Darwin showed that Pisum sativum and Lathyrus\nodoratus belong to plants in which self-pollination is regularly\neffected, and that this accounts for the constancy of certain sorts of\nthese plants, while a variety of form is produced by crossing. Indeed\namong his culture plants were some which derived no benefit from\ncrossing. Thus in the sixth self-fertilised generation of his Ipomoea\ncultures the \"Hero\" made its appearance, a form slightly exceeding its\ncrossed companion in height; this was in the highest degree self-fertile\nand handed on its characteristics to both children and grandchildren.\nSimilar forms were found in Mimulus luteus and Nicotiana (In Pisum\nsativum also the crossing of two individuals of the same variety\nproduced no advantage; Darwin attributed this to the fact that the\nplants had for several generations been self-fertilised and in each\ngeneration cultivated under almost the same conditions. Tschermak\n(\"Ueber kunstliche Kreuzung an Pisum sativum\") afterwards recorded the\nsame result; but he found on crossing different varieties that usually\nthere was no superiority as regards height over the products of\nself-fertilisation, while Darwin found a greater height represented by\nthe ratios 100:75 and 100:60.), types which, after self-fertilisation,\nhave an enhanced power of seed-production and of attaining a greater\nheight than the plants of the corresponding generation which are crossed\ntogether and self-fertilised and grown under the same conditions.\n\"Some observations made on other plants lead me to suspect that\nself-fertilisation is in some respects beneficial; although the benefit\nthus derived is as a rule very small compared with that from a cross\nwith a distinct plant.\" (\"Cross and Self fertilisation\", page 350.) We\nare as ignorant of the reason why plants behave differently when\ncrossed and self-fertilised as we are in regard to the nature of the\ndifferentiation of the sexual cells, which determines whether a union of\nthe sexual cells will prove favourable or unfavourable.\n\nIt is impossible to discuss the different results of\ncross-fertilisation; one point must, however, be emphasised, because\nDarwin attached considerable importance to it. It is inevitable that\npollen of different kinds must reach the stigma. It was known that\npollen of the same \"species\" is dominant over the pollen of another\nspecies, that, in other words, it is prepotent. Even if the pollen of\nthe same species reaches the stigma rather later than that of another\nspecies, the latter does not effect fertilisation.\n\nDarwin showed that the fertilising power of the pollen of another\nvariety or of another individual is greater than that of the plant's\nown pollen. (\"Cross and Self fertilisation\", page 391.) This has\nbeen demonstrated in the case of Mimulus luteus (for the fixed\nwhite-flowering variety) and Iberis umbellata with pollen of another\nvariety, and observations on cultivated plants, such as cabbage,\nhorseradish, etc. gave similar results. It is, however, especially\nremarkable that pollen of another individual of the same variety may be\nprepotent over the plant's own pollen. This results from the superiority\nof plants crossed in this manner over self-fertilised plants. \"Scarcely\nany result from my experiments has surprised me so much as this of the\nprepotency of pollen from a distinct individual over each plant's own\npollen, as proved by the greater constitutional vigour of the crossed\nseedlings.\" (Ibid. page 397.) Similarly, in self-fertile plants the\nflowers of which have not been deprived of the male organs, pollen\nbrought to the stigma by the wind or by insects from another plant\neffects fertilisation, even if the plant's own pollen has reached the\nstigma somewhat earlier.\n\nHave the results of his experimental investigations modified the point\nof view from which Darwin entered on his researches, or not? In the\nfirst place the question is, whether or not the opinion expressed in\nthe Orchid book that there is \"Something injurious\" connected with\nself-fertilisation, has been confirmed. We can, at all events, affirm\nthat Darwin adhered in essentials to his original position; but\nself-fertilisation afterwards assumed a greater importance than it\nformerly possessed. Darwin emphasised the fact that \"the difference\nbetween the self-fertilised and crossed plants raised by me cannot be\nattributed to the superiority of the crossed, but to the inferiority\nof the self-fertilised seedlings, due to the injurious effects of\nself-fertilisation.\" (Ibid. page 437.) But he had no doubt that in\nfavourable circumstances self-fertilised plants were able to persist for\nseveral generations without crossing. An occasional crossing appears to\nbe useful but not indispensable in all cases; its sporadic occurrence\nin plants in which self-pollination habitually occurs is not excluded.\nSelf-fertilisation is for the most part relatively and not absolutely\ninjurious and always better than no fertilisation. \"Nature abhors\nperpetual self-fertilisation\" (It is incorrect to say, as a writer has\nlately said, that the aphorism expressed by Darwin in 1859 and 1862,\n\"Nature abhors perpetual self-fertilisation,\" is not repeated in his\nlater works. The sentence is repeated in \"Cross and Self fertilisation\"\n(page 8), with the addition, \"If the word perpetual had been omitted,\nthe aphorism would have been false. As it stands, I believe that it is\ntrue, though perhaps rather too strongly expressed.\") is, however, a\npregnant expression of the fact that cross-fertilisation is exceedingly\nwidespread and has been shown in the majority of cases to be beneficial,\nand that in those plants in which we find self-pollination regularly\noccurring cross-pollination may occasionally take place.\n\nAn attempt has been made to express in brief the main results of\nDarwin's work on the biology of flowers. We have seen that his object\nwas to elucidate important general questions, particularly the question\nof the significance of sexual reproduction.\n\nIt remains to consider what influence his work has had on botanical\nscience. That this influence has been very considerable, is shown by\na glance at the literature on the biology of flowers published since\nDarwin wrote. Before the book on orchids was published there was nothing\nbut the old and almost forgotten works of Kolreuter and Sprengel with\nthe exception of a few scattered references. Darwin's investigations\ngave the first stimulus to the development of an extensive literature on\nfloral biology. In Knuth's \"Handbuch der Blutenbiologie\" (\"Handbook\nof Flower Pollination\", Oxford, 1906) as many as 3792 papers on this\nsubject are enumerated as having been published before January 1, 1904.\nThese describe not only the different mechanisms of flowers, but deal\nalso with a series of remarkable adaptations in the pollinating insects.\nAs a fertilising rain quickly calls into existence the most varied\nassortment of plants on a barren steppe, so activity now reigns in a\nfield which men formerly left deserted. This development of the biology\nof flowers is of importance not only on theoretical grounds but also\nfrom a practical point of view. The rational breeding of plants is\npossible only if the flower-biology of the plants in question (i.e. the\nquestion of the possibility of self-pollination, self-sterility, etc.)\nis accurately known. And it is also essential for plant-breeders that\nthey should have \"the power of fixing each fleeting variety of colour,\nif they will fertilise the flowers of the desired kind with their own\npollen for half-a-dozen generations, and grow the seedlings under the\nsame conditions.\" (\"Cross and Self fertilisation\" (1st edition), page\n460.)\n\nBut the influence of Darwin on floral biology was not confined to the\ndevelopment of this branch of Botany. Darwin's activity in this domain\nhas brought about (as Asa Gray correctly pointed out) the revival of\nteleology in Botany and Zoology. Attempts were now made to determine,\nnot only in the case of flowers but also in vegetative organs, in what\nrelation the form and function of organs stand to one another and\nto what extent their morphological characters exhibit adaptation to\nenvironment. A branch of Botany, which has since been called Ecology\n(not a very happy term) has been stimulated to vigorous growth by floral\nbiology.\n\nWhile the influence of the work on the biology of flowers was\nextraordinarily great, it could not fail to elicit opinions at variance\nwith Darwin's conclusions. The opposition was based partly on reasons\nvalueless as counterarguments, partly on problems which have still to\nbe solved; to some extent also on that tendency against teleological\nconceptions which has recently become current. This opposing trend\nof thought is due to the fact that many biologists are content with\nteleological explanations, unsupported by proof; it is also closely\nconnected with the fact that many authors estimate the importance of\nnatural selection less highly than Darwin did. We may describe\nthe objections which are based on the widespread occurrence of\nself-fertilisation and geitonogamy as of little importance. Darwin did\nnot deny the occurrence of self-fertilisation, even for a long series\nof generations; his law states only that \"Nature abhors PERPETUAL\nself-fertilisation.\" (It is impossible (as has been attempted) to\nexpress Darwin's point of view in a single sentence, such as H.\nMuller's statement of the \"Knight-Darwin law.\" The conditions of life in\norganisms are so various and complex that laws, such as are formulated\nin physics and chemistry, can hardly be conceived.) An exception to\nthis rule would therefore occur only in the case of plants in which the\npossibility of cross-pollination is excluded. Some of the plants with\ncleistogamous flowers might afford examples of such cases. We have\nalready seen, however, that such a case has not as yet been shown to\noccur. Burck believed that he had found an instance in certain\ntropical plants (Anonaceae, Myrmecodia) of the complete exclusion of\ncross-fertilisation. The flowers of these plants, in which, however,--in\ncontrast to the cleistogamous flowers--the corolla is well developed,\nremain closed and fruit is produced.\n\nLoew (E. Loew, \"Bemerkungen zu Burck... \", \"Biolog. Centralbl.\" XXVI.\n(1906).) has shown that cases occur in which cross-fertilisation may be\neffected even in these \"cleistopetalous\" flowers: humming birds visit\nthe permanently closed flowers of certain species of Nidularium and\ntransport the pollen. The fact that the formation of hybrids may occur\nas the result of this shows that pollination may be accomplished.\n\nThe existence of plants for which self-pollination is of greater\nimportance than it is for others is by no means contradictory to\nDarwin's view. Self-fertilisation is, for example, of greater importance\nfor annuals than for perennials as without it seeds might fail to be\nproduced. Even in the case of annual plants with small inconspicuous\nflowers in which self-fertilisation usually occurs, such as Senecio\nvulgaris, Capsella bursa-pastoris and Stellaria media, A. Bateson (Anna\nBateson, \"The effects of cross-fertilisation on inconspicuous\nflowers\", \"Annals of Botany\", Vol. I. 1888, page 255.) found that\ncross-fertilisation gave a beneficial result, although only in a slight\ndegree. If the favourable effects of sexual reproduction, according to\nDarwin's view, are correlated with change of environment, it is quite\npossible that this is of less importance in plants which die after\nripening their seeds (\"hapaxanthic\") and which in any case constantly\nchange their situation. Objections which are based on the proof of the\nprevalence of self-fertilisation are not, therefore, pertinent. At first\nsight another point of view, which has been more recently urged, appears\nto have more weight.\n\nW. Burck (Burck, \"Darwin's Kreuzeungsgesetz... \", \"Biol. Centralbl\".\nXXVIII. 1908, page 177.) has expressed the opinion that the beneficial\nresults of cross-fertilisation demonstrated by Darwin concern only\nhybrid plants. These alone become weaker by self-pollination; while\npure species derive no advantage from crossing and no disadvantage from\nself-fertilisation. It is certain that some of the plants used by Darwin\nwere of hybrid origin. (It is questionable if this was always the case.)\nThis is evident from his statements, which are models of clearness and\nprecision; he says that his Ipomoea plants \"were probably the offspring\nof a cross.\" (\"Cross and Self fertilisation\" (1st edition), page 55.)\nThe fixed forms of this plant, such as Hero, which was produced by\nself-fertilisation, and a form of Mimulus with white flowers spotted\nwith red probably resulted from splitting of the hybrids. It is true\nthat the phenomena observed in self-pollination, e.g. in Ipomoea, agree\nwith those which are often noticed in hybrids; Darwin himself drew\nattention to this.\n\nLet us next call to mind some of the peculiarities connected with\nhybridisation. We know that hybrids are often characterized by their\nlarge size, rapidity of growth, earlier production of flowers, wealth of\nflower-production and a longer life; hybrids, if crossed with one of the\ntwo parent forms, are usually more fertile than when they are crossed\ntogether or with another hybrid. But the characters which hybrids\nexhibit on self-fertilisation are rather variable. The following\ninstance may be quoted from Gartner: \"There are many hybrids which\nretain the self-fertility of the first generation during the second\nand later generations, but very often in a less degree; a considerable\nnumber, however, become sterile.\" But the hybrid varieties may be more\nfertile in the second generation than in the first, and in some hybrids\nthe fertility with their own pollen increases in the second, third,\nand following generations. (K.F. Gartner, \"Versuche uber die\nBastarderzeugung\", Stuttgart, 1849, page 149.) As yet it is impossible\nto lay down rules of general application for the self-fertility of\nhybrids. That the beneficial influence of crossing with a fresh stock\nrests on the same ground--a union of sexual cells possessing somewhat\ndifferent characters--as the fact that many hybrids are distinguished\nby greater luxuriance, wealth of flowers, etc. corresponds entirely\nwith Darwin's conclusions. It seems to me to follow clearly from\nhis investigations that there is no essential difference between\ncross-fertilisation and hybridisation. The heterostyled plants are\nnormally dependent on a process corresponding to hybridisation. The view\nthat specifically distinct species could at best produce sterile hybrids\nwas always opposed by Darwin. But if the good results of crossing were\nEXCLUSIVELY dependent on the fact that we are concerned with hybrids,\nthere must then be a demonstration of two distinct things. First, that\ncrossing with a fresh stock belonging to the same systematic entity\nor to the same hybrid, but cultivated for a considerable time under\ndifferent conditions, shows no superiority over self-fertilisation,\nand that in pure species crossing gives no better results than\nself-pollination. If this were the case, we should be better able to\nunderstand why in one plant crossing is advantageous while in others,\nsuch as Darwin's Hero and the forms of Mimulus and Nicotiana no\nadvantage is gained; these would then be pure species. But such a\nproof has not been supplied; the inference drawn from cleistogamous and\ncleistopetalous plants is not supported by evidence, and the experiments\non geitonogamy and on the advantage of cross-fertilisation in species\nwhich are usually self-fertilised are opposed to this view. There are\nstill but few researches on this point; Darwin found that in Ononis\nminutissima, which produces cleistogamous as well as self-fertile\nchasmogamous flowers, the crossed and self-fertilised capsules\nproduced seed in the proportion of 100:65 and that the average bore the\nproportion 100:86. Facts previously mentioned are also applicable to\nthis case. Further, it is certain that the self-sterility exhibited by\nmany plants has nothing to do with hybridisation. Between self-sterility\nand reduced fertility as the result of self-fertilisation there is\nprobably no fundamental difference.\n\nIt is certain that so difficult a problem as that of the significance\nof sexual reproduction requires much more investigation. Darwin was\nanything but dogmatic and always ready to alter an opinion when it was\nnot based on definite proof: he wrote, \"But the veil of secrecy is\nas yet far from lifted; nor will it be, until we can say why it is\nbeneficial that the sexual elements should be differentiated to a\ncertain extent, and why, if the differentiation be carried still\nfurther, injury follows.\" He has also shown us the way along which\nto follow up this problem; it is that of carefully planned and exact\nexperimental research. It may be that eventually many things will be\nviewed in a different light, but Darwin's investigations will always\nform the foundation of Floral Biology on which the future may continue\nto build.\n\n\n\n\nXXI. MENTAL FACTORS IN EVOLUTION. By C. Lloyd Morgan, LL.D., F.R.S.\n\nIn developing his conception of organic evolution Charles Darwin was\nof necessity brought into contact with some of the problems of mental\nevolution. In \"The Origin of Species\" he devoted a chapter to \"the\ndiversities of instinct and of the other mental faculties in animals of\nthe same class.\" (\"Origin of Species\" (6th edition), page 205.) When\nhe passed to the detailed consideration of \"The Descent of Man\", it\nwas part of his object to show \"that there is no fundamental difference\nbetween man and the higher mammals in their mental faculties.\" (\"Descent\nof Man\" (2nd edition 1888), Vol. I. page 99; Popular edition page 99.)\n\"If no organic being excepting man,\" he said, \"had possessed any mental\npower, or if his powers had been of a wholly different nature from those\nof the lower animals, then we should never have been able to convince\nourselves that our high faculties had been gradually developed.\" (Ibid.\npage 99.) In his discussion of \"The Expression of the Emotions\" it\nwas important for his purpose \"fully to recognise that actions readily\nbecome associated with other actions and with various states of the\nmind.\" (\"The Expression of the Emotions\" (2nd edition), page 32.) His\nhypothesis of sexual selection is largely dependent upon the exercise\nof choice on the part of the female and her preference for \"not only the\nmore attractive but at the same time the more vigorous and victorious\nmales.\" (\"Descent of Man\", Vol. II. page 435.) Mental processes and\nphysiological processes were for Darwin closely correlated; and he\naccepted the conclusion \"that the nervous system not only regulates most\nof the existing functions of the body, but has indirectly influenced\nthe progressive development of various bodily structures and of certain\nmental qualities.\" (Ibid. pages 437, 438.)\n\nThroughout his treatment, mental evolution was for Darwin incidental\nto and contributory to organic evolution. For specialised research\nin comparative and genetic psychology, as an independent field of\ninvestigation, he had neither the time nor the requisite training.\nNone the less his writings and the spirit of his work have exercised a\nprofound influence on this department of evolutionary thought. And, for\nthose who follow Darwin's lead, mental evolution is still in a\nmeasure subservient to organic evolution. Mental processes are the\naccompaniments or concomitants of the functional activity of specially\ndifferentiated parts of the organism. They are in some way dependent on\nphysiological and physical conditions. But though they are not physical\nin their nature, and though it is difficult or impossible to conceive\nthat they are physical in their origin, they are, for Darwin and his\nfollowers, factors in the evolutionary process in its physical or\norganic aspect. By the physiologist within his special and well-defined\nuniverse of discourse they may be properly regarded as epiphenomena; but\nby the naturalist in his more catholic survey of nature they cannot\nbe so regarded, and were not so regarded by Darwin. Intelligence has\ncontributed to evolution of which it is in a sense a product.\n\nThe facts of observation or of inference which Darwin accepted are\nthese: Conscious experience accompanies some of the modes of animal\nbehaviour; it is concomitant with certain physiological processes; these\nprocesses are the outcome of development in the individual and\nevolution in the race; the accompanying mental processes undergo a like\ndevelopment. Into the subtle philosophical questions which arise out\nof the naive acceptance of such a creed it was not Darwin's province\nto enter; \"I have nothing to do,\" he said (\"Origin of Species\" (6th\nedition), page 205.), \"with the origin of the mental powers, any more\nthan I have with that of life itself.\" He dealt with the natural history\nof organisms, including not only their structure but their modes of\nbehaviour; with the natural history of the states of consciousness which\naccompany some of their actions; and with the relation of behaviour\nto experience. We will endeavour to follow Darwin in his modesty and\ncandour in making no pretence to give ultimate explanations. But we must\nnote one of the implications of this self-denying ordinance of science.\nDevelopment and evolution imply continuity. For Darwin and his followers\nthe continuity is organic through physical heredity. Apart from\nspeculative hypothesis, legitimate enough in its proper place but here\nout of court, we know nothing of continuity of mental evolution as such:\nconsciousness appears afresh in each succeeding generation. Hence it is\nthat for those who follow Darwin's lead, mental evolution is and must\never be, within his universe of discourse, subservient to organic\nevolution. Only in so far as conscious experience, or its neural\ncorrelate, effects some changes in organic structure can it influence\nthe course of heredity; and conversely only in so far as changes in\norganic structure are transmitted through heredity, is mental evolution\nrendered possible. Such is the logical outcome of Darwin's teaching.\n\nThose who abide by the cardinal results of this teaching are bound to\nregard all behaviour as the expression of the functional activities\nof the living tissues of the organism, and all conscious experience\nas correlated with such activities. For the purposes of scientific\ntreatment, mental processes are one mode of expression of the same\nchanges of which the physiological processes accompanying behaviour\nare another mode of expression. This is simply accepted as a fact\nwhich others may seek to explain. The behaviour itself is the adaptive\napplication of the energies of the organism; it is called forth by some\nform of presentation or stimulation brought to bear on the organism by\nthe environment. This presentation is always an individual or personal\nmatter. But in order that the organism may be fitted to respond to the\npresentation of the environment it must have undergone in some way\na suitable preparation. According to the theory of evolution this\npreparation is primarily racial and is transmitted through heredity.\nDarwin's main thesis was that the method of preparation is predominantly\nby natural selection. Subordinate to racial preparation, and always\ndependent thereon, is individual or personal preparation through\nsome kind of acquisition; of which the guidance of behaviour through\nindividually won experience is a typical example. We here introduce\nthe mental factor because the facts seem to justify the inference. Thus\nthere are some modes of behaviour which are wholly and solely dependent\nupon inherited racial preparation; there are other modes of behaviour\nwhich are also dependent, in part at least, on individual preparation.\nIn the former case the behaviour is adaptive on the first occurrence\nof the appropriate presentation; in the latter case accommodation to\ncircumstances is only reached after a greater or less amount of acquired\norganic modification of structure, often accompanied (as we assume) in\nthe higher animals by acquired experience. Logically and biologically\nthe two classes of behaviour are clearly distinguishable: but the\nanalysis of complex cases of behaviour where the two factors cooperate,\nis difficult and requires careful and critical study of life-history.\n\nThe foundations of the mental life are laid in the conscious experience\nthat accompanies those modes of behaviour, dependent entirely on racial\npreparation, which may broadly be described as instinctive. In the\neighth chapter of \"The Origin of Species\" Darwin says (\"Origin of\nSpecies\" (6th edition), page 205.), \"I will not attempt any definition\nof instinct... Every one understands what is meant, when it is said\nthat instinct impels the cuckoo to migrate and to lay her eggs in other\nbirds' nests. An action, which we ourselves require experience to enable\nus to perform, when performed by an animal, more especially by a very\nyoung one, without experience, and when performed by many individuals in\nthe same way, without their knowing for what purpose it is performed, is\nusually said to be instinctive.\" And in the summary at the close of the\nchapter he says (\"Origin of Species\" (6th edition), page 233.), \"I have\nendeavoured briefly to show that the mental qualities of our domestic\nanimals vary, and that the variations are inherited. Still more briefly\nI have attempted to show that instincts vary slightly in a state of\nnature. No one will dispute that instincts are of the highest importance\nto each animal. Therefore there is no real difficulty, under changing\nconditions of life, in natural selection accumulating to any extent\nslight modifications of instinct which are in any way useful. In many\ncases habit or use and disuse have probably come into play.\"\n\nInto the details of Darwin's treatment there is neither space nor need\nto enter. There are some ambiguous passages; but it may be said that for\nhim, as for his followers to-day, instinctive behaviour is wholly the\nresult of racial preparation transmitted through organic heredity. For\nthe performance of the instinctive act no individual preparation under\nthe guidance of personal experience is necessary. It is true that Darwin\nquotes with approval Huber's saying that \"a little dose of judgment\nor reason often comes into play, even with animals low in the scale of\nnature.\" (Ibid. page 205.) But we may fairly interpret his meaning to be\nthat in behaviour, which is commonly called instinctive, some element of\nintelligent guidance is often combined. If this be conceded the strictly\ninstinctive performance (or part of the performance) is the outcome of\nheredity and due to the direct transmission of parental or ancestral\naptitudes. Hence the instinctive response as such depends entirely on\nhow the nervous mechanism has been built up through heredity; while\nintelligent behaviour, or the intelligent factor in behaviour, depends\nalso on how the nervous mechanism has been modified and moulded by use\nduring its development and concurrently with the growth of individual\nexperience in the customary situations of daily life. Of course it is\nessential to the Darwinian thesis that what Sir E. Ray Lankester has\ntermed \"educability,\" not less than instinct, is hereditary. But it is\nalso essential to the understanding of this thesis that the differentiae\nof the hereditary factors should be clearly grasped.\n\nFor Darwin there were two modes of racial preparation, (1) natural\nselection, and (2) the establishment of individually acquired habit. He\nshowed that instincts are subject to hereditary variation; he saw that\ninstincts are also subject to modification through acquisition in the\ncourse of individual life. He believed that not only the variations but\nalso, to some extent, the modifications are inherited. He therefore held\nthat some instincts (the greater number) are due to natural selection\nbut that others (less numerous) are due, or partly due, to the\ninheritance of acquired habits. The latter involve Lamarckian\ninheritance, which of late years has been the centre of so much\ncontroversy. It is noteworthy however that Darwin laid especial emphasis\non the fact that many of the most typical and also the most\ncomplex instincts--those of neuter insects--do not admit of such an\ninterpretation. \"I am surprised,\" he says (\"Origin of Species\"\n(6th edition), page 233.), \"that no one has hitherto advanced this\ndemonstrative case of neuter insects, against the well-known doctrine of\ninherited habit, as advanced by Lamarck.\" None the less Darwin admitted\nthis doctrine as supplementary to that which was more distinctively his\nown--for example in the case of the instincts of domesticated animals.\nStill, even in such cases, \"it may be doubted,\" he says (Ibid. pages\n210, 211.), \"whether any one would have thought of training a dog to\npoint, had not some one dog naturally shown a tendency in this line... so\nthat habit and some degree of selection have probably concurred in\ncivilising by inheritance our dogs.\" But in the interpretation of the\ninstincts of domesticated animals, a more recently suggested hypothesis,\nthat of organic selection (Independently suggested, on somewhat\ndifferent lines, by Profs. J. Mark Baldwin, Henry F. Osborn and the\nwriter.), may be helpful. According to this hypothesis any intelligent\nmodification of behaviour which is subject to selection is probably\ncoincident in direction with an inherited tendency to behave in this\nfashion. Hence in such behaviour there are two factors: (1) an\nincipient variation in the line of such behaviour, and (2) an acquired\nmodification by which the behaviour is carried further along the same\nline. Under natural selection those organisms in which the two factors\ncooperate are likely to survive. Under artificial selection they are\ndeliberately chosen out from among the rest.\n\nOrganic selection has been termed a compromise between the more strictly\nDarwinian and the Lamarckian principles of interpretation. But it is not\nin any sense a compromise. The principle of interpretation of that which\nis instinctive and hereditary is wholly Darwinian. It is true that some\nof the facts of observation relied upon by Lamarckians are introduced.\nFor Lamarckians however the modifications which are admittedly factors\nin survival, are regarded as the parents of inherited variations; for\nbelievers in organic selection they are only the foster parents or\nnurses. It is because organic selection is the direct outcome of and a\nnatural extension of Darwin's cardinal thesis that some reference to it\nhere is justifiable. The matter may be put with the utmost brevity as\nfollows. (1) Variations (V) occur, some of which are in the direction\nof increased adaptation (+), others in the direction of decreased\nadaptation (-). (2) Acquired modifications (M) also occur. Some of these\nare in the direction of increased accommodation to circumstances (+),\nwhile others are in the direction of diminished accommodation (-). Four\nmajor combinations are\n\n     (a)  + V with + M,\n     (b)  + V with - M,\n     (c)  - V with + M,\n     (d)  - V with - M.\n\nOf these (d) must inevitably be eliminated while (a) are selected.\nThe predominant survival of (a) entails the survival of the adaptive\nvariations which are inherited. The contributory acquisitions (+M) are\nnot inherited; but they are none the less factors in determining the\nsurvival of the coincident variations. It is surely abundantly clear\nthat this is Darwinism and has no tincture of Lamarck's essential\nprinciple, the inheritance of acquired characters.\n\nWhether Darwin himself would have accepted this interpretation of some\nat least of the evidence put forward by Lamarckians is unfortunately\na matter of conjecture. The fact remains that in his interpretation\nof instinct and in allied questions he accepted the inheritance of\nindividually acquired modifications of behaviour and structure.\n\nDarwin was chiefly concerned with instinct from the biological rather\nthan from the psychological point of view. Indeed it must be confessed\nthat, from the latter standpoint, his conception of instinct as a\n\"mental faculty\" which \"impels\" an animal to the performance of certain\nactions, scarcely affords a satisfactory basis for genetic treatment. To\ncarry out the spirit of Darwin's teaching it is necessary to link more\nclosely biological and psychological evolution. The first step towards\nthis is to interpret the phenomena of instinctive behaviour in terms\nof stimulation and response. It may be well to take a particular case.\nSwimming on the part of a duckling is, from the biological point\nof view, a typical example of instinctive behaviour. Gently lower a\nrecently hatched bird into water: coordinated movements of the limbs\nfollow in rhythmical sequence. The behaviour is new to the individual\nthough it is no doubt closely related to that of walking, which is\nno less instinctive. There is a group of stimuli afforded by the\n\"presentation\" which results from partial immersion: upon this\nthere follows as a complex response an application of the functional\nactivities in swimming; the sequence of adaptive application on the\nappropriate presentation is determined by racial preparation. We know,\nit is true, but little of the physiological details of what takes place\nin the central nervous system; but in broad outline the nature of the\norganic mechanism and the manner of its functioning may at least\nbe provisionally conjectured in the present state of physiological\nknowledge. Similarly in the case of the pecking of newly-hatched chicks;\nthere is a visual presentation, there is probably a cooperating group of\nstimuli from the alimentary tract in need of food, there is an adaptive\napplication of the activities in a definite mode of behaviour. Like\ndata are afforded in a great number of cases of instinctive procedure,\nsometimes occurring very early in life, not infrequently deferred until\nthe organism is more fully developed, but all of them dependent upon\nracial preparation. No doubt there is some range of variation in the\nbehaviour, just such variation as the theory of natural selection\ndemands. But there can be no question that the higher animals inherit\na bodily organisation and a nervous system, the functional working of\nwhich gives rise to those inherited modes of behaviour which are termed\ninstinctive.\n\nIt is to be noted that the term \"instinctive\" is here employed in the\nadjectival form as a descriptive heading under which may be grouped many\nand various modes of behaviour due to racial preparation. We speak\nof these as inherited; but in strictness what is transmitted through\nheredity is the complex of anatomical and physiological conditions under\nwhich, in appropriate circumstances, the organism so behaves. So far the\nterm \"instinctive\" has a restricted biological connotation in terms\nof behaviour. But the connecting link between biological evolution and\npsychological evolution is to be sought,--as Darwin fully realised,--in\nthe phenomena of instinct, broadly considered. The term \"instinctive\"\nhas also a psychological connotation. What is that connotation?\n\nLet us take the case of the swimming duckling or the pecking chick, and\nfix our attention on the first instinctive performance. Grant that just\nas there is, strictly speaking, no inherited behaviour, but only the\nconditions which render such behaviour under appropriate circumstances\npossible; so too there is no inherited experience, but only the\nconditions which render such experience possible; then the cerebral\nconditions in both cases are the same. The biological behaviour-complex,\nincluding the total stimulation and the total response with the\nintervening or resultant processes in the sensorium, is accompanied by\nan experience-complex including the initial stimulation-consciousness\nand resulting response-consciousness. In the experience-complex are\ncomprised data which in psychological analysis are grouped under the\nheadings of cognition, affective tone and conation. But the complex is\nprobably experienced as an unanalysed whole. If then we use the term\n\"instinctive\" so as to comprise all congenital modes of behaviour which\ncontribute to experience, we are in a position to grasp the view that\nthe net result in consciousness constitutes what we may term the\nprimary tissue of experience. To the development of this experience each\ninstinctive act contributes. The nature and manner of organisation of\nthis primary tissue of experience are dependent on inherited biological\naptitudes; but they are from the outset onwards subject to secondary\ndevelopment dependent on acquired aptitudes. Biological values are\nsupplemented by psychological values in terms of satisfaction or the\nreverse.\n\nIn our study of instinct we have to select some particular phase of\nanimal behaviour and isolate it so far as is possible from the life of\nwhich it is a part. But the animal is a going concern, restlessly active\nin many ways. Many instinctive performances, as Darwin pointed out\n(\"Origin of Species\" (6th edition), page 206.), are serial in their\nnature. But the whole of active life is a serial and coordinated\nbusiness. The particular instinctive performance is only an episode in\na life-history, and every mode of behaviour is more or less closely\ncorrelated with other modes. This coordination of behaviour is\naccompanied by a correlation of the modes of primary experience. We may\nclassify the instinctive modes of behaviour and their accompanying modes\nof instinctive experience under as many heads as may be convenient\nfor our purposes of interpretation, and label them instincts of\nself-preservation, of pugnacity, of acquisition, the reproductive\ninstincts, the parental instincts, and so forth. An instinct, in this\nsense of the term (for example the parental instinct), may be described\nas a specialised part of the primary tissue of experience differentiated\nin relation to some definite biological end. Under such an instinct\nwill fall a large number of particular and often well-defined modes of\nbehaviour, each with its own peculiar mode of experience.\n\nIt is no doubt exceedingly difficult as a matter of observation and of\ninference securely based thereon to distinguish what is primary from\nwhat is in part due to secondary acquisition--a fact which Darwin fully\nappreciated. Animals are educable in different degrees; but where they\nare educable they begin to profit by experience from the first. Only,\ntherefore, on the occasion of the first instinctive act of a given type\ncan the experience gained be weighed as WHOLLY primary; all subsequent\nperformance is liable to be in some degree, sometimes more, sometimes\nless, modified by the acquired disposition which the initial behaviour\nengenders. But the early stages of acquisition are always along the\nlines predetermined by instinctive differentiation. It is the task of\ncomparative psychology to distinguish the primary tissue of experience\nfrom its secondary and acquired modifications. We cannot follow up the\nmatter in further detail. It must here suffice to suggest that this\nconception of instinct as a primary form of experience lends itself\nbetter to natural history treatment than Darwin's conception of an\nimpelling force, and that it is in line with the main trend of Darwin's\nthought.\n\nIn a characteristic work,--characteristic in wealth of detail, in\ncloseness and fidelity of observation, in breadth of outlook, in candour\nand modesty,--Darwin dealt with \"The Expression of the Emotions in\nMan and Animals\". Sir Charles Bell in his \"Anatomy of Expression\" had\ncontended that many of man's facial muscles had been specially created\nfor the sole purpose of being instrumental in the expression of his\nemotions. Darwin claimed that a natural explanation, consistent with the\ndoctrine of evolution, could in many cases be given and would in other\ncases be afforded by an extension of the principles he advocated. \"No\ndoubt,\" he said (\"Expression of the Emotions\", page 13. The passage is\nhere somewhat condensed.), \"as long as man and all other animals are\nviewed as independent creations, an effectual stop is put to our natural\ndesire to investigate as far as possible the causes of Expression.\nBy this doctrine, anything and everything can be equally well\nexplained... With mankind, some expressions... can hardly be understood,\nexcept on the belief that man once existed in a much lower and\nanimal-like condition. The community of certain expressions in distinct\nthough allied species... is rendered somewhat more intelligible, if we\nbelieve in their descent from a common progenitor. He who admits on\ngeneral grounds that the structure and habits of all animals have been\ngradually evolved, will look at the whole subject of Expression in a new\nand interesting light.\"\n\nDarwin relied on three principles of explanation. \"The first of these\nprinciples is, that movements which are serviceable in gratifying some\ndesire, or in relieving some sensation, if often repeated, become\nso habitual that they are performed, whether or not of any service,\nwhenever the same desire or sensation is felt, even in a very weak\ndegree.\" (Ibid. page 368.) The modes of expression which fall under\nthis head have become instinctive through the hereditary transmission of\nacquired habit. \"As far as we can judge, only a few expressive movements\nare learnt by each individual; that is, were consciously and voluntarily\nperformed during the early years of life for some definite object, or in\nimitation of others, and then became habitual. The far greater number of\nthe movements of expression, and all the more important ones, are innate\nor inherited; and such cannot be said to depend on the will of the\nindividual. Nevertheless, all those included under our first principle\nwere at first voluntarily performed for a definite object,--namely,\nto escape some danger, to relieve some distress, or to gratify some\ndesire.\" (Ibid. pages 373, 374.)\n\n\"Our second principle is that of antithesis. The habit of voluntarily\nperforming opposite movements under opposite impulses has become firmly\nestablished in us by the practice of our whole lives. Hence, if certain\nactions have been regularly performed, in accordance with our first\nprinciple, under a certain frame of mind, there will be a strong and\ninvoluntary tendency to the performance of directly opposite actions,\nwhether or not these are of any use, under the excitement of an opposite\nframe of mind.\" (\"Expression of the Emotions\", page 368.) This principle\nof antithesis has not been widely accepted. Nor is Darwin's own position\neasy to grasp.\n\n\"Our third principle,\" he says (Ibid. page 369.), \"is the direct action\nof the excited nervous system on the body, independently of the will,\nand independently, in large part, of habit. Experience shows that\nnerve-force is generated and set free whenever the cerebro-spinal system\nis excited. The direction which this nerve-force follows is necessarily\ndetermined by the lines of connection between the nerve-cells, with each\nother and with various parts of the body.\"\n\nLack of space prevents our following up the details of Darwin's\ntreatment of expression. Whether we accept or do not accept his three\nprinciples of explanation we must regard his work as a masterpiece of\ndescriptive analysis, packed full of observations possessing lasting\nvalue. For a further development of the subject it is essential that\nthe instinctive factors in expression should be more fully distinguished\nfrom those which are individually acquired--a difficult task--and that\nthe instinctive factors should be rediscussed in the light of modern\ndoctrines of heredity, with a view to determining whether Lamarckian\ninheritance, on which Darwin so largely relied, is necessary for an\ninterpretation of the facts.\n\nThe whole subject as Darwin realised is very complex. Even the term\n\"expression\" has a certain amount of ambiguity. When the emotion is in\nfull flood the animal fights, flees, or faints. Is this full-tide effect\nto be regarded as expression; or are we to restrict the term to the\npremonitory or residual effects--the bared canine when the fighting mood\nis being roused, the ruffled fur when reminiscent representations of the\nobject inducing anger cross the mind? Broadly considered both should\nbe included. The activity of premonitory expression as a means of\ncommunication was recognised by Darwin; he might, perhaps, have\nemphasised it more strongly in dealing with the lower animals. Man so\nlargely relies on a special means of communication, that of language,\nthat he sometimes fails to realise that for animals with their keen\npowers of perception, and dependent as they are on such means of\ncommunication, the more strictly biological means of expression are full\nof subtle suggestiveness. Many modes of expression, otherwise useless,\nare signs of behaviour that may be anticipated,--signs which stimulate\nthe appropriate attitude of response. This would not, however, serve to\naccount for the utility of the organic accompaniments--heart-affection,\nrespiratory changes, vaso-motor effects and so forth, together\nwith heightened muscular tone,--on all of which Darwin lays stress\n(\"Expression of the Emotions\", pages 65 ff.) under his third principle.\nThe biological value of all this is, however, of great importance,\nthough Darwin was hardly in a position to take it fully into account.\n\nHaving regard to the instinctive and hereditary factors of emotional\nexpression we may ask whether Darwin's third principle does not alone\nsuffice as an explanation. Whether we admit or reject Lamarckian\ninheritance it would appear that all hereditary expression must be due\nto pre-established connections within the central nervous system and to\na transmitted provision for coordinated response under the appropriate\nstimulation. If this be so, Darwin's first and second principles are\nsubordinate and ancillary to the third, an expression, so far as it is\ninstinctive or hereditary, being \"the direct result of the constitution\nof the nervous system.\"\n\nDarwin accepted the emotions themselves as hereditary or acquired\nstates of mind and devoted his attention to their expression. But\nthese emotions themselves are genetic products and as such dependent\non organic conditions. It remained, therefore, for psychologists who\naccepted evolution and sought to build on biological foundations to\ntrace the genesis of these modes of animal and human experience. The\nsubject has been independently developed by Professors Lange and James\n(Cf. William James, \"Principles of Psychology\", Vol. II. Chap. XXV,\nLondon, 1890.); and some modification of their view is regarded by many\nevolutionists as affording the best explanation of the facts. We must\nfix our attention on the lower emotions, such as anger or fear, and on\ntheir first occurrence in the life of the individual organism. It is\na matter of observation that if a group of young birds which have been\nhatched in an incubator are frightened by an appropriate presentation,\nauditory or visual, they instinctively respond in special ways. If we\nspeak of this response as the expression, we find that there are many\nfactors. There are certain visible modes of behaviour, crouching at\nonce, scattering and then crouching, remaining motionless, the braced\nmuscles sustaining an attitude of arrest, and so forth. There are also\ncertain visceral or organic effects, such as affections of the heart and\nrespiration. These can be readily observed by taking the young bird in\nthe hand. Other effects cannot be readily observed; vaso-motor changes,\naffections of the alimentary canal, the skin and so forth. Now the\nessence of the James-Lange view, as applied to these congenital effects,\nis that though we are justified in speaking of them as effects of the\nstimulation, we are not justified, without further evidence, in speaking\nof them as effects of the emotional state. May it not rather be that the\nemotion as a primary mode of experience is the concomitant of the\nnet result of the organic situation--the initial presentation, the\ninstinctive mode of behaviour, the visceral disturbances? According to\nthis interpretation the primary tissue of experience of the emotional\norder, felt as an unanalysed complex, is generated by the stimulation\nof the sensorium by afferent or incoming physiological impulses from the\nspecial senses, from the organs concerned in the responsive behaviour,\nfrom the viscera and vaso-motor system.\n\nSome psychologists, however, contend that the emotional experience\nis generated in the sensorium prior to, and not subsequent to, the\nbehaviour-response and the visceral disturbances. It is a direct and not\nan indirect outcome of the presentation to the special senses. Be\nthis as it may, there is a growing tendency to bring into the closest\npossible relation, or even to identify, instinct and emotion in their\nprimary genesis. The central core of all such interpretations is that\ninstinctive behaviour and experience, its emotional accompaniments, and\nits expression, are but different aspects of the outcome of the\nsame organic occurrences. Such emotions are, therefore, only a\ndistinguishable aspect of the primary tissue of experience and exhibit\na like differentiation. Here again a biological foundation is laid for a\npsychological doctrine of the mental development of the individual.\n\nThe intimate relation between emotion as a psychological mode of\nexperience and expression as a group of organic conditions has an\nimportant bearing on biological interpretation. The emotion, as the\npsychological accompaniment of orderly disturbances in the central\nnervous system profoundly influences behaviour and often renders it more\nvigorous and more effective. The utility of the emotions in the struggle\nfor existence can, therefore, scarcely be over-estimated. Just as\nkeenness of perception has survival-value; just as it is obviously\nsubject to variation; just as it must be enhanced under natural\nselection, whether individually acquired increments are inherited\nor not; and just as its value lies not only in this or that special\nperceptive act but in its importance for life as a whole; so the\nvigorous effectiveness of activity has survival-value; it is subject\nto variation; it must be enhanced under natural selection; and its\nimportance lies not only in particular modes of behaviour but in its\nvalue for life as a whole. If emotion and its expression as a congenital\nendowment are but different aspects of the same biological occurrence;\nand if this is a powerful supplement to vigour effectiveness and\npersistency of behaviour, it must on Darwin's principles be subject to\nnatural selection.\n\nIf we include under the expression of the emotions not only the\npremonitory symptoms of the initial phases of the organic and mental\nstate, not only the signs or conditions of half-tide emotion, but the\nfull-tide manifestation of an emotion which dominates the situation, we\nare naturally led on to the consideration of many of the phenomena\nwhich are discussed under the head of sexual selection. The subject\nis difficult and complex, and it was treated by Darwin with all the\nstrength he could summon to the task. It can only be dealt with here\nfrom a special point of view--that which may serve to illustrate the\ninfluence of certain mental factors on the course of evolution. From\nthis point of view too much stress can scarcely be laid on the dominance\nof emotion during the period of courtship and pairing in the more highly\norganised animals. It is a period of maximum vigour, maximum activity,\nand, correlated with special modes of behaviour and special organic and\nvisceral accompaniments, a period also of maximum emotional excitement.\nThe combats of males, their dances and aerial evolutions, their\nelaborate behaviour and display, or the flood of song in birds, are\nemotional expressions which are at any rate coincident in time with\nsexual periodicity. From the combat of the males there follows on\nDarwin's principles the elimination of those which are deficient in\nbodily vigour, deficient in special structures, offensive or protective,\nwhich contribute to success, deficient in the emotional supplement\nof which persistent and whole-hearted fighting is the expression,\nand deficient in alertness and skill which are the outcome of the\npsychological development of the powers of perception. Few biologists\nquestion that we have here a mode of selection of much importance,\nthough its influence on psychological evolution often fails to receive\nits due emphasis. Mr Wallace (\"Darwinism\", pages 282, 283, London,\n1889.) regards it as \"a form of natural selection\"; \"to it,\" he says,\n\"we must impute the development of the exceptional strength, size, and\nactivity of the male, together with the possession of special offensive\nand defensive weapons, and of all other characters which arise from\nthe development of these or are correlated with them.\" So far there is\nlittle disagreement among the followers of Darwin--for Mr Wallace,\nwith fine magnanimity, has always preferred to be ranked as such,\nnotwithstanding his right, on which a smaller man would have constantly\ninsisted, to the claim of independent originator of the doctrine of\nnatural selection. So far with regard to sexual selection Darwin and Mr\nWallace are agreed; so far and no farther. For Darwin, says Mr Wallace\n(Ibid. page 283.), \"has extended the principle into a totally different\nfield of action, which has none of that character of constancy and of\ninevitable result that attaches to natural selection, including male\nrivalry; for by far the larger portion of the phenomena, which he\nendeavours to explain by the direct action of sexual selection, can only\nbe so explained on the hypothesis that the immediate agency is female\nchoice or preference. It is to this that he imputes the origin of\nall secondary sexual characters other than weapons of offence and\ndefence... In this extension of sexual selection to include the action of\nfemale choice or preference, and in the attempt to give to that choice\nsuch wide-reaching effects, I am unable to follow him more than a very\nlittle way.\"\n\nInto the details of Mr Wallace's criticisms it is impossible to enter\nhere. We cannot discuss either the mode of origin of the variations in\nstructure which have rendered secondary sexual characters possible\nor the modes of selection other than sexual which have rendered them,\nwithin narrow limits, specifically constant. Mendelism and mutation\ntheories may have something to say on the subject when these theories\nhave been more fully correlated with the basal principles of selection.\nIt is noteworthy that Mr Wallace says (\"Darwinism\", pages 283, 284.):\n\"Besides the acquisition of weapons by the male for the purpose of\nfighting with other males, there are some other sexual characters which\nmay have been produced by natural selection. Such are the various sounds\nand odours which are peculiar to the male, and which serve as a call to\nthe female or as an indication of his presence. These are evidently a\nvaluable addition to the means of recognition of the two sexes, and\nare a further indication that the pairing season has arrived; and the\nproduction, intensification, and differentiation of these sounds and\nodours are clearly within the power of natural selection. The same\nremark will apply to the peculiar calls of birds, and even to the\nsinging of the males.\" Why the same remark should not apply to their\ncolours and adornments is not obvious. What is obvious is that \"means\nof recognition\" and \"indication that the pairing season has arrived\" are\ndependent on the perceptive powers of the female who recognises and for\nwhom the indication has meaning. The hypothesis of female preference,\nstripped of the aesthetic surplusage which is psychologically both\nunnecessary and unproven, is really only different in degree from that\nwhich Mr Wallace admits in principle when he says that it is probable\nthat the female is pleased or excited by the display.\n\nLet us for our present purpose leave on one side and regard as sub\njudice the question whether the specific details of secondary sexual\ncharacters are the outcome of female choice. For us the question is\nwhether certain psychological accompaniments of the pairing situation\nhave influenced the course of evolution and whether these psychological\naccompaniments are themselves the outcome of evolution. As a matter of\nobservation, specially differentiated modes of behaviour, often very\nelaborate, frequently requiring highly developed skill, and apparently\nhighly charged with emotional tone, are the precursors of pairing. They\nare generally confined to the males, whose fierce combats during the\nperiod of sexual activity are part of the emotional manifestation. It is\ninconceivable that they have no biological meaning; and it is difficult\nto conceive that they have any other biological end than to evoke in\nthe generally more passive female the pairing impulse. They are based\non instinctive foundations ingrained in the nervous constitution\nthrough natural (or may we not say sexual?) selection in virtue of\ntheir profound utility. They are called into play by a specialised\npresentation such as the sight or the scent of the female at, or a\nlittle in advance of, a critical period of the physiological rhythm.\nThere is no necessity that the male should have any knowledge of the\nend to which his strenuous activity leads up. In presence of the female\nthere is an elaborate application of all the energies of behaviour,\njust because ages of racial preparation have made him biologically and\nemotionally what he is--a functionally sexual male that must dance or\nsing or go through hereditary movements of display, when the appropriate\nstimulation comes. Of course after the first successful courtship\nhis future behaviour will be in some degree modified by his previous\nexperience. No doubt during his first courtship he is gaining the\nprimary data of a peculiarly rich experience, instinctive and emotional.\nBut the biological foundations of the behaviour of courtship are laid\nin the hereditary coordinations. It would seem that in some cases, not\nindeed in all, but perhaps especially in those cases in which secondary\nsexual behaviour is most highly evolved,--correlative with the ardour\nof the male is a certain amount of reluctance in the female. The pairing\nact on her part only takes place after prolonged stimulation, for\naffording which the behaviour of male courtship is the requisite\npresentation. The most vigorous, defiant and mettlesome male is\npreferred just because he alone affords a contributory stimulation\nadequate to evoke the pairing impulse with its attendant emotional tone.\n\nIt is true that this places female preference or choice on a much lower\npsychological plane than Darwin in some passages seems to contemplate\nwhere, for example, he says that the female appreciates the display of\nthe male and places to her credit a taste for the beautiful. But Darwin\nhimself distinctly states (\"Descent of Man\" (2nd edition), Vol. II.\npages 136, 137; (Popular edition), pages 642, 643.) that \"it is not\nprobable that she consciously deliberates; but she is most excited or\nattracted by the most beautiful, or melodious, or gallant males.\" The\nview here put forward, which has been developed by Prof. Groos (\"The\nPlay of Animals\", page 244, London, 1898.), therefore seems to have\nDarwin's own sanction. The phenomena are not only biological; there are\npsychological elements as well. One can hardly suppose that the female\nis unconscious of the male's presence; the final yielding must surely be\naccompanied by heightened emotional tone. Whether we call it choice or\nnot is merely a matter of definition of terms. The behaviour is in part\ndetermined by supplementary psychological values. Prof. Groos regards\nthe coyness of females as \"a most efficient means of preventing the\ntoo early and too frequent yielding to the sexual impulse.\" (Ibid. page\n283.) Be that as it may, it is, in any case, if we grant the facts, a\nmeans through which male sexual behaviour with all its biological and\npsychological implications, is raised to a level otherwise perhaps\nunattainable by natural means, while in the female it affords\nopportunities for the development in the individual and evolution in the\nrace of what we may follow Darwin in calling appreciation, if we empty\nthis word of the aesthetic implications which have gathered round it in\nthe mental life of man.\n\nRegarded from this standpoint sexual selection, broadly considered, has\nprobably been of great importance. The psychological accompaniments\nof the pairing situation have profoundly influenced the course of\nbiological evolution and are themselves the outcome of that evolution.\n\nDarwin makes only passing reference to those modes of behaviour in\nanimals which go by the name of play. \"Nothing,\" he says (\"Descent of\nMan\", Vol. II. page 60; (Popular edition), page 566.), \"is more common\nthan for animals to take pleasure in practising whatever instinct they\nfollow at other times for some real good.\" This is one of the very\nnumerous cases in which a hint of the master has served to stimulate\nresearch in his disciples. It was left to Prof. Groos to develop this\nsubject on evolutionary lines and to elaborate in a masterly manner\nDarwin's suggestion. \"The utility of play,\" he says (\"The Play of\nAnimals\", page 76.), \"is incalculable. This utility consists in the\npractice and exercise it affords for some of the more important duties\nof life,\"--that is to say, for the performance of activities which will\nin adult life be essential to survival. He urges (Ibid. page 75.) that\n\"the play of young animals has its origin in the fact that certain very\nimportant instincts appear at a time when the animal does not seriously\nneed them.\" It is, however, questionable whether any instincts appear\nat a time when they are not needed. And it is questionable whether\nthe instinctive and emotional attitude of the play-fight, to take\none example, can be identified with those which accompany fighting in\nearnest, though no doubt they are closely related and have some common\nfactors. It is probable that play, as preparatory behaviour, differs in\nbiological detail (as it almost certainly does in emotional attributes)\nfrom the earnest of after-life and that it has been evolved through\ndifferentiation and integration of the primary tissue of experience,\nas a preparation through which certain essential modes of skill may be\nacquired--those animals in which the preparatory play-propensity was\nnot inherited in due force and requisite amount being subsequently\neliminated in the struggle for existence. In any case there is little\nquestion that Prof. Groos is right in basing the play-propensity on\ninstinctive foundations. (\"The Play of Animals\" page 24.) None the less,\nas he contends, the essential biological value of play is that it is a\nmeans of training the educable nerve-tissue, of developing that part of\nthe brain which is modified by experience and which thus acquires new\ncharacters, of elaborating the secondary tissue of experience on the\npredetermined lines of instinctive differentiation and thus furthering\nthe psychological activities which are included under the comprehensive\nterm \"intelligent.\"\n\nIn \"The Descent of Man\" Darwin dealt at some length with intelligence\nand the higher mental faculties. (\"Descent of Man\" (1st edition),\nChapters II, III, V; (2nd edition), Chapters III, IV, V.) His object, he\nsays, is to show that there is no fundamental difference between man and\nthe higher mammals in their mental faculties; that these faculties are\nvariable and the variations tend to be inherited; and that under natural\nselection beneficial variations of all kinds will have been preserved\nand injurious ones eliminated.\n\nDarwin was too good an observer and too honest a man to minimise\nthe \"enormous difference\" between the level of mental attainment of\ncivilised man and that reached by any animal. His contention was that\nthe difference, great as it is, is one of degree and not of kind. He\nrealised that, in the development of the mental faculties of man,\nnew factors in evolution have supervened--factors which play but\na subordinate and subsidiary part in animal intelligence.\nIntercommunication by means of language, approbation and blame, and\nall that arises out of reflective thought, are but foreshadowed in the\nmental life of animals. Still he contends that these may be explained\non the doctrine of evolution. He urges (Ibid. Vol. I. pages 70, 71;\n(Popular edition), pages 70, 71.)\" that man is variable in body\nand mind; and that the variations are induced, either directly or\nindirectly, by the same general causes, and obey the same general laws,\nas with the lower animals.\" He correlates mental development with\nthe evolution of the brain. (Ibid. page 81.) \"As the various mental\nfaculties gradually developed themselves, the brain would almost\ncertainly become larger. No one, I presume, doubts that the large\nproportion which the size of man's brain bears to his body, compared to\nthe same proportion in the gorilla or orang, is closely connected with\nhis higher mental powers.\" \"With respect to the lower animals,\" he says\n(\"Descent of Man\" (Popular edition), page 82.), \"M.E. Lartet (\"Comptes\nRendus des Sciences\", June 1, 1868.), by comparing the crania of\ntertiary and recent mammals belonging to the same groups, has come to\nthe remarkable conclusion that the brain is generally larger and the\nconvolutions are more complex in the more recent form.\"\n\nSir E. Ray Lankester has sought to express in the simplest terms the\nimplications of the increase in size of the cerebrum. \"In what,\" he\nasks, \"does the advantage of a larger cerebral mass consist?\" \"Man,\"\nhe replies \"is born with fewer ready-made tricks of the\nnerve-centres--these performances of an inherited nervous mechanism so\noften called by the ill-defined term 'instincts'--than are the monkeys\nor any other animal. Correlated with the absence of inherited ready-made\nmechanism, man has a greater capacity of developing in the course of\nhis individual growth similar nervous mechanisms (similar to but not\nidentical with those of 'instinct') than any other animal... The power of\nbeing educated--'educability' as we may term it--is what man possesses\nin excess as compared with the apes. I think we are justified in forming\nthe hypothesis that it is this 'educability' which is the correlative of\nthe increased size of the cerebrum.\" There has been natural selection\nof the more educable animals, for \"the character which we describe as\n'educability' can be transmitted, it is a congenital character. But the\nRESULTS of education can NOT be transmitted. In each generation they\nhave to be acquired afresh, and with increased 'educability' they are\nmore readily acquired and a larger variety of them... The fact is\nthat there is no community between the mechanisms of instinct and the\nmechanisms of intelligence, and that the latter are later in the history\nof the evolution of the brain than the former and can only develop in\nproportion as the former become feeble and defective.\" (\"Nature\", Vol.\nLXI. pages 624, 625 (1900).)\n\nIn this statement we have a good example of the further development\nof views which Darwin foreshadowed but did not thoroughly work out. It\nstates the biological case clearly and tersely. Plasticity of behaviour\nin special accommodation to special circumstances is of survival value;\nit depends upon acquired characters; it is correlated with increase in\nsize and complexity of the cerebrum; under natural selection therefore\nthe larger and more complex cerebrum as the organ of plastic behaviour\nhas been the outcome of natural selection. We have thus the biological\nfoundations for a further development of genetic psychology.\n\nThere are diversities of opinion, as Darwin showed, with regard to the\nrange of instinct in man and the higher animals as contrasted with lower\ntypes. Darwin himself said (\"Descent of Man\", Vol. I. page 100.) that\n\"Man, perhaps, has somewhat fewer instincts than those possessed by the\nanimals which come next to him in the series.\" On the other hand, Prof.\nWm. James says (\"Principles of Psychology,\" Vol. II. page 289.) that man\nis probably the animal with most instincts. The true position is that\nman and the higher animals have fewer complete and self-sufficing\ninstincts than those which stand lower in the scale of mental\nevolution, but that they have an equally large or perhaps larger mass of\ninstinctive raw material which may furnish the stuff to be elaborated\nby intelligent processes. There is, perhaps, a greater abundance of\nthe primary tissue of experience to be refashioned and integrated by\nsecondary modification; there is probably the same differentiation in\nrelation to the determining biological ends, but there is at the outset\nless differentiation of the particular and specific modes of behaviour.\nThe specialised instinctive performances and their concomitant\nexperience-complexes are at the outset more indefinite. Only through\nacquired connections, correlated with experience, do they become\ndefinitely organised.\n\nThe full working-out of the delicate and subtle relationship of instinct\nand educability--that is, of the hereditary and the acquired factors in\nthe mental life--is the task which lies before genetic and comparative\npsychology. They interact throughout the whole of life, and their\ninteractions are very complex. No one can read the chapters of \"The\nDescent of Man\" which Darwin devotes to a consideration of the mental\ncharacters of man and animals without noticing, on the one hand, how\nsedulous he is in his search for hereditary foundations, and, on the\nother hand, how fully he realises the importance of acquired habits of\nmind. The fact that educability itself has innate tendencies--is in fact\na partially differentiated educability--renders the unravelling of the\nfactors of mental progress all the more difficult.\n\nIn his comparison of the mental powers of men and animals it was\nessential that Darwin should lay stress on points of similarity rather\nthan on points of difference. Seeking to establish a doctrine of\nevolution, with its basal concept of continuity of process and community\nof character, he was bound to render clear and to emphasise the\ncontention that the difference in mind between man and the higher\nanimals, great as it is, is one of degree and not of kind. To this end\nDarwin not only recorded a large number of valuable observations of\nhis own, and collected a considerable body of information from reliable\nsources, he presented the whole subject in a new light and showed that\na natural history of mind might be written and that this method of study\noffered a wide and rich field for investigation. Of course those who\nregarded the study of mind only as a branch of metaphysics smiled at\nthe philosophical ineptitude of the mere man of science. But the\ninvestigation, on natural history lines, has been prosecuted with a\nlarge measure of success. Much indeed still remains to be done; for\nspecial training is required, and the workers are still few. Promise\nfor the future is however afforded by the fact that investigation is\nprosecuted on experimental lines and that something like organised\nmethods of research are taking form. There is now but little reliance\non casual observations recorded by those who have not undergone the\nnecessary discipline in these methods. There is also some change of\nemphasis in formulating conclusions. Now that the general evolutionary\nthesis is fully and freely accepted by those who carry on such\nresearches, more stress is laid on the differentiation of the stages of\nevolutionary advance than on the fact of their underlying community of\nnature. The conceptual intelligence which is especially characteristic\nof the higher mental procedure of man is more firmly distinguished\nfrom the perceptual intelligence which he shares with the lower\nanimals--distinguished now as a higher product of evolution, no longer\nas differing in origin or different in kind. Some progress has been\nmade, on the one hand in rendering an account of intelligent profiting\nby experience under the guidance of pleasure and pain in the perceptual\nfield, on lines predetermined by instinctive differentiation for\nbiological ends, and on the other hand in elucidating the method of\nconceptual thought employed, for example, by the investigator himself in\ninterpreting the perceptual experience of the lower animals.\n\nThus there is a growing tendency to realise more fully that there\nare two orders of educability--first an educability of the perceptual\nintelligence based on the biological foundation of instinct, and\nsecondly an educability of the conceptual intelligence which\nrefashions and rearranges the data afforded by previous inheritance\nand acquisition. It is in relation to this second and higher order of\neducability that the cerebrum of man shows so large an increase of\nmass and a yet larger increase of effective surface through its rich\nconvolutions. It is through educability of this order that the human\nchild is brought intellectually and affectively into touch with the\nideal constructions by means of which man has endeavoured, with more\nor less success, to reach an interpretation of nature, and to guide the\ncourse of the further evolution of his race--ideal constructions which\nform part of man's environment.\n\nIt formed no part of Darwin's purpose to consider, save in broad\noutline, the methods, or to discuss in any fulness of detail the results\nof the process by which a differentiation of the mental faculties of\nman from those of the lower animals has been brought about--a\ndifferentiation the existence of which he again and again\nacknowledges. His purpose was rather to show that, notwithstanding\nthis differentiation, there is basal community in kind. This must be\nremembered in considering his treatment of the biological foundations\non which man's systems of ethics are built. He definitely stated that he\napproached the subject \"exclusively from the side of natural history.\"\n(\"Descent of Man\", Vol. I. page 149.) His general conclusion is that the\nmoral sense is fundamentally identical with the social instincts, which\nhave been developed for the good of the community; and he suggests\nthat the concept which thus enables us to interpret the biological\nground-plan of morals also enables us to frame a rational ideal of the\nmoral end. \"As the social instincts,\" he says (Ibid. page 185.), \"both\nof man and the lower animals have no doubt been developed by nearly the\nsame steps, it would be advisable, if found practicable, to use the same\ndefinition in both cases, and to take as the standard of morality,\nthe general good or welfare of the community, rather than the general\nhappiness.\" But the kind of community for the good of which the social\ninstincts of animals and primitive men were biologically developed may\nbe different from that which is the product of civilisation, as Darwin\nno doubt realised. Darwin's contention was that conscience is a social\ninstinct and has been evolved because it is useful to the tribe in the\nstruggle for existence against other tribes. On the other hand, J.S.\nMill urged that the moral feelings are not innate but acquired, and Bain\nheld the same view, believing that the moral sense is acquired by each\nindividual during his life-time. Darwin, who notes (Ibid. page 150\n(footnote).) their opinion with his usual candour, adds that \"on the\ngeneral theory of evolution this is at least extremely improbable. It\nis impossible to enter into the question here: much turns on the exact\nconnotation of the terms \"conscience\" and \"moral sense,\" and on the\nmeaning we attach to the statement that the moral sense is fundamentally\nidentical with the social instincts.\"\n\nPresumably the majority of those who approach the subjects discussed in\nthe third, fourth and fifth chapters of \"The Descent of Man\" in the full\nconviction that mental phenomena, not less than organic phenomena,\nhave a natural genesis, would, without hesitation, admit that the\nintellectual and moral systems of civilised man are ideal constructions,\nthe products of conceptual thought, and that as such they are, in\ntheir developed form, acquired. The moral sentiments are the emotional\nanalogues of highly developed concepts. This does not however imply that\nthey are outside the range of natural history treatment. Even though\nit may be desirable to differentiate the moral conduct of men from the\nsocial behaviour of animals (to which some such term as \"pre-moral\" or\n\"quasi-moral\" may be applied), still the fact remains that, as Darwin\nshowed, there is abundant evidence of the occurrence of such social\nbehaviour--social behaviour which, even granted that it is in large part\nintelligently acquired, and is itself so far a product of educability,\nis of survival value. It makes for that integration without which no\nsocial group could hold together and escape elimination. Furthermore,\neven if we grant that such behaviour is intelligently acquired, that\nis to say arises through the modification of hereditary instincts and\nemotions, the fact remains that only through these instinctive and\nemotional data is afforded the primary tissue of the experience which is\nsusceptible of such modification.\n\nDarwin sought to show, and succeeded in showing, that for the\nintellectual and moral life there are instinctive foundations which a\nbiological treatment alone can disclose. It is true that he did not\nin all cases analytically distinguish the foundations from the\nsuperstructure. Even to-day we are scarcely in a position to do so\nadequately. But his treatment was of great value in giving an impetus to\nfurther research. This value indeed can scarcely be overestimated.\nAnd when the natural history of the mental operations shall have been\nwritten, the cardinal fact will stand forth, that the instinctive and\nemotional foundations are the outcome of biological evolution and have\nbeen ingrained in the race through natural selection. We shall more\nclearly realise that educability itself is a product of natural\nselection, though the specific results acquired through cerebral\nmodifications are not transmitted through heredity. It will, perhaps,\nalso be realised that the instinctive foundations of social behaviour\nare, for us, somewhat out of date and have undergone but little change\nthroughout the progress of civilisation, because natural selection\nhas long since ceased to be the dominant factor in human progress. The\nhistory of human progress has been mainly the history of man's\nhigher educability, the products of which he has projected on to his\nenvironment. This educability remains on the average what it was a dozen\ngenerations ago; but the thought-woven tapestry of his surroundings is\nrefashioned and improved by each succeeding generation. Few men have in\ngreater measure enriched the thought-environment with which it is the\naim of education to bring educable human beings into vital contact, than\nhas Charles Darwin. His special field of work was the wide province of\nbiology; but he did much to help us realise that mental factors have\ncontributed to organic evolution and that in man, the highest product of\nEvolution, they have reached a position of unquestioned supremacy.\n\n\n\n\nXXII. THE INFLUENCE OF THE CONCEPTION OF EVOLUTION ON MODERN PHILOSOPHY.\nBy H. Hoffding.\n\nProfessor of Philosophy in the University of Copenhagen.\n\n\nI.\n\nIt is difficult to draw a sharp line between philosophy and natural\nscience. The naturalist who introduces a new principle, or demonstrates\na fact which throws a new light on existence, not only renders an\nimportant service to philosophy but is himself a philosopher in the\nbroader sense of the word. The aim of philosophy in the stricter sense\nis to attain points of view from which the fundamental phenomena and\nthe principles of the special sciences can be seen in their relative\nimportance and connection. But philosophy in this stricter sense\nhas always been influenced by philosophy in the broader sense. Greek\nphilosophy came under the influence of logic and mathematics, modern\nphilosophy under the influence of natural science. The name of Charles\nDarwin stands with those of Galileo, Newton, and Robert Mayer--names\nwhich denote new problems and great alterations in our conception of the\nuniverse.\n\nFirst of all we must lay stress on Darwin's own personality. His deep\nlove of truth, his indefatigable inquiry, his wide horizon, and his\nsteady self-criticism make him a scientific model, even if his results\nand theories should eventually come to possess mainly an historical\ninterest. In the intellectual domain the primary object is to reach\nhigh summits from which wide surveys are possible, to reach them toiling\nhonestly upwards by way of experience, and then not to turn dizzy when\na summit is gained. Darwinians have sometimes turned dizzy, but Darwin\nnever. He saw from the first the great importance of his hypothesis, not\nonly because of its solution of the old problem as to the value of the\nconcept of species, not only because of the grand picture of natural\nevolution which it unrolls, but also because of the life and inspiration\nits method would impart to the study of comparative anatomy, of instinct\nand of heredity, and finally because of the influence it would exert on\nthe whole conception of existence. He wrote in his note-book in the\nyear 1837: \"My theory would give zest to recent and fossil comparative\nanatomy; it would lead to the study of instinct, heredity, and\nmind-heredity, whole (of) metaphysics.\" (\"Life and Letters of Charles\nDarwin\", Vol. I. page 8.)\n\nWe can distinguish four main points in which Darwin's investigations\npossess philosophical importance.\n\nThe evolution hypothesis is much older than Darwin; it is, indeed, one\nof the oldest guessings of human thought. In the eighteenth century it\nwas put forward by Diderot and Lamettrie and suggested by Kant (1786).\nAs we shall see later, it was held also by several philosophers in the\nfirst half of the nineteenth century. In his preface to \"The Origin of\nSpecies\", Darwin mentions the naturalists who were his forerunners.\nBut he has set forth the hypothesis of evolution in so energetic\nand thorough a manner that it perforce attracts the attention of\nall thoughtful men in a much higher degree than it did before the\npublication of the \"Origin\".\n\nAnd further, the importance of his teaching rests on the fact that he,\nmuch more than his predecessors, even than Lamarck, sought a foundation\nfor his hypothesis in definite facts. Modern science began by\ndemanding--with Kepler and Newton--evidence of verae causae; this\ndemand Darwin industriously set himself to satisfy--hence the wealth of\nmaterial which he collected by his observations and his experiments.\nHe not only revived an old hypothesis, but he saw the necessity of\nverifying it by facts. Whether the special cause on which he founded the\nexplanation of the origin of species--Natural Selection--is sufficient,\nis now a subject of discussion. He himself had some doubt in regard\nto this question, and the criticisms which are directed against his\nhypothesis hit Darwinism rather than Darwin. In his indefatigable search\nfor empirical evidence he is a model even for his antagonists: he has\ncompelled them to approach the problems of life along other lines than\nthose which were formerly followed.\n\nWhether the special cause to which Darwin appealed is sufficient or not,\nat least to it is probably due the greater part of the influence which\nhe has exerted on the general trend of thought. \"Struggle for existence\"\nand \"natural selection\" are principles which have been applied, more or\nless, in every department of thought. Recent research, it is true, has\ndiscovered greater empirical discontinuity--leaps, \"mutations\"--whereas\nDarwin believed in the importance of small variations slowly\naccumulated. It has also been shown by the experimental method, which\nin recent biological work has succeeded Darwin's more historical method,\nthat types once constituted possess great permanence, the fluctuations\nbeing restricted within clearly defined boundaries. The problem has\nbecome more precise, both as to variation and as to heredity. The inner\nconditions of life have in both respects shown a greater independence\nthan Darwin had supposed in his theory, though he always admitted that\nthe cause of variation was to him a great enigma, \"a most perplexing\nproblem,\" and that the struggle for life could only occur where\nvariation existed. But, at any rate, it was of the greatest importance\nthat Darwin gave a living impression of the struggle for life which is\neverywhere going on, and to which even the highest forms of existence\nmust be amenable. The philosophical importance of these ideas does not\nstand or fall with the answer to the question, whether natural selection\nis a sufficient explanation of the origin of species or not: it has\nan independent, positive value for everyone who will observe life and\nreality with an unbiassed mind.\n\nIn accentuating the struggle for life Darwin stands as a\ncharacteristically English thinker: he continues a train of ideas which\nHobbes and Malthus had already begun. Moreover in his critical views as\nto the conception of species he had English forerunners; in the middle\nages Occam and Duns Scotus, in the eighteenth century Berkeley and Hume.\nIn his moral philosophy, as we shall see later, he is an adherent of the\nschool which is represented by Hutcheson, Hume and Adam Smith. Because\nhe is no philosopher in the stricter sense of the term, it is of great\ninterest to see that his attitude of mind is that of the great thinkers\nof his nation.\n\nIn considering Darwin's influence on philosophy we will begin with an\nexamination of the attitude of philosophy to the conception of evolution\nat the time when \"The Origin of Species\" appeared. We will then examine\nthe effects which the theory of evolution, and especially the idea\nof the struggle for life, has had, and naturally must have, on the\ndiscussion of philosophical problems.\n\nII.\n\nWhen \"The Origin of Species\" appeared fifty years ago Romantic\nspeculation, Schelling's and Hegel's philosophy, still reigned on the\ncontinent, while in England Positivism, the philosophy of Comte and\nStuart Mill, represented the most important trend of thought. German\nspeculation had much to say on evolution, it even pretended to be a\nphilosophy of evolution. But then the word \"evolution\" was to be taken\nin an ideal, not in a real, sense. To speculative thought the forms and\ntypes of nature formed a system of ideas, within which any form could\nlead us by continuous transitions to any other. It was a classificatory\nsystem which was regarded as a divine world of thought or images, within\nwhich metamorphoses could go on--a condition comparable with that in\nthe mind of the poet when one image follows another with imperceptible\nchanges. Goethe's ideas of evolution, as expressed in his \"Metamorphosen\nder Pflanzen und der Thiere\", belong to this category; it is, therefore,\nincorrect to call him a forerunner of Darwin. Schelling and Hegel\nheld the same idea; Hegel expressly rejected the conception of a real\nevolution in time as coarse and materialistic. \"Nature,\" he says, \"is\nto be considered as a SYSTEM OF STAGES, the one necessarily arising from\nthe other, and being the nearest truth of that from which it proceeds;\nbut not in such a way that the one is NATURALLY generated by the other;\non the contrary (their connection lies) in the inner idea which is the\nground of nature. The METAMORPHOSIS can be ascribed only to the notion\nas such, because it alone is evolution... It has been a clumsy idea in\nthe older as well as in the newer philosophy of nature, to regard the\ntransformation and the transition from one natural form and sphere to\na higher as an outward and actual production.\" (\"Encyclopaedie der\nphilosophischen Wissenschaften\" (4th edition), Berlin, 1845, paragraph\n249.)\n\nThe only one of the philosophers of Romanticism who believed in a\nreal, historical evolution, a real production of new species, was Oken.\n(\"Lehrbuch der Naturphilosophie\", Jena, 1809.) Danish philosophers, such\nas Treschow (1812) and Sibbern (1846), have also broached the idea of\nan historical evolution of all living beings from the lowest to the\nhighest. Schopenhauer's philosophy has a more realistic character than\nthat of Schelling's and Hegel's, his diametrical opposites, though he\nalso belongs to the romantic school of thought. His philosophical and\npsychological views were greatly influenced by French naturalists and\nphilosophers, especially by Cabanis and Lamarck. He praises the \"ever\nmemorable Lamarck,\" because he laid so much stress on the \"will to\nlive.\" But he repudiates as a \"wonderful error\" the idea that the\norgans of animals should have reached their present perfection through\na development in time, during the course of innumerable generations. It\nwas, he said, a consequence of the low standard of contemporary French\nphilosophy, that Lamarck came to the idea of the construction of living\nbeings in time through succession! (\"Ueber den Willen in der Natur\" (2nd\nedition), Frankfurt a. M., 1854, pages 41-43.)\n\nThe positivistic stream of thought was not more in favour of a real\nevolution than was the Romantic school. Its aim was to adhere to\npositive facts: it looked with suspicion on far-reaching speculation.\nComte laid great stress on the discontinuity found between the different\nkingdoms of nature, as well as within each single kingdom. As he\nregarded as unscientific every attempt to reduce the number of physical\nforces, so he rejected entirely the hypothesis of Lamarck concerning the\nevolution of species; the idea of species would in his eyes absolutely\nlose its importance if a transition from species to species under the\ninfluence of conditions of life were admitted. His disciples (Littre,\nRobin) continued to direct against Darwin the polemics which their\nmaster had employed against Lamarck. Stuart Mill, who, in the theory\nof knowledge, represented the empirical or positivistic movement in\nphilosophy--like his English forerunners from Locke to Hume--founded\nhis theory of knowledge and morals on the experience of the single\nindividual. He sympathised with the theory of the original likeness of\nall individuals and derived their differences, on which he practically\nand theoretically laid much stress, from the influence both of\nexperience and education, and, generally, of physical and social causes.\nHe admitted an individual evolution, and, in the human species, an\nevolution based on social progress; but no physiological evolution of\nspecies. He was afraid that the hypothesis of heredity would carry us\nback to the old theory of \"innate\" ideas.\n\nDarwin was more empirical than Comte and Mill; experience disclosed to\nhim a deeper continuity than they could find; closer than before the\nnature and fate of the single individual were shown to be interwoven in\nthe great web binding the life of the species with nature as a whole.\nAnd the continuity which so many idealistic philosophers could find\nonly in the world of thought, he showed to be present in the world of\nreality.\n\nIII.\n\nDarwin's energetic renewal of the old idea of evolution had its chief\nimportance in strengthening the conviction of this real continuity in\nthe world, of continuity in the series of form and events. It was a\ngreat support for all those who were prepared to base their conception\nof life on scientific grounds. Together with the recently discovered law\nof the conservation of energy, it helped to produce the great realistic\nmovement which characterises the last third of the nineteenth century.\nAfter the decline of the Romantic movement people wished to have firmer\nground under their feet and reality now asserted itself in a more\nemphatic manner than in the period of Romanticism. It was easy for Hegel\nto proclaim that \"the real\" was \"the rational,\" and that \"the\nrational\" was \"the real\": reality itself existed for him only in the\ninterpretation of ideal reason, and if there was anything which could\nnot be merged in the higher unity of thought, then it was only an\nexample of the \"impotence of nature to hold to the idea.\" But now\nconcepts are to be founded on nature and not on any system of categories\ntoo confidently deduced a priori. The new devotion to nature had its\nrecompense in itself, because the new points of view made us see that\nnature could indeed \"hold to ideas,\" though perhaps not to those which\nwe had cogitated beforehand.\n\nA most important question for philosophers to answer was whether the\nnew views were compatible with an idealistic conception of life and\nexistence. Some proclaimed that we have now no need of any philosophy\nbeyond the principles of the conservation of matter and energy and the\nprinciple of natural evolution: existence should and could be definitely\nand completely explained by the laws of material nature. But abler\nthinkers saw that the thing was not so simple. They were prepared to\ngive the new views their just place and to examine what alterations the\nold views must undergo in order to be brought into harmony with the new\ndata.\n\nThe realistic character of Darwin's theory was shown not only in the\nidea of natural continuity, but also, and not least, in the idea of the\ncause whereby organic life advances step by step. This idea--the idea of\nthe struggle for life--implied that nothing could persist, if it had no\npower to maintain itself under the given conditions. Inner value\nalone does not decide. Idealism was here put to its hardest trial. In\ncontinuous evolution it could perhaps still find an analogy to the inner\nevolution of ideas in the mind; but in the demand for power in order to\nstruggle with outward conditions Realism seemed to announce itself in\nits most brutal form. Every form of Idealism had to ask itself seriously\nhow it was going to \"struggle for life\" with this new Realism.\n\nWe will now give a short account of the position which leading thinkers\nin different countries have taken up in regard to this question.\n\nI. Herbert Spencer was the philosopher whose mind was best prepared by\nhis own previous thinking to admit the theory of Darwin to a place in\nhis conception of the world. His criticism of the arguments which had\nbeen put forward against the hypothesis of Lamarck, showed that Spencer,\nas a young man, was an adherent to the evolution idea. In his\n\"Social Statics\" (1850) he applied this idea to human life and moral\ncivilisation. In 1852 he wrote an essay on \"The Development Hypothesis\",\nin which he definitely stated his belief that the differentiation of\nspecies, like the differentiation within a single organism, was the\nresult of development. In the first edition of his \"Psychology\" (1855)\nhe took a step which put him in opposition to the older English school\n(from Locke to Mill): he acknowledged \"innate ideas\" so far as to\nadmit the tendency of acquired habits to be inherited in the course of\ngenerations, so that the nature and functions of the individual are only\nto be understood through its connection with the life of the species.\nIn 1857, in his essay on \"Progress\", he propounded the law of\ndifferentiation as a general law of evolution, verified by examples from\nall regions of experience, the evolution of species being only one of\nthese examples. On the effect which the appearance of \"The Origin of\nSpecies\" had on his mind he writes in his \"Autobiography\": \"Up to\nthat time... I held that the sole cause of organic evolution is the\ninheritance of functionally-produced modifications. The \"Origin of\nSpecies\" made it clear to me that I was wrong, and that the larger part\nof the facts cannot be due to any such cause... To have the theory of\norganic evolution justified was of course to get further support for\nthat theory of evolution at large with which... all my conceptions were\nbound up.\" (Spencer, \"Autobiography\", Vol. II. page 50, London, 1904.)\nInstead of the metaphorical expression \"natural selection,\" Spencer\nintroduced the term \"survival of the fittest,\" which found favour with\nDarwin as well as with Wallace.\n\nIn working out his ideas of evolution, Spencer found that\ndifferentiation was not the only form of evolution. In its simplest form\nevolution is mainly a concentration, previously scattered elements being\nintegrated and losing independent movement. Differentiation is only\nforthcoming when minor wholes arise within a greater whole. And the\nhighest form of evolution is reached when there is a harmony between\nconcentration and differentiation, a harmony which Spencer calls\nequilibration and which he defines as a moving equilibrium. At the same\ntime this definition enables him to illustrate the expression \"survival\nof the fittest.\" \"Every living organism exhibits such a moving\nequilibrium--a balanced set of functions constituting its life; and the\noverthrow of this balanced set of functions or moving equilibrium is\nwhat we call death. Some individuals in a species are so constituted\nthat their moving equilibria are less easily overthrown than those of\nother individuals; and these are the fittest which survive, or, in Mr\nDarwin's language, they are the select which nature preserves.\" (Ibid.\npage 100.) Not only in the domain of organic life, but in all domains,\nthe summit of evolution is, according to Spencer, characterised by such\na harmony--by a moving equilibrium.\n\nSpencer's analysis of the concept of evolution, based on a great variety\nof examples, has made this concept clearer and more definite than\nbefore. It contains the three elements; integration, differentiation and\nequilibration. It is true that a concept which is to be valid for all\ndomains of experience must have an abstract character, and between the\nseveral domains there is, strictly speaking, only a relation of analogy.\nSo there is only analogy between psychical and physical evolution. But\nthis is no serious objection, because general concepts do not express\nmore than analogies between the phenomena which they represent. Spencer\ntakes his leading terms from the material world in defining evolution\n(in the simplest form) as integration of matter and dissipation of\nmovement; but as he--not always quite consistently (Cf. my letter\nto him, 1876, now printed in Duncan's \"Life and Letters of Herbert\nSpencer\", page 178, London, 1908.)--assumed a correspondence of mind and\nmatter, he could very well give these terms an indirect importance for\npsychical evolution. Spencer has always, in my opinion with full right,\nrepudiated the ascription of materialism. He is no more a materialist\nthan Spinoza. In his \"Principles of Psychology\" (paragraph 63) he\nexpressed himself very clearly: \"Though it seems easier to translate\nso-called matter into so-called spirit, than to translate so-called\nspirit into so-called matter--which latter is indeed wholly\nimpossible--yet no translation can carry us beyond our symbols.\" These\nwords lead us naturally to a group of thinkers whose starting-point\nwas psychical evolution. But we have still one aspect of Spencer's\nphilosophy to mention.\n\nSpencer founded his \"laws of evolution\" on an inductive basis, but\nhe was convinced that they could be deduced from the law of the\nconservation of energy. Such a deduction is, perhaps, possible for the\nmore elementary forms of evolution, integration and differentiation; but\nit is not possible for the highest form, the equilibration, which is a\nharmony of integration and differentiation. Spencer can no more deduce\nthe necessity for the eventual appearance of \"moving equilibria\" of\nharmonious totalities than Hegel could guarantee the \"higher unities\"\nin which all contradictions should be reconciled. In Spencer's hands the\ntheory of evolution acquired a more decidedly optimistic character\nthan in Darwin's; but I shall deal later with the relation of Darwin's\nhypothesis to the opposition of optimism and pessimism.\n\nII. While the starting-point of Spencer was biological or cosmological,\npsychical evolution being conceived as in analogy with physical, a group\nof eminent thinkers--in Germany Wundt, in France Fouillee, in Italy\nArdigo--took, each in his own manner, their starting-point in psychical\nevolution as an original fact and as a type of all evolution, the\nhypothesis of Darwin coming in as a corroboration and as a special\nexample. They maintain the continuity of evolution; they find this\ncharacter most prominent in psychical evolution, and this is for them a\nmotive to demand a corresponding continuity in the material, especially\nin the organic domain.\n\nTo Wundt and Fouillee the concept of will is prominent. They see the\ntype of all evolution in the transformation of the life of will from\nblind impulse to conscious choice; the theories of Lamarck and Darwin\nare used to support the view that there is in nature a tendency to\nevolution in steady reciprocity with external conditions. The struggle\nfor life is here only a secondary fact. Its apparent prominence is\nexplained by the circumstance that the influence of external conditions\nis easily made out, while inner conditions can be verified only\nthrough their effects. For Ardigo the evolution of thought was the\nstarting-point and the type: in the evolution of a scientific hypothesis\nwe see a progress from the indefinite (indistinto) to the definite\n(distinto), and this is a characteristic of all evolution, as Ardigo has\npointed out in a series of works. The opposition between indistinto and\ndistinto corresponds to Spencer's opposition between homogeneity and\nheterogeneity. The hypothesis of the origin of differences of species\nfrom more simple forms is a special example of the general law of\nevolution.\n\nIn the views of Wundt and Fouillee we find the fundamental idea of\nidealism: psychical phenomena as expressions of the innermost nature of\nexistence. They differ from the older Idealism in the great stress which\nthey lay on evolution as a real, historical process which is going on\nthrough steady conflict with external conditions. The Romantic dread\nof reality is broken. It is beyond doubt that Darwin's emphasis on the\nstruggle for life as a necessary condition of evolution has been a very\nimportant factor in carrying philosophy back to reality from the heaven\nof pure ideas. The philosophy of Ardigo, on the other side, appears\nmore as a continuation and deepening of positivism, though the Italian\nthinker arrived at his point of view independently of French-English\npositivism. The idea of continuous evolution is here maintained in\nopposition to Comte's and Mill's philosophy of discontinuity. From Wundt\nand Fouillee Ardigo differs in conceiving psychical evolution not as an\nimmediate revelation of the innermost nature of existence, but only as a\nsingle, though the most accessible example, of evolution.\n\nIII. To the French philosophers Boutroux and Bergson, evolution proper\nis continuous and qualitative, while outer experience and physical\nscience give us fragments only, sporadic processes and mechanical\ncombinations. To Bergson, in his recent work \"L'Evolution Creatrice\",\nevolution consists in an elan de vie which to our fragmentary\nobservation and analytic reflexion appears as broken into a manifold of\nelements and processes. The concept of matter in its scientific form\nis the result of this breaking asunder, essential for all scientific\nreflexion. In these conceptions the strongest opposition between\ninner and outer conditions of evolution is expressed: in the domain of\ninternal conditions spontaneous development of qualitative forms--in the\ndomain of external conditions discontinuity and mechanical combination.\n\nWe see, then, that the theory of evolution has influenced philosophy\nin a variety of forms. It has made idealistic thinkers revise their\nrelation to the real world; it has led positivistic thinkers to find a\ncloser connection between the facts on which they based their views; it\nhas made us all open our eyes for new possibilities to arise through\nthe prima facie inexplicable \"spontaneous\" variations which are the\ncondition of all evolution. This last point is one of peculiar interest.\nDeeper than speculative philosophy and mechanical science saw in the\ndays of their triumph, we catch sight of new streams, whose sources and\nlaws we have still to discover. Most sharply does this appear in the\ntheory of mutation, which is only a stronger accentuation of a main\npoint in Darwinism. It is interesting to see that an analogous\nproblem comes into the foreground in physics through the discovery\nof radioactive phenomena, and in psychology through the assumption\nof psychical new formations (as held by Boutroux, William James and\nBergson). From this side, Darwin's ideas, as well as the analogous\nideas in other domains, incite us to renewed examination of our first\nprinciples, their rationality and their value. On the other hand,\nhis theory of the struggle for existence challenges us to examine the\nconditions and discuss the outlook as to the persistence of human life\nand society and of the values that belong to them. It is not enough to\nhope (or fear?) the rising of new forms; we have also to investigate the\npossibility of upholding the forms and ideals which have hitherto been\nthe bases of human life. Darwin has here given his age the most earnest\nand most impressive lesson. This side of Darwin's theory is of peculiar\ninterest to some special philosophical problems to which I now pass.\n\nIV.\n\nAmong philosophical problems the problem of knowledge has in the last\ncentury occupied a foremost place. It is natural, then, to ask how\nDarwin and the hypothesis whose most eminent representative he is, stand\nto this problem.\n\nDarwin started an hypothesis. But every hypothesis is won by inference\nfrom certain presuppositions, and every inference is based on\nthe general principles of human thought. The evolution hypothesis\npresupposes, then, human thought and its principles. And not only\nthe abstract logical principles are thus presupposed. The evolution\nhypothesis purports to be not only a formal arrangement of phenomena,\nbut to express also the law of a real process. It supposes, then,\nthat the real data--all that in our knowledge which we do not produce\nourselves, but which we in the main simply receive--are subjected\nto laws which are at least analogous to the logical relations of our\nthoughts; in other words, it assumes the validity of the principle of\ncausality. If organic species could arise without cause there would\nbe no use in framing hypotheses. Only if we assume the principle of\ncausality, is there a problem to solve.\n\nThough Darwinism has had a great influence on philosophy considered as\na striving after a scientific view of the world, yet here is a point of\nview--the epistemological--where philosophy is not only independent but\nreaches beyond any result of natural science. Perhaps it will be said:\nthe powers and functions of organic beings only persist (perhaps also\nonly arise) when they correspond sufficiently to the conditions under\nwhich the struggle of life is to go on. Human thought itself is, then, a\nvariation (or a mutation) which has been able to persist and to\nsurvive. Is not, then, the problem of knowledge solved by the evolution\nhypothesis? Spencer had given an affirmative answer to this question\nbefore the appearance of \"The Origin of Species\". For the individual, he\nsaid, there is an a priori, original, basis (or Anlage) for all mental\nlife; but in the species all powers have developed in reciprocity with\nexternal conditions. Knowledge is here considered from the practical\npoint of view, as a weapon in the struggle for life, as an \"organon\"\nwhich has been continuously in use for generations. In recent years the\neconomic or pragmatic epistemology, as developed by Avenarius and Mach\nin Germany, and by James in America, points in the same direction.\nScience, it is said, only maintains those principles and presuppositions\nwhich are necessary to the simplest and clearest orientation in\nthe world of experience. All assumptions which cannot be applied to\nexperience and to practical work, will successively be eliminated.\n\nIn these views a striking and important application is made of the idea\nof struggle for life to the development of human thought. Thought must,\nas all other things in the world, struggle for life. But this whole\nconsideration belongs to psychology, not to the theory of knowledge\n(epistemology), which is concerned only with the validity of knowledge,\nnot with its historical origin. Every hypothesis to explain the\norigin of knowledge must submit to cross-examination by the theory of\nknowledge, because it works with the fundamental forms and principles\nof human thought. We cannot go further back than these forms and\nprinciples, which it is the aim of epistemology to ascertain and for\nwhich no further reason can be given. (The present writer, many years\nago, in his \"Psychology\" (Copenhagen, 1882; English translation London,\n1891), criticised the evolutionistic treatment of the problem of\nknowledge from the Kantian point of view.)\n\nBut there is another side of the problem which is, perhaps, of more\nimportance and which epistemology generally overlooks. If new variations\ncan arise, not only in organic but perhaps also in inorganic nature, new\ntasks are placed before the human mind. The question is, then, if it has\nforms in which there is room for the new matter? We are here touching\na possibility which the great master of epistemology did not bring to\nlight. Kant supposed confidently that no other matter of knowledge could\nstream forth from the dark source which he called \"the thing-in-itself,\"\nthan such as could be synthesised in our existing forms of knowledge.\nHe mentions the possibility of other forms than the human, and warns us\nagainst the dogmatic assumption that the human conception of existence\nshould be absolutely adequate. But he seems to be quite sure that the\nthing-in-itself works constantly, and consequently always gives us only\nwhat our powers can master. This assumption was a consequence of Kant's\nrationalistic tendency, but one for which no warrant can be given.\nEvolutionism and systematism are opposing tendencies which can never\nbe absolutely harmonised one with the other. Evolution may at any time\nbreak some form which the system-monger regards as finally established.\nDarwin himself felt a great difference in looking at variation as an\nevolutionist and as a systematist. When he was working at his evolution\ntheory, he was very glad to find variations; but they were a hindrance\nto him when he worked as a systematist, in preparing his work on\nCirripedia. He says in a letter: \"I had thought the same parts of the\nsame species more resemble (than they do anyhow in Cirripedia) objects\ncast in the same mould. Systematic work would be easy were it not\nfor this confounded variation, which, however, is pleasant to me as a\nspeculatist, though odious to me as a systematist.\" (\"Life and Letters\",\nVol. II. page 37.) He could indeed be angry with variations even as\nan evolutionist; but then only because he could not explain them, not\nbecause he could not classify them. \"If, as I must think, external\nconditions produce little DIRECT effect, what the devil determines each\nparticular variation?\" (Ibid. page 232.) What Darwin experienced in\nhis particular domain holds good of all knowledge. All knowledge is\nsystematic, in so far as it strives to put phenomena in quite definite\nrelations, one to another. But the systematisation can never be\ncomplete. And here Darwin has contributed much to widen the world for\nus. He has shown us forces and tendencies in nature which make absolute\nsystems impossible, at the same time that they give us new objects and\nproblems. There is still a place for what Lessing called \"the unceasing\nstriving after truth,\" while \"absolute truth\" (in the sense of a closed\nsystem) is unattainable so long as life and experience are going on.\n\nThere is here a special remark to be made. As we have seen above, recent\nresearch has shown that natural selection or struggle for life is no\nexplanation of variations. Hugo de Vries distinguishes between partial\nand embryonal variations, or between variations and mutations, only the\nlast-named being heritable, and therefore of importance for the origin\nof new species. But the existence of variations is not only of interest\nfor the problem of the origin of species; it has also a more general\ninterest. An individual does not lose its importance for knowledge,\nbecause its qualities are not heritable. On the contrary, in higher\nbeings at least, individual peculiarities will become more and more\nindependent objects of interest. Knowledge takes account of the\nbiographies not only of species, but also of individuals: it seeks to\nfind the law of development of the single individual. (The new science\nof Ecology occupies an intermediate position between the biography of\nspecies and the biography of individuals. Compare \"Congress of Arts and\nScience\", St Louis, Vol. V. 1906 (the Reports of Drude and Robinson)\nand the work of my colleague E. Warming.) As Leibniz said long ago,\nindividuality consists in the law of the changes of a being. \"La loi du\nchangement fait l'individualite de chaque substance.\" Here is a world\nwhich is almost new for science, which till now has mainly occupied\nitself with general laws and forms. But these are ultimately only means\nto understand the individual phenomena, in whose nature and history\na manifold of laws and forms always cooperate. The importance of this\nremark will appear in the sequel.\n\nV.\n\nTo many people the Darwinian theory of natural selection or struggle\nfor existence seemed to change the whole conception of life, and\nparticularly all the conditions on which the validity of ethical ideas\ndepends. If only that has persistence which can be adapted to a given\ncondition, what will then be the fate of our ideals, of our standards\nof good and evil? Blind force seems to reign, and the only thing that\ncounts seems to be the most heedless use of power. Darwinism, it was\nsaid, has proclaimed brutality. No other difference seems permanent save\nthat between the sound, powerful and happy on the one side, the sick,\nfeeble and unhappy on the other; and every attempt to alleviate this\ndifference seems to lead to general enervation. Some of those who\ninterpreted Darwinism in this manner felt an aesthetic delight in\ncontemplating the heedlessness and energy of the great struggle for\nexistence and anticipated the realisation of a higher human type as the\noutcome of it: so Nietzsche and his followers. Others recognising the\nsame consequences in Darwinism regarded these as one of the strongest\nobjections against it; so Duhring and Kropotkin (in his earlier works).\n\nThis interpretation of Darwinism was frequent in the interval between\nthe two main works of Darwin--\"The Origin of Species\" and \"The Descent\nof Man\". But even during this interval it was evident to an attentive\nreader that Darwin himself did not found his standard of good and evil\non the features of the life of nature he had emphasised so strongly. He\ndid not justify the ways along which nature reached its ends; he only\npointed them out. The \"real\" was not to him, as to Hegel, one with\nthe \"rational.\" Darwin has, indeed, by his whole conception of nature,\nrendered a great service to ethics in making the difference between the\nlife of nature and the ethical life appear in so strong a light. The\nethical problem could now be stated in a sharper form than before. But\nthis was not the first time that the idea of the struggle for life\nwas put in relation to the ethical problem. In the seventeenth century\nThomas Hobbes gave the first impulse to the whole modern discussion of\nethical principles in his theory of bellum omnium contra omnes. Men, he\ntaught, are in the state of nature enemies one of another, and they live\neither in fright or in the glory of power. But it was not the opinion\nof Hobbes that this made ethics impossible. On the contrary, he found a\nstandard for virtue and vice in the fact that some qualities and actions\nhave a tendency to bring us out of the state of war and to secure\npeace, while other qualities have a contrary tendency. In the eighteenth\ncentury even Immanuel Kant's ideal ethics had--so far as can be seen--a\nsimilar origin. Shortly before the foundation of his definitive ethics,\nKant wrote his \"Idee zu einer allgemeinen Weltgeschichte\" (1784),\nwhere--in a way which reminds us of Hobbes, and is prophetic of\nDarwin--he describes the forward-driving power of struggle in the human\nworld. It is here as with the struggle of the trees for light and air,\nthrough which they compete with one another in height. Anxiety about\nwar can only be allayed by an ordinance which gives everyone his full\nliberty under acknowledgment of the equal liberty of others. And such\nordinance and acknowledgment are also attributes of the content of the\nmoral law, as Kant proclaimed it in the year after the publication\nof his essay (1785) (Cf. my \"History of Modern Philosophy\" (English\ntranslation London, 1900), I. pages 76-79.) Kant really came to his\nethics by the way of evolution, though he afterwards disavowed it.\nSimilarly the same line of thought may be traced in Hegel though it has\nbeen disguised in the form of speculative dialectics. (\"Herrschaft und\nKnechtschaft\", \"Phanomenologie des Geistes\", IV. A., Leiden, 1907.) And\nin Schopenhauer's theory of the blind will to live and its abrogation by\nthe ethical feeling, which is founded on universal sympathy, we have a\nmore individualistic form of the same idea.\n\nIt was, then, not entirely a foreign point of view which Darwin\nintroduced into ethical thought, even if we take no account of the\npoetical character of the word \"struggle\" and of the more direct\nadaptation, through the use and non-use of power, which Darwin also\nemphasised. In \"The Descent of Man\" he has devoted a special chapter\n(\"The Descent of Man\", Vol. I. Ch. iii.) to a discussion of the origin\nof the ethical consciousness. The characteristic expression of this\nconsciousness he found, just as Kant did, in the idea of \"ought\"; it was\nthe origin of this new idea which should be explained. His hypothesis\nwas that the ethical \"ought\" has its origin in the social and parental\ninstincts, which, as well as other instincts (e.g. the instinct of\nself-preservation), lie deeper than pleasure and pain. In many species,\nnot least in the human species, these instincts are fostered by natural\nselection; and when the powers of memory and comparison are developed,\nso that single acts can be valued according to the claims of the deep\nsocial instinct, then consciousness of duty and remorse are possible.\nBlind instinct has developed to conscious ethical will.\n\nAs already stated, Darwin, as a moral philosopher belongs to the school\nthat was founded by Shaftesbury, and was afterwards represented by\nHutcheson, Hume, Adam Smith, Comte and Spencer. His merit is, first,\nthat he has given this tendency of thought a biological foundation, and\nthat he has stamped on it a doughty character in showing that ethical\nideas and sentiments, rightly conceived, are forces which are at work in\nthe struggle for life.\n\nThere are still many questions to solve. Not only does the ethical\ndevelopment within the human species contain features still unexplained\n(The works of Westermarck and Hobhouse throw new light on many of these\nfeatures.); but we are confronted by the great problem whether after all\na genetic historical theory can be of decisive importance here. To\nevery consequent ethical consciousness there is a standard of value, a\nprimordial value which determines the single ethical judgments as their\nlast presupposition, and the \"rightness\" of this basis, the \"value\"\nof this value can as little be discussed as the \"rationality\" of our\nlogical principles. There is here revealed a possibility of ethical\nscepticism which evolutionistic ethics (as well as intuitive or\nrationalistic ethics) has overlooked. No demonstration can show that the\nresults of the ethical development are definitive and universal. We\nmeet here again with the important opposition of systematisation and\nevolution. There will, I think, always be an open question here, though\ncomparative ethics, of which we have so far only the first attempts, can\ndo much to throw light on it.\n\nIt would carry us too far to discuss all the philosophical works\non ethics, which have been influenced directly or indirectly by\nevolutionism. I may, however, here refer to the book of C.M. Williams,\n\"A Review of the Systems of Ethics founded on the Theory of Evolution\"\n(New York and London, 1893.), in which, besides Darwin, the following\nauthors are reviewed: Wallace, Haeckel, Spencer, Fiske, Rolph, Barratt,\nStephen, Carneri, Hoffding, Gizycki, Alexander, Ree. As works which\ncriticise evolutionistic ethics from an intuitive point of view and\nin an instructive way, may be cited: Guyau \"La morale anglaise\ncontemporaine\" (Paris, 1879.), and Sorley, \"Ethics of Naturalism\". I\nwill only mention some interesting contributions to ethical discussion\nwhich can be found in Darwinism besides the idea of struggle for life.\n\nThe attention which Darwin has directed to variations has opened our\neyes to the differences in human nature as well as in nature generally.\nThere is here a fact of great importance for ethical thought, no matter\nfrom what ultimate premiss it starts. Only from a very abstract point of\nview can different individuals be treated in the same manner. The most\neminent ethical thinkers, men such as Jeremy Bentham and Immanuel Kant,\nwho discussed ethical questions from very opposite standpoints, agreed\nin regarding all men as equal in respect of ethical endowment. In regard\nto Bentham, Leslie Stephen remarks: \"He is determined to be thoroughly\nempirical, to take men as he found them. But his utilitarianism supposed\nthat men's views of happiness and utility were uniform and clear, and\nthat all that was wanted was to show them the means by which their ends\ncould be reached.\" (\"English literature and society in the eighteenth\ncentury\", London, 1904, page 187.) And Kant supposed that every man\nwould find the \"categorical imperative\" in his consciousness, when he\ncame to sober reflexion, and that all would have the same qualifications\nto follow it. But if continual variations, great or small, are going on\nin human nature, it is the duty of ethics to make allowance for them,\nboth in making claims, and in valuing what is done. A new set of ethical\nproblems have their origin here. (Cf. my paper, \"The law of relativity\nin Ethics,\" \"International Journal of Ethics\", Vol. I. 1891, pages\n37-62.) It is an interesting fact that Stuart Mill's book \"On Liberty\"\nappeared in the same year as \"The Origin of Species\". Though Mill agreed\nwith Bentham about the original equality of all men's endowments, he\nregarded individual differences as a necessary result of physical and\nsocial influences, and he claimed that free play shall be allowed to\ndifferences of character so far as is possible without injury to other\nmen. It is a condition of individual and social progress that a man's\nmode of action should be determined by his own character and not\nby tradition and custom, nor by abstract rules. This view was to be\ncorroborated by the theory of Darwin.\n\nBut here we have reached a point of view from which the criticism,\nwhich in recent years has often been directed against Darwin--that\nsmall variations are of no importance in the struggle for life--is of\nno weight. From an ethical standpoint, and particularly from the\nethical standpoint of Darwin himself, it is a duty to foster individual\ndifferences that can be valuable, even though they can neither be of\nservice for physical preservation nor be physically inherited. The\ndistinction between variation and mutation is here without importance.\nIt is quite natural that biologists should be particularly interested in\nsuch variations as can be inherited and produce new species. But in the\nhuman world there is not only a physical, but also a mental and social\nheredity. When an ideal human character has taken form, then there\nis shaped a type, which through imitation and influence can become an\nimportant factor in subsequent development, even if it cannot form a\nspecies in the biological sense of the word. Spiritually strong\nmen often succumb in the physical struggle for life; but they can\nnevertheless be victorious through the typical influence they exert,\nperhaps on very distant generations, if the remembrance of them is kept\nalive, be it in legendary or in historical form. Their very failure\ncan show that a type has taken form which is maintained at all risks,\na standard of life which is adhered to in spite of the strongest\nopposition. The question \"to be or not to be\" can be put from\nvery different levels of being: it has too often been considered a\nconsequence of Darwinism that this question is only to be put from\nthe lowest level. When a stage is reached, where ideal (ethical,\nintellectual, aesthetic) interests are concerned, the struggle for life\nis a struggle for the preservation of this stage. The giving up of a\nhigher standard of life is a sort of death; for there is not only a\nphysical, there is also a spiritual, death.\n\nVI.\n\nThe Socratic character of Darwin's mind appears in his wariness in\ndrawing the last consequences of his doctrine, in contrast both with the\naudacious theories of so many of his followers and with the consequences\nwhich his antagonists were busy in drawing. Though he, as we have seen,\nsaw from the beginning that his hypothesis would occasion \"a whole of\nmetaphysics,\" he was himself very reserved as to the ultimate questions,\nand his answers to such questions were extorted from him.\n\nAs to the question of optimism and pessimism, Darwin held that though\npain and suffering were very often the ways by which animals were led\nto pursue that course of action which is most beneficial to the species,\nyet pleasurable feelings were the most habitual guides. \"We see this in\nthe pleasure from exertion, even occasionally from great exertion of the\nbody or mind, in the pleasure of our daily meals, and especially in the\npleasure derived from sociability, and from loving our families.\" But\nthere was to him so much suffering in the world that it was a strong\nargument against the existence of an intelligent First Cause. (\"Life and\nLetters\" Vol. I. page 310.)\n\nIt seems to me that Darwin was not so clear on another question, that\nof the relation between improvement and adaptation. He wrote to Lyell:\n\"When you contrast natural selection and 'improvement,' you seem always\nto overlook... that every step in the natural selection of each species\nimplies improvement in that species IN RELATION TO ITS CONDITION OF\nLIFE... Improvement implies, I suppose, EACH FORM OBTAINING MANY PARTS\nOR ORGANS, all excellently adapted for their functions.\" \"All this,\" he\nadds, \"seems to me quite compatible with certain forms fitted for simple\nconditions, remaining unaltered, or being degraded.\" (Ibid. Vol. II.\npage 177.) But the great question is, if the conditions of life will in\nthe long run favour \"improvement\" in the sense of differentiation\n(or harmony of differentiation and integration). Many beings are best\nadapted to their conditions of life if they have few organs and few\nnecessities. Pessimism would not only be the consequence, if suffering\noutweighed happiness, but also if the most elementary forms of happiness\nwere predominant, or if there were a tendency to reduce the standard\nof life to the simplest possible, the contentment of inertia or stable\nequilibrium. There are animals which are very highly differentiated and\nactive in their young state, but later lose their complex organisation\nand concentrate themselves on the one function of nutrition. In the\nhuman world analogies to this sort of adaptation are not wanting. Young\n\"idealists\" very often end as old \"Philistines.\" Adaptation and progress\nare not the same.\n\nAnother question of great importance in respect to human evolution\nis, whether there will be always a possibility for the existence of\nan impulse to progress, an impulse to make great claims on life, to be\nactive and to alter the conditions of life instead of adapting to them\nin a passive manner. Many people do not develop because they have\ntoo few necessities, and because they have no power to imagine other\nconditions of life than those under which they live. In his remarks\non \"the pleasure from exertion\" Darwin has a point of contact with\nthe practical idealism of former times--with the ideas of Lessing and\nGoethe, of Condorcet and Fichte. The continual striving which was\nthe condition of salvation to Faust's soul, is also the condition\nof salvation to mankind. There is a holy fire which we ought to keep\nburning, if adaptation is really to be improvement. If, as I have\ntried to show in my \"Philosophy of Religion\", the innermost core of all\nreligion is faith in the persistence of value in the world, and if\nthe highest values express themselves in the cry \"Excelsior!\" then the\ncapital point is, that this cry should always be heard and followed. We\nhave here a corollary of the theory of evolution in its application to\nhuman life.\n\nDarwin declared himself an agnostic, not only because he could not\nharmonise the large amount of suffering in the world with the idea of a\nGod as its first cause, but also because he \"was aware that if we admit\na first cause, the mind still craves to know whence it came and how it\narose.\" (\"Life and Letters\", Vol. I. page 306.) He saw, as Kant had\nseen before him and expressed in his \"Kritik der Urtheilskraft\", that we\ncannot accept either of the only two possibilities which we are able\nto conceive: chance (or brute force) and design. Neither mechanism\nnor teleology can give an absolute answer to ultimate questions.\nThe universe, and especially the organic life in it, can neither be\nexplained as a mere combination of absolute elements nor as the effect\nof a constructing thought. Darwin concluded, as Kant, and before him\nSpinoza, that the oppositions and distinctions which our experience\npresents, cannot safely be regarded as valid for existence in itself.\nAnd, with Kant and Fichte, he found his stronghold in the conviction\nthat man has something to do, even if he cannot solve all enigmas. \"The\nsafest conclusion seems to me that the whole subject is beyond the scope\nof man's intellect; but man can do his duty.\" (Ibid. page 307.)\n\nIs this the last word of human thought? Does not the possibility,\nthat man can do his duty, suppose that the conditions of life allow of\ncontinuous ethical striving, so that there is a certain harmony\nbetween cosmic order and human ideals? Darwin himself has shown how\nthe consciousness of duty can arise as a natural result of evolution.\nMoreover there are lines of evolution which have their end in ethical\nidealism, in a kingdom of values, which must struggle for life as all\nthings in the world must do, but a kingdom which has its firm foundation\nin reality.\n\n\n\n\nXXIII. DARWINISM AND SOCIOLOGY. By C. Bougle.\n\nProfessor of Social Philosophy in the University of Toulouse and\nDeputy-Professor at the Sorbonne, Paris.\n\n\nHow has our conception of social phenomena, and of their history,\nbeen affected by Darwin's conception of Nature and the laws of its\ntransformations? To what extent and in what particular respects have\nthe discoveries and hypotheses of the author of \"The Origin of Species\"\naided the efforts of those who have sought to construct a science of\nsociety?\n\nTo such a question it is certainly not easy to give any brief or precise\nanswer. We find traces of Darwinism almost everywhere. Sociological\nsystems differing widely from each other have laid claim to its\nauthority; while, on the other hand, its influence has often made itself\nfelt only in combination with other influences. The Darwinian thread is\nworked into a hundred patterns along with other threads.\n\nTo deal with the problem, we must, it seems, first of all distinguish\nthe more general conclusions in regard to the evolution of living\nbeings, which are the outcome of Darwinism, from the particular\nexplanations it offers of the ways and means by which that evolution\nis effected. That is to say, we must, as far as possible, estimate\nseparately the influence of Darwin as an evolutionist and Darwin as a\nselectionist.\n\nThe nineteenth century, said Cournot, has witnessed a mighty effort to\n\"reintegrer l'homme dans la nature.\" From divers quarters there has been\na methodical reaction against the persistent dualism of the Cartesian\ntradition, which was itself the unconscious heir of the Christian\ntradition. Even the philosophy of the eighteenth century, materialistic\nas were for the most part the tendencies of its leaders, seemed to\nrevere man as a being apart, concerning whom laws might be formulated a\npriori. To bring him down from his pedestal there was needed the marked\npredominance of positive researches wherein no account was taken of\nthe \"pride of man.\" There can be no doubt that Darwin has done much to\nfamiliarise us with this attitude. Take for instance the first part\nof \"The Descent of Man\": it is an accumulation of typical facts, all\ntending to diminish the distance between us and our brothers, the lower\nanimals. One might say that the naturalist had here taken as his motto,\n\"Whosoever shall exalt himself shall be abased; and he that shall humble\nhimself shall be exalted.\" Homologous structures, the survival in man of\ncertain organs of animals, the rudiments in the animal of certain\nhuman faculties, a multitude of facts of this sort, led Darwin to the\nconclusion that there is no ground for supposing that the \"king of the\nuniverse\" is exempt from universal laws. Thus belief in the imperium\nin imperio has been, as it were, whittled away by the progress of the\nnaturalistic spirit, itself continually strengthened by the conquests of\nthe natural sciences. The tendency may, indeed, drag the social sciences\ninto overstrained analogies, such, for instance, as the assimilation\nof societies to organisms. But it will, at least, have had the merit of\nhelping sociology to shake off the pre-conception that the groups formed\nby men are artificial, and that history is completely at the mercy of\nchance. Some years before the appearance of \"The Origin of Species\",\nAuguste Comte had pointed out the importance, as regards the unification\nof positive knowledge, of the conviction that the social world, the last\nrefuge of spiritualism, is itself subject to determininism. It cannot be\ndoubted that the movement of thought which Darwin's discoveries promoted\ncontributed to the spread of this conviction, by breaking down the\ntraditional barrier which cut man off from Nature.\n\nBut Nature, according to modern naturalists, is no immutable thing: it\nis rather perpetual movement, continual progression. Their discoveries\nbatter a breach directly into the Aristotelian notion of species; they\nrefuse to see in the animal world a collection of immutable types,\ndistinct from all eternity, and corresponding, as Cuvier said, to so\nmany particular thoughts of the Creator. Darwin especially congratulated\nhimself upon having been able to deal this doctrine the coup de grace:\nimmutability is, he says, his chief enemy; and he is concerned to\nshow--therein following up Lyell's work--that everything in the organic\nworld, as in the inorganic, is explained by insensible but incessant\ntransformations. \"Nature makes no leaps\"--\"Nature knows no gaps\": these\ntwo dicta form, as it were, the two landmarks between which Darwin's\nidea of transformation is worked out. That is to say, the development of\nDarwinism is calculated to further the application of the philosophy of\nBecoming to the study of human institutions.\n\nThe progress of the natural sciences thus brings unexpected\nreinforcements to the revolution which the progress of historical\ndiscipline had begun. The first attempt to constitute an actual science\nof social phenomena--that, namely, of the economists--had resulted in\nlaws which were called natural, and which were believed to be\neternal and universal, valid for all times and all places. But this\nperpetuality, brother, as Knies said, of the immutability of the old\nzoology, did not long hold out against the ever swelling tide of the\nhistorical movement. Knowledge of the transformations that had taken\nplace in language, of the early phases of the family, of religion, of\nproperty, had all favoured the revival of the Heraclitean view: panta\nrei. As to the categories of political economy, it was soon to be\nrecognised, as by Lassalle, that they too are only historical. The\nphilosophy of history, moreover, gave expression under various forms to\nthe same tendency. Hegel declares that \"all that is real is rational,\"\nbut at the same time he shows that all that is real is ephemeral, and\nthat for history there is nothing fixed beneath the sun. It is this\nsense of universal evolution that Darwin came with fresh authority\nto enlarge. It was in the name of biological facts themselves that he\ntaught us to see only slow metamorphoses in the history of institutions,\nand to be always on the outlook for survivals side by side with\nrudimentary forms. Anyone who reads \"Primitive Culture\", by Tylor,--a\nwriter closely connected with Darwin--will be able to estimate the\nservices which these cardinal ideas were to render to the social\nsciences when the age of comparative research had succeeded to that of a\npriori construction.\n\nLet us note, moreover, that the philosophy of Becoming in passing\nthrough the Darwinian biology became, as it were, filtered: it got\nrid of those traces of finalism, which, under different forms, it had\npreserved through all the systems of German Romanticism. Even in Herbert\nSpencer, it has been plausibly argued, one can detect something of that\nsort of mystic confidence in forces spontaneously directing life, which\nforms the very essence of those systems. But Darwin's observations\nwere precisely calculated to render such an hypothesis futile. At first\npeople may have failed to see this; and we call to mind the ponderous\nsarcasms of Flourens when he objected to the theory of Natural Selection\nthat it attributed to nature a power of free choice. \"Nature endowed\nwith will! That was the final error of last century; but the nineteenth\nno longer deals in personifications.\" (P. Flourens, \"Examen du Livre\nde M. Darwin sur l'Origine des Especes\", page 53, Paris, 1864. See also\nHuxley, \"Criticisms on the 'Origin of Species'\", \"Collected Essays\",\nVol. II, page 102, London, 1902.) In fact Darwin himself put his\nreaders on their guard against the metaphors he was obliged to use. The\nprocesses by which he explains the survival of the fittest are far from\naffording any indication of the design of some transcendent breeder.\nNor, if we look closely, do they even imply immanent effort in the\nanimal; the sorting out can be brought about mechanically, simply by\nthe action of the environment. In this connection Huxley could with\ngood reason maintain that Darwin's originality consisted in showing\nhow harmonies which hitherto had been taken to imply the agency of\nintelligence and will could be explained without any such intervention.\nSo, when later on, objective sociology declares that, even when\nsocial phenomena are in question, all finalist preconceptions must be\ndistrusted if a science is to be constituted, it is to Darwin that its\nthanks are due; he had long been clearing paths for it which lay\nwell away from the old familiar road trodden by so many theories of\nevolution.\n\nThis anti-finalist doctrine, when fully worked out, was, moreover,\ncalculated to aid in the needful dissociation of two notions: that of\nevolution and that of progress. In application to society these had long\nbeen confounded; and, as a consequence, the general idea seemed to be\nthat only one type of evolution was here possible. Do we not detect\nsuch a view in Comte's sociology, and perhaps even in Herbert Spencer's?\nWhoever, indeed, assumes an end for evolution is naturally inclined to\nthink that only one road leads to that end. But those whose minds the\nDarwinian theory has enlightened are aware that the transformations of\nliving beings depend primarily upon their conditions, and that it is\nthese conditions which are the agents of selection from among individual\nvariations. Hence, it immediately follows that transformations are not\nnecessarily improvements. Here, Darwin's thought hesitated. Logically\nhis theory proves, as Ray Lankester pointed out, that the struggle for\nexistence may have as its outcome degeneration as well as amelioration:\nevolution may be regressive as well as progressive. Then, too--and this\nis especially to be borne in mind--each species takes its good where\nit finds it, seeks its own path and survives as best it can. Apply this\nnotion to society and you arrive at the theory of multilinear evolution.\nDivergencies will no longer surprise you. You will be forewarned not to\napply to all civilisations the same measure of progress, and you will\nrecognise that types of evolution may differ just as social species\nthemselves differ. Have we not here one of the conceptions which mark\noff sociology proper from the old philosophy of history?\n\nBut if we are to estimate the influence of Darwinism upon sociological\nconceptions, we must not dwell only upon the way in which Darwin\nimpressed the general notion of evolution upon the minds of thinkers. We\nmust go into details. We must consider the influence of the particular\ntheories by which he explained the mechanism of this evolution. The name\nof the author of \"The Origin of Species\" has been especially attached,\nas everyone knows, to the doctrines of \"natural selection\" and of\n\"struggle for existence,\" completed by the notion of \"individual\nvariation.\" These doctrines were turned to account by very different\nschools of social philosophy. Pessimistic and optimistic, aristocratic\nand democratic, individualistic and socialistic systems were to war\nwith each other for years by casting scraps of Darwinism at each other's\nheads.\n\nIt was the spectacle of human contrivance that suggested to Darwin\nhis conception of natural selection. It was in studying the methods of\npigeon breeders that he divined the processes by which nature, in the\nabsence of design, obtains analogous results in the differentiation\nof types. As soon as the importance of artificial selection in the\ntransformation of species of animals was understood, reflection\nnaturally turned to the human species, and the question arose, How far\ndo men observe, in connection with themselves, those laws of which they\nmake practical application in the case of animals? Here we come upon one\nof the ideas which guided the researches of Galton, Darwin's cousin. The\nauthor of \"Inquiries into Human Faculty and its Development\" (\"Inquiries\ninto Human Faculty\", pages 1, 2, 3 sq., London, 1883.), has often\nexpressed his surprise that, considering all the precautions taken,\nfor example, in the breeding of horses, none whatever are taken in the\nbreeding of the human species. It seems to be forgotten that the species\nsuffers when the \"fittest\" are not able to perpetuate their type.\nRitchie, in his \"Darwinism and Politics\" (\"Darwinism and Politics\" pages\n9, 22, London, 1889.) reminds us of Darwin's remark that the institution\nof the peerage might be defended on the ground that peers, owing to the\nprestige they enjoy, are enabled to select as wives \"the most beautiful\nand charming women out of the lower ranks.\" (\"Life and Letters of\nCharles Darwin\", II. page 385.) But, says Galton, it is as often as not\n\"heiresses\" that they pick out, and birth statistics seem to show that\nthese are either less robust or less fecund than others. The truth is\nthat considerations continue to preside over marriage which are entirely\nforeign to the improvement of type, much as this is a condition of\ngeneral progress. Hence the importance of completing Odin's and De\nCandolle's statistics which are designed to show how characters are\nincorporated in organisms, how they are transmitted, how lost, and\naccording to what law eugenic elements depart from the mean or return to\nit.\n\nBut thinkers do not always content themselves with undertaking merely\nthe minute researches which the idea of Selection suggests. They are\neager to defend this or that thesis. In the name of this idea certain\nsocial anthropologists have recast the conception of the process of\ncivilisation, and have affirmed that Social Selection generally works\nagainst the trend of Natural Selection. Vacher de Lapouge--following\nup an observation by Broca on the point--enumerates the various\ninstitutions, or customs, such as the celibacy of priests and military\nconscription, which cause elimination or sterilisation of the bearers of\ncertain superior qualities, intellectual or physical. In a more general\nway he attacks the democratic movement, a movement, as P. Bourget says,\nwhich is \"anti-physical\" and contrary to the natural laws of progress;\nthough it has been inspired \"by the dreams of that most visionary of all\ncenturies, the eighteenth.\" (V. de Lapouge, \"Les Selections sociales\",\npage 259, Paris, 1896.) The \"Equality\" which levels down and mixes\n(justly condemned, he holds, by the Comte de Gobineau), prevents the\naristocracy of the blond dolichocephales from holding the position and\nplaying the part which, in the interests of all, should belong to them.\nOtto Ammon, in his \"Natural Selection in Man\", and in \"The Social Order\nand its Natural Bases\" (\"Die naturliche Auslese beim Menschen\", Jena,\n1893; \"Die Gesellschaftsordnung und ihre naturlichen Grundlagen\".\n\"Entwurf einer Sozialanthropologie\", Jena, 1896.), defended analogous\ndoctrines in Germany; setting the curve representing frequency of talent\nover against that of income, he attempted to show that all democratic\nmeasures which aim at promoting the rise in the social scale of the\ntalented are useless, if not dangerous; that they only increase the\npanmixia, to the great detriment of the species and of society.\n\nAmong the aristocratic theories which Darwinism has thus inspired\nwe must reckon that of Nietzsche. It is well known that in order to\ncomplete his philosophy he added biological studies to his philological;\nand more than once in his remarks upon the \"Wille zur Macht\" he\ndefinitely alludes to Darwin; though it must be confessed that it is\ngenerally in order to proclaim the in sufficiency of the processes by\nwhich Darwin seeks to explain the genesis of species. Nevertheless,\nNietzsche's mind is completely possessed by an ideal of Selection.\nHe, too, has a horror of panmixia. The naturalists' conception of \"the\nfittest\" is joined by him to that of the \"hero\" of romance to furnish a\nbasis for his doctrine of the Superman. Let us hasten to add, moreover,\nthat at the very moment when support was being sought in the theory of\nSelection for the various forms of the aristocratic doctrine, those same\nforms were being battered down on another side by means of that very\ntheory. Attention was drawn to the fact that by virtue of the laws which\nDarwin himself had discovered isolation leads to etiolation. There is\na risk that the privilege which withdraws the privileged elements of\nSociety from competition will cause them to degenerate. In fact, Jacoby\nin his \"Studies in Selection, in connexion with Heredity in Man\",\n(\"Etudes sur la Selection dans ses rapports avec l'heredite chez\nl'homme\", Paris, page 481, 1881.), concludes that \"sterility, mental\ndebility, premature death and, finally, the extinction of the stock\nwere not specially and exclusively the fate of sovereign dynasties; all\nprivileged classes, all families in exclusively elevated positions share\nthe fate of reigning families, although in a minor degree and in direct\nproportion to the loftiness of their social standing. From the mass of\nhuman beings spring individuals, families, races, which tend to raise\nthemselves above the common level; painfully they climb the rugged\nheights, attain the summits of power, of wealth, of intelligence, of\ntalent, and then, no sooner are they there than they topple down and\ndisappear in gulfs of mental and physical degeneracy.\" The demographical\nresearches of Hansen (\"Die drei Bevolkerungsstufen\", Munich, 1889.)\n(following up and completing Dumont's) tended, indeed, to show that\nurban as well as feudal aristocracies, burgher classes as well as noble\ncastes, were liable to become effete. Hence it might well be concluded\nthat the democratic movement, operating as it does to break down class\nbarriers, was promoting instead of impeding human selection.\n\nSo we see that, according to the point of view, very different\nconclusions have been drawn from the application of the Darwinian idea\nof Selection to human society. Darwin's other central idea, closely\nbound up with this, that, namely, of the \"struggle for existence\" also\nhas been diversely utilised. But discussion has chiefly centered upon\nits signification. And while some endeavour to extend its application to\neverything, we find others trying to limit its range. The conception of\na \"struggle for existence\" has in the present day been taken up into\nthe social sciences from natural science, and adopted. But originally it\ndescended from social science to natural. Darwin's law is, as he himself\nsaid, only Malthus' law generalised and extended to the animal world: a\ngrowing disproportion between the supply of food and the number of\nthe living is the fatal order whence arises the necessity of universal\nstruggle, a struggle which, to the great advantage of the species,\nallows only the best equipped individuals to survive. Nature is regarded\nby Huxley as an immense arena where all living beings are gladiators.\n(\"Evolution and Ethics\", page 200; \"Collected Essays\", Vol. IX, London,\n1894.)\n\nSuch a generalisation was well adapted to feed the stream of pessimistic\nthought; and it furnished to the apologists of war, in particular, new\narguments, weighted with all the authority which in these days attaches\nto scientific deliverances. If people no longer say, as Bonald did, and\nMoltke after him, that war is a providential fact, they yet lay stress\non the point that it is a natural fact. To the peace party Dragomirov's\nobjection is urged that its attempts are contrary to the fundamental\nlaws of nature, and that no sea wall can hold against breakers that come\nwith such gathered force.\n\nBut in yet another quarter Darwinism was represented as opposed to\nphilanthropic intervention. The defenders of the orthodox political\neconomy found in it support for their tenets. Since in the organic world\nuniversal struggle is the condition of progress, it seemed obvious that\nfree competition must be allowed to reign unchecked in the economic\nworld. Attempts to curb it were in the highest degree imprudent. The\nspirit of Liberalism here seemed in conformity with the trend of nature:\nin this respect, at least, contemporary naturalism, offspring of the\ndiscoveries of the nineteenth century, brought reinforcements to the\nindividualist doctrine, begotten of the speculations of the eighteenth:\nbut only, it appeared, to turn mankind away for ever from humanitarian\ndreams. Would those whom such conclusions repelled be content to oppose\nto nature's imperatives only the protests of the heart? There were some\nwho declared, like Brunetiere, that the laws in question, valid though\nthey might be for the animal kingdom, were not applicable to the human.\nAnd so a return was made to the classic dualism. This indeed seems to be\nthe line that Huxley took, when, for instance, he opposed to the cosmic\nprocess an ethical process which was its reverse.\n\nBut the number of thinkers whom this antithesis does not satisfy grows\ndaily. Although the pessimism which claims authorisation from Darwin's\ndoctrines is repugnant to them, they still are unable to accept the\ndualism which leaves a gulf between man and nature. And their endeavour\nis to link the two by showing that while Darwin's laws obtain in both\nkingdoms, the conditions of their application are not the same: their\nforms, and, consequently, their results, vary with the varying mediums\nin which the struggle of living beings takes place, with the means\nthese beings have at disposal, with the ends even which they propose to\nthemselves.\n\nHere we have the explanation of the fact that among determined opponents\nof war partisans of the \"struggle for existence\" can be found: there are\ndisciples of Darwin in the peace party. Novicow, for example, admits\nthe \"combat universel\" of which Le Dantec (\"Les Luttes entre Societies\nhumaines et leurs phases successives\", Paris, 1893,) speaks; but he\nremarks that at different stages of evolution, at different stages of\nlife the same weapons are not necessarily employed. Struggles of brute\nforce, armed hand to hand conflicts, may have been a necessity in the\nearly phases of human societies. Nowadays, although competition may\nremain inevitable and indispensable, it can assume milder forms.\nEconomic rivalries, struggles between intellectual influences, suffice\nto stimulate progress: the processes which these admit are, in the\nactual state of civilisation, the only ones which attain their end\nwithout waste, the only ones logical. From one end to the other of the\nladder of life, struggle is the order of the day; but more and more\nas the higher rungs are reached, it takes on characters which are\nproportionately more \"humane.\"\n\nReflections of this kind permit the introduction into the economic order\nof limitations to the doctrine of \"laisser faire, laisser passer.\" This\nappeals, it is said, to the example of nature where creatures, left to\nthemselves, struggle without truce and without mercy; but the fact\nis forgotten that upon industrial battlefields the conditions are\ndifferent. The competitors here are not left simply to their natural\nenergies: they are variously handicapped. A rich store of artificial\nresources exists in which some participate and others do not. The sides\nthen are unequal; and as a consequence the result of the struggle is\nfalsified. \"In the animal world,\" said De Laveleye (\"Le socialisme\ncontemporain\", page 384 (6th edition), Paris, 1891.), criticising\nSpencer, \"the fate of each creature is determined by its individual\nqualities; whereas in civilised societies a man may obtain the highest\nposition and the most beautiful wife because he is rich and well-born,\nalthough he may be ugly, idle or improvident; and then it is he who will\nperpetuate the species. The wealthy man, ill constituted, incapable,\nsickly, enjoys his riches and establishes his stock under the protection\nof the laws.\" Haycraft in England and Jentsch in Germany have strongly\nemphasised these \"anomalies,\" which nevertheless are the rule. That is\nto say that even from a Darwinian point of view all social reforms\ncan readily be justified which aim at diminishing, as Wallace said,\ninequalities at the start.\n\nBut we can go further still. Whence comes the idea that all measures\ninspired by the sentiment of solidarity are contrary to Nature's\ntrend? Observe her carefully, and she will not give lessons only in\nindividualism. Side by side with the struggle for existence do we not\nfind in operation what Lanessan calls \"association for existence.\" Long\nago, Espinas had drawn attention to \"societies of animals,\" temporary or\npermanent, and to the kind of morality that arose in them. Since then,\nnaturalists have often insisted upon the importance of various forms\nof symbiosis. Kropotkin in \"Mutual Aid\" has chosen to enumerate many\nexamples of altruism furnished by animals to mankind. Geddes and Thomson\nwent so far as to maintain that \"Each of the greater steps of progress\nis in fact associated with an increased measure of subordination\nof individual competition to reproductive or social ends, and of\ninterspecific competition to co-operative association.\" (Geddes and\nThomson, \"The Evolution of Sex\", page 311, London, 1889.) Experience\nshows, according to Geddes, that the types which are fittest to surmount\ngreat obstacles are not so much those who engage in the fiercest\ncompetitive struggle for existence, as those who contrive to temper it.\nFrom all these observations there resulted, along with a limitation\nof Darwinian pessimism, some encouragement for the aspirations of the\ncollectivists.\n\nAnd Darwin himself would, doubtless, have subscribed to these\nrectifications. He never insisted, like his rival, Wallace, upon the\nnecessity of the solitary struggle of creatures in a state of nature,\neach for himself and against all. On the contrary, in \"The Descent of\nMan\", he pointed out the serviceableness of the social instincts, and\ncorroborated Bagehot's statements when the latter, applying laws of\nphysics to politics, showed the great advantage societies derived from\nintercourse and communion. Again, the theory of sexual evolution which\nmakes the evolution of types depend increasingly upon preferences,\njudgments, mental factors, surely offers something to qualify what seems\nhard and brutal in the theory of natural selection.\n\nBut, as often happens with disciples, the Darwinians had out-Darwined\nDarwin. The extravagancies of social Darwinism provoked a useful\nreaction; and thus people were led to seek, even in the animal kingdom,\nfor facts of solidarity which would serve to justify humane effort.\n\nOn quite another line, however, an attempt has been made to connect\nsocialist tendencies with Darwinian principles. Marx and Darwin have\nbeen confronted; and writers have undertaken to show that the work of\nthe German philosopher fell readily into line with that of the English\nnaturalist and was a development of it. Such has been the endeavour of\nFerri in Italy and of Woltmann in Germany, not to mention others. The\nfounders of \"scientific socialism\" had, moreover, themselves thought of\nthis reconciliation. They make more than one allusion to Darwin in works\nwhich appeared after 1859. And sometimes they use his theory to define\nby contrast their own ideal. They remark that the capitalist system, by\ngiving free course to individual competition, ends indeed in a bellum\nomnium contra omnes; and they make it clear that Darwinism, thus\nunderstood, is as repugnant to them as to Duhring.\n\nBut it is at the scientific and not at the moral point of view that they\nplace themselves when they connect their economic history with\nDarwin's work. Thanks to this unifying hypothesis, they claim to have\nconstructed--as Marx does in his preface to \"Das Kapital\"--a veritable\nnatural history of social evolution. Engels speaks in praise of his\nfriend Marx as having discovered the true mainspring of history hidden\nunder the veil of idealism and sentimentalism, and as having proclaimed\nin the primum vivere the inevitableness of the struggle for existence.\nMarx himself, in \"Das Kapital\", indicated another analogy when he dwelt\nupon the importance of a general technology for the explanation of this\npsychology:--a history of tools which would be to social organs what\nDarwinism is to the organs of animal species. And the very importance\nthey attach to tools, to apparatus, to machines, abundantly proves that\nneither Marx nor Engels were likely to forget the special characters\nwhich mark off the human world from the animal. The former always\nremains to a great extent an artificial world. Inventions change the\nface of its institutions. New modes of production revolutionise not only\nmodes of government, but modes even of collective thought. Therefore it\nis that the evolution of society is controlled by laws special to it, of\nwhich the spectacle of nature offers no suggestion.\n\nIf, however, even in this special sphere, it can still be urged that\nthe evolution of the material conditions of society is in accord\nwith Darwin's theory, it is because the influence of the methods of\nproduction is itself to be explained by the incessant strife of the\nvarious classes with each other. So that in the end Marx, like Darwin,\nfinds the source of all progress in struggle. Both are grandsons of\nHeraclitus:--polemos pater panton. It sometimes happens, in these days,\nthat the doctrine of revolutionary socialism is contrasted as rude and\nhealthy with what may seem to be the enervating tendency of \"solidarist\"\nphilanthropy: the apologists of the doctrine then pride themselves above\nall upon their faithfulness to Darwinian principles.\n\nSo far we have been mainly concerned to show the use that social\nphilosophies have made of the Darwinian laws for practical purposes:\nin order to orientate society towards their ideals each school tries to\nshow that the authority of natural science is on its side. But even\nin the most objective of theories, those which systematically make\nabstraction of all political tendencies in order to study the social\nreality in itself, traces of Darwinism are readily to be found.\n\nLet us take for example Durkheim's theory of Division of Labour (\"De la\nDivision du Travail social\", Paris, 1893.) The conclusions he\nderives from it are that whenever professional specialisation causes\nmultiplication of distinct branches of activity, we get organic\nsolidarity--implying differences--substituted for mechanical solidarity,\nbased upon likenesses. The umbilical cord, as Marx said, which connects\nthe individual consciousness with the collective consciousness is cut.\nThe personality becomes more and more emancipated. But on what does this\nphenomenon, so big with consequences, itself depend? The author goes to\nsocial morphology for the answer: it is, he says, the growing density\nof population which brings with it this increasing differentiation of\nactivities. But, again, why? Because the greater density, in thrusting\nmen up against each other, augments the intensity of their competition\nfor the means of existence; and for the problems which society thus has\nto face differentiation of functions presents itself as the gentlest\nsolution.\n\nHere one sees that the writer borrows directly from Darwin. Competition\nis at its maximum between similars, Darwin had declared; different\nspecies, not laying claim to the same food, could more easily coexist.\nHere lay the explanation of the fact that upon the same oak hundreds\nof different insects might be found. Other things being equal, the same\napplies to society. He who finds some unadopted speciality possesses a\nmeans of his own for getting a living. It is by this division of their\nmanifold tasks that men contrive not to crush each other. Here\nwe obviously have a Darwinian law serving as intermediary in the\nexplanation of that progress of division of labour which itself explains\nso much in the social evolution.\n\nAnd we might take another example, at the other end of the series of\nsociological systems. G. Tarde is a sociologist with the most pronounced\nanti-naturalistic views. He has attempted to show that all application\nof the laws of natural science to society is misleading. In his\n\"Opposition Universelle\" he has directly combatted all forms of\nsociological Darwinism. According to him the idea that the evolution of\nsociety can be traced on the same plan as the evolution of species is\nchimerical. Social evolution is at the mercy of all kinds of inventions,\nwhich by virtue of the laws of imitation modify, through individual to\nindividual, through neighbourhood to neighbourhood, the general state\nof those beliefs and desires which are the only \"quantities\" whose\nvariation matters to the sociologist. But, it may be rejoined, that\nhowever psychical the forces may be, they are none the less subject\nto Darwinian laws. They compete with each other; they struggle for the\nmastery of minds. Between types of ideas, as between organic forms,\nselection operates. And though it may be that these types are ushered\ninto the arena by unexpected discoveries, we yet recognise in the\npsychological accidents, which Tarde places at the base of everything,\nnear relatives of those small accidental variations upon which Darwin\nbuilds. Thus, accepting Tarde's own representations, it is\nquite possible to express in Darwinian terms, with the necessary\ntranspositions, one of the most idealistic sociologies that have ever\nbeen constructed.\n\nThese few examples suffice. They enable us to estimate the extent of the\nfield of influence of Darwinism. It affects sociology not only through\nthe agency of its advocates but through that of its opponents. The\nquestionings to which it has given rise have proved no less fruitful\nthan the solutions it has suggested. In short, few doctrines, in the\nhistory of social philosophy, will have produced on their passage a\nfiner outcrop of ideas.\n\n\n\n\nXXIV. THE INFLUENCE OF DARWIN UPON RELIGIOUS THOUGHT. By P.N. Waggett,\nM.A., S.S.J.E.\n\n\nI.\n\nThe object of this paper is first to point out certain elements of the\nDarwinian influence upon Religious thought, and then to show reason\nfor the conclusion that it has been, from a Christian point of view,\nsatisfactory. I shall not proceed further to urge that the Christian\napologetic in relation to biology has been successful. A variety of\nopinions may be held on this question, without disturbing the conclusion\nthat the movements of readjustment have been beneficial to those who\nremain Christians, and this by making them more Christian and not only\nmore liberal. The theologians may sometimes have retreated, but there\nhas been an advance of theology. I know that this account incurs\nthe charge of optimism. It is not the worst that could be made. The\ninfluence has been limited in personal range, unequal, even divergent,\nin operation, and accompanied by the appearance of waste and mischievous\nproducts. The estimate which follows requires for due balance a full\ndevelopment of many qualifying considerations. For this I lack space,\nbut I must at least distinguish my view from the popular one that our\ndifficulties about religion and natural science have come to an end.\n\nConcerning the older questions about origins--the origin of the world,\nof species, of man, of reason, conscience, religion--a large measure of\nunderstanding has been reached by some thoughtful men. But meanwhile\nnew questions have arisen, questions about conduct, regarding both\nthe reality of morals and the rule of right action for individuals and\nsocieties. And these problems, still far from solution, may also be\ntraced to the influence of Darwin. For they arise from the renewed\nattention to heredity, brought about by the search for the causes of\nvariation, without which the study of the selection of variations has no\nsufficient basis.\n\nEven the existing understanding about origins is very far from\nuniversal. On these points there were always thoughtful men who denied\nthe necessity of conflict, and there are still thoughtful men who deny\nthe possibility of a truce.\n\nIt must further be remembered that the earlier discussion now, as I hope\nto show, producing favourable results, created also for a time grave\ndamage, not only in the disturbance of faith and the loss of men--a\nloss not repaired by a change in the currents of debate--but in what I\nbelieve to be a still more serious respect. I mean the introduction of\na habit of facile and untested hypothesis in religious as in other\ndepartments of thought.\n\nDarwin is not responsible for this, but he is in part the cause of\nit. Great ideas are dangerous guests in narrow minds; and thus it has\nhappened that Darwin--the most patient of scientific workers, in whom\nhypothesis waited upon research, or if it provisionally outstepped it\ndid so only with the most scrupulously careful acknowledgment--has led\nsmaller and less conscientious men in natural science, in history, and\nin theology to an over-eager confidence in probable conjecture and a\nloose grip upon the facts of experience. It is not too much to say that\nin many quarters the age of materialism was the least matter-of-fact age\nconceivable, and the age of science the age which showed least of the\npatient temper of inquiry.\n\nI have indicated, as shortly as I could, some losses and dangers which\nin a balanced account of Darwin's influence would be discussed at\nlength.\n\nOne other loss must be mentioned. It is a defect in our thought which,\nin some quarters, has by itself almost cancelled all the advantages\nsecured. I mean the exaggerated emphasis on uniformity or continuity;\nthe unwillingness to rest any part of faith or of our practical\nexpectation upon anything that from any point of view can be called\nexceptional. The high degree of success reached by naturalists in\ntracing, or reasonably conjecturing, the small beginnings of great\ndifferences, has led the inconsiderate to believe that anything may in\ntime become anything else.\n\nIt is true that this exaggeration of the belief in uniformity has\nproduced in turn its own perilous reaction. From refusing to believe\nwhatever can be called exceptional, some have come to believe whatever\ncan be called wonderful.\n\nBut, on the whole, the discontinuous or highly various character of\nexperience received for many years too little deliberate attention. The\nconception of uniformity which is a necessity of scientific description\nhas been taken for the substance of history. We have accepted a\npostulate of scientific method as if it were a conclusion of scientific\ndemonstration. In the name of a generalisation which, however just on\nthe lines of a particular method, is the prize of a difficult exploit of\nreflexion, we have discarded the direct impressions of experience;\nor, perhaps it is more true to say, we have used for the criticism of\nalleged experiences a doctrine of uniformity which is only valid in the\nregion of abstract science. For every science depends for its advance\nupon limitation of attention, upon the selection out of the whole\ncontent of consciousness of that part or aspect which is measurable by\nthe method of the science. Accordingly there is a science of life which\nrightly displays the unity underlying all its manifestations. But there\nis another view of life, equally valid, and practically sometimes more\nimportant, which recognises the immediate and lasting effect of\ncrisis, difference, and revolution. Our ardour for the demonstration\nof uniformity of process and of minute continuous change needs to be\nbalanced by a recognition of the catastrophic element in experience, and\nalso by a recognition of the exceptional significance for us of events\nwhich may be perfectly regular from an impersonal point of view.\n\nAn exorbitant jealousy of miracle, revelation, and ultimate moral\ndistinctions has been imported from evolutionary science into religious\nthought. And it has been a damaging influence, because it has taken\nmen's attention from facts, and fixed them upon theories.\n\nII.\n\nWith this acknowledgment of important drawbacks, requiring many words\nfor their proper description, I proceed to indicate certain results\nof Darwin's doctrine which I believe to be in the long run wholly\nbeneficial to Christian thought. These are:\n\nThe encouragement in theology of that evolutionary method of observation\nand study, which has shaped all modern research:\n\nThe recoil of Christian apologetics towards the ground of religious\nexperience, a recoil produced by the pressure of scientific criticism\nupon other supports of faith:\n\nThe restatement, or the recovery of ancient forms of statement, of the\ndoctrines of Creation and of divine Design in Nature, consequent upon\nthe discussion of evolution and of natural selection as its guiding\nfactor.\n\n(1) The first of these is quite possibly the most important of all.\nIt was well defined in a notable paper read by Dr Gore, now Bishop of\nBirmingham, to the Church Congress at Shrewsbury in 1896. We have learnt\na new caution both in ascribing and in denying significance to items of\nevidence, in utterance or in event. There has been, as in art, a study\nof values, which secures perspective and solidity in our representation\nof facts. On the one hand, a given utterance or event cannot be drawn\ninto evidence as if all items were of equal consequence, like sovereigns\nin a bag. The question whence and whither must be asked, and the\nparticular thing measured as part of a series. Thus measured it is not\nless truly important, but it may be important in a lower degree. On the\nother hand, and for exactly the same reason, nothing that is real is\nunimportant. The \"failures\" are not mere mistakes. We see them, in St\nAugustine's words, as \"scholar's faults which men praise in hope of\nfruit.\"\n\nWe cannot safely trace the origin of the evolutionistic method to the\ninfluence of natural science. The view is tenable that theology led the\nway. Probably this is a case of alternate and reciprocal debt. Quite\ncertainly the evolutionist method in theology, in Christian history,\nand in the estimate of scripture, has received vast reinforcement\nfrom biology, in which evolution has been the ever present and ever\nvictorious conception.\n\n(2) The second effect named is the new willingness of Christian thinkers\nto take definite account of religious experience. This is related to\nDarwin through the general pressure upon religious faith of scientific\ncriticism. The great advance of our knowledge of organisms has been an\nimportant element in the general advance of science. It has acted,\nby the varied requirements of the theory of organisms, upon all other\nbranches of natural inquiry, and it held for a long time that leading\nplace in public attention which is now occupied by speculative physics.\nConsequently it contributed largely to our present estimation of science\nas the supreme judge in all matters of inquiry (F.R. Tennant: \"The Being\nof God in the light of Physical Science\", in \"Essays on some theological\nquestions of the day\". London, 1905.), to the supposed destruction of\nmystery and the disparagement of metaphysic which marked the last age,\nas well as to the just recommendation of scientific method in branches\nof learning where the direct acquisitions of natural science had no\nplace.\n\nBesides this, the new application of the idea of law and mechanical\nregularity to the organic world seemed to rob faith of a kind of refuge.\nThe romantics had, as Berthelot (\"Evolutionisme et Platonisme\", pages\n45, 46, 47. Paris, 1908.) shows, appealed to life to redress the\njudgments drawn from mechanism. Now, in Spencer, evolution gave us a\nvitalist mechanic or mechanical vitalism, and the appeal seemed cut off.\nWe may return to this point later when we consider evolution; at\npresent I only endeavour to indicate that general pressure of scientific\ncriticism which drove men of faith to seek the grounds of reassurance\nin a science of their own; in a method of experiment, of observation,\nof hypothesis checked by known facts. It is impossible for me to do more\nthan glance across the threshold of this subject. But it is necessary to\nsay that the method is in an elementary stage of revival. The imposing\nsuccess that belongs to natural science is absent: we fall short of\nthe unchallengeable unanimity of the Biologists on fundamentals. The\nexperimental method with its sure repetitions cannot be applied to our\nsubject-matter. But we have something like the observational method of\npalaeontology and geographical distribution; and in biology there are\nstill men who think that the large examination of varieties by way\nof geography and the search of strata is as truly scientific, uses as\ngenuinely the logical method of difference, and is as fruitful in sure\nconclusions as the quasi-chemical analysis of Mendelian laboratory work,\nof which last I desire to express my humble admiration. Religion also\nhas its observational work in the larger and possibly more arduous\nmanner.\n\nBut the scientific work in religion makes its way through difficulties\nand dangers. We are far from having found the formula of its combination\nwith the historical elements of our apologetic. It is exposed,\ntherefore, to a damaging fire not only from unspiritualist psychology\nand pathology but also from the side of scholastic dogma. It is hard to\nadmit on equal terms a partner to the old undivided rule of books and\nlearning. With Charles Lamb, we cry in some distress, \"must knowledge\ncome to me, if it come at all, by some awkward experiment of intuition,\nand no longer by this familiar process of reading?\" (\"Essays of Elia\",\n\"New Year's Eve\", page 41; Ainger's edition. London, 1899.) and we are\nanswered that the old process has an imperishable value, only we have\nnot yet made clear its connection with other contributions. And all\nthe work is young, liable to be drawn into unprofitable excursions,\nside-tracked by self-deceit and pretence; and it fatally attracts, like\nthe older mysticism, the curiosity and the expository powers of those\nleast in sympathy with it, ready writers who, with all the air of\nextended research, have been content with narrow grounds for induction.\nThere is a danger, besides, which accompanies even the most genuine\nwork of this science and must be provided against by all its serious\nstudents. I mean the danger of unbalanced introspection both for\nindividuals and for societies; of a preoccupation comparable to our\nmodern social preoccupation with bodily health; of reflection upon\nmental states not accompanied by exercise and growth of the mental\npowers; the danger of contemplating will and neglecting work, of\nanalysing conviction and not criticising evidence.\n\nStill, in spite of dangers and mistakes, the work remains full of\nhopeful indications, and, in the best examples (Such an example is given\nin Baron F. von Hugel's recently finished book, the result of thirty\nyears' research: \"The Mystical Element of Religion, as studied in\nSaint Catherine of Genoa and her Friends\". London, 1908.), it is truly\nscientific in its determination to know the very truth, to tell what\nwe think, not what we think we ought to think. (G. Tyrrell, in\n\"Mediaevalism\", has a chapter which is full of the important MORAL\nelement in a scientific attitude. \"The only infallible guardian of truth\nis the spirit of truthfulness.\" \"Mediaevalism\" page 182, London, 1908.),\ntruly scientific in its employment of hypothesis and verification, and\nin growing conviction of the reality of its subject-matter through the\nrepeated victories of a mastery which advances, like science, in the\nBaconian road of obedience. It is reasonable to hope that progress in\nthis respect will be more rapid and sure when religious study enlists\nmore men affected by scientific desire and endowed with scientific\ncapacity.\n\nThe class of investigating minds is a small one, possibly even smaller\nthan that of reflecting minds. Very few persons at any period are able\nto find out anything whatever. There are few observers, few discoverers,\nfew who even wish to discover truth. In how many societies the problems\nof philology which face every person who speaks English are left\nunattempted! And if the inquiring or the successfully inquiring class\nof minds is small, much smaller, of course, is the class of those\npossessing the scientific aptitude in an eminent degree. During the last\nage this most distinguished class was to a very great extent absorbed\nin the study of phenomena, a study which had fallen into arrears. For\nwe stood possessed, in rudiment, of means of observation, means for\ntravelling and acquisition, qualifying men for a larger knowledge than\nhad yet been attempted. These were now to be directed with new accuracy\nand ardour upon the fabric and behaviour of the world of sense. Our\ndebt to the great masters in physical science who overtook and almost\nout-stripped the task cannot be measured; and, under the honourable\nleadership of Ruskin, we may all well do penance if we have failed \"in\nthe respect due to their great powers of thought, or in the admiration\ndue to the far scope of their discovery.\" (\"Queen of the Air\", Preface,\npage vii. London, 1906.) With what miraculous mental energy and divine\ngood fortune--as Romans said of their soldiers--did our men of curiosity\nface the apparently impenetrable mysteries of nature! And how natural\nit was that immense accessions of knowledge, unrelated to the spiritual\nfacts of life, should discredit Christian faith, by the apparent\nsuperiority of the new work to the feeble and unprogressive knowledge of\nChristian believers! The day is coming when men of this mental character\nand rank, of this curiosity, this energy and this good fortune in\ninvestigation, will be employed in opening mysteries of a spiritual\nnature. They will silence with masterful witness the over-confident\ndenials of naturalism. They will be in danger of the widespread\nrecognition which thirty years ago accompanied every utterance of\nHuxley, Tyndall, Spencer. They will contribute, in spite of adulation,\nto the advance of sober religious and moral science.\n\nAnd this result will be due to Darwin, first because by raising the\ndignity of natural science, he encouraged the development of the\nscientific mind; secondly because he gave to religious students the\nexample of patient and ardent investigation; and thirdly because by the\npressure of naturalistic criticism the religious have been driven to\nascertain the causes of their own convictions, a work in which they were\nnot without the sympathy of men of science. (The scientific rank of its\nwriter justifies the insertion of the following letter from the late Sir\nJohn Burdon-Sanderson to me. In the lecture referred to I had described\nthe methods of Professor Moseley in teaching Biology as affording a\nsuggestion of the scientific treatment of religion.)\n\nOxford, April 30, 1902.\n\nDear Sir,\n\nI feel that I must express to you my thanks for the discourse which I\nhad the pleasure of listening to yesterday afternoon.\n\nI do not mean to say that I was able to follow all that you said as to\nthe identity of Method in the two fields of Science and Religion, but I\nrecognise that the \"mysticism\" of which you spoke gives us the only way\nby which the two fields can be brought into relation.\n\nAmong much that was memorable, nothing interested me more than what you\nsaid of Moseley.\n\nNo one, I am sure, knew better than you the value of his teaching and in\nwhat that value consisted.\n\nYours faithfully\n\nJ. Burdon-Sanderson. 31-2.)\n\nIn leaving the subject of scientific religious inquiry, I will only add\nthat I do not believe it receives any important help--and certainly\nit suffers incidentally much damaging interruption--from the study of\nabnormal manifestations or abnormal conditions of personality.\n\n(3) Both of the above effects seem to me of high, perhaps the very\nhighest, importance to faith and to thought. But, under the third head,\nI name two which are more directly traceable to the personal work of\nDarwin, and more definitely characteristic of the age in which his\ninfluence was paramount: viz. the influence of the two conceptions of\nevolution and natural selection upon the doctrine of creation and of\ndesign respectively.\n\nIt is impossible here, though it is necessary for a complete sketch of\nthe matter, to distinguish the different elements and channels of this\nDarwinian influence; in Darwin's own writings, in the vigorous polemic\nof Huxley, and strangely enough, but very actually for popular thought,\nin the teaching of the definitely anti-Darwinian evolutionist Spencer.\n\nUnder the head of the directly and purely Darwinian elements I should\nclass as preeminent the work of Wallace and of Bates; for no two sets\nof facts have done more to fix in ordinary intelligent minds a belief\nin organic evolution and in natural selection as its guiding factor\nthan the facts of geographical distribution and of protective colour and\nmimicry. The facts of geology were difficult to grasp and the public and\ntheologians heard more often of the imperfection than of the extent of\nthe geological record. The witness of embryology, depending to a great\nextent upon microscopic work, was and is beyond the appreciation of\npersons occupied in fields of work other than biology.\n\nIII.\n\nFrom the influence in religion of scientific modes of thought we pass\nto the influence of particular biological conceptions. The former effect\ncomes by way of analogy, example, encouragement and challenge; inspiring\nor provoking kindred or similar modes of thought in the field of\ntheology; the latter by a collision of opinions upon matters of fact or\nconjecture which seem to concern both science and religion.\n\nIn the case of Darwinism the story of this collision is familiar, and\nfalls under the heads of evolution and natural selection, the doctrine\nof descent with modification, and the doctrine of its guidance or\ndetermination by the struggle for existence between related varieties.\nThese doctrines, though associated and interdependent, and in popular\nthought not only combined but confused, must be considered separately.\nIt is true that the ancient doctrine of Evolution, in spite of the\ningenuity and ardour of Lamarck, remained a dream tantalising the\nintellectual ambition of naturalists, until the day when Darwin made it\nconceivable by suggesting the machinery of its guidance. And, further,\nthe idea of natural selection has so effectively opened the door of\nresearch and stimulated observation in a score of principal directions\nthat, even if the Darwinian explanation became one day much less\nconvincing than, in spite of recent criticism, it now is, yet its\npassing, supposing it to pass, would leave the doctrine of Evolution\nimmeasurably and permanently strengthened. For in the interests of the\ntheory of selection, \"Fur Darwin,\" as Muller wrote, facts have been\ncollected which remain in any case evidence of the reality of descent\nwith modification.\n\nBut still, though thus united in the modern history of convictions,\nthough united and confused in the collision of biological and\ntraditional opinion, yet evolution and natural selection must be\nseparated in theological no less than in biological estimation.\nEvolution seemed inconsistent with Creation; natural selection with\nProvidence and Divine design.\n\nDiscussion was maintained about these points for many years and with\nmuch dark heat. It ranged over many particular topics and engaged minds\ndifferent in tone, in quality, and in accomplishment. There was at\nmost times a degree of misconception. Some naturalists attributed to\ntheologians in general a poverty of thought which belonged really to\nmen of a particular temper or training. The \"timid theism\" discerned in\nDarwin by so cautious a theologian as Liddon (H.P. Liddon, \"The Recovery\nof S. Thomas\"; a sermon preached in St Paul's, London, on April 23rd,\n1882 (the Sunday after Darwin's death).) was supposed by many biologists\nto be the necessary foundation of an honest Christianity. It was really\nmore characteristic of devout NATURALISTS like Philip Henry Gosse,\nthan of religious believers as such. (Dr Pusey (\"Unscience not Science\nadverse to Faith\" 1878) writes: \"The questions as to 'species,' of what\nvariations the animal world is capable, whether the species be more or\nfewer, whether accidental variations may become hereditary... and\nthe like, naturally fall under the province of science. In all these\nquestions Mr Darwin's careful observations gained for him a deserved\napprobation and confidence.\") The study of theologians more considerable\nand even more typically conservative than Liddon does not confirm the\ndescription of religious intolerance given in good faith, but in serious\nignorance, by a disputant so acute, so observant and so candid as\nHuxley. Something hid from each other's knowledge the devoted pilgrims\nin two great ways of thought. The truth may be, that naturalists took\ntheir view of what creation was from Christian men of science who\nnaturally looked in their own special studies for the supports and\nillustrations of their religious belief. Of almost every laborious\nstudent it may be said \"Hic ab arte sua non recessit.\" And both the\nbelieving and the denying naturalists, confining habitual attention to a\npart of experience, are apt to affirm and deny with trenchant vigour\nand something of a narrow clearness \"Qui respiciunt ad pauca, de facili\npronunciant.\" (Aristotle, in Bacon, quoted by Newman in his \"Idea of a\nUniversity\", page 78. London, 1873.)\n\nNewman says of some secular teachers that \"they persuade the world of\nwhat is false by urging upon it what is true.\" Of some early opponents\nof Darwin it might be said by a candid friend that, in all sincerity of\ndevotion to truth, they tried to persuade the world of what is true\nby urging upon it what is false. If naturalists took their version\nof orthodoxy from amateurs in theology, some conservative Christians,\ninstead of learning what evolution meant to its regular exponents,\ntook their view of it from celebrated persons, not of the front rank in\ntheology or in thought, but eager to take account of public movements\nand able to arrest public attention.\n\nCleverness and eloquence on both sides certainly had their share in\nproducing the very great and general disturbance of men's minds in the\nearly days of Darwinian teaching. But by far the greater part of that\ndisturbance was due to the practical novelty and the profound importance\nof the teaching itself, and to the fact that the controversy about\nevolution quickly became much more public than any controversy of equal\nseriousness had been for many generations.\n\nWe must not think lightly of that great disturbance because it has, in\nsome real sense, done its work, and because it is impossible in days\nof more coolness and light, to recover a full sense of its very real\ndifficulties.\n\nThose who would know them better should add to the calm records of\nDarwin (\"Life and Letters\" and \"More Letters of Charles Darwin\".) and to\nthe story of Huxley's impassioned championship, all that they can learn\nof George Romanes. (\"Life and Letters\", London, 1896. \"Thoughts on\nReligion\", London, 1895. \"Candid Examination of Theism\", London, 1878.)\nFor his life was absorbed in this very struggle and reproduced\nits stages. It began in a certain assured simplicity of biblical\ninterpretation; it went on, through the glories and adventures of a\npaladin in Darwin's train, to the darkness and dismay of a man who saw\nall his most cherished beliefs rendered, as he thought, incredible.\n(\"Never in the history of man has so terrific a calamity befallen the\nrace as that which all who look may now (viz. in consequence of the\nscientific victory of Darwin) behold advancing as a deluge, black with\ndestruction, resistless in might, uprooting our most cherished hopes,\nengulphing our most precious creed, and burying our highest life in\nmindless destruction.\"--\"A Candid Examination of Theism\", page 51.)\nHe lived to find the freer faith for which process and purpose are\nnot irreconcilable, but necessary to one another. His development,\nscientific, intellectual and moral, was itself of high significance; and\nits record is of unique value to our own generation, so near the age of\nthat doubt and yet so far from it; certainly still much in need of\nthe caution and courage by which past endurance prepares men for\nnew emergencies. We have little enough reason to be sure that in the\ndiscussions awaiting us we shall do as well as our predecessors in\ntheirs. Remembering their endurance of mental pain, their ardour\nin mental labour, the heroic temper and the high sincerity of\ncontroversialists on either side, we may well speak of our fathers in\nsuch words of modesty and self-judgment as Drayton used when he sang the\nvictors of Agincourt. The progress of biblical study, in the departments\nof Introduction and Exegesis, resulting in the recovery of a point\nof view anciently tolerated if not prevalent, has altered some of the\nconditions of that discussion. In the years near 1858, the witness of\nScripture was adduced both by Christian advocates and their critics as\nif unmistakeably irreconcilable with Evolution.\n\nHuxley (\"Science and Christian Tradition\". London, 1904.) found the path\nof the blameless naturalist everywhere blocked by \"Moses\": the believer\nin revelation was generally held to be forced to a choice between\nrevealed cosmogony and the scientific account of origins. It is not\nclear how far the change in Biblical interpretation is due to natural\nscience, and how far to the vital movements of theological study which\nhave been quite independent of the controversy about species. It belongs\nto a general renewal of Christian movement, the recovery of a heritage.\n\"Special Creation\"--really a biological rather than a theological\nconception,--seems in its rigid form to have been a recent element even\nin English biblical orthodoxy.\n\nThe Middle Ages had no suspicion that religious faith forbad\ninquiry into the natural origination of the different forms of life.\nBartholomaeus Anglicus, an English Franciscan of the thirteenth century,\nwas a mutationist in his way, as Aristotle, \"the Philosopher\" of\nthe Christian Schoolmen, had been in his. So late as the seventeenth\ncentury, as we learn not only from early proceedings of the Royal\nSociety, but from a writer so homely and so regularly pious as\nWalton, the variation of species and \"spontaneous\" generations had no\ntheological bearing, except as instances of that various wonder of the\nworld which in devout minds is food for devotion.\n\nIt was in the eighteenth century that the harder statement took shape.\nSomething in the preciseness of that age, its exaltation of law, its\ncold passion for a stable and measured universe, its cold denial, its\ncold affirmation of the power of God, a God of ice, is the occasion of\nthat rigidity of religious thought about the living world which Darwin\nby accident challenged, or rather by one of those movements of genius\nwhich, Goethe (\"No productiveness of the highest kind... is in the power\nof anyone.\"--\"Conversations of Goethe with Eckermann and Soret\". London,\n1850.) declares, are \"elevated above all earthly control.\"\n\nIf religious thought in the eighteenth century was aimed at a fixed and\nnearly finite world of spirit, it followed in all these respects the\nsecular and critical lead. (\"La philosophie reformatrice du XVIIIe\nsiecle\" (Berthelot, \"Evolutionisme et Platonisme\", Paris, 1908, page\n45.) ramenait la nature et la societe a des mecanismes que la pensee\nreflechie peut concevoir et recomposer.\" In fact, religion in a\nmechanical age is condemned if it takes any but a mechanical tone.\nButler's thought was too moving, too vital, too evolutionary, for the\nsceptics of his time. In a rationalist, encyclopaedic period, religion\nalso must give hard outline to its facts, it must be able to display\nits secret to any sensible man in the language used by all sensible men.\nMilton's prophetic genius furnished the eighteenth century, out of the\ndepth of the passionate age before it, with the theological tone it was\nto need. In spite of the austere magnificence of his devotion, he gives\nto smaller souls a dangerous lead. The rigidity of Scripture exegesis\nbelonged to this stately but imperfectly sensitive mode of thought. It\npassed away with the influence of the older rationalists whose precise\ndenials matched the precise and limited affirmations of the static\northodoxy.\n\nI shall, then, leave the specially biblical aspect of the\ndebate--interesting as it is and even useful, as in Huxley's\ncorrespondence with the Duke of Argyll and others in 1892 (\"Times\",\n1892, passim.)--in order to consider without complication the permanent\nelements of Christian thought brought into question by the teaching of\nevolution.\n\nSuch permanent elements are the doctrine of God as Creator of the\nuniverse, and the doctrine of man as spiritual and unique. Upon both the\ndoctrine of evolution seemed to fall with crushing force.\n\nWith regard to Man I leave out, acknowledging a grave omission, the\ndoctrine of the Fall and of Sin. And I do so because these have not yet,\nas I believe, been adequately treated: here the fruitful reaction to the\nstimulus of evolution is yet to come. The doctrine of sin, indeed, falls\nprincipally within the scope of that discussion which has followed or\ndisplaced the Darwinian; and without it the Fall cannot be usefully\nconsidered. For the question about the Fall is a question not merely of\norigins, but of the interpretation of moral facts whose moral reality\nmust first be established.\n\nI confine myself therefore to Creation and the dignity of man.\n\nThe meaning of evolution, in the most general terms, is that the\ndifferentiation of forms is not essentially separate from their\nbehaviour and use; that if these are within the scope of study, that is\nalso; that the world has taken the form we see by movements not unlike\nthose we now see in progress; that what may be called proximate origins\nare continuous in the way of force and matter, continuous in the way of\nlife, with actual occurrences and actual characteristics. All this has\nno revolutionary bearing upon the question of ultimate origins. The\nwhole is a statement about process. It says nothing to metaphysicians\nabout cause. It simply brings within the scope of observation or\nconjecture that series of changes which has given their special\ncharacters to the different parts of the world we see. In particular,\nevolutionary science aspires to the discovery of the process or order\nof the appearance of life itself: if it were to achieve its aim it\ncould say nothing of the cause of this or indeed of the most familiar\noccurrences. We should have become spectators or convinced historians of\nan event which, in respect of its cause and ultimate meaning, would be\nstill impenetrable.\n\nWith regard to the origin of species, supposing life already\nestablished, biological science has the well founded hopes and the\nmeasure of success with which we are all familiar. All this has, it\nwould seem, little chance of collision with a consistent theism, a\ndoctrine which has its own difficulties unconnected with any particular\nview of order or process. But when it was stated that species had\narisen by processes through which new species were still being made,\nevolutionism came into collision with a statement, traditionally\nreligious, that species were formed and fixed once for all and long ago.\n\nWhat is the theological import of such a statement when it is regarded\nas essential to belief in God? Simply that God's activity, with respect\nto the formation of living creatures, ceased at some point in past time.\n\n\"God rested\" is made the touchstone of orthodoxy. And when, under the\npressure of the evidences, we found ourselves obliged to acknowledge and\nassert the present and persistent power of God, in the maintenance and\nin the continued formation of \"types,\" what happened was the abolition\nof a time-limit. We were forced only to a bolder claim, to a theistic\nlanguage less halting, more consistent, more thorough in its own line,\nas well as better qualified to assimilate and modify such schemes as\nVon Hartmann's philosophy of the unconscious--a philosophy, by the way,\nquite intolerant of a merely mechanical evolution. (See Von Hartmann's\n\"Wahrheit und Irrthum in Darwinismus\". Berlin, 1875.)\n\nHere was not the retrenchment of an extravagant assertion, but the\nexpansion of one which was faltering and inadequate. The traditional\nstatement did not need paring down so as to pass the meshes of a new and\nexacting criticism. It was itself a net meant to surround and enclose\nexperience; and we must increase its size and close its mesh to hold\nnewly disclosed facts of life. The world, which had seemed a fixed\npicture or model, gained first perspective and then solidity and\nmovement. We had a glimpse of organic HISTORY; and Christian thought\nbecame more living and more assured as it met the larger view of life.\n\nHowever unsatisfactory the new attitude might be to our critics, to\nChristians the reform was positive. What was discarded was a limitation,\na negation. The movement was essentially conservative, even actually\nreconstructive. For the language disused was a language inconsistent\nwith the definitions of orthodoxy; it set bounds to the infinite, and by\nimplication withdrew from the creative rule all such processes as could\nbe brought within the descriptions of research. It ascribed fixity and\nfinality to that \"creature\" in which an apostle taught us to recognise\nthe birth-struggles of an unexhausted progress. It tended to banish\nmystery from the world we see, and to confine it to a remote first age.\n\nIn the reformed, the restored, language of religion, Creation became\nagain not a link in a rational series to complete a circle of the\nsciences, but the mysterious and permanent relation between the infinite\nand the finite, between the moving changes we know in part, and the\nPower, after the fashion of that observation, unknown, which is itself\n\"unmoved all motion's source.\" (Hymn of the Church-- Rerum Deus tenax\nvigor,  Immotus in te permanens.)\n\nWith regard to man it is hardly necessary, even were it possible, to\nillustrate the application of this bolder faith. When the record of his\nhigh extraction fell under dispute, we were driven to a contemplation of\nthe whole of his life, rather than of a part and that part out of sight.\nWe remembered again, out of Aristotle, that the result of a process\ninterprets its beginnings. We were obliged to read the title of such\ndignity as we may claim, in results and still more in aspirations.\n\nSome men still measure the value of great present facts in life--reason\nand virtue and sacrifice--by what a self-disparaged reason can collect\nof the meaner rudiments of these noble gifts. Mr Balfour has admirably\ndisplayed the discrepancy, in this view, between the alleged origin and\nthe alleged authority of reason. Such an argument ought to be used not\nto discredit the confident reason, but to illuminate and dignify its\ndark beginnings, and to show that at every step in the long course of\ngrowth a Power was at work which is not included in any term or in all\nthe terms of the series.\n\nI submit that the more men know of actual Christian teaching, its\nfidelity to the past, and its sincerity in face of discovery, the more\ncertainly they will judge that the stimulus of the doctrine of evolution\nhas produced in the long run vigour as well as flexibility in the\ndoctrine of Creation and of man.\n\nI pass from Evolution in general to Natural Selection.\n\nThe character in religious language which I have for short called\nmechanical was not absent in the argument from design as stated before\nDarwin. It seemed to have reference to a world conceived as fixed. It\npointed, not to the plastic capacity and energy of living matter, but\nto the fixed adaptation of this and that organ to an unchanging place or\nfunction.\n\nMr Hobhouse has given us the valuable phrase \"a niche of organic\nopportunity.\" Such a phrase would have borne a different sense in\nnon-evolutionary thought. In that thought, the opportunity was\nan opportunity for the Creative Power, and Design appeared in the\npreparation of the organism to fit the niche. The idea of the niche\nand its occupant growing together from simpler to more complex mutual\nadjustment was unwelcome to this teleology. If the adaptation was traced\nto the influence, through competition, of the environment, the old\nteleology lost an illustration and a proof. For the cogency of the proof\nin every instance depended upon the absence of explanation. Where the\nprocess of adaptation was discerned, the evidence of Purpose or Design\nwas weak. It was strong only when the natural antecedents were not\ndiscovered, strongest when they could be declared undiscoverable.\n\nPaley's favourite word is \"Contrivance\"; and for him contrivance is\nmost certain where production is most obscure. He points out the\nphysiological advantage of the valvulae conniventes to man, and the\nadvantage for teleology of the fact that they cannot have been formed by\n\"action and pressure.\" What is not due to pressure may be attributed to\ndesign, and when a \"mechanical\" process more subtle than pressure was\nsuggested, the case for design was so far weakened. The cumulative proof\nfrom the multitude of instances began to disappear when, in selection,\na natural sequence was suggested in which all the adaptations might be\nreached by the motive power of life, and especially when, as in Darwin's\nteaching, there was full recognition of the reactions of life to the\nstimulus of circumstance. \"The organism fits the niche,\" said the\nteleologist, \"because the Creator formed it so as to fit.\" \"The organism\nfits the niche,\" said the naturalist, \"because unless it fitted it\ncould not exist.\" \"It was fitted to survive,\" said the theologian.\n\"It survives because it fits,\" said the selectionist. The two forms of\nstatement are not incompatible; but the new statement, by provision of\nan ideally universal explanation of process, was hostile to a doctrine\nof purpose which relied upon evidences always exceptional however\nnumerous. Science persistently presses on to find the universal\nmachinery of adaptation in this planet; and whether this be found in\nselection, or in direct-effect, or in vital reactions resulting in large\nchanges, or in a combination of these and other factors, it must always\nbe opposed to the conception of a Divine Power here and there but not\neverywhere active.\n\nFor science, the Divine must be constant, operative everywhere and in\nevery quality and power, in environment and in organism, in stimulus and\nin reaction, in variation and in struggle, in hereditary equilibrium,\nand in \"the unstable state of species\"; equally present on both sides of\nevery strain, in all pressures and in all resistances, in short in\nthe general wonder of life and the world. And this is exactly what the\nDivine Power must be for religious faith.\n\nThe point I wish once more to make is that the necessary readjustment of\nteleology, so as to make it depend upon the contemplation of the whole\ninstead of a part, is advantageous quite as much to theology as to\nscience. For the older view failed in courage. Here again our theism was\nnot sufficiently theistic.\n\nWhere results seemed inevitable, it dared not claim them as God-given.\nIn the argument from Design it spoke not of God in the sense of\ntheology, but of a Contriver, immensely, not infinitely wise and good,\nworking within a world, the scene, rather than the ever dependent\noutcome, of His Wisdom; working in such emergencies and opportunities\nas occurred, by forces not altogether within His control, towards an end\nbeyond Himself. It gave us, instead of the awful reverence due to the\nCause of all substance and form, all love and wisdom, a dangerously\ndetached appreciation of an ingenuity and benevolence meritorious in aim\nand often surprisingly successful in contrivance.\n\nThe old teleology was more useful to science than to religion, and the\ndesign-naturalists ought to be gratefully remembered by Biologists.\nTheir search for evidences led them to an eager study of adaptations\nand of minute forms, a study such as we have now an incentive to in the\ntheory of Natural Selection. One hardly meets with the same ardour in\nmicroscopical research until we come to modern workers. But the argument\nfrom Design was never of great importance to faith. Still, to rid it of\nthis character was worth all the stress and anxiety of the gallant old\nwar. If Darwin had done nothing else for us, we are to-day deeply in\nhis debt for this. The world is not less venerable to us now, not less\neloquent of the causing mind, rather much more eloquent and sacred.\nBut our wonder is not that \"the underjaw of the swine works under the\nground\" or in any or all of those particular adaptations which Paley\ncollected with so much skill, but that a purpose transcending, though\nresembling, our own purposes, is everywhere manifest; that what we live\nin is a whole, mutually sustaining, eventful and beautiful, where the\n\"dead\" forces feed the energies of life, and life sustains a stranger\nexistence, able in some real measure to contemplate the whole, of which,\nmechanically considered, it is a minor product and a rare ingredient.\nHere, again, the change was altogether positive. It was not the escape\nof a vessel in a storm with loss of spars and rigging, not a shortening\nof sail to save the masts and make a port of refuge. It was rather the\nemergence from narrow channels to an open sea. We had propelled the\ngreat ship, finding purchase here and there for slow and uncertain\nmovement. Now, in deep water, we spread large canvas to a favouring\nbreeze.\n\nThe scattered traces of design might be forgotten or obliterated. But\nthe broad impression of Order became plainer when seen at due distance\nand in sufficient range of effect, and the evidence of love and wisdom\nin the universe could be trusted more securely for the loss of the\nparticular calculation of their machinery.\n\nMany other topics of faith are affected by modern biology. In some of\nthese we have learnt at present only a wise caution, a wise uncertainty.\nWe stand before the newly unfolded spectacle of suffering, silenced;\nwith faith not scientifically reassured but still holding fast certain\nother clues of conviction. In many important topics we are at a loss.\nBut in others, and among them those I have mentioned, we have passed\nbeyond this negative state and find faith positively strengthened and\nmore fully expressed.\n\nWe have gained also a language and a habit of thought more fit for the\ngreat and dark problems that remain, less liable to damaging conflicts,\nequipped for more rapid assimilation of knowledge. And by this change\nbiology itself is a gainer. For, relieved of fruitless encounters with\npopular religion, it may advance with surer aim along the path of\nreally scientific life-study which was reopened for modern men by the\npublication of \"The Origin of Species\".\n\nCharles Darwin regretted that, in following science, he had not done\n\"more direct good\" (\"Life and Letters\", Vol. III. page 359.) to his\nfellow-creatures. He has, in fact, rendered substantial service to\ninterests bound up with the daily conduct and hopes of common men;\nfor his work has led to improvements in the preaching of the Christian\nfaith.\n\n\n\n\nXXV. THE INFLUENCE OF DARWINISM ON THE STUDY OF RELIGIONS. By Jane Ellen\nHarrison.\n\nHon. D.Litt. (Durham), Hon. LL.D. (Aberdeen), Staff Lecturer and\nsometime Fellow of Newnham College, Cambridge.\n\nCorresponding member of the German Archaeological Institute.\n\nThe title of my paper might well have been \"the creation by Darwinism of\nthe scientific study of Religions,\" but that I feared to mar my tribute\nto a great name by any shadow of exaggeration. Before the publication of\n\"The Origin of Species\" and \"The Descent of Man\", even in the eighteenth\ncentury, isolated thinkers, notably Hume and Herder, had conjectured\nthat the orthodox beliefs of their own day were developments from the\ncruder superstitions of the past. These were however only particular\nspeculations of individual sceptics. Religion was not yet generally\nregarded as a proper subject for scientific study, with facts to be\ncollected and theories to be deduced. A Congress of Religions such as\nthat recently held at Oxford would have savoured of impiety.\n\nIn the brief space allotted me I can attempt only two things; first,\nand very briefly, I shall try to indicate the normal attitude towards\nreligion in the early part of the last century; second, and in more\ndetail, I shall try to make clear what is the outlook of advanced\nthinkers to-day. (To be accurate I ought to add \"in Europe.\" I advisedly\nomit from consideration the whole immense field of Oriental mysticism,\nbecause it has remained practically untouched by the influence of\nDarwinism.) From this second inquiry it will, I hope, be abundantly\nmanifest that it is the doctrine of evolution that has made this outlook\npossible and even necessary.\n\nThe ultimate and unchallenged presupposition of the old view was that\nreligion was a DOCTRINE, a body of supposed truths. It was in fact what\nwe should now call Theology, and what the ancients called Mythology.\nRitual was scarcely considered at all, and, when considered, it was held\nto be a form in which beliefs, already defined and fixed as dogma,\nfound a natural mode of expression. This, it will be later shown, is\na profound error or rather a most misleading half-truth. Creeds,\ndoctrines, theology and the like are only a part, and at first the least\nimportant part, of religion.\n\nFurther, and the fact is important, this DOGMA, thus supposed to be\nthe essential content of the \"true\" religion, was a teleological scheme\ncomplete and unalterable, which had been revealed to man once and for\nall by a highly anthropomorphic God, whose existence was assumed. The\nduty of man towards this revelation was to accept its doctrines and obey\nits precepts. The notion that this revelation had grown bit by bit out\nof man's consciousness and that his business was to better it would\nhave seemed rank blasphemy. Religion, so conceived, left no place for\ndevelopment. \"The Truth\" might be learnt, but never critically examined;\nbeing thus avowedly complete and final, it was doomed to stagnation.\n\nThe details of this supposed revelation seem almost too naive for\nenumeration. As Hume observed, \"popular theology has a positive appetite\nfor absurdity.\" It is sufficient to recall that \"revelation\" included\nsuch items as the Creation (It is interesting to note that the very\nword \"Creator\" has nowadays almost passed into the region of mythology.\nInstead we have \"L'Evolution Creatrice\".) of the world out of nothing in\nsix days; the making of Eve from one of Adam's ribs; the Temptation by\na talking snake; the confusion of tongues at the tower of Babel; the\ndoctrine of Original Sin; a scheme of salvation which demanded the\nVirgin Birth, Vicarious Atonement, and the Resurrection of the material\nbody. The scheme was unfolded in an infallible Book, or, for one section\nof Christians, guarded by the tradition of an infallible Church, and on\nthe acceptance or refusal of this scheme depended an eternity of weal or\nwoe. There is not one of these doctrines that has not now been recast,\nsoftened down, mysticised, allegorised into something more conformable\nwith modern thinking. It is hard for the present generation, unless\ntheir breeding has been singularly archaic, to realise that these\namazing doctrines were literally held and believed to constitute the\nvery essence of religion; to doubt them was a moral delinquency.\n\nIt had not, however, escaped the notice of travellers and missionaries\nthat savages carried on some sort of practices that seemed to be\nreligious, and believed in some sort of spirits or demons. Hence, beyond\nthe confines illuminated by revealed truth, a vague region was assigned\nto NATURAL Religion. The original revelation had been kept intact only\nby one chosen people, the Jews, by them to be handed on to Christianity.\nOutside the borders of this Goshen the world had sunk into the darkness\nof Egypt. Where analogies between savage cults and the Christian\nreligions were observed, they were explained as degradations; the\nheathen had somehow wilfully \"lost the light.\" Our business was not to\nstudy but, exclusively, to convert them, to root out superstition and\ncarry the torch of revelation to \"Souls in heathen darkness lying.\" To\nus nowadays it is a commonplace of anthropological research that we\nmust seek for the beginnings of religion in the religions of primitive\npeoples, but in the last century the orthodox mind was convinced that\nit possessed a complete and luminous ready-made revelation; the study of\nwhat was held to be a mere degradation seemed idle and superfluous.\n\nBut, it may be asked, if, to the orthodox, revealed religion was\nsacrosanct and savage religion a thing beneath consideration, why did\nnot the sceptics show a more liberal spirit, and pursue to their logical\nissue the conjectures they had individually hazarded? The reason is\nsimple and significant. The sceptics too had not worked free from\nthe presupposition that the essence of religion is dogma. Their\nintellectualism, expressive of the whole eighteenth century, was\nprobably in England strengthened by the Protestant doctrine of an\ninfallible Book. Hume undoubtedly confused religion with dogmatic\ntheology. The attention of orthodox and sceptics alike was focussed on\nthe truth or falsity of certain propositions. Only a few minds of rare\nquality were able dimly to conceive that religion might be a necessary\nstep in the evolution of human thought.\n\nIt is not a little interesting to note that Darwin, who was leader and\nintellectual king of his generation, was also in this matter to some\nextent its child. His attitude towards religion is stated clearly, in\nChapter VIII. of the \"Life and Letters\". (Vol. I. page 304. For Darwin's\nreligious views see also \"Descent of Man\", 1871, Vol. I. page 65; 2nd\nedition. Vol. I. page 142.) On board the \"Beagle\" he was simply orthodox\nand was laughed at by several of the officers for quoting the Bible as\nan unanswerable authority on some point of morality. By 1839 he had come\nto see that the Old Testament was no more to be trusted than the sacred\nbooks of the Hindoos. Next went the belief in miracles, and next Paley's\n\"argument from design\" broke down before the law of natural selection;\nthe suffering so manifest in nature is seen to be compatible rather with\nNatural Selection than with the goodness and omnipotence of God. Darwin\nfelt to the full all the ignorance that lay hidden under specious\nphrases like \"the plan of creation\" and \"Unity of design.\" Finally, he\ntells us \"the mystery of the beginning of all things is insoluble by us;\nand I for one must be content to remain an Agnostic.\"\n\nThe word Agnostic is significant not only of the humility of the man\nhimself but also of the attitude of his age. Religion, it is clear,\nis still conceived as something to be KNOWN, a matter of true or\nfalse OPINION. Orthodox religion was to Darwin a series of erroneous\nhypotheses to be bit by bit discarded when shown to be untenable. The\nACTS of religion which may result from such convictions, i.e. devotion\nin all its forms, prayer, praise, sacraments, are left unmentioned.\nIt is clear that they are not, as now to us, sociological survivals\nof great interest and importance, but rather matters too private, too\npersonal, for discussion.\n\nHuxley, writing in the \"Contemporary Review\" (1871.), says, \"In a dozen\nyears \"The Origin of Species\" has worked as complete a revolution in\nbiological science as the \"Principia\" did in astronomy.\" It has done\nso because, in the words of Helmholtz, it contained \"an essentially\nnew creative thought,\" that of the continuity of life, the absence of\nbreaks. In the two most conservative subjects, Religion and Classics,\nthis creative ferment was slow indeed to work. Darwin himself felt\nstrongly \"that a man should not publish on a subject to which he has\nnot given special and continuous thought,\" and hence wrote little on\nreligion and with manifest reluctance, though, as already seen, in\nanswer to pertinacious inquiry he gave an outline of his own views. But\nnone the less he foresaw that his doctrine must have, for the history\nof man's mental evolution, issues wider than those with which he was\nprepared personally to deal. He writes, in \"The Origin of Species\"\n(6th edition, page 428.), \"In the future I see open fields for far\nmore important researches. Psychology will be securely based on\nthe foundation already well laid by Mr Herbert Spencer, that of the\nnecessary acquirement of each mental power and capacity by gradation.\"\n\nNowhere, it is true, does Darwin definitely say that he regarded\nreligion as a set of phenomena, the development of which may be studied\nfrom the psychological standpoint. Rather we infer from his PIETY--in\nthe beautiful Roman sense--towards tradition and association, that\nreligion was to him in some way sacrosanct. But it is delightful to see\nhow his heart went out towards the new method in religious study which\nhe had himself, if half-unconsciously, inaugurated. Writing in 1871 to\nDr Tylor, on the publication of his \"Primitive Culture\", he says (\"Life\nand Letters\", Vol. III. page 151.), \"It is wonderful how you trace\nanimism from the lower races up the religious belief of the highest\nraces. It will make me for the future look at religion--a belief in the\nsoul, etc.--from a new point of view.\"\n\nPsychology was henceforth to be based on \"the necessary acquirement of\neach mental capacity by gradation.\" With these memorable words the\ndoor closes on the old and opens on the new horizon. The mental focus\nhenceforth is not on the maintaining or refuting of an orthodoxy but\non the genesis and evolution of a capacity, not on perfection but on\nprocess. Continuous evolution leaves no gap for revelation sudden and\ncomplete. We have henceforth to ask, not when was religion revealed\nor what was the revelation, but how did religious phenomena arise and\ndevelop. For an answer to this we turn with new and reverent eyes to\nstudy \"the heathen in his blindness\" and the child \"born in sin.\" We\nstill indeed send out missionaries to convert the heathen, but here\nat least in Cambridge before they start they attend lectures on\nanthropology and comparative religion. The \"decadence\" theory is dead\nand should be buried.\n\nThe study of primitive religions then has been made possible and even\ninevitable by the theory of Evolution. We have now to ask what new facts\nand theories have resulted from that study. This brings us to our second\npoint, the advanced outlook on religion to-day.\n\nThe view I am about to state is no mere personal opinion of my own.\nTo my present standpoint I have been led by the investigations of such\nmasters as Drs Wundt, Lehmann, Preuss, Bergson, Beck and in our own\ncountry Drs Tylor and Frazer. (I can only name here the books that\nhave specially influenced my own views. They are W. Wundt,\n\"Volkerpsychologie\", Leipzig, 1900, P. Beck, \"Die Nachahmung\", Leipzig,\n1904, and \"Erkenntnisstheorie des primitiven Denkens\" in \"Zeitschrift\nf. Philos. und Philos. Kritik\", 1903, page 172, and 1904, page 9. Henri\nBergson, \"L'Evolution Creatrice\" and \"Matiere et Memoire\", 1908, K. Th.\nPreuss, various articles published in the \"Globus\" (see page 507, note\n1), and in the \"Archiv. f. Religionswissenschaft\", and for the subject\nof magic, MM. Hubert et Mauss, \"Theorie generale de la Magie\", in\n\"L'Annee Sociologique\", VII.)\n\nReligion always contains two factors. First, a theoretical factor, what\na man THINKS about the unseen--his theology, or, if we prefer so to call\nit, his mythology. Second, what he DOES in relation to this unseen--his\nritual. These factors rarely if ever occur in complete separation; they\nare blended in very varying proportions. Religion we have seen was\nin the last century regarded mainly in its theoretical aspect as a\ndoctrine. Greek religion for example meant to most educated persons\nGreek mythology. Yet even a cursory examination shows that neither\nGreek nor Roman had any creed or dogma, any hard and fast formulation\nof belief. In the Greek Mysteries (See my \"Prolegomena to the Study of\nGreek Religion\", page 155, Cambridge, 1903.) only we find what we should\ncall a Confiteor; and this is not a confession of faith, but an avowal\nof rites performed. When the religion of primitive peoples came to be\nexamined it was speedily seen that though vague beliefs necessarily\nabound, definite creeds are practically non-existent. Ritual is dominant\nand imperative.\n\nThis predominance and priority of ritual over definite creed was first\nforced upon our notice by the study of savages, but it promptly and\nhappily joined hands with modern psychology. Popular belief says, I\nthink, therefore I act; modern scientific psychology says, I act (or\nrather, REact to outside stimulus), and so I come to think. Thus there\nis set going a recurrent series: act and thought become in their turn\nstimuli to fresh acts and thoughts. In examining religion as envisaged\nto-day it would therefore be more correct to begin with the practice\nof religion, i.e. ritual, and then pass to its theory, theology or\nmythology. But it will be more convenient to adopt the reverse\nmethod. The theoretical content of religion is to those of us who are\nProtestants far more familiar and we shall thus proceed from the known\nto the comparatively unknown.\n\nI shall avoid all attempt at rigid definition. The problem before the\nmodern investigator is, not to determine the essence and definition of\nreligion but to inquire how religious phenomena, religious ideas and\npractices arose. Now the theoretical content of religion, the domain of\ntheology or mythology, is broadly familiar to all. It is the world of\nthe unseen, the supersensuous; it is the world of what we call the soul\nand the supposed objects of the soul's perception, sprites, demons,\nghosts and gods. How did this world grow up?\n\nWe turn to our savages. Intelligent missionaries of bygone days used to\nply savages with questions such as these: Had they any belief in God?\nDid they believe in the immortality of the soul? Taking their own\nclear-cut conceptions, discriminated by a developed terminology, these\nmissionaries tried to translate them into languages that had neither the\nwords nor the thoughts, only a vague, inchoate, tangled substratum, out\nof which these thoughts and words later differentiated themselves. Let\nus examine this substratum.\n\nNowadays we popularly distinguish between objective and subjective;\nand further, we regard the two worlds as in some sense opposed. To\nthe objective world we commonly attribute some reality independent of\nconsciousness, while we think of the subjective as dependent for its\nexistence on the mind. The objective world consists of perceptible\nthings, or of the ultimate constituents to which matter is reduced by\nphysical speculation. The subjective world is the world of beliefs,\nhallucinations, dreams, abstract ideas, imaginations and the like.\nPsychology of course knows that the objective and subjective worlds are\ninterdependent, inextricably intertwined, but for practical purposes the\ndistinction is convenient.\n\nBut primitive man has not yet drawn the distinction between objective\nand subjective. Nay, more, it is foreign to almost the whole of ancient\nphilosophy. Plato's Ideas (I owe this psychological analysis of the\nelements of the primitive supersensuous world mainly to Dr Beck,\n\"Erkenntnisstheorie des primitiven Denkens\", see page 498, note 1.), his\nGoodness, Truth, Beauty, his class-names, horse, table, are it is true\ndematerialised as far as possible, but they have outside existence,\napart from the mind of the thinker, they have in some shadowy way\nspatial extension. Yet ancient philosophies and primitive man alike\nneeded and possessed for practical purposes a distinction which served\nas well as our subjective and objective. To the primitive savage all his\nthoughts, every object of which he was conscious, whether by perception\nor conception, had reality, that is, it had existence outside himself,\nbut it might have reality of various kinds or different degrees.\n\nIt is not hard to see how this would happen. A man's senses may mislead\nhim. He sees the reflection of a bird in a pond. To his eyes it is a\nreal bird. He touches it, HE PUTS IT TO THE TOUCH, and to his touch it\nis not a bird at all. It is real then, but surely not quite so real as\na bird that you can touch. Again, he sees smoke. It is real to his eyes.\nHe tries to grasp it, it vanishes. The wind touches him, but he cannot\nsee it, which makes him feel uncanny. The most real thing is that which\naffects most senses and especially what affects the sense of touch.\nApparently touch is the deepest down, most primitive, of senses. The\nrest are specialisations and complications. Primitive man has no formal\nrubric \"optical delusion,\" but he learns practically to distinguish\nbetween things that affect only one sense and things that affect two or\nmore--if he did not he would not survive. But both classes of things are\nreal to him. Percipi est esse.\n\nSo far, primitive man has made a real observation; there are things that\nappeal to one sense only. But very soon creeps in confusion fraught with\ndisaster. He passes naturally enough, being economical of any mental\neffort, from what he really sees but cannot feel to what he thinks\nhe sees, and gives to it the same secondary reality. He has dreams,\nvisions, hallucinations, nightmares. He dreams that an enemy is beating\nhim, and he wakes rubbing his head. Then further he remembers things;\nthat is, for him, he sees them. A great chief died the other day and\nthey buried him, but he sees him still in his mind, sees him in his\nwar-paint, splendid, victorious. So the image of the past goes together\nwith his dreams and visions to the making of this other less real,\nbut still real world, his other-world of the supersensuous, the\nsupernatural, a world, the outside existence of which, independent of\nhimself, he never questions.\n\nAnd, naturally enough, the future joins the past in this supersensuous\nworld. He can hope, he can imagine, he can prophesy. And again the\nimages of his hope are real; he sees them with that mind's eye which\nas yet he has not distinguished from his bodily eye. And so the\nsupersensuous world grows and grows big with the invisible present, and\nbig also with the past and the future, crowded with the ghosts of the\ndead and shadowed with oracles and portents. It is this supersensuous,\nsupernatural world which is the eternity, the other-world, of primitive\nreligion, not an endlessness of time, but a state removed from full\nsensuous reality, a world in which anything and everything may happen,\na world peopled by demonic ancestors and liable to a splendid vagueness,\nto a \"once upon a time-ness\" denied to the present. It not unfrequently\nhappens that people who know that the world nowadays obeys fixed laws\nhave no difficulty in believing that six thousand years ago man was\nmade direct from a lump of clay, and woman was made from one of man's\nsuperfluous ribs.\n\nThe fashioning of the supersensuous world comes out very clearly in\nprimitive man's views about the soul and life after death. Herbert\nSpencer noted long ago the influence of dreams in forming a belief in\nimmortality, but being very rational himself, he extended to primitive\nman a quite alien quality of rationality. Herbert Spencer argued that\nwhen a savage has a dream he seeks to account for it, and in so doing\ninvents a spirit world. The mistake here lies in the \"seeks to account\nfor it.\" (Primitive man, as Dr Beck observes, is not impelled by an\nErkenntnisstrieb. Dr Beck says he has counted upwards of 30 of these\nmythological Triebe (tendencies) with which primitive man has been\nendowed.) Man is at first too busy LIVING to have any time for\ndisinterested THINKING. He dreams a dream and it is real for him. He\ndoes not seek to account for it any more than for his hands and feet. He\ncannot distinguish between a CONception and a PERception, that is all.\nHe remembers his ancestors or they appear to him in a dream; therefore\nthey are alive still, but only as a rule to about the third generation.\nThen he remembers them no more and they cease to be.\n\nNext as regards his own soul. He feels something within him,\nhis life-power, his will to live, his power to act, his\npersonality--whatever we like to call it. He cannot touch this thing\nthat is himself, but it is real. His friend too is alive and one day he\nis dead; he cannot move, he cannot act. Well, something has gone that\nwas his friend's self. He has stopped breathing. Was it his breath? or\nhe is bleeding; is it his blood? This life-power IS something; does it\nlive in his heart or his lungs or his midriff? He did not see it go;\nperhaps it is like wind, an anima, a Geist, a ghost. But again it comes\nback in a dream, only looking shadowy; it is not the man's life, it is\na thin copy of the man; it is an \"image\" (eidolon). It is like that\nshifting distorted thing that dogs the living man's footsteps in the\nsunshine; it is a \"shade\" (skia). (The two conceptions of the soul, as a\nlife-essence, inseparable from the body, and as a separable phantom seem\nto occur in most primitive systems. They are distinct conceptions but\nare inextricably blended in savage thought. The two notions Korperseele\nand Psyche have been very fully discussed in Wundt's \"Volkerpsychologie\"\nII. pages 1-142, Leipzig, 1900.)\n\nGhosts and sprites, ancestor worship, the soul, oracles, prophecy; all\nthese elements of the primitive supersensuous world we willingly admit\nto be the proper material of religion; but other elements are more\nsurprising; such are class-names, abstract ideas, numbers, geometrical\nfigures. We do not nowadays think of these as of religious content, but\nto primitive men they were all part of the furniture of his supernatural\nworld.\n\nWith respect to class-names, Dr Tylor (\"Primitive Culture\", Vol. II.\npage 245 (4th edition), 1903.) has shown how instructive are the first\nattempts of the savage to get at the idea of a class. Things in which\nsimilarity is observed, things indeed which can be related at all are\nto the savage KINDRED. A species is a family or a number of individuals\nwith a common god to look after them. Such for example is the Finn\ndoctrine of the haltia. Every object has its haltia, but the haltiat\nwere not tied to the individual, they interested themselves in every\nmember of the species. Each stone had its haltia, but that haltia was\ninterested in other stones; the individuals disappeared, the haltia\nremained.\n\nNor was it only class-names that belonged to the supersensuous world. A\nman's own proper-name is a sort of spiritual essence of him, a kind\nof soul to be carefully concealed. By pronouncing a name you bring the\nthing itself into being. When Elohim would create Day \"he called out to\nthe Light 'Day,' and to the Darkness he called out 'Night'\"; the great\nmagician pronounced the magic Names and the Things came into being. \"In\nthe beginning was the Word\" is literally true, and this reflects the\nfact that our CONCEPTUAL world comes into being by the mental process of\nnaming. (For a full discussion of this point see Beck, \"Nachahmung\" page\n41, \"Die Sprache\".) In old times people went further; they thought that\nby naming events they could bring them to be, and custom even to-day\nkeeps up the inveterate magical habit of wishing people \"Good Morning\"\nand a \"Happy Christmas.\"\n\nNumber, too, is part of the supersensuous world that is thoroughly\nreligious. We can see and touch seven apples, but seven itself, that\nwonderful thing that shifts from object to object, giving it\nits SEVENness, that living thing, for it begets itself anew in\nmultiplication--surely seven is a fit denizen of the upper-world.\nOriginally all numbers dwelt there, and a certain supersensuous sanctity\nstill clings to seven and three. We still say \"Holy, Holy, Holy,\" and in\nsome mystic way feel the holier.\n\nThe soul and the supersensuous world get thinner and thinner, rarer and\nmore rarified, but they always trail behind them clouds of smoke and\nvapour from the world of sense and space whence they have come. It is\ndifficult for us even nowadays to use the word \"soul\" without lapsing\ninto a sensuous mythology. The Cartesians' sharp distinction between res\nextensa non cogitans and res cogitans non extansa is remote.\n\nSo far then man, through the processes of his thinking, has provided\nhimself with a supersensuous world, the world of sense-delusion, of\nsmoke and cloud, of dream and phantom, of imagination, of name and\nnumber and image. The natural course would now seem to be that this\nsupersensuous world should develop into the religious world as we know\nit, that out of a vague animism with ghosts of ancestors, demons,\nand the like, there should develop in due order momentary gods\n(Augenblicks-Gotter), tribal gods, polytheism, and finally a pure\nmonotheism.\n\nThis course of development is usually assumed, but it is not I think\nquite what really happens. The supersensuous world as we have got it so\nfar is too theoretic to be complete material of religion. It is indeed\nonly one factor, or rather it is as it were a lifeless body that waits\nfor a living spirit to possess and inform it. Had the theoretic factor\nremained uninformed it would eventually have separated off into its\nconstituent elements of error and truth, the error dying down as a\nbelated metaphysic, the truth developing into a correct and scientific\npsychology of the subjective. But man has ritual as well as mythology;\nthat is, he feels and acts as well as thinks; nay more he probably feels\nand acts long before he definitely thinks. This contradicts all our\npreconceived notions of theology. Man, we imagine, believes in a god\nor gods and then worships. The real order seems to be that, in a sense\npresently to be explained, he worships, he feels and acts, and out\nof his feeling and action, projected into his confused thinking,\nhe develops a god. We pass therefore to our second factor in\nreligion:--ritual.\n\nThe word \"ritual\" brings to our modern minds the notion of a church\nwith a priesthood and organised services. Instinctively we think of a\ncongregation meeting to confess sins, to receive absolution, to pray,\nto praise, to listen to sermons, and possibly to partake of sacraments.\nWere we to examine these fully developed phenomena we should hardly get\nfurther in the analysis of our religious conceptions than the notion\nof a highly anthropomorphic god approached by purely human methods of\npersonal entreaty and adulation.\n\nFurther, when we first come to the study of primitive religions we\nexpect a priori to find the same elements, though in a ruder form. We\nexpect to see \"The heathen in his blindness bow down to wood and stone,\"\nbut the facts that actually confront us are startlingly dissimilar.\nBowing down to wood and stone is an occupation that exists mainly in the\nminds of hymn-writers. The real savage is more actively engaged. Instead\nof asking a god to do what he wants done, he does it or tries to do\nit himself; instead of prayers he utters spells. In a word he is busy\npractising magic, and above all he is strenuously engaged in dancing\nmagical dances. When the savage wants rain or wind or sunshine, he does\nnot go to church; he summons his tribe and they dance a rain-dance or\nwind-dance or sun-dance. When a savage goes to war we must not picture\nhis wife on her knees at home praying for the absent; instead we must\npicture her dancing the whole night long; not for mere joy of heart\nor to pass the weary hours; she is dancing his war-dance to bring him\nvictory.\n\nMagic is nowadays condemned alike by science and by religion; it is\nboth useless and impious. It is obsolete, and only practised by malign\nsorcerers in obscure holes and corners. Undoubtedly magic is neither\nreligion nor science, but in all probability it is the spiritual\nprotoplasm from which religion and science ultimately differentiated.\nAs such the doctrine of evolution bids us scan it closely. Magic may\nbe malign and private; nowadays it is apt to be both. But in early days\nmagic was as much for good as for evil; it was publicly practised for\nthe common weal.\n\nThe gist of magic comes out most clearly in magical dances. We think of\ndancing as a light form of recreation, practised by the young from sheer\njoie de vivre and unsuitable for the mature. But among the Tarahumares\n(Carl Lumholtz, \"Unknown Mexico\", page 330, London, 1903.) in Mexico the\nword for dancing, nolavoa, means \"to work.\" Old men will reproach young\nmen saying \"Why do you not go to work?\" meaning why do you not dance\ninstead of only looking on. The chief religious sin of which the\nTarahumare is conscious is that he has not danced enough and not made\nenough tesvino, his cereal intoxicant.\n\nDancing then is to the savage WORKING, DOING, and the dance is in its\norigin an imitation or perhaps rather an intensification of processes of\nwork. (Karl Bucher, \"Arbeit und Rhythmus\", Leipzig (3rd edition), 1902,\npassim.) Repetition, regular and frequent, constitutes rhythm and rhythm\nheightens the sense of will power in action. Rhythmical action may even,\nas seen in the dances of Dervishes, produce a condition of ecstasy.\nEcstasy among primitive peoples is a condition much valued; it is often,\nthough not always, enhanced by the use of intoxicants. Psychologically\nthe savage starts from the sense of his own will power, he stimulates\nit by every means at his command. Feeling his will strongly and knowing\nnothing of natural law he recognises no limits to his own power; he\nfeels himself a magician, a god; he does not pray, he WILLS. Moreover\nhe wills collectively (The subject of collective hallucination as an\nelement in magic has been fully worked out by MM. Hubert and Mauss.\n\"Theorie generale de la Magie\", In \"L'Annee Sociologique\", 1902--3, page\n140.), reinforced by the will and action of his whole tribe. Truly of\nhim it may be said \"La vie deborde l'intelligence, l'intelligence c'est\nun retrecissement.\" (Henri Bergson, \"L'Evolution Creatrice\", page 50.)\n\nThe magical extension and heightening of personality come out very\nclearly in what are rather unfortunately known as MIMETIC dances. Animal\ndances occur very frequently among primitive peoples. The dancers\ndress up as birds, beasts, or fishes, and reproduce the characteristic\nmovements and habits of the animals impersonated. (So characteristic is\nthis impersonation in magical dancing that among the Mexicans the\nword for magic, navali, means \"disguise.\" K. Th. Preuss, \"Archiv f.\nReligionswissenschaft\", 1906, page 97.) A very common animal dance is\nthe frog-dance. When it rains the frogs croak. If you desire rain you\ndress up like a frog and croak and jump. We think of such a performance\nas a conscious imitation. The man, we think, is more or less LIKE a\nfrog. That is not how primitive man thinks; indeed, he scarcely thinks\nat all; what HE wants done the frog can do by croaking and jumping, so\nhe croaks and jumps and, for all he can, BECOMES a frog. \"L'intelligence\nanimale JOUE sans doute les representations plutot qu'elle ne les\npense.\" (Bergson, \"L'Evolution Creatrice\", page 205.)\n\nWe shall best understand this primitive state of mind if we study\nthe child \"born in sin.\" If a child is \"playing at lions\" he does not\nIMITATE a lion, i.e. he does not consciously try to be a thing more or\nless like a lion, he BECOMES one. His reaction, his terror, is the same\nas if the real lion were there. It is this childlike power of utter\nimpersonation, of BEING the thing we act or even see acted, this\nextension and intensification of our own personality that lives deep\ndown in all of us and is the very seat and secret of our joy in the\ndrama.\n\nA child's mind is indeed throughout the best clue to the understanding\nof savage magic. A young and vital child knows no limit to his own will,\nand it is the only reality to him. It is not that he wants at the outset\nto fight other wills, but that they simply do not exist for him. Like\nthe artist he goes forth to the work of creation, gloriously alone. His\nattitude towards other recalcitrant wills is \"they simply must.\" Let\neven a grown man be intoxicated, be in love, or subject to an intense\nexcitement, the limitations of personality again fall away. Like the\nomnipotent child he is again a god, and to him all things are possible.\nOnly when he is old and weary does he cease to command fate.\n\nThe Iroquois (Hewitt, \"American Anthropologist\", IV. I. page 32, 1902,\nN.S.) of North America have a word, orenda, the meaning of which is\neasier to describe than to define, but it seems to express the very soul\nof magic. This orenda is your power to do things, your force, sometimes\nalmost your personality. A man who hunts well has much and good orenda;\nthe shy bird who escapes his snares has a fine orenda. The orenda of the\nrabbit controls the snow and fixes the depth to which it will fall. When\na storm is brewing the magician is said to be making its orenda. When\nyou yourself are in a rage, great is your orenda. The notes of birds\nare utterances of their orenda. When the maize is ripening, the Iroquois\nknow it is the sun's heat that ripens it, but they know more; it is the\ncigala makes the sun to shine and he does it by chirping, by uttering\nhis orenda. This orenda is sometimes very like the Greek thumos, your\nbodily life, your vigour, your passion, your power, the virtue that is\nin you to feel and do. This notion of orenda, a sort of pan-vitalism, is\nmore fluid than animism, and probably precedes it. It is the projection\nof man's inner experience, vague and unanalysed, into the outer world.\n\nThe mana of the Melanesians (Codrington, \"The Melanesians\", pages 118,\n119, 192, Oxford, 1891.) is somewhat more specialised--all men do not\npossess mana--but substantially it is the same idea. Mana is not only a\nforce, it is also an action, a quality, a state, at once a substantive,\nan adjective, and a verb. It is very closely neighboured by the idea\nof sanctity. Things that have mana are tabu. Like orenda it manifests\nitself in noises, but specially mysterious ones, it is mana that is\nrustling in the trees. Mana is highly contagious, it can pass from a\nholy stone to a man or even to his shadow if it cross the stone. \"All\nMelanesian religion,\" Dr Codrington says, \"consists in getting mana\nfor oneself or getting it used for one's benefit.\" (Codrington, \"The\nMelanesians\", page 120, Oxford, 1891.)\n\nSpecially instructive is a word in use among the Omaka (See Prof.\nHaddon, \"Magic and Fetishism\", page 60, London, 1906. Dr Vierkandt\n(\"Globus\", July, 1907, page 41) thinks that \"Fernzauber\" is a later\ndevelopment from Nahzauber.), wazhin-dhedhe, \"directive energy, to\nsend.\" This word means roughly what we should call telepathy, sending\nout your thought or will-power to influence another and affect his\naction. Here we seem to get light on what has always been a puzzle, the\nbelief in magic exercised at a distance. For the savage will, distance\nis practically non-existent, his intense desire feels itself as\nnon-spatial. (This notion of mana, orenda, wazhin-dhedhe and the like\nlives on among civilised peoples in such words as the Vedic brahman in\nthe neuter, familiar to us in its masculine form Brahman. The neuter,\nbrahman, means magic power of a rite, a rite itself, formula, charm,\nalso first principle, essence of the universe. It is own cousin to the\nGreek dunamis and phusis. See MM. Hubert et Mauss, \"Theorie generale de\nla Magie\", page 117, in \"L'Annee Sociologique\", VII.)\n\nThrough the examination of primitive ritual we have at last got at one\ntangible, substantial factor in religion, a real live experience, the\nsense, that is, of will, desire, power actually experienced in person\nby the individual, and by him projected, extended into the rest of the\nworld.\n\nAt this stage it may fairly be asked, though the question cannot with\nany certainty be answered, \"at what point in the evolution of man does\nthis religious experience come in?\"\n\nSo long as an organism reacts immediately to outside stimulus, with a\ncertainty and conformity that is almost chemical, there is, it would\nseem, no place, no possibility for magical experience. But when the\ngerm appears of an intellect that can foresee an end not immediately\nrealised, or rather when a desire arises that we feel and recognise as\nnot satisfied, then comes in the sense of will and the impulse magically\nto intensify that will. The animal it would seem is preserved by\ninstinct from drawing into his horizon things which do not immediately\nsubserve the conservation of his species. But the moment man's\nlife-power began to make on the outside world demands not immediately\nand inevitably realised in action (I owe this observation to Dr K. Th.\nPreuss. He writes (\"Archiv f. Relig.\" 1906, page 98), \"Die Betonung des\nWillens in den Zauberakten ist der richtige Kern. In der Tat muss der\nMensch den Willen haben, sich selbst und seiner Umgebung besondere\nFahigkeiten zuzuschreiben, und den Willen hat er, sobald sein Verstand\nihn befahigt, EINE UBER DEN INSTINKT HINAUSGEHEN DER FURSORGE fur\nsich zu zeigen. SO LANGE IHN DER INSTINKT ALLEIN LEITET, KONNEN\nZAUBERHANDLUNGEN NICHT ENSTEHEN.\" For more detailed analysis of the\norigin of magic, see Dr Preuss \"Ursprung der Religion und Kunst\",\n\"Globus\", LXXXVI. and LXXXVII.), then a door was opened to magic, and\nin the train of magic followed errors innumerable, but also religion,\nphilosophy, science and art.\n\nThe world of mana, orenda, brahman is a world of feeling, desiring,\nwilling, acting. What element of thinking there may be in it is not yet\ndifferentiated out. But we have already seen that a supersensuous world\nof thought grew up very early in answer to other needs, a world of\nsense-illusions, shadows, dreams, souls, ghosts, ancestors, names,\nnumbers, images, a world only wanting as it were the impulse of mana to\nlive as a religion. Which of the two worlds, the world of thinking or\nthe world of doing, developed first it is probably idle to inquire. (If\nexternal stimuli leave on organisms a trace or record such as is known\nas an Engram, this physical basis of memory and hence of thought is\nalmost coincident with reaction of the most elementary kind. See Mr\nFrancis Darwin's Presidential Address to the British Association,\nDublin, 1908, page 8, and again Bergson places memory at the very root\nof conscious existence, see \"L'Evolution Creatrice\", page 18, \"le\nfond meme de notre existence consciente est memoire, c'est a dire\nprolongation du passee dans le present,\" and again \"la duree mord dans\nle temps et y laisse l'enpreint de son dent,\" and again, \"l'Evolution\nimplique une continuation reelle du passee par le present.\")\n\nIt is more important to ask, Why do these two worlds join? Because,\nit would seem, mana, the egomaniac or megalomaniac element, cannot get\nsatisfied with real things, and therefore goes eagerly out to a false\nworld, the supersensuous other-world whose growth we have sketched. This\njunction of the two is fact, not fancy. Among all primitive peoples dead\nmen, ghosts, spirits of all kinds, become the chosen vehicle of mana.\nEven to this day it is sometimes urged that religion, i.e. belief in\nthe immortality of the soul, is true \"because it satisfies the deepest\ncraving of human nature.\" The two worlds, of mana and magic on the one\nhand, of ghosts and other-world on the other, combine so easily because\nthey have the same laws, or rather the same comparative absence of law.\nAs in the world of dreams and ghosts, so in the world of mana, space and\ntime offer no obstacles; with magic all things are possible. In the one\nworld what you imagine is real; in the other what you desire is ipso\nfacto accomplished. Both worlds are egocentric, megalomaniac, filled to\nthe full with unbridled human will and desire.\n\nWe are all of us born in sin, in that sin which is to science\n\"the seventh and deadliest,\" anthropomorphism, we are egocentric,\nego-projective. Hence necessarily we make our gods in our own image.\nAnthropomorphism is often spoken of in books on religion and mythology\nas if it were a last climax, a splendid final achievement in religious\nthought. First, we are told, we have the lifeless object as god\n(fetichism), then the plant or animal (phytomorphism, theriomorphism),\nand last God is incarnate in the human form divine. This way of putting\nthings is misleading. Anthropomorphism lies at the very beginning of\nour consciousness. Man's first achievement in thought is to realise that\nthere is anything at all not himself, any object to his subject. When\nhe has achieved however dimly this distinction, still for long, for very\nlong he can only think of those other things in terms of himself; plants\nand animals are people with ways of their own, stronger or weaker than\nhimself but to all intents and purposes human.\n\nAgain the child helps us to understand our own primitive selves. To\nchildren animals are always people. You promise to take a child for a\ndrive. The child comes up beaming with a furry bear in her arms. You say\nthe bear cannot go. The child bursts into tears. You think it is because\nthe child cannot endure to be separated from a toy. It is no such thing.\nIt is the intolerable hurt done to the bear's human heart--a hurt not\nto be healed by any proffer of buns. He wanted to go, but he was a shy,\nproud bear, and he would not say so.\n\nThe relation of magic to religion has been much disputed. According to\none school religion develops out of magic, according to another, though\nthey ultimately blend, they are at the outset diametrically opposed,\nmagic being a sort of rudimentary and mistaken science (This view held\nby Dr Frazer is fully set forth in his \"Golden Bough\" (2nd edition),\npages 73-79, London, 1900. It is criticised by Mr R.R. Marett in \"From\nSpell to Prayer\", \"Folk-Lore\" XI. 1900, page 132, also very fully by\nMM. Hubert and Mauss, \"Theorie generale de la Magie\", in \"L'Annee\nSociologique\", VII. page 1, with Mr Marett's view and with that of MM.\nHubert and Mauss I am in substantial agreement.), religion having to do\nfrom the outset with spirits.\n\nBut, setting controversy aside, at the present stage of our inquiry\ntheir relation becomes, I think, fairly clear. Magic is, if my view\n(This view as explained above is, I believe, my own most serious\ncontribution to the subject. In thinking it out I was much helped by\nProf. Gilbert Murray.) be correct, the active element which informs a\nsupersensuous world fashioned to meet other needs. This blend of\ntheory and practice it is convenient to call religion. In practice the\ntransition from magic to religion, from Spell to Prayer, has always been\nfound easy. So long as mana remains impersonal you order it about; when\nit is personified and bulks to the shape of an overgrown man, you drop\nthe imperative and cringe before it. \"My will be done\" is magic,\n\"Thy Will be done\" is the last word in religion. The moral discipline\ninvolved in the second is momentous, the intellectual advance not\nstriking.\n\nI have spoken of magical ritual as though it were the informing\nlife-spirit without which religion was left as an empty shell. Yet the\nword ritual does not, as normally used, convey to our minds this notion\nof intense vitalism. Rather we associate ritual with something cut\nand dried, a matter of prescribed form and monotonous repetition. The\nassociation is correct; ritual tends to become less and less informed by\nthe life-impulse, more and more externalised. Dr Beck (\"Die Nachahmung\nund ihre Bedeutung fur Psychologie und Volkerkunde\", Leipzig, 1904.)\nin his brilliant monograph on \"Imitation\" has laid stress on the almost\nboundless influence of the imitation of one man by another in the\nevolution of civilisation. Imitation is one of the chief spurs to\naction. Imitation begets custom, custom begets sanctity. At first all\ncustom is sacred. To the savage it is as much a religious duty to tattoo\nhimself as to sacrifice to his gods. But certain customs naturally\nsurvive, because they are really useful; they actually have good\neffects, and so need no social sanction. Others are really useless;\nbut man is too conservative and imitative to abandon them. These become\nritual. Custom is cautious, but la vie est aleatoire. (Bergson, op. cit.\npage 143.)\n\nDr Beck's remarks on ritual are I think profoundly true and suggestive,\nbut with this reservation--they are true of ritual only when uninformed\nby personal experience. The very elements in ritual on which Dr\nBeck lays such stress, imitation, repetition, uniformity and social\ncollectivity, have been found by the experience of all time to have\na twofold influence--they inhibit the intellect, they stimulate and\nsuggest emotion, ecstasy, trance. The Church of Rome knows what she is\nabout when she prescribes the telling of the rosary. Mystery-cults and\nsacraments, the lineal descendants of magic, all contain rites charged\nwith suggestion, with symbols, with gestures, with half-understood\nformularies, with all the apparatus of appeal to emotion and will--the\nmore unintelligible they are the better they serve their purpose of\ninhibiting thought. Thus ritual deadens the intellect and stimulates\nwill, desire, emotion. \"Les operations magiques... sont le resultat d'une\nscience et d'une habitude qui exaltent la volonte humaine au-dessus de\nses limites habituelles.\" (Eliphas Levi, \"Dogme et Rituel de la haute\nMagie\", II. page 32, Paris, 1861, and \"A defence of Magic\", by Evelyn\nUnderhill, \"Fortnightly Review\", 1907.) It is this personal EXPERIENCE,\nthis exaltation, this sense of immediate, non-intellectual revelation,\nof mystical oneness with all things, that again and again rehabilitates\na ritual otherwise moribund.\n\nTo resume. The outcome of our examination of ORIGINES seems to be that\nreligious phenomena result from two delusive processes--a delusion of\nthe non-critical intellect, a delusion of the over-confident will. Is\nreligion then entirely a delusion? I think not. (I am deeply conscious\nthat what I say here is a merely personal opinion or sentiment,\nunsupported and perhaps unsupportable by reason, and very possibly quite\nworthless, but for fear of misunderstanding I prefer to state it.) Every\ndogma religion has hitherto produced is probably false, but for all that\nthe religious or mystical spirit may be the only way of apprehending\nsome things and these of enormous importance. It may also be that the\ncontents of this mystical apprehension cannot be put into language\nwithout being falsified and misstated, that they have rather to be felt\nand lived than uttered and intellectually analysed, and thus do not\nproperly fall under the category of true or false, in the sense in which\nthese words are applied to propositions; yet they may be something\nfor which \"true\" is our nearest existing word and are often, if not\nnecessary at least highly advantageous to life. That is why man through\na series of more or less grossly anthropomorphic mythologies and\ntheologies with their concomitant rituals tries to restate them.\nMeantime we need not despair. Serious psychology is yet young and has\nonly just joined hands with physiology. Religious students are still\nhampered by mediaevalisms such as Body and Soul, and by the perhaps\nscarcely less mythological segregations of Intellect, Emotion, Will. But\nnew facts (See the \"Proceedings\" of the Society for Psychical Research,\nLondon, passim, and especially Vols. VII.-XV. For a valuable collection\nof the phenomena of mysticism, see William James, \"Varieties of\nReligious Experience\", Edinburgh, 1901-2.) are accumulating, facts about\nthe formation and flux of personality, and the relations between the\nconscious and the sub-conscious. Any moment some great imagination may\nleap out into the dark, touch the secret places of life, lay bare the\ncardinal mystery of the marriage of the spatial with the non-spatial. It\nis, I venture to think, towards the apprehension of such mysteries,\nnot by reason only, but by man's whole personality, that the religious\nspirit in the course of its evolution through ancient magic and modern\nmysticism is ever blindly yet persistently moving.\n\nBe this as it may, it is by thinking of religion in the light of\nevolution, not as a revelation given, not as a realite faite but as a\nprocess, and it is so only, I think, that we attain to a spirit of real\npatience and tolerance. We have ourselves perhaps learnt laboriously\nsomething of the working of natural law, something of the limitations of\nour human will, and we have therefore renounced the practice of magic.\nYet we are bidden by those in high places to pray \"Sanctify this water\nto the mystical washing away of sin.\" Mystical in this connection spells\nmagical, and we have no place for a god-magician: the prayer is to us\nunmeaning, irreverent. Or again, after much toil we have ceased, or\nhope we have ceased, to think anthropomorphically. Yet we are invited\nto offer formal thanks to God for a meal of flesh whose sanctity is the\nlast survival of that sacrifice of bulls and goats he has renounced.\nSuch a ritual confuses our intellect and fails to stir our emotion. But\nto others this ritual, magical or anthropomorphic as it is, is charged\nwith emotional impulse, and others, a still larger number, think that\nthey act by reason when really they are hypnotised by suggestion and\ntradition; their fathers did this or that and at all costs they must do\nit. It was good that primitive man in his youth should bear the yoke of\nconservative custom; from each man's neck that yoke will fall, when and\nbecause he has outgrown it. Science teaches us to await that moment with\nher own inward and abiding patience. Such a patience, such a gentleness\nwe may well seek to practise in the spirit and in the memory of Darwin.\n\n\n\n\nXXVI. EVOLUTION AND THE SCIENCE OF LANGUAGE. By P. Giles, M.A., LL.D.\n(Aberdeen),\n\nReader in Comparative Philology in the University of Cambridge.\n\n\nIn no study has the historical method had a more salutary influence\nthan in the Science of Language. Even the earliest records show that the\nmeaning of the names of persons, places, and common objects was then, as\nit has always been since, a matter of interest to mankind. And in every\nage the common man has regarded himself as competent without special\ntraining to explain by inspection (if one may use a mathematical phrase)\nthe meaning of any words that attracted his attention. Out of this\namateur etymologising has sprung a great amount of false history, a kind\nof historical mythology invented to explain familiar names. A single\nexample will illustrate the tendency. According to the local legend the\nancestor of the Earl of Erroll--a husbandman who stayed the flight of\nhis countrymen in the battle of Luncarty and won the victory over the\nDanes by the help of the yoke of his oxen--exhausted with the fray\nuttered the exclamation \"Hoch heigh!\" The grateful king about to ennoble\nthe victorious ploughman at once replied:\n\n     \"Hoch heigh! said ye\n     And Hay shall ye be.\"\n\nThe Norman origin of the name Hay is well-known, and the battle of\nLuncarty long preceded the appearance of Normans in Scotland, but the\nlegend nevertheless persists.\n\nThough the earliest European treatise on philological questions which\nis now extant--the \"Cratylus\" of Plato,--as might be expected from its\nauthorship, contains some acute thinking and some shrewd guesses, yet\nthe work as a whole is infantine in its handling of language, and it\nhas been doubted whether Plato was more than half serious in some of\nthe suggestions which he puts forward. (For an account of the \"Cratylus\"\nwith references to other literature see Sandys' \"History of Classical\nScholarship\", I. page 92 ff., Cambridge, 1903.) In the hands of the\nRomans things were worse even than they had been in the hands of Plato\nand his Greek successors. The lack of success on the part of Varro and\nlater Roman writers may have been partly due to the fact that, from the\netymological point of view, Latin is a much more difficult language than\nGreek; it is by no means so closely connected with Greek as the ancients\nimagined, and they had no knowledge of the Celtic languages from which,\non some sides at least, much greater light on the history of the\nLatin language might have been obtained. Roman civilisation was a late\ndevelopment compared with Greek, and its records dating earlier than\n300 B.C.--a period when the best of Greek literature was already in\nexistence--are very few and scanty. Varro it is true was much more of\nan antiquary than Plato, but his extant works seem to show that he was\nrather a \"dungeon of learning\" than an original thinker.\n\nA scientific knowledge of language can be obtained only by comparison\nof different languages of the same family and the contrasting of their\ncharacteristics with those of another family or other families. It never\noccurred to the Greeks that any foreign language was worthy of serious\nstudy. Herodotus and other travellers and antiquaries indeed picked up\nindividual words from various languages, either as being necessary\nin communication with the inhabitants of the countries where they\nsojourned, or because of some point which interested them personally.\nPlato and others noticed the similarity of some Phrygian words to Greek,\nbut no systematic comparison seems ever to have been instituted.\n\nIn the Middle Ages the treatment of language was in a sense more\nhistorical. The Middle Ages started with the hypothesis, derived\nfrom the book of Genesis, that in the early world all men were of one\nlanguage and of one speech. Though on the same authority they believed\nthat the plain of Shinar has seen that confusion of tongues whence\nsprang all the languages upon earth, they seem to have considered that\nthe words of each separate language were nevertheless derived from this\noriginal tongue. And as Hebrew was the language of the Chosen People,\nit was naturally assumed that this original tongue was Hebrew. Hence\nwe find Dante declaring in his treatise on the Vulgar Tongue (Dante \"de\nVulgari Eloquio\", I. 4.) that the first word man uttered in Paradise\nmust have been \"El,\" the Hebrew name of his Maker, while as a result of\nthe fall of Adam, the first utterance of every child now born into this\nworld of sin and misery is \"heu,\" Alas! After the splendidly engraved\nbronze plates containing, as we now know, ritual regulations for certain\ncults, were discovered in 1444 at the town of Gubbio, in Umbria, they\nwere declared, by some authorities, to be written in excellent Hebrew.\nThe study of them has been the fascination and the despair of many a\nphilologist. Thanks to the devoted labours of numerous scholars, mainly\nin the last sixty years, the general drift of these inscriptions is\nnow known. They are the only important records of the ancient Umbrian\nlanguage, which was related closely to that of the Samnites and,\nthough not so closely, to that of the Romans on the other side of\nthe Apennines. Yet less than twenty years ago a book was published in\nGermany, which boasts itself the home of Comparative Philology,\nwherein the German origin of the Umbrian language was no less solemnly\ndemonstrated than had been its Celtic origin by Sir William Betham in\n1842.\n\nIt is good that the study of language should be historical, but the\nfirst requisite is that the history should be sound. How little had been\nlearnt of the true history of language a century ago may be seen from a\nlittle book by Stephen Weston first published in 1802 and several\ntimes reprinted, where accidental assonance is considered sufficient to\nestablish connection. Is there not a word \"bad\" in English and a word\n\"bad\" in Persian which mean the same thing? Clearly therefore Persian\nand English must be connected. The conclusion is true, but it is drawn\nfrom erroneous premises. As stated, this identity has no more value\nthan the similar assonance between the English \"cover\" and the Hebrew\n\"kophar\", where the history of \"cover\" as coming through French from a\nLatin \"co-operire\" was even in 1802 well-known to many. To this day,\nin spite of recent elaborate attempts (Most recently in H. Moller's\n\"Semitisch und Indogermanisch\", Erster Teil, Kopenhagen, 1907.) to\nestablish connection between the Indo-Germanic and the Semitic families\nof languages, there is no satisfactory evidence of such relation between\nthese families. This is not to deny the possibility of such a connection\nat a very early period; it is merely to say that through the lapse\nof long ages all trustworthy record of such relationship, if it ever\nexisted, has been, so far as present knowledge extends, obliterated.\n\nBut while Stephen Weston was publishing, with much public approval, his\ncollection of amusing similarities between languages--similarities which\nproved nothing--the key to the historical study of at least one family\nof languages had already been found by a learned Englishman in a distant\nland. In 1783 Sir William Jones had been sent out as a judge in the\nsupreme court of judicature in Bengal. While still a young man at Oxford\nhe was noted as a linguist; his reputation as a Persian scholar had\npreceded him to the East. In the intervals of his professional duties\nhe made a careful study of the language which was held sacred by\nthe natives of the country in which he was living. He was mainly\ninstrumental in establishing a society for the investigation of language\nand related subjects. He was himself the first president of the society,\nand in the \"third anniversary discourse\" delivered on February 2, 1786,\nhe made the following observations: \"The Sanscrit language, whatever be\nits antiquity, is of a wonderful structure; more perfect than the GREEK,\nmore copious than the LATIN, and more exquisitely refined than either,\nyet bearing to both of them a stronger affinity, both in the roots\nof verbs and in the forms of grammar, than could possibly have been\nproduced by accident; so strong indeed, that no philologer could examine\nthem all three, without believing them to have sprung from some common\nsource, which, perhaps, no longer exists: there is a similar reason,\nthough not quite so forcible, for supposing that both the Gothick and\nthe Celtick, though blended with a very different idiom, had the same\norigin with the Sanscrit; and the old Persian might be added to the same\nfamily, if this was the place for discussing any question concerning the\nantiquities of Persia.\" (\"Asiatic Researches\", I. page 422, \"Works of\nSir W. Jones\", I. page 26, London, 1799.)\n\nNo such epoch-making discovery was probably ever announced with less\nflourish of trumpets. Though Sir William Jones lived for eight years\nmore and delivered other anniversary discourses, he added nothing of\nimportance to this utterance. He had neither the time nor the health\nthat was needed for the prosecution of so arduous an undertaking.\n\nBut the good seed did not fall upon stony ground. The news was speedily\nconveyed to Europe. By a happy chance, the sudden renewal of war between\nFrance and England in 1803 gave Friedrich Schlegel the opportunity of\nlearning Sanscrit from Alexander Hamilton, an Englishman who, like many\nothers, was confined in Paris during the long struggle with Napoleon.\nThe influence of Schlegel was not altogether for good in the history of\nthis research, but he was inspiring. Not upon him but upon Franz Bopp,\na struggling German student who spent some time in Paris and London\na dozen years later, fell the mantle of Sir William Jones. In Bopp's\nComparative Grammar of the Indo-Germanic languages which appeared in\n1833, three-quarters of a century ago, the foundations of Comparative\nPhilology were laid. Since that day the literature of the subject has\ngrown till it is almost, if not altogether, beyond the power of any\nsingle man to cope with it. But long as the discourse may be, it is but\nthe elaboration of the text that Sir William Jones supplied.\n\nWith the publication of Bopp's Comparative Grammar the historical study\nof language was put upon a stable footing. Needless to say much remained\nto be done, much still remains to be done. More than once there has been\ndanger of the study following erroneous paths. Its terminology and its\npoint of view have in some degree changed. But nothing can shake the\ntruth of the statement that the Indo-Germanic languages constitute in\nthemselves a family sprung from the same source, marked by the same\ncharacteristics, and differentiated from all other languages by\nformation, by vocabulary, and by syntax. The historical method was\napplied to language long before it reached biology. Nearly a quarter of\na century before Charles Darwin was born, Sir William Jones had made the\nfirst suggestion of a comparative study of languages. Bopp's Comparative\nGrammar began to be published nine years before the first draft of\nDarwin's treatise on the Origin of Species was put on paper in 1842.\n\nIt is not therefore on the history of Comparative Philology in general\nthat the ideas of Darwin have had most influence. Unfortunately, as\nJowett has said in the introduction to his translation of Plato's\n\"Republic\", most men live in a corner. The specialisation of knowledge\nhas many advantages, but it has also disadvantages, none worse perhaps\nthan that it tends to narrow the specialist's horizon and to make it\nmore difficult for one worker to follow the advances that are being made\nby workers in other departments. No longer is it possible as in earlier\ndays for an intellectual prophet to survey from a Pisgah height all the\nPromised Land. And the case of linguistic research has been specially\nhard. This study has, if the metaphor may be allowed, a very extended\nfrontier. On one side it touches the domain of literature, on other\nsides it is conterminous with history, with ethnology and anthropology,\nwith physiology in so far as language is the production of the brain and\ntissues of a living being, with physics in questions of pitch and stress\naccent, with mental science in so far as the principles of similarity,\ncontrast, and contiguity affect the forms and the meanings of words\nthrough association of ideas. The territory of linguistic study\nis immense, and it has much to supply which might be useful to the\nneighbours who border on that territory. But they have not regarded her\neven with that interest which is called benevolent because it is not\nactively maleficent. As Horne Tooke remarked a century ago, Locke had\nfound a whole philosophy in language. What have the philosophers done\nfor language since? The disciples of Kant and of Wilhelm von Humboldt\nsupplied her plentifully with the sour grapes of metaphysics; otherwise\nher neighbours have left her severely alone save for an occasional\n\"Ausflug,\" on which it was clear they had sadly lost their bearings.\nSome articles in Psychological Journals, Wundt's great work on\n\"Volkerpsychologie\" (Erster Band: \"Die Sprache\", Leipzig, 1900. New\nedition, 1904. This work has been fertile in producing both opponents\nand supporters. Delbruck, \"Grundfragen der Sprachforschung\",\nStrassburg, 1901, with a rejoinder by Wundt, \"Sprachgeschichte\" and\n\"Sprachpsychologie\", Leipzig, 1901; L. Sutterlin, \"Das Wesen der\nSprachgebilde\", Heidelberg, 1902; von Rozwadowski, \"Wortbildung\nund Wortbedeutung\", Heidelberg, 1904; O. Dittrich, \"Grundzuge der\nSprachpsychologie\", Halle, 1904, Ch. A. Sechehaye, \"Programme et\nmethodes de la linguistique theorique\", Paris, 1908.), and Mauthner's\nbrilliantly written \"Beitrage zu einer Kritik der Sprache\" (In three\nparts: (i) \"Sprache und Psychologie, (ii) \"Zur Sprachwissenschaft\", both\nStuttgart 1901, (iii) \"Zur Grammatic und Logik\" (with index to all three\nvolumes), Stuttgart and Berlin, 1902.) give some reason to hope that, on\none side at least, the future may be better than the past.\n\nWhere Charles Darwin's special studies came in contact with the Science\nof Language was over the problem of the origin and development of\nlanguage. It is curious to observe that, where so many fields of\nlinguistic research have still to be reclaimed--many as yet can hardly\nbe said to be mapped out,--the least accessible field of all--that\nof the Origin of Language--has never wanted assiduous tillers.\nUnfortunately it is a field beyond most others where it may be said that\n\n\"Wilding oats and luckless darnel grow.\"\n\nIf Comparative Philology is to work to purpose here, it must be on\nresults derived from careful study of individual languages and groups of\nlanguages. But as yet the group which Sir William Jones first mapped out\nand which Bopp organised is the only one where much has been achieved.\nInvestigation of the Semitic group, in some respects of no less moment\nin the history of civilisation and religion, where perhaps the labour\nof comparison is not so difficult, as the languages differ less among\nthemselves, has for some reason strangely lagged behind. Some years ago\nin the \"American Journal of Philology\" Paul Haupt pointed out that if\nadvance was to be made, it must be made according to the principles\nwhich had guided the investigation of the Indo-Germanic languages to\nsuccess, and at last a Comparative Grammar of an elaborate kind is in\nprogress also for the Semitic languages. (Brockelmann, \"Vergleichende\nGrammatik der semitischen Sprachen\", Berlin, 1907 ff. Brockelmann and\nZimmern had earlier produced two small hand-books. The only large work\nwas William Wright's \"Lectures on the Comparative Grammar of the\nSemitic Languages\", Cambridge, 1890.) For the great group which includes\nFinnish, Hungarian, Turkish and many languages of northern Asia, a\nbeginning, but only a beginning has been made. It may be presumed from\nthe great discoveries which are in progress in Turkestan that presently\nmuch more will be achieved in this field. But for a certain utterance\nto be given by Comparative Philology on the question of the origin of\nlanguage it is necessary that not merely for these languages but also\nfor those in other quarters of the globe, the facts should be collected,\nsifted and tabulated. England rules an empire which contains a greater\nvariety of languages by far than were ever held under one sway before.\nThe Government of India is engaged in producing, under the editorship of\nDr Grierson, a linguistic survey of India, a remarkable undertaking and,\nso far as it has gone, a remarkable achievement. Is it too much to ask\nthat, with the support of the self-governing colonies, a similar survey\nshould be undertaken for the whole of the British Empire?\n\nNotwithstanding the great number of books that have been written on the\norigin of language in the last three and twenty centuries, the results\nof the investigation which can be described as certain are very meagre.\nThe question originally raised was whether language came into being\nthesei or phusei, by convention or by nature. The first alternative, in\nits baldest form at least, has passed from out the field of controversy.\nNo one now claims that names were given to living things or objects or\nactivities by formal agreement among the members of an early community,\nor that the first father of mankind passed in review every living thing\nand gave it its name. Even if the record of Adam's action were to be\ntaken literally there would still remain the question, whence had he\nthis power? Did he develop it himself or was it a miraculous gift with\nwhich he was endowed at his creation? If the latter, then as Wundt says\n(\"Volkerpsychologie\", I. 2, page 585.), \"the miracle of language is\nsubsumed in the miracle of creation.\" If Adam developed language of\nhimself, we are carried over to the alternative origin of phusei. On\nthis hypothesis we must assume that the natural growth which modern\ntheories of development regard as the painful progress of multitudinous\ngenerations was contracted into the experience of a single individual.\n\nBut even if the origin of language is admitted to be NATURAL there may\nstill be much variety of signification attached to the word: NATURE,\nlike most words which are used by philosophers, has accumulated\nmany meanings, and as research into the natural world proceeds, is\naccumulating more.\n\nForty years ago an animated controversy raged among the supporters of\nthe theories which were named for short the bow-wow, the pooh-pooh and\nthe ding-dong theories of the origin of language. The third, which was\nthe least tenacious of life, was made known to the English-speaking\nworld by the late Professor Max Muller who, however, when questioned,\nrepudiated it as his own belief. (\"Science of Thought\", London, 1887,\npage 211.) It was taken by him from Heyse's lectures on language which\nwere published posthumously by Steinthal. Put shortly the theory is\nthat \"everything which is struck, rings. Each substance has its peculiar\nring. We can tell the more or less perfect structure of metals by their\nvibrations, by the answer which they give. Gold rings differently\nfrom tin, wood rings differently from stone; and different sounds are\nproduced according to the nature of each percussion. It may be the same\nwith man, the most highly organised of nature's work.\" (Max Muller as\nabove, translating from Heyse.) Max Muller's repudiation of this theory\nwas, however, not very whole-hearted for he proceeds later in the same\nargument: \"Heyse's theory, which I neither adopted nor rejected, but\nwhich, as will be seen, is by no means incompatible with that which for\nmany years has been gaining on me, and which of late has been so clearly\nformulated by Professor Noire, has been assailed with ridicule and torn\nto pieces, often by persons who did not even suspect how much truth was\nhidden behind its paradoxical appearance. We are still very far from\nbeing able to identify roots with nervous vibrations, but if it should\nappear hereafter that sensuous vibrations supply at least the raw\nmaterial of roots, it is quite possible that the theory, proposed by\nOken and Heyse, will retain its place in the history of the various\nattempts at solving the problem of the origin of language, when other\ntheories, which in our own days were received with popular applause,\nwill be completely forgotten.\" (\"Science of Thought\", page 212.)\n\nLike a good deal else that has been written on the origin of language,\nthis statement perhaps is not likely to be altogether clear to the plain\nman, who may feel that even the \"raw material of roots\" is some distance\nremoved from nervous vibrations, though obviously without the existence\nof afferent and efferent nerves articulate speech would be impossible.\nBut Heyse's theory undoubtedly was that every thought or idea which\noccurred to the mind of man for the first time had its own special\nphonetic expression, and that this responsive faculty, when its object\nwas thus fulfilled, became extinct. Apart from the philosophical\nquestion whether the mind acts without external stimulus, into which it\nis not necessary to enter here, it is clear that this theory can neither\nbe proved nor disproved, because it postulates that this faculty existed\nonly when language first began, and later altogether disappeared. As we\nhave already seen, it is impossible for us to know what happened at the\nfirst beginnings of language, because we have no information from any\nperiod even approximately so remote; nor are we likely to attain it.\nEven in their earliest stages the great families of language which\npossess a history extending over many centuries--the Indo-Germanic and\nthe Semitic--have very little in common. With the exception of Chinese,\nthe languages which are apparently of a simpler or more primitive\nformation have either a history which, compared with that of the\nfamilies mentioned, is very short, or, as in the case of the vast\nmajority, have no history beyond the time extending only over a few\nyears or, at most, a few centuries when they have been observed by\ncompetent scholars of European origin. But, if we may judge by the\nhistory of geology and other studies, it is well to be cautious in\nassuming for the first stages of development forces which do not operate\nin the later, unless we have direct evidence of their existence.\n\nIt is unnecessary here to enter into a prolonged discussion of the other\nviews christened by Max Muller, not without energetic protest from their\nsupporters, the bow-wow and pooh-pooh theories of language. Suffice it\nto say that the former recognises as a source of language the imitation\nof the sounds made by animals, the fall of bodies into water or on\nto solid substances and the like, while the latter, also called the\ninterjectional theory, looks to the natural ejaculations produced by\nparticular forms of effort for the first beginnings of speech. It would\nbe futile to deny that some words in most languages come from\nimitation, and that others, probably fewer in number, can be traced\nto ejaculations. But if either of these sources alone or both in\ncombination gave rise to primitive speech, it clearly must have been a\nsimple form of language and very limited in amount. There is no reason\nto think that it was otherwise. Presumably in its earliest stages\nlanguage only indicated the most elementary ideas, demands for food\nor the gratification of other appetites, indications of danger, useful\nanimals and plants. Some of these, such as animals or indications of\ndanger, could often be easily represented by imitative sounds: the need\nfor food and the like could be indicated by gesture and natural cries.\nBoth sources are verae causae; to them Noire, supported by Max Muller,\nhas added another which has sometimes been called the Yo-heave-ho\ntheory. Noire contends that the real crux in the early stages of\nlanguage is for primitive man to make other primitive men understand\nwhat he means. The vocal signs which commend themselves to one may not\nhave occurred to another, and may therefore be unintelligible. It may be\nadmitted that this difficulty exists, but it is not insuperable. The\nold story of the European in China who, sitting down to a meal and being\ndoubtful what the meat in the dish might be, addressed an interrogative\nQuack-quack? to the waiter and was promptly answered by Bow-wow,\nillustrates a simple situation where mutual understanding was easy.\nBut obviously many situations would be more complex than this, and to\ngrapple with them Noire has introduced his theory of communal action.\n\"It was common effort directed to a common object, it was the most\nprimitive (uralteste) labour of our ancestors, from which sprang\nlanguage and the life of reason.\" (Noire \"Der Ursprung der Sprache\",\npage 331, Mainz, 1877.) As illustrations of such common effort he cites\nbattle cries, the rescue of a ship running on shore (a situation not\nlikely to occur very early in the history of man), and others. Like Max\nMuller he holds that language is the utterance and the organ of thought\nfor mankind, the one characteristic which separates man from the\nbrute. \"In common action the word was first produced; for long it was\ninseparably connected with action; through long-continued connection it\ngradually became the firm, intelligible symbol of action, and then in\nits development indicated also things of the external world in so far\nas the action affected them and finally the sound began to enter into a\nconnexion with them also.\" (Op. cit. page 339.) In so far as this theory\nrecognises language as a social institution it is undoubtedly correct.\nDarwin some years before Noire had pointed to the same social origin\nof language in the fourth chapter of his work on \"The Expression of the\nEmotions in Man and Animals\". \"Naturalists have remarked, I believe with\ntruth, that social animals, from habitually using their vocal organs\nas a means of intercommunication, use them on other occasions much more\nfreely than other animals... The principle, also, of association, which\nis so widely extended in its power, has likewise played its part. Hence\nit allows that the voice, from having been employed as a serviceable\naid under certain conditions, inducing pleasure, pain, rage, etc., is\ncommonly used whenever the same sensations or emotions are excited,\nunder quite different conditions, or in a lesser degree.\" (\"The\nExpression of the Emotions\", page 84 (Popular Edition, 1904).\n\nDarwin's own views on language which are set forth most fully in\n\"The Descent of Man\" (page 131 ff. (Popular Edition, 1906).) are\ncharacterised by great modesty and caution. He did not profess to be a\nphilologist and the facts are naturally taken from the best known works\nof the day (1871). In the notes added to the second edition he remarks\non Max Muller's denial of thought without words, \"what a strange\ndefinition must here be given to the word thought!\" (Op. cit. page\n135, footnote 63.) He naturally finds the origin of language in \"the\nimitation and modification of various natural sounds, the voices of\nother animals, and man's own instinctive cries aided by signs and\ngestures (op. cit. page 132.)... As the voice was used more and more,\nthe vocal organs would have been strengthened and perfected through the\nprinciple of the inherited effects of use; and this would have reacted\non the power of speech.\" (Op. cit. page 133.) On man's own instinctive\ncries, he has more to say in \"The Expression of the Emotions\". (Page 93\n(Popular Edition, 1904) and elsewhere.) These remarks have been utilised\nby Prof. Jespersen of Copenhagen in propounding an ingenious theory of\nhis own to the effect that speech develops out of singing. (\"Progress in\nLanguage\", page 361, London, 1894.)\n\nFor many years and in many books Max Muller argued against Darwin's\nviews on evolution on the one ground that thought is impossible without\nspeech; consequently as speech is confined to the human race, there is a\ngulf which cannot be bridged between man and all other creatures.\n(Some interesting comments on the theory will be found in a lecture\non \"Thought and Language\" in Samuel Butler's \"Essays on Life, Art and\nScience\", London, 1908.) On the title-page of his \"Science of Thought\"\nhe put the two sentences \"No Reason without Language: No Language\nwithout Reason.\" It may be readily admitted that the second dictum is\ntrue, that no language properly so-called can exist without reason.\nVarious birds can learn to repeat words or sentences used by their\nmasters or mistresses. In most cases probably the birds do not attach\ntheir proper meaning to the words they have learnt; they repeat them in\nseason and out of season, sometimes apparently for their own amusement,\ngenerally in the expectation, raised by past experience, of being\nrewarded for their proficiency. But even here it is difficult to prove\na universal negative, and most possessors of such pets would repudiate\nindignantly the statement that the bird did not understand what was said\nto it, and would also contend that in many cases the words which it used\nwere employed in their ordinary meaning. The first dictum seems to be\ninconsistent with fact. The case of deaf mutes, such as Laura Bridgeman,\nwho became well educated, or the still more extraordinary case of Helen\nKeller, deaf, dumb, and blind, who in spite of these disadvantages\nhas learnt not only to reason but to reason better than the average of\npersons possessed of all their senses, goes to show that language and\nreason are not necessarily always in combination. Reason is but the\nconscious adaptation of means to ends, and so defined is a faculty which\ncannot be denied to many of the lower animals. In these days when so\nmany books on Animal Intelligence are issued from the press, it seems\nunnecessary to labour the point. Yet none of these animals, except by\nparrot-imitation, makes use of speech, because man alone possesses in a\nsufficient degree of development the centres of nervous energy which are\nrequired for the working of articulation in speech. On this subject much\ninvestigation was carried on during the last years of Darwin's life\nand much more in the period since his death. As early as 1861 Broca,\nfollowing up observations made by earlier French writers, located the\ncentre of articulate speech in the third left frontal convolution of\nthe brain. In 1876 he more definitely fixed the organ of speech in\n\"the posterior two-fifths of the third frontal convolution\" (Macnamara,\n\"Human Speech\", page 197, London, 1908.), both sides and not merely the\nleft being concerned in speech production. Owing however to the greater\nuse by most human beings of the right side of the body, the left side of\nthe brain, which is the motor centre for the right side of the body, is\nmore highly developed than its right side, which moves the left side\nof the body. The investigations of Professors Ferrier, Sherrington and\nGrunbaum have still more precisely defined the relations between brain\nareas and certain groups of muscles. One form of aphasia is the result\nof injury to or disease in the third frontal convolution because the\nmotor centre is no longer equal to the task of setting the necessary\nmuscles in motion. In the brain of idiots who are unable to speak,\nthe centre for speech is not developed. (Op. cit. page 226.) In the\nanthropoid apes the brain is similarly defective, though it has been\ndemonstrated by Professors Cunningham and Marchand \"that there is a\ntendency, especially in the gorilla's brain, for the third frontal\nconvolution to assume the human form... But if they possessed a centre\nfor speech, those parts of the hemispheres of their brains which form\nthe mechanism by which intelligence is elaborated are so ill-developed,\nas compared with the rest of their bodies, that we can not conceive,\neven with more perfect frontal convolutions, that these animals could\nformulate ideas expressible in intelligent speech.\" (Op. cit. page 223.)\n\nWhile Max Muller's theory is Shelley's\n\n\"He gave man speech, and speech created thought, Which is the measure of\nthe universe\" (\"Prometheus Unbound\" II. 4.),\n\nit seems more probable that the development was just the opposite--that\nthe development of new activities originated new thoughts which required\nnew symbols to express them, symbols which may at first have been, even\nto a greater extent than with some of the lower races at present, sign\nlanguage as much as articulation. When once the faculty of articulation\nwas developed, which, though we cannot trace the process, was probably a\nvery gradual growth, there is no reason to suppose that words developed\nin any other way then they do at present. An erroneous notion of the\ndevelopment of language has become widely spread through the adoption\nof the metaphorical term \"roots\" for the irreducible elements of human\nspeech. Men never talked in roots; they talked in words. Many words of\nkindred meaning have a part in common, and a root is nothing but that\ncommon part stripped of all additions. In some cases it is obvious that\none word is derived from another by the addition of a fresh element; in\nother cases it is impossible to say which of two kindred words is the\nmore primitive. A root is merely a convenient term for an abstraction.\nThe simplest word may be called a root, but it is nevertheless a\nword. How are new words added to a language in the present day? Some\ncommunities, like the Germans, prefer to construct new words for new\nideas out of the old material existing in the language; others, like the\nEnglish, prefer to go to the ancient languages of Greece and Rome for\nterms to express new ideas. The same chemical element is described in\nthe two languages as sour stuff (Sauerstoff) and as oxygen. Both terms\nmean the same thing etymologically as well as in fact. On behalf of the\nGerman method, it may be contended that the new idea is more closely\nattached to already existing ideas, by being expressed in elements of\nthe language which are intelligible even to the meanest capacity. For\nthe English practice it may be argued that, if we coin a new word which\nmeans one thing, and one thing only, the idea which it expresses is\nmore clearly defined than if it were expressed in popularly intelligible\nelements like \"sour stuff.\" If the etymological value of words were\nalways present in the minds of their users, \"oxygen\" would undoubtedly\nhave an advantage over \"sour stuff\" as a technical term. But the\ntendency in language is to put two words of this kind which express but\none idea under a single accent, and when this has taken place, no one\nbut the student of language any longer observes what the elements really\nmean. When the ordinary man talks of a \"blackbird\" it is certainly not\npresent to his consciousness that he is talking of a black bird, unless\nfor some reason conversation has been dwelling upon the colour rather\nthan other characteristics of the species.\n\nBut, it may be said, words like \"oxygen\" are introduced by learned men,\nand do not represent the action of the man in the street, who, after\nall, is the author of most additions to the stock of human language. We\nmay go back therefore some four centuries to a period, when scientific\nstudy was only in its infancy, and see what process was followed. With\nthe discovery of America new products never seen before reached Europe,\nand these required names. Three of the most characteristic were tobacco,\nthe potato, and the turkey. How did these come to be so named? The first\npeople to import these products into Europe were naturally the Spanish\ndiscoverers. The first of these words--tobacco--appears in forms which\ndiffer only slightly in the languages of all civilised countries:\nSpanish tabaco, Italian tabacco, French tabac, Dutch and German tabak,\nSwedish tobak, etc. The word in the native dialect of Hayti is said to\nhave been tabaco, but to have meant not the plant (According to William\nBarclay, \"Nepenthes, or the Virtue of Tobacco\", Edinburgh, 1614, \"the\ncountrey which God hath honoured and blessed with this happie and holy\nherbe doth call it in their native language 'Petum'.\") but the pipe\nin which it was smoked. It thus illustrates a frequent feature of\nborrowing--that the word is not borrowed in its proper signification,\nbut in some sense closely allied thereto, which a foreigner,\nunderstanding the language with difficulty, might readily mistake for\nthe real meaning. Thus the Hindu practice of burning a wife upon the\nfuneral pyre of her husband is called in English \"suttee\", this word\nbeing in fact but the phonetic spelling of the Sanskrit \"sati\", \"a\nvirtuous woman,\" and passing into its English meaning because formerly\nthe practice of self-immolation by a wife was regarded as the highest\nvirtue.\n\nThe name of the potato exhibits greater variety. The English name was\nborrowed from the Spanish \"patata\", which was itself borrowed from a\nnative word for the \"yam\" in the dialect of Hayti. The potato appeared\nearly in Italy, for the mariners of Genoa actively followed the\nfootsteps of their countryman Columbus in exploring America. In Italian\ngenerally the form \"patata\" has survived. The tubers, however,\nalso suggested a resemblance to truffles, so that the Italian word\n\"tartufolo\", a diminutive of the Italian modification of the Latin\n\"terrae tuber\" was applied to them. In the language of the Rhaetian Alps\nthis word appears as \"tartufel\". From there it seems to have passed\ninto Germany where potatoes were not cultivated extensively till the\neighteenth century, and \"tartufel\" has in later times through some\npopular etymology been metamorphosed into \"Kartoffel\". In France the\nshape of the tubers suggested the name of earth-apple (pomme de terre),\na name also adopted in Dutch (aard-appel), while dialectically in German\na form \"Grumbire\" appears, which is a corruption of \"Grund-birne\",\n\"ground pear\". (Kluge \"Etymologisches Worterbuch der deutschen Sprache\"\n(Strassburg), s.v. \"Kartoffel\".) Here half the languages have adopted\nthe original American word for an allied plant, while others have\nadopted a name originating in some more or less fanciful resemblance\ndiscovered in the tubers; the Germans alone in Western Europe, failing\nto see any meaning in their borrowed name, have modified it almost\nbeyond recognition. To this English supplies an exact parallel in\n\"parsnep\" which, though representing the Latin \"pastinaca\" through the\nOld French \"pastenaque\", was first assimilated in the last syllable to\nthe \"nep\" of \"turnep\" (\"pasneppe\" in Elizabethan English), and later had\nan \"r\" introduced into the first syllable, apparently on the analogy of\n\"parsley\".\n\nThe turkey on the other hand seems never to be found with its original\nAmerican name. In England, as the name implies, the turkey cock was\nregarded as having come from the land of the Turks. The bird no doubt\nspread over Europe from the Italian seaports. The mistake, therefore,\nwas not unnatural, seeing that these towns conducted a great trade\nwith the Levant, while the fact that America when first discovered was\nidentified with India helped to increase the confusion. Thus in French\nthe \"coq d'Inde\" was abbreviated to \"d'Inde\" much as \"turkey cock\" was\nto \"turkey\"; the next stage was to identify \"dinde\" as a feminine word\nand create a new \"dindon\" on the analogy of \"chapon\" as the masculine.\nIn Italian the name \"gallo d'India\" besides survives, while in German\nthe name \"Truthahn\" seems to be derived onomatopoetically from\nthe bird's cry, though a dialectic \"Calecutischer Hahn\" specifies\nerroneously an origin for the bird from the Indian Calicut. In the\nSpanish \"pavo\", on the other hand, there is a curious confusion with\nthe peacock. Thus in these names for objects of common knowledge,\nthe introduction of which into Europe can be dated with tolerable\ndefiniteness, we see evinced the methods by which in remoter ages\nobjects were named. The words were borrowed from the community whence\ncame the new object, or the real or fancied resemblance to some known\nobject gave the name, or again popular etymology might convert the\nunknown term into something that at least approached in sound a\nwell-known word.\n\n\"The Origin of Species\" had not long been published when the parallelism\nof development in natural species and in languages struck investigators.\nAt the time, one of the foremost German philologists was August\nSchleicher, Professor at Jena. He was himself keenly interested in the\nnatural sciences, and amongst his colleagues was Ernst Haeckel, the\nprotagonist in Germany of the Darwinian theory. How the new ideas struck\nSchleicher may be seen from the following sentences by his colleague\nHaeckel. \"Speech is a physiological function of the human organism,\nand has been developed simultaneously with its organs, the larynx and\ntongue, and with the functions of the brain. Hence it will be quite\nnatural to find in the evolution and classification of languages the\nsame features as in the evolution and classification of organic species.\nThe various groups of languages that are distinguished in philology as\nprimitive, fundamental, parent, and daughter languages, dialects, etc.,\ncorrespond entirely in their development to the different categories\nwhich we classify in zoology and botany as stems, classes, orders,\nfamilies, genera, species and varieties. The relation of these groups,\npartly coordinate and partly subordinate, in the general scheme is just\nthe same in both cases; and the evolution follows the same lines in\nboth.\" (Haeckel, \"The Evolution of Man\", page 485, London, 1905. This\nrepresents Schleicher's own words: Was die Naturforscher als Gattung\nbezeichnen wurden, heisst bei den Glottikern Sprachstamm, auch\nSprachsippe; naher verwandte Gattungen bezeichnen sie wohl auch als\nSprachfamilien einer Sippe oder eines Sprachstammes... Die Arten einer\nGattung nennen wir Sprachen eines Stammes; die Unterarten einer Art sind\nbei uns die Dialekte oder Mundarten einer Sprache; den Varietaten\nund Spielarten entsprechen die Untermundarten oder Nebenmundarten und\nendlich den einzelnen Individuen die Sprechweise der einzelnen\ndie Sprachen redenden Menschen. \"Die Darwinische Theorie und die\nSprachwissenschaft\", Weimar, 1863, page 12 f. Darwin makes a more\ncautious statement about the classification of languages in \"The Origin\nof Species\", page 578, (Popular Edition, 1900).) These views were set\nforth in an open letter addressed to Haeckel in 1863 by Schleicher\nentitled, \"The Darwinian theory and the science of language\".\nUnfortunately Schleicher's views went a good deal farther than is\nindicated in the extract given above. He appended to the pamphlet a\ngenealogical tree of the Indo-Germanic languages which, though to a\nlarge extent confirmed by later research, by the dichotomy of each\nbranch into two other branches, led the unwary reader to suppose their\nphylogeny (to use Professor Haeckel's term) was more regular than our\nevidence warrants.\n\nWithout qualification Schleicher declared languages to be \"natural\norganisms which originated unconditioned by the human will,\ndeveloped according to definite laws, grow old and die; they also are\ncharacterised by that series of phenomena which we designate by the\nterm 'Life.' Consequently Glottic, the science of language, is a natural\nscience; its method is in general the same as that of the other natural\nsciences.\" (\"Die Darwinische Theorie\", page 6 f.) In accordance with\nthis view he declared (op. cit. page 23.) that the root in language\nmight be compared with the simple cell in physiology, the linguistic\nsimple cell or root being as yet not differentiated into special organs\nfor the function of noun, verb, etc.\n\nIn this probably all recent philologists admit that Schleicher went too\nfar. One of the most fertile theories in the modern science of language\noriginated with him, and was further developed by his pupil, August\nLeskien (\"Die Declination im Slavisch-litanischen und Germanischen\",\nLeipzig, 1876; Osthoff and Brugmann, \"Morphologische Untersuchungen\",\nI. (Introduction), 1878. The general principles of this school were\nformulated (1880) in a fuller form in H. Paul's \"Prinzipien der\nSprachgeschichte\", Halle (3rd edition, 1898). Paul and Wundt (in his\n\"Volkerpsychologie\") deal largely with the same matter, but begin their\ninvestigations from different points of view, Paul being a philologist\nwith leanings to philosophy and Wundt a philosopher interested in\nlanguage.), and by Leskien's colleagues and friends, Brugmann and\nOsthoff. This was the principle that phonetic laws have no exceptions.\nUnder the influence of this generalisation much greater precision in\netymology was insisted upon, and a new and remarkably active period in\nthe study of language began. Stated broadly in the fashion given above\nthe principle is not true. A more accurate statement would be that an\noriginal sound is represented in a given dialect at a given time and in\na given environment only in one way; provided that the development of\nthe original sound into its representation in the given dialect has not\nbeen influenced by the working of analogy.\n\nIt is this proviso that is most important for the characterisation of\nthe science of language. As I have said elsewhere, it is at this point\nthat this science parts company with the natural sciences. \"If the\nchemist compounds two pure simple elements, there can be but one result,\nand no power of the chemist can prevent it. But the minds of men do\nact upon the sounds which they produce. The result is that, when this\nhappens, the phonetic law which would have acted in the case is stopped,\nand this particular form enters on the same course of development as\nother forms to which it does not belong.\" (P. Giles, \"Short Manual of\nComparative Philology\", 2nd edition, page 57, London, 1901.)\n\nSchleicher was wrong in defining a language to be an organism in the\nsense in which a living being is an organism. Regarded physiologically,\nlanguage is a function or potentiality of certain human organs; regarded\nfrom the point of view of the community it is of the nature of an\ninstitution. (This view of language is worked out at some length by\nProf. W.D. Whitney in an article in the \"Contemporary Review\" for 1875,\npage 713 ff. This article forms part of a controversy with Max Muller,\nwhich is partly concerned with Darwin's views on language. He criticises\nSchleicher's views severely in his \"Oriental and Linguistic Studies\",\npage 298 ff., New York, 1873. In this volume will be found criticisms of\nvarious other views mentioned in this essay.) More than most influences\nit conduces to the binding together of the elements that form a state.\nThat geographical or other causes may effectively counteract the\ninfluence of identity of language is obvious. One need only read the\nhistory of ancient Greece, or observe the existing political separation\nof Germany and Austria, of Great Britain and the United States of\nAmerica. But however analogous to an organism, language is not an\norganism. In a less degree Schleicher, by defining languages as such,\ncommitted the same mistake which Bluntschli made regarding the State,\nand which led him to declare that the State is by nature masculine and\nthe Church feminine. (Bluntschli, \"Theory of the State\", page 24, Second\nEnglish Edition, Oxford, 1892.) The views of Schleicher were to some\nextent injurious to the proper methods of linguistic study. But this\nmisfortune was much more than fully compensated by the inspiration\nwhich his ideas, collected and modified by his disciples, had upon the\nscience. In spite of the difference which the psychological element\nrepresented by analogy makes between the science of language and the\nnatural sciences, we are entitled to say of it as Schleicher said of\nDarwin's theory of the origin of species, \"it depends upon observation,\nand is essentially an attempt at a history of development.\"\n\nOther questions there are in connection with language and evolution\nwhich require investigation--the survival of one amongst several\ncompeting words (e.g. why German keeps only as a high poetic word\n\"ross\", which is identical in origin with the English work-a-day\n\"horse\", and replaces it by \"pferd\", whose congener the English\n\"palfrey\" is almost confined to poetry and romance), the persistence\nof evolution till it becomes revolution in languages like English or\nPersian which have practically ceased to be inflectional languages, and\nmany other problems. Into these Darwin did not enter, and they require\na fuller investigation than is possible within the limits of the present\npaper.\n\n\n\n\nXXVII. DARWINISM AND HISTORY. By J.B. Bury, Litt.D., LL.D.\n\nRegius Professor of Modern History in the University of Cambridge.\n\n\n1. Evolution, and the principles associated with the Darwinian theory,\ncould not fail to exert a considerable influence on the studies\nconnected with the history of civilised man. The speculations which\nare known as \"philosophy of history,\" as well as the sciences of\nanthropology, ethnography, and sociology (sciences which though they\nstand on their own feet are for the historian auxiliary), have been\ndeeply affected by these principles. Historiographers, indeed, have\nwith few exceptions made little attempt to apply them; but the growth\nof historical study in the nineteenth century has been determined and\ncharacterised by the same general principle which has underlain the\nsimultaneous developments of the study of nature, namely the GENETIC\nidea. The \"historical\" conception of nature, which has produced the\nhistory of the solar system, the story of the earth, the genealogies of\ntelluric organisms, and has revolutionised natural science, belongs\nto the same order of thought as the conception of human history as\na continuous, genetic, causal process--a conception which has\nrevolutionised historical research and made it scientific. Before\nproceeding to consider the application of evolutional principles, it\nwill be pertinent to notice the rise of this new view.\n\n2. With the Greeks and Romans history had been either a descriptive\nrecord or had been written in practical interests. The most eminent of\nthe ancient historians were pragmatical; that is, they regarded history\nas an instructress in statesmanship, or in the art of war, or in morals.\nTheir records reached back such a short way, their experience was so\nbrief, that they never attained to the conception of continuous process,\nor realised the significance of time; and they never viewed the history\nof human societies as a phenomenon to be investigated for its own sake.\nIn the middle ages there was still less chance of the emergence of the\nideas of progress and development. Such notions were excluded by the\nfundamental doctrines of the dominant religion which bounded and bound\nmen's minds. As the course of history was held to be determined from\nhour to hour by the arbitrary will of an extra-cosmic person, there\ncould be no self-contained causal development, only a dispensation\nimposed from without. And as it was believed that the world was within\nno great distance from the end of this dispensation, there was no motive\nto take much interest in understanding the temporal, which was to be\nonly temporary.\n\nThe intellectual movements of the fifteenth and sixteenth centuries\nprepared the way for a new conception, but it did not emerge\nimmediately. The historians of the Renaissance period simply reverted to\nthe ancient pragmatical view. For Machiavelli, exactly as for Thucydides\nand Polybius, the use of studying history was instruction in the art of\npolitics. The Renaissance itself was the appearance of a new culture,\ndifferent from anything that had gone before; but at the time men were\nnot conscious of this; they saw clearly that the traditions of classical\nantiquity had been lost for a long period, and they were seeking to\nrevive them, but otherwise they did not perceive that the world had\nmoved, and that their own spirit, culture, and conditions were\nentirely unlike those of the thirteenth century. It was hardly till the\nseventeenth century that the presence of a new age, as different from\nthe middle ages as from the ages of Greece and Rome, was fully realised.\nIt was then that the triple division of ancient, medieval, and modern\nwas first applied to the history of western civilisation. Whatever\nobjections may be urged against this division, which has now become\nalmost a category of thought, it marks a most significant advance in\nman's view of his own past. He has become conscious of the immense\nchanges in civilisation which have come about slowly in the course of\ntime, and history confronts him with a new aspect. He has to explain how\nthose changes have been produced, how the transformations were effected.\nThe appearance of this problem was almost simultaneous with the rise\nof rationalism, and the great historians and thinkers of the eighteenth\ncentury, such as Montesquieu, Voltaire, Gibbon, attempted to explain\nthe movement of civilisation by purely natural causes. These brilliant\nwriters prepared the way for the genetic history of the following\ncentury. But in the spirit of the Aufklarung, that eighteenth-century\nEnlightenment to which they belonged, they were concerned to judge all\nphenomena before the tribunal of reason; and the apotheosis of \"reason\"\ntended to foster a certain superior a priori attitude, which was\nnot favourable to objective treatment and was incompatible with\na \"historical sense.\" Moreover the traditions of pragmatical\nhistoriography had by no means disappeared.\n\n3. In the first quarter of the nineteenth century the meaning of genetic\nhistory was fully realised. \"Genetic\" perhaps is as good a word as can\nbe found for the conception which in this century was applied to so many\nbranches of knowledge in the spheres both of nature and of mind. It\ndoes not commit us to the doctrine proper of evolution, nor yet to any\nteleological hypothesis such as is implied in \"progress.\" For history\nit meant that the present condition of the human race is simply and\nstrictly the result of a causal series (or set of causal series)--a\ncontinuous succession of changes, where each state arises causally out\nof the preceding; and that the business of historians is to trace this\ngenetic process, to explain each change, and ultimately to grasp the\ncomplete development of the life of humanity. Three influential writers,\nwho appeared at this stage and helped to initiate a new period\nof research, may specially be mentioned. Ranke in 1824 definitely\nrepudiated the pragmatical view which ascribes to history the duties\nof an instructress, and with no less decision renounced the function,\nassumed by the historians of the Aufklarung, to judge the past; it\nwas his business, he said, merely to show how things really happened.\nNiebuhr was already working in the same spirit and did more than any\nother writer to establish the principle that historical transactions\nmust be related to the ideas and conditions of their age. Savigny about\nthe same time founded the \"historical school\" of law. He sought to show\nthat law was not the creation of an enlightened will, but grew out of\ncustom and was developed by a series of adaptations and rejections, thus\napplying the conception of evolution. He helped to diffuse the notion\nthat all the institutions of a society or a notion are as closely\ninterconnected as the parts of a living organism.\n\n4. The conception of the history of man as a causal development meant\nthe elevation of historical inquiry to the dignity of a science. Just\nas the study of bees cannot become scientific so long as the student's\ninterest in them is only to procure honey or to derive moral lessons\nfrom the labours of \"the little busy bee,\" so the history of human\nsocieties cannot become the object of pure scientific investigation so\nlong as man estimates its value in pragmatical scales. Nor can it become\na science until it is conceived as lying entirely within a sphere\nin which the law of cause and effect has unreserved and unrestricted\ndominion. On the other hand, once history is envisaged as a causal\nprocess, which contains within itself the explanation of the development\nof man from his primitive state to the point which he has reached, such\na process necessarily becomes the object of scientific investigation and\nthe interest in it is scientific curiosity.\n\nAt the same time, the instruments were sharpened and refined. Here Wolf,\na philologist with historical instinct, was a pioneer. His \"Prolegomena\"\nto Homer (1795) announced new modes of attack. Historical investigation\nwas soon transformed by the elaboration of new methods.\n\n5. \"Progress\" involves a judgment of value, which is not involved in the\nconception of history as a genetic process. It is also an idea distinct\nfrom that of evolution. Nevertheless it is closely related to the ideas\nwhich revolutionised history at the beginning of the last century;\nit swam into men's ken simultaneously; and it helped effectively to\nestablish the notion of history as a continuous process and to emphasise\nthe significance of time. Passing over earlier anticipations, I may\npoint to a \"Discours\" of Turgot (1750), where history is presented as a\nprocess in which \"the total mass of the human race\" \"marches continually\nthough sometimes slowly to an ever increasing perfection.\" That is\na clear statement of the conception which Turgot's friend Condorcet\nelaborated in the famous work, published in 1795, \"Esquisse d'un tableau\nhistorique des progres de l'esprit humain\". This work first treated with\nexplicit fulness the idea to which a leading role was to fall in the\nideology of the nineteenth century. Condorcet's book reflects the\ntriumphs of the Tiers etat, whose growing importance had also inspired\nTurgot; it was the political changes in the eighteenth century which led\nto the doctrine, emphatically formulated by Condorcet, that the masses\nare the most important element in the historical process. I dwell\non this because, though Condorcet had no idea of evolution, the\npre-dominant importance of the masses was the assumption which made\nit possible to apply evolutional principles to history. And it enabled\nCondorcet himself to maintain that the history of civilisation, a\nprogress still far from being complete, was a development conditioned by\ngeneral laws.\n\n6. The assimilation of society to an organism, which was a governing\nnotion in the school of Savigny, and the conception of progress,\ncombined to produce the idea of an organic development, in which the\nhistorian has to determine the central principle or leading character.\nThis is illustrated by the apotheosis of democracy in Tocqueville's\n\"Democratie en Amerique\", where the theory is maintained that \"the\ngradual and progressive development of equality is at once the past and\nthe future of the history of men.\" The same two principles are combined\nin the doctrine of Spencer (who held that society is an organism,\nthough he also contemplated its being what he calls a \"super-organic\naggregate\") (A society presents suggestive analogies with an organism,\nbut it certainly is not an organism, and sociologists who draw\ninferences from the assumption of its organic nature must fall into\nerror. A vital organism and a society are radically distinguished by the\nfact that the individual components of the former, namely the cells,\nare morphologically as well as functionally differentiated, whereas the\nindividuals which compose a society are morphologically homogeneous and\nonly functionally differentiated. The resemblances and the differences\nare worked out in E. de Majewski's striking book \"La Science de la\nCivilisation\", Paris, 1908.), that social evolution is a progressive\nchange from militarism to industrialism.\n\n7. the idea of development assumed another form in the speculations of\nGerman idealism. Hegel conceived the successive periods of history as\ncorresponding to the ascending phases or ideas in the self-evolution\nof his Absolute Being. His \"Lectures on the Philosophy of History\" were\npublished in 1837 after his death. His philosophy had a considerable\neffect, direct and indirect, on the treatment of history by historians,\nand although he was superficial and unscientific himself in dealing with\nhistorical phenomena, he contributed much towards making the idea of\nhistorical development familiar. Ranke was influenced, if not by Hegel\nhimself, at least by the Idealistic philosophies of which Hegel's was\nthe greatest. He was inclined to conceive the stages in the process of\nhistory as marked by incarnations, as it were, of ideas, and sometimes\nspeaks as if the ideas were independent forces, with hands and feet. But\nwhile Hegel determined his ideas by a priori logic, Ranke obtained his\nby induction--by a strict investigation of the phenomena; so that he\nwas scientific in his method and work, and was influenced by Hegelian\nprepossessions only in the kind of significance which he was disposed\nto ascribe to his results. It is to be noted that the theory of Hegel\nimplied a judgment of value; the movement was a progress towards\nperfection.\n\n8. In France, Comte approached the subject from a different side, and\nexercised, outside Germany, a far wider influence than Hegel. The 4th\nvolume of his \"Cours de philosophie positive\", which appeared in 1839,\ncreated sociology and treated history as a part of this new science,\nnamely as \"social dynamics.\" Comte sought the key for unfolding\nhistorical development, in what he called the social-psychological point\nof view, and he worked out the two ideas which had been enunciated by\nCondorcet: that the historian's attention should be directed not, as\nhitherto, principally to eminent individuals, but to the collective\nbehaviour of the masses, as being the most important element in the\nprocess; and that, as in nature, so in history, there are general laws,\nnecessary and constant, which condition the development. The two points\nare intimately connected, for it is only when the masses are moved into\nthe foreground that regularity, uniformity, and law can be conceived\nas applicable. To determine the social-psychological laws which\nhave controlled the development is, according to Comte, the task of\nsociologists and historians.\n\n9. The hypothesis of general laws operative in history was carried\nfurther in a book which appeared in England twenty years later and\nexercised an influence in Europe far beyond its intrinsic merit,\nBuckle's \"History of Civilisation in England\" (1857-61). Buckle owed\nmuch to Comte, and followed him, or rather outdid him, in regarding\nintellect as the most important factor conditioning the upward\ndevelopment of man, so that progress, according to him, consisted in the\nvictory of the intellectual over the moral laws.\n\n10. The tendency of Comte and Buckle to assimilate history to the\nsciences of nature by reducing it to general \"laws,\" derived stimulus\nand plausibility from the vista offered by the study of statistics, in\nwhich the Belgian Quetelet, whose book \"Sur l'homme\" appeared in 1835,\ndiscerned endless possibilities. The astonishing uniformities which\nstatistical inquiry disclosed led to the belief that it was only a\nquestion of collecting a sufficient amount of statistical material, to\nenable us to predict how a given social group will act in a particular\ncase. Bourdeau, a disciple of this school, looks forward to the time\nwhen historical science will become entirely quantitative. The actions\nof prominent individuals, which are generally considered to have altered\nor determined the course of things, are obviously not amenable to\nstatistical computation or explicable by general laws. Thinkers like\nBuckle sought to minimise their importance or explain them away.\n\n11. These indications may suffice to show that the new efforts to\ninterpret history which marked the first half of the nineteenth century\nwere governed by conceptions closely related to those which were current\nin the field of natural science and which resulted in the doctrine of\nevolution. The genetic principle, progressive development, general\nlaws, the significance of time, the conception of society as an organic\naggregate, the metaphysical theory of history as the self-evolution of\nspirit,--all these ideas show that historical inquiry had been advancing\nindependently on somewhat parallel lines to the sciences of nature. It\nwas necessary to bring this out in order to appreciate the influence of\nDarwinism.\n\n12. In the course of the dozen years which elapsed between the\nappearances of \"The Origin of Species\" (observe that the first volume of\nBuckle's work was published just two years before) and of \"The Descent\nof Man\" (1871), the hypothesis of Lamarck that man is the co-descendant\nwith other species of some lower extinct form was admitted to have been\nraised to the rank of an established fact by most thinkers whose brains\nwere not working under the constraint of theological authority.\n\nOne important effect of the discovery of this fact (I am not speaking\nnow of the Darwinian explanation) was to assign to history a definite\nplace in the coordinated whole of knowledge, and relate it more closely\nto other sciences. It had indeed a defined logical place in systems\nsuch as Hegel's and Comte's; but Darwinism certified its standing\nconvincingly and without more ado. The prevailing doctrine that man\nwas created ex abrupto had placed history in an isolated position,\ndisconnected with the sciences of nature. Anthropology, which deals with\nthe animal anthropos, now comes into line with zoology, and brings it\ninto relation with history. (It is to be observed that history is not\nonly different in scope but) not coextensive with anthropology IN TIME.\nFor it deals only with the development of man in societies, whereas\nanthropology includes in its definition the proto-anthropic period\nwhen anthropos was still non-social, whether he lived in herds like\nthe chimpanzee, or alone like the male ourang-outang. (It has been well\nshown by Majewski that congregations--herds, flocks, packs, etc.--of\nanimals are not SOCIETIES; the characteristic of a society is\ndifferentiation of function. Bee hives, ant hills, may be called\nquasi-societies; but in their case the classes which perform distinct\nfunctions are morphologically different.) Man's condition at the present\nday is the result of a series of transformations, going back to the most\nprimitive phase of society, which is the ideal (unattainable) beginning\nof history. But that beginning had emerged without any breach of\ncontinuity from a development which carries us back to a quadrimane\nancestor, still further back (according to Darwin's conjecture) to a\nmarine animal of the ascidian type, and then through remoter periods to\nthe lowest form of organism. It is essential in this theory that though\nlinks have been lost there was no break in the gradual development;\nand this conception of a continuous progress in the evolution of\nlife, resulting in the appearance of uncivilised Anthropos, helped to\nreinforce, and increase a belief in, the conception of the history of\ncivilised Anthropos as itself also a continuous progressive development.\n\n13. Thus the diffusion of the Darwinian theory of the origin of man,\nby emphasising the idea of continuity and breaking down the barriers\nbetween the human and animal kingdoms, has had an important effect in\nestablishing the position of history among the sciences which deal with\ntelluric development. The perspective of history is merged in a larger\nperspective of development. As one of the objects of biology is to find\nthe exact steps in the genealogy of man from the lowest organic form,\nso the scope of history is to determine the stages in the unique\ncausal series from the most rudimentary to the present state of human\ncivilisation.\n\nIt is to be observed that the interest in historical research implied\nby this conception need not be that of Comte. In the Positive Philosophy\nhistory is part of sociology; the interest in it is to discover the\nsociological laws. In the view of which I have just spoken, history\nis permitted to be an end in itself; the reconstruction of the\ngenetic process is an independent interest. For the purpose of the\nreconstruction, sociology, as well as physical geography, biology,\npsychology, is necessary; the sociologist and the historian play\ninto each other's hands; but the object of the former is to establish\ngeneralisations; the aim of the latter is to trace in detail a singular\ncausal sequence.\n\n14. The success of the evolutional theory helped to discredit\nthe assumption or at least the invocation of transcendent causes.\nPhilosophically of course it is compatible with theism, but historians\nhave for the most part desisted from invoking the naive conception of a\n\"god in history\" to explain historical movements. A historian may be a\ntheist; but, so far as his work is concerned, this particular belief is\notiose. Otherwise indeed (as was remarked above) history could not be a\nscience; for with a deus ex machina who can be brought on the stage to\nsolve difficulties scientific treatment is a farce. The transcendent\nelement had appeared in a more subtle form through the influence of\nGerman philosophy. I noticed how Ranke is prone to refer to ideas as\nif they were transcendent existences manifesting themselves in the\nsuccessive movements of history. It is intelligible to speak of certain\nideas as controlling, in a given period,--for instance, the idea of\nnationality; but from the scientific point of view, such ideas have\nno existence outside the minds of individuals and are purely psychical\nforces; and a historical \"idea,\" if it does not exist in this form, is\nmerely a way of expressing a synthesis of the historian himself.\n\n15. From the more general influence of Darwinism on the place of history\nin the system of human knowledge, we may turn to the influence of the\nprinciples and methods by which Darwin explained development. It had\nbeen recognised even by ancient writers (such as Aristotle and\nPolybius) that physical circumstances (geography, climate) were factors\nconditioning the character and history of a race or society. In the\nsixteenth century Bodin emphasised these factors, and many subsequent\nwriters took them into account. The investigations of Darwin, which\nbrought them into the foreground, naturally promoted attempts to\ndiscover in them the chief key to the growth of civilisation. Comte had\nexpressly denounced the notion that the biological methods of Lamarck\ncould be applied to social man. Buckle had taken account of natural\ninfluences, but had relegated them to a secondary plane, compared with\npsychological factors. But the Darwinian theory made it tempting to\nexplain the development of civilisation in terms of \"adaptation to\nenvironment,\" \"struggle for existence,\" \"natural selection,\" \"survival\nof the fittest,\" etc. (Recently O. Seeck has applied these principles to\nthe decline of Graeco-Roman civilisation in his \"Untergang der antiken\nWelt\", 2 volumes, Berlin, 1895, 1901.)\n\nThe operation of these principles cannot be denied. Man is still an\nanimal, subject to zoological as well as mechanical laws. The dark\ninfluence of heredity continues to be effective; and psychical\ndevelopment had begun in lower organic forms,--perhaps with life itself.\nThe organic and the social struggles for existence are manifestations of\nthe same principle. Environment and climatic influence must be called in\nto explain not only the differentiation of the great racial sections of\nhumanity, but also the varieties within these sub-species and, it may\nbe, the assimilation of distinct varieties. Ritter's \"Anthropogeography\"\nhas opened a useful line of research. But on the other hand, it is urged\nthat, in explaining the course of history, these principles do not take\nus very far, and that it is chiefly for the primitive ultra-prehistoric\nperiod that they can account for human development. It may be said\nthat, so far as concerns the actions and movements of men which are\nthe subject of recorded history, physical environment has ceased to act\nmechanically, and in order to affect their actions must affect their\nwills first; and that this psychical character of the causal relations\nsubstantially alters the problem. The development of human societies, it\nmay be argued, derives a completely new character from the dominance\nof the conscious psychical element, creating as it does new conditions\n(inventions, social institutions, etc.) which limit and counteract the\noperation of natural selection, and control and modify the influence of\nphysical environment. Most thinkers agree now that the chief clews to\nthe growth of civilisation must be sought in the psychological\nsphere. Imitation, for instance, is a principle which is probably\nmore significant for the explanation of human development than natural\nselection. Darwin himself was conscious that his principles had only\na very restricted application in this sphere, as is evident from his\ncautious and tentative remarks in the 5th chapter of his \"Descent of\nMan\". He applied natural selection to the growth of the intellectual\nfaculties and of the fundamental social instincts, and also to the\ndifferentiation of the great races or \"sub-species\" (Caucasian, African,\netc.) which differ in anthropological character. (Darwinian formulae may\nbe suggestive by way of analogy. For instance, it is characteristic of\nsocial advance that a multitude of inventions, schemes and plans are\nframed which are never carried out, similar to, or designed for the same\nend as, an invention or plan which is actually adopted because it has\nchanced to suit better the particular conditions of the hour (just as\nthe works accomplished by an individual statesman, artist or savant are\nusually only a residue of the numerous projects conceived by his brain).\nThis process in which so much abortive production occurs is analogous to\nelimination by natural selection.)\n\n16. But if it is admitted that the governing factors which concern\nthe student of social development are of the psychical order, the\npreliminary success of natural science in explaining organic evolution\nby general principles encouraged sociologists to hope that social\nevolution could be explained on general principles also. The idea of\nCondorcet, Buckle, and others, that history could be assimilated to\nthe natural sciences was powerfully reinforced, and the notion that the\nactual historical process, and every social movement involved in it, can\nbe accounted for by sociological generalisations, so-called \"laws,\" is\nstill entertained by many, in one form or another. Dissentients from\nthis view do not deny that the generalisations at which the sociologist\narrives by the comparative method, by the analysis of social factors,\nand by psychological deduction may be an aid to the historian; but they\ndeny that such uniformities are laws or contain an explanation of the\nphenomena. They can point to the element of chance coincidence. This\nelement must have played a part in the events of organic evolution, but\nit has probably in a larger measure helped to determine events in social\nevolution. The collision of two unconnected sequences may be fraught\nwith great results. The sudden death of a leader or a marriage without\nissue, to take simple cases, has again and again led to permanent\npolitical consequences. More emphasis is laid on the decisive actions\nof individuals, which cannot be reduced under generalisations and which\ndeflect the course of events. If the significance of the individual will\nhad been exaggerated to the neglect of the collective activity of the\nsocial aggregate before Condorcet, his doctrine tended to eliminate as\nunimportant the roles of prominent men, and by means of this elimination\nit was possible to found sociology. But it may be urged that it is\npatent on the face of history that its course has constantly been\nshaped and modified by the wills of individuals (We can ignore here the\nmetaphysical question of freewill and determinism. For the character of\nthe individual's brain depends in any case on ante-natal accidents\nand coincidences, and so it may be said that the role of individuals\nultimately depends on chance,--the accidental coincidence of independent\nsequences.), which are by no means always the expression of the\ncollective will; and that the appearance of such personalities at the\ngiven moments is not a necessary outcome of the conditions and cannot be\ndeduced. Nor is there any proof that, if such and such an individual\nhad not been born, some one else would have arisen to do what he did. In\nsome cases there is no reason to think that what happened need ever have\ncome to pass. In other cases, it seems evident that the actual change\nwas inevitable, but in default of the man who initiated and guided it,\nit might have been postponed, and, postponed or not, might have borne\na different cachet. I may illustrate by an instance which has just come\nunder my notice. Modern painting was founded by Giotto, and the Italian\nexpedition of Charles VIII, near the close of the sixteenth century,\nintroduced into France the fashion of imitating Italian painters.\nBut for Giotto and Charles VIII, French painting might have been very\ndifferent. It may be said that \"if Giotto had not appeared, some other\ngreat initiator would have played a role analogous to his, and that\nwithout Charles VIII there would have been the commerce with Italy,\nwhich in the long run would have sufficed to place France in relation\nwith Italian artists. But the equivalent of Giotto might have been\ndeferred for a century and probably would have been different; and\ncommercial relations would have required ages to produce the rayonnement\nimitatif of Italian art in France, which the expedition of the royal\nadventurer provoked in a few years.\" (I have taken this example from G.\nTarde's \"La logique sociale\" 2 (page 403), Paris, 1904, where it is used\nfor quite a different purpose.) Instances furnished by political history\nare simply endless. Can we conjecture how events would have moved if the\nson of Philip of Macedon had been an incompetent? The aggressive action\nof Prussia which astonished Europe in 1740 determined the subsequent\nhistory of Germany; but that action was anything but inevitable; it\ndepended entirely on the personality of Frederick the Great.\n\nHence it may be argued that the action of individual wills is a\ndetermining and disturbing factor, too significant and effective to\nallow history to be grasped by sociological formulae. The types and\ngeneral forms of development which the sociologist attempts to disengage\ncan only assist the historian in understanding the actual course\nof events. It is in the special domains of economic history and\nCulturgeschichte which have come to the front in modern times that\ngeneralisation is most fruitful, but even in these it may be contended\nthat it furnishes only partial explanations.\n\n17. The truth is that Darwinism itself offers the best illustration of\nthe insufficiency of general laws to account for historical\ndevelopment. The part played by coincidence, and the part played\nby individuals--limited by, and related to, general social\nconditions--render it impossible to deduce the course of the past\nhistory of man or to predict the future. But it is just the same with\norganic development. Darwin (or any other zoologist) could not deduce\nthe actual course of evolution from general principles. Given an\norganism and its environment, he could not show that it must evolve into\na more complex organism of a definite pre-determined type; knowing\nwhat it has evolved into, he could attempt to discover and assign the\ndetermining causes. General principles do not account for a particular\nsequence; they embody necessary conditions; but there is a chapter of\naccidents too. It is the same in the case of history.\n\n18. Among the evolutional attempts to subsume the course of history\nunder general syntheses, perhaps the most important is that of\nLamprecht, whose \"kulturhistorische Methode,\" which he has deduced from\nand applied to German history, exhibits the (indirect) influence of the\nComtist school. It is based upon psychology, which, in his view, holds\namong the sciences of mind (Geisteswissenschaften) the same place (that\nof a Grundwissenschaft) which mechanics holds among the sciences of\nnature. History, by the same comparison, corresponds to biology, and,\naccording to him, it can only become scientific if it is reduced to\ngeneral concepts (Begriffe). Historical movements and events are of\na psychical character, and Lamprecht conceives a given phase of\ncivilisation as \"a collective psychical condition (seelischer\nGesamtzustand)\" controlling the period, \"a diapason which penetrates\nall psychical phenomena and thereby all historical events of the time.\"\n(\"Die kulturhistorische Methode\", Berlin, 1900, page 26.) He has worked\nout a series of such phases, \"ages of changing psychical diapason,\" in\nhis \"Deutsche Geschichte\" with the aim of showing that all the feelings\nand actions of each age can be explained by the diapason; and has\nattempted to prove that these diapasons are exhibited in other social\ndevelopments, and are consequently not singular but typical. He\nmaintains further that these ages succeed each other in a definite\norder; the principle being that the collective psychical development\nbegins with the homogeneity of all the individual members of a society\nand, through heightened psychical activity, advances in the form of a\ncontinually increasing differentiation of the individuals (this is akin\nto the Spencerian formula). This process, evolving psychical freedom\nfrom psychical constraint, exhibits a series of psychical phenomena\nwhich define successive periods of civilisation. The process depends on\ntwo simple principles, that no idea can disappear without leaving behind\nit an effect or influence, and that all psychical life, whether in\na person or a society, means change, the acquisition of new mental\ncontents. It follows that the new have to come to terms with the old,\nand this leads to a synthesis which determines the character of a new\nage. Hence the ages of civilisation are defined as the \"highest\nconcepts for subsuming without exception all psychical phenomena of\nthe development of human societies, that is, of all historical events.\"\n(Ibid. pages 28, 29.) Lamprecht deduces the idea of a special historical\nscience, which might be called \"historical ethnology,\" dealing with the\nages of civilisation, and bearing the same relation to (descriptive or\nnarrative) history as ethnology to ethnography. Such a science obviously\ncorresponds to Comte's social dynamics, and the comparative method,\non which Comte laid so much emphasis, is the principal instrument of\nLamprecht.\n\n19. I have dwelt on the fundamental ideas of Lamprecht, because they are\nnot yet widely known in England, and because his system is the ablest\nproduct of the sociological school of historians. It carries the\nmore weight as its author himself is a historical specialist, and his\nhistorical syntheses deserve the most careful consideration. But there\nis much in the process of development which on such assumptions is\nnot explained, especially the initiative of individuals. Historical\ndevelopment does not proceed in a right line, without the choice of\ndiverging. Again and again, several roads are open to it, of which it\nchooses one--why? On Lamprecht's method, we may be able to assign the\nconditions which limit the psychical activity of men at a particular\nstage of evolution, but within those limits the individual has so many\noptions, such a wide room for moving, that the definition of those\nconditions, the \"psychical diapasons,\" is only part of the explanation\nof the particular development. The heel of Achilles in all historical\nspeculations of this class has been the role of the individual.\n\nThe increasing prominence of economic history has tended to encourage\nthe view that history can be explained in terms of general concepts or\ntypes. Marx and his school based their theory of human development on\nthe conditions of production, by which, according to them, all social\nmovements and historical changes are entirely controlled. The leading\npart which economic factors play in Lamprecht's system is significant,\nillustrating the fact that economic changes admit most readily this\nkind of treatment, because they have been less subject to direction or\ninterference by individual pioneers.\n\nPerhaps it may be thought that the conception of SOCIAL ENVIRONMENT\n(essentially psychical), on which Lamprecht's \"psychical diapasons\"\ndepend, is the most valuable and fertile conception that the historian\nowes to the suggestion of the science of biology--the conception of\nall particular historical actions and movements as (1) related to and\nconditioned by the social environment, and (2) gradually bringing about\na transformation of that environment. But no given transformation can be\nproved to be necessary (pre-determined). And types of development do not\nrepresent laws; their meaning and value lie in the help they may give\nto the historian, in investigating a certain period of civilisation,\nto enable him to discover the interrelations among the diverse features\nwhich it presents. They are, as some one has said, an instrument of\nheuretic method.\n\n20. The men engaged in special historical researches--which have been\npursued unremittingly for a century past, according to scientific\nmethods of investigating evidence (initiated by Wolf, Niebuhr,\nRanke)--have for the most part worked on the assumptions of genetic\nhistory or at least followed in the footsteps of those who fully grasped\nthe genetic point of view. But their aim has been to collect and sift\nevidence, and determine particular facts; comparatively few have given\nserious thought to the lines of research and the speculations which\nhave been considered in this paper. They have been reasonably shy\nof compromising their work by applying theories which are still much\ndebated and immature. But historiography cannot permanently evade the\nquestions raised by these theories. One may venture to say that no\nhistorical change or transformation will be fully understood until it is\nexplained how social environment acted on the individual components of\nthe society (both immediately and by heredity), and how the individuals\nreacted upon their environment. The problem is psychical, but it is\nanalogous to the main problem of the biologist.\n\n\n\n\nXXVIII. THE GENESIS OF DOUBLE STARS. By Sir George Darwin, K.C.B.,\nF.R.S.\n\nPlumian Professor of Astronomy and Experimental Philosophy in the\nUniversity of Cambridge.\n\nIn ordinary speech a system of any sort is said to be stable when it\ncannot be upset easily, but the meaning attached to the word is usually\nsomewhat vague. It is hardly surprising that this should be the case,\nwhen it is only within the last thirty years, and principally through\nthe investigations of M. Poincare, that the conception of stability has,\neven for physicists, assumed a definiteness and clearness in which it\nwas previously lacking. The laws which govern stability hold good in\nregions of the greatest diversity; they apply to the motion of planets\nround the sun, to the internal arrangement of those minute corpuscles of\nwhich each chemical atom is constructed, and to the forms of celestial\nbodies. In the present essay I shall attempt to consider the laws of\nstability as relating to the last case, and shall discuss the succession\nof shapes which may be assumed by celestial bodies in the course of\ntheir evolution. I believe further that homologous conceptions are\napplicable in the consideration of the transmutations of the various\nforms of animal and of vegetable life and in other regions of thought.\nEven if some of my readers should think that what I shall say on this\nhead is fanciful, yet at least the exposition will serve to illustrate\nthe meaning to be attached to the laws of stability in the physical\nuniverse.\n\nI propose, therefore, to begin this essay by a sketch of the principles\nof stability as they are now formulated by physicists.\n\nI.\n\nIf a slight impulse be imparted to a system in equilibrium one of two\nconsequences must ensue; either small oscillations of the system will\nbe started, or the disturbance will increase without limit and the\narrangement of the system will be completely changed. Thus a stick may\nbe in equilibrium either when it hangs from a peg or when it is balanced\non its point. If in the first case the stick is touched it will swing to\nand fro, but in the second case it will topple over. The first position\nis a stable one, the second is unstable. But this case is too simple to\nillustrate all that is implied by stability, and we must consider cases\nof stable and of unstable motion. Imagine a satellite and its planet,\nand consider each of them to be of indefinitely small size, in fact\nparticles; then the satellite revolves round its planet in an ellipse. A\nsmall disturbance imparted to the satellite will only change the ellipse\nto a small amount, and so the motion is said to be stable. If, on the\nother hand, the disturbance were to make the satellite depart from its\ninitial elliptic orbit in ever widening circuits, the motion would be\nunstable. This case affords an example of stable motion, but I have\nadduced it principally with the object of illustrating another point\nnot immediately connected with stability, but important to a proper\ncomprehension of the theory of stability.\n\nThe motion of a satellite about its planet is one of revolution or\nrotation. When the satellite moves in an ellipse of any given degree\nof eccentricity, there is a certain amount of rotation in the system,\ntechnically called rotational momentum, and it is always the same at\nevery part of the orbit. (Moment of momentum or rotational momentum\nis measured by the momentum of the satellite multiplied by the\nperpendicular from the planet on to the direction of the path of the\nsatellite at any instant.)\n\nNow if we consider all the possible elliptic orbits of a satellite about\nits planet which have the same amount of \"rotational momentum,\" we find\nthat the major axis of the ellipse described will be different according\nto the amount of flattening (or the eccentricity) of the ellipse\ndescribed. A figure titled \"A 'family' of elliptic orbits with constant\nrotational momentum\" (Fig. 1) illustrates for a given planet and\nsatellite all such orbits with constant rotational momentum, and with\nall the major axes in the same direction. It will be observed that there\nis a continuous transformation from one orbit to the next, and that the\nwhole forms a consecutive group, called by mathematicians \"a family\"\nof orbits. In this case the rotational momentum is constant and the\nposition of any orbit in the family is determined by the length of the\nmajor axis of the ellipse; the classification is according to the major\naxis, but it might have been made according to anything else which would\ncause the orbit to be exactly determinate.\n\nI shall come later to the classification of all possible forms of ideal\nliquid stars, which have the same amount of rotational momentum, and the\nclassification will then be made according to their densities, but the\nidea of orderly arrangement in a \"family\" is just the same.\n\nWe thus arrive at the conception of a definite type of motion, with\na constant amount of rotational momentum, and a classification of all\nmembers of the family, formed by all possible motions of that type,\naccording to the value of some measurable quantity (this will hereafter\nbe density) which determines the motion exactly. In the particular case\nof the elliptic motion used for illustration the motion was stable,\nbut other cases of motion might be adduced in which the motion would\nbe unstable, and it would be found that classification in a family and\nspecification by some measurable quantity would be equally applicable.\n\nA complex mechanical system may be capable of motion in several distinct\nmodes or types, and the motions corresponding to each such type may\nbe arranged as before in families. For the sake of simplicity I will\nsuppose that only two types are possible, so that there will only be two\nfamilies; and the rotational momentum is to be constant. The two types\nof motion will have certain features in common which we denote in a sort\nof shorthand by the letter A. Similarly the two types may be described\nas A + a and A + b, so that a and b denote the specific differences\nwhich discriminate the families from one another. Now following in\nimagination the family of the type A + a, let us begin with the case\nwhere the specific difference a is well marked. As we cast our eyes\nalong the series forming the family, we find the difference a becoming\nless conspicuous. It gradually dwindles until it disappears; beyond this\npoint it either becomes reversed, or else the type has ceased to be\na possible one. In our shorthand we have started with A + a, and have\nwatched the characteristic a dwindling to zero. When it vanishes we have\nreached a type which may be specified as A; beyond this point the type\nwould be A - a or would be impossible.\n\nFollowing the A + b type in the same way, b is at first well marked, it\ndwindles to zero, and finally may become negative. Hence in shorthand\nthis second family may be described as A + b,... A,... A - b.\n\nIn each family there is one single member which is indistinguishable\nfrom a member of the other family; it is called by Poincare a form of\nbifurcation. It is this conception of a form of bifurcation which forms\nthe important consideration in problems dealing with the forms of liquid\nor gaseous bodies in rotation.\n\nBut to return to the general question,--thus far the stability of these\nfamilies has not been considered, and it is the stability which renders\nthis way of looking at the matter so valuable. It may be proved that if\nbefore the point of bifurcation the type A + a was stable, then A + b\nmust have been unstable. Further as a and b each diminish A + a becomes\nless pronouncedly stable, and A + b less unstable. On reaching the point\nof bifurcation A + a has just ceased to be stable, or what amounts to\nthe same thing is just becoming unstable, and the converse is true\nof the A + b family. After passing the point of bifurcation A + a has\nbecome definitely unstable and A + b has become stable. Hence the point\nof bifurcation is also a point of \"exchange of stabilities between the\ntwo types.\" (In order not to complicate unnecessarily this explanation\nof a general principle I have not stated fully all the cases that may\noccur. Thus: firstly, after bifurcation A + a may be an impossible type\nand A + a will then stop at this point; or secondly, A + b may have been\nan impossible type before bifurcation, and will only begin to be a real\none after it; or thirdly, both A + a and A + b may be impossible after\nthe point of bifurcation, in which case they coalesce and disappear.\nThis last case shows that types arise and disappear in pairs, and that\non appearance or before disappearance one must be stable and the other\nunstable.)\n\nIn nature it is of course only the stable types of motion which can\npersist for more than a short time. Thus the task of the physical\nevolutionist is to determine the forms of bifurcation, at which he must,\nas it were, change carriages in the evolutionary journey so as always\nto follow the stable route. He must besides be able to indicate\nsome natural process which shall correspond in effect to the ideal\narrangement of the several types of motion in families with gradually\nchanging specific differences. Although, as we shall see hereafter, it\nmay frequently or even generally be impossible to specify with exactness\nthe forms of bifurcation in the process of evolution, yet the conception\nis one of fundamental importance.\n\nThe ideas involved in this sketch are no doubt somewhat recondite, but I\nhope to render them clearer to the non-mathematical reader by homologous\nconsiderations in other fields of thought (I considered this subject in\nmy Presidential address to the British Association in 1905, \"Report of\nthe 75th Meeting of the British Assoc.\" (S. Africa, 1905), London, 1906,\npage 3. Some reviewers treated my speculations as fanciful, but as I\nbelieve that this was due generally to misapprehension, and as I hold\nthat homologous considerations as to stability and instability are\nreally applicable to evolution of all sorts, I have thought it well to\nreturn to the subject in the present paper.), and I shall pass on thence\nto illustrations which will teach us something of the evolution of\nstellar systems.\n\nStates or governments are organised schemes of action amongst groups of\nmen, and they belong to various types to which generic names, such as\nautocracy, aristocracy or democracy, are somewhat loosely applied. A\ndefinite type of government corresponds to one of our types of\nmotion, and while retaining its type it undergoes a slow change as the\ncivilisation and character of the people change, and as the relationship\nof the nation to other nations changes. In the language used before, the\ngovernment belongs to a family, and as time advances we proceed through\nthe successive members of the family. A government possesses a certain\ndegree of stability--hardly measurable in numbers however--to resist\ndisintegrating influences such as may arise from wars, famines, and\ninternal dissensions. This stability gradually rises to a maximum and\ngradually declines. The degree of stability at any epoch will depend on\nthe fitness of some leading feature of the government to suit the\nslowly altering circumstances, and that feature corresponds to the\ncharacteristic denoted by a in the physical problem. A time at length\narrives when the stability vanishes, and the slightest shock will\noverturn the government. At this stage we have reached the crisis of\na point of bifurcation, and there will then be some circumstance,\napparently quite insignificant and almost unnoticed, which is such as\nto prevent the occurrence of anarchy. This circumstance or condition\nis what we typified as b. Insignificant although it may seem, it has\nstarted the government on a new career of stability by imparting to it\na new type. It grows in importance, the form of government becomes\nobviously different, and its stability increases. Then in its turn this\nnewly acquired stability declines, and we pass on to a new crisis or\nrevolution. There is thus a series of \"points of bifurcation\" in history\nat which the continuity of political history is maintained by means of\nchanges in the type of government. These ideas seem, to me at least, to\ngive a true account of the history of states, and I contend that it is\nno mere fanciful analogy but a true homology, when in both realms of\nthought--the physical and the political--we perceive the existence of\nforms of bifurcation and of exchanges of stability.\n\nFurther than this, I would ask whether the same train of ideas does not\nalso apply to the evolution of animals? A species is well adapted to its\nenvironment when the individual can withstand the shocks of famine or\nthe attacks and competition of other animals; it then possesses a high\ndegree of stability. Most of the casual variations of individuals are\nindifferent, for they do not tell much either for or against success\nin life; they are small oscillations which leave the type unchanged. As\ncircumstances change, the stability of the species may gradually dwindle\nthrough the insufficiency of some definite quality, on which in earlier\ntimes no such insistent demands were made. The individual animals will\nthen tend to fail in the struggle for life, the numbers will dwindle and\nextinction may ensue. But it may be that some new variation, at first of\ninsignificant importance, may just serve to turn the scale. A new\ntype may be formed in which the variation in question is preserved and\naugmented; its stability may increase and in time a new species may be\nproduced.\n\nAt the risk of condemnation as a wanderer beyond my province into the\nregion of biological evolution, I would say that this view accords with\nwhat I understand to be the views of some naturalists, who recognise the\nexistence of critical periods in biological history at which extinction\noccurs or which form the starting-point for the formation of new\nspecies. Ought we not then to expect that long periods will elapse\nduring which a type of animal will remain almost constant, followed by\nother periods, enormously long no doubt as measured in the life of man,\nof acute struggle for existence when the type will change more rapidly?\nThis at least is the view suggested by the theory of stability in\nthe physical universe. (I make no claim to extensive reading on this\nsubject, but refer the reader for example to a paper by Professor A.A.W.\nHubrecht on \"De Vries's theory of Mutations\", \"Popular Science Monthly\",\nJuly 1904, especially to page 213.)\n\nAnd now I propose to apply these ideas of stability to the theory of\nstellar evolution, and finally to illustrate them by certain recent\nobservations of a very remarkable character.\n\nStars and planets are formed of materials which yield to the enormous\nforces called into play by gravity and rotation. This is obviously true\nif they are gaseous or fluid, and even solid matter becomes plastic\nunder sufficiently great stresses. Nothing approaching a complete study\nof the equilibrium of a heterogeneous star has yet been found possible,\nand we are driven to consider only bodies of simpler construction. I\nshall begin therefore by explaining what is known about the shapes which\nmay be assumed by a mass of incompressible liquid of uniform density\nunder the influences of gravity and of rotation. Such a liquid mass may\nbe regarded as an ideal star, which resembles a real star in the fact\nthat it is formed of gravitating and rotating matter, and because its\nshape results from the forces to which it is subject. It is unlike a\nstar in that it possesses the attributes of incompressibility and\nof uniform density. The difference between the real and the ideal is\ndoubtless great, yet the similarity is great enough to allow us\nto extend many of the conclusions as to ideal liquid stars to the\nconditions which must hold good in reality. Thus with the object of\nobtaining some insight into actuality, it is justifiable to discuss an\navowedly ideal problem at some length.\n\nThe attraction of gravity alone tends to make a mass of liquid assume\nthe shape of a sphere, and the effects of rotation, summarised under\nthe name of centrifugal force, are such that the liquid seeks to spread\nitself outwards from the axis of rotation. It is a singular fact that\nit is unnecessary to take any account of the size of the mass of liquid\nunder consideration, because the shape assumed is exactly the same\nwhether the mass be small or large, and this renders the statement of\nresults much easier than would otherwise be the case.\n\nA mass of liquid at rest will obviously assume the shape of a sphere,\nunder the influence of gravitation, and it is a stable form, because\nany oscillation of the liquid which might be started would gradually die\naway under the influence of friction, however small. If now we impart\nto the whole mass of liquid a small speed of rotation about some axis,\nwhich may be called the polar axis, in such a way that there are no\ninternal currents and so that it spins in the same way as if it were\nsolid, the shape will become slightly flattened like an orange. Although\nthe earth and the other planets are not homogeneous they behave in the\nsame way, and are flattened at the poles and protuberant at the equator.\nThis shape may therefore conveniently be described as planetary.\n\nIf the planetary body be slightly deformed the forces of restitution\nare slightly less than they were for the sphere; the shape is stable\nbut somewhat less so than the sphere. We have then a planetary spheroid,\nrotating slowly, slightly flattened at the poles, with a high degree of\nstability, and possessing a certain amount of rotational momentum. Let\nus suppose this ideal liquid star to be somewhere in stellar space far\nremoved from all other bodies; then it is subject to no external forces,\nand any change which ensues must come from inside. Now the amount\nof rotational momentum existing in a system in motion can neither be\ncreated nor destroyed by any internal causes, and therefore, whatever\nhappens, the amount of rotational momentum possessed by the star must\nremain absolutely constant.\n\nA real star radiates heat, and as it cools it shrinks. Let us suppose\nthen that our ideal star also radiates and shrinks, but let the process\nproceed so slowly that any internal currents generated in the liquid\nby the cooling are annulled so quickly by fluid friction as to be\ninsignificant; further let the liquid always remain at any instant\nincompressible and homogeneous. All that we are concerned with is that,\nas time passes, the liquid star shrinks, rotates in one piece as if it\nwere solid, and remains incompressible and homogeneous. The condition is\nof course artificial, but it represents the actual processes of nature\nas well as may be, consistently with the postulated incompressibility\nand homogeneity. (Mathematicians are accustomed to regard the density\nas constant and the rotational momentum as increasing. But the way of\nlooking at the matter, which I have adopted, is easier of comprehension,\nand it comes to the same in the end.)\n\nThe shrinkage of a constant mass of matter involves an increase of its\ndensity, and we have therefore to trace the changes which supervene as\nthe star shrinks, and as the liquid of which it is composed increases\nin density. The shrinkage will, in ordinary parlance, bring the weights\nnearer to the axis of rotation. Hence in order to keep up the rotational\nmomentum, which as we have seen must remain constant, the mass must\nrotate quicker. The greater speed of rotation augments the importance of\ncentrifugal force compared with that of gravity, and as the flattening\nof the planetary spheroid was due to centrifugal force, that flattening\nis increased; in other words the ellipticity of the planetary spheroid\nincreases.\n\nAs the shrinkage and corresponding increase of density proceed, the\nplanetary spheroid becomes more and more elliptic, and the succession\nof forms constitutes a family classified according to the density of\nthe liquid. The specific mark of this family is the flattening or\nellipticity.\n\nNow consider the stability of the system, we have seen that the spheroid\nwith a slow rotation, which forms our starting-point, was slightly less\nstable than the sphere, and as we proceed through the family of ever\nflatter ellipsoids the stability continues to diminish. At length when\nit has assumed the shape shown in a figure titled \"Planetary spheroid\njust becoming unstable\" (Fig. 2.) where the equatorial and polar axes\nare proportional to the numbers 1000 and 583, the stability has just\ndisappeared. According to the general principle explained above this\nis a form of bifurcation, and corresponds to the form denoted A. The\nspecific difference a of this family must be regarded as the excess\nof the ellipticity of this figure above that of all the earlier ones,\nbeginning with the slightly flattened planetary spheroid. Accordingly\nthe specific difference a of the family has gradually diminished from\nthe beginning and vanishes at this stage.\n\nAccording to Poincare's principle the vanishing of the stability serves\nus with notice that we have reached a figure of bifurcation, and\nit becomes necessary to inquire what is the nature of the specific\ndifference of the new family of figures which must be coalescent with\nthe old one at this stage. This difference is found to reside in the\nfact that the equator, which in the planetary family has hitherto been\ncircular in section, tends to become elliptic. Hitherto the rotational\nmomentum has been kept up to its constant value partly by greater speed\nof rotation and partly by a symmetrical bulging of the equator. But now\nwhile the speed of rotation still increases (The mathematician familiar\nwith Jacobi's ellipsoid will find that this is correct, although in\nthe usual mode of exposition, alluded to above in a footnote, the speed\ndiminishes.), the equator tends to bulge outwards at two diametrically\nopposite points and to be flattened midway between these protuberances.\nThe specific difference in the new family, denoted in the general sketch\nby b, is this ellipticity of the equator. If we had traced the planetary\nfigures with circular equators beyond this stage A, we should have found\nthem to have become unstable, and the stability has been shunted off\nalong the A + b family of forms with elliptic equators.\n\nThis new series of figures, generally named after the great\nmathematician Jacobi, is at first only just stable, but as the density\nincreases the stability increases, reaches a maximum and then declines.\nAs this goes on the equator of these Jacobian figures becomes more\nand more elliptic, so that the shape is considerably elongated in a\ndirection at right angles to the axis of rotation.\n\nAt length when the longest axis of the three has become about three\ntimes as long as the shortest (The three axes of the ellipsoid are\nthen proportional to 1000, 432, 343.), the stability of this family of\nfigures vanishes, and we have reached a new form of bifurcation and must\nlook for a new type of figure along which the stable development will\npresumably extend. Two sections of this critical Jacobian figure, which\nis a figure of bifurcation, are shown by the dotted lines in a figure\ntitled \"The 'pear-shaped figure' and the Jocobian figure from which it\nis derived\" (Fig. 3.) comprising two figures, one above the other: the\nupper figure is the equatorial section at right angles to the axis of\nrotation, the lower figure is a section through the axis.\n\nNow Poincare has proved that the new type of figure is to be derived\nfrom the figure of bifurcation by causing one of the ends to be\nprolonged into a snout and by bluntening the other end. The snout forms\na sort of stalk, and between the stalk and the axis of rotation the\nsurface is somewhat flattened. These are the characteristics of a pear,\nand the figure has therefore been called the \"pear-shaped figure of\nequilibrium.\" The firm line shows this new type of figure, whilst, as\nalready explained, the dotted line shows the form of bifurcation\nfrom which it is derived. The specific mark of this new family is the\nprotrusion of the stalk together with the other corresponding smaller\ndifferences. If we denote this difference by c, while A + b denotes the\nJacobian figure of bifurcation from which it is derived, the new family\nmay be called A + b + c, and c is zero initially. According to my\ncalculations this series of figures is stable (M. Liapounoff contends\nthat for constant density the new series of figures, which M. Poincare\ndiscovered, has less rotational momentum than that of the figure of\nbifurcation. If he is correct, the figure of bifurcation is a limit of\nstable figures, and none can exist with stability for greater rotational\nmomentum. My own work seems to indicate that the opposite is true, and,\nnotwithstanding M. Liapounoff's deservedly great authority, I venture\nto state the conclusions in accordance with my own work.), but I do not\nknow at what stage of its development it becomes unstable.\n\nProfessor Jeans has solved a problem which is of interest as throwing\nlight on the future development of the pear-shaped figure, although\nit is of a still more ideal character than the one which has been\ndiscussed. He imagines an INFINITELY long circular cylinder of liquid\nto be in rotation about its central axis. The existence is virtually\npostulated of a demon who is always occupied in keeping the axis of the\ncylinder straight, so that Jeans has only to concern himself with the\nstability of the form of the section of the cylinder, which as I have\nsaid is a circle with the axis of rotation at the centre. He then\nsupposes the liquid forming the cylinder to shrink in diameter, just as\nwe have done, and finds that the speed of rotation must increase so as\nto keep up the constancy of the rotational momentum. The circularity of\nsection is at first stable, but as the shrinkage proceeds the stability\ndiminishes and at length vanishes. This stage in the process is a form\nof bifurcation, and the stability passes over to a new series consisting\nof cylinders which are elliptic in section. The circular cylinders are\nexactly analogous with our planetary spheroids, and the elliptic ones\nwith the Jacobian ellipsoids.\n\nWith further shrinkage the elliptic cylinders become unstable, a new\nform of bifurcation is reached, and the stability passes over to a\nseries of cylinders whose section is pear-shaped. Thus far the analogy\nis complete between our problem and Jeans's, and in consequence of\nthe greater simplicity of the conditions, he is able to carry his\ninvestigation further. He finds that the stalk end of the pear-like\nsection continues to protrude more and more, and the flattening between\nit and the axis of rotation becomes a constriction. Finally the neck\nbreaks and a satellite cylinder is born. Jeans's figure for an advanced\nstage of development is shown in a figure titled \"Section of a rotating\ncylinder of liquid\" (Fig. 4.), but his calculations do not enable him\nactually to draw the state of affairs after the rupture of the neck.\n\nThere are certain difficulties in admitting the exact parallelism\nbetween this problem and ours, and thus the final development of our\npear-shaped figure and the end of its stability in a form of bifurcation\nremain hidden from our view, but the successive changes as far as they\nhave been definitely traced are very suggestive in the study of stellar\nevolution.\n\nAttempts have been made to attack this problem from the other end. If\nwe begin with a liquid satellite revolving about a liquid planet and\nproceed backwards in time, we must make the two masses expand so that\ntheir density will be diminished. Various figures have been drawn\nexhibiting the shapes of two masses until their surfaces approach close\nto one another and even until they just coalesce, but the discussion of\ntheir stability is not easy. At present it would seem to be impossible\nto reach coalescence by any series of stable transformations, and\nif this is so Professor Jeans's investigation has ceased to be truly\nanalogous to our problem at some undetermined stage. However this may be\nthis line of research throws an instructive light on what we may expect\nto find in the evolution of real stellar systems.\n\nIn the second part of this paper I shall point out the bearing which\nthis investigation of the evolution of an ideal liquid star may have on\nthe genesis of double stars.\n\nII.\n\nThere are in the heavens many stars which shine with a variable\nbrilliancy. Amongst these there is a class which exhibits special\npeculiarities; the members of this class are generally known as Algol\nVariables, because the variability of the star Beta Persei or Algol was\nthe first of such cases to attract the attention of astronomers, and\nbecause it is perhaps still the most remarkable of the whole class. But\nthe circumstances which led to this discovery were so extraordinary that\nit seems worth while to pause a moment before entering on the subject.\n\nJohn Goodricke, a deaf-mute, was born in 1764; he was grandson and heir\nof Sir John Goodricke of Ribston Hall, Yorkshire. In November 1782,\nhe noted that the brilliancy of Algol waxed and waned (It is said that\nGeorg Palitzch, a farmer of Prohlis near Dresden, had about 1758 already\nnoted the variability of Algol with the naked eye. \"Journ. Brit. Astron.\nAssoc.\" Vol. XV. (1904-5), page 203.), and devoted himself to observing\nit on every fine night from the 28th December 1782 to the 12th May 1783.\nHe communicated his observations to the Royal Society, and suggested\nthat the variation in brilliancy was due to periodic eclipses by a dark\ncompanion star, a theory now universally accepted as correct. The\nRoyal Society recognised the importance of the discovery by awarding to\nGoodricke, then only 19 years of age, their highest honour, the Copley\nmedal. His later observations of Beta Lyrae and of Delta Cephei were\nalmost as remarkable as those of Algol, but unfortunately a career of\nsuch extraordinary promise was cut short by death, only a fortnight\nafter his election to the Royal Society. (\"Dict. of National Biography\";\narticle Goodricke (John). The article is by Miss Agnes Clerke. It is\nstrange that she did not then seem to be aware that he was a deaf-mute,\nbut she notes the fact in her \"Problems of Astrophysics\", page 337,\nLondon, 1903.)\n\nIt was not until 1889 that Goodricke's theory was verified, when it\nwas proved by Vogel that the star was moving in an orbit, and in such\na manner that it was only possible to explain the rise and fall in the\nluminosity by the partial eclipse of a bright star by a dark companion.\n\nThe whole mass of the system of Algol is found to be half as great again\nas that of our sun, yet the two bodies complete their orbit in the short\nperiod of 2d 20h 48m 55s. The light remains constant during each period,\nexcept for 9h 20m when it exhibits a considerable fall in brightness\n(Clerke, \"Problems of Astrophysics\" page 302 and chapter XVIII.); the\ncurve which represents the variation in the light is shown in a figure\ntitled \"The light-curve and system of Beta Lyrae\" (Fig. 7.).\n\nThe spectroscope has enabled astronomers to prove that many stars,\nalthough apparently single, really consist of two stars circling around\none another (If a source of light is approaching with a great velocity\nthe waves of light are crowded together, and conversely they are spaced\nout when the source is receding. Thus motion in the line of sight\nvirtually produces an infinitesimal change of colour. The position\nof certain dark lines in the spectrum affords an exceedingly accurate\nmeasurement of colour. Thus displacements of these spectral lines\nenables us to measure the velocity of the source of light towards or\naway from the observer.); they are known as spectroscopic binaries.\nCampbell of the Lick Observatory believes that about one star in six is\na binary (\"Astrophysical Journ.\" Vol. XIII. page 89, 1901. See also A.\nRoberts, \"Nature\", Sept. 12, 1901, page 468.); thus there must be many\nthousand such stars within the reach of our spectroscopes.\n\nThe orientation of the planes of the orbits of binary stars appears to\nbe quite arbitrary, and in general the star does not vary in brightness.\nAmongst all such orbits there must be some whose planes pass nearly\nthrough the sun, and in these cases the eclipse of one of the stars by\nthe other becomes inevitable, and in each circuit there will occur two\neclipses of unequal intensities.\n\nIt is easy to see that in the majority of such cases the two components\nmust move very close to one another.\n\nThe coincidence between the spectroscopic and the photometric evidence\npermits us to feel complete confidence in the theory of eclipses. When\nthen we find a star with a light-curve of perfect regularity and with\na characteristics of that of Algol, we are justified in extending the\ntheory of eclipses to it, although it may be too faint to permit of\nadequate spectroscopic examination. This extension of the theory secures\na considerable multiplication of the examples available for observation,\nand some 30 have already been discovered.\n\nDr Alexander Roberts, of Lovedale in Cape Colony, truly remarks that\nthe study of Algol variables \"brings us to the very threshold of the\nquestion of stellar evolution.\" (\"Proc. Roy. Soc. Edinburgh\", XXIV. Part\nII. (1902), page 73.) It is on this account that I propose to explain\nin some detail the conclusion to which he and some other observers have\nbeen led.\n\nAlthough these variable stars are mere points of light, it has been\nproved by means of the spectroscope that the law of gravitation holds\ngood in the remotest regions of stellar space, and further it seems now\nto have become possible even to examine the shapes of stars by indirect\nmethods, and thus to begin the study of their evolution. The chain of\nreasoning which I shall explain must of necessity be open to criticism,\nyet the explanation of the facts by the theory is so perfect that it is\nnot easy to resist the conviction that we are travelling along the path\nof truth.\n\nThe brightness of a star is specified by what is called its \"magnitude.\"\nThe average brightness of all the stars which can just be seen with\nthe naked eye defines the sixth magnitude. A star which only gives\ntwo-fifths as much light is said to be of the seventh magnitude; while\none which gives 2 1/2 times as much light is of the fifth magnitude,\nand successive multiplications or divisions by 2 1/2 define the lower or\nhigher magnitudes. Negative magnitudes have clearly to be contemplated;\nthus Sirius is of magnitude minus 1.4, and the sun is of magnitude minus\n26.\n\nThe definition of magnitude is also extended to fractions; for example,\nthe lights given by two candles which are placed at 100 feet and 100\nfeet 6 inches from the observer differ in brightness by one-hundredth of\na magnitude.\n\nA great deal of thought has been devoted to the measurement of the\nbrightness of stars, but I will only describe one of the methods used,\nthat of the great astronomer Argelander. In the neighbourhood of the\nstar under observation some half dozen standard stars are selected of\nknown invariable magnitudes, some being brighter and some fainter than\nthe star to be measured; so that these stars afford a visible scale of\nbrightness. Suppose we number them in order of increasing brightness\nfrom 1 to 6; then the observer estimates that on a given night his star\nfalls between stars 2 and 3, on the next night, say between 3 and 4, and\nthen again perhaps it may return to between 2 and 3, and so forth. With\npractice he learns to evaluate the brightness down to small fractions\nof a magnitude, even a hundredth part of a magnitude is not quite\nnegligible.\n\nFor example, in observing the star RR Centauri five stars were in\ngeneral used for comparison by Dr Roberts, and in course of three months\nhe secured thereby 300 complete observations. When the period of the\ncycle had been ascertained exactly, these 300 values were reduced to\nmean values which appertained to certain mean places in the cycle, and\na mean light-curve was obtained in this way. Figures titled \"Light curve\nof RR Centauri\" (Fig. 5) and \"The light-curve and system of Beta Lyrae\"\n(Fig. 7) show examples of light curves.\n\nI shall now follow out the results of the observation of RR Centauri\nnot only because it affords the easiest way of explaining these\ninvestigations, but also because it is one of the stars which furnishes\nthe most striking results in connection with the object of this essay.\n(See \"Monthly notices R.A.S.\" Vol. 63, 1903, page 527.) This star has\na mean magnitude of about 7 1/2, and it is therefore invisible to\nthe naked eye. Its period of variability is 14h 32m 10s.76, the last\nrefinement of precision being of course only attained in the final\nstages of reduction. Twenty-nine mean values of the magnitude were\ndetermined, and they were nearly equally spaced over the whole cycle of\nchanges. The black dots in Fig. 5 exhibit the mean values determined by\nDr Roberts. The last three dots on the extreme right are merely the same\nas the first three on the extreme left, and are repeated to show how\nthe next cycle would begin. The smooth dotted curve will be explained\nhereafter, but, by reference to the scale of magnitudes on the margins\nof the figure, it may be used to note that the dots might be brought\ninto a perfectly smooth curve by shifting some few of the dots by about\na hundredth of a magnitude.\n\nThis light-curve presents those characteristics which are due to\nsuccessive eclipses, but the exact form of the curve must depend on the\nnature of the two mutually eclipsing stars. If we are to interpret the\ncurve with all possible completeness, it is necessary to make certain\nassumptions as to the stars. It is assumed then that the stars are\nequally bright all over their disks, and secondly that they are not\nsurrounded by an extensive absorptive atmosphere. This last appears to\nme to be the most dangerous assumption involved in the whole theory.\n\nMaking these assumptions, however, it is found that if each of the\neclipsing stars were spherical it would not be possible to generate such\na curve with the closest accuracy. The two stars are certainly close\ntogether, and it is obvious that in such a case the tidal forces\nexercised by each on the other must be such as to elongate the figure\nof each towards the other. Accordingly it is reasonable to adopt the\nhypothesis that the system consists of a pair of elongated ellipsoids,\nwith their longest axes pointed towards one another. No supposition\nis adopted a priori as to the ratio of the two masses, or as to their\nrelative size or brightness, and the orbit may have any degree of\neccentricity. These last are all to be determined from the nature of the\nlight-curve.\n\nIn the case of RR Centauri, however, Dr Roberts finds the conditions are\nbest satisfied by supposing the orbit to be circular, and the sizes and\nmasses of the components to be equal, while their luminosities are to\none another in the ratio of 4 to 3. As to their shapes he finds them\nto be so much elongated that they overlap, as exhibited in his figure\ntitled \"The shape of the star RR Centauri\" (Fig. 6.). The dotted curve\nshows a form of equilibrium of rotating liquid as computed by me some\nyears before, and it was added for the sake of comparison.\n\nOn turning back to Fig. 5 the reader will see in the smooth dotted curve\nthe light variation which would be exhibited by such a binary system as\nthis. The curve is the result of computation and it is impossible not to\nbe struck by the closeness of the coincidence with the series of black\ndots which denote the observations.\n\nIt is virtually certain that RR Centauri is a case of an eclipsing\nbinary system, and that the two stars are close together. It is not\nof course proved that the figures of the stars are ellipsoids, but\ngravitation must deform them into a pair of elongated bodies, and, on\nthe assumptions that they are not enveloped in an absorptive atmosphere\nand that they are ellipsoidal, their shapes must be as shown in the\nfigure.\n\nThis light-curve gives an excellent illustration of what we have reason\nto believe to be a stage in the evolution of stars, when a single star\nis proceeding to separate into a binary one.\n\nAs the star is faint, there is as yet no direct spectroscopic evidence\nof orbital motion. Let us turn therefore to the case of another star,\nnamely V Puppis, in which such evidence does already exist. I give an\naccount of it, because it presents a peculiarly interesting confirmation\nof the correctness of the theory.\n\nIn 1895 Pickering announced in the \"Harvard Circular\" No. 14 that the\nspectroscopic observations at Arequipa proved V Puppis to be a double\nstar with a period of 3d 2h 46m. Now when Roberts discussed its\nlight-curve he found that the period was 1d 10h 54m 27s, and on account\nof this serious discrepancy he effected the reduction only on the simple\nassumption that the two stars were spherical, and thus obtained a fairly\ngood representation of the light-curve. It appeared that the orbit was\ncircular and that the two spheres were not quite in contact. Obviously\nif the stars had been assumed to be ellipsoids they would have been\nfound to overlap, as was the case for RR Centauri. (\"Astrophysical\nJourn.\" Vol. XIII. (1901), page 177.) The matter rested thus for some\nmonths until the spectroscopic evidence was re-examined by Miss Cannon\non behalf of Professor Pickering, and we find in the notes on page\n177 of Vol. XXVIII. of the \"Annals of the Harvard Observatory\" the\nfollowing: \"A.G.C. 10534. This star, which is the Algol variable V\nPuppis, has been found to be a spectroscopic binary. The period 1d.454\n(i.e. 1d 10h 54m) satisfies the observations of the changes in light,\nand of the varying separation of the lines of the spectrum. The spectrum\nhas been examined on 61 plates, on 23 of which the lines are double.\"\nThus we have valuable evidence in confirmation of the correctness of the\nconclusions drawn from the light-curve. In the circumstances, however,\nI have not thought it worth while to reproduce Dr Roberts's provisional\nfigure.\n\nI now turn to the conclusions drawn a few years previously by another\nobserver, where we shall find the component stars not quite in contact.\nThis is the star Beta Lyrae which was observed by Goodricke, Argelander,\nBelopolsky, Schur, Markwick and by many others. The spectroscopic method\nhas been successfully applied in this case, and the component stars are\nproved to move in an orbit about one another. In 1897, Mr. G.W. Myers\napplied the theory of eclipses to the light-curve, on the hypothesis\nthat the stars are elongated ellipsoids, and he obtained the interesting\nresults exhibited in Fig. 7. (\"Astrophysical Journ.\" Vol. VII. (1898),\npage 1.)\n\nThe period of Beta Lyrae is relatively long, being 12d 21h 47m, the\norbit is sensibly eccentric, and the two spheroids are not so much\nelongated as was the case with RR Centauri. The mass of the system is\nenormous, one of the two stars being 10 times and the other 21 times as\nheavy as our sun.\n\nFurther illustrations of this subject might be given, but enough has\nbeen said to explain the nature of the conclusions which have been drawn\nfrom this class of observation.\n\nIn my account of these remarkable systems the consideration of one very\nimportant conclusion has been purposely deferred. Since the light-curve\nis explicable by eclipses, it follows that the sizes of the two stars\nare determinable relatively to the distance between them. The period of\ntheir orbital motion is known, being identical with the complete period\nof the variability of their light, and an easy application of Kepler's\nlaw of periodic times enables us to compute the sum of the masses of the\ntwo stars divided by the cube of the distance between their centres.\nNow the sizes of the bodies being known, the mean density of the whole\nsystem may be calculated. In every case that density has been found to\nbe much less than the sun's, and indeed the average of a number of mean\ndensities which have been determined only amounts to one-eighth of that\nof the sun. In some cases the density is extremely small, and in no case\nis it quite so great as half the solar density.\n\nIt would be absurd to suppose that these stars can be uniform in\ndensity throughout, and from all that is known of celestial bodies it\nis probable that they are gaseous in their external parts with great\ncondensation towards their centres. This conclusion is confirmed by\narguments drawn from the theory of rotating masses of liquid. (See J.H.\nJeans, \"On the density of Algol variables\", \"Astrophysical Journ.\" Vol.\nXXII. (1905), page 97.)\n\nAlthough, as already explained, a good deal is known about the shapes\nand the stability of figures consisting of homogeneous incompressible\nliquid in rotation, yet comparatively little has hitherto been\ndiscovered about the equilibrium of rotating gaseous stars. The figures\ncalculated for homogeneous liquid can obviously only be taken to afford\na general indication of the kind of figure which we might expect to find\nin the stellar universe. Thus the dotted curve in Fig. 5, which exhibits\none of the figures which I calculated, has some interest when placed\nalongside the figures of the stars in RR Centauri, as computed from the\nobservations, but it must not be accepted as the calculated form of such\na system. I have moreover proved more recently that such a figure of\nhomogeneous liquid is unstable. Notwithstanding this instability it does\nnot necessarily follow that the analogous figure for compressible fluid\nis also unstable, as will be pointed out more fully hereafter.\n\nProfessor Jeans has discussed in a paper of great ability the difficult\nproblems offered by the conditions of equilibrium and of stability of a\nspherical nebula. (\"Phil. Trans. R.S.\" Vol. CXCIX. A (1902), page 1. See\nalso A. Roberts, \"S. African Assoc. Adv. Sci.\" Vol. I. (1903), page 6.)\nIn a later paper (\"Astrophysical Journ.\" Vol. XXII. (1905), page 97.),\nin contrasting the conditions which must govern the fission of a star\ninto two parts when the star is gaseous and compressible with the\ncorresponding conditions in the case of incompressible liquid, he points\nout that for a gaseous star (the agency which effects the separation\nwill no longer be rotation alone; gravitation also will tend towards\nseparation... From numerical results obtained in the various papers of\nmy own,... I have been led to the conclusion that a gravitational\ninstability of the kind described must be regarded as the primary agent\nat work in the actual evolution of the universe, Laplace's rotation\nplaying only the secondary part of separating the primary and satellite\nafter the birth of the satellite.)\n\nIt is desirable to add a word in explanation of the expression\n\"gravitational instability\" in this passage. It means that when the\nconcentration of a gaseous nebula (without rotation) has proceeded to\na certain stage, the arrangement in spherical layers of equal density\nbecomes unstable, and a form of bifurcation has been reached. For\nfurther concentration concentric spherical layers become unstable, and\nthe new stable form involves a concentration about two centres. The\nfirst sign of this change is that the spherical layers cease to be\nquite concentric and then the layers of equal density begin to assume\na somewhat pear-shaped form analogous to that which we found to occur\nunder rotation for an incompressible liquid. Accordingly it appears that\nwhile a sphere of liquid is stable a sphere of gas may become unstable.\nThus the conditions of stability are different in these two simple\ncases, and it is likely that while certain forms of rotating liquid are\nunstable the analogous forms for gas may be stable. This furnishes a\nreason why it is worth while to consider the unstable forms of rotating\nliquid.\n\nThere can I think be little doubt but that Jeans is right in looking to\ngravitational instability as the primary cause of fission, but when we\nconsider that a binary system, with a mass larger than the sun's, is\nfound to rotate in a few hours, there seems reason to look to rotation\nas a contributory cause scarcely less important than the primary one.\n\nWith the present extent of our knowledge it is only possible to\nreconstruct the processes of the evolution of stars by means of\ninferences drawn from several sources. We have first to rely on the\ngeneral principles of stability, according to which we are to look for a\nseries of families of forms, each terminating in an unstable form, which\nitself becomes the starting-point of the next family of stable forms.\nSecondly we have as a guide the analogy of the successive changes in\nthe evolution of ideal liquid stars; and thirdly we already possess some\nslender knowledge as to the equilibrium of gaseous stars.\n\nFrom these data it is possible to build up in outline the probable\nhistory of binary stars. Originally the star must have been single, it\nmust have been widely diffused, and must have been endowed with a slow\nrotation. In this condition the strata of equal density must have been\nof the planetary form. As it cooled and contracted the symmetry round\nthe axis of rotation must have become unstable, through the effects of\ngravitation, assisted perhaps by the increasing speed of rotation. (I\nlearn from Professor Jeans that he now (December 1908) believes that\nhe can prove that some small amount of rotation is necessary to induce\ninstability in the symmetrical arrangement.) The strata of equal\ndensity must then become somewhat pear-shaped, and afterwards like an\nhour-glass, with the constriction more pronounced in the internal than\nin the external strata. The constrictions of the successive strata then\nbegin to rupture from the inside progressively outwards, and when at\nlength all are ruptured we have the twin stars portrayed by Roberts and\nby others.\n\nAs we have seen, the study of the forms of equilibrium of rotating\nliquid is almost complete, and Jeans has made a good beginning in the\ninvestigation of the equilibrium of gaseous stars, but much more remains\nto be discovered. The field for the mathematician is a wide one, and in\nproportion as the very arduous exploration of that field is attained so\nwill our knowledge of the processes of cosmical evolution increase.\n\nFrom the point of view of observation, improved methods in the use of\nthe spectroscope and increase of accuracy in photometry will certainly\nlead to a great increase in our knowledge within the next few years.\nProbably the observational advance will be more rapid than that of\ntheory, for we know how extraordinary has been the success attained\nwithin the last few years, and the theory is one of extreme difficulty;\nbut the two ought to proceed together hand in hand. Human life is\ntoo short to permit us to watch the leisurely procedure of cosmical\nevolution, but the celestial museum contains so many exhibits that it\nmay become possible, by the aid of theory, to piece together bit by bit\nthe processes through which stars pass in the course of their evolution.\n\nIn the sketch which I have endeavoured to give of this fascinating\nsubject, I have led my reader to the very confines of our present\nknowledge. It is not much more than a quarter of a century since this\nclass of observation has claimed the close attention of astronomers;\nsomething considerable has been discovered already and there seems\nscarcely a discernible limit to what will be known in this field a\ncentury from now. Some of the results which I have set forth may then be\nshown to be false, but it seems profoundly improbable that we are being\nled astray by a Will-of-the-Wisp.\n\n\n\n\nXXIX. THE EVOLUTION OF MATTER. By W.C.D. Whetham, M.A., F.R.S.\n\nTrinity College, Cambridge.\n\n\nThe idea of evolution in the organic world, made intelligible by the\nwork of Charles Darwin, has little in common with the recent conception\nof change in certain types of matter. The discovery that a process of\ndisintegration may take place in some at least of the chemical atoms,\npreviously believed to be indestructible and unalterable, has modified\nour view of the physical universe, even as Darwin's scheme of the mode\nof evolution changed the trend of thought concerning the organic world.\nBoth conceptions have in common the idea of change throughout extended\nrealms of space and time, and, therefore, it is perhaps not unfitting\nthat some account of the most recent physical discoveries should be\nincluded in the present volume.\n\nThe earliest conception of the evolution of matter is found in the\nspeculation of the Greeks. Leucippus and Democritus imagined unchanging\neternal atoms, Heracleitus held that all things were in a continual\nstate of flux--Panta rei.\n\nBut no one in the Ancient World--no one till quite modern times--could\nappreciate the strength of the position which the theory of the\nevolution of matter must carry before it wins the day. Vague\nspeculation, even by the acute minds of philosophers, is of little use\nin physical science before experimental facts are available. The true\nproblems at issue cannot even be formulated, much less solved, till the\nhumble task of the observer and experimenter has given us a knowledge of\nthe phenomena to be explained.\n\nIt was only through the atomic theory, at first apparently diametrically\nopposed to it, that the conception of evolution in the physical world\nwas to gain an established place. For a century the atomic theory, when\nput into a modern form by Dalton, led farther and farther away from\nthe idea of change in matter. The chemical elements seemed quite\nunalterable, and the atoms, of which each element in modern view is\ncomposed, bore to Clerk Maxwell, writing about 1870, \"the stamp of\nmanufactured articles\" exactly similar in kind, unchanging, eternal.\n\nNevertheless throughout these years, on the whole so unfavourable to its\nexistence, there persisted the idea of a common origin of the distinct\nkinds of matter known to chemists. Indeed, this idea of unity in\nsubstance in nature seems to accord with some innate desire or intimate\nstructure of the human mind. As Mr Arthur Balfour well puts it, \"There\nis no a priori reason that I know of for expecting that the material\nworld should be a modification of a single medium, rather than a\ncomposite structure built out of sixty or seventy elementary substances,\neternal and eternally different. Why then should we feel content with\nthe first hypothesis and not with the second? Yet so it is. Men of\nscience have always been restive under the multiplication of entities.\nThey have eagerly watched for any sign that the different chemical\nelements own a common origin, and are all compounded out of some\nprimordial substance. Nor, for my part, do I think that such instincts\nshould be ignored... that they exist is certain; that they modify the\nindifferent impartiality of pure empiricism can hardly be denied.\"\n(\"Report of the 74th Meeting of the British Association\" (Presidential\nAddress, Cambridge 1904), page 9, London, 1905.)\n\nWhen Dalton's atomic theory had been in existence some half century, it\nwas noted that certain numerical relations held good between the atomic\nweights of elements chemically similar to one another. Thus the weight\n(88) of an atom of strontium compared with that of hydrogen as unity,\nis about the mean of those of calcium (40) and barium (137). Such\nrelations, in this and other chemical groups, were illustrated by\nBeguyer de Chancourtois in 1862 by the construction of a spiral diagram\nin which the atomic weights are placed in order round a cylinder and\nelements chemically similar are found to fall on vertical lines.\n\nNewlands seems to have been the first to see the significance of such\na diagram. In his \"law of octaves,\" formulated in 1864, he advanced\nthe hypothesis that, if arranged in order of rising atomic weight, the\nelements fell into groups, so that each eighth element was chemically\nsimilar. Stated thus, the law was too definite; no room was left for\nnewly-discovered elements, and some dissimilar elements were perforce\ngrouped together.\n\nBut in 1869 Mendeleeff developed Newland's hypothesis in a form that\nattracted at once general attention. Placing the elements in order of\nrising atomic weight, but leaving a gap where necessary to bring similar\nelements into vertical columns, he obtained a periodic table with\nnatural vacancies to be filled as new elements were discovered, and with\na certain amount of flexibility at the ends of the horizontal lines.\nFrom the position of the vacancies, the general chemical and physical\nproperties of undiscovered elements could be predicted, and the\nsuccess of such predictions gave a striking proof of the usefulness of\nMendeleeff's generalisation.\n\nWhen the chemical and physical properties of the elements were known\nto be periodic functions of their atomic weights, the idea of a common\norigin and common substance became much more credible. Differences in\natomic weight and differences in properties alike might reasonably be\nexplained by the differences in the amount of the primordial substance\npresent in the various atoms; an atom of oxygen being supposed to be\ncomposed of sixteen times as much stuff as the atom of hydrogen, but to\nbe made of the same ultimate material. Speculations about the mode of\norigin of the elements now began to appear, and put on a certain air\nof reality. Of these speculations perhaps the most detailed was that of\nCrookes, who imagined an initial chaos of a primordial medium he named\nprotyle, and a process of periodic change in which the chemical elements\nsuccessively were precipitated.\n\nFrom another side too, suggestions were put forward by Sir Norman\nLockyer and others that the differences in spectra observed in\ndifferent classes of stars, and produced by different conditions in\nthe laboratory, were to be explained by changes in the structure of the\nvibrating atoms.\n\nThe next step in advance gave a theoretical basis for the idea of a\ncommon structure of matter, and was taken in an unexpected direction.\nClerk Maxwell's electromagnetic theory of light, accepted in England,\nwas driven home to continental minds by the confirmatory experiments of\nHertz, who in 1888 detected and measured the electromagnetic waves\nthat Maxwell had described twenty years earlier. But, if light be an\nelectromagnetic phenomenon, the light waves radiated by hot bodies must\ntake their origin in the vibrations of electric systems. Hence within\nthe atoms must exist electric charges capable of vibration. On these\nlines Lorentz and Larmor have developed an electronic theory of matter,\nwhich is imagined in its essence to be a conglomerate of electric\ncharges, with electro-magnetic inertia to explain mechanical inertia.\n(Larmor, \"Aether and Matter\", Cambridge, 1900.) The movement of electric\ncharges would be affected by a magnetic field, and hence the discovery\nby Zeeman that the spectral lines of sodium were doubled by a strong\nmagnetic force gave confirmatory evidence to the theory of electrons.\n\nThen came J.J. Thomson's great discovery of minute particles, much\nsmaller than any chemical atom, forming a common constituent of many\ndifferent kinds of matter. (Thomson, \"Conduction of Electricity through\nGases\" (2nd edition), Cambridge, 1906.) If an electric discharge be\npassed between metallic terminals through a glass vessel containing\nair at very low pressure, it is found that rectilinear rays, known\nas cathode rays, proceed from the surface of the cathode or negative\nterminal. Where these rays strike solid objects, they give rise to\nthe Rontgen rays now so well known; but it is with the cathode rays\nthemselves that we are concerned. When they strike an insulated\nconductor, they impart to it a negative charge, and Thomson found that\nthey were deflected from their path both by magnetic and electric forces\nin the direction in which negatively electrified particles would be\ndeflected. Cathode rays then were accepted as flights of negatively\ncharged particles, moving with high velocities. The electric and\nmagnetic deflections give two independent measurements which may be made\non a cathode ray, and both the deflections involve theoretically three\nunknown quantities, the mass of the particles, their electric charge\nand their velocity. There is strong cumulative evidence that all\nsuch particles possess the same charge, which is identical with that\nassociated with a univalent atom in electrolytic liquids. The number of\nunknown quantities was thus reduced to two--the mass and the velocity.\nThe measurement of the magnetic and electric deflections gave two\nindependent relations between the unknowns, which could therefore be\ndetermined. The velocities of the cathode ray particles were found to\nvary round a value about one-tenth that of light, but the mass was found\nalways to be the same within the limits of error, whatever the nature of\nthe terminals, of the residual gas in the vessel, and of the conditions\nof the experiment. The mass of a cathode ray particle, or corpuscle, as\nThomson, adopting Newton's name, called it, is about the eight-hundredth\npart of the mass of a hydrogen atom.\n\nThese corpuscles, found in so many different kinds of substance,\nare inevitably regarded as a common constituent of matter. They are\nassociated each with a unit of negative electricity. Now electricity in\nmotion possesses electromagnetic energy, and produces effects like those\nof mechanical inertia. In other words, an electric charge possesses\nmass, and there is evidence to show that the effective mass of a\ncorpuscle increases as its velocity approaches that of light in the way\nit would do if all its mass were electromagnetic. We are led therefore\nto regard the corpuscle from one aspect as a disembodied charge of\nelectricity, and to identify it with the electron of Lorentz and Larmor.\n\nThus, on this theory, matter and electricity are identified; and a great\nsimplification of our conception of the physical structure of Nature is\nreached. Moreover, from our present point of view, a common basis for\nmatter suggests or implies a common origin, and a process of development\npossibly intelligible to our minds. The idea of the evolution of matter\nbecomes much more probable.\n\nThe question of the nature and physical meaning of a corpuscle or\nelectron remains for consideration. On the hypothesis of a universal\nluminiferous aether, Larmor has suggested a centre of aethereal strain\n\"a place where the continuity of the medium has been broken and cemented\ntogether again (to use a crude but effective image) without accurately\nfitting the parts, so that there is a residual strain all round the\nplace.\" (Larmor, loc. cit.) Thus he explains in quasi-mechanical terms\nthe properties of an electron. But whether we remain content for the\ntime with our identification of matter and electricity, or attempt to\nexpress both of them in terms of hypothetical aether, we have made a\ngreat step in advance on the view that matter is made up of chemical\natoms fundamentally distinct and eternally isolated.\n\nSuch was the position when the phenomena of radio-activity threw a new\nlight on the problem, and, for the first time in the history of science,\ngave definite experimental evidence of the transmutation of matter from\none chemical element to another.\n\nIn 1896 H. Becquerel discovered that compounds of the metal uranium\ncontinually emitted rays capable of penetrating opaque screens and\naffecting photographic plates. Like cathode and Rontgen rays, the\nrays from uranium make the air through which they pass a conductor\nof electricity, and this property gives the most convenient method of\ndetecting the rays and of measuring their intensity. An electroscope may\nbe made of a strip of gold-leaf attached to an insulated brass plate\nand confined in a brass vessel with glass windows. When the gold-leaf is\nelectrified, it is repelled from the similarly electrified brass plate,\nand the angle at which it stands out measures the electrification. Such\na system, if well insulated, holds its charge for hours, the leakage\nof electricity through the air being very slow. But, if radio-active\nradiation reach the air within, the gold-leaf falls, and the rate of\nits fall, as watched through a microscope with a scale in the eye-piece,\nmeasures the intensity of the radiation. With some form of this simple\ninstrument, or with the more complicated quadrant electrometer, most\nradio-active measurements have been made.\n\nIt was soon discovered that the activity of uranium compounds\nwas proportional to the amount of uranium present in them. Thus\nradio-activity is an atomic property dependent on the amount of an\nelement and independent of its state of chemical combination.\n\nIn a search for radio-activity in different minerals, M. and Mme Curie\nfound a greater effect in pitch-blende than its contents of uranium\nwarranted, and, led by the radio-active property alone, they succeeded,\nby a long series of chemical separations, in isolating compounds of a\nnew and intensely radio-active substance which they named radium.\n\nRadium resembles barium in its chemical properties, and is precipitated\nwith barium in the ordinary course of chemical analysis. It is separated\nby a prolonged course of successive crystallisation, the chloride of\nradium being less soluble than that of barium, and therefore sooner\nseparated from an evaporating solution. When isolated, radium chloride\nhas a composition, which, on the assumption that one atom of metal\ncombines with two of chlorine as in barium chloride, indicates that the\nrelative weight of the atom of radium is about 225. As thus prepared,\nradium is a well-marked chemical element, forming a series of compounds\nanalogous to those of barium and showing a characteristic line spectrum.\nBut, unlike most other chemical elements, it is intensely radio-active,\nand produces effects some two million times greater than those of\nuranium.\n\nIn 1899 E. Rutherford, then of Montreal, discovered that the\nradiation from uranium, thorium and radium was complex. (Rutherford,\n\"Radio-activity\" (2nd edition), Cambridge, 1905.) Three types of rays\nwere soon distinguished. The first, named by Rutherford alpha-rays, are\nabsorbed by thin metal foil or a few centimetres of air. When examined\nby measurements of the deflections caused by magnetic and electric\nfields, the alpha-rays are found to behave as would positively\nelectrified particles of the magnitude of helium atoms possessing a\ndouble ionic charge and travelling with a velocity about one-tenth that\nof light. The second or beta type of radiation is much more penetrating.\nIt will pass through a considerable thickness of metallic foil, or many\ncentimetres of air, and still affect photographic plates or discharge\nelectroscopes. Magnetic and electric forces deflect beta-rays much\nmore than alpha-rays, indicating that, although the speed is greater,\napproaching in some cases within five per cent. that of light, the mass\nis very much less. The beta-rays must be streams of particles, identical\nwith those of cathode rays, possessing the minute mass of J.J. Thomson's\ncorpuscle, some eight-hundredth part of that of a hydrogen atom. A third\nor gamma type of radiation was also detected. More penetrating even than\nbeta-rays, the gamma-rays have never been deflected by any magnetic\nor electric force yet applied. Like Rontgen rays, it is probable that\ngamma-rays are wave-pulses in the luminiferous aether, though the\npossibility of explaining them as flights of non-electrified particles\nis before the minds of some physicists.\n\nStill another kind of radiation has been discovered more recently by\nThomson, who has found that in high vacua, rays become apparent which\nare absorbed at once by air at any ordinary pressure.\n\nThe emission of all these different types of radiation involves a\ncontinual drain of energy from the radio-active body. When M. and Mme\nCurie had prepared as much as a gramme of radium chloride, the energy of\nthe radiation became apparent as an evolution of heat. The radium salt\nitself, and the case containing it, absorbed the major part of the\nradiation, and were thus maintained at a temperature measurably higher\nthan that of the surroundings. The rate of thermal evolution was such\nthat it appeared that one gramme of pure radium must emit about 100\ngramme-calories of heat in an hour. This observation, naturally as it\nfollows from the phenomena previously discovered, first called attention\nto the question of the source of the energy which maintains indefinitely\nand without apparent diminution the wonderful stream of radiation\nproceeding from a radio-active substance. In the solution of this\nproblem lies the point of the present essay.\n\nIn order to appreciate the evidence which bears on the question we must\nnow describe two other series of phenomena.\n\nIt is a remarkable fact that the intensity of the radiation from\na radio-active body is independent of the external conditions of\ntemperature, pressure, etc. which modify so profoundly almost all other\nphysical and chemical processes. Exposure to the extreme cold of liquid\nair, or to the great heat of a furnace, leaves the radio-activity of a\nsubstance unchanged, apparent exceptions to this statement having been\ntraced to secondary causes.\n\nThen, it is found that radio-activity is always accompanied by some\nchemical change; a new substance always appears as the parent substance\nemits these radiations. Thus by chemical reactions it is possible to\nseparate from uranium and thorium minute quantities of radio-active\nmaterials to which the names of uranium-X and thorium-X have been given.\nThese bodies behave differently from their parents uranium and thorium,\nand show all the signs of distinct chemical individuality. They are\nstrongly radio-active, while, after the separation, the parents uranium\nand thorium are found to have lost some of their radio-activity. If the\nX-substances be kept, their radio-activity decays, while that of the\nuranium or thorium from which they were obtained gradually rises to the\ninitial value it had before the separation. At any moment, the sum of\nthe radio-activity is constant, the activity lost by the product being\nequal to that gained by the parent substance. These phenomena are\nexplained if we suppose that the X-product is slowly produced in the\nsubstance of the parent, and decays at a constant rate. Uranium,\nas usually seen, contains a certain amount of uranium-X, and its\nradio-activity consists of two parts--that of the uranium itself, and\nthat of the X product. When the latter is separated by means of its\nchemical reactions, its radio-activity is separated also, and the rates\nof decay and recovery may be examined.\n\nRadium and thorium, but not uranium, give rise to radio-active gases\nwhich have been called emanations. Rutherford has shown that their\nradio-activity, like that of the X products, suffers decay, while\nthe walls of the vessel in which the emanation is confined, become\nthemselves radio-active. If washed with certain acids, however, the\nwalls lose their activity, which is transferred to the acid, and can be\ndeposited by evaporation from it on to a solid surface. Here again it\nis clear that the emanation gives rise to a radio-active substance which\nclings to the walls of the vessel, and is soluble in certain liquids,\nbut not in others.\n\nWe shall return to this point, and trace farther the history of the\nradio-active matter. At present we wish to emphasise the fact that, as\nin other cases, the radio-activity of the emanation is accompanied\nby the appearance of a new kind of substance with distinct chemical\nproperties.\n\nWe are now in a position to consider as a whole the evidence on the\nquestion of the source of radio-active energy.\n\n(1) Radio-activity is accompanied by the appearance of new chemical\nsubstances. The energy liberated is therefore probably due to the\nassociated chemical change. (2) The activity of a series of compounds is\nfound to accompany the presence of a radio-active element, the activity\nof each compound depends only on the contents of the element, and is\nindependent of the nature of its combination. Thus radio-activity is a\nproperty of the element, and is not affected by its state of isolation\nor chemical combination. (3) The radio-activity of a simple transient\nproduct decays in a geometrical progression, the loss per second being\nproportional to the mass of substance still left at the moment, and\nindependent of its state of concentration or dilution. This type of\nreaction is well known in chemistry to mark a mono-molecular\nchange, where each molecule is dissociated or altered in structure\nindependently. If two or more molecules were concerned simultaneously,\nthe rate of reaction would depend on the nearness of the molecules\nto each other, that is, to the concentration of the material. (4) The\namount of energy liberated by the change of a given mass of material far\ntranscends the amount set free by any known ordinary chemical action.\nThe activity of radium decays so slowly that it would not sink to half\nits initial value in less than some two thousand years, and yet one\ngramme of radium emits about 100 calories of heat during each hour of\nits existence.\n\nThe energy of radio-activity is due to chemical change, but clearly\nto no chemical change hitherto familiar to science. It is an atomic\nproperty, characteristic of a given element, and the atoms undergo the\nchange individually, not by means of interaction among each other. The\nconclusion is irresistible that we are dealing with a fundamental\nchange in the structure of the individual atoms, which, one by one, are\ndissociating into simpler parts. We are watching the disintegration\nof the \"atoms\" of the chemist, hitherto believed indestructible and\neternal, and measuring the liberation of some of the long-suspected\nstore of internal atomic energy. We have stumbled on the transmutation\ndreamed by the alchemist, and discovered the process of a veritable\nevolution of matter.\n\nThe transmutation theory of radio-activity was formulated by Rutherford\n(Rutherford, \"Radio-activity\" (2nd edition), Cambridge, 1905, page 307.)\nand Soddy in 1903. By its light, all recent work on the subject has been\nguided; it has stood the supreme test of a hypothesis, and shown power\nto suggest new investigations and to co-ordinate and explain them, when\ncarried out. We have summarised the evidence which led to the conception\nof the theory; we have now to consider the progress which has been made\nin tracing the successive disintegration of radio-active atoms.\n\nSoon after the statement of the transmutation theory, a striking\nverification of one of its consequences appeared. The measurement of\nthe magnetic and electric deflection of the alpha-rays suggested\nto Rutherford the idea that the stream of projectiles of which they\nconsisted was a flight of helium atoms. Ramsay and Soddy, confining a\nminute bubble of radium emanation in a fine glass tube, were able\nto watch the development of the helium spectrum as, day by day, the\nemanation decayed. By isolating a very narrow pencil of alpha-rays,\nand watching through a microscope their impact on a fluorescent screen,\nRutherford has lately counted the individual alpha-projectiles, and\nconfirmed his original conclusion that their mass corresponded to that\nof helium atoms and their charge to double that on a univalent atom.\n(\"Proc. Roy. Soc.\" A, page 141, 1908.) Still more recently, he has\ncollected the alpha-particles shot through an extremely thin wall of\nglass, and demonstrated by direct spectroscopic evidence the presence of\nhelium. (\"Phil. Mag.\" February 1909.)\n\nBut the most thorough investigation of a radio-active pedigree is found\nin Rutherford's classical researches on the successive disintegration\nproducts of radium, in order to follow the evidence on which his results\nare founded, we must describe more fully the process of decay of the\nactivity of a simple radio-active substance. The decay of activity of\nthe body known as uranium-X is shown in a falling curve (Fig. 1.). It\nwill be seen that, in each successive 22 days, the activity falls to\nhalf the value it possessed at the beginning.\n\nThis change in a geometrical progression is characteristic of simple\nradio-active processes, and can be expressed mathematically by a simple\nexponential formula.\n\nAs we have said above, solid bodies exposed to the emanations of radium\nor thorium become coated with a radio-active deposit. The rate of decay\nof this activity depends on the time of exposure to the emanation, and\ndoes not always show the usual simple type of curve. Thus the activity\nof a rod exposed to radium emanation for 1 minute decays in accordance\nwith a curve (Fig. 2) which represents the activity as measured by the\nalpha-rays. If the electroscope be screened from the alpha-rays, it is\nfound that the activity of the rod in beta- an gamma-rays increases for\nsome 35 minutes and then diminishes (Fig. 3.).\n\nThese complicated relations have been explained satisfactorily and\ncompletely by Rutherford on the hypothesis of successive changes of\nthe radio-active matter into one new body after another. (Rutherford,\n\"Radio-activity\" (2nd edition), Cambridge, 1905, page 379.) The\nexperimental curve represents the resultant activity of all the\nmatter present at a given moment, and the process of disentangling the\ncomponent effects consists in finding a number of curves, which express\nthe rise and fall of activity of each kind of matter as it is produced\nand decays, and, fitted together, give the curve of the experiments.\n\nOther methods of investigation also are open. They have enabled\nRutherford to complete the life-history of radium and its products, and\nto clear up doubtful points left by the analysis of the curves. By the\nremoval of the emanation, the activity of radium itself has been shown\nto consist solely of alpha-rays. This removal can be effected by passing\nair through the solution of a radium salt. The emanation comes away, and\nthe activity of the deposit which it leaves behind decays rapidly to a\nsmall fraction of its initial value. Again, some of the active deposits\nof the emanation are more volatile than others, and can be separated\nfrom them by the agency of heat.\n\nFrom such evidence Rutherford has traced a long series of disintegration\nproducts of radium, all but the first of which exist in much too minute\nquantities to be detected otherwise than by their radio-activities.\nMoreover, two of these products are not themselves appreciably\nradio-active, though they are born from radio-active parents, and give\nrise to a series of radio-active descendants. Their presence is inferred\nfrom such evidence as the rise of beta and gamma radio-activity in the\nsolid newly deposited by the emanation; this rise measuring the growth\nof the first radio-active offspring of one of the non-active bodies.\nSome of the radium products give out alpha-rays only, one beta- and\ngamma-rays, while one yields all three types of radiation. The pedigree\nof the radium family may be expressed in the following table, the time\nnoted in the second column being the time required for a given quantity\nto be half transformed into its next derivative.\n\n\n             Time of half      Radio-       Properties\n             decay             activity\n\n  Radium     About 2600 years  alpha rays   Element chemically analogous\n                                            to barium.\n\n  Emanation  3.8 days          alpha rays   Chemically inert gas;\n                                             condenses at -150 deg C.\n\n  Radium-A   3 minutes         alpha rays   Behaves as a solid deposited on\n                                             surfaces; concentrated on a\n                                             negative electrode.\n\n  Radium-B   21 minutes        no rays      Soluble in strong acids;\n                                             volatile at a white heat; more\n                                             volatile than A or C.\n\n  Radium-C   28 minutes        alpha, beta, Soluble in strong acids; less\n                               gamma rays    volatile than B.\n\n  Radium-D   about 40 years    no rays      Soluble in strong acids; volatile\n                                             below 1000 deg C.\n\n  Radium-E   6 days            beta, gamma  Non-volatile at 1000 deg C.\n                               rays\n\n  Radium-F   143 days          alpha rays   Volatile at 1000 deg C.\n                                             Deposited from solution on a\n                                             bismuth plate.\n\n\nOf these products, A, B, and C constitute that part of the active\ndeposit of the emanation which suffers rapid decay and nearly disappears\nin a few hours. Radium-D, continually producing its short-lived\ndescendants E and F, remains for years on surfaces once exposed to the\nemanation, and makes delicate radio-active researches impossible\nin laboratories which have been contaminated by an escape of radium\nemanation.\n\nA somewhat similar pedigree has been made out in the case of thorium.\nHere thorium-X is interposed between thorium and its short-lived\nemanation, which decays to half its initial quantity in 54 seconds. Two\nactive deposits, thorium A and B, arise successively from the emanation.\nIn uranium, we have the one obvious derivative uranium-X, and the\nquestion remains whether this one descent can be connected with any\nother individual or family. Uranium is long-lived, and emits only\nalpha-rays. Uranium-X decays to half value in 22 days, giving out beta-\nand gamma-rays. Since our evidence goes to show that radio-activity is\ngenerally accompanied by the production of new elements, it is natural\nto search for the substance of uranium-X in other forms, and perhaps\nunder other names, rather than to surrender immediately our belief in\nthe conservation of matter.\n\nWith this idea in mind we see at once the significance of the\nconstitution of uranium minerals. Formed in the remote antiquity of\npast geological ages, these minerals must become store-houses of all\nthe products of uranium except those which may have escaped as gases\nor possibly liquids. Even gases may be expected to some extent to be\nretained by occlusion. Among the contents of uranium minerals, then, we\nmay look for the descendants of the parent uranium. If the descendants\nare permanent or more long-lived than uranium, they will accumulate\ncontinually. If they are short-lived, they will accumulate at a steady\nrate till enough is formed for the quantity disintegrating to be equal\nto the quantity developed. A state of mobile equilibrium will then\nbe reached, and the amount of the product will remain constant. This\nconstant amount of substance will depend only on the amount of uranium\nwhich is its source, and, for different minerals, if all the product\nis retained, the quantity of the product will be proportional to the\nquantity of uranium. In a series of analyses of uranium minerals,\ntherefore, we ought to be able to pick out its more short-lived\ndescendants by seeking for instances of such proportionality.\n\nNow radium itself is a constituent of uranium minerals, and two series\nof experiments by R.J. Strutt and B.B. Boltwood have shown that the\ncontent of radium, as measured by the radio-activity of the emanation,\nis directly proportional to the content of uranium. (Strutt, \"Proc.\nRoy. Soc.\" A, February 1905; Boltwood, \"Phil. Mag.\" April, 1905.) In\nBoltwood's investigation, some twenty minerals, with amounts of uranium\nvarying from that in a specimen of uraninite with 74.65 per cent.,\nto that in a monazite with 0.30 per cent., gave a ratio of uranium to\nradium, constant within about one part in ten.\n\nThe conclusion is irresistible that radium is a descendant of uranium,\nthough whether uranium is its parent or a more remote ancestor requires\nfurther investigation by the radio-active genealogist. On the hypothesis\nof direct parentage, it is easy to calculate that the amount of radium\nproduced in a month by a kilogramme of a uranium salt would be enough\nto be detected easily by the radio-activity of its emanation. The\ninvestigation has been attempted by several observers, and the results,\nespecially those of a careful experiment of Boltwood, show that from\npurified uranium salts the growth of radium, if appreciable at all, is\nmuch less than would be found if the radium was the first product of\nchange of the uranium. It is necessary, therefore, to look for one or\nmore intermediate substances.\n\nWhile working in 1899 with the uranium residues used by M. and Mme\nCurie for the preparation of radium, Debierne discovered and partially\nseparated another radio-active element which he called actinium. It\ngives rise to an intermediate product actinium-X, which yields an\nemanation with the short half-life of 3.9 seconds. The emanation\ndeposits two successive disintegration products actinium-A and\nactinium-B.\n\nEvidence gradually accumulated that the amounts of actinium in\nradio-active minerals were, roughly at any rate, proportional to the\namounts of uranium. This result pointed to a lineal connection between\nthem, and led Boltwood to undertake a direct attack on the problem.\nSeparating a quantity of actinium from a kilogramme of ore, Boltwood\nobserved a growth of 8.5 x (10 to the power -9) gramme of radium in\n193 days, agreeing with that indicated by theory within the limits of\nexperimental error. (\"American Journal of Science\", December, 1906.)\nWe may therefore insert provisionally actinium and its series of\nderivatives between uranium and radium in the radio-active pedigree.\n\nTurning to the other end of the radium series we are led to ask what\nbecomes of radium-F when in turn it disintegrates? What is the final\nnon-active product of the series of changes we have traced from uranium\nthrough actinium and radium?\n\nOne such product has been indicated above. The alpha-ray particles\nappear to possess the mass of helium atoms, and the growth of helium has\nbeen detected by its spectrum in a tube of radium emanation. Moreover,\nhelium is found occluded in most if not all radio-active minerals in\namount which approaches, but never exceeds, the quantity suggested by\ntheory. We may safely regard such helium as formed by the accumulation\nof alpha-ray particles given out by successive radio-active changes.\n\nIn considering the nature of the residue left after the expulsion of the\nfive alpha-particles, and the consequent passage of radium to radium-F\nwe are faced by the fact that lead is a general constituent of uranium\nminerals. Five alpha-particles, each of atomic weight 4, taken from the\natomic weight (about 225) of radium gives 205--a number agreeing fairly\nwell with the 207 of lead. Since lead is more permanent than uranium, it\nmust steadily accumulate, no radio-active equilibrium will be reached,\nand the amount of lead will depend on the age of the mineral as well as\non the quantity of uranium present in it. In primary minerals from\nthe same locality, Boltwood has shown that the contents of lead are\nproportional to the amounts of uranium, while, accepting this theory,\nthe age of minerals with a given content of uranium may be calculated\nfrom the amount of lead they contain. The results vary from 400 to\n2000 million years. (\"American Journal of Science\", October, 1905, and\nFebruary, 1907.)\n\nWe can now exhibit in tabular form the amazing pedigree of radio-active\nchange shown by this one family of elements. An immediate descent is\nindicated by >, while one which may either be immediate or involve an\nintermediate step is shown by.... No place is found in this pedigree\nfor thorium and its derivatives. They seem to form a separate and\nindependent radio-active family.\n\n\n                       Atomic Weight  Time of half     Radio-Activity\n                                         decay\n\n   Uranium               238.5                         alpha\n\n   Uranium-X             ?            22 days          beta, gamma\n   ...\n   Actinium              ?            ?                no rays\n\n   Actinium-X            ?            10.2 days        alpha (beta, gamma)\n\n   Actinium Emanation    ?            3.9 seconds      alpha\n\n   Actinium-A            ?            35.7 minutes     no rays\n\n   Actinium-B            ?            2.15 minutes      alpha, beta, gamma\n   ...\n   Radium                225          about 2600 years  alpha\n\n   Radium Emanation      ?            3.8 days          alpha\n\n   Radium-A              ?            3 minutes         alpha\n\n   Radium-B              ?            21 minutes        no rays\n\n   Radium-C              ?            28 minutes        alpha, beta, gamma\n\n   Radium-D              ?            about 40 years    no rays\n\n   Radium-E              ?            6 days            beta (gamma)\n\n   Radium-F              ?            143 days          alpha\n   ...\n   Lead                  207          ?                 no rays\n\n\nAs soon as the transmutation theory of radio-activity was accepted,\nit became natural to speculate about the intimate structure of the\nradio-active atoms, and the mode in which they broke up with the\nliberation of some of their store of internal energy. How could we\nimagine an atomic structure which would persist unchanged for long\nperiods of time, and yet eventually spontaneously explode, as here an\natom and there an atom reached a condition of instability?\n\nThe atomic theory of corpuscles or electrons fortunately was ready to\nbe applied to this new problem. Of the resulting speculations the most\ndetailed and suggestive is that of J.J. Thomson. (\"Phil. Mag.\" March,\n1904.) Thomson regards the atom as composed of a number of mutually\nrepelling negative corpuscles or electrons held together by some central\nattractive force which he represents by supposing them immersed in a\nuniform sphere of positive electricity. Under the action of the two\nforces, the electrons space themselves in symmetrical patterns, which\ndepend on the number of electrons. Three place themselves at the corner\nof an equilateral triangle, four at those of a square, and five form\na pentagon. With six, however, the single ring becomes unstable, one\ncorpuscle moves to the middle and five lie round it. But if we imagine\nthe system rapidly to rotate, the centrifugal force would enable the\nsix corpuscles to remain in a single ring. Thus internal kinetic energy\nwould maintain a configuration which would become unstable as the energy\ndrained away. Now in a system of electrons, electromagnetic radiation\nwould result in a loss of energy, and at one point of instability we\nmight well have a sudden spontaneous redistribution of the constituents,\ntaking place with an explosive violence, and accompanied by the ejection\nof a corpuscle as a beta-ray, or of a large fragment of the atom as an\nalpha-ray.\n\nThe discovery of the new property of radio-activity in a small number of\nchemical elements led physicists to ask whether the property might not\nbe found in other elements, though in a much less striking form. Are\nordinary materials slightly radio-active? Does the feeble electric\nconductivity always observed in the air contained within the walls of\nan electroscope depend on ionizing radiations from the material of the\nwalls themselves? The question is very difficult, owing to the wide\ndistribution of slight traces of radium. Contact with radium emanation\nresults in a deposit of the fatal radium-D, which in 40 years is but\nhalf removed. Is the \"natural\" leak of a brass electroscope due to\nan intrinsic radio-activity of brass, or to traces of a radio-active\nimpurity on its surface? Long and laborious researches have succeeded in\nestablishing the existence of slight intrinsic radio-activity in a\nfew metals such as potassium, and have left the wider problem still\nunsolved.\n\nIt should be noted, however, that, even if ordinary elements are not\nradio-active, they may still be undergoing spontaneous disintegration.\nThe detection of ray-less changes by Rutherford, when those changes\nare interposed between two radio-active transformations which can\nbe followed, show that spontaneous transmutation is possible without\nmeasureable radio-activity. And, indeed, any theory of disintegration,\nsuch as Thomson's corpuscular hypothesis, would suggest that atomic\nrearrangements are of much more general occurrence than would be\napparent to one who could observe them only by the effect of the\nprojectiles, which, in special cases, owing to some peculiarity of\natomic configuration, happened to be shot out with the enormous velocity\nneeded to ionize the surrounding gas. No evidence for such ray-less\nchanges in ordinary elements is yet known, perhaps none may ever be\nobtained; but the possibility should not be forgotten.\n\nIn the strict sense of the word, the process of atomic disintegration\nrevealed to us by the new science of radio-activity can hardly be called\nevolution. In each case radio-active change involves the breaking up of\na heavier, more complex atom into lighter and simpler fragments. Are\nwe to regard this process as characteristic of the tendencies in accord\nwith which the universe has reached its present state, and is passing\nto its unknown future? Or have we chanced upon an eddy in a backwater,\nopposed to the main stream of advance? In the chaos from which the\npresent universe developed, was matter composed of large highly complex\natoms, which have formed the simpler elements by radio-active or\nray-less disintegration? Or did the primaeval substance consist\nof isolated electrons, which have slowly come together to form the\nelements, and yet have left here and there an anomaly such as that\nillustrated by the unstable family of uranium and radium, or by some\nsuch course are returning to their state of primaeval simplicity?\n\n\n\n\nINDEX.\n\nAbraxas grossulariata.\n\nAcquired characters, transmission of.\n\nAcraea johnstoni.\n\nAdaptation.\n\nAdloff.\n\nAdlumia cirrhosa.\n\nAgassiz, A.\n\nAgassiz, L.\n\nAlexander.\n\nAllen, C.A.\n\nAlternation of generations.\n\nAmeghino.\n\nAmmon, O., Works of.\n\nAmmonites, Descent of.\n\nAmphidesmus analis.\n\nAnaea divina.\n\nAndrews, C.W.\n\nAngiosperms, evolution of.\n\nAnglicus, Bartholomaeus.\n\nAnkyroderma.\n\nAnomma.\n\nAntedon rosacea.\n\nAntennularia antennina.\n\nAnthropops.\n\nAnts, modifications of.\n\nArber, E.A.N.,--and J. Parkin, on the origin of Angiosperms.\n\nArchaeopteryx.\n\nArctic regions, velocity of development of life in.\n\nArdigo.\n\nArgelander.\n\nArgyll, Huxley and the Duke of.\n\nAristotle.\n\nArrhenius.\n\nAsterias, Loeb on hybridisation of.\n\nAutogamy.\n\nAvena fatua.\n\nAvenarius.\n\nBacon, on mutability of species.\n\nBaehr, von, on Cytology.\n\nBaer, law of von.\n\nBain.\n\nBaldwin, J.M.\n\nBalfour, A.J.\n\nBall, J.\n\nBarber, Mrs M.E., on Papilio nireus.\n\nBarclay, W.\n\nBarratt.\n\nBary, de.\n\nBates, H.W., on Mimicry.--Letters from Darwin to.--elsewhere.\n\nBateson, A.\n\nBATESON, W., on \"Heredity and Variation in Modern lights\".--on\ndiscontinuous evolution.--on hybridisation.\n\nBateson, W. and R.P. Gregory.\n\nBathmism.\n\nBeche, de la.\n\nBeck, P.\n\nBecquerel, H.\n\nBeebe, C.W., on the plumage of birds.--on sexual selection.\n\nBeguyer de Chancourtois.\n\nBell's (Sir Charles) \"Anatomy of Expression\".\n\nBelopolsky.\n\nBelt, T., on Mimicry.\n\nBeneden, E. van.\n\nBenson, M.\n\nBentham, G., on Darwin's species-theory.--on geographical distribution.\n\nBentham, Jeremy.\n\nBergson, H.\n\nBerkeley.\n\nBerthelot.\n\nBetham, Sir W.\n\nBickford, E., experiments on degeneration by.\n\nBignonia capreolata.\n\nBiophores.\n\nBirds, geological history of.\n\nBlanford, W.T.\n\nBlaringhem, on wounding.\n\nBlumenbach.\n\nBodin.\n\nBoltwood, B.B.\n\nBonald, on war.\n\nBonnet.\n\nBonney, T.G.\n\nBonnier, G.\n\nBopp, F., on language.\n\nBOUGLE C., on \"Darwinism and Sociology\".\n\nBourdeau.\n\nBourget, P.\n\nBoutroux.\n\nBoveri, T.\n\nBrachiopods, history of.\n\nBrassica, hybrids of.\n\nBrassica Napus.\n\nBroca.\n\nBrock, on Kant.\n\nBrown, Robert.\n\nBrugmann and Osthoff.\n\nBrugmann.\n\nBrunetiere.\n\nBruno, on Evolution.\n\nBuch, von.\n\nBucher, K.\n\nBuckland.\n\nBuckle.\n\nBuffon.\n\nBurchell, W.J.\n\nBurck, W.\n\nBurdon-Sanderson, J., letter from.\n\nBURY, J.B., on \"Darwinism and History\".\n\nButler, A.G.\n\nButler, Samuel.\n\nButschli, O.\n\nButterflies, mimicry in.--sexual characters in.\n\nCabanis.\n\nCampbell.\n\nCamels, geological history of.\n\nCamerarius, R.J.\n\nCandolle, A. de.\n\nCannon and Davenport, experiments on Daphniae by.\n\nCapsella bursapastoris.\n\nCarneri.\n\nCastnia linus.\n\nCatasetum barbatum.\n\nCatasetum tridentatum.\n\nCaterpillars, variation in.\n\nCelosia, variability of.\n\nCereals, variability in.\n\nCesnola, experiments on Mantis by.\n\nChaerocampa, colouring of.\n\nChambers, R., \"The Vestiges of Creation\" by.\n\nChromosomes and Chromomeres.\n\nChun.\n\nCieslar, experiments by.\n\nCircumnutation, Darwin on.\n\nClaus.\n\nCleistogamy.\n\nClerke, Miss A.\n\nClodd, E.\n\nCluer.\n\nClytus arietis.\n\nCoadaptation.\n\nCodrington.\n\nCohen and Peter.\n\nCollingwood.\n\nColobopsis truncata.\n\nColour, E.B. Poulton on The Value in the Struggle for life\nof.--influence and temperature on changes in.--in relation to Sexual\nSelection.\n\nColours, incidental.--warning.\n\nComte, A.\n\nCondorcet.\n\nCope.\n\nCoral reefs, Darwin's work on.\n\nCorrelation of organisms, Darwin's idea of the.\n\nCorrelation of parts.\n\nCorydalis claviculata.\n\nCournot.\n\nCouteur, Col. Le.\n\nCrooks, Sir William.\n\nCruger, on Orchids.\n\nCunningham and Marchand, on the brain.\n\nCurie, M. and Mme.\n\nCuvier.\n\nCycadeoidea dacotensis.\n\nCycads, geological history of.\n\nCystidea, an ancient group.\n\nCytology and heredity.\n\nCytolysis and fertilisation.\n\nCzapek.\n\nDalton's atomic theory.\n\nDana, J.D., on marine faunas.\n\nDanaida chrysippus.\n\nDanaida genutia.\n\nDanaida plexippus.\n\nDante.\n\nDantec, Le,\n\nDarwin, Charles, as an Anthropologist.--on ants.--and the \"Beagle\"\nVoyage.--on the Biology of Flowers.--as a Botanist.--his influence on\nBotany.--and S. Butler.--at Cambridge.--on Cirripedia.--on climbing\nplants.--on colour.--on coral reefs.--on the Descent of Man.--his work\non Drosera.--at Edinburgh.--his influence on Animal Embryology.--on\nGeographical Distribution.--his work on Earthworms.--evolutionist\nauthors referred to in the \"Origin\" by.--and E. Forbes.--on the\ngeological record.--and Geology.--his early love for geology.--his\nconnection with the Geological Society of London.--and Haeckel.--and\nHenslow.--and History.--and Hooker.--and Huxley.--on ice-action.--on\nigneous rocks.--on Lamarck.--on Language.--his Scientific Library.--and\nthe Linnean Society.--and Lyell.--and Malthus.--on Patrick Matthew.--on\nmental evolution.--on Mimicry.--a \"Monistic Philosopher.\"--on the\nmovements of plants.--on Natural Selection.--a \"Naturalist for\nNaturalists.\"--on Paley.\n\nDarwin, Charles, his Pangenesis hypothesis.--on the permanence\nof continents.--his personality.--his influence on\nPhilosophy.--predecessors of.--his views on religion, etc.--his\ninfluence on religious thought.--his influence on the study of\nreligions.--his methods of research.--and Sedgwick.--on Sexual\nSelection.--the first germ of his species theory.--on H.\nSpencer.--causes of his success.--on Variation.--on the \"Vestiges\nof Creation\".--on volcanic islands.--and Wallace.--letter to Wallace\nfrom.--letter to E.B. Wilson from.\n\nDarwin, E., on the colour of animals.--Charles Darwin's reference\nto.--on evolution.\n\nDARWIN, F., on \"Darwin's work on the Movements of Plants\".--on Darwin\nas a botanist.--observations on Earthworms by.--on Lamarckism.--on\nMemory.--on Prichard's \"Anticipations\".--various.\n\nDARWIN, SIR G., on \"The Genesis of Double Stars\".--on the earth's mass.\n\nDarwin, H.\n\nDarwin, W.\n\nDarwinism, Sociology, Evolution and.\n\nDavenport and Cannon, experiments on Daphniae by.\n\nDavid, T.E., his work on Funafuti.\n\nDeath, cause of natural.\n\nDebey, on Cretaceous plants.\n\nDebierne.\n\nDegeneration.\n\nDelage, experiments on parthenogenesis by.\n\nDelbruck.\n\nDemocritus.\n\nDeniker.\n\nDescartes.\n\nDescent, history of doctrine of.\n\n\"Descent of Man\", G. Schwalbe on \"The\".--Darwin on Sexual Selection in\n\"The\".--rejection in Germany of \"The\".\n\nDesmatippus.\n\nDesmoulins, A., on Geographical Distribution.\n\nDetto.\n\nDevelopment, effect of environment on.\n\nDianthus caryophyllus.\n\nDiderot.\n\nDigitalis purpurea.\n\nDimorphism, seasonal.\n\nDismorphia astynome.\n\nDismorphia orise.\n\nDistribution, H. Gadow on Geographical.--Sir W. Thiselton-Dyer on.\n\nDittrick, O.\n\nDixey, F.A., on the scent of Butterflies.\n\nDolichonyx oryzivorus.\n\nDorfmeister.\n\nDown, Darwin at.\n\nDraba verna.\n\nDragomirov.\n\nDriesch, experiments by.--elsewhere.\n\nDrosera, Darwin's work on.\n\nDryopithecus.\n\nDubois, E., on Pithecanthropus.\n\nDuhring.\n\nDuhamel.\n\nDuncan, J.S.\n\nDuncan, P.B.\n\nDuns Scotus.\n\nDuret, C.\n\nDurkheim, on division of labour.\n\nDutrochet.\n\nEchinoderms, ancestry of.\n\nEcology.\n\nEimer.\n\nEkstam.\n\nElephants, geological history of.\n\nElymnias phegea.\n\nE. undularis.\n\nEmbleton, A.L.\n\nEmbryology, A. Sedgwick on the influence of Darwin on.\n\nEmbryology, as a clue to Phylogeny.--the Origin of Species and.\n\nEmpedocles.\n\nEngles.\n\nEnvironment, action of.--Klebs on the influence on plants of.--Loeb on\nexperimental study in relation to.\n\nEohippus.\n\nEpicurus, a poet of Evolution.\n\nEristalis.\n\nErnst.\n\nErnst, A., on the Flora of Krakatau.\n\nEschscholzia californica.\n\nEspinas.\n\nEudendrium racemosum.\n\nEvolution, in relation to Astronomy.--and creation.--conception\nof.--discontinuous.--experimental.--factors of.--fossil plants\nas evidence of.--and language.--of matter, W.C.D. Whetham\non.--mental.--Lloyd Morgan on mental factors in.--Darwinism and\nSocial.--Saltatory.--Herbert Spencer on.--Uniformitarian.--Philosophers\nand modern methods of studying.\n\nExpression of the Emotions.\n\nFabricius, J.C., on geographical distribution.\n\nFarmer, J.B.\n\nFarrer, Lord.\n\nFearnsides, W.G.\n\nFelton, S., on protective resemblance.\n\nFerri.\n\nFerrier, his work on the brain.\n\nFertilisation, experimental work on animal-.\n\nFertilisation of Flowers.\n\nFichte.\n\nField, Admiral A.M.\n\nFischer, experiments on Butterflies by.\n\nFitting.\n\nFlemming, W.\n\nFlourens.\n\nFlowering plants, ancestry of.\n\nFlowers, K. Goebel on the Biology of.\n\nFlowers and Insects.\n\nFlowers, relation of external influences to the production of.\n\nFol, H.\n\nForbes, E.--and C. Darwin.\n\nFord, S.O. and A.C. Seward, on the Araucarieae.\n\nFossil Animals, W.B. Scott on their bearing on evolution.\n\nFossil Plants, D.H. Scott on their bearing on evolution.\n\nFouillee.\n\nFraipont, on skulls from Spy.\n\nFRAZER, J.G., on \"Some Primitive Theories of the Origin of\nMan\".--various.\n\nFruwirth.\n\nFumaria officinalis.\n\nFunafuti, coral atoll of.\n\nFundulus.\n\nF. heteroclitus.\n\nGADOW, H., on \"Geographical Distribution of Animals\".--elsewhere.\n\nGartner, K.F.\n\nGallus bankiva.\n\nGalton, F.\n\nGamble, F.W. and F.W. Keeble.\n\nGasca, La.\n\nGeddes, P.\n\nGeddes, P. and A.W. Thomson.\n\nGegenbauer.\n\nGeikie, Sir A.\n\nGeitonogamy.\n\nGenetics.\n\nGeographical Distribution of Animals.--of Plants.--influence of \"The\nOrigin of Species\" on.--Wallace's contribution to.\n\nGeography of former periods, reconstruction of.\n\nGeology, Darwin and.\n\nGeranium spinosum.\n\nGerm-plasm, continuity of.--Weismann on.\n\nGerminal Selection.\n\nGibbon.\n\nGilbert.\n\nGILES, P., on \"Evolution and the Science of Language\".\n\nGiuffrida-Ruggeri.\n\nGiotto.\n\nGizycki.\n\nGlossopteris Flora.\n\nGmelin.\n\nGodlewski, on hybridisation.\n\nGOEBEL, K., on \"The Biology of Flowers\".--his work on Morphology.\n\nGoethe and Evolution.--on the relation between Man and\nMammals.--elsewhere.\n\nGoldfarb.\n\nGondwana Land.\n\nGoodricke, J.\n\nGore, Dr.\n\nGorjanovic-Kramberger.\n\nGosse, P.H.\n\nGrabau, A.W., on Fusus.\n\nGrand'Eury, F.C., on fossil plants.\n\nGrapta C. album.\n\nGravitation, effect on life-phenomena of.\n\nGray, Asa.\n\nGregoire, V.\n\nGroom, T.T., on heliotropism.\n\nGroos.\n\nGrunbaum, on the brain.\n\nGuignard, L.\n\nGulick.\n\nGuppy, on plant-distribution.\n\nGuyau.\n\nGwynne-Vaughan, D.T., on Osmundaceae.\n\nGymnadenia conopsea.\n\nHaberlandt, G.\n\nHaddon, A.C.\n\nHAECKEL, E., on \"Charles Darwin as an Anthropologist\".--on Colour.--and\nDarwin.--on the Descent of Man.--contributions to Evolution by.\n\nHaeckel, E., on Lamarck.--on Language.--a leader in the Darwinian\ncontroversy.--on Lyell's influence on Darwin.--various.\n\nHacker.\n\nHagedoorn, on hybridisation.\n\nHales, S.\n\nHansen.\n\nHarker, A.\n\nHARRISON, J.E., on \"The Influence of Darwinism on the Study of\nReligions\".\n\nHartmann, von.\n\nHarvey.\n\nHaupt, P., on Language.\n\nHaycraft.\n\nHays, W.M.\n\nHegel.\n\nHeliconius narcaea.\n\nHeliotropism in animals.\n\nHenslow, Rev. J.S. and Darwin.\n\nHensen, Van.\n\nHerbst, his experiments on sea urchins.\n\nHeracleitus.\n\nHerder.\n\nHeredity and Cytology.--Haeckel on.--and Variation.--various.\n\nHering, E., on Memory.\n\nHerschel, J.\n\nHertwig, R.\n\nHertwig, O.\n\nHertz.\n\nHeteromorphosis.\n\nHeterostylism.\n\nHeuser, E.\n\nHewitt.\n\nHeyse's theory of language.\n\nHinde, G.J., his work on Funafuti.\n\nHipparion.\n\nHippolyte cranchii.\n\nHirase.\n\nHistory, Darwin and.\n\nHobbes, T.\n\nHobhouse.\n\nHOFFDING, H., on \"The Influence of the Conception of Evolution on Modern\nPhilosophy\".\n\nHofmeister, W.\n\nHolmes, S.J., on Arthropods.\n\nHolothurians, calcareous bodies in skin of.\n\nHomo heidelbergensis.\n\nHomo neandertalensis.\n\nHomo pampaeus.\n\nHomo primigenius.\n\nHomunculus.\n\nHooker, Sir J.D., and Darwin.--on Distribution of Plants.--on\nFerns.--Letter to the Editor from.\n\nHorner, L.\n\nHorse, Geological history of the.\n\nHuber.\n\nHubert and Mauss.\n\nHubrecht, A.R.W.\n\nHugel, F. von.\n\nHumboldt, A. von.\n\nHumboldt, W. von.\n\nHume.\n\nHutcheson.\n\nHutton.\n\nHuxley, T.H., and Darwin.--and the Duke of Argyll.--on Embryology.--on\nGeographical Distribution.--on Lamarck.--Letter to J.W. Judd from.--on\nLyell.--on Man.--on \"The Origin of Species\".--on Selection.--on\nTeleology.--on transmission of acquired characters.--various.\n\nHybridisation.\n\nHybrids, Sterility of.\n\nHyracodon.\n\nIberis umbellata.\n\nIkeno.\n\nImperfection of the Geological Record.\n\nIngenhousz, on plant physiology.\n\nInheritance of acquired characters.\n\nInsects and Flowers.\n\nInstinct.\n\nInstincts, experimental control of animal.\n\nIpomaea purpurea.\n\nIrish Elk, an example of co-adaptation.\n\nJacobian figures.\n\nJacoby, \"Studies in Selection\" by.\n\nJames, W.\n\nJanczewski.\n\nJeans, J.H.\n\nJennings, H.S., on Paramoecium.\n\nJentsch.\n\nJespersen, Prof., Theory of.\n\nJohannsen, on Species.\n\nJones, Sir William, on Language.\n\nJordan.\n\nJUDD, J.W., on \"Darwin and Geology\".\n\nKallima, protective colouring of.\n\nKallima inachis.\n\nKammerer's experiments on Salamanders.\n\nKant, I.\n\nKeane, on the Primates.\n\nKeeble, F.W. and F.W. Gamble, on Colour-change.\n\nKeith, on Anthropoid Apes.\n\nKellogg, V., on heliotropism.\n\nKepler.\n\nKerguelen Island.\n\nKidd.\n\nKidston, R., on fossil plants.\n\nKillmann, on origin of human races.\n\nKing, Sir George.\n\nKlaatsch, on Ancestry of Man.\n\nKlaatsch and Hauser.\n\nKLEBS, G., on \"The influence of Environment on the forms of plants\".\n\nKniep.\n\nKnies.\n\nKnight, A., experiments on plants by.--on Geotropism.\n\nKnight-Darwin law.\n\nKnuth.\n\nKolliker, his views on Evolution.\n\nKolreuter, J.G.\n\nKohl.\n\nKorschinsky.\n\nKowalevsky, on fossil horses.\n\nKrakatau, Ernst on the Flora of.\n\nKrause, E.\n\nKreft, Dr.\n\nKropotkin.\n\nKupelwieser, on hybridisation.\n\nLagopus hyperboreus.\n\nLamarck, his division of the Animal Kingdom.--Darwin's opinion of.--on\nEvolution.--on Man.--various.\n\nLamarckian principle.\n\nLamb, C.\n\nLamettrie.\n\nLamprecht.\n\nLanessan, J.L. de.\n\nLang.\n\nLange.\n\nLanguage, Darwin on.--Evolution and the Science of.--various.\n\nLankester, Sir E. Ray, on degeneration.--on educability.--on the\ngerm-plasm theory.--elsewhere.\n\nLapouge, Vacher de.\n\nLarmor, J.\n\nLartet, M.E.\n\nLassalle.\n\nLathyrus odoratus.\n\nLavelaye, de.\n\nLawrence, W.\n\nLehmann.\n\nLehmann-Nitsche.\n\nLeibnitz.\n\nLepidium Draba.\n\nLepidoptera, variation in.\n\nLeskien, A., on language.\n\nLessing.\n\nLeucippus.\n\nLevi, E.\n\nLewes, G.H.\n\nLewin, Capt.\n\nLiapounoff.\n\nLiddon, H.P.\n\nLight, effect on organisms of.\n\nLimenitis archippus.--arthemis.\n\nLinnaeus.\n\nLivingstone, on plant-forms.\n\nLlamas, geological history of.\n\nLockyer, Sir N.\n\nLocy, W.A.\n\nLOEB, J., on \"The Experimental Study of the influence of environment on\nAnimals.\n\nLoew, E.\n\nLongstaff, G.B., on the Scents of Butterflies.\n\nLorentz.\n\nLotsy, J.P.\n\nLove, A.E.W.\n\nLovejoy.\n\nLubbock.\n\nLucas, K.\n\nLucretius, a poet of Evolution.\n\nLumholtz, C.\n\nLuteva macrophthalma.\n\nLycorea halia.\n\nLyell, Sir Charles, and Darwin.--the influence of.--on geographical\ndistribution.--on \"The Origin of Species\".--on the permanence of\nOcean-basins.--publication of the \"Principles\" by.--the uniformitarian\nteaching of.\n\nLythrum salicaria.\n\nMacacus, ear of.\n\nMacDougal, on wounding.\n\nMach, E.\n\nMacromytis flexuosa, colour-change in.\n\nMagic and religion.\n\nMahoudeau.\n\nMaillet, de.\n\nMajewski.\n\nMalthus, his influence on Darwin.--various.\n\nMammalia, history of.\n\nMan, Descent of.--J.G. Frazer on some primitive theories of the origin\nof.--mental and moral qualities of animals and.--pre-Darwinian views on\nthe Descent of.--religious views of primitive.--Tertiary flints worked\nby.\n\n\"Man\", G. Schwalbe on Darwin's \"Descent of\".\n\nManouvrier.\n\nMantis religiosa, colour experiments on.\n\nMarett, R.R.\n\nMarkwick.\n\nMarshall, G.A.K.\n\nMarx.\n\nMassart.\n\nMasters, M.\n\nMatonia pectinata.\n\nMatthew, P., and Natural Selection.\n\nMaupertuis.\n\nMaurandia semperflorens.\n\nMauss and Herbert.\n\nMauthner.\n\nMaxwell.\n\nMaxwell, Clerk.\n\nMayer, R.\n\nMechanitis lysimnia.\n\nMeehan, T.\n\nMeldola, R., Letters from Darwin to.\n\nMelinaea ethra.\n\nMendel.\n\nMendeleeff.\n\nMerrifield.\n\nMerz, J.T.\n\nMesembryanthemum truncatum.\n\nMesohippus.\n\nMesopithecus.\n\nMetschnikoff.\n\nMill, J.S.\n\nMimicry.--H.W. Bates on.--F. Muller on.\n\nMimulus luteus.\n\nMiquel, F.W.A.\n\nMobius.\n\nMohl, H. von.\n\nMoltke, on war.\n\nMonachanthus viridis.\n\nMonkeys, fossil.\n\nMontesquieu.\n\nMontgomery, T.H.\n\nMonstrosoties.\n\nMonticelli.\n\nMoore, J.E.S.\n\nMORGAN, C. LLOYD, on \"Mental Factors in Evolution\".--on Organic\nSelection.\n\nMorgan, T.H.\n\nMorse, E.S., on colour.\n\nMorselli.\n\nMortillet.\n\nMoseley.\n\nMottier, M.\n\nMuller, Fritz, \"Fur Darwin\" by.--on Mimicry.\n\nMuller, Fritz.\n\nMuller, J.\n\nMuller, Max, on language.\n\nMurray, A., on geographical distribution.\n\nMurray, G.\n\nMutability.\n\nMutation.\n\nMyanthus barbatus.\n\nMyers, G.W., on Eclipses.\n\nNageli.\n\nNathorst, A.G.\n\nNathusius.\n\nNatural Selection, and adaptation.--Darwin's views on.--Darwin and\nWallace on.--and design.--and educability.--Fossil plants in relation\nto.--and human development.--and Mimicry.--and Mutability.--various.\n\nNaudin.\n\nNeandertal skulls.\n\nNemec.\n\nNeoclytus curvatus.\n\nNeodarwinism.\n\nNeumayr, M.\n\nNewton, A.\n\nNewton, I.\n\nNiebuhr.\n\nNietzsche.\n\nNilsson, on cereals.\n\nNitsche.\n\nNoire.\n\nNoll.\n\nNovicow.\n\nNuclear division.\n\nNussbaum, M.\n\nNuttall, G.H.F.\n\nOccam.\n\nOdin.\n\nOecology, see Ecology.\n\nOenothera biennis.\n\nOenothera gigas.\n\nOenothera Lamarckiana.\n\nOenothera muricata.\n\nOenothera nanella.\n\nOestergren, on Holothurians.\n\nOken, L.\n\nOliver, F.W., on Palaeozoic Seeds.\n\nOnonis minutissima.\n\nOphyrs apifera.\n\nOrchids, Darwin's work on the fertilisation of.\n\nOrganic Selection.\n\n\"Origin of Species\", first draft of the.--geological chapter in the.\n\nOrthogenesis.\n\nOrtmann, A.E.\n\nOsborn, H.F.--\"From the Greeks to Darwin\" by.\n\nOsthoff and Brugmann.\n\nOstwald, W.\n\nOvibos moschatus.\n\nOwen, Sir Richard.\n\nOxford, Ashmolean Museum at.\n\nPackard, A.S.\n\nPalaeontological Record, D.H. Scott on the.--W.B. Scott on the.\n\nPalaeopithecus.\n\nPaley.\n\nPalitzch, G.\n\nPalm.\n\nPangenesis.\n\nPanmixia, Weismann's principle of.\n\nPapilio dardanus.\n\nPapilio meriones.\n\nPapilio merope.\n\nPapilio nireus.\n\nParamoecium, Jennings on.\n\nParker, G.H., on Butterflies.\n\nParkin, J. and E.A.N. Arber, on the origin of Angiosperms.\n\nParthenogenesis, artificial.\n\nPaul, H. and Wundt.\n\nPearson, K.\n\nPeckham, Dr and Mrs, on the Attidae.\n\nPenck.\n\nPenzig.\n\nPeripatus, distribution of.\n\nPeridineae.\n\nPermanence of continents.\n\nPerrier, E.\n\nPerrhybris pyrrha.\n\nPerthes, B. de.\n\nPeter, on sea urchin's eggs.\n\nPetunia violacea.\n\nPfeffer, W.\n\nPfitzner, W.\n\nPflueger.\n\nPhillips.\n\nPhilosophy, influence of the conception of evolution on modern.\n\nPhryniscus nigricans.\n\nPhylogeny, embryology as a clue to.--Palaeontological evidence on.\n\nPhysiology of plants, development of.\n\nPiccard, on Geotropism.\n\nPickering, spectroscopic observations by.\n\nPiranga erythromelas.\n\nPisum sativum.\n\nPithecanthropus.\n\nPitheculites.\n\nPlanema epaea.\n\nPlants, Darwin's work on the movements of.--geographical distribution\nof.--Palaeontological record of fossil.\n\nPlatanthera bifolia.\n\nPlate.\n\nPlato.\n\nPlayfair.\n\nPliopithecus.\n\nPocock, R.I.\n\nPoincare.\n\nPolarity, Vochting on.\n\nPolymorphic species.--variability in cereals.\n\nPolypodium incanum.\n\nPorthesia chrysorrhoea.\n\nPotonie, R.\n\nPouchet, G.\n\nPOULTON, E.B., on \"The Value of Colour in the Struggle for\nLife\".--experiments on Butterflies by.--on J.C. Prichard.--on\nMimicry.--various.\n\nPratt.\n\nPratz, du.\n\nPremutation.\n\nPreuss, K. Th.\n\nPrichard, J.C.\n\nPrimula, heterostylism in.\n\nPrimula acaulis.\n\nPrimula elatior.\n\nPrimula officinalis.\n\nPromeces viridis.\n\nPronuba yuccasella.\n\nProtective resemblance.\n\nProtocetus.\n\nProtohippus.\n\nPsychology.\n\nPteridophytes, history of.\n\nPteridospermeae.\n\nPucheran.\n\nPusey.\n\nQuatrefages, A. de.\n\nQuetelet, statistical investigations by.\n\nRabl, C.\n\nRadio-activity.\n\nRadiolarians.\n\nRaimannia odorata.\n\nRamsay, Sir W. and Soddy.\n\nRanke.\n\nRau, A.\n\nRay, J.\n\nReade, Mellard.\n\nRecapitulation, the theory of.\n\nReduction.\n\nRegeneration.\n\nReid, C.\n\nReinke.\n\nReligion, Darwin's attitude towards.--Darwin's influence on the study\nof.--and Magic.\n\nReligious thought, Darwin's influence on.\n\nRenard, on Darwin's work on volcanic islands.\n\nReproduction, effect of environment on.\n\nReptiles, history of.\n\nReversion.\n\nRhinoceros, the history of the.\n\nRidley, H.N.\n\nRiley, C.V.\n\nRitchie.\n\nRitual.\n\nRoberts, A.\n\nRobertson, T.B.\n\nRobinet.\n\nRolfe, R.A.\n\nRolph.\n\nRomanes, G.J.\n\nRothert.\n\nRoux.\n\nRozwadowski, von.\n\nRuskin.\n\nRutherford, E.\n\nRutot.\n\nSachs, J.\n\nSt Hilaire, E.G. de.\n\nSalamandra atra.\n\nSalamandra maculosa.\n\nSaltatory Evolution, (see also Mutations).\n\nSanders, experiments on Vanessa by.\n\nSaporta, on the Evolution of Angiosperms.\n\nSargant, Ethel, on the Evolution of Angiosperms.\n\nSavigny.\n\nScardafella inca.\n\nScent, in relation to Sexual Selection.\n\nScharff, R.F.\n\nSchelling.\n\nSchlegel.\n\nSchleicher, A., on language.\n\nSchleiden and Schwann, Cell-theory of.\n\nSchmarda, L.K., on geographical distribution.\n\nSchoetensack, on Homo heidelbergensis.\n\nSchreiner, K.E.\n\nSchubler, on cereals.\n\nSchultze, O., experiments on Frogs.\n\nSchur.\n\nSchutt.\n\nSCHWALBE, G., on \"The Descent of Man\".\n\nSclater, P.L., on geographical distribution.\n\nSCOTT, D.H., on \"The Palaeontological Record (Plants)\".--elsewhere.\n\nSCOTT, W.B., on \"The Palaeontological Record (Animals)\".\n\nScrope.\n\nScyllaea.\n\nSechehaye, C.A.\n\nSEDGWICK, A., on \"The Influence of Darwin on Animal Embryology\".\n\nSedgwick, A., Darwin's Geological Expedition with.\n\nSeeck, O.\n\nSeed-plants, origin of.\n\nSegregation.\n\nSelection, artificial.--germinal.\n\nSelection, natural (see Natural Selection).--organic.--sexual.--social\nand natural.--various.\n\nSelenka.\n\nSemnopithecus.\n\nSemon, R.\n\nSemper.\n\nSenebier.\n\nSenecio vulgaris.\n\nSergi.\n\nSeward, A.C.--and S.O. Ford.--and J. Gowan.\n\nSex, recent investigations on.\n\nSharpe, D.\n\nSherrington, C.S.\n\nShirreff, P.\n\nShrewsbury, Darwin's recollections of.\n\nSibbern.\n\nSinapis alba.\n\nSmerinthus ocellata.\n\nSmerinthus populi.\n\nSmerinthus tiliae.\n\nSmith, A.\n\nSmith, W.\n\nSnyder.\n\nSociology, Darwinism and.--History and.\n\nSoddy.\n\nSollas, W.J.\n\nSorley, W.R.\n\nSpecies, Darwin's early work on transmutation of.--geographical\ndistribution and origin of.--immutability of.--influence on\nenvironment on.--Lamarck on.--multiple origin of.--the nature of\na.--polymorphic.--production by physico-chemical means of.--and\nvarieties.--de Vries's work on.\n\nSpencer, H., on evolution.--on Lyell's \"Principles\".--on the nature of\nthe living cell.--on primitive man.--on the theory of Selection.--on\nSociology.\n\nSpencer, H., on the transmission of acquired characters.--on\nWeismann.--various.\n\nSphingidae, variation in.\n\nSpinoza.\n\nSports.\n\nSprengel, C.K.\n\nStability, principle of.\n\nStahl.\n\nStandfuss.\n\nStars, evolution of double.\n\nStellaria media.\n\nStephen, L.\n\nSterility in hybrids.\n\nSterne, C.\n\nStockard, his experiments on fish embryos.\n\nSTRASBURBER, E., on \"The Minute Structure of Cells in relation to\nHeredity\".\n\nStrongylocentrotus franciscanus.\n\nStrongylocentrotus purpuratus.\n\nStruggle for existence.\n\nStrutt, R.J.\n\nStuart, A.\n\nSturdee, F.C.D.\n\nSutterlin, L.\n\nSully.\n\nSutton, A.W.\n\nSutton, W.S.\n\nSvalof, agricultural station of.\n\nSwainson, W.\n\nSynapta, calcareous bodies in skin of.\n\nS. lappa.\n\nSyrphus.\n\nTarde, G.\n\nTeleology and adaptation.\n\nTennant, F.R.\n\nTeratology.\n\nTetraprothomo.\n\nTHISELTON-DYER, SIR WILLIAM, on \"Geographical distribution of\nPlants\".--on Burchell.--on protective resemblance.--elsewhere.\n\nTHOMSON, J.A., on \"Darwin's Predecessors.--elsewhere.--and P. Geddes.\n\nThomson, Sir J.J.\n\nTheology, Darwin and.\n\nTiedemann, F.\n\nTooke, Horne.\n\nTotemism.\n\nTreschow.\n\nTreviranus.\n\nTrifolium pratense quinquefolium.\n\nTrigonias.\n\nTrilobites, phylogeny of.\n\nTschermack.\n\nTurgot.\n\nTurner, Sir W.\n\nTwins, artificial production of.\n\nTylor.\n\nTyndall, W.\n\nTyrrell, G.\n\nUhlenhuth, on blood reactions.\n\nUnderhill, E.\n\nUse and disuse.\n\nVanessa.\n\nVanessa antiope.\n\nVanessa levana.\n\nVanessa polychloros.\n\nVanessa urticae.\n\nVan 't Hoff.\n\nVaranus Salvator.\n\nVariability, Darwin's attention directed to.--W. Bateson on.--and\ncultivation.--causes of.--polymorphic.\n\nVariation, continuous and discontinuous.--Darwin's views as\nan evolutionist, and as a systematist, on.--definite and\nindefinite.--environment and.--and heredity.--as seen in the\nlife-history of an organism.--minute.--mutability and.--in relation to\nspecies.--H. de Vries on.\n\nVarigny, H. de.\n\nVarro, on language.\n\nVeronica chamaedrys.\n\nVerworn.\n\n\"Vestiges of Creation\", Darwin on \"The\".\n\nVierkandt.\n\nVilmorin, L. de.\n\nVirchow, his opposition to Darwin.\n\nVirchow, on the transmission of acquired characters.\n\nVochting.\n\nVogt, C.\n\nVoltaire.\n\nVolvox.\n\nVRIES, H. de, on \"Variation\"--the Mutation theory of.\n\nWAGGETT, REV. P.N., on \"The Influence of Darwin upon religious thought\".\n\nWagner.\n\nWaldeyer, W.\n\nWallace, A.R., on Malayan Butterflies.--on Colour.--and Darwin.--on\nthe Descent of Man.--on distribution.--on Malthus.--on Natural\nSelection.--on the permanence of continents.--on social reforms.--on\nSexual Selection.\n\nWaller, A.D.\n\nWalton.\n\nWatson, H.C.\n\nWatson, S.\n\nWatt, J., and Natural Selection.\n\nWatts, W.W.\n\nWedgwood, L.\n\nWeir, J.J.\n\nWEISMANN, A., on \"The Selection Theory\".--on Amphimixis.\n\nWeismann, A., his germ-plasm theory.--on ontogeny.--and Prichard.--and\nSpencer.--on the transmission of acquired characters.--various.\n\nWells, W.C., and Natural Selection.\n\nWeston, S., on language.\n\nWHETHAM, W.C.D., on \"The Evolution of Matter\".\n\nWhewell.\n\nWhite, G.\n\nWichmann.\n\nWieland, G.R., on fossil Cycads.\n\nWiesner, on Darwin's work on plant movements.\n\nWilliams, C.M.\n\nWilliamson, W.C.\n\nWilson, E.B., on cytology.--letter from Darwin to.\n\nWolf.\n\nWollaston's, T.V. \"Variation of Species\".\n\nWoltmann.\n\nWoolner.\n\nWundt, on language.\n\nXylina vetusta.\n\nYucca, fertilisation of.\n\nZeiller, R., on Fossil Plants.\n\nZeller, E.\n\nZimmermann, E.A.W.\n\nZittel, on palaeontological research.\n\n\"Zoonomia\", Erasmus Darwin's.","title":"Darwin and Modern Science","tradition":"philosophy-ethics","translated_text":null,"word_count":268782}