{"collection":"philosophy-ethics","full_text_available":true,"graph_url":"https://unchartedknowledge.5gfusion.net/v2/api/page/gutenberg_40472/graph","html_url":"https://unchartedknowledge.5gfusion.net/v2/page/gutenberg_40472","id":"gutenberg_40472","license":"Public Domain (US)","rights_basis":"gutenberg_metadata_copyright_false","source":"gutenberg","source_url":"https://www.gutenberg.org/ebooks/40472","summary":null,"tags":["Category: History - Modern (1750+)","Category: Philosophy & Ethics","Category: Science - Biology","Category: Science - Earth/Agricultural/Farming","Evolution","Heredity","Human beings -- Origin"],"text":"+------------------------------------------------------------------+\n  | Transcriber\u2019s note:                                              |\n  |                                                                  |\n  | This book was published in two volumes, of which this is the     |\n  | first. The second volume was released as Project Gutenberg ebook |\n  | #40473, available at https://www.gutenberg.org/ebooks/40473       |\n  |                                                                  |\n  | Numbers enclosed in square brackets, e.g. [1], relate to         |\n  | footnotes, which have been placed at the end of the text.        |\n  | Numbers enclosed in parentheses, e.g. (1), relate to works       |\n  | referred to in the text and listed at the end of volume II.      |\n  |                                                                  |\n  | In the text versions of these two volumes, words in _italics_    |\n  | are enclosed in underscores, +bold+ words are enclosed in plus   |\n  | signs, and words in =Gothic script= are enclosed in equal signs. |\n  | Curly brackets are used to represent subscripts, e.g. k{1}.      |\n  +------------------------------------------------------------------+\n\n\n\n\n  THE HISTORY OF CREATION.\n\n\n\n\n[Illustration: Development of a Calcareous Sponge (Olynthus).]\n\n\n\n\n  THE\n  HISTORY OF CREATION:\n\n  _OR THE DEVELOPMENT OF THE EARTH AND ITS\n  INHABITANTS BY THE ACTION OF NATURAL CAUSES._\n\n  A POPULAR EXPOSITION OF\n  THE DOCTRINE OF EVOLUTION IN GENERAL, AND OF THAT OF\n  DARWIN, GOETHE, AND LAMARCK IN PARTICULAR.\n\n  FROM THE GERMAN OF\n  ERNST HAECKEL,\n  PROFESSOR IN THE UNIVERSITY OF JENA.\n\n  THE TRANSLATION REVISED BY\n  E. RAY LANKESTER, M.A., FELLOW OF EXETER COLLEGE, OXFORD.\n\n  _IN TWO VOLUMES._\n  VOL. I.\n\n  NEW YORK:\n  D. APPLETON AND COMPANY,\n  1, 3, AND 5 BOND STREET.\n  1880.\n\n\n\n\n                        A sense sublime\n  Of something far more deeply interfused,\n  Whose dwelling is the light of setting suns,\n  And the round ocean, and the living air,\n  And the blue sky, and in the mind of man;\n  A motion and a spirit that impels\n  All thinking things, all objects of all thought,\n  And rolls through all things.\n\n  In all things, in all natures, in the stars\n  Of azure heaven, the unenduring clouds,\n  In flower and tree, in every pebbly stone\n  That paves the brooks, the stationary rocks,\n  The moving waters and the invisible air.\n\n                                   WORDSWORTH.\n\n\n\n\nCONTENTS OF VOL. I.\n\n\n  CHAPTER I.\n\n  NATURE AND IMPORTANCE OF THE DOCTRINE OF FILIATION,\n  OR DESCENT-THEORY.\n                                                                    PAGE\n  General Importance and Essential Nature of the Theory of\n  Descent as reformed by Darwin.\u2014Its Special Importance to\n  Biology (Zoology and Botany).\u2014Its Special Importance to\n  the History of the Natural Development of the Human\n  Race.\u2014The Theory of Descent as the Non-Miraculous History\n  of Creation.\u2014Idea of Creation.\u2014Knowledge and\n  Belief.\u2014History of Creation and History of\n  Development.\u2014The Connection between the History of\n  Individual and Pal\u00e6ontological Development.\u2014The Theory of\n  Purposelessness, or the Science of Rudimentary\n  Organs.\u2014Useless and Superfluous Arrangements in\n  Organisms.\u2014Contrast between the two entirely Opposed\n  Views of Nature: the Monistic (mechanical, causal) and the\n  Dualistic (teleological, vital).\u2014Proof of the former by\n  the Theory of Descent.\u2014Unity of Organic and Inorganic\n  Nature, and the Identity of the Active Causes in\n  both.\u2014The Importance of the Theory of Descent to the\n  Monistic Conception of all Nature                                    1\n\n\n  CHAPTER II.\n\n  SCIENTIFIC JUSTIFICATION OF THE THEORY OF DESCENT.\n  HISTORY OF CREATION ACCORDING TO LINN\u00c6US.\n\n  The Theory of Descent, or Doctrine of Filiation, as the\n  Monistic Explanation of Organic Natural Phenomena.\u2014Its\n  Comparison with Newton\u2019s Theory of Gravitation.\u2014Limits of\n  Scientific Explanation and of Human Knowledge in\n  general.\u2014All Knowledge founded originally on Sensuous\n  Experience, _\u00e0 posteriori_.\u2014Transition of _\u00e0 posteriori_\n  knowledge, by inheritance, into _\u00e0 priori_\n  knowledge.\u2014Contrast between the Supernatural Hypotheses\n  of the Creation according to Linn\u00e6us, Cuvier, Agassiz,\n  and the Natural Theories of Development according to\n  Lamarck, Goethe, and Darwin.\u2014Connection of the former\n  with the Monistic (mechanical), of the latter with the\n  Dualistic Conception of the Universe.\u2014Monism and\n  Materialism.\u2014Scientific and Moral Materialism.\u2014The\n  History of Creation according to Moses.\u2014Linn\u00e6us as the\n  Founder of the Systematic Description of Nature and\n  Distinction of Species.\u2014Linn\u00e6us\u2019 Classification and\n  Binary Nomenclature.\u2014Meaning of Linn\u00e6us\u2019 Idea of\n  Species.\u2014His History of Creation.\u2014Linn\u00e6us\u2019 view of the\n  Origin of Species                                                   24\n\n\n  CHAPTER III.\n\n  THE HISTORY OF CREATION ACCORDING TO CUVIER\n  AND AGASSIZ.\n\n  General Theoretical Meaning of the Idea of\n  Species.\u2014Distinction between the Theoretical and\n  Practical Definition of the Idea of Species.\u2014Cuvier\u2019s\n  Definition of Species.\u2014Merits of Cuvier as the Founder of\n  Comparative Anatomy.\u2014Distinction of the Four Principal\n  Forms (types or branches) of the Animal Kingdom, by Cuvier\n  and B\u00e4r.\u2014Cuvier\u2019s Services to Pal\u00e6ontology.\u2014His\n  Hypothesis of the Revolutions of our Globe, and the Epochs\n  of Creation separated by them.\u2014Unknown Supernatural\n  Causes of the Revolutions, and the subsequent New\n  Creations.\u2014Agassiz\u2019s Teleological System of Nature.\u2014His\n  Conception of the Plan of Creation, and its six Categories\n  (groups in classification).\u2014Agassiz\u2019s Views of the\n  Creation of Species.\u2014Rude Conception of the Creator as a\n  man-like being in Agassiz\u2019s Hypothesis of Creation.\u2014Its\n  internal Inconsistency and Contradictions with the\n  important Pal\u00e6ontological Laws discovered by Agassiz                47\n\n\n  CHAPTER IV.\n\n  THEORY OF DEVELOPMENT ACCORDING TO GOETHE\n  AND OKEN.\n\n  Scientific Insufficiency of all Conceptions of a Creation\n  of Individual Species.\u2014Necessity of the Counter Theories\n  of Development.\u2014Historical Survey of the most Important\n  Theories of Development.\u2014Aristotle.\u2014His Doctrine of\n  Spontaneous Generation.\u2014The Meaning of\n  Nature-philosophy.\u2014Goethe.\u2014His Merits as a\n  Naturalist.\u2014His Metamorphosis of Plants.\u2014His Vertebral\n  Theory of the Skull.\u2014His Discovery of the Mid Jawbone in\n  Man.\u2014Goethe\u2019s Interest in the Dispute between Cuvier and\n  Geoffroy St. Hilaire.\u2014Goethe\u2019s Discovery of the two\n  Organic Formative Principles, of the Conservative\n  Principle of Specification (by Inheritance), and of the\n  Progressive Principle of Transformation (by\n  Adaptation).\u2014Goethe\u2019s Views of the Common Descent of all\n  Vertebrate Animals, including Man.\u2014Theory of Development\n  according to Gottfried Reinhold Treviranus.\u2014His Monistic\n  Conception of Nature.\u2014Oken.\u2014His\n  Nature-philosophy.\u2014Oken\u2019s Theory of Protoplasm.\u2014Oken\u2019s\n  Theory of Infusoria (Cell Theory).\u2014Oken\u2019s Theory of\n  Development                                                         72\n\n\n  CHAPTER V.\n\n  THEORY OF DEVELOPMENT ACCORDING TO KANT AND\n  LAMARCK.\n\n  Kant\u2019s Dualistic Biology.\u2014His Conception of the Origin of\n  Inorganic Nature by Mechanical Causes, of Organic Nature\n  by Causes acting for a Definite Purpose.\u2014Contradiction of\n  this Conception with his leaning towards the Theory of\n  Descent.\u2014Kant\u2019s Genealogical Theory of Development.\u2014Its\n  Limitation by his Teleology.\u2014Comparison of Genealogical\n  Biology with Comparative Philology.\u2014Views in favour of\n  the Theory of Descent entertained by Leopold Buch, B\u00e4r,\n  Schleiden, Unger, Schaafhausen, Victor Carus,\n  B\u00fcchner.\u2014French Nature-philosophy.\u2014Lamarck\u2019s Philosophic\n  Zoologique.\u2014Lamarck\u2019s Monistic (mechanical) System of\n  Nature.\u2014His Views of the Interaction of the two Organic\n  Formative Tendencies of Inheritance and\n  Adaptation.\u2014Lamarck\u2019s Conception of Man\u2019s Development\n  from Ape-like Mammals.\u2014Geoffroy St. Hilaire\u2019s, Naudin\u2019s,\n  and Lecoq\u2019s Defence of the Theory of Descent.\u2014English\n  Nature-philosophy.\u2014Views in favour of the Theory of\n  Descent entertained by Erasmus Darwin, W. Herbert, Grant,\n  Freke, Herbert Spencer, Hooker, Huxley.\u2014The Double Merit\n  of Charles Darwin                                                  100\n\n\n  CHAPTER VI.\n\n  THEORY OF DEVELOPMENT ACCORDING TO LYELL\n  AND DARWIN.\n\n  Charles Lyell\u2019s Principles of Geology.\u2014His Natural\n  History of the Earth\u2019s Development.\u2014Origin of the\n  Greatest Effects through the Multiplication of the\n  Smallest Causes.\u2014Unlimited Extent of Geological\n  Periods.\u2014Lyell\u2019s Refutation of Cuvier\u2019s History of\n  Creation.\u2014The Establishment of the Uninterrupted\n  Connection of Historical Development by Lyell and\n  Darwin.\u2014Biographical Notice of Charles Darwin.\u2014His\n  Scientific Works.\u2014His Theory of Coral\n  Reefs.\u2014Development of the Theory of Selection.\u2014A Letter\n  of Darwin\u2019s.\u2014The Contemporaneous Appearance of Darwin\u2019s\n  and Alfred Wallace\u2019s Theory of Selection.\u2014Darwin\u2019s Study\n  of Domestic Animals and Cultivated Plants.\u2014Andreas\n  Wagner\u2019s Notions as to the Special Creation of Cultivated\n  Organisms for the good of Man.\u2014The Tree of Knowledge in\n  Paradise.\u2014Comparison between Wild and Cultivated\n  Organisms.\u2014Darwin\u2019s Study of Domestic\n  Pigeons.\u2014Importance of Pigeon Breeding.\u2014Common Descent\n  of all Races of Pigeons                                            125\n\n\n  CHAPTER VII.\n\n  THE THEORY OF SELECTION (DARWINISM).\n\n  Darwinism (Theory of Selection) and Lamarckism (Theory of\n  Descent).\u2014The Process of Artificial Breeding.\u2014Selection\n  of the Different Individuals for After-breeding.\u2014The\n  Active Causes of Transmutation.\u2014Change connected with\n  Food and Transmission by Inheritance connected with\n  Propagation.\u2014Mechanical Nature of these Two Physiological\n  Functions.\u2014The Process of Natural Breeding: Selection in\n  the Struggle for Existence.\u2014Malthus\u2019 Theory of\n  Population.\u2014The Proportion between the Numbers of\n  Potential and Actual Individuals of every Species of\n  Organisms.\u2014General Struggle for Existence, or Competition\n  to attain the Necessaries of Life.\u2014Transforming Force of\n  the Struggle for Existence.\u2014Comparison of Natural and\n  Artificial Breeding.\u2014Selection in the Life of\n  Man.\u2014Military and Medical Selection                                149\n\n\n  CHAPTER VIII.\n\n  TRANSMISSION BY INHERITANCE AND PROPAGATION.\n\n  Universality of Inheritance and Transmission by\n  Inheritance.\u2014Special Evidences of the same.\u2014Human Beings\n  with four, six, or seven Fingers and Toes.\u2014Porcupine\n  Men.\u2014Transmission of Diseases, especially Diseases of the\n  Mind.\u2014Original Sin.\u2014Hereditary Monarchies.\u2014Hereditary\n  Aristocracy.\u2014Hereditary Talents and Mental\n  Qualities.\u2014Material Causes of Transmission by\n  Inheritance.\u2014Connection between Transmission by\n  Inheritance and Propagation.\u2014Spontaneous Generation and\n  Propagation.\u2014Non-sexual or Monogonous\n  Propagation.\u2014Propagation by Self-Division.\u2014Monera and\n  Am\u0153ba.\u2014Propagation by the formation of Buds, by the\n  formation of Germ-Buds, by the formation of\n  Germ-Cells.\u2014Sexual or Amphigonous Propagation.\u2014Formation\n  of Hermaphrodites.\u2014Distinction of Sexes, or\n  Gonochorism.\u2014Virginal Breeding, or\n  Parthenogenesis.\u2014Material Transmission of Peculiarities\n  of both Parents to the Child by Sexual\n  Propagation.\u2014Difference between Transmission by\n  Inheritance in Sexual and in Asexual Propagation                   175\n\n\n  CHAPTER IX.\n\n  LAWS OF TRANSMISSION BY INHERITANCE. ADAPTATION AND\n  NUTRITION.\n\n  Distinction between Conservative and Progressive\n  Transmission by Inheritance.\u2014Laws of Conservative\n  Transmission: Transmission of Inherited\n  Characters.\u2014Uninterrupted or Continuous\n  Transmission.\u2014Interrupted or Latent\n  Transmission.\u2014Alternation of\n  Generations.\u2014Relapse.\u2014Degeneracy.\u2014Sexual\n  Transmission.\u2014Secondary Sexual Characters.\u2014Mixed or\n  Amphigonous Transmission.\u2014Hybrids.\u2014Abridged or\n  Simplified Transmission.\u2014Laws of Progressive Inheritance:\n  Transmission of Acquired Characters.\u2014Adapted or Acquired\n  Transmission.\u2014Fixed or Established\n  Transmission.\u2014Homochronous Transmission (Identity in\n  Epoch).\u2014Homotopic Transmission (Identity in\n  Part).\u2014Adaptation and Mutability.\u2014Connection between\n  Adaptation and Nutrition.\u2014Distinction between Indirect\n  and Direct Adaptation                                              203\n\n\n  CHAPTER X.\n\n  LAWS OF ADAPTATION.\n\n  Laws of Indirect or Potential Adaptation.\u2014Individual\n  Adaptation.\u2014Monstrous or Sudden Adaptation.\u2014Sexual\n  Adaptation.\u2014Laws of Direct or Actual\n  Adaptation.\u2014Universal Adaptation.\u2014Cumulative\n  Adaptation.\u2014Cumulative Influence of External Conditions\n  of Existence and Cumulative Counter-Influence of the\n  Organism.\u2014Free Will.\u2014Use and Non-use of\n  Organs.\u2014Practice and Habit.\u2014Correlative\n  Adaptation.\u2014Correlation of Development.\u2014Correlation of\n  Organs.\u2014Explanation of Indirect or Potential Adaptation\n  by the Correlation of the Sexual Organs and of the other\n  parts of the Body.\u2014Divergent Adaptation.\u2014Unlimited or\n  Infinite Adaptation                                                227\n\n\n  CHAPTER XI.\n\n  NATURAL SELECTION BY THE STRUGGLE FOR EXISTENCE. DIVISION\n  OF LABOUR AND PROGRESS.\n\n  Interaction of the two Organic Formative Causes,\n  Inheritance and Adaptation.\u2014Natural and Artificial\n  Selection.\u2014Struggle for Existence, or Competition for the\n  Necessaries of Life.\u2014Disproportion between the Number of\n  Possible or Potential, and the Number of Real or Actual\n  Individuals.\u2014Complicated Correlations of all Neighbouring\n  Organisms.\u2014Mode of Action in Natural\n  Selection.\u2014Homochromic Selection as the Cause of\n  Sympathetic Colourings.\u2014Sexual Selection as the Cause of\n  the Secondary Sexual Characters.\u2014Law of Separation or\n  Division of Labour (Polymorphism, Differentiation,\n  Divergence of Characters).\u2014Transition of Varieties into\n  Species.\u2014Idea of Species.\u2014Hybridism.\u2014Law of Progress or\n  Perfecting (Progresses, Teleosis)                                  252\n\n\n  CHAPTER XII.\n\n  LAWS OF DEVELOPMENT OF ORGANIC TRIBES AND OF INDIVIDUALS.\n  PHYLOGENY AND ONTOGENY.\n\n  Laws of the Development of Mankind: Differentiation and\n  Perfecting.\u2014Mechanical Cause of these two Fundamental\n  Laws.\u2014Progress without Differentiation, and\n  Differentiation without Progress.\u2014Origin of Rudimentary\n  Organs by Non-use and Discontinuance of\n  Habit.\u2014Ontogenesis, or Individual Development of\n  Organisms.\u2014Its General Importance.\u2014Ontogeny, or the\n  Individual History of Development of Vertebrate Animals,\n  including Man.\u2014The Fructification of the Egg.\u2014Formation\n  of the Three Germ Layers.\u2014History of the Development of\n  the Central Nervous System, of the Extremities, of the\n  Branchial Arches, and of the Tail of Vertebrate\n  Animals.\u2014Causal Connection and Parallelism of Ontogenesis\n  and Phylogenesis, that is, of the Development of\n  Individuals and Tribes.\u2014Causal Connection of the\n  Parallelism of Phylogenesis and of Systematic\n  Development.\u2014Parallelism of the three Organic Series of\n  Development                                                        280\n\n\n  CHAPTER XIII.\n\n  THEORY OF THE DEVELOPMENT OF THE UNIVERSE AND OF THE\n  EARTH. SPONTANEOUS GENERATION. THE CARBON THEORY. THE\n  PLASTID THEORY.\n\n  History of the Development of the Earth.\u2014Kant\u2019s Theory of\n  the Development of the Universe, or the Cosmological Gas\n  Theory.\u2014Development of Suns, Planets, and Moons.\u2014First\n  Origin of Water.\u2014Comparison of Organisms and\n  Anorgana.\u2014Organic and Inorganic Substances.\u2014Degrees of\n  Density, or Conditions of Aggregation.\u2014Albuminous\n  Combinations of Carbon.\u2014Organic and Inorganic\n  Forms.\u2014Crystals and Formless Organisms without\n  Organs.Stereometrical Fundamental Forms of Crystals and\n  of Organisms.\u2014Organic and Inorganic Forces.\u2014Vital\n  Force.\u2014Growth and Adaptation in Crystals and in\n  Organisms.\u2014Formative Tendencies of Crystals.\u2014Unity of\n  Organic and Inorganic Nature.\u2014Spontaneous Generation, or\n  Archigony.\u2014Autogony and Plasmogony.\u2014Origin of Monera by\n  Spontaneous Generation.\u2014Origin of Cells from Monera.\u2014The\n  Cell Theory.\u2014The Plastid Theory.\u2014Plastids, or\n  Structural-Units.\u2014Cytods and Cells.\u2014Four Different Kinds\n  of Plastids                                                        316\n\n\n  CHAPTER XIV.\n\n  MIGRATION AND DISTRIBUTION OF ORGANISMS. CHOROLOGY AND THE\n  ICE-PERIOD OF THE EARTH.\n\n  Chorological Facts and Causes.\u2014Origin of most Species in\n  one Single Locality.\u2014\u201cCentres of Creation.\u201d\u2014Distribution\n  by Migration.\u2014Active and Passive Migrations of Animals\n  and Plants.\u2014Means of Transport.\u2014Transport of Germs by\n  Water and by Wind.\u2014Continual Change of the Area of\n  Distribution by Elevations and Depressions of the\n  Ground.\u2014Chorological Importance of Geological\n  Processes.\u2014Influence of the Change of Climate.\u2014Ice or\n  Glacial Period.\u2014Its Importance to Chorology.\u2014Importance\n  of Migrations for the Origin of New Species.\u2014Isolation of\n  Colonists.\u2014Wagner\u2019s Law of Migration.\u2014Connection between\n  the Theory of Migration and the Theory of\n  Selection.\u2014Agreement of its Results with the Theory of\n  Descent                                                            350\n\n\n\n\nLIST OF ILLUSTRATIONS.\n\n\n  PLATES.\n                                                                    PAGE\n\n  Development of a Calcareous Sponge (Olynthus)           _Frontispiece_\n\n  I.\u2014Life History of a Simplest Organism              _To face page_ 184\n\n  II., III.\u2014Germs or Embryos of Four Vertebrates               \u201d     306\n\n\n  FIGURES.\n\n  1.\u2014Propagation of Moneron                                          186\n\n  2.\u2014Propagation of Am\u0153ba                                            188\n\n  3.\u2014Egg of Mammal                                                   189\n\n  4.\u2014First Development of Mammal\u2019s Egg                               190\n\n  5.\u2014The Human Egg Enlarged                                          297\n\n  6.\u2014Development of Mammal\u2019s Egg                                     299\n\n  7.\u2014Embryo of a Mammal or Bird                                      304\n\n\n\n\nAUTHOR\u2019S PREFACE TO THE ENGLISH EDITION.\n\n\nI am desirous of prefacing the English edition of the \u201cHistory of\nCreation\u201d with a few remarks which may serve to explain the origin and\nobject of this book. In the year 1866 I published, under the title\n\u201cGenerelle Morphologie,\u201d a somewhat comprehensive work, which\nconstituted the first attempt to apply the general doctrine of\ndevelopment to the whole range of organic morphology (Anatomy and\nBiogenesis), and thus to make use of the vast march onwards which the\ngenius of Charles Darwin has effected in all biological science by his\nreform of the Descent Theory and its establishment through the doctrine\nof selection. At the same time, in the \u201cGenerelle Morphologie,\u201d the\nfirst attempt was made to introduce the Descent Theory into the\nsystematic classification of animals and plants, and to found a \u201cnatural\nsystem\u201d on the basis of genealogy; that is, to construct hypothetical\npedigrees for the various species of organisms.\n\nThe \u201cGenerelle Morphologie\u201d found but few readers, for which the\nvoluminous and unpopular style of treatment, and its too extensive Greek\nterminology, may be chiefly to blame. But a proportionately large\nmeasure of approval has met the \u201cNat\u00fcrliche Sch\u00f6pfungsgeschichte\u201d in\nGermany. This book took its origin in the shorthand notes of a course of\nlectures which treated, before a mixed audience and in a popular form,\nthe most important topics discussed in the \u201cGenerelle Morphologie.\u201d The\nnotes were subsequently revised, and received considerable additions.\nThe book appeared first in 1868, its fourth edition in 1873, and has\nbeen translated into several languages. I hope that it may also find\nsympathy in the fatherland of Darwin, the more so since it contains\nspecial morphological evidence in favour of many of the important\ndoctrines with which this greatest naturalist of our century has\nenriched science. Proud as England may be to be called the fatherland of\nNewton, who, with his law of gravitation, brought inorganic nature under\nthe dominion of natural laws of cause and effect, yet may she with even\ngreater pride reckon Charles Darwin among her sons\u2014he who solved the\nyet harder problem of bringing the complicated phenomena of organic\nnature under the sway of the same natural laws.\n\nThe reproach which is now oftenest made against the Descent Theory is\nthat it is not securely founded, not sufficiently proven. Not only its\ndistinct opponents maintain that there is a want of satisfactory proofs,\nbut even faint-hearted and wavering adherents declare that Darwin\u2019s\nhypothesis is still wanting fundamental proof. Neither the former nor\nthe latter estimate rightly the immeasurable weight which the great\nseries of phenomena of comparative anatomy and ontogeny, pal\u00e6ontology\nand taxonomy, chorology and \u0153cology, cast into the scale in favour of\nthe doctrine of filiation. Darwin\u2019s Theory of Selection, which\ncompletely explains the origin of species through the combined action of\nInheritance and Adaptation in the struggle for existence, also appears\nto these persons not sufficient. They demand, over and above, that the\ndescent of species from common ancestral forms shall be proved in a\nparticular case; that, in contradistinction to the _synthetic_ proofs\nadduced for the Descent Theory, the _analytic_ proof of the genealogical\ncontinuity of the several species shall be brought forward.\n\nThis \u201canalytical solution of the problem of the origin of species\u201d I\nhave myself endeavoured to afford in my recently published \u201cMonograph of\nthe Calcareous Sponges.\u201d For five consecutive years I have investigated\nthis small but highly instructive group of animals in all its forms in\nthe most careful manner, and I venture to maintain that the monograph,\nwhich is the result of those studies, is the most complete and accurate\nmorphological analysis of an entire organic group which has up to this\ntime been made. Provided with the whole of the material for study as yet\nbrought together, and assisted by numerous contributions from all parts\nof the world, I was able to work over the whole group of organic forms\nknown as the Calcareous Sponges in that greatest possible degree of\nfulness which appeared indispensable for the proof of the common origin\nof its species. This particular animal group is especially fitted for\nthe analytical solution of the species problem, because it presents\nexceedingly simple conditions of organisation, because in it the\nmorphological conditions possess a greatly superior, and the\nphysiological conditions an inferior, import, and because all species of\nCalcispongi\u00e6 are remarkable for the fluidity and plasticity of their\nform. With a view to these facts, I made two journeys to the sea-coast\n(1869 to Norway, 1871 to Dalmatia), in order to study as large a number\nof individuals as possible in their natural circumstances, and to\ncollect specimens for comparison. Of many species, I compared several\nhundred individuals in the most careful way. I examined with the\nmicroscope and measured in the most accurate manner the details of form\nof all the species. As the final result of these exhaustive and almost\nendless examinations and measurements it appeared that \u201cgood species,\u201d\nin the ordinary dogmatic sense of the systematists, have no existence at\nall among the Calcareous Sponges; that the most different forms are\nconnected one with another by numberless gradational transition forms;\nand that all the different species of Calcareous Sponges are derived\nfrom a single exceedingly simple ancestral form, the Olynthus. A drawing\nof the Olynthus and its earliest stages of development (observe\nespecially the highly important Gastrula) is given in the frontispiece\nof the present edition. Illustrations of the various structural details\nwhich establish the derivation of all Calcareous Sponges from the\nOlynthus, are given in the atlas of sixty plates which accompanies my\nmonograph of the group. In the gastrula, moreover, is now also found the\ncommon ancestral form from which all the tribes of animals (the lowest\ngroup, that of the protozoa, alone being excepted) can without\ndifficulty be derived. It is one of the most ancient and important\nancestors of the human race!\n\nIf we take for the limitation of genus and species an average standard,\nderived from the actual practice of systematists, and apply this to the\nwhole of the Calcareous Sponges at present known, we can distinguish\nabout twenty-one genera, with one hundred and eleven species (as I have\ndone in the second volume of the Monograph). I have, however, shown that\nwe may draw up, in addition to this, another systematic arrangement\n(more nearly agreeing with the arrangement of the Calcispongi\u00e6 hitherto\nin vogue) which gives thirty-nine genera and two hundred and eighty-nine\nspecies. A systematist who gives a more limited extension to the \u201cideal\nspecies\u201d might arrange the same series of forms in forty-three genera\nand three hundred and eighty-one species, or even in one hundred and\nthirteen genera and five hundred and ninety species; another systematist\non the other hand, who takes a wider limit for the \u201cabstract species,\u201d\nwould use in arranging the same series of forms only three genera, with\ntwenty-one species, or might even satisfy himself with one genus and\nseven species. The delimitation of species and genera appears to be so\narbitrary a matter, on account of endless varieties and transitional\nforms in this group, that their number is entirely left to the\nsubjective taste of the individual systematist. In truth, from the point\nof view of the theory of descent, it appears altogether an unimportant\nquestion as to whether we give a wider or a narrower signification to\nallied groups of forms\u2014whether we choose, that is to say, to call them\ngenera or species, varieties or sub-species. The main fact remains\nundeniable, viz., the common origin of all the species from one\nancestral form. The many-shaped Calcareous Sponges furnish, in the very\nremarkable conditions of their varieties of aggregation (metrocormy), a\nbody of evidence in favour of this view which could hardly be more\nconvincing. Not unfrequently the case occurs of several different forms\ngrowing out from a single \u201cstock\u201d or \u201ccormus\u201d\u2014forms which until now\nhave been regarded by systematists, not only as belonging to different\nspecies, but even to different genera. Fig. 10 in the frontispiece\nrepresents such a composite stock. This solid and tangible piece of\nevidence in favour of the common descent of different species ought, one\nwould think, to satisfy the most determined sceptic!\n\nIn point of fact, I have a right to expect of my opponents that they\nshall carefully consider the \u201cexact empirical proof\u201d here brought\nforward for them, as they have so eagerly demanded. The opponents of the\ndoctrine of filiation, who have too little power of weighing evidence,\nor possess too little knowledge to appreciate the overpowering weight of\nproof afforded by the synthetical argument (comparative anatomy,\nontogeny, taxonomy, etc.), may yet be able to follow me along the path\nof analytical proof, and attempt to upset the conclusion as to the\ncommon origin of all species of all Calcareous Sponges which I have\ngiven in my Monograph. I must, however, repeat that this conclusion is\nbased on the most minute investigation of an extraordinarily rich mass\nof material,\u2014that it is securely established by thousands of the most\ncareful microscopical observations, measurements, and comparisons of\nevery single part, and that thousands of collected microscopic\npreparations render, at any moment, the most searching criticism of my\nresults confirmatory of their correctness. One may hope, then, that\nopponents will endeavour to confront me on the ground of this \u201cexact\nempiricism,\u201d instead of trying to damn my \u201cnature-philosophical\nspeculations.\u201d One may hope that they will endeavour to bring forward\nsome evidence to show that the latter do not follow as the legitimate\nconsequences of the former. May they, however, spare me the\nempty\u2014though by even respectable naturalists oft-repeated\u2014phrase, that\nthe monistic nature-philosophy, as expounded in the \u201cGeneral\nMorphology,\u201d and in the \u201cHistory of Creation,\u201d is wanting in actual\nproofs. The proofs are there. Of course those who turn their eyes away\nfrom them will not see them. Precisely that \u201cexact\u201d form of analytical\nproof which the opponents of the descent theory demand is to be found,\nby anybody who wishes to find it, in the \u201cMonograph of the Calcareous\nSponges.\u201d\n\n\n  ERNST HEINRICH HAECKEL.\n\n  _Jena, June 24th, 1873._\n\n\n\n\nNOTE.\n\n\nFeeling sure that such a book as Professor Haeckel\u2019s\n\u201cSch\u00f6pfungsgeschichte\u201d would do a great deal of good, if placed in the\nhands of the English reading public, and of commencing students of\nNatural History, I gladly undertook to revise for the publishers the\npresent translation, which was made by a young lady. I have not\nattempted to escape a difficulty by ignoring the German names made use\nof by Professor Haeckel for classes, orders, and genera, but have\nadopted English equivalents. I do not submit these names as a maturely\nconsidered English nomenclature, they appear here simply as necessary\nparts of a close rendering of the German work. I do, however, hold that\nsome such series of English terms is both possible and useful, and do\nnot doubt\u2014in spite of the pretended hostility of the genius of our\nlanguage, and the curious sentimental objection that English names are\n_unscientific_\u2014that we shall before long make use of plain English in\nspeaking of the various groups of plants and animals\u2014much to the gain\nof the larger public, and without detriment to the latinized\nnomenclature established for the purposes of the professional student.\n\n\n  E. R. L.\n\n  _Oxford, October, 1874._\n\n\n\n\nTHE HISTORY OF CREATION.\n\n\n\n\nCHAPTER I.\n\nNATURE AND IMPORTANCE OF THE DOCTRINE OF FILIATION, OR DESCENT-THEORY.\n\n\n   General Importance and Essential Nature of the Theory of\n   Descent as reformed by Darwin.\u2014Its Special Importance to\n   Biology (Zoology and Botany).\u2014Its Special Importance to\n   the History of the Natural Development of the Human\n   Race.\u2014The Theory of Descent as the Non-Miraculous\n   History of Creation.\u2014Idea of Creation.\u2014Knowledge and\n   Belief.\u2014History of Creation and History of\n   Development.\u2014The Connection between the History of\n   Individual and Pal\u00e6ontological Development.\u2014The Theory\n   of Purposelessness, or the Science of Rudimentary\n   Organs.\u2014Useless and Superfluous Arrangements in\n   Organisms.\u2014Contrast between the two entirely opposed\n   Views of Nature: the Monistic (mechanical, causal) and\n   the Dualistic (teleological, vital).\u2014Proof of the former\n   by the Theory of Descent.\u2014Unity of Organic and Inorganic\n   Nature, and the Identity of the Active Causes in\n   both.\u2014The Importance of the Theory of Descent to the\n   Monistic Conception of all Nature.\n\n\nThe intellectual movement to which the impulse was given, thirteen years\nago, by the English naturalist, Charles Darwin, in his celebrated work,\n\u201cOn the Origin of Species,\u201d(1) has, within this short period, assumed\ndimensions which cannot but excite the most universal interest. It is\ntrue the scientific theory set forth in that work, which is commonly\ncalled briefly Darwinism, is only a small fragment of a far more\ncomprehensive doctrine\u2014a part of the universal Theory of Development,\nwhich embraces in its vast range the whole domain of human knowledge.\n\nBut the manner in which Darwin has firmly established the latter by the\nformer is so convincing, and the direction which has been given by the\nunavoidable conclusions of that theory to all our views of the universe,\nmust appear to every thinking man of such deep significance, that its\ngeneral importance cannot be over estimated. There is no doubt that this\nimmense extension of our intellectual horizon must be looked upon as by\nfar the most important, and rich in results, among all the numerous and\ngrand advances which natural science has made in our day.\n\nWhen our century, with justice, is called the age of natural science,\nwhen we look with pride upon the immensely important progress made in\nall its branches, we are generally in the habit of thinking more of\nimmediate practical results, and less of the extension of our general\nknowledge of nature. We call to mind the complete reform, so infinitely\nrich in consequences to human intercourse, which has been effected by\nthe development of machinery, by railways, steamships, telegraphs, and\nother inventions of physics. Or we think of the enormous influence which\nchemistry has brought to bear upon medicine, agriculture, and upon all\narts and trades.\n\nBut much as we may value this influence of modern science upon practical\nlife, still it must, estimated from a higher and more general point of\nview, stand most assuredly below the enormous influence which the\ntheoretical progress of modern science will have on the entire range of\nhuman knowledge, on our conception of the universe, and on the\nperfecting of man\u2019s culture.\n\nThink of the immense revolutions in all our theoretical views which we\nowe to the general application of the microscope. Think of the cell\ntheory, which explains the apparent unity of the human organism as the\ncombined result of the union of a mass of elementary vital units. Or\nconsider the immense extension of our theoretical horizon which we owe\nto spectral analysis and to the mechanical theory of heat. But among all\nthese wonderful theoretical advances, the theory wrought out by Darwin\noccupies by far the highest rank.\n\nEvery one of my readers has heard of the name of Darwin. But most\npersons have probably only an imperfect idea of the real value of his\ntheory. If a reader estimates as of equal value all that has been\nwritten upon Darwin\u2019s memorable work since its appearance, the value of\nthe theory will appear very doubtful to him, supposing that he has not\nbeen engaged in the organic natural sciences, and has not penetrated\ninto the inner secrets of zoology and botany. The criticisms of it are\nso full of contradictions, and for the most part so defective, that we\nought not to be at all astonished that even now, after the lapse of\nthirteen years since the appearance of Darwin\u2019s work, it has not gained\nhalf that importance which is justly due to it, and which sooner or\nlater it certainly will attain.\n\nMost of the innumerable writings which have been published during these\nyears, both for and against Darwinism, are the productions of persons\nwho are entirely wanting in the necessary amount of biological, and\nespecially of zoological, knowledge. Although almost all of the more\ncelebrated naturalists of the present day are adherents of the theory,\nyet only a few of them have endeavoured to procure its acceptance and\nrecognition in larger circles. Hence the odd contradictions and the\nstrange opinions which may still be heard everywhere about Darwinism.\nThis is the reason which induces me to make Darwin\u2019s theory, and those\nfurther doctrines which are connected with it, the subject of these\npages, which, I hope, will be generally intelligible. I hold it to be\nthe duty of naturalists, not merely to meditate upon improvements and\ndiscoveries in the narrow circle to which their speciality confines\nthem, not merely to pore over their one study with love and care, but\nalso to seek to make the important general results of it fruitful to the\nmass, and to assist in spreading the knowledge of physical science among\nthe people. The highest triumph of the human mind, the true knowledge of\nthe most general laws of nature, ought not to remain the private\npossession of a privileged class of savans, but ought to become the\ncommon property of all mankind.\n\nThe theory which, through Darwin, has been placed at the head of all our\nknowledge of nature, is usually called the Doctrine of Filiation, or the\nTheory of Descent. Others term it the Transmutation Theory. Both\ndesignations are correct. For this doctrine affirms, that _all\norganisms_ (viz., all species of animals, all species of plants, which\nhave ever existed or still exist on the earth) _are derived from one\nsingle, or from a few simple original forms, and that they have\ndeveloped themselves from these in the natural course of a gradual\nchange_. Although this theory of development had already been brought\nforward and defended by several great naturalists, and especially by\nLamarck and Goethe, in the beginning of our century, still it was\nthrough Darwin, thirteen years ago, that it received its complete\ndemonstration and causal foundation; and this is the reason why now it\nis commonly and exclusively (though not quite correctly) designated as\n_Darwin\u2019s Theory_.\n\nThe great and really inestimable value of the Theory of Descent appears\nin a different light, accordingly as we merely consider its more\nimmediate connection with organic natural science, or its larger\ninfluence upon the whole range of man\u2019s knowledge of the universe.\nOrganic natural science, or Biology, which as Zoology treats of animals,\nas Botany of plants, is completely reformed and founded anew by the\nTheory of Descent. For by this theory we are made acquainted with the\nactive causes of organic forms, while up to the present time Zoology and\nBotany have simply been occupied with the facts of these forms. We may\ntherefore also term the theory of descent a _mechanical explanation of\norganic forms_, or the science of the true causes of Organic Nature.\n\nAs I cannot take for granted that my readers are all familiar with the\nterms \u201corganic and inorganic nature,\u201d and as the contrast of both these\nnatural bodies will, in future, occupy much of our attention, I must say\na few words in explanation of them. We designate as _Organisms_, or\n_Organic bodies_, all _living creatures_ or _animated bodies_; therefore\nall plants and animals, man included; for in them we can almost always\nprove a combination of various parts (instruments or organs) which work\ntogether for the purpose of producing the phenomena of life. Such a\ncombination we do not find in _Anorgana_, or inorganic natural\nbodies\u2014the so-called dead or _inanimate bodies_, such as minerals or\nstones, water, the atmospheric air, etc. Organisms always contain\nalbuminous combinations of carbon in a semi-fluid condition of\naggregation, which are always wanting in the Anorgana. Upon this\nimportant distinction rests the division of all natural history into two\ngreat and principal parts\u2014_Biology_, or the science of Organisms\n(Zoology and Botany), and _Anorganology_, or the science of Anorgana\n(Mineralogy, Geology, Meteorology, etc.).\n\nThe great value of the Theory of Descent in regard to Biology consists,\nas I have already remarked, in its explaining to us the origin of\norganic forms in a mechanical way, and pointing out their active causes.\nBut however highly and justly this service of the Theory of Descent may\nbe valued, yet it is almost eclipsed by the immense importance which a\nsingle necessary inference from it claims for itself alone. This\nnecessary and unavoidable inference is the theory of the _animal descent\nof the human race_.\n\nThe determination of the position of man in nature, and of his relations\nto the totality of things\u2014this question of all questions for mankind,\nas Huxley justly calls it\u2014is finally solved by the knowledge that man\nis descended from animals. In consequence of Darwin\u2019s reformed Theory of\nDescent, we are now in a position to establish scientifically the\ngroundwork of a _non-miraculous history of the development of the human\nrace_. All those who have defended Darwin\u2019s theory, as well as all its\nthoughtful opponents, have acknowledged that, as a matter of necessity,\nit follows from his theory that the human race, in the first place, must\nbe traced to ape-like mammals, and further back to the lower vertebrate\nanimals.\n\nIt is true Darwin himself did not express at first this most important\nof all the inferences from his theory. In his work, \u201cOn the Origin of\nSpecies,\u201d not a word is found about the animal descent of man. The\ncourageous but cautious naturalist was at that time purposely silent on\nthe subject, for he anticipated that this most important of all the\nconclusions of the Theory of Descent was at the same time the greatest\nobstacle to its being generally accepted and acknowledged. Certain it is\nthat Darwin\u2019s book would have created, from the beginning, even much\nmore opposition and offence, if this most important inference had at\nonce been clearly expressed. It was not till twelve years later, in his\nwork on \u201cThe Descent of Man, and Selection in Relation to Sex,\u201d that\nDarwin openly acknowledged that far-reaching conclusion, and expressly\ndeclared his entire agreement with those naturalists who had, in the\nmeantime, themselves formed that conclusion. Manifestly the effect of\nthis conclusion is immense, and _no_ science will be able to escape from\nthe consequences. Anthropology, or the science of man, and consequently\nall philosophy, are thereby thoroughly reformed in all their various\nbranches.\n\nIt will be a later task in these pages to discuss this special point. I\nshall not treat of the theory of the animal descent of man till I have\nspoken of Darwin\u2019s theory, and its general foundation and importance. To\nexpress it in one word, that most important, but (to most men) at first\nrepulsive, conclusion is nothing more than a special deduction, which we\nmust draw from the general inductive law of the descent theory (now\nfirmly established), according to the stern commands of inexorable\nlogic.\n\nPerhaps nothing will make the full meaning of the theory of descent\nclearer than calling it the \u201c_non-miraculous history of creation_.\u201d I\nhave therefore chosen that name for this work. It is, however, correct\nonly in a certain sense, and it must be borne in mind that, strictly\nspeaking, the expression \u201cnon-miraculous history of creation\u201d contains a\n\u201c_contradictio in adjecto_.\u201d\n\nIn order to understand this, let us for a moment examine somewhat more\nclosely what we understand by _creation_. If we understand the creation\nto mean the _coming into existence of a body_ by a creative power or\nforce, we may then either think of the _coming into existence of its\nsubstance_ (corporeal matter), or of the _coming into existence of its\nform_ (the corporeal form).\n\nCreation in the former sense, as the _coming into existence of matter_,\ndoes not concern us here at all. This process, if indeed it ever took\nplace, is completely beyond human comprehension, and can therefore never\nbecome a subject of scientific inquiry. Natural science teaches that\nmatter is eternal and imperishable, for experience has never shown us\nthat even the smallest particle of matter has come into existence or\npassed away. Where a natural body seems to disappear, as for example by\nburning, decaying, evaporation, etc., it merely changes its form, its\nphysical composition or chemical combination. In like manner the coming\ninto existence of a natural body, for example, of a crystal, a fungus,\nan infusorium, depends merely upon the different particles, which had\nbefore existed in a certain form or combination, assuming a new form or\ncombination in consequence of changed conditions of existence. But never\nyet has an instance been observed of even the smallest particle of\nmatter having vanished, or even of an atom being added to the already\nexisting mass. Hence a naturalist can no more imagine the coming into\nexistence of matter, than he can imagine its disappearance, and he\ntherefore looks upon the existing quantity of matter in the universe as\na given fact. If any person feels the necessity of conceiving the coming\ninto existence of this matter as the work of a supernatural creative\npower, of the creative force of something outside of matter, we have\nnothing to say against it. But we must remark, that thereby not even the\nsmallest advantage is gained for a scientific knowledge of nature. Such\na conception of an immaterial force, which at the first creates matter,\nis an article of faith which has nothing whatever to do with human\nscience. _Where faith commences, science ends._ Both these arts of the\nhuman mind must be strictly kept apart from each other. Faith has its\norigin in the poetic imagination; knowledge, on the other hand,\noriginates in the reasoning intelligence of man. Science has to pluck\nthe blessed fruits from the tree of knowledge, unconcerned whether these\nconquests trench upon the poetical imaginings of faith or not.\n\nIf, therefore, science makes the \u201chistory of creation\u201d its highest, most\ndifficult, and most comprehensive problem, it must accept as its idea of\ncreation the second explanation of the word, viz., _the coming into\nbeing of the form_ of natural bodies. In this way geology, which tries\nto investigate the origin of the inorganic surface of the earth as it\nnow appears, and the manifold historical changes in the form of the\nsolid crust of the earth, may be called the history of the creation of\nthe earth. In like manner, the history of the development of animals and\nplants, which investigates the origin of living forms, and the manifold\nhistorical changes in animal and vegetable forms, may be termed the\nhistory of the creation of organisms. As, however, in the idea of\ncreation, although used in this sense, the unscientific idea of a\ncreator existing outside of matter, and changing it, may easily creep\nin, it will perhaps be better in future to substitute for it the more\naccurate term, _development_.\n\nThe great value which the _History of Development_ possesses for the\nscientific understanding of animal and vegetable forms, has now been\ngenerally acknowledged for many years, and without it it would be\nimpossible to make any sure progress in organic morphology, or the\ntheory of forms. But by the history of development, only one part of\nthis science has generally been understood, namely, that of organic\nindividuals, usually called Embryology, but more correctly and\ncomprehensively, _Ontogeny_. But, besides this, there is another history\nof development of organic species, genera, and tribes (phyla), which has\nthe most important relations to the former.\n\nThe subject of this is furnished to us by the science of petrifactions,\nor pal\u00e6ontology, which shows us that each tribe of animals and plants,\nduring different periods of the earth\u2019s history, has been represented by\na series of entirely different genera and species. Thus, for example,\nthe tribe of vertebrated animals was represented by classes of fish,\namphibious animals, reptiles, birds, and mammals, and each of these\ngroups, at different periods, by quite different kinds. This\npal\u00e6ontological history of the development of organisms, which we may\nterm _Phylogeny_, stands in the most important and remarkable relation\nto the other branch of organic history of development, I mean that of\nindividuals, or Ontogeny. On the whole, the one runs parallel to the\nother. In fact, the history of individual development, or Ontogeny, is a\nshort and quick recapitulation of pal\u00e6ontological development, or\nPhylogeny, dependent on the laws of Inheritance and Adaptation.\n\nAs I shall have, later, to explain this most interesting and important\ncoincidence more fully, I shall not dwell further upon it here, and\nmerely call attention to the fact that it can only be explained and its\ncauses understood by the Theory of Descent, while without that theory it\nremains completely incomprehensible and inexplicable. The Theory of\nDescent in the same way shows us _why_ individual animals and plants\nmust develop at all, and why they do not come into life at once in a\nperfect and developed state. No supernatural history of creation can in\nany way explain to us the great mystery of organic development. To this\nmost weighty question, as well as to all other biological questions, the\nTheory of Descent gives us perfectly satisfactory answers\u2014and always\nanswers which refer to purely mechanical causes, and point to purely\nphysico-chemical forces as the causes of phenomena which we were\nformerly accustomed to ascribe to the direct action of supernatural,\ncreative forces. Hence, by our theory the mystic veil of the miraculous\nand supernatural, which has hitherto been allowed to hide the\ncomplicated phenomena of this branch of natural knowledge, is removed.\nAll the departments of Botany and Zoology, and especially the most\nimportant portion of the latter, Anthropology, become reasonable. The\ndimming mirage of mythological fiction can no longer exist in the clear\nsunlight of scientific knowledge.\n\nOf special interest among general biological phenomena are those which\nare quite irreconcilable with the usual supposition, that every organism\nis the product of a creative power, acting for a definite object.\nNothing in this respect caused the earlier naturalists greater\ndifficulty than the explanation of the so-called \u201c_rudimentary\norgans_,\u201d\u2014those parts in animal and vegetable bodies which really have\nno function, which have no physiological importance, and yet exist in\nform. These parts deserve the most careful attention, although most\nunscientific men know little or nothing about them. Almost every\norganism, almost every animal and plant possesses, besides the obviously\nuseful arrangements of its organization, other arrangements the purpose\nof which it is utterly impossible to make out.\n\nExamples of this are found everywhere. In the embryos of many ruminating\nanimals\u2014among others, in our common cattle\u2014fore-teeth, or incisors,\nare placed in the mid-bone of the upper jaw, which never fully develop,\nand therefore serve no purpose. The embryos of many whales\u2014which\nafterwards possess the well-known whalebone instead of teeth\u2014yet have\nbefore they are born, and while they take no nourishment, teeth in their\njaws, which set of teeth never comes into use. Moreover, most of the\nhigher animals possess muscles which are never employed; even man has\nsuch rudimentary muscles. Most of us are incapable of moving our ears as\nwe wish, although the muscles for this movement exist, and although\nindividual persons who have taken the trouble to exercise these muscles\ndo succeed in moving their ears. It is still possible, by special\nexercise, by the persevering influence of the will upon the nervous\nsystem, to reanimate the almost extinct activity in the existing but\nimperfect organs, which are on the road to complete disappearance. On\nthe other hand, we can no longer do this with another set of small\nrudimentary muscles, which still exist in the cartilage of the outer\near, but which are always perfectly inactive. Our long-eared ancestors\nof the tertiary period\u2014apes, semi-apes, and pouched animals, like most\nother mammals, moved their large ear-flaps freely and actively; their\nmuscles were much more strongly developed and of great importance. In a\nsimilar way, many varieties of dogs and rabbits, under the influence of\ncivilized life, have left off \u201cpricking up\u201d their ears, and thereby have\nacquired imperfect auricular muscles and loose-hanging ears, although\ntheir wild ancestors moved their stiff ears in many ways.\n\nMan has also these rudimentary organs on other parts of his body; they\nare of no importance to life, and never perform any function. One of the\nmost remarkable, although the smallest organ of this kind, is the little\ncrescent-like fold, the so-called \u201cplica semilunaris,\u201d which we have in\nthe inner corner of the eye, near the root of the nose. This\ninsignificant fold of skin, which is quite useless to our eye, is the\nimperfect remnant of a third inner eyelid which, besides the upper and\nunder eyelid, is highly developed in other mammals, and in birds and\nreptiles. Even our very remote ancestors of the Silurian period, the\nPrimitive Fishes, seem to have possessed this third eyelid, the\nso-called nictitating membrane. For many of their nearest kin, who still\nexist in our day but little changed in form, viz., many sharks, possess\na very strong nictitating membrane, which they can draw right across the\nwhole eyeball, from the inner corner of the eye.\n\nEyes which do not see form the most striking example of rudimentary\norgans. These are found in very many animals, which live in the dark, as\nin caves or underground. Their eyes often exist in a well-developed\ncondition, but they are covered by membrane, so that no ray of light\ncan enter, and they can never see. Such eyes, without the function of\nsight, are found in several species of moles and mice which live\nunderground, in serpents and lizards, in amphibious animals (Proteus,\nC\u00e6cilia), and in fishes; also in numerous invertebrate animals, which\npass their lives in the dark, as do many beetles, crabs, snails, worms,\netc.\n\nAn abundance of the most interesting examples of rudimentary organs is\nfurnished by Comparative Osteology, or the study of the skeletons of\nvertebrate animals, one of the most attractive branches of Comparative\nAnatomy. In most of the vertebrate animals we find two pairs of limbs on\nthe body, a pair of fore-legs and a pair of hind-legs. Very often,\nhowever, one or the other pair is imperfect; it is seldom that both are,\nas in the case of serpents and some varieties of eel-like fish. But some\nserpents, viz., the giant serpents (Boa, Python), have still in the\nhinder portion of the body some useless little bones, which are the\nremains of lost hind-legs.\n\nIn like manner the mammals of the whale tribe (Cetacea), which have only\nfore-legs fully developed (breast-fins,), have further back in their\nbody another pair of utterly superfluous bones, which are remnants of\nundeveloped hind-legs. The same thing occurs in many genuine fishes, in\nwhich the hind-legs have in like manner been lost.\n\nAgain, in our slow-worm (Anguis), and in some other lizards, no\nfore-legs exist, although they have a perfect shoulder apparatus within\ntheir bodies, which should serve as a means of affixing the legs.\nMoreover, in various vertebrate animals, the single bones of both pairs\nof legs are found in all the different stages of imperfection, and often\nthe degenerate bones and those muscles belonging to them are partially\npreserved, without their being able in any way to perform any function.\nThe instrument is still there, but it can no longer play.\n\nMoreover, we can, almost as generally, find rudimentary organs in the\nblossoms of plants, inasmuch as one part or another of the male organs\nof propagation\u2014the stamen and anther, or of the female organs of\npropagation\u2014the style, germ, etc.\u2014is more or less imperfect or\nabortive. Among these we can trace, in various closely connected species\nof plants, the organ in all stages of degeneration. Thus, for example,\nthe great natural family of lip-blossomed plants (Labiat\u00e6), to which the\nbalm, peppermint, marjoram, ground-ivy, thyme, etc., belong, are\ndistinguished by the fact that their mouth-like, two-lipped flower\ncontains two long and two short stamens. But in many exceptional plants\nof this family, _e.g._ in different species of sage, and in the\nrosemary, only one pair of stamens is developed; the other pair is more\nor less imperfect, or has quite disappeared. Sometimes stamens exist,\nbut without the anthers, so that they are utterly useless. Less\nfrequently the rudiment or imperfect remnant of a fifth stamen is found,\nphysiologically (for the functions of life) quite useless, but\nmorphologically (for the knowledge of the form and of the natural\nrelationship) a most valuable organ. In my \u201cGeneral Morphology of\nOrganisms,\u201d(4) in the chapter on \u201cPurposelessness, or Dysteleology,\u201d I\nhave given a great number of other examples (Gen. Morph. ii. 226).\n\nNo biological phenomenon has perhaps ever placed zoologists or botanists\nin greater embarrassment than these rudimentary or abortive organs. They\nare instruments without employment, parts of the body which exist\nwithout performing any service\u2014adapted for a purpose, but without in\nreality fulfilling that purpose. When we consider the attempts which the\nearlier naturalists have made in order to explain this mystery, we can\nscarcely help smiling at the strange ideas to which they were led. Being\nunable to find a true explanation, they came, for example, to the\nconclusion that the Creator had placed these organs there \u201cfor the sake\nof symmetry,\u201d or they believed that it had appeared unwise and\nunsuitable to the Creator (seeing that their nearest kin did possess\nsuch organs) that these organs should be completely wanting in\ncreatures, where they are incapable of performing a function, and where\nit cannot be otherwise from the special mode of life. In compensation\nfor the non-existing function, he had at least furnished them with the\noutward but empty form; nearly in the same manner as civil officers, in\nuniform, are furnished with an innocent sword, which is never drawn from\nthe scabbard. I scarcely believe, however, that any of my readers will\nbe content with such an explanation.\n\nNow, it is precisely this widely spread and mysterious phenomenon of\nrudimentary organs, in regard to which all other attempts at explanation\nfail, which is perfectly explained, and indeed in the simplest and\nclearest way, by Darwin\u2019s _Theory of Inheritance_ and _Adaptation_. We\ncan trace the important laws of inheritance and adaptation in the\ndomestic animals which we breed, and the plants which we cultivate; and\na series of such laws of inheritance have already been established.\nWithout going further into this at present, I will only remark that some\nof them perfectly explain, in a mechanical way, the coming into\nexistence of rudimentary organs, so that we must look upon the\nappearance of such structures as an entirely natural process, arising\nfrom the _disuse of the organs_.\n\nBy _adaptation_ to special conditions of life, the formerly active and\nreally working organs have gradually ceased to be used or employed. In\nconsequence of their not being exercised they have become more and more\nimperfect, but in spite of this have always been handed down from one\ngeneration to another by _inheritance_, until at last they vanish\npartially or entirely. Now, if we admit that all the vertebrate animals\nmentioned above are derived from one common ancestor, possessing two\nseeing eyes and two well developed pairs of legs, the different stages\nof suppression and degeneration of these organs are easily accounted for\nin such of the descendants as could no longer use them. In like manner\nthe various stages of suppression of the stamens, originally existing to\nthe number of five (in the flower-bud), among the Labiat\u00e6 is explained,\nif we admit that all the plants of this family sprung from one common\nancestor, provided with five stamens.\n\nI have here spoken somewhat fully of the phenomena of rudimentary\norgans, because they are of the utmost general importance, and because\nthey lead us to the great, general, and fundamental questions in\nphilosophy and natural science, for the solution of which the Theory of\nDescent has now become the indispensable guide. As soon, in fact, as,\naccording to this theory, we acknowledge the exclusive activity of\nphysico-chemical causes in living (organic) bodies, as well as in\nso-called inanimate (inorganic) nature, we concede exclusive dominion to\nthat view of the universe, which we may designate as the _mechanical_,\nand which is opposed to the _teleological_ conception. If we compare\nall the ideas of the universe prevalent among different nations at\ndifferent times, we can divide them all into two sharply contrasted\ngroups\u2014a _causal_ or _mechanical_, and a _teleological_ or\n_vitalistic_. The latter has prevailed generally in Biology until now,\nand accordingly the animal and vegetable kingdoms have been considered\nas the products of a creative power, acting for a definite purpose. In\nthe contemplation of every organism the unavoidable conviction seemed to\npress itself upon us, that such a wonderful machine, so complicated an\napparatus for motion as exists in the organism, could only be produced\nby a power analogous to, but infinitely more perfect than, the power of\nman in the construction of his machines.\n\nHowever sublime the former idea of a Creator, and his creative power,\nmay have been; however much it may be attempted to divest it of all\nhuman analogy, yet in the end this analogy still remains unavoidable and\nnecessary in the teleological conception of nature. In reality the\nCreator must himself be conceived of as an organism, that is, as a being\nwho, analogous to man, even though in an infinitely more perfect form,\nreflects on his constructive power, lays down a plan of his mechanisms,\nand then, by the application of suitable materials, makes them answer\ntheir purpose. Such conceptions necessarily suffer from the fundamental\nerror of _anthropomorphism_, or man-likening. In such a view, however\nexalted the Creator may be imagined, we assign to him the human\nattributes of designing a plan, and therefrom suitably constructing the\norganism. This is, in fact, quite clearly expressed in that view which\nis most sharply opposed to Darwin\u2019s theory, and which has found among\nnaturalists its most distinguished representative in Agassiz. His\ncelebrated work, \u201cAn Essay on Classification,\u201d(5) which is entirely\nopposed to Darwin\u2019s, and appeared almost at the same time, has\nelaborated quite consistently, and to the utmost extent, these\nanthropomorphic conceptions of the Creator.\n\nI maintain with regard to the much-talked-of \u201cpurpose in nature,\u201d that\nit really has no existence but for those persons who observe phenomena\nin animals and plants in the most superficial manner. Without going more\ndeeply into the matter, we can see at once that the rudimentary organs\nare a formidable obstacle to this theory. And, indeed, everyone who\nmakes a really close study of the organization and mode of life of the\nvarious animals and plants, and becomes familiar with the reciprocity or\ninteraction of the phenomena of life, and the so-called \u201ceconomy of\nnature,\u201d must necessarily come to the conclusion that this\n\u201cpurposiveness\u201d no more exists than the much-talked-of \u201cbeneficence\u201d of\nthe Creator. These optimistic views have, unfortunately, as little real\nfoundation as the favourite phrase, the \u201cmoral order of the universe,\u201d\nwhich is illustrated in an ironical way by the history of all nations.\nThe dominion of the \u201cmoral\u201d popes, and their pious inquisition, in the\nmedi\u00e6val times, is not less significant of this than the present\nprevailing militarism, with its \u201cmoral\u201d apparatus of needle-guns and\nother refined instruments of murder.\n\nIf we contemplate the common life and the mutual relations between\nplants and animals (man included), we shall find everywhere, and at all\ntimes, the very opposite of that kindly and peaceful social life which\nthe goodness of the Creator ought to have prepared for his creatures\u2014we\nshall rather find everywhere a pitiless, most embittered _Struggle of\nAll against All_. Nowhere in nature, no matter where we turn our eyes,\ndoes that idyllic peace, celebrated by the poets, exist; we find\neverywhere a struggle and a striving to annihilate neighbours and\ncompetitors. Passion and selfishness\u2014conscious or unconscious\u2014is\neverywhere the motive force of life. The well-known words of the German\npoet\u2014\n\n  \u201cDie Welt ist vollkommen \u00fcberall\n   Wo der Mensch nicht hinkommt mit seiner Qual.\u201d[1]\n\nare beautiful, but, unfortunately, not true. Man in this respect\ncertainly forms no exception to the rest of the animal world. The\nremarks which we shall have to make on the theory of \u201cStruggle for\nExistence\u201d will sufficiently justify this assertion. It is, in fact,\nDarwin who has placed this important point, in its high and general\nsignificance, very clearly before our eyes, and the chapter in his\ntheory which he himself calls \u201cStruggle for Existence\u201d is one of the\nmost important parts of it.\n\nWhilst, then, we emphatically oppose the vital or teleological view of\nanimate nature which presents animal and vegetable forms as the\nproductions of a kind Creator, acting for a definite purpose, or of a\ncreative, natural force acting for a definite purpose, we must, on the\nother hand, decidedly adopt that view of the universe which is called\nthe _mechanical_ or _causal_. It may also be called the _monistic_, or\n_single-principle_ theory, as opposed to the _twofold principle_, or\n_dualistic_ theory, which is necessarily implied in the teleological\nconception of the universe. The mechanical view of nature has for many\nyears been so firmly established in certain domains of natural science,\nthat it is here unnecessary to say much about it. It no longer occurs to\nphysicists, chemists, mineralogists, or astronomers, to seek to find in\nthe phenomena which continually appear before them in their scientific\ndomain the action of a Creator acting for a definite purpose. They\nuniversally, and without hesitation, look upon the phenomena which\nappear in their different departments of study as the necessary and\ninvariable effects of physical and chemical forces which are inherent in\nmatter. Thus far their view is purely _materialistic_, in a certain\nsense of that \u201cword of many meanings.\u201d\n\nWhen a physicist traces the phenomena of motion in electricity or\nmagnetism, the fall of a heavy body, or the undulations in the waves of\nlight, he never, in the whole course of his research, thinks of looking\nfor the interference of a supernatural power. In this respect, Biology,\nas the science of so-called \u201c_animated_\u201d natural bodies, was formerly\nplaced in sharp opposition to the above-mentioned inorganic natural\nsciences (Anorganology). It is true modern Physiology, the science of\nthe phenomena of motion in animals and plants, has completely adopted\nthe mechanical view; but Morphology, the science of the forms of animals\nand plants, has not been affected at all by it. Morphologists, in spite\nof the position of physiology, have continued, as before, in opposition\nto the mechanical view of functions, to look upon the forms of animals\nand plants as something which cannot be at all explained mechanically,\nbut which must owe its origin necessarily to a higher, supernatural\ncreative power, acting for a definite purpose.\n\nIn this general view it is quite indifferent whether the creative power\nbe worshipped as a personal god, or whether it be termed the power of\nlife (vis vitalis), or final cause (causa finalis). In any case, to\nexpress it in one word, its supporters have recourse to a _miracle_ for\nan explanation. They throw themselves into the arms of a poetic faith,\nwhich as such can have no value in the domain of scientific knowledge.\n\nAll that was done before Darwin, to establish a natural mechanical\nconception of the origin of animals and plants, has been in vain, and\nuntil his time no theory gained a general recognition. Darwin\u2019s theory\nfirst succeeded in doing this, and thus has rendered an immense service.\nFor the idea of the _unity of organic and inorganic nature_ is now\nfirmly established; and that branch of natural science which had longest\nand most obstinately opposed mechanical conception and explanation,\nviz., the science of the structure of animate forms, is launched on to\nidentically the same road towards perfection as that along which all the\nrest of the natural sciences are travelling. The unity of _all_ natural\nphenomena is by Darwin\u2019s theory finally established.\n\nThis unity of all nature, the animating of all matter, the\ninseparability of mental power and corporeal substance, Goethe has\nasserted in the words: \u201cMatter can never exist and be active without\nmind, nor can mind without matter.\u201d These first principles of the\nmechanical conception of the universe have been taught by the great\nmonistic philosophers of all ages. Even Democritus of Abdera, the\nimmortal founder of the Atomic theory, clearly expressed them about 500\nyears before Christ; but the great Dominican friar, Giordano Bruno, did\nso even more explicitly. For this he was burnt at the stake, by the\nChristian inquisition in Rome, on the 17th of Feb., 1600, on the same\nday on which, 36 years before, Galileo, his great fellow-countryman and\nfellow-worker, was born. Such men, who live and die for a great idea,\nare usually stigmatized as \u201cmaterialists\u201d; but their opponents, whose\narguments were torture and the stake, are praised as \u201cspiritualists.\u201d\n\nBy the Theory of Descent we are for the first time enabled to conceive\nof the unity of nature in such a manner that a mechanico-causal\nexplanation of even the most intricate organic phenomena, for example,\nthe origin and structure of the organs of sense, is no more difficult\n(in a general way) than is the mechanical explanation of any physical\nprocess; as, for example, earthquakes, the courses of the wind, or the\ncurrents of the ocean. We thus arrive at the extremely important\nconviction that _all natural bodies_ which are known to us are _equally\nanimated_, that the distinction which has been made between animate and\ninanimate bodies does _not_ exist. When a stone is thrown into the air,\nand falls to earth according to definite laws, or when in a solution of\nsalt a crystal is formed, the phenomenon is neither more nor less a\nmechanical manifestation of life than the growth and flowering of\nplants, than the propagation of animals or the activity of their senses,\nthan the perception or the formation of thought in man. This final\ntriumph of the monistic conception of nature constitutes the highest and\nmost general merit of the Theory of Descent, as reformed by Darwin.\n\n\n\n\nCHAPTER II.\n\n   SCIENTIFIC JUSTIFICATION OF THE THEORY OF DESCENT.\n   HISTORY OF CREATION ACCORDING TO LINN\u00c6US.\n\n\n   The Theory of Descent, or Doctrine of Filiation, as the\n   Monistic Explanation of Organic Natural Phenomena.\u2014Its\n   Comparison with Newton\u2019s Theory of Gravitation.\u2014Limits\n   of Scientific Explanation and of Human Knowledge in\n   general.\u2014All Knowledge founded originally on Sensuous\n   Experience, _a posteriori_.\u2014Transition of _a posteriori_\n   knowledge, by Inheritance, into _a priori_\n   knowledge.\u2014Contrast between the Supernatural Hypotheses\n   of the Creation according to Linn\u00e6us, Cuvier, Agassiz,\n   and the Natural Theories of Development according to\n   Lamarck, Goethe, and Darwin.\u2014Connection of the former\n   with the Monistic (mechanical), of the latter with the\n   Dualistic Conception of the Universe.\u2014Monism and\n   Materialism.\u2014Scientific and Moral Materialism.\u2014The\n   History of Creation according to Moses.\u2014Linn\u00e6us as the\n   Founder of the Systematic Description of Nature and\n   Distinction of Species.\u2014Linn\u00e6us\u2019 Classification and\n   Binary Nomenclature.\u2014Meaning of Linn\u00e6us\u2019 Idea of\n   Species.\u2014His History of Creation.\u2014Linn\u00e6us\u2019 view of the\n   Origin of Species.\n\n\nThe value which every scientific theory possesses is measured by the\nnumber and importance of the objects which can be explained by it, as\nwell as by the simplicity and universality of the causes which are\nemployed in it as grounds of explanation. On the one hand, the greater\nthe number and the more important the meaning of the phenomena explained\nby the theory, and the simpler, on the other hand, and the more general\nthe causes which the theory assigns as explanations, the greater is its\nscientific value, the more safely we are guided by it, and the more\nstrongly are we bound to adopt it.\n\nLet us call to mind, for example, that theory which has ranked up to the\npresent time as the greatest achievement of the human mind\u2014the Theory\nof Gravitation, which Newton, two hundred years ago, established in his\nMathematical Principles of Natural Philosophy. Here we find that the\nobject to be explained is as large as one can well imagine. He undertook\nto reduce the phenomena of the motion of the planets, and the structure\nof the universe, to mathematical laws. As the most simple cause of these\nintricate phenomena of motion, Newton established the law of weight or\nattraction, the same law which is the cause of the fall of bodies, of\nadhesion, cohesion, and many other phenomena.\n\nIf we apply the same standard of valuation to Darwin\u2019s theory, we must\narrive at the conclusion that this theory, also, is one of the greatest\nachievements of the human mind, and that it may be placed quite on a\nlevel with Newton\u2019s Theory of Gravitation. Perhaps this opinion will\nseem a little exaggerated, or at any rate very bold, but I hope in the\ncourse of this treatise to convince the reader that this estimate is not\ntoo high. In the preceding chapter, some of the most important and most\ngeneral phenomena in organic nature, which have been explained by\nDarwin\u2019s theory, have been named. Among them are the variations in form\nwhich accompany the individual development of organisms, most varied and\ncomplicated phenomena, which until now presented the greatest\ndifficulties in the way of mechanical explanation, that is, in the\ntracing of them to active causes. We have mentioned the _rudimentary\norgans_, those exceedingly remarkable structures in animals and plants\nwhich have no object and refute every teleological explanation seeking\nfor the final purpose of the organism. A great number of other phenomena\nmight have been mentioned, which are no less important, and are\nexplained in the simplest manner by Darwin\u2019s reformed Theory of Descent.\nFor the present I will only mention the phenomena presented to us by the\n_geographical distribution of animals and plants_ on the surface of our\nplanet, as well as the _geological distribution of the extinct and\npetrified organisms_ in the different strata of the earth\u2019s crust. These\nimportant pal\u00e6ontological and geographical phenomena, which were\nformerly only known to us as _facts_, are now traced to their active\n_causes_ by the Theory of Descent.\n\nThe same statement applies further to all the general laws of\n_Comparative Anatomy_, especially to the great law of _division of\nlabour_ or _separation_ (polymorphism, or differentiation), a law which\ndetermines the form or structure of human society, as well as the\norganization of individual animals and plants. It is this law which\nnecessitates an ever _increasing variety_, as well as a _progressive\ndevelopment_ of organic forms. This law of the division of labour has,\nup to the present time, been only recognized as a fact, and it, like the\nlaw of progressive development, or the law of progress which we perceive\nactive everywhere in the history of nations (as also in that of animals\nand plants), is explained by Darwin\u2019s Doctrine of Descent. Then, if we\nturn our attention to the great whole of organic nature, if we compare\nall the individual groups of phenomena of this immense domain of life,\nit cannot fail to appear, in the light of the Doctrine of Descent, no\nlonger as the ingeniously designed work of a Creator building up\naccording to a definite purpose, but as the necessary consequence of\nactive causes, which are inherent in the chemical combination of matter\nitself, and in its physical properties.\n\nIn fact, we can most positively assert, and I shall justify this\nassertion in the course of these pages, that by the Doctrine of\nFiliation, or Descent, we are enabled for the first time to reduce all\norganic phenomena to a single law, and to discover a single active cause\nfor the infinitely intricate mechanism of the whole of this rich world\nof phenomena. In this respect, Darwin\u2019s theory stands quite on a level\nwith Newton\u2019s Theory of Gravitation; indeed, it even rises higher than\nNewton\u2019s theory!\n\nThe grounds of explanation are equally simple in the two theories. In\nexplaining this most intricate world of phenomena, Darwin does not make\nuse of new or hitherto unknown properties of matter, nor does he, as one\nmight suppose, make use of discoveries of new combinations of matter or\nof new forces of organization; but it is simply by extremely ingenious\ncombination, by the synthetic comprehension, and by the thoughtful\ncomparison of a number of well-known facts, that Darwin has solved the\n\u201choly mystery\u201d of the living world of forms. The consideration of the\ninterchanging relations which exist between two general properties of\norganisms, viz., _Inheritance and Adaptation_, is what has here been of\nthe first importance. Merely by considering the relations between these\ntwo vital actions or physiological functions of organisms, also further\nby considering the reciprocal interaction which all animals and plants,\nliving in one and the same place, necessarily exert on one\nanother\u2014solely by the correct estimate of these simple facts, and by\nskilfully combining them, Darwin has succeeded in finding the true\nactive causes (caus\u00e6 efficientes) of the immensely intricate world of\nforms in organic nature.\n\nIn any case we are in duty bound to accept this theory till a better one\nbe found, which will undertake to explain the same amount of facts in an\nequally simple manner. Until now we have been in utter want of such a\ntheory. The fundamental idea that all different animal and vegetable\nforms must be descended from a few or even from one single, most simple\nprimary form, was indeed not new. This idea was long since distinctly\nformulated\u2014first by the great Lamarck, at the beginning of our century.\nBut Lamarck in reality only expressed the hypothesis of the Doctrine of\nFiliation, without establishing it by an explanation of the active\ncauses. And it is just the demonstration of these causes which marks the\nextraordinary progress which Darwin\u2019s theory has made beyond that of\nLamarck. In the physiological properties of Inheritance and Adaptation\nof organic matter, Darwin discovered the true cause of the genealogical\nrelationship of organisms. It was not possible for the genius of Lamarck\nin his day to command that colossal material of biological facts which\nhas been collected by the patient zoological and botanical\ninvestigations of the last fifty years, and which has been used by\nDarwin as an overpowering apparatus of evidence.\n\nDarwin\u2019s theory is therefore not what his opponents frequently represent\nit as being\u2014an unwarranted hypothesis taken up at random. It is not for\nzoologists or botanists to accept or reject this as an explanatory\ntheory, as they please; they are rather compelled and obliged to accept\nit, according to the general principle observed in all natural sciences,\nthat we must accept and retain for the explanation of phenomena any\ntheory which, though it has only a feeble basis, is compatible with the\nactual facts\u2014until it is replaced by a better one. If we do not adopt\nit, we renounce a scientific explanation of phenomena, and this is, in\nfact, the position which many biologists still maintain. They look upon\nthe whole domain of animate nature as a perfect mystery, and upon the\norigin of animals and plants, the phenomena of their development and\naffinities, as quite inexplicable and miraculous; in fact, they will not\nallow that there _can_ be a true understanding of them.\n\nThose opponents of Darwin who do not exactly wish to renounce a\nscientific explanation are in the habit of saying, \u201cDarwin\u2019s theory of\nthe common origin of the different species is only _one_ hypothesis; we\noppose to it _another_, the hypothesis that the individual animal and\nvegetable species have not developed one from another by descent, but\nthat they have come into existence independently of one another, by a\nstill undiscovered law of nature.\u201d But as long as it is not shown how\nthis coming into existence is to be conceived of, and what that \u201claw of\nnature\u201d is\u2014as long as not even _probable_ grounds of explanation can be\nbrought forward to account for the independent coming into existence of\nanimal and vegetable species, so long this counter-hypothesis is in fact\nno hypothesis, but an empty unmeaning phrase. Darwin\u2019s theory ought,\nmoreover, not to be called an hypothesis. For a scientific hypothesis is\na supposition, postulating the existence of unknown properties or\nmotional phenomena of natural bodies, which properties have not as yet\nbeen observed by the experience of the senses. But Darwin\u2019s theory does\nnot assume such unknown conditions; it is based upon general properties\nof organisms that have long been recognized, and\u2014as has been\nremarked\u2014it is the exceedingly ingenious and comprehensive combination\nof a number of phenomena which had hitherto stood isolated, which gives\nthe theory its extraordinarily great and intrinsic value. By it we are\nfor the first time in a position to demonstrate an active cause for all\nthe known morphological phenomena in the animal and vegetable kingdoms;\nand, in fact, this cause is always one and the same, viz., the alternate\naction of Adaptation and Inheritance, therefore a physiological, that\nis, a physico-chemical or mechanical, relationship. For these reasons\nthe acceptance of the Doctrine of Filiation, as mechanically established\nby Darwin, is a binding and unavoidable necessity for the whole domain\nof zoology and botany.\n\nAs, therefore, in my opinion the immense importance of Darwin\u2019s theory\nlies in the fact that it has _mechanically explained those organic\nphenomena of forms_ which had hitherto been unexplained, it is perhaps\nnecessary that I should here say a few words about the different ideas\nconnected with the word \u201cexplanation.\u201d It is very frequently said, in\nopposition to Darwin\u2019s theory, that it does indeed explain those\nphenomena by Inheritance and Adaptation, but that it does not at the\nsame time explain those properties of organic matter, and that therefore\nwe do not arrive at first causes. This objection is quite correct, but\nit applies equally to _all_ explanations of phenomena. We _nowhere_\narrive at a knowledge of first causes. The origin of every simple salt\ncrystal, which we obtain by evaporating its mother liquor, is no less\nmysterious to us, as far as concerns its first cause, and in itself no\nless incomprehensible than the origin of every animal which is developed\nout of a simple cell. In explaining the most simple physical or chemical\nphenomena, as the falling of a stone, or the formation of a chemical\ncombination, we arrive, by discovering and establishing the active\ncauses\u2014for example, the gravitation or the chemical affinity\u2014at other\nremoter phenomena, which in themselves are mysterious. This arises from\nthe limitation or relativity of our powers of understanding. We must not\nforget that human knowledge is absolutely limited, and possesses only a\nrelative extension. It is, in its essence, limited by the very nature of\nour senses and of our brains.\n\nAll knowledge springs from sensuous perceptions. In opposition to this\nstatement, the innate, _\u00e0 priori_ knowledge of man may be brought up;\nbut we can see that the so-called _\u00e0 priori_ knowledge can by Darwin\u2019s\ntheory be proved to have been acquired _\u00e0 posteriori_, being based on\nexperience as its first cause. Knowledge which is based originally upon\npurely empirical observations, and which is therefore a purely sensuous\nexperience, but has then been transmitted from generation to generation\nby inheritance, appears in later generations as if it were independent,\ninnate, and _\u00e0 priori_. In our late animal ancestors, all our so-called\n\u201c_\u00e0 priori_ knowledge\u201d was originally acquired _\u00e0 posteriori_, and only\ngradually became _\u00e0 priori_ by inheritance. It is based in the first\ninstance upon experiences, and by the laws of Inheritance and Adaptation\nwe can positively prove that knowledge _\u00e0 priori_ and knowledge _\u00e0\nposteriori_ cannot rightly be placed in opposition, as is usually done.\nOn the contrary, sensuous experience is the original source of _all_\nknowledge. For this reason alone, all our knowledge is limited, and we\ncan never apprehend the _first causes_ of any phenomena. The force of\ncrystallization, the force of gravitation, and chemical affinity remain\nin themselves just as incomprehensible as do Adaptation and Inheritance.\n\nSeeing that Darwin\u2019s theory explains from a single point of view the\ntotality of all those phenomena of which we have given a brief survey,\nthat it demonstrates one and the same quality of the organism as the\nactive cause in all cases, we must allow that it gives us for the\npresent _all_ that we can desire. Moreover, we have good reason to hope\nthat at some future time we shall learn to explain the first causes at\nwhich Darwin has arrived, namely, the properties of Adaptation and\nInheritance; and that we shall succeed in discovering in the composition\nof albuminous matter certain molecular relations as the remoter, simpler\ncauses of these phenomena. There is indeed no prospect of this in the\nimmediate future, and we content ourselves for the present with the\ntracing back of organic phenomena to two mysterious properties, just as\nin the case of Newton\u2019s theory we are satisfied with tracing the\nplanetary motions to the force of gravitation, which itself is likewise\na mystery to us and not cognizable in itself.\n\nBefore commencing our principal task, which is the careful discussion of\nthe Doctrine of Descent, and the consequences that arise out of it, let\nus take an historical retrospect of the most important and most widely\nspread of those views, which before Darwin men had elaborated\nconcerning organic creation, and the coming into existence of the many\nanimal and vegetable species. In doing this I have no intention of\nentertaining the reader with a statement of all the innumerable stories\nabout the creation which have been current among the different human\nspecies, races, or tribes. However interesting and gratifying this task\nwould be, from an ethnographical point of view, as well as in a history\nof civilization, it would lead us here much too far from our subject.\nBesides, the great majority of all these legends about creation bear too\nclearly the stamp of arbitrary fiction, and of a want of a close\nobservance of nature, to be of interest in a scientific treatment of the\nhistory of creation. I shall therefore only select the Mosaic history\nfrom among those that are not founded on scientific investigation, on\naccount of the unparalleled influence which it has gained in the western\ncivilized world; and then I shall immediately take up the scientific\nhypothesis about creation, which originated with Linn\u00e6us as late as the\ncommencement of last century.\n\nAll the different conceptions which man has ever formed about the coming\ninto existence of the different animal and vegetable species may\nconveniently be divided into two great contrasted groups\u2014the natural\nand supernatural histories of creation.\n\nThese two groups, on the whole, correspond with the two different\nprincipal forms of the human notions of the universe which we have\nalready contrasted as the _monistic and the dualistic_ conception of\nnature. In the usual dualistic or teleological (vital) conception of the\nuniverse, organic nature is regarded as the purposely executed\nproduction of a Creator working according to a definite plan. Its\nadherents see in every individual species of animal and plant an\n\u201cembodied creative thought,\u201d the material expression of a _definite\nfirst cause_ (causa finalis) acting for a set purpose. They must\nnecessarily assume supernatural (not mechanical) processes for the\norigin of organisms. With justice, we may therefore designate their\nscheme of the world\u2019s growth as the _Supernatural History of Creation_.\nAmong all such teleological histories of creation, that of Moses has\ngained the greatest influence, since even so distinguished a naturalist\nas Linn\u00e6us has claimed admittance for it in Natural Science. Cuvier\u2019s\nand Agassiz\u2019s views of creation also belong to this group, as do in fact\nthose of the great majority of both scientific and unscientific men.\n\nOn the other hand, the theory of development carried out by Darwin,\nwhich we shall have to treat of here as the _Non-miraculous_ or _Natural\nHistory of Creation_, and which has already been put forward by Goethe\nand Lamarck, must, if carried out logically, lead to the monistic or\nmechanical (causal) conception of the universe. In opposition to the\ndualistic or teleological conception of nature, our theory considers\norganic, as well as inorganic, bodies to be the necessary products of\nnatural forces. It does not see in every individual species of animal\nand plant the embodied thought of a personal Creator, but the expression\nfor the time being of a mechanical process of development of matter, the\nexpression of a necessarily active cause, that is, of a mechanical cause\n(causa efficiens). Where teleological Dualism seeks the arbitrary\nthoughts of a capricious Creator in the miracles of creation, causal\nMonism finds in the process of development the necessary effects of\neternal immutable laws of nature.\n\nThe Monism here maintained by us is often considered identical with\nMaterialism. Now, as Darwinism, and in fact the whole theory of\ndevelopment, has been designated as \u201c_materialistic_,\u201d I cannot avoid\nhere at once guarding myself against this ambiguous word, and against\nthe malice with which, in certain quarters, it is employed to stigmatize\nour doctrine.\n\nBy the word \u201c_Materialism_,\u201d two completely different things are very\nfrequently confounded and mixed up, which in reality have nothing\nwhatever to do with each other, namely, scientific and moral\nmaterialism. Scientific materialism, which is identical with our Monism,\naffirms in reality no more than that everything in the world goes on\nnaturally\u2014that every effect has its cause, and every cause its effect.\nIt therefore assigns to causal law\u2014that is, the law of a necessary\nconnection between cause and effect\u2014its place over the entire series of\nphenomena that can be known. At the same time, scientific materialism\npositively rejects every belief in the miraculous, and every conception,\nin whatever form it appears, of supernatural processes. Accordingly,\nnowhere in the whole domain of human knowledge does it recognize real\nmetaphysics, but throughout only physics; through it the inseparable\nconnection between matter, form, and force becomes self evident. This\nscientific materialism has long since been so universally acknowledged\nin the wide domain of inorganic science, in Physics and Chemistry, in\nMineralogy and Geology, that no one now doubts its sole authority. But\nin Biology, or Organic science, the case is very different; here its\nvalue is still continually a matter of dispute in many quarters. There\nis, however, nothing else which can be set up against it, excepting the\nmetaphysical spectre of a vital power, or empty theological dogma. If we\ncan prove that all nature, so far as it can be known, is only _one_,\nthat the same \u201cgreat, eternal, iron laws\u201d are active in the life of\nanimals and plants, as in the growth of crystals and in the force of\nsteam, we may with reason maintain the monistic or mechanical view of\nthings throughout the domain of Biology\u2014in Zoology and Botany\u2014whether\nit be stigmatized as \u201cmaterialism\u201d or not. In such a sense all exact\nscience, and the law of cause and effect at its head, is purely\nmaterialistic.\n\n_Moral_, or _ethical Materialism_, is something quite distinct from\nscientific materialism, and has nothing whatever in common with the\nlatter. This real materialism proposes no other aim to man in the course\nof his life than the most refined possible gratification of his senses.\nIt is based on the delusion that purely material enjoyment can alone\ngive satisfaction to man; but as he can find that satisfaction in no one\nform of sensuous pleasure, he dashes on weariedly from one to another.\nThe profound truth that the real value of life does not lie in material\nenjoyment, but in moral action\u2014that true happiness does not depend upon\nexternal possessions, but only in a virtuous course of life\u2014this is\nunknown to ethical materialism. We therefore look in vain for such\nmaterialism among naturalists and philosophers, whose highest happiness\nis the intellectual enjoyment of Nature, and whose highest aim is the\nknowledge of her laws. We find it in the palaces of ecclesiastical\nprinces, and in those hypocrites who, under the outward mask of a pious\nworship of God, solely aim at hierarchical tyranny over, and material\nspoliation of, their fellow-men. Blind to the infinite grandeur of the\nso-called \u201craw material,\u201d and the glorious world of phenomena arising\nfrom it\u2014insensible to the inexhaustible charms of Nature, and without a\nknowledge of her laws\u2014they stigmatize all natural science, and the\nculture arising from it, as sinful \u201cmaterialism,\u201d while really it is\nthis which they themselves exhibit in a most shocking form. Satisfactory\nproofs of this are furnished, not only by the whole history of the\nCatholic Popes, with their long series of crimes, but also by the\nhistory of the morals of orthodoxy in every form of religion.\n\nIn order, then, to avoid in future the usual confusion of this utterly\nobjectionable Moral Materialism with our Scientific Materialism, we\nthink it necessary to call the latter either _Monism_ or _Realism_. The\nprinciple of this _Monism_ is the same as what Kant terms the\n\u201cprinciple of mechanism,\u201d and of which he expressly asserts, that\n_without it there can be no natural science at all_. This principle is\nquite inseparable from our Non-miraculous History of Creation, and\ncharacterizes it as opposed to the teleological belief in the miracles\nof a Supernatural History of Creation.\n\nLet us now first of all glance at the most important of all the\nsupernatural histories of creation, I mean that of Moses, as it has been\nhanded down to us in the Bible, the ancient document of the history and\nlaws of the Jewish people. The Mosaic history of creation, since in the\nfirst chapter of Genesis it forms the introduction to the Old Testament,\nhas enjoyed, down to the present day, general recognition in the whole\nJewish and Christian world of civilization. Its extraordinary success is\nexplained not only by its close connection with Jewish and Christian\ndoctrines, but also by the simple and natural chain of ideas which runs\nthrough it, and which contrasts favourably with the confused mythology\nof creation current among most of the other ancient nations. First the\nLord God creates the earth as an inorganic body; then he separates light\nfrom darkness, then water from the dry land. Now the earth has become\ninhabitable for organisms, and plants are first created, animals\nlater\u2014and among the latter the inhabitants of the water and the air\nfirst, afterwards the inhabitants of the dry land. Finally God creates\nman, the last of all organisms, in his own image, and as the ruler of\nthe earth.\n\nTwo great and fundamental ideas, common also to the non-miraculous\ntheory of development, meet us in this Mosaic hypothesis of creation,\nwith surprising clearness and simplicity\u2014the idea of separation or\n_differentiation_, and the idea of progressive development or\n_perfecting_. Although Moses looks upon the results of the great laws of\norganic development (which we shall later point out as the necessary\nconclusions of the Doctrine of Descent) as the direct actions of a\nconstructing Creator, yet in his theory there lies hidden the ruling\nidea of a progressive development and a differentiation of the\noriginally simple matter. We can therefore bestow our just and sincere\nadmiration on the Jewish lawgiver\u2019s grand insight into nature, and his\nsimple and natural hypothesis of creation, without discovering in it a\nso-called \u201cdivine revelation.\u201d That it cannot be such is clear from the\nfact that two great fundamental errors are asserted in it, namely,\nfirst, the _geocentric_ error that the earth is the fixed central point\nof the whole universe, round which the sun, moon, and stars move; and\nsecondly, the _anthropocentric_ error, that man is the premeditated aim\nof the creation of the earth, for whose service alone all the rest of\nnature is said to have been created. The former of these errors was\ndemolished by Copernicus\u2019 System of the Universe in the beginning of the\n16th century, the latter by Lamarck\u2019s Doctrine of Descent in the\nbeginning of the 19th century.\n\nAlthough the geocentric error of the Mosaic history was demonstrated by\nCopernicus, and thereby its authority as an absolutely perfect divine\nrevelation was destroyed, yet it has maintained, down to the present\nday, such influence, that it forms in many wide circles the principle\nobstacle to the adoption of a natural theory of development. Even in our\ncentury, many naturalists, especially geologists, have tried to bring\nthe Mosaic theory into harmony with the recent results of natural\nscience, and have, for example, interpreted Moses\u2019 seven days of\ncreation as seven great geological periods. However, all these ingenious\nattempts at interpretation have so utterly failed, that they require no\nrefutation here. The Bible is no scientific book, but consists of\nrecords of the history, the laws, and the religion of the Jewish people,\nthe high merit of which, as a history of civilization, is not impaired\nby the fact that in all scientific questions it has no commanding\nimportance, and is full of gross errors.\n\nWe may now make a great stride over more than three thousand years, from\nMoses, who died about the year 1480 before Christ, to Linn\u00e6us, who was\nborn in the year 1707 after Christ. During this whole period no history\nof creation was brought forward that gained any lasting importance, or\nthe closer examination of which would here be of any interest. Indeed,\nduring the last fifteen hundred years, since Christianity gained its\nsupremacy, the Mosaic history of creation, together with the dogmas\nconnected with it, has become so generally predominant, that the 19th\ncentury is the first that has dared positively to rise against it. Even\nthe great Swedish naturalist, Linn\u00e6us, the founder of modern natural\nhistory, linked his System of Nature most closely to the Mosaic history\nof creation.\n\nThe extraordinary progress which Charles Linn\u00e6us made in the so-called\ndescriptive natural sciences, consists, as is well known, in his having\nestablished a system of nomenclature of animals and plants, which he\ncarried out in a manner so perfectly logical and consistent, that down\nto the present day it has remained in many respects the standard for all\nsucceeding naturalists engaged in the study of the forms of animals and\nplants. Although Linn\u00e6us\u2019 system was artificial, although in classifying\nanimal and vegetable species he only sought and employed single parts as\nthe foundation for his divisions, it has, nevertheless, gained the\ngreatest success; firstly, in consequence of its being carried out\nconsistently, and secondly, by its nomenclature of natural bodies, which\nhas become extremely important, and at which we must here briefly\nglance.\n\nBefore Linn\u00e6us\u2019 time, many vain attempts had been made to throw light\nupon the endless chaos of different animal and vegetable forms (then\nknown) by adopting for them suitable names and groupings; but Linn\u00e6us,\nby a happy hit, succeeded in accomplishing this important and difficult\ntask, when he established the so-called \u201c_binary nomenclature_.\u201d The\nbinary nomenclature, or the twofold designation, as Linn\u00e6us first\nestablished it, is still universally applied by all zoologists and\nbotanists, and will, no doubt, maintain itself, for a long time to come,\nwith undiminished authority. It consists in this, that every species of\nanimal and plant is designated by two names, which stand to each other\nin the same relation as do the christian and surnames of a man. The\nspecial name which corresponds with the christian name, and expresses\nthe idea of \u201ca species,\u201d serves as the common designation of all\nindividual animals or plants, which are equal in all essential matters\nof form, and are only distinguished by quite subordinate features. The\nmore general name, on the other hand, corresponding with the surname,\nand which expresses the idea of a genus, serves for the common\ndesignation of all the most nearly similar kinds or species.\n\nAccording to Linn\u00e6us\u2019 plan, the more general and comprehensive generic\nname is written first; the special subordinate name of the species\nfollows it. Thus, for example, the common cat is called Felis domestica;\nthe wild cat, Felis catus; the panther, Felis pardus; the jaguar, Felis\nonca; the tiger, Felis tigris; the lion, Felis leo. All these six kinds\nof animals of prey are different species of one and the same\ngenus\u2014Felis. Or, to add an example from the vegetable kingdom,\naccording to Linn\u00e6us\u2019 designation the pine is Pinus abies; the fir,\nPinus picea; the larch, Pinus larix; the Italian pine, Pinus pinea; the\nSiberian stone pine, Pinus cembra; the knee timber, Pinus mughus; the\ncommon pine, Pinus silvestris. All these seven kinds of pines are\ndifferent species of one and the same genus\u2014Pinus.\n\nPerhaps this advance made by Linn\u00e6us may seem to some only of\nsubordinate importance in the practical distinction and designation of\nthe variously formed organisms. But in reality it was of the very\ngreatest importance, both from a practical and theoretical point of\nview. For now, for the first time, it became possible to arrange the\nimmense mass of different organic forms according to their greater or\nless degree of resemblance, and to obtain an easy survey of the general\noutlines of such a \u201csystem.\u201d Linn\u00e6us facilitated the tabulation and\nsurvey of this \u201csystem\u201d of plants and animals still more by placing\ntogether the most nearly similar genera into so-called orders (ordines);\nand by uniting the most nearly similar orders into still more\ncomprehensive main divisions or classes. Thus, according to Linn\u00e6us,\neach of the two organic kingdoms were broken up into a number of\nclasses, the vegetable kingdom into twenty-four, and the animal kingdom\ninto six. Each class again contains several orders. Every single order\nmay contain a number of genera, and, again, every single genus several\nspecies.\n\nValuable as was Linn\u00e6us\u2019 binary nomenclature in a _practical_ way, in\nbringing about a comprehensive systematic distinction, designation,\narrangement, and division of the organic world of forms, yet the\nincalculable _theoretical_ influence which it gained forthwith in\nrelation to the history of creation was no less important. Even now all\nthe important fundamental questions as to the history of creation turn\nfinally upon the decision of the very remote and unimportant question,\n_What really are kinds or species?_ Even now the _idea of organic\nspecies_ may be termed the central point of the whole question of\ncreation, the disputed centre, about the different conceptions of which\nDarwinists and Anti-Darwinists fight.\n\nAccording to Darwin\u2019s opinion, and that of his adherents, the different\nspecies of one and the same genus of animals and plants are nothing else\nthan differently developed descendants of one and the same original\nprimary form. The different kinds of pine mentioned above would\naccordingly have originated from a single prim\u00e6val form of pine. In like\nmanner the origin of all the species of cat mentioned above would be\ntraced to a single common form of Felis, the ancestor of the whole\ngenus. But further, in accordance with the Doctrine of Descent, all the\ndifferent genera of one and the same order ought also to be descended\nfrom one common primary ancestor, and so, in like manner, all orders of\na class from a single primary form.\n\nOn the other hand, according to the idea of Darwin\u2019s opponents, all\nspecies of animals and plants are quite independent of each other, and\nonly the individuals of each species have originated from a single\nprimary form. But if we ask them how they conceive these original\nprimary forms of each species to have come into existence, they answer\nwith a leap into the incomprehensible, \u201cThey were created.\u201d\n\nLinn\u00e6us himself defined the idea of species in this manner by saying,\n\u201cThere are as many different species as there were different forms\ncreated in the beginning by the infinite Being.\u201d (\u201cSpecies tot sunt\ndivers\u00e6, quot diversas formas ab initio creavit infinitum ens.\u201d) In this\nrespect, therefore, he follows most closely the Mosaic history of\ncreation, which in the same way maintains that animals and plants were\ncreated \u201ceach one after its kind.\u201d Linn\u00e6us, accepting this, held that\noriginally of each species of animals and plants either a single\nindividual or a pair had been created; in fact a pair, or, as Moses\nsays, \u201ca male and a female\u201d of those species which have separate sexes,\nbut of those species in which each individual combines both sexual\norgans (hermaphrodites), as for instance the earthworm, the garden and\nvineyard snails, as well as the great majority of plants, a single\nindividual.\n\nLinn\u00e6us further follows the Mosaic legend in regard to the flood, by\nsupposing that the great general flood destroyed all existing organisms,\nexcept those few individuals of each species (seven pairs of the birds\nand of clean animals, one pair of unclean animals) which Noah saved in\nthe ark, and which were placed again on land, on Mount Ararat, after the\nflood had subsided. He tried to explain the geographical difficulty of\nthe living together of the most different animals and plants, as\nfollows: Mount Ararat, in Armenia, being situated in a warm climate, and\nrising over 16,000 feet in height, combines in itself the conditions for\na temporary common abode of such animals as live in different zones.\nAccordingly, animals accustomed to the polar regions could climb up the\ncold mountain ridges, those accustomed to a warm climate could go down\nto the foot of the mountain, and the inhabitants of a temperate zone\ncould remain midway up the mountain. From this point it was possible for\nthem to spread north and south over the earth.\n\nIt is scarcely necessary to remark that this Linn\u00e6an hypothesis of\ncreation, which evidently was intended to harmonize most closely with\nthe prevailing belief in the Bible, requires no serious refutation. When\nwe consider Linn\u00e6us\u2019 clearness and sagacity in other matters, we may\ndoubt whether he believed it himself. As to the simultaneous origin of\nall individuals of each species from one pair of ancestors respectively\n(or in the case of the hermaphrodite species, from one original\nhermaphrodite), it is clearly quite untenable; for, apart from other\nreasons, in the first days after the creation, the few animals of prey\nwould have sufficed to have utterly demolished all the herbivorous\nanimals, as the herbivorous animals must have destroyed the few\nindividuals of the different species of plants. The existence of such an\nequilibrium in the economy of nature as obtains at present cannot\npossibly be conceived, if only one individual of each species, or only\none pair, had originally and simultaneously been created.\n\nMoreover, how little importance Linn\u00e6us himself attached to this\nuntenable hypothesis of creation is clear, among other things, from the\nfact that he recognized _Hybridism_ (crossing) as a source of the\nproduction of new species. He assumed that a great number of independent\nnew species had originated by the interbreeding of two different\nspecies. Indeed, such hybrids are not at all rare in nature, and it is\nnow proved that a great number of species, for example, of the genus\nRubus (bramble), mullen (Verbascum), willow (Salix), thistle (Cirsium),\nare hybrids of different species of these genera. We also know of\nhybrids between hares and rabbits (two species of the genus Lepus),\nfurther of hybrids between different species of dog (genus Canis), etc.,\nwhich can be propagated as independent species.\n\nIt is certainly very remarkable that Linn\u00e6us asserted the physiological\n(therefore mechanical) origin of new species in this process of\nhybridism. It clearly stands in direct opposition to the supernatural\norigin of the other species by creation, which he accepted as put\nforward in the Mosaic account. The one set of species would therefore\nhave originated by dualistic (teleological) creation, the other by\nmonistic (mechanical) development.\n\nThe great and well merited authority which Linn\u00e6us gained by his\nsystematic classification and by his other services to Biology, was\nclearly the reason why his views of creation also remained, throughout\nthe whole of the last century, undisputed and generally recognized. If\nthroughout systematic Zoology and Botany the distinctions,\nclassification, and designations of species, introduced by Linn\u00e6us, and\nthe dogmatic ideas connected therewith had not been maintained\u2014more or\nless unaltered\u2014we should be at a loss to understand how his idea of an\nindependent creation of single species could have stood, by itself down\nto the present day. It is only owing to his great authority, and through\nhis attaching himself to the prevailing Biblical belief, that his\nhypothesis of creation has retained its position so long.\n\n\n\n\nCHAPTER III.\n\nTHE HISTORY OF CREATION ACCORDING TO CUVIER AND AGASSIZ.\n\n\n   General Theoretical Meaning of the Idea of\n   Species.\u2014Distinction between the Theoretical and\n   Practical Definition of the Idea of Species.\u2014Cuvier\u2019s\n   Definition of Species.\u2014Merits of Cuvier as the Founder\n   of Comparative Anatomy.\u2014Distinction of the Four\n   Principal Forms (types or branches) of the Animal\n   Kingdom, by Cuvier and B\u00e4r.\u2014Cuvier\u2019s Services to\n   Pal\u00e6ontology.\u2014His Hypothesis of the Revolutions of our\n   Globe, and the Epochs of Creation separated by\n   them.\u2014Unknown Supernatural Causes of the Revolutions,\n   and the subsequent New Creations.\u2014Agassiz\u2019s Teleological\n   System of Nature.\u2014His Conception of the Plan of\n   Creation, and its six Categories (groups in\n   classification).\u2014Agassiz\u2019s Views of the Creation of\n   Species.\u2014Rude Conception of the Creator as a man-like\n   being in Agassiz\u2019s Hypothesis of Creation.\u2014Its internal\n   Inconsistency and Contradictions with the important\n   Pal\u00e6ontological Laws discovered by Agassiz.\n\n\nThe real matter of dissension in the contest carried on by naturalists\nas to the origin of organisms, their creation and development, lies in\nthe conceptions which are entertained about the _nature of species_.\nNaturalists either agree with Linn\u00e6us, and look upon the different\nspecies as distinct forms of creation, independent of one another, or\nthey assume with Darwin their blood-relationship. If we share Linn\u00e6us\u2019\nview (which was discussed in our last chapter), that the different\norganic species came into existence independently\u2014that they have no\nblood-relationship\u2014we are forced to admit that they were created\nindependently, and we must either suppose that every single organic\nindividual was a special act of creation (to which surely no naturalist\nwill agree), or we must derive all individuals of every species from a\nsingle individual, or from a single pair, which did not arise in a\nnatural manner, but was called into being by command of a Creator. In so\ndoing, however, we turn aside from the safe domain of a rational\nknowledge of nature, and take refuge in the mythological belief in\nmiracles.\n\nIf, on the other hand, with Darwin, we refer the similarity of form of\nthe different species to real blood-relationship, we must consider all\nthe different species of animals and plants as the altered descendants\nof one or a few most simple original forms. Viewed in this way, the\nNatural System of organisms (that is, their tree-like and branching\narrangement and division into classes, orders, families, genera, and\nspecies) acquires the significance of a real genealogical tree, whose\nroot is formed by those original archaic forms which have long since\ndisappeared. But a truly natural and consistent view of organisms can\nassume no supernatural act of creation for even those simplest original\nforms, but only a coming into existence by _spontaneous generation_[2]\n(archigony, or generatio spontanea). From Darwin\u2019s view of the nature of\nspecies, we arrive therefore at a _natural theory of development_; but\nfrom Linn\u00e6us\u2019 conception of the idea of species, we must assume a\n_supernatural dogma of creation_.\n\nMost naturalists after Linn\u00e6us, whose great services in\nsystematic and descriptive natural history won for him such high\nauthority, followed in his footsteps, and without further inquiry into\nthe origin of organization, they assumed, in the sense of Linn\u00e6us, an\nindependent creation of individual species, in conformity with the\nMosaic account of creation. The foundation of their conception was based\nupon Linn\u00e6us\u2019 words: \u201cThere are as many different species as there were\ndifferent forms created in the beginning by the Infinite Being.\u201d We must\nhere remark at once, without going further into the definition of\nspecies, that all zoologists and botanists in their classificatory\nsystems, in the practical distinction and designation of species of\nanimals and plants, never troubled, or even could trouble, themselves in\nthe slightest degree about this assumed creation of the parent forms. In\nreference to this, one of our first zoologists, the ingenious Fritz\nM\u00fcller, makes the following striking observation: \u201cJust as in Christian\ncountries there is a catechism of morals, which every one knows by\nheart, but which no one considers it his duty to follow, or expects to\nsee followed by others,\u2014so zoology also has its dogmas, which are just\nas generally professed as they are denied in practice.\u201d (F\u00fcr Darwin, p.\n71.)(16)\n\nLinn\u00e6us\u2019 venerated dogma of species is just such an irrational dogma,\nand for that very reason it is powerful. Although most naturalists\nblindly submitted to it, yet they were, of course, never in a position\nto demonstrate the descent of individuals belonging to one species from\nthe common, originally created, primitive form. Zoologists and\nbotanists, in their systems of nomenclature, confined themselves\nentirely to the similarity of forms, in order to distinguish and name\nthe different species. They placed in one species all organic\nindividuals which were very similar, or almost identical in form, and\nwhich could only be distinguished from one another by very unimportant\ndifferences. On the other hand, they considered as different species\nthose individuals which presented more essential or more striking\ndifferences in the formation of their bodies. But of course this opened\nthe flood-gates to the most arbitrary proceedings in the systematic\ndistinctions of species. For as all the individuals of one species are\nnever completely alike in all their parts, but as every species varies\nmore or less, no one could point out which degree of variation\nconstituted a really \u201cgood species,\u201d or which degree indicated a \u201cmere\nvariety.\u201d\n\nThis dogmatic conception of the idea of species, and the arbitrary\nproceedings connected with it, necessarily led to the most perplexing\ncontradictions, and to the most untenable suppositions. This is clearly\ndemonstrable in the case of the celebrated Cuvier (born in 1769), who\nnext to Linn\u00e6us has exercised the greatest influence on the study of\nzoology. In his conception and definition of the idea of species, he\nagreed on the whole with Linn\u00e6us, and shared also his belief in an\nindependent creation of individual species. Cuvier considered their\nimmutability of such importance that he was led to the foolish\nassertion\u2014\u201cThe immutability of species is a necessary condition of the\nexistence of scientific natural history.\u201d As Linn\u00e6us\u2019 definition of\nspecies did not satisfy him, he made an attempt to give a more exact\nand, for systematic practice, a more useful definition, in the following\nwords: \u201cAll those individual animals and plants belong to one species\nwhich can be proved to be either descended from one another, or from\ncommon ancestors, or which are as similar to these as the latter are\namong themselves.\u201d\n\nIn dealing with this matter, Cuvier reasoned in the following\nmanner:\u2014\u201cIn those organic individuals, of which we know that they are\ndescended from one and the same common form of ancestors\u2014in which,\ntherefore, their common ancestry is empirically proved\u2014there can be no\ndoubt that they belong to one species, whether they differ much or\nlittle from one another, or whether they are almost alike or very\nunlike. Moreover, all those individuals also belong to this species\nwhich differ no more from the latter (those proved to be derived from a\ncommon stock) than these differ from one another.\u201d In a closer\nexamination of this definition of species given by Cuvier, it becomes at\nonce evident that it is neither theoretically satisfactory nor\npractically applicable. Cuvier, with this definition, began to move in\nthe same circle in which almost all subsequent definitions of species\nhave moved, through the assumption of their immutability.\n\nConsidering the extraordinary authority which George Cuvier has gained\nin the science of organic nature, and in consequence of the almost\nunlimited supremacy which his views exercised in zoology, during the\nfirst half of our century, it seems appropriate here to examine his\ninfluence a little more closely. This is all the more necessary as we\nhave to combat, in Cuvier, the most formidable opponent to the Theory of\nDescent and the monistic conception of nature.\n\nOne of the many and great merits of Cuvier is that he stands forth as\nthe founder of Comparative Anatomy. While Linn\u00e6us established the\ndistinction of species, genera, orders, and classes mostly upon external\ncharacters, and upon separate and easily discoverable signs in the\nnumber, size, place, and form of individual organic parts of the body,\nCuvier penetrated much more deeply into the essence of organization. He\ndemonstrated great and wide differences in the inner structure of\nanimals, as the real foundation of a scientific knowledge and\nclassification of them. He distinguished natural families in the classes\nof animals, and established his natural system of the animal kingdom on\ntheir comparative anatomy.\n\nThe progress from Linn\u00e6us\u2019 artificial system to Cuvier\u2019s natural system\nwas exceedingly important. Linn\u00e6us had arranged all animals in a single\nseries, which he divided into six classes, two classes of Invertebrate,\nand four classes of Vertebrate animals. He distinguished these\nartificially, according to the nature of their blood and heart. Cuvier,\non the other hand, showed that in the animal kingdom there were four\ngreat natural divisions to be distinguished, which he termed Principal\nForms, or General Plans, or Branches of the animal kingdom\n(Embranchments), namely\u20141. The Vertebrate animals (Vertebrata); 2. The\nArticulate animals (Articulata); 3. The Molluscous animals (Mollusca);\nand 4. The Radiate animals (Radiata). He further demonstrated that in\neach of these four branches a peculiar plan of structure or type was\ndiscernible, distinguishing each branch from the three others. In the\nVertebrate animals it is distinctly expressed by the form of the\nskeleton, or bony framework, as also by the structure and position of\nthe dorsal nerve-chord, apart from many other peculiarities. The\nArticulate animals are characterized by their ventral nerve-chord and\ntheir dorsal heart. In Molluscs the sack-shaped and non-articulate body\nis the distinguishing feature. The Radiate animals, finally, differ\nfrom the three other principal forms by their body being the combination\nof four or more main sections united in the form of radii (antimera).\n\nThe distinction of these four principal forms of animals, which has\nbecome extremely productive in the development of zoology, is commonly\nascribed entirely to Cuvier. However, the same thought was expressed\nalmost simultaneously, and independently of Cuvier, by B\u00e4r, one of the\ngreatest naturalists, and still living, who did the most eminent service\nin the study of animal development. B\u00e4r showed that in the development\nof animals, also, four different main forms (or types) must be\ndistinguished.(20) These correspond with the four plans of structure in\nanimals, which Cuvier distinguished on the ground of comparative\nanatomy. Thus, for example, the individual development of all Vertebrate\nanimals agrees, from the commencement, so much in its fundamental\nfeatures that the germs or embryos of different Vertebrate animals (for\nexample, of reptiles, birds, and mammals) in their earlier stages cannot\nbe distinguished at all. It is only at a late stage of development that\nthere gradually appear the more marked differences of form which\nseparate those different classes and orders from one another. The plan\nof structure, which shows itself in the individual development of\nArticulate animals (insects, spiders, crabs), is from the beginning\nessentially the same in all Articulate animals, but different from that\nof all Vertebrate animals. The same holds good, with certain\nlimitations, in Molluscous and Radiated animals.\n\nNeither B\u00e4r, who arrived at the distinction of the four animal types or\nprincipal forms through the history of the individual development\n(Embryology), nor Cuvier, who arrived at the same conclusion by means\nof comparative anatomy, recognized the true cause of this difference.\nThis is disclosed to us by the Theory of Descent. The wonderful and\nastonishing similarity in the inner organization and in the anatomical\nrelations of structure, and the still more remarkable agreement in the\nembryonic development of all animals belonging to one and the same type\n(for example, to the branch of the Vertebrate animals), is explained in\nthe simplest manner by the supposition of their common descent from a\nsingle primary original form. If this view is not accepted, then the\ncomplete agreement of the most different Vertebrate animals, in their\ninner structure and their manner of development, remains perfectly\ninexplicable. In fact it can only be explained by the law of\n_inheritance_.\n\nNext to the comparative anatomy of animals and the systematic zoology\nfounded anew by it, it was specially to the science of petrifactions, or\nPal\u00e6ontology, that Cuvier rendered great service. We must draw special\nattention to this, because these very pal\u00e6ontological views, and the\ngeological ideas connected with them, were held almost universally in\nthe highest esteem during the first half of the present century, and\ncaused the greatest hindrance to the working out of a truly natural\nhistory of creation.\n\nPetrifactions, the scientific study of which Cuvier promoted at the\nbeginning of our century in a most extensive manner, and established\nquite anew for the Vertebrate animals, play one of the most important\nparts in the \u201cnon-miraculous history of creation.\u201d For these remains and\nimpressions of extinct animals and plants, preserved to us in a\npetrified condition, are the true \u201cmonuments of the creation,\u201d the\ninfallible and indisputable records which fix the correct history of\norganisms upon an irrefragable foundation. All petrified or fossil\nremains and impressions tell us of the forms and structure of such\nanimals and plants as are either the progenitors and ancestors of the\npresent living organisms, or they are the representatives of extinct\ncollateral lines, which, together with the present living organisms,\nbranched off from a common stem.\n\nThese inestimable records of the history of creation throughout a long\nperiod played a subordinate part in science. Their true nature was\nindeed correctly understood, even more than five hundred years before\nChrist, by the great Greek philosopher, Xenophanes of Colophon, the same\nwho founded the so-called Eleatic philosophy, and who was the first to\ndemonstrate with convincing precision that all conceptions of personal\ngods result in more or less rude anthropomorphism.\n\nXenophanes for the first time, asserted that the fossil impressions of\nanimals and plants were real remains of formerly living creatures, and\nthat the mountains in whose rocks they were found must at an earlier\ndate have stood under water. But although other great philosophers of\nantiquity, and among them Aristotle, also possessed this true knowledge,\nyet throughout the illiterate Middle Ages, and even with some\nnaturalists of the last century, the idea prevailed that petrifactions\nwere so-called freaks of nature (lusus natur\u00e6), or products of an\nunknown formative power or instinct of nature (nisus formativus, vis\nplastica). Respecting the nature of this mysterious and mystic creative\npower, the strangest ideas were formed. Some believed that this\nconstructive power\u2014the same to which they also ascribed the coming\ninto existence of the present species of animals and plants\u2014had made\nnumerous attempts to create organisms of different forms, but that these\nattempts had only partially succeeded, had often failed, and that\npetrifactions were nothing more than such unsuccessful attempts.\nAccording to others, petrifactions originated from the influence of the\nstars upon the interior of the earth.\n\nOthers, again, had the still cruder notion that the Creator had first\nmade models (out of mineral substances\u2014for example, of gypsum or clay)\nof those forms of animals and plants which he afterwards executed in\norganic substances, and into which he breathed his living breath;\npetrifactions were accordingly such rude inorganic models. Even as late\nas the last century these crude ideas prevailed, and it was assumed, for\nexample, that there existed a special \u201cseminal air,\u201d which was said to\npenetrate into the earth with the water, and by fructifying the stones\nformed petrifactions or \u201cstony flesh\u201d (caro fossilis).\n\nIt took a very long time before the simple and natural view was\naccepted, namely, that petrifactions are in reality nothing but what\nthey appear to simple observation\u2014the indestructible remains of extinct\norganisms. It is true the celebrated painter, Leonardo da Vinci, in the\n15th century, ventured to assert that the mud which was constantly\ndeposited by water was the cause of petrifactions, as it surrounded the\nindestructible shells of mussels and snails which lay at the bottom of\nthe waters, and gradually turned them into solid stone. The same idea\nwas maintained in the 16th century by a Parisian potter, Palissy by\nname, who became celebrated on account of his invention of china.\nHowever, the so-called \u201cprofessional men\u201d were very far from paying any\nregard to these correct assertions of a simple and healthy human\nunderstanding; it was not till the end of the last century that it was\ngenerally accepted, in consequence of the foundation of the Neptunian\ngeology by Werner.\n\nThe foundation of a more strictly scientific pal\u00e6ontology, however,\nbelongs to the beginning of our century, when Cuvier published his\nclassic researches on petrified Vertebrate animals, and when his great\nopponent, Lamarck, made known his remarkable investigations on fossil\nInvertebrate animals, especially on petrified snails and clams. In\nCuvier\u2019s celebrated work \u201cOn the Fossil Bones\u201d of Vertebrate\nanimals\u2014principally of mammals and reptiles\u2014we see that he had already\narrived at the knowledge of some very important and general\npal\u00e6ontological laws, which are of great consequence to the history of\ncreation. Foremost among them stands the assertion that the extinct\nspecies of animals, whose remains we find petrified in the different\nstrata of the earth\u2019s crust, lying one above another, differ all the\nmore strikingly from the still living kindred species of animals the\ndeeper those strata lie\u2014in other words, the earlier the animals lived\nin past ages. In fact, in every perpendicular section of the stratified\ncrust of the earth we find that the different strata, deposited by the\nwater in a certain historical succession, are characterized by different\npetrifactions, and that these extinct organisms become more like those\nof the present day the higher the strata lie; in other words, the more\nrecent the period in the earth\u2019s history in which they lived, died, and\nbecame encrusted by the deposited and hardened strata of mud.\n\nHowever important this general observation of Cuvier\u2019s was in one\nsense, yet in another it became to him the source of a very serious\nerror. For as he considered the characteristic petrifactions of each\nindividual group of strata (which had been deposited during one main\nperiod of the earth\u2019s history) to be entirely different from those of\nthe strata lying above or below, and as he erroneously believed that one\nand the same species of animal was never found in two succeeding groups\nof strata, he arrived at the false idea, which was accepted as a law by\nmost subsequent naturalists, that a series of quite distinct periods of\ncreation had succeeded one another. Each period was supposed to have had\nits special animal and vegetable world, each its peculiar specific Fauna\nand Flora.\n\nCuvier imagined that the whole history of the earth\u2019s crust, since the\ntime when living creatures had first appeared on the surface, must be\ndivided into a number of perfectly distinct periods, or divisions of\ntime, and that the individual periods must have been separated from one\nanother by peculiar revolutions of an unknown nature (cataclysms, or\ncatastrophes). Each revolution was followed by the utter annihilation of\nthe till then existing animals and plants, and after its termination a\ncompletely new creation of organic forms took place. A new world of\nanimals and plants, absolutely and specifically distinct from those of\nthe preceding historical periods, was called into existence at once, and\nnow again peopled the globe for thousands of years, till it again\nperished suddenly in the crash of a new revolution.\n\nAbout the nature and causes of these revolutions, Cuvier expressly said\nthat no idea could be formed, and that the present active forces in\nnature were not sufficient for their explanation. Cuvier points out four\nactive causes as the natural forces, or mechanical agents, at present\nconstantly but slowly at work in changing the earth\u2019s surface: first,\n_rain_, which washes down the steep mountain slopes and heaps up d\u00e9bris\nat their foot; secondly, _flowing waters_, which carry away this d\u00e9bris\nand deposit it as mud in stagnant waters; thirdly, the sea, whose\nbreakers gnaw at the steep _sea_ coasts, and throw up \u201cdunes\u201d on the\nflat sea margins; finally and fourthly, _volcanos_, which break through\nand heave up the strata of the earth\u2019s hardened crust, and pile up and\nscatter about the products of their eruptions. Whilst Cuvier recognizes\nthe constant slow transformation of the present surface of the earth by\nthese four mighty causes, he asserts at the same time that they would\nnot have sufficed to effect the revolutions of the remote ages, and that\nthe anatomical structure of the earth\u2019s surface cannot be explained by\nthe necessary action of those mechanical agents: the great and\nmarvellous revolutions of the whole earth\u2019s surface must, according to\nhim, have been rather the effects of very peculiar causes, completely\nunknown to us; the usual thread of development was broken by them, and\nthe course of nature altered.\n\nThese views Cuvier explained in a special work \u201cOn the Revolutions of\nthe Earth\u2019s Surface, and the Changes which they have wrought in the\nAnimal World.\u201d They were maintained, and generally accepted for a long\ntime, and became the greatest obstacle to the development of a natural\nhistory of the creation. For if such all-destructive revolutions had\nactually occurred, of course a continuity of the development of species,\na connecting thread in the organic history of the earth, could not be\nadmitted at all, and we should be obliged to have recourse to the\naction of supernatural forces; that is, to the interference of miracles\nin the natural course of things. It is only through miracles that these\nrevolutions of the earth could have been brought about, and it is only\nthrough miracles that, after their cessation and at the commencement of\neach new period, a new animal and vegetable kingdom could have been\ncreated. But science has no room for miracles, for by miracles we\nunderstand an interference of supernatural forces in the natural course\nof development of matter.\n\nJust as the great authority which Linn\u00e6us gained by his system of\ndistinguishing and naming organic species led his successors to a\ncomplete ossification, as it were, of the dogmatic idea of species and\nto a real abuse of the systematic distinction implied by it, so the\ngreat services which Cuvier had rendered to the knowledge and\ndistinction of extinct species became the cause of a general adoption of\nhis theory of revolutions and catastrophes, and of the false views of\ncreation connected therewith. The consequence of this was that, during\nthe first half of our century, most zoologists and botanists clung to\nthe opinion that a series of independent periods in the organic history\nof the earth had existed; that each period was distinguished by distinct\nand peculiar kinds of animal and vegetable species; that these were\nannihilated at the termination of the period by a general revolution;\nand that, after the cessation of the latter, a new world of different\nspecies of animals and plants was created.\n\nIt is true some independent thinkers, above all the great physical\nphilosopher, Lamarck, even at an early period, set forth a series of\nweighty reasons which refuted Cuvier\u2019s theory of cataclysms, and\npointed to a perfectly continuous and uninterrupted developmental\nhistory of all the organic inhabitants of the earth through all ages.\nThey maintained that the animal and vegetable species of each period\nwere derived from those of the preceding period, and were only the\naltered descendants of the former. This true conception, however, being\nopposed to Cuvier\u2019s great authority, was then unable to make way. Nay,\neven after Cuvier\u2019s theory of catastrophes had been completely cast out\nfrom the domain of geology by Lyell\u2019s classic Principles of Geology,\nwhich appeared in 1830, still his idea of the specific distinctness of a\nseries of organic creations maintained its influence, in many ways, in\nthe science of Pal\u00e6ontology. (Gen. Morph. ii. 312.)\n\nBy a curious coincidence, thirteen years ago, almost at the same time\nthat Cuvier\u2019s History of Creation received its death-blow by Darwin\u2019s\nbook, another celebrated naturalist made an attempt to re-establish it,\nand to adopt it in the roughest manner, as a part of a\nteleologico-theological system of nature. This was the Swiss geologist,\nLouis Agassiz, who attained a great reputation by his theory of glaciers\nand the ice-period, borrowed from Schimper and Charpentier, and who has\nbeen living in North America for many years. He commenced in 1858 to\npublish a work planned on a very large scale, which bears the title of\n\u201cContributions to the Natural History of the United States of North\nAmerica.\u201d The first volume of this work, although large and costly,\nowing to the patriotism of the Americans, had an unprecedented sale; its\ntitle is, \u201cAn Essay on Classification.\u201d(5)\n\nIn this essay Agassiz not only discusses the natural series of\norganisms, and the different attempts of naturalists at classification,\nbut also all the general biological phenomena which have reference to\nit. The history of the development of organisms, both the embryonal and\nthe pal\u00e6ontological, comparative anatomy, the general economy of nature,\nthe geographical and topographical distribution of animals and\nplants\u2014in short, almost all the general phenomena of organic nature are\ndiscussed in Agassiz\u2019s Essay on Classification, and are explained in a\nsense and from a point of view which is thoroughly opposed to that of\nDarwin. While Darwin\u2019s chief merit lies in the fact that he demonstrates\nnatural causes for the coming into existence of animal and vegetable\nspecies, and thereby establishes the mechanical or monistic view of the\nuniverse as regards this most difficult branch of the history of\ncreation, Agassiz, on the contrary, strives to exclude every mechanical\nhypothesis from the subject, and to put the supernatural interference of\na personal Creator in the place of the natural forces of matter;\nconsequently, to establish a thoroughly teleological or dualistic view\nof the universe. It will not be out of place if I examine a little more\nclosely Agassiz\u2019s biological views, and especially his ideas of\ncreation, because no other work of our opponents treats the important\nfundamental questions with equal minuteness, and because the utter\nuntenableness of the dualistic conception of nature becomes very evident\nfrom the failure of this attempt.\n\nThe organic _species_, the various conceptions of which we have above\ndesignated as the real centre of dispute in the opposed views of\ncreation, is looked upon by Agassiz, as by Cuvier and Linn\u00e6us, as a form\nunchangeable in all its essential characteristics. The species may\nindeed change and vary within certain narrow limits; never in essential\nqualities, but only in unessential points. No new species could ever\nproceed from the changes or varieties of a species. Not one of all\norganic species, therefore, is ever derived from another, but each\nindividual species has been separately created by God. Each individual\nspecies, as Agassiz expresses it, is \u201can embodied creative thought\u201d of\nGod.\n\nIn direct opposition to the fact established by pal\u00e6ontological\nexperience, that the duration of the individual organic species is most\nunequal, and that many species continue unchanged through several\nsuccessive periods of the earth\u2019s history, while others only existed\nduring a small portion of such a period, Agassiz maintains that one and\nthe same species never occurs in two different periods, but that each\nindividual period is characterized by species of animals and plants\nwhich are quite peculiar, and belong to it exclusively. He further\nshares Cuvier\u2019s opinion that the whole of these inhabitants were\nannihilated by the great and universal revolutions of the earth\u2019s\nsurface, which divide two successive periods, and that after its\ndestruction a new and specifically different assemblage of organisms was\ncreated. This new creation Agassiz supposes to have taken place in this\nmanner: viz., that at each creation all the inhabitants of the earth, in\ntheir full average number of individuals, and in the peculiar relations\ncorresponding to the economy of nature, were, as a whole, suddenly\nplaced upon the earth by the Creator. In saying this he puts himself in\nopposition to one of the most firmly established and most important laws\nof animal and vegetable geography\u2014namely, to the law that each species\nhas a single original locality of origin, or a so-called \u201ccentre of\ncreation,\u201d from which it has gradually spread over the rest of the\nearth. Instead of this, Agassiz assumes each species to have been\ncreated at several points of the earth\u2019s surface, and that in each case\na large number of individuals was created.\n\nThe \u201cnatural system\u201d of organisms, the different groups and categories\nof which arranged above one another\u2014namely, the branches, classes,\norders, families, genera, and species\u2014we consider, in accordance with\nthe Theory of Descent, as different branches and twigs of the organic\nfamily-tree, is, according to Agassiz, the direct expression of the\ndivine plan of creation, and the naturalist, while investigating the\nnatural system, repeats the creative thoughts of God. In this Agassiz\nfinds the strongest proof that man is the image and child of God. The\ndifferent stages of groups or categories of the natural system\ncorrespond with the different stages of development which the divine\nplan of creation had attained. The Creator, in projecting and carrying\nout this plan, starting from the most general ideas of creation, plunged\nmore and more into specialities. For instance, when creating the animal\nkingdom, God had in the first place four totally distinct ideas of\nanimal bodies, which he embodied in the different structures of the four\ngreat, principal forms, types, or branches of the animal kingdom;\nnamely, vertebrate animals, articulate animals, molluscous animals, and\nradiate animals. The Creator then, having reflected in what manner he\nmight vary these four different plans of structure, next created within\neach of the four principal forms, several different classes\u2014for\nexample, in the vertebrate animal form, the classes of mammals, birds,\nreptiles, amphibious animals, and fishes. Then God further reflected\nupon the individual classes, and by various modifications in the\nstructure of each class, he produced the individual orders. By further\nvariation in the order, he created natural families. As the Creator\nfurther varied the peculiarities of structure of individual parts in\neach family, genera arose. In further meditation on his plan of\ncreation, he entered so much into detail that individual species came\ninto existence, which, consequently, are embodied creative thoughts of\nthe most special kind. It is only to be regretted that the Creator\nexpressed these most special and most deeply considered \u201ccreative\nthoughts\u201d in so very indistinct and loose a manner, and that he\nimprinted so vague a stamp upon them, and permitted them to vary so\nfreely that not one naturalist is able to distinguish the \u201cgood\u201d from\nthe \u201cbad species,\u201d or a genuine species from varieties, races, etc.\n(Gen. Morph. ii. 373.)\n\nWe see, then, according to Agassiz\u2019s conception, that the Creator, in\nproducing organic forms, goes to work exactly as a human architect, who\nhas taken upon himself the task of devising and producing as many\ndifferent buildings as possible, for the most manifold purposes, in the\nmost different styles, in various degrees of simplicity, splendour,\ngreatness, and perfection. This architect would perhaps at first choose\nfour different styles for all these buildings, say the Gothic,\nByzantine, Chinese, and Rococo styles. In each of these styles he would\nbuild a number of churches, palaces, garrisons, prisons, and\ndwelling-houses. Each of these different buildings he would execute in\nruder and more perfect, in greater and smaller, in simpler and grander\nfashion, etc. However, the human architect would perhaps, in this\nrespect, be better off than the divine Creator, as he would have perfect\nliberty in the number of graduated subordinate groups. The Creator,\nhowever, according to Agassiz, can only move within six groups or\ncategories: the species, genus, family, order, class, and type. More\nthan these six categories do not exist for him.\n\nWhen we read Agassiz\u2019s book on classification, and see how he carries\nout and establishes these strange ideas, we can scarcely understand how,\nwith all the appearance of scientific earnestness, he can persevere in\nhis idea of the divine Creator as a man-like being (anthropomorphism),\nfor by his explanation of details he produces a picture of the most\nabsurd nonsense. In the whole series of these suppositions the Creator\nis nothing but an all-mighty man, who, plagued with _ennui_, amuses\nhimself with planning and constructing most varied toys in the shape of\norganic species. After having diverted himself with these for thousands\nof years, they become tiresome to him, he destroys them by a general\nrevolution of the earth\u2019s surface, and thus throws the whole of the\nuseless toys in heaps together; then, in order to while away his time\nwith something new and better, he calls a new and more perfect animal\nand vegetable world into existence. But in order not to have the trouble\nof beginning the work of creation over again, he keeps, in the main, to\nhis original plan of creation, and creates merely new species, or at\nmost only new genera, and much more rarely new families, new orders, or\nclasses. He never succeeds in producing a new style or type, and always\nkeeps strictly within the six categories or graduated groups.\n\nWhen, according to Agassiz, the Creator has thus amused himself for\nthousands of millions of years with constructing and destroying a series\nof different creations, at last (but very late) he is struck with the\nhappy thought of creating something like himself, and so makes man in\nhis own image. The end of all the history of creation is thus arrived at\nand the series of revolutions of the earth is closed. Man, the child and\nimage of God, gives him so much to do, causes him so much pleasure and\ntrouble, that he is wearied no longer, and therefore need not undertake\na new creation. It is clear that if, according to Agassiz, we once\nassign to the Creator entirely human attributes and qualities, and\nregard his work of creation as entirely analogous to human creative\nactivity, we are necessarily obliged to admit such utterly absurd\ninferences as those just stated.\n\nThe many intrinsic contradictions and perversities in Agassiz\u2019s view of\ncreation\u2014a view which necessarily led him to the most decided\nopposition to the Theory of Descent\u2014must excite our astonishment all\nthe more because, in his earlier scientific works, he had in many\nrespects actually paved the way for Darwin, especially by his researches\nin Pal\u00e6ontology. Among the numerous investigations which created general\ninterest in the then young science of Pal\u00e6ontology, those of Agassiz,\nespecially his celebrated work on \u201cFossil Fish,\u201d rank next in importance\nto Cuvier\u2019s work, which formed the foundation of the science. The\npetrified fish, with which Agassiz has made us acquainted, have not only\nan extremely great importance for the understanding of all groups of\nVertebrate animals, and their historical development, but we have\narrived through them at a sure knowledge of important general laws of\ndevelopment, some of which were first discovered by Agassiz. He it was\nwho drew special attention to the remarkable parallelism between the\nembryonal and the pal\u00e6ontological development\u2014between ontogeny and\nphylogeny, which I have already (p. 10) claimed as one of the strongest\npillars of the Theory of Descent. No one before had so distinctly stated\nas Agassiz did, that, of the Vertebrate animals, fishes alone existed,\nat first, that amphibious animals came later, and that birds and mammals\nappeared only at a much later period, further, that among mammals, as\namong fishes, imperfect and lower orders had appeared first, but more\nperfect and higher orders at a later period. Agassiz, therefore, showed\nthat the pal\u00e6ontological development of the whole Vertebrate group was\nnot only parallel with the embryonic, but also with the systematic\ndevelopment, that is, with the graduated series which we see everywhere\nin the system, ascending from the lower to the higher classes, orders,\netc.\n\nIn the earth\u2019s history lower forms appeared first, the higher forms\nlater. This important fact, as well as the agreement of the embryonic\nand pal\u00e6ontological development, is explained quite simply and naturally\nby the Doctrine of Descent, and without it is perfectly inexplicable.\nThis cause holds good also in the great law of _progressive\ndevelopment_, that is, of the historical progress of organization, which\nis traceable, broadly and as a whole, in the historical succession of\nall organisms, as well as in the special perfecting of individual parts\nof animal bodies. Thus, for example, the skeleton of Vertebrate animals\nacquired at first slowly, and by degrees, that high degree of perfection\nwhich it now possesses in man and the other higher Vertebrate animals.\nThis progress, acknowledged in point of fact by Agassiz, necessarily\nfollows from Darwin\u2019s Doctrine of Descent, which demonstrates its active\ncauses. If this doctrine is correct, the perfecting and diversification\nof animal and vegetable species must of necessity have gradually\nincreased in the course of the organic history of the earth, and could\nonly attain its highest perfection in most recent times.\n\nThe above-mentioned laws of development, together with some other\ngeneral ones, which have been expressly admitted and justly emphasized\nby Agassiz, and some of which have first been set forth by him, are, as\nwe shall see later, only explicable by the Theory of Descent, and\nwithout it remain perfectly incomprehensible. The conjoint action of\nInheritance and Adaptation, as explained by Darwin, can alone be their\ntrue cause. But they all stand in sharp and irreconcilable opposition to\nthe hypothesis of creation maintained by Agassiz, as well as to the idea\nof a personal Creator who acts for a definite purpose. If we seriously\nwish to explain those remarkable phenomena and their inter-connection by\nAgassiz\u2019s theory, then we are necessarily driven to the curious\nsupposition that the Creator himself has developed, together with the\norganic nature which he created and modelled. We can, in that case, no\nlonger rid ourselves of the idea that the Creator himself, like a human\nbeing, designed, improved, and finally, with many alterations, carried\nout his plans. \u201cMan grows as higher grow his aims,\u201d and the same\nsupposition, so unworthy of a God, must be applied to him. Although,\nfrom the reverence with which, in every page, Agassiz speaks of the\nCreator, it might appear that, on his theory, we attain to the sublimest\nconception of the divine activity in nature, yet the contrary is in\ntruth the case. The divine Creator is degraded to the level of an\nidealized man, of an organism progressing in development!\n\nConsidering the wide popularity and great authority which Agassiz\u2019s work\nhas gained, and which is perhaps justified on account of earlier\nscientific services rendered by the author, I have thought it my duty\nhere to show the utter untenableness of his general conceptions. So far\nas this work pretends to be a scientific history of creation, it is\nundoubtedly a complete failure. But still it has great value, being the\nonly detailed attempt, adorned with scientific arguments, which an\neminent naturalist of our day has made to found a teleological or\ndualistic history of creation. The utter impossibility of such a history\nhas thus been made obvious to every one. No opponent of Agassiz could\nhave refuted the dualistic conception of organic nature and its origin\nmore strikingly than he himself has done by the intrinsic contradictions\nwhich present themselves everywhere in his theory.\n\nThe opponents of the monistic or mechanical conception of the world have\nwelcomed Agassiz\u2019s work with delight, and find in it a perfect proof of\nthe direct creative action of a personal God. But they overlook the fact\nthat this personal Creator is only an idealized organism, endowed with\nhuman attributes. This low dualistic conception of God corresponds with\na low animal stage of development of the human organism. The more\ndeveloped man of the present day is capable of, and justified in,\nconceiving that infinitely nobler and sublimer idea of God which alone\nis compatible with the monistic conception of the universe, and which\nrecognizes God\u2019s spirit and power in all phenomena without exception.\nThis monistic idea of God, which belongs to the future, has already been\nexpressed by Giordano Bruno in the following words:\u2014\u201cA spirit exists in\nall things, and no body is so small but contains a part of the divine\nsubstance within itself, by which it is animated.\u201d It is of this noble\nidea of God that Goethe says:\u2014\u201cCertainly there does not exist a more\nbeautiful worship of God than that which needs no image, but which\narises in our heart from converse with Nature.\u201d By it we arrive at the\nsublime idea of the Unity of God and Nature.\n\n\n\n\nCHAPTER IV.\n\nTHEORY OF DEVELOPMENT ACCORDING TO GOETHE AND OKEN.\n\n\n   Scientific Insufficiency of all Conceptions of a Creation\n   of Individual Species.\u2014Necessity of the Counter Theories\n   of Development.\u2014Historical Survey of the Most Important\n   Theories of Development.\u2014Aristotle.\u2014His Doctrine of\n   Spontaneous Generation.\u2014The Meaning of Natural\n   Philosophy.\u2014Goethe.\u2014His Merits as a Naturalist.\u2014His\n   Metamorphosis of Plants.\u2014His Vertebral Theory of the\n   Skull.\u2014His Discovery of the Mid Jawbone in\n   Man.\u2014Goethe\u2019s Interest in the Dispute between Cuvier and\n   Geoffroy St. Hilaire.\u2014Goethe\u2019s Discovery of the Two\n   Organic Formative Principles, of the Conservative\n   Principle of Specification (by Inheritance), and of the\n   Progressive Principle of Transformation (by\n   Adaptation).\u2014Goethe\u2019s Views of the Common Descent of all\n   Vertebrate Animals, including Man.\u2014Theory of Development\n   according to Gottfried Reinhold Treviranus.\u2014His Monistic\n   Conception of Nature.\u2014Oken.\u2014His Natural\n   Philosophy.\u2014Oken\u2019s Theory of Protoplasm.\u2014Oken\u2019s Theory\n   of Infusoria (Cell Theory).\u2014Oken\u2019s Theory of\n   Development.\n\n\nAll the different ideas which we may form of a separate and independent\norigin of the individual organic species by creation lead us, when\nlogically carried out, to a so-called _anthropomorphism_, that is, to\nimagining the Creator as a man-like being, as was shown in our last\nchapter. The Creator becomes an organism who designs a plan, reflects\nupon and varies this plan, and finally forms creatures according to this\nplan, as a human architect would his building. If even such eminent\nnaturalists as Linn\u00e6us, Cuvier, and Agassiz, the principal\nrepresentatives of the dualistic hypothesis of creation, could not\narrive at a more satisfactory view, we may take it as evidence of the\ninsufficiency of all those conceptions which would derive the various\nforms of organic nature from a creation of individual species.\n\nSome naturalists, indeed, seeing the complete insufficiency of these\nviews, have tried to replace the idea of a personal Creator by that of\nan unconsciously active and creative Force of Nature; yet this\nexpression is evidently merely an evasive phrase, as long as it is not\nclearly shown what this force of nature is, and how it works. Hence\nthese attempts, also, have been absolute failures. In fact, whenever an\nindependent origin of the different forms of animals and plants has been\nassumed, naturalists have found themselves compelled to fall back upon\nso many \u201cacts of creation,\u201d that is, on supernatural interferences of\nthe Creator in the natural course of things, which in all other cases\ngoes on without interference.\n\nIt is true that several teleological naturalists, feeling the scientific\ninsufficiency of a supernatural \u201c_creation_,\u201d have endeavoured to save\nthe hypothesis by wishing it to be understood that creation \u201cis nothing\nelse than a way of coming into being, unknown and inconceivable to us.\u201d\nThe eminent Fritz M\u00fcller has cut off from this sophistic evasion every\nchance of escape by the following striking remark:\u2014\u201cIt is intended here\nonly to express in a disguised manner the shamefaced confession, that\nthey neither have, nor care to have, _any opinion_ about the origin of\nspecies. According to this explanation of the word, we might as well\nspeak of the creation of cholera, or syphilis, of the creation of a\nconflagration, or of a railway accident, as of the creation of man.\u201d\n(Jenaische Zestscrift, bd. v. p. 272.)\n\nIn the face, then, of these hypotheses of creation, which are\nscientifically insufficient, we are forced to seek refuge in the\n_counter-theory of development_ of organisms, if we wish to come to a\nrational conception of the origin of organisms. We are forced and\nobliged to do so, even if the theory of development only throws a\nglimmer of probability upon a mechanical, natural origin of the animal\nand vegetable species; but all the more if, as we shall see, this theory\nexplains all facts simply and clearly, as well as completely and\ncomprehensively. The theories of development are by no means, as they\noften falsely are represented to be, arbitrary fancies, or wilful\nproducts of the imagination, which only attempt approximately to explain\nthe origin of this or that individual organism; but they are theories\nfounded strictly on science, which explain in the simplest manner, from\na fixed and clear point of view, the whole of organic natural phenomena,\nand more especially the origin of organic species, and demonstrate them\nto be the necessary consequences of mechanical processes in nature.\n\nAs I have already shown in the second chapter, all these theories of\ndevelopment coincide naturally with that general theory of the universe\nwhich is usually designated as the uniform or _monistic_, often also as\nthe _mechanical_ or causal, because it only assumes mechanical causes,\nor _causes working by necessity_ (caus\u00e6 efficientes), for the\nexplanation of natural phenomena. In like manner, on the other hand, the\nsupernatural hypotheses of creation which we have already discussed\ncoincide completely with the opposite view of the universe, which in\ncontrast to the former is called the twofold or _dualistic_, often the\n_teleological_ or vital, because it traces the organic natural phenomena\nto final causes, acting and _working for a definite purpose_ (caus\u00e6\nfinales). It is this deep and intrinsic connection of the different\ntheories of creation with the most important questions of philosophy\nthat incites us to their closer examination.\n\nThe fundamental idea, which must necessarily lie at the bottom of all\nnatural theories of development, is that of a _gradual development of\nall (even the most perfect) organisms_ out of a single, or out of a very\nfew, quite simple, and quite imperfect original beings, which came into\nexistence, not by supernatural creation, but by _spontaneous\ngeneration_, or archigony, out of inorganic matter. In reality, there\nare two distinct conceptions united in this fundamental idea, but which\nhave, nevertheless, a deep intrinsic connection\u2014namely, first, the idea\nof spontaneous generation (or archigony) of the original primary beings;\nand secondly, the idea of the progressive development of the various\nspecies of organisms from those most simple primary beings. These two\nimportant mechanical conceptions are the inseparable fundamental ideas\nof every theory of development, if scientifically carried out. As it\nmaintains the derivation of the different species of animals and plants\nfrom the simplest, common primary species, we may term it also the\nDoctrine of Filiation, or _Theory of Descent_; as there is also a change\nof species connected with it, it may also be termed the _Transmutation\nTheory_.\n\nWhile the supernatural histories of creation must have originated\nthousands of years ago, in that very remote primitive age when man,\nfirst developing out of the monkey-state, began for the first time to\nthink more closely about himself, and about the origin of the world\naround him, the natural theories of development, on the other hand, are\nnecessarily of much more recent origin. These views are met with only\namong nations of a more matured civilization, to whom, by philosophic\nculture, the necessity of a knowledge of natural causes has become\napparent; and even among these, only individual and specially gifted\nnatures can be expected to have recognized the origin of the world of\nphenomena, as well as its course of development, as the necessary\nconsequences of mechanical, naturally active causes. In no nation have\nthese preliminary conditions, for the origin of a natural theory of\ndevelopment, ever existed in so high a degree as among the Greeks of\nclassic antiquity. But, on the other hand, they lacked a close\nacquaintance with the facts of the processes and forms of nature, and,\nconsequently, the foundation based upon experience, for a satisfactory\nunravelling of the problem of development. Exact investigation of\nnature, and the knowledge of nature founded on an experimental basis,\nwas of course almost unknown to antiquity, as well as to the Middle\nAges, and is only an acquisition of modern times. We have therefore here\nno special occasion to examine the natural theories of development of\nthe various Greek philosophers, since they were wanting in the knowledge\ngained by experience, both of organic and inorganic nature, and since\nthey almost always, as the consequence, lost themselves in airy\nspeculations.\n\nOne man only must be mentioned here by way of exception,\u2014Aristotle, the\ngreatest and the only truly great naturalist of antiquity and the Middle\nAges, one of the grandest geniuses of all time. To what a degree he\nstands there alone, during a period of more than two thousand years, in\nthe region of empirico-philosophical knowledge of nature, and especially\nin his knowledge of organic nature, is proved to us by the precious\nremains of his but partially surviving works. In them many traces are\nfound of a theory of natural development. Aristotle assumes, as a matter\nof certainty, that spontaneous generation was the natural manner in\nwhich the lower organic creatures came into existence. He describes\nanimals and plants originating from matter itself, through its own\noriginal force; as, for example, moths from wool, fleas from putrid\ndung, wood-lice from damp wood, etc. But as the distinction of organic\nspecies, which Linn\u00e6us only arrived at two thousand years later, was\nunknown to him, he could form no ideas about their genealogical\nrelations.\n\nThe fundamental notion of the theory of development, that the different\nspecies of animals and plants have been developed from a common primary\nspecies by transformation, could of course only be clearly asserted\nafter the kinds of species themselves had become better known, and after\nthe extinct species had been carefully examined and compared with the\nliving ones. This was not done until the end of the last and the\nbeginning of the present century. It was not until the year 1801 that\nthe great Lamarck expressed the theory of development, which he, in\n1809, further elaborated in his classical \u201cPhilosophie Zoologique.\u201d\nWhile Lamarck and his countryman, Geoffroy St. Hilaire, in France,\nopposed Cuvier\u2019s views, and maintained a natural development of organic\nspecies by transformation and descent, Goethe and Oken at the same time\npursued the same course in Germany, and helped to establish the theory\nof development. As these naturalists are generally called\nnature-philosophers (Naturphilosophen), and as this ambiguous\ndesignation is correct in a certain sense, it appears to me appropriate\nhere to say a few words about the correct estimate of the\n\u201cNatur-philosophie.\u201d\n\nAlthough for many years in England the ideas of natural science and\nphilosophy have been looked upon as almost equivalent, and as every\ntruly scientific investigator of nature is most justly called there a\n\u201cnatural philosopher,\u201d yet in Germany for more than half a century\nnatural science has been kept strictly distinct from philosophy, and the\nunion of the two into a true philosophy of nature is recognized only by\nthe few. This misapprehension is owing to the fantastic eccentricities\nof earlier German natural-philosophers, such as Oken, Schelling, etc.;\nthey believed that they were able to construct the laws of nature in\ntheir own heads, without being obliged to take their stand upon the\ngrounds of actual experience. When the complete hollowness of their\nassumptions had been demonstrated, naturalists, in \u201cthe nation of\nthinkers,\u201d fell into the very opposite extreme, believing that they\nwould be able to reach the high aim of science, that is, the knowledge\nof truth, by the mere experience of the senses, and without any\nphilosophical activity of thought.\n\nFrom that time, but especially since 1830, most naturalists have shown a\nstrong aversion to any general, philosophical view of nature. The real\naim of natural science was now supposed to consist in the knowledge of\ndetails, and it was believed that this would be attained in the study of\nbiology, when the forms and the phenomena of life, in all individual\norganisms, had become accurately known, by the help of the finest\ninstruments and means of observation. It is true that among these\nstrictly empirical, or so-called exact naturalists, there were always\nvery many who rose above this narrow point of view, and sought the final\naim in a knowledge of the general laws of organization. Yet the great\nmajority of zoologists and botanists, during the thirty or forty years\npreceding Darwin, refused to concern themselves about such general laws;\nall they admitted was, that perhaps in the far distant future, when the\nend of all empiric knowledge should have been arrived at, when all\nindividual animals and plants should have been thoroughly examined,\nnaturalists might begin to think of discovering general biological laws.\n\nIf we consider and compare the most important advances which the human\nmind has made in the knowledge of truth, we shall soon see that it is\nalways owing to philosophical mental operations that these advances have\nbeen made, and that the experience of the senses which certainly and\nnecessarily precedes these operations, and the knowledge of details\ngained thereby, only furnish the basis for those general laws.\nExperience and philosophy, therefore, by no means stand in such\nexclusive opposition to each other as most men have hitherto supposed;\nthey rather necessarily supplement each other. The philosopher who is\nwanting in the firm foundation of sensuous experience, of empirical\nknowledge, is very apt to arrive at false conclusions in his general\nspeculations, which even a moderately informed naturalist can refute at\nonce. On the other hand, the purely empiric naturalists, who do not\ntrouble themselves about the philosophical comprehension of their\nsensuous experiences, and who do not strive after general knowledge, can\npromote science only in a very slight degree, and the chief value of\ntheir hard-won knowledge of details lies in the general results which\nmore comprehensive minds will one day derive from them.\n\nFrom a general survey of the course of biological development since\nLinn\u00e6us\u2019 time, we can easily see, as B\u00e4r has pointed out, a continual\nvacillation between these two tendencies, at one time a prevalence of\nthe empirical\u2014the so-called exact\u2014and then again of the philosophical\nor speculative tendency. Thus at the end of the last century, in\nopposition to Linn\u00e6us\u2019 purely empirical school, a natural-philosophical\nreaction took place, the moving spirits of which, Lamarck, Geoffroy St.\nHilaire, Goethe, and Oken, endeavoured by their mental work to introduce\nlight and order into the chaos of the accumulated empirical raw\nmaterial. In opposition to the many errors and speculations of these\nnatural philosophers, who went too far, Cuvier then came forward,\nintroducing a second, purely empirical period. It reached its most\none-sided development between the years 1830-1860, and there now\nfollowed a second philosophical reaction, caused by Darwin\u2019s work. Thus\nduring the last ten years, men again have begun to endeavour to obtain a\nknowledge of the general laws of nature, to which, after all, all\ndetailed knowledge of experience serves only as a foundation, and\nthrough which alone it acquires its true value. It is through philosophy\nalone that natural knowledge becomes a true science, that is, a\nphilosophy of nature. (Gen. Morph. i. 63-108.)\n\nJean Lamarck and Wolfgang Goethe stand at the head of all the great\nphilosophers of nature who first established a theory of organic\ndevelopment, and who are the illustrious fellow-workers of Darwin. I\nturn first to our beloved Goethe, who, among all, stands in the closest\nrelations to us Germans. However, before I explain his special services\nto the theory of development, it seems to me necessary to say a few\nwords about his importance as a naturalist in general, as it is commonly\nvery little known.\n\nI am sure most of my readers honour Goethe only as a poet and a man;\nonly a few have any conception of the high value of his scientific\nworks, and of the gigantic stride with which he advanced before his own\nage\u2014advanced so much that most naturalists of that time were unable to\nfollow him. In several passages of his scientific writings he bitterly\ncomplains of the narrow-mindedness of professed naturalists, who do not\nknow how to value his works (who cannot see the wood for the trees), and\nwho cannot rouse themselves to discover the general laws of nature among\nthe mass of details. He is only too just when he utters the\nreproach\u2014\u201cThe philosophers will very soon discover that observers\nrarely rise to a stand-point from which they can survey so many\nimportant objects.\u201d It is true, at the same time, that their want of\nappreciation was caused by the false road into which Goethe was led in\nhis theory of colours.\n\nThis theory of colours, which he himself designates as the favourite\nproduction of his leisure, however much that is beautiful it may\ncontain, is a complete failure in regard to its foundations. The exact\nmathematical method by means of which alone it is possible, in inorganic\nsciences, but above all in physics, to raise a structure step by step on\na thoroughly firm basis, was altogether repugnant to Goethe. In\nrejecting it he allowed himself not only to be very unjust towards the\nmost eminent physicists, but to be led into errors which have greatly\ninjured the fame of his other valuable works. It is quite different in\nthe organic sciences, in which we are but rarely able to proceed, from\nthe beginning, upon a firm mathematical basis; we are rather compelled,\nby the infinitely difficult and intricate nature of the problem, at the\nfirst to form inductions\u2014that is, we are obliged to endeavour to\nestablish general laws by numerous individual observations, which are\nnot quite complete. A comparison of kindred series of phenomena, or the\nmethod of combination, is here the most important instrument for\ninquiry, and this method was applied by Goethe with as much success as\nwith conscious knowledge of its value, in his works relating to the\nphilosophy of nature.\n\nThe most celebrated among Goethe\u2019s writings relating to organic nature\nis his _Metamorphosis of Plants_, which appeared in 1790, a work which\ndistinctly shows a grasp of the fundamental idea of the theory of\ndevelopment, inasmuch as Goethe, in it, was labouring to point out a\nsingle organ, by the infinitely varied development and metamorphosis of\nwhich the whole of the endless variety of forms in the world of plants\nmight be conceived to have arisen; this fundamental organ he found in\nthe _leaf_. If at that time the microscope had been generally employed,\nif Goethe had examined the structure of organisms by the means of the\nmicroscope he would have gone still further, and would have seen that\nthe leaf is itself a compound of individual parts of a lower order, that\nis, of _cells_. He would then not have declared that the leaf, but that\nthe _cell_ is the real fundamental organ by the multiplication,\ntransformation, and combination (synthesis) of which, in the first\nplace, the leaf is formed; and that, in the next place, by\ntransformation, variation, and combination of leaves there arise all\nthe varied beauties in form and colour which we admire in the green\nparts, as well as in the organs of propagation, or the flowers of\nplants. Goethe here showed that in order to comprehend the whole of the\nphenomena, we must in the first place compare them, and, secondly,\nsearch for a simple type, a simple fundamental form, of which all other\nforms are only infinite variations.\n\nSomething similar to what he had here done for the metamorphosis of\nplants he then did for the Vertebrate animals, in his celebrated\n_vertebral theory of the skull_. Goethe was the first to show,\nindependently of Oken, who almost simultaneously arrived at the same\nthought, that the skull of man and of all Vertebrate animals, in\nparticular mammals, is nothing more than a bony case, formed of the same\nbones,\u2014that is, vertebr\u00e6,\u2014out of which the spine also is composed. The\nvertebr\u00e6 of the skull are like those of the spine, bony rings lying\nbehind each other, but in the skull are peculiarly changed and\nspecialized (differentiated). Although this idea has been strongly\nmodified by recent discoveries, yet in Goethe\u2019s day it was one of the\ngreatest advances in comparative anatomy, and was not only one of the\nfirst advances towards the understanding of the structure of Vertebrate\nanimals, but at the same time explained many individual phenomena. When\ntwo parts of a body, such as the skull and spine, which appear at first\nsight so different, were proved to be parts originally the same,\ndeveloped out of one and the same foundation, one of the difficult\nproblems of the philosophy of nature was solved. Here again we meet the\nnotion of a single type\u2014the conception of a single principle, which\nbecomes infinitely varied in the different species, and in the parts of\nindividual species.\n\nBut Goethe did not merely endeavour to search for such far-reaching\nlaws, he also occupied himself most actively for a long time with\nnumerous individual researches, especially in comparative anatomy. Among\nthese, none is perhaps more interesting than the discovery of the _mid\njawbone in man_. As this is, in several respects, of importance to the\ntheory of development, I shall briefly explain it here. There exist in\nall mammals two little bones in the upper jaw, which meet in the centre\nof the face, below the nose, and which lie between the two halves of the\nreal upper jawbone. These two bones, which hold the four upper cutting\nteeth, are recognized without difficulty in most mammals; in man,\nhowever, they were at that time unknown, and celebrated comparative\nanatomists even laid great stress upon this want of a mid jawbone, as\nthey considered it to constitute the principal difference between men\nand apes\u2014the want of a mid jawbone was, curiously enough, looked upon\nas the most human of all human characteristics. But Goethe could not\naccept the notion that man, who in all other corporeal respects was\nclearly only a mammal of higher development, should lack this mid\njawbone.\n\nBy the general law of induction as to the mid jawbone he arrived at the\nspecial deductive conclusion that it must exist in man also, and Goethe\ndid not rest until, after comparing a great number of human skulls, he\nreally found the mid jawbone. In some individuals it is preserved\nthroughout a whole lifetime, but usually at an early age it coalesces\nwith the neighbouring upper jawbone, and is therefore only to be found\nas an independent bone in very youthful skulls. In human embryos it can\nnow be pointed out at any moment. In man, therefore, the mid jawbone\nactually exists, and to Goethe the honour is due of having first firmly\nestablished this fact, so important in many respects; and this he did\nwhile opposed by the celebrated anatomist, Peter Camper, one of the most\nimportant professional authorities. The way by which Goethe succeeded in\nestablishing this fact is especially interesting; it is the way by which\nwe continually advance in biological science, namely, by way of\ninduction and deduction. _Induction_ is the inference of a general law\nfrom the observation of numerous individual cases; _deduction_, on the\nother hand, is an inference from this general law applied to a single\ncase which has not yet been actually observed. From the collected\nempirical knowledge of those days, the inductive conclusion was arrived\nat that all mammals had mid jawbones. Goethe drew from this the\ndeductive conclusion, that man, whose organization was in all other\nrespects not essentially different from mammals, must also possess this\nmid jawbone; and on close examination it was actually found. The\ndeductive conclusion was confirmed and verified by experience.\n\nEven these few remarks may serve to show the great value which we must\nascribe to Goethe\u2019s biological researches. Unfortunately most of his\nlabours devoted to this subject are so hidden in his collected works,\nand his most important observations and remarks so scattered in numerous\nindividual treatises\u2014devoted to other subjects\u2014that it is difficult to\nfind them out. It also sometimes happens that an excellent, truly\nscientific remark is so much interwoven with a mass of useless\nphilosophical fancies, that the latter greatly detract from the former.\n\nNothing is perhaps more characteristic of the extraordinary interest\nwhich Goethe took in the investigation of organic nature than the lively\nway in which, even in his last years, he followed the dispute which\nbroke out in France between Cuvier and Geoffroy de St. Hilaire. Goethe,\nin a special treatise which was only finished a few days before his\ndeath, in March, 1832, has given an interesting description of this\nremarkable dispute and its general importance, as well as an excellent\nsketch of the two great opponents. This treatise bears the title\n\u201cPrincipes de Philosophic Zoologique par M. Geoffroy de Saint Hilaire\u201d;\nit is Goethe\u2019s last work, and forms the conclusion of the collected\nedition of his works. The dispute itself was, in several respects, of\nthe highest interest. It turned essentially upon the justification of\nthe theory of development. It was carried on, moreover, in the bosom of\nthe French Academy, by both opponents, with a personal vehemence almost\nunheard of in the dignified sessions of that learned body; this proved\nthat both naturalists were fighting for their most sacred and deepest\nconvictions. The conflict began on the 22nd of February, and was\nfollowed by several others; the fiercest took place on the 19th of July,\n1830. Geoffroy, as the chief of the French nature-philosophers,\nrepresented the theory of natural development and the monistic\nconception of nature. He maintained the mutability of organic species,\nthe common descent of the individual species from common primary forms,\nand the unity of their organization\u2014or the unity of the plan of\nstructure, as it was then called.\n\nCuvier was the most decided opponent of these views, and according to\nwhat we have seen, it could not be otherwise. He endeavoured to show\nthat the nature-philosophers had no right to rear such comprehensive\nconclusions on the basis of the empirical knowledge then possessed, and\nthat the unity of organization\u2014or plan of structure of organisms\u2014as\nmaintained by them, did not exist. He represented the teleological\n(dualistic) conception of nature, and maintained that \u201cthe immutability\nof species was a necessary condition for the existence of a scientific\nhistory of nature,\u201d Cuvier had the great advantage over his opponent,\nthat he was able to bring towards the proof of his assertions things\nobvious to the eye; these, however, were only individual facts taken out\nof their connection with others. Geoffroy was not able to prove the\nhigher and general connection of individual phenomena which he\nmaintained, by equally tangible details. Hence Cuvier, in the eyes of\nthe majority, gained the victory, and decided the defeat of the\nnature-philosophy and the supremacy of the strictly empiric tendency for\nthe next thirty years.\n\nGoethe of course supported Geoffroy\u2019s views. How deeply interested he\nwas, even in his 81st year, in this great contest is proved by the\nfollowing anecdote related by Soret:\u2014\n\n\u201cMonday, Aug. 2nd, 1830.\u2014The news of the outbreak of the revolution of\nJuly arrived in Weimar to-day, and has caused general excitement. In the\ncourse of the afternoon I went to Goethe. \u2018Well?\u2019 he exclaimed as I\nentered, \u2018what do you think of this great event? The volcano has burst\nforth, all is in flames, and there are no more negotiations behind\nclosed doors.\u2019 \u2018A dreadful affair,\u2019 I answered; \u2018but what else could be\nexpected under the circumstances, and with such a ministry, except that\nit would end in the expulsion of the present royal family?\u2019 \u2018We do not\nseem to understand each other, my dear friend,\u2019 replied Goethe. \u2018I am\nnot speaking of those people at all; I am interested in something very\ndifferent, I mean the dispute between Cuvier and Geoffroy de Saint\nHilaire, which has broken out in the Academy, and which is of such great\nimportance to science.\u2019 This remark of Goethe\u2019s came upon me so\nunexpectedly, that I did not know what to say, and my thoughts for some\nminutes seemed to have come to a complete standstill. \u2018The affair is of\nthe utmost importance,\u2019 he continued, \u2018and you cannot form any idea of\nwhat I felt on receiving the news of the meeting on the 19th. In\nGeoffroy de Saint Hilaire we have now a mighty ally for a long time to\ncome. But I see also how great the sympathy of the French scientific\nworld must be in this affair, for, in spite of the terrible political\nexcitement, the meeting on the 19th was attended by a full house. The\nbest of it is, however, that the synthetic treatment of nature,\nintroduced into France by Geoffroy, can now no longer be stopped. This\nmatter has now become public through the discussions in the Academy,\ncarried on in the presence of a large audience; it can no longer be\nreferred to secret committees, or be settled or suppressed behind closed\ndoors.\u2019\u201d\n\nIn my book on \u201cThe General Morphology of Organisms\u201d I have placed as\nheadings to the different books and chapters a selection of the numerous\ninteresting and important sentences in which Goethe clearly expresses\nhis view of organic nature and its constant development. I will here\nquote a passage from the poem entitled, \u201cThe Metamorphosis of Animals\u201d\n(1819).\n\n \u201cAll members develop themselves according to eternal laws,\n  And the rarest form mysteriously preserves the primitive type,\n  Form therefore determines the animal\u2019s way of life,\n  And in turn the way of life powerfully reacts upon all form.\n  Thus the orderly growth of form is seen to hold\n  Whilst yielding to change from externally acting causes.\u201d[3]\n\nHere, clearly enough, the contrast between two different organic\nconstructive forms is intimated, which are opposed to one another, and\nwhich by their interaction determine the form of the organism; on the\none hand, a common inner original type, firmly maintaining itself,\nconstitutes the foundation of the most different forms; on the other\nhand, the externally active influence of surroundings and mode of life,\nwhich influence the original type and transform it. This contrast is\nstill more definitely pointed out in the following passage:\u2014\n\n\u201cAn inner original community forms the foundation of all organization;\nthe variety of forms, on the other hand, arises from the necessary\nrelations to the outer world, and we may therefore justly assume an\noriginal difference of conditions, together with an uninterruptedly\nprogressive transformation, in order to be able to comprehend the\nconstancy as well as the variations of the phenomena of form.\u201d\n\nThe \u201coriginal type\u201d which constitutes the foundation of\nevery organic form \u201cas the inner original community\u201d is the _inner\nconstructive force_, which receives the original direction of\nform-production\u2014that is, the tendency to give rise to a particular\nform\u2014and is propagated by _Inheritance_. The \u201cuninterruptedly\nprogressive transformation,\u201d on the other hand, which \u201csprings from the\nnecessary relations to the outer world,\u201d acting as an _external\nformative force_, produces, by _Adaptation_ to the surrounding\nconditions of life, the \u201cinfinite variety of forms\u201d (Gen. Morph. i. 154;\nii. 224). The internal formative tendency of _Inheritance_, which\nretains the unity of the original type, is called by Goethe in another\npassage the _centripetal force_ of the organism, or its tendency to\nspecification; in contrast with this he calls the external formative\ntendency of _Adaptation_, which produces the variety of organic forms,\nthe _centrifugal force_ of organisms, or their tendency to variation.\nThe passage in which he clearly indicates the \u201cequilibrium\u201d of these two\nextremely important organic formative tendencies, runs as follows: \u201cThe\nidea of _metamorphosis_ resembles the vis centrifuga, and would lose\nitself in the infinite, if a counterpoise were not added to it: I mean\nthe tendency to _specification_, the strong power to preserve what once\nhas come into being, a vis centripeta, which in its deepest foundation\ncannot be affected by anything external.\u201d\n\nMetamorphosis, according to Goethe, consists not merely, as the word is\nnow generally understood, in the changes of form which the organic\nindividual experiences during its individual development, but, in a\nwider sense, in the transformation of organic forms in general. His idea\nof metamorphosis is almost synonymous with the theory of development.\nThis is clear, among other things, from the following passage:\u2014\u201cThe\ntriumph of physiological metamorphosis manifests itself where the whole\nseparates and transforms itself into families, the families into genera,\nthe genera into species, and then again into other varieties down to the\nindividual. This operation of nature goes on ad infinitum; she cannot\nrest inactive, but neither can she keep and preserve all that she has\nproduced. From seeds there are always developed varying plants,\nexhibiting the relations of their parts to one another in an altered\nmanner.\u201d\n\nGoethe had, in truth, discovered two great mechanical forces of nature,\nwhich are the active causes of organic formations, his two organic\nformative tendencies\u2014on the one hand the conservative, centripetal, and\ninternal formative tendency of Inheritance or specification; and on the\nother hand the progressive, centrifugal, and external formative tendency\nof Adaptation, or metamorphosis. This profound biological intuition\ncould not but lead him naturally to the fundamental idea of the Doctrine\nof Filiation, that is, to the conception that the organic species\nresembling one another in form are actually related by blood, and that\nthey are descended from a common original type. In regard to the most\nimportant of all animal groups, namely that of Vertebrate animals,\nGoethe expresses this doctrine in the following passage (1796):\u2014\u201cThus\nmuch then we have gained, that we may assert without hesitation that all\nthe more perfect organic natures, such as fishes, amphibious animals,\nbirds, mammals, and man at the head of the last, were all formed upon\none original type, which only varies more or less in parts which are\nnone the less permanent, and still daily changes and modifies its form\nby propagation.\u201d\n\nThis sentence is of interest in more than one way. The theory that all\n\u201cthe more perfect organic natures,\u201d that is all Vertebrate animals, are\ndescended from one common prototype, that they have arisen from it by\npropagation (Inheritance) and transformation (Adaptation), may be\ndistinctly inferred. But it is especially interesting to observe that\nGoethe admits no exceptional position for man, but rather expressly\nincludes him in the tribe of the other Vertebrate animals. The most\nimportant special inference of the Doctrine of Filiation, that man is\ndescended from other Vertebrate animals, may here be recognized in the\ngerm.(3)\n\nThis exceedingly important fundamental idea is expressed by Goethe still\nmore clearly in another passage (1807), in the following words:\u2014\u201cIf we\nconsider plants and animals in their most imperfect condition, they can\nscarcely be distinguished. But this much we can say, that the creatures\nwhich by degrees emerge as plants and animals out of a common phase,\nwhere they are barely distinguishable, arrive at perfection in two\nopposite directions; so that the plant in the end reaches its highest\nglory in the tree, which is immovable and stiff, the animal in man, who\npossesses the greatest elasticity and freedom.\u201d This remarkable passage\nnot only indicates most explicitly the genealogical relationship between\nthe vegetable and animal kingdoms, but contains the germ of the\nmonophyletic hypothesis of descent, the importance of which I shall have\nto explain hereafter. (Compare Chapter XVI. and the Pedigree, p. 398.)\n\nAt the time when Goethe in this way sketched the fundamental features of\nthe Theory of Descent, another German philosopher, Gottfried Reinhold\nTreviranus, of Bremen (born 1776, died 1837), was zealously engaged at\nthe same work. As Wilhelm Focke has recently shown, Treviranus, even in\nthe earliest of his greater works, \u201cThe Biology or Philosophy of Animate\nNature,\u201d which appeared at the beginning of the present century, had\nalready developed monistic views of the unity of nature, and of the\ngenealogical connection of the species of organisms, which entirely\ncorrespond with our present view of the matter. In the first three\nvolumes of the Biology, which appeared successively in 1802, 1803, and\n1805 (therefore several years before Oken\u2019s and Lamarck\u2019s principal\nworks), we find numerous passages which are of interest in this respect.\nI shall here quote only a few of the most important.\n\nIn speaking of the principal question of our theory, the question of the\norigin of organic species, Treviranus makes the following\nremarks:\u2014\u201cEvery form of life can be produced by physical forces in one\nof two ways: either by coming into being out of formless matter, or by\nmodification of an already existing form by a continued process of\nshaping. In the latter case the cause of this modification may lie\neither in the influence of a dissimilar male generative matter upon the\nfemale germ, or in the influence of other powers which operate only\nafter procreation. In every living being there exists the capability of\nan endless variety of form-assumption; each possesses the power to adapt\nits organization to the changes of the outer world, and it is this power\nput into action by the change of the universe that has raised the simple\nzoophytes of the primitive world to continually higher stages of\norganization, and has introduced a countless variety of species into\nanimate nature.\u201d\n\nBy _zoophytes_, Treviranus here means organisms of the lowest order and\nof the simplest character, namely, those neutral primitive beings which\nstand midway between animals and plants, and on the whole correspond\nwith our _protista_. \u201cThese zoophytes,\u201d he remarks in another passage,\n\u201care the original forms out of which all the organisms of the higher\nclasses have arisen by gradual development. We are further of opinion\nthat every species, as well as every individual, has certain periods of\ngrowth, of bloom, and of decay, but that the decay of a species is\n_degeneration_, not dissolution, as in the case of the individual. From\nthis it appears to us to follow that it was not the great catastrophes\nof the earth (as is generally supposed) which destroyed the animals of\nthe primitive world, but that many survived them, and it is more\nprobable that they have disappeared from existing nature, because the\nspecies to which they belonged have completed the circle of their\nexistence, and have become changed into other kinds.\u201d\n\nWhen Treviranus, in this and other passages, points to _degeneration_ as\nthe most important cause of the transformation of the animal and\nvegetable species, he does not understand by it what is now commonly\ncalled degeneration. With him \u201cdegeneration\u201d is exactly what we now call\n_Adaptation_ or _modification_, by the action of external formative\nforces. That Treviranus explained this trans-transformation of organic\nspecies by Adaptation, and its preservation by Inheritance, and thus the\nwhole variety of organic forms by the interaction of Adaptation and\nInheritance, is clear also from several other passages. How profoundly\nhe grasped the mutual dependence of all living creatures on one another,\nand in general the _universal connection between cause and effect_\u2014that\nis, the monistic causal connection between all members and parts of the\nuniverse\u2014is further shown, among others, by the following remarks in\nhis Biology:\u2014\u201cThe living individual is dependent upon the species, the\nspecies upon the fauna, the fauna upon the whole of animate nature, and\nthe latter upon the organism of the earth. The individual possesses\nindeed a peculiar life, and so far forms its own world. But just because\nits life is limited it constitutes at the same time an organ in the\ngeneral organism. Every living body exists in consequence of the\nuniverse, but the universe, on the other hand, exists in consequence of\nit.\u201d\n\nIt is self-evident that so profound and clear a thinker as Treviranus,\nin accordance with this grand mechanical conception of the universe,\ncould not admit for man a privileged and exceptional position in nature,\nbut assumed his gradual development from lower animal forms. And it is\nequally self-evident, on the other hand, that he did not admit a chasm\nbetween organic and inorganic nature, but maintained the absolute unity\nof the organization of the whole universe. This is specially attested by\nthe following sentence:\u2014\u201cEvery inquiry into the influence of the whole\nof nature on the living world must start from the principle, that all\nliving forms are products of physical influences, which are acting even\nnow, and are changed only in degree, or in their direction.\u201d Hereby, as\nTreviranus himself says, \u201cThe fundamental problem of biology is solved,\u201d\nand we add, solved in a purely mechanical or monistic sense.\n\nNeither Treviranus nor Goethe is commonly considered the most eminent of\nthe German nature-philosophers, but Lorenz Oken, who, in establishing\nthe vertebral theory of the skull, came forward as a rival to Goethe,\nand did not entertain a very kindly feeling towards him. Although they\nlived for some time in the same neighbourhood, yet the natures of these\ntwo men were so very different, that they could not well be drawn\ntowards each other. Oken\u2019s \u201cManual of the Philosophy of Nature,\u201d which\nmay be designated as the most important production of the\nnature-philosophy school then existing in Germany, appeared in 1809, the\nsame year in which Lamarck\u2019s fundamental work, the \u201cPhilosophie\nZoologique,\u201d was published. As early as 1802, Oken had published an\n\u201cOutline of the Philosophy of Nature.\u201d As we have already intimated, in\nOken\u2019s as in Goethe\u2019s works, a number of valuable and profound thoughts\nare hidden among a mass of erroneous, very eccentric, and fantastic\nconceptions. Some of these ideas have only quite recently and gradually\nbecome recognized in science, many years after they were first\nexpressed. I shall here quote only two thoughts, which are almost\nprophetic, and which at the same time stand in the closest relation to\nthe theory of development.\n\nOne of the most important of Oken\u2019s theories, which was formerly very\nmuch decried, and was most strongly combatted, especially by the\nso-called \u201cexact experimentalists,\u201d is the idea that the phenomena of\nlife in all organisms proceed from a common chemical substance, so to\nsay, from a general simple _vital-substance_, which he designated by the\nname _Urschleim_, or _original slime_. By it he meant, as the name\nindicates, a mucilaginous substance, an albuminous combination, which\nexists in a semi-fluid condition of aggregation, and possesses the\npower, by adaptation to different conditions of existence in the outer\nworld and by interaction with its material, of producing the most\nvarious forms. Now, we need only change the expression \u201coriginal slime\u201d\n(Urschleim) into _Protoplasm_, or _cell-substance_, in order to arrive\nat one of the grandest results which we owe to microscopic\ninvestigations during the last ten years, more especially to those of\nMax Schultze. By these investigations it has been shown that in all\nliving bodies, without exception, there exists a certain quantity of\nmucilaginous albuminous matter, in a semi-fluid condition; and that this\nnitrogen-holding carbon-compound is exclusively the original seat and\nagent of all the phenomena of life, and of all production of organic\nforms. All other substances which appear in the organism, besides these,\nare either formed by this active matter of life, or have been introduced\nfrom without. The organic egg, the original cell out of which every\nanimal and plant is first developed, consists essentially only of one\nround little lump of such albuminous matter. Even the yolk of an egg is\nnothing but albumen, mixed with granules of fat. Oken was therefore\nright when, more divining than knowing, he made the assertion\u2014\u201cEvery\norganic thing has arisen out of slime, and is nothing but slime in\ndifferent forms. This primitive slime originated in the sea, from\ninorganic matter in the course of planetary-evolution.\u201d\n\nAnother equally grand idea of the same philosopher is closely connected\nwith his theory of primitive slime, which coincides with the extremely\nimportant _Protoplasm theory_. For Oken, as early as 1809, asserted that\nthe primitive slime produced in the sea by spontaneous generation, at\nonce assumed the form of microscopically small bladders, which he called\n\u201c_Mile_,\u201d or \u201c_Infusoria_.\u201d \u201cOrganic nature has for its basis an\ninfinity of such vesicles.\u201d These little bladders arise from original\nsemi-fluid globules of the primitive slime, by the fact of their\nperiphery becoming condensed. The simplest organism, as well as every\nanimal and every plant of higher kind, is nothing else than \u201can\naccumulation (synthesis) of such infusorial bladders, which by various\ncombinations assume various forms, and thus develop into higher\norganisms.\u201d Here again we need only translate the expression _little\nbladder_, or _infusorium_, by the word _cell_, and we arrive at the Cell\ntheory, one of the grandest biological theories of our century.\nSchleiden and Schwann, about thirty years ago, were the first to furnish\nexperiential proof that all organisms are either simple cells, or\naccumulations (syntheses) of such cells, and the more recent protoplasm\ntheory has shown that protoplasm (the original slime) is the most\nessential (and sometimes the only) constituent part of the genuine cell.\nThe properties which Oken ascribes to his Infusoria are exactly the\nproperties of cells, the properties of elementary beings, by whose\naccumulation, combination, and varying development, the higher organisms\nare formed.\n\nThese two extremely fruitful thoughts of Oken, on account of the absurd\nform in which he expressed them, were at first little heeded, or\nentirely misunderstood, and it was reserved for a much later era to\nestablish them by actual observation. The supposition that the\nindividual species of plants and animals originated from common\nprototypes by a slow and gradual development of the higher organisms out\nof lower ones, was of course most closely connected with these ideas.\nMan\u2019s descent from lower organisms was likewise asserted by Oken\u2014\u201cMan\nhas been developed, not created.\u201d Although many arbitrary perversities\nand extravagant fancies may be found in Oken\u2019s philosophy of nature,\nthey must not prevent us paying our just admiration to these grand\nideas, which were so far in advance of their age. This much is clearly\nevident from the statements of Goethe and Oken which we have quoted, and\nfrom the views of Lamarck and Geoffroy which have to be discussed next,\nthat during the first decade of our century no doctrine approached so\nnearly to the natural Theory of Descent, newly established by Darwin, as\nthe much decried \u201cNatur-philosophie.\u201d\n\n\n\n\nCHAPTER V.\n\nTHEORY OF DEVELOPMENT ACCORDING TO KANT AND LAMARCK.\n\n\n   Kant\u2019s Dualistic Biology.\u2014His Conception of the Origin\n   of Inorganic Nature by Mechanical Causes, of Organic\n   Nature by Causes acting for a Definite\n   Purpose.\u2014Contradiction of this Conception with his\n   leaning towards the Theory of Descent.\u2014Kant\u2019s\n   Genealogical Theory of Development.\u2014Its Limitation by\n   his Teleology.\u2014Comparison of Genealogical Biology with\n   Comparative Philology.\u2014Views in favour of the Theory of\n   Descent entertained by Leopold Buch, B\u00e4r, Schleiden,\n   Unger, Schaafhausen, Victor Carus, B\u00fcchner.\u2014French\n   Nature-philosophy.\u2014Lamarck\u2019s Philosophie\n   Zoologique.\u2014Lamarck\u2019s Monistic (mechanical) System of\n   Nature.\u2014His Views of the Interaction of the Two Organic\n   Formative Tendencies of Inheritance and\n   Adaptation.\u2014Lamarck\u2019s Conception of Man\u2019s Development\n   from Ape-like Mammals.\u2014Geoffroy St. Hilaire\u2019s, Naudin\u2019s,\n   and Lecoq\u2019s Defence of the Theory of Descent.\u2014English\n   Nature-philosophy.\u2014Views in favour of the Theory of\n   Descent, entertained by Erasmus Darwin, W. Herbert,\n   Grant, Freke, Herbert Spencer, Hooker, Huxley.\u2014The\n   Double Merit of Charles Darwin.\n\n\nThe teleological view of nature, which explains the phenomena of the\norganic world by the action of a personal Creator acting for a definite\npurpose, necessarily leads, when carried to its extreme consequences,\neither to utterly untenable contradictions, or to a twofold (dualistic)\nconception of nature, which most directly contradicts the unity and\nsimplicity of the supreme laws which are everywhere perceptible. The\nphilosophers who embrace teleology must necessarily assume two\nfundamentally different natures: an _inorganic_ nature, which must be\nexplained by causes acting _mechanically_ (caus\u00e6 efficientes), and an\n_organic_ nature, which must be explained by _causes acting for a\ndefinite purpose_ (caus\u00e6 finales). (Compare p. 34.)\n\nThis dualism meets us in a striking manner when considering the\nconceptions of nature formed by Kant, one of the greatest German\nphilosophers, and his ideas of the coming into being of organisms. A\ncloser examination of these ideas is forced upon us here, because in\nKant we honour one of the few philosophers who combine a solid\nscientific culture with an extraordinary clearness and profundity of\nspeculation. The K\u00f6nigsberg philosopher gained the highest celebrity,\nnot only among speculative philosophers as the founder of critical\nphilosophy, but acquired a brilliant name also among naturalists by his\nmechanical cosmogeny. Even in the year 1755, in his \u201cGeneral History of\nNature, and Theory of the Heavens,\u201d(22) he made the bold attempt \u201cto\ndiscuss the constitution and the mechanical origin of the whole\nuniverse, according to Newton\u2019s principles,\u201d and to explain them\nmechanically by the natural course of development, to the exclusion of\nall miracles. This cosmogeny of Kant, or \u201ccosmological gas theory,\u201d\nwhich we shall briefly discuss in a future chapter, was at a later day\nfully established by the French mathematician Laplace and the English\nastronomer Herschel, and enjoys at the present day almost universal\nrecognition. On account of this important work alone, in which exact\nknowledge is coupled with most profound speculation, Kant deserves the\nhonourable name of a natural philosopher in the best and purest sense of\nthe word.\n\nIf we read Kant\u2019s Criticism of the Teleological Faculty of Judgment, his\nmost important biological work, we perceive that in contemplating\norganic nature he always maintains what is essentially the teleological\nor dualistic point of view; whilst for inorganic nature he,\nunconditionally and without reserve, assumes the mechanical or monistic\nmethod of explanation. He affirms that in the domain of inorganic nature\nall the phenomena can be explained by mechanical causes, by the moving\nforces of matter itself, but not so in the domain of organic nature. In\nthe whole of Anorganology (in Geology and Mineralogy, in Meteorology and\nAstronomy, in the physics and chemistry of inorganic natural bodies),\nall phenomena are said to be explicable merely by _mechanism_ (causa\nefficiens), without the intervention of a final purpose. In the whole\ndomain of Biology, on the other hand\u2014in Botany, Zoology, and\nAnthropology\u2014mechanism is not considered sufficient to explain to us\nall their phenomena; but we are supposed to be able to comprehend them\nonly by an assumption of a _final cause_ acting for a definite purpose\n(causa finalis). In several passages Kant emphatically remarks that,\nfrom a strictly scientific point of view, _all_ phenomena, without\nexception, require a mechanical interpretation, and that _mechanism\nalone can offer a true explanation_. But at the same time he thinks,\nthat in regard to living natural bodies, animals and plants, our human\npower of comprehension is limited, and not sufficient for arriving at\nthe real cause of organic processes, especially at the origin of organic\nforms. The _right_ of human reason to explain all phenomena mechanically\nis unlimited, he says, but its _power_ is limited by the fact that\norganic nature can be conceived only from a teleological point of view.\n\nSome passages are, however, very remarkable, in which Kant in a\nsurprising manner deviates from this mode of viewing things, and\nexpresses, more or less distinctly, the fundamental idea of the Theory\nof Descent. He even asserts the necessity of a genealogical conception\nof the series of organisms, if we at all wish to understand it\nscientifically. The most important and remarkable of these passages\noccurs in his \u201cMethodical System of the Teleological Faculty of\nJudgment\u201d (\u00a7 79), which appeared in 1790 in the \u201cCriticism of the\nFaculty of Judgment.\u201d Considering the extraordinary interest which this\npassage possesses, both for forming a correct estimate of Kant\u2019s\nphilosophy, as well as for the Theory of Descent, I shall here insert it\n_verbatim_.\n\n\u201cIt is desirable to examine the great domain of organized nature by\nmeans of a methodical comparative anatomy, in order to discover whether\nwe may not find in it something resembling a system, and that too in\nconnection with the mode of generation, so that we may no longer be\ncompelled to stop short with a mere consideration of forms as they\nare\u2014which gives us no insight into their generation\u2014and need no longer\ngive up in despair all hope of gaining a full insight into this\ndepartment of nature. The agreement of so many kinds of animals in a\ncertain common plan of structure, which seems to be visible not only in\ntheir skeletons, but also in the arrangement of the remaining parts\u2014so\nthat a wonderfully simple typical form, by the shortening and\nlengthening of some parts, and by the suppression and development of\nothers, might be able to produce an immense variety of species\u2014gives us\na ray of hope, though feeble, that here perhaps some result may be\nobtained, by the application of the principle of the _mechanism of\nnature_, without which, in fact, no science can exist. This analogy of\nforms (in so far as they seem to have been produced in accordance with a\ncommon prototype, notwithstanding their great variety) strengthens the\nsupposition that they have an actual blood-relationship, due to\norigination from a common parent; a supposition which is arrived at by\nobservation of the graduated approximation of one class of animals to\nanother, beginning with the one in which the principle of purposiveness\nseems to be most conspicuous, that is man, and extending down to the\npolyps, and from these even down to mosses and lichens, and arriving\nfinally at raw matter, the lowest stage of nature observable by us. From\nthis matter and its forces the whole apparatus of Nature seems to have\ndescended according to mechanical laws (such as those which she follows\nin the production of crystals); yet this apparatus, as seen in organic\nbeings, is so incomprehensible to us, that we feel ourselves compelled\nto conceive for it a different principle. But it would seem that the\narch\u00e6ologist of Nature is at liberty to regard the great _Family_ of\ncreatures (for as a Family we must conceive it, if the above-mentioned\ncontinuous and connected relationship has a real foundation) as having\nsprung from the immediate results of her earliest revolutions, judging\nfrom all the laws of their mechanism known to or conjectured by him.\u201d\n\nIf we take this remarkable passage out of Kant\u2019s \u201cCriticism of the\nTeleological Faculty of Judgment,\u201d and consider it by itself, we cannot\nbut be astonished to find how profoundly and clearly the great thinker,\neven in 1790, had recognized the inevitable necessity of the Doctrine of\nDescent, and designated it as the only possible way of explaining\norganic nature by mechanical laws\u2014that is, by true scientific\nreasoning. On account of this one passage taken by itself, we might\nplace Kant beside Goethe and Lamarck, as one of the first founders of\nthe Doctrine of Descent; and considering the high authority which Kant\u2019s\nCritical Philosophy most justly enjoys, this circumstance might perhaps\ninduce many a philosopher to decide in favour of the theory. But as soon\nas we consider this passage in connection with the other train of\nthoughts in the \u201cCriticism of the Faculty of Judgment,\u201d and balance it\nagainst other directly contradictory passages, we see clearly that Kant,\nin these and some similar (but weaker) sentences, went beyond himself,\nand abandoned the teleological point of view which he usually adopts in\nBiology.\n\nDirectly after the admirable passage which I have just quoted, there\nfollows a remark which completely takes off its edge. After having quite\ncorrectly maintained the origin of organic forms out of raw matter by\nmechanical laws (in the manner of crystallization), as well as a gradual\ndevelopment of the different species by descent from one common original\nparent, Kant adds, \u201cBut he (the arch\u00e6ologist of nature, that is the\npal\u00e6ontologist) must for this end ascribe to the common mother an\norganization ordained purposely with a view to the needs of all her\noffspring, otherwise the possibility of suitability of form in the\nproducts of the animal and vegetable kingdoms (_i.e._ teleological\nadaptation) cannot be conceived at all.\u201d This addition clearly\ncontradicts the most important fundamental thought of the preceding\npassage, viz., that a purely mechanical explanation of organic nature\nbecomes possible through the Theory of Descent. And that the\nteleological conception of organic nature predominated with Kant, is\nshown by the heading of the remarkable \u00a7 79, which contains the two\ncontradictory passages cited: \u201c_Of the Necessary Subordination of the\nMechanical to the Teleological Principle, in the explanation of a thing\nas a purpose or object of Nature._\u201d\n\nHe expresses himself most decidedly against the mechanical explanation\nof organic nature in the following passage (\u00a7 74): \u201cIt is quite certain\nthat we cannot become sufficiently acquainted with organized creatures\nand their hidden potentialities by aid of purely mechanical natural\nprinciples, much less can we explain them; and this is so certain, that\nwe may boldly assert that it is absurd for man even to conceive such an\nidea, or to hope that a Newton may one day arise able to make the\nproduction of a blade of grass comprehensible, according to natural laws\nordained by no intention; such an insight we must absolutely deny to\nman.\u201d Now, however, this impossible Newton has really appeared seventy\nyears later in Darwin, whose Theory of Selection has actually solved the\nproblem, the solution of which Kant had considered absolutely\ninconceivable!\n\nIn connection with Kant and the German philosophers whose theories of\ndevelopment have already occupied us in the preceding chapter, it seems\njustifiable to consider briefly some other German naturalists and\nphilosophers, who, in the course of our century, have more or less\ndistinctly resisted the prevailing teleological views of creation, and\nvindicated the mechanical conception of things which is the basis of the\nDoctrine of Filiation. Sometimes general philosophical considerations,\nsometimes special empirical observations, were the motives which led\nthese thinking men to form the idea that the various individual species\nof organisms must have originated from common primary forms. Among them\nI must first mention the great German geologist, Leopold Buch. Important\nobservations as to the geographical distribution of plants led him to\nthe following remarkable assertion in his excellent \u201cPhysical\nDescription of the Canary Islands\u201d:\u2014\n\n\u201cThe individuals of genera, on continents, spread and widely diffuse\nthemselves, and by the difference of localities, nourishment, and soil,\nform varieties; and being in consequence of their isolation never\ncrossed by other varieties, and so brought back to the main type, they\nin the end become a permanent and a distinct species. Then, perhaps, in\nother ways, they once more become associated with other descendants of\nthe original form\u2014which have likewise become new varieties\u2014and both\nnow appear as very distinct species, no longer mingling with one\nanother. Not so on islands. Being commonly confined in narrow valleys or\nwithin the limit of small zones, individuals can reach one another and\ndestroy every commencing production of a permanent variety. Much in the\nsame way the peculiarities or faults in language, originating with the\nhead of some family, become, through the extension of the family,\nindigenous throughout a whole district. If the district is separated and\nisolated, and if the language is not brought back to its former purity\nby constant connection with that spoken in neighbouring districts, a\ndialect will be the result. If natural obstacles, forests, constitution,\nform of government, unite the inhabitants of the separate district still\nmore closely, and separate them still more completely from their\nneighbours, the dialect is fixed, and becomes a completely distinct\nlanguage.\u201d (Uebersicht der Flora auf den Canarien, S. 133.)\n\nWe perceive that Buch is here led to the fundamental idea of the Theory\nof Descent by the phenomena of the geography of plants, a department of\nbiological knowledge which in fact furnishes a mass of proofs in favour\nof it. Darwin has minutely discussed these proofs in two separate\nchapters of his book (the 11th and 12th). Buch\u2019s remark is further of\ninterest, because it leads us to the exceedingly instructive comparison\nof the different branches of language with the species of organisms, a\ncomparison which is of the greatest use to Comparative Philology, as\nwell as to Comparative Botany and Zoology. Just as, for example, the\ndifferent dialects, provincialisms, branches, and off-shoots of the\nGerman, Slavonic, Greco-Latin, and Irano-Indian parent language, are\nderived from a single common Indo-Germanic parent tongue, and just as\ntheir _differences_ are explained by _Adaptation_, and their common\n_fundamental characters_ explained by _Inheritance_, so in like manner\nthe different species, genera, families, orders, and classes of\nVertebrate animals are derived from a single common vertebrate form of\nanimal. Here also Adaptation is the cause of differences, Inheritance\nthe cause of community of character. This interesting parallelism in the\ndivergent development of the forms of speech and the forms of organisms\nhas been discussed in the clearest manner by one of our first\ncomparative philologists, the talented Augustus Schleicher, whose\npremature death, four years ago, remains an irreparable loss, not only\nto our University of Jena, but to the whole of monistic science.(6)\n\nAmong other eminent German naturalists who have expressed their belief\nin the Theory of Descent more or less distinctly, arriving at their\nconclusion in very various ways, I must next mention Carl Ernst B\u00e4r,\nthe great reformer of animal embryology. In a lecture delivered in 1834,\nentitled \u201cThe Most General Laws of Nature in All Development,\u201d he shows,\nin the clearest way, that only in a very childish view of nature could\norganic species be regarded as permanent and unchangeable types, and\nthat really they can be only passing series of generations, which have\ndeveloped by transformation from a common original form. The same\nconception again received firm support from Baer, in 1859, through a\nconsideration of the laws of the geographical distribution of organisms.\n\nJ. M. Schleiden, who founded, thirty years ago, in Jena, a new epoch in\nBotany by his strictly empirico-philosophical and truly scientific\nmethod, illustrated the philosophical significance of the conception of\norganic species in his incisive \u201cOutlines of Scientific Botany,\u201d(7) and\nshowed that it had only a subjective origin in the general _law of\nspecification_. The different species of plants are only the specified\nproductions of the formative tendencies of plants, which arise from the\nvarious combinations of the fundamental forces of organic matter.\n\nThe eminent botanist, F. Unger, of Vienna, was led by his profound and\ncomprehensive investigations on extinct vegetable species, to a\npal\u00e6ontological history of the development of the vegetable kingdom,\nwhich distinctly asserts the principle of the Theory of Descent. In his\n\u201cAttempt at a History of the World of Plants\u201d (1852), he maintains the\nderivation of all different species of plants from a few primary forms,\nand perhaps from a single original plant, a simple vegetable cell. He\nshows that this view is founded on the genetic connection of all\nvegetable forms, and is necessary, not merely upon philosophical\ngrounds, but upon those of experience and observation.(8)\n\nVictor Carus, of Leipzig, in the Introduction to his excellent \u201cSystem\nof Animal Morphology,\u201d(9) published in 1853, in which he endeavours to\nestablish in a philosophical manner the universal constructive laws of\nthe animal body through comparative anatomy and the history of\ndevelopment, makes the following remark:\u2014\u201cThe organisms buried in the\nmost ancient geological strata must be looked upon as the ancestors from\nwhom the rich diversity of forms of the present creation have originated\nby continued generation, and by accommodation to progressive and very\ndifferent conditions of life.\u201d\n\nIn the same year (1853) Schaaffhausen, the anthropologist of Bonn, in an\nEssay \u201cOn the Permanence and Transformation of Species,\u201d declared\nhimself decidedly in favour of the Theory of Descent. According to him,\nthe living species of animals and plants are the transformed descendants\nof extinct species, from which they have arisen by gradual modification.\nThe divergence or separation of the most nearly allied species takes\nplace by the destruction of the connecting intermediate stages.\nSchaaffhausen also maintained, with distinctness, the origin of the\nhuman race from animals, and its gradual development from ape-like\nanimals, the most important deduction from the Doctrine of Filiation.\n\nLastly, we have still to mention among the German Nature-philosophers\nthe name of Louis B\u00fcchner, who, in his celebrated work, \u201cForce and\nMatter\u201d (1855), also independently developed the principles of the\nTheory of Descent, taking his stand mainly on the ground of the\nundeniable evidences of fact which are furnished by the pal\u00e6ontological\nand individual development of organisms, as well as by their\ncomparative anatomy and by the parallelism of these series of\ndevelopment. B\u00fcchner showed very clearly that, even from such data\nalone, the derivation of the different organic species from common\nprimary forms followed as a necessary conclusion, and that the origin of\nthese original primary forms could only be conceived of as the result of\na spontaneous generation.\n\nWe now turn from the German to the French Nature-philosophers, who have\nlikewise held the Theory of Descent, since the beginning of the present\ncentury. At their head stands Jean Lamarck, who occupies the first place\nnext to Darwin and Goethe in the history of the Doctrine of Filiation.\nTo him will always belong the immortal glory of having for the first\ntime worked out the Theory of Descent, as an independent scientific\ntheory of the first order, and as the philosophical foundation of the\nwhole science of Biology. Although Lamarck was born as early as 1744, he\ndid not begin the publication of his theory until the commencement of\nthe present century, in 1801, and established it more fully only in\n1809, in his classic \u201cPhilosophie Zoologique.\u201d(2) This admirable work is\nthe first connected exposition of the Theory of Descent carried out\nstrictly into all its consequences. By its purely mechanical method of\nviewing organic nature, and the strictly philosophical proofs brought\nforward in it, Lamarck\u2019s work is raised far above the prevailing\ndualistic views of his time; and with the exception of Darwin\u2019s work,\nwhich appeared just half a century later, we know of none which we could\nin this respect place by the side of the \u201cPhilosophie Zoologique.\u201d How\nfar it was in advance of its time is perhaps best seen from the\ncircumstance that it was not understood by most men, and for fifty\nyears was not spoken of at all. Cuvier, Lamarck\u2019s greatest opponent, in\nhis \u201cReport on the Progress of Natural Sciences,\u201d in which the most\nunimportant anatomical investigations are enumerated, does not devote a\nsingle word to this work, which forms an epoch in science. Goethe, also,\nwho took such a lively interest in the French nature-philosophy and in\n\u201cthe thoughts of kindred minds beyond the Rhine,\u201d nowhere mentions\nLamarck, and does not seem to have known the \u201cPhilosophie Zoologique\u201d at\nall. The great reputation which Lamarck gained as a naturalist he does\nnot owe to his highly important general work, but to numerous special\ntreatises on the lower animals, particularly on Molluscs, as well as to\nan excellent \u201cNatural History of Invertebrate Animals,\u201d which appeared,\nin seven volumes, between the years 1815-1822. The first volume of this\ncelebrated work contains in the general introduction a detailed\nexposition of his theory of filiation. I can, perhaps, give no better\nidea of the extraordinary importance of the \u201cPhilosophie Zoologique\u201d\nthan by quoting _verbatim_ some of the most important passages\ntherefrom:\u2014\n\n\u201cThe systematic divisions of classes, orders, families, genera, and\nspecies, as well as their designations, are the arbitrary and artificial\nproductions of man. The kinds or species of organisms are of unequal\nage, developed one after the other, and show only a relative and\ntemporary persistence; species arise out of varieties. The differences\nin the conditions of life have a modifying influence on the\norganization, the general form, and the parts of animals, and so has the\nuse or disuse of organs. In the first beginning only the very simplest\nand lowest animals and plants came into existence; those of a more\ncomplex organization only at a later period. The course of the earth\u2019s\ndevelopment, and that of its organic inhabitants, was continuous, not\ninterrupted by violent revolutions. Life is purely a physical\nphenomenon. All the phenomena of life depend on mechanical, physical,\nand chemical causes, which are inherent in the nature of matter itself.\nThe simplest animals and the simplest plants, which stand at the lowest\npoint in the scale of organization, have originated and still originate\nby spontaneous generation. All animate natural bodies or organisms are\nsubject to the same laws as inanimate natural bodies or anorgana. The\nideas and actions of the understanding are the motional phenomena of the\ncentral nervous system. The will is in truth never free. Reason is only\na higher degree of development and combination of judgments.\u201d\n\nThese are indeed astonishingly bold, grand, and far-reaching views, and\nwere expressed by Lamarck sixty years ago; in fact, at a time when their\nestablishment, by a mass of facts, was not nearly as possible as it is\nin our day. Indeed Lamarck\u2019s work is really a complete and strictly\nmonistic (mechanical) system of nature, and all the important general\nprinciples of monistic Biology are already enunciated by him: the unity\nof the active causes in organic and inorganic nature; the ultimate\nexplanation of these causes in the chemical and physical properties of\nmatter itself; the absence of a special vital power, or of an organic\nfinal cause; the derivation of all organisms from some few, most simple\noriginal forms, which have come into existence by spontaneous generation\nout of inorganic matter; the coherent course of the whole earth\u2019s\nhistory; the absence of violent cataclysmic revolutions; and in general\nthe inconceivableness of any miracle, of any supernatural interference,\nin the natural course of the development of matter.\n\nThe fact that Lamarck\u2019s wonderful intellectual feat met with scarcely\nany recognition, arises partly from the immense length of the gigantic\nstride with which he had advanced beyond the next fifty years, partly\nfrom its defective empirical foundation, and from the somewhat one-sided\ncharacter of some of his arguments. Lamarck quite correctly recognizes\n_Adaptation_ as the first mechanical cause which effects the continual\ntransformation of organic forms, while he traces with equal justice the\nsimilarity in form of different species, genera, families, etc., to\ntheir blood-relationship, and thus explains it by _Inheritance_.\nAdaptation, according to him, consists in this, that the perpetual, slow\nchange of the outer world causes a corresponding change in the actions\nof organisms, and thereby also causes a further change in their forms.\nHe lays the greatest stress upon the effect of _habit_ upon the use and\ndisuse of organs. This is certainly of great importance in the\ntransformation of organic forms, as we shall see later. However, the way\nin which Lamarck wished to explain exclusively, or at any rate mainly,\nthe change of forms, is after all in most cases not possible. He says,\nfor example, that the long neck of the giraffe has arisen from its\nconstantly stretching out its neck at high trees, and from the endeavour\nto pick the leaves off their branches; as giraffes generally inhabit dry\ndistricts, where only the foliage of trees afford them nourishment, they\nwere forced to this action. In like manner the long tongues of\nwood-peckers, humming-birds, and ant-eaters, are said by him to have\narisen from the habit of fetching their food out of narrow, small, and\ndeep crevices or channels. The webs between the toes of the webbed feet\nin frogs and other aquatic animals have arisen solely from the constant\nendeavour to swim, from striking their feet against the water, and from\nthe very movements of swimming. Inheritance fixed these habits on the\ndescendants, and finally, by further elaboration, the organs were\nentirely transformed. However correct, as a whole, this fundamental\nthought may be, yet Lamarck lays the stress too exclusively on _habit_\n(use and non-use of organs), certainly one of the most important, but\nnot the only cause of the change of forms. Still this cannot prevent our\nacknowledging that Lamarck quite correctly appreciated the mutual\nco-operation of the two organic formative tendencies of Adaptation and\nInheritance. What he failed to grasp is the exceedingly important\nprinciple of \u201cNatural Selection in the Struggle for Existence,\u201d with\nwhich Darwin, fifty years later, made us acquainted.\n\nIt still remains to be mentioned as a special merit of Lamarck, that he\nendeavoured to prove the _development of the human race_ from other\nprimitive, ape-like mammals. Here again it was, above all, to habit that\nhe ascribed the transforming, the ennobling influence. He assumed that\nthe lowest, original men had originated out of men-like apes, by the\nlatter accustoming themselves to walk upright. The raising of the body,\nthe constant effort to keep upright, in the first place led to a\ntransformation of the limbs, to a stronger differentiation or separation\nof the fore and hinder extremities, which is justly considered one of\nthe most essential distinctions between man and the ape. Behind, the\ncalf of the leg and the flat soles of the feet were developed; in\nfront, the arms and hands, for the purpose of seizing objects. The\nupright walk was then followed by a freer view over the surrounding\nobjects, and led consequently to an important progress in mental\ndevelopment. Human apes thereby soon gained a great advantage over the\nother apes, and further, over surrounding organisms in general. In order\nto maintain the supremacy over them, they formed themselves into\ncompanies, and there arose, as in the case of all animals living in\ncompany, the desire of communicating to one another their desires and\nthoughts. Thus arose the necessity of language, which, consisting at\nfirst of rough and disjointed sounds, soon became more connected,\ndeveloped, and articulate. The development of articulate speech now in\nturn became the strongest lever for a further progressive development of\nthe organism, and above all, of the brain, and so ape-like men became\ngradually and slowly transformed into real men. In this way the actual\ndescent of the lowest and rudest primitive men from the most highly\ndeveloped apes was distinctly maintained by Lamarck, and supported by a\nseries of the most important proofs.\n\nThe honour of being the chief French nature-philosopher is not usually\nassigned to Lamarck, but to Etienne Geoffroy St. Hilaire (the elder),\nborn in 1771, the same in whom Goethe was especially interested, and\nwith whom we have already become acquainted as Cuvier\u2019s most prominent\nopponent. He developed his ideas about the transformation of organic\nspecies as far back as the end of the last century, but published them\nonly in the year 1828, and then in the following years, especially in\n1830, defended them bravely against Cuvier. Geoffroy St. Hilaire in all\nessentials adopted Lamarck\u2019s Theory of Descent, yet he believed that\nthe transformation of animal and vegetable species was less effected by\nthe action of the organism itself (by habit, practice, use, or disuse of\norgans) than by the \u201cmonde ambiant,\u201d that is, by the continual change of\nthe outer world, especially of the atmosphere. He conceives the organism\nas passive, in regard to the vital conditions of the outer world, while\nLamarck, on the contrary, regards it as active. Geoffroy thinks, for\nexample, that birds originated from lizard-like reptiles, simply by a\ndiminution of the carbonic acid in the atmosphere, in consequence of\nwhich the breathing process became more animated and energetic through\nthe increased proportion of oxygen in the atmosphere. Thus there arose a\nhigher temperature of the blood, an increased activity of the nerves and\nmuscles, and the scales of the reptiles became the feathers of the\nbirds, etc. This conception is based upon a correct thought, but\nalthough the change of the atmosphere, as well as the change of every\nother external condition of existence, certainly effects directly or\nindirectly the transformation of the organism, yet this single cause is\nby itself too unimportant for such effects to be ascribed to it. It is\neven less important than practice and habit, upon which Lamarck lays too\nmuch stress. Geoffroy\u2019s chief merit consists in his having vindicated\nthe monistic conception of nature, the unity of organic forms, and the\ndeep genealogical connection of the different organic types in the face\nof Cuvier\u2019s powerful influence. I have already mentioned in the\npreceding chapter (pp. 87, 88) the celebrated disputes between the two\ngreat opponents in the Academy of Paris, especially the fierce conflicts\non the 22nd of February, and on the 19th of July, in which Goethe took\nso lively an interest. On that occasion Cuvier remained the\nacknowledged victor, and since that time very little, or rather nothing,\nmore has been done in France to further the development of the Doctrine\nof Filiation, and complete the monistic theory of development. This is\nevidently to be ascribed principally to the repressive influence\nexercised by Cuvier\u2019s great authority. Even at the present day the\nmajority of the French naturalists are the disciples and blind followers\nof Cuvier. In no civilized country of Europe has Darwin\u2019s doctrine had\nso little effect and been so little understood as in France, so that in\nthe further course of our examination we need not take the French\nnaturalists into consideration. At most, there are two distinguished\nbotanists, among the recent French naturalists, whom we may mention as\nhaving ventured to express themselves in favour of the mutability and\ntransformation of species. These two men are Naudin (1852) and Lecoq\n(1854).\n\nHaving discussed the early services of German and French\nnature-philosophy in establishing the doctrine of descent, we turn to\nthe third great country of Europe, to free England, which during the\nlast ten years has become the chief seat and starting-point for the\nfurther working out and definite establishment of the theory of\ndevelopment. Englishmen, who now take such an active part in every great\nscientific progress of humanity, and are the first to promote the\neternal truths of natural science, at the beginning of the century took\nbut little part in the continental nature-philosophy and its most\nimportant progress, the Theory of Descent. Almost the only earlier\nEnglish naturalist whom we have here to mention is Erasmus Darwin, the\ngrandfather of the reformer of the Theory of Descent. In 1795 he\npublished, under the title of \u201cZoonomia,\u201d a scientific work in which he\nexpresses views very similar to those of Goethe and Lamarck, without,\nhowever, then knowing anything about these two men. It is evident that\nthe Theory of Descent at that time pervaded the intellectual atmosphere.\nErasmus Darwin lays great stress upon the transformation of animal and\nvegetable species by their own vital action and by their becoming\naccustomed to changed conditions of existence, etc. Next, W. Herbert, in\n1822, expressed the opinion that species of animals and plants are\nnothing but varieties which have become permanent. In like manner Grant,\nin Edinburgh, in 1826, declared that new species proceed from existing\nspecies by continued transformation. In 1841 Freke maintained that all\norganic beings must be descended from a single primitive type. In 1852\nHerbert Spencer demonstrated minutely, and in a very clear and\nphilosophic manner, the necessity of the Doctrine of Filiation, and\nestablished it more firmly in his excellent \u201cEssays,\u201d which appeared in\n1858, and in his \u201cPrinciples of Biology,\u201d which was published at a later\ndate. He has, at the same time, the great merit of having applied the\ntheory of development to psychology, and of having shown that the\nemotional and intellectual faculties could only have been acquired by\ndegrees and developed gradually. Lastly, we have to mention that in 1859\nHuxley, the first of English zoologists, spoke of the Theory of Descent\nas the only hypothesis of creation reconcilable with scientific\nphysiology. The same year produced the \u201cIntroduction to the Flora of\nTasmania,\u201d in which Hooker, the celebrated English botanist, adopts the\nTheory of Descent, supporting it with important observations of his\nown.\n\nAll the naturalists and philosophers with whom we have become acquainted\nin this brief historical survey, as men adopting the Theory of\nDevelopment, merely arrived at the conception that all the different\nspecies of animals and plants which at any time have lived, and still\nlive, upon the earth, are the gradually changed and transformed\ndescendants of one or some few original and very simple prototypes,\nwhich latter arose out of inorganic matter by spontaneous generation.\nBut none of them succeeded in placing this fundamental element of the\ndoctrine of descent in relation with some cause, nor in satisfactorily\nexplaining the transformation of organic species by the true\ndemonstration of its mechanical antecedents. Charles Darwin was the\nfirst who solved this most difficult problem, and this forms the broad\ngulf which separates him from his predecessors.\n\nThe special merit of Charles Darwin is, in my opinion, twofold: in the\nfirst place, the doctrine of descent, the fundamental idea of which was\nalready clearly expressed by Goethe and Lamarck, has been developed by\nhim much more comprehensively, has been traced much more minutely in all\ndirections, and carried out much more strictly and connectedly than by\nany of his predecessors; and secondly, he has established a new theory,\nwhich reveals to us the natural causes of organic development, the\nacting causes (caus\u00e6 efficientes) of organic form-production, and of the\nchanges and transformations of animal and vegetable species. This is the\ntheory which we call the Theory of Selection, or more accurately, the\nTheory of Natural Selection (selectio naturalis).\n\nWhen we reflect that (with the few exceptions above mentioned) the\nwhole science of Biology, before Darwin\u2019s time, was elaborated in\naccordance with the opposite views, and that almost all zoologists and\nbotanists regarded the absolute independence of organic species as a\nself-evident inference from the results of all study of forms, we shall\ncertainly not lightly value the twofold merit of Darwin. The false\ndoctrine of the constancy and independent creation of individual species\nhad gained such high authority, was so generally recognized, and was,\nmoreover, so much favoured by delusive appearances, accepted by\nsuperficial observation, that, indeed, no small degree of courage,\nstrength, and intelligence was required to rise as a reformer against\nits omnipotence, and to dash to pieces the structure artificially\nerected upon it. But, in addition to this, Darwin added to Lamarck\u2019s and\nGoethe\u2019s doctrine of descent the new and highly important principle of\n\u201cnatural selection.\u201d\n\nWe must sharply distinguish the two points\u2014though this is usually not\ndone\u2014first, Lamarck\u2019s Theory of Descent, which only asserts _that_ all\nanimal and vegetable species are descended from common, most simple, and\nspontaneously generated prototypes; and secondly, Darwin\u2019s Theory of\nSelection, which shows us _why_ this progressive transformation of\norganic forms took place, and what causes, acting mechanically, effected\nthe uninterrupted production of new forms, and the ever increasing\nvariety of animals and plants.\n\nDarwin\u2019s immortal merit cannot be justly estimated until a later period,\nwhen the Theory of Development, after overthrowing all other theories of\ncreation, will be recognized as the supreme principle of explanation in\nAnthropology, and, consequently, in all other sciences. At present,\nwhile in the hot contest for truth the name of Darwin is the watchword\nto the advocates of the natural theory of development, his merits are\ninaccurately appreciated on both sides, for some persons overestimate\nthem as much as others underestimate them.\n\nHis merit is overestimated when he is regarded as the founder of the\nTheory of Descent, or of the whole of the Theory of Development. We have\nseen from the historical sketch in this and the preceding chapters, that\nthe Theory of Development, as such, is not new; all philosophers who\nhave refused to be led captive by the blind dogma of a supernatural\ncreation, have been compelled to assume a natural development. But the\nTheory of Descent constituting the specially biological part of the\nuniversal Theory of Development, had already been so clearly expressed\nby Lamarck, and carried out so fully by him to its most important\nconsequences, that we must honour him as the real founder of it. Hence\nit is only the Theory of Selection, and not that of Descent, which may\nbe called _Darwinism_; but this is in itself of so much importance, that\nits value can scarcely be overestimated.\n\nDarwin\u2019s merit is naturally underestimated by all his opponents. But it\nis scarcely possible in this matter to point to scientific opponents,\nwho are entitled by profound biological culture to pronounce an opinion.\nFor among all the works opposed to Darwin and the Theory of Descent yet\npublished, with the exception of that of Agassiz, not one deserves\nconsideration, much less refutation; all have so evidently been written\neither without thorough knowledge of biological facts, or without a\nclear philosophical understanding of the question in hand. We need not\ntrouble ourselves at all about the attacks of theologians and other\nunscientific men, who really know nothing whatever of nature.\n\nThe only eminent scientific adversary who still remains opposed to\nDarwin and the whole theory of development is Louis Agassiz; but the\nprinciple of his opposition in reality deserves notice only as a\nphilosophical curiosity. In a French translation of his \u201cEssay on\nClassification,\u201d(5) which we have spoken of before, published in Paris\nin 1869, Agassiz has most formally announced his opposition to\nDarwinism, which he had previously expressed in many ways. To this\ntranslation he has appended a treatise of sixteen pages, bearing the\ntitle, \u201cLe Darwinisme. Classification de Haeckel.\u201d This curious chapter\ncontains the most wonderful things; as, for example, \u201cDarwin\u2019s idea is a\nconception _\u00e0 priori_. Darwinism is a burlesque of facts. Science would\nrenounce the claim which it has hitherto possessed to the confidence of\nearnest minds if such sketches were to be accepted as indications of a\ntrue progress.\u201d The following passage, however, is the climax of this\nstrange polemic: \u201cDarwinism shuts out almost the whole mass of acquired\nknowledge in order to retain and assimilate to itself that only which\nmay serve its doctrine.\u201d\n\nSurely this is what we may call turning the whole affair topsy-turvy!\nThe biologist who knows the facts must be astounded at Agassiz\u2019s courage\nin uttering such sentences\u2014sentences without a word of truth in them,\nand which he cannot himself believe! The impregnable strength of the\nTheory of Descent lies just in the fact that all biological facts are\nexplicable only through it, and that without it they remain\nunintelligible miracles. All our \u201claborious knowledge\u201d in comparative\nanatomy and physiology\u2014in embryology and pal\u00e6ontology\u2014in the doctrine\nof the geographical and topographical distribution of organisms, etc.,\nconstitutes an irrefutable testimony to the truth of the Theory of\nDescent.\n\nIn my General Morphology, especially in the sixth book (in the General\nPhylogeny), I have minutely refuted Agassiz\u2019s \u201cEssay on Classification\u201d\nin all essential points. The twenty-fourth chapter I have devoted to a\nvery detailed and strictly scientific discussion of that section which\nAgassiz himself considers the most important (the groups or categories\nof systematic zoology and botany), and have shown that this part of his\nwork is purely chimerical, without any trace of real foundation. Agassiz\ntakes good care not to venture anywhere to touch upon my refutation,\nbecause, forsooth, he is not in a position to produce anything\nsubstantial against it. He fights not with arguments, but with phrases.\nHowever, such opposition will not delay the complete victory of the\nTheory of Development, but only accelerate it.\n\n\n\n\nCHAPTER VI.\n\nTHEORY OF DEVELOPMENT ACCORDING TO LYELL AND DARWIN.\n\n\n  Charles Lyell\u2019s Principles of Geology.\u2014His Natural\n  History of the Earth\u2019s Development.\u2014Origin of the\n  Greatest Effects through the Multiplication of the\n  Smallest Causes.\u2014Unlimited Extent of Geological\n  Periods.\u2014Lyell\u2019s Refutation of Cuvier\u2019s History of\n  Creation.\u2014The Establishment of the Uninterrupted\n  Connection of Historical Development by Lyell and\n  Darwin.\u2014Biographical Notice of Charles Darwin.\u2014His\n  Scientific Works.\u2014His Theory of Coral Reefs.\u2014Development\n  of the Theory of Selection.\u2014A Letter of Darwin\u2019s.\u2014The\n  Contemporaneous Appearance of Darwin\u2019s and Alfred\n  Wallace\u2019s Theory of Selection.\u2014Darwin\u2019s Study of Domestic\n  Animals and Cultivated Plants.\u2014Andreas Wagner\u2019s notions\n  as to the Special Creation of Cultivated Organisms for the\n  good of Man.\u2014The Tree of Knowledge in\n  Paradise.\u2014Comparison between Wild and Cultivated\n  Organisms.\u2014Darwin\u2019s Study of Domestic\n  Pigeons.\u2014Importance of Pigeon Breeding.\u2014Common Descent\n  of all Races of Pigeons.\n\n\nDuring the thirty years, from 1830 until 1859, when Darwin\u2019s work\nappeared, the ideas of creation introduced by Cuvier remained\npredominant in the sciences of organic nature. People rested satisfied\nwith the unscientific assumption, that in the course of the earth\u2019s\nhistory, a series of inexplicable revolutions had periodically\nannihilated the whole world of animals and plants, and that at the end\nof each revolution, and the beginning of a new period, a new enlarged,\nand improved edition of the organic population had appeared. Although\nthe number of these editions of creation was altogether problematical,\nand in truth could not be fixed at all, and although the numerous\nadvances which, during this time, were made in all the departments of\nzoology and botany demonstrated more and more that Cuvier\u2019s hypothesis\nwas unfounded and untenable, and that Lamarck\u2019s natural theory of\ndevelopment was nearer the truth, yet the former maintained its\nauthority almost universally among biologists. This must, above all, be\nascribed to the veneration which Cuvier had acquired, and strikingly\nillustrates how injurious to the progress of humanity a faith in any\ndefinite authority may become. Authority, as Goethe once admirably said,\nperpetuates the individual, which as an individual should pass away,\nrejects and allows to pass that which should be held fast, and is the\nmain obstacle to the advance of humanity.\n\nIt is only by having regard to the great weight of Cuvier\u2019s authority,\nand to the mighty potency of human indolence, which is with difficulty\ninduced to depart from the broad and comfortable way of everyday\nconceptions, and to enter upon new paths not yet made easy, that we can\ncomprehend how it is that Lamarck\u2019s Theory of Descent did not gain its\ndue recognition until 1859, after Darwin had given it a new foundation.\nThe soil had long been prepared for it by the works of Charles Lyell,\nanother English naturalist, whose views are of great importance for the\nnatural history of creation, and must accordingly here be briefly\nexplained.\n\nIn 1830 Charles Lyell published, under the title of \u201cPrinciples of\nGeology,\u201d a work in which he thoroughly reformed the science of Geology\nand the history of the earth\u2019s development, and effected this reform in\na manner similar to that in which, thirty years later, Darwin in his\nwork reformed the science of Biology. Lyell\u2019s great treatise, which\nradically destroyed Cuvier\u2019s hypothesis of creation, appeared in the\nsame year in which Cuvier celebrated his triumph over the\nnature-philosophy, and established his supremacy in the domain of\nmorphology for the following thirty years. Whilst Cuvier, by his\nartificial hypothesis of creation and his theory of catastrophes\nconnected with it, directly obstructed the path of the theory of natural\ndevelopment, and cut off all chance of a natural explanation, Lyell once\nmore opened a free road, and brought forward convincing geological\nevidence to show that Cuvier\u2019s dualistic conceptions were as unfounded\nas they were superfluous. He demonstrated that those changes of the\nearth\u2019s surface, which are still taking place before our eyes, are\nperfectly sufficient to explain everything we know of the development of\nthe earth\u2019s crust in general, and that it is superfluous and useless to\nseek for mysterious causes in inexplicable revolutions. He showed that\nwe need only have recourse to the hypothesis of exceedingly long periods\nof time in order to explain the formation of the crust of the earth in\nthe simplest and most natural manner by means of the very same causes\nwhich are still active. Many geologists had previously imagined that the\nhighest chains of mountains which rise on the surface of the earth could\nowe their origin only to enormous revolutions transforming a great part\nof the earth\u2019s surface, especially to colossal volcanic eruptions. Such\nchains of mountains as those of the Alps or the Cordilleras were\nbelieved to have arisen direct from the fiery fluid of the interior of\nthe earth, through an enormous chasm in the broken crust. Lyell, on the\nother hand, showed that we can explain the formation of such enormous\nchains of mountains quite naturally by the same slow and imperceptible\nrisings and depressions of the earth\u2019s surface which are still\ncontinually taking place, and the causes of which are by no means\nmiraculous. Although these depressions and risings may perhaps amount\nonly to a few inches, or at most a few feet, in the course of a century;\nstill, in the course of some millions of years they are perfectly\nsufficient to raise up the highest chains of mountains, without the aid\nof mysterious and incomprehensible revolutions. In like manner, the\nmeteorological action of the atmosphere, the influence of rain and snow,\nand, lastly, the breakers on the coasts, which by themselves seem to\nproduce an insignificant effect, must cause the greatest changes if we\nonly allow sufficiently long periods for their action. The\nmultiplication of the smallest causes produces the greatest effects.\nDrops of water produce a cavity in a rock.\n\nI shall afterwards be obliged again to recur to the immeasurable length\nof geological periods which are necessary for this purpose, for, as we\nshall see, Darwin\u2019s theory, as well as that of Lyell, renders the\nassumption of immense periods absolutely necessary. If the earth and its\norganisms have actually developed in a natural way, this slow and\ngradual development must certainly have taken a length of time which\nsurpasses our powers of comprehension. But as many men see in this very\ncircumstance one of the principal difficulties in the way of those\ntheories of development, I beg leave here to remark that we have not a\nsingle rational ground for conceiving the time requisite to be limited\nin any way. Not only many ordinary persons, but even eminent\nnaturalists, make it their chief objection to these theories, that they\narbitrarily claim too great a length of time: yet the ground of\nobjection is scarcely intelligible. For it is absolutely impossible to\nsee what can, in any way, limit us in assuming long periods of time. We\nhave long known, even from the structure of the stratified crust of the\nearth alone, that its origin and the formation of neptunic rocks from\nwater must have taken, at least, several millions of years. From a\nstrictly philosophical point of view, it makes no difference whether we\nhypothetically assume for this process ten millions or ten thousand\nbillions of years. Before us and behind us lies eternity. If the\nassumption of such enormous periods is opposed to the feelings of many,\nI regard this simply as the consequence of false notions which are\nimpressed upon us from our earliest youth concerning the short history\nof the earth, which is said to embrace only a few thousands of years.\nAlbert Lange, in his \u201cHistory of Materialism,\u201d(12) has convincingly\nshown that from a strictly philosophical point of view it is far less\nobjectionable in a scientific hypothesis to assume periods which are too\nlong than periods which are too short. Every process of development is\nthe more intelligible the longer it is assumed to last. A short and\nlimited period is the most improbable.\n\nI have no space here to enter minutely into Lyell\u2019s great work, and will\ntherefore mention only its most important result, which is, that he\ncompletely refuted Cuvier\u2019s history of creation with its mythical\nrevolutions, and established in its place the constant and slow\ntransformation of the earth\u2019s crust by the continued action of forces,\nwhich are still working on the earth\u2019s surface, viz., the movement of\nwater and the volcanic fluid of the interior of earth. Lyell thus\ndemonstrated a continuous and uninterrupted connection of the whole\nhistory of the earth, and he proved it so irrefutably, and established\nso convincingly the supremacy of the \u201cexisting causes,\u201d that is, of the\ncauses which are still active in the transformation of the earth\u2019s\ncrust, that Geology in a short time completely renounced Cuvier\u2019s\nhypothesis.\n\nNow, it is remarkable that Pal\u00e6ontology, the science of petrifactions,\nso far as it was pursued by botanists and zoologists, remained\napparently unaffected by this great progress in geology. Biology still\ncontinued to assume repeated new creations of the whole animal and\nvegetable kingdoms, at the beginning of every new period of the earth\u2019s\nhistory, although this hypothesis of individual creations, shoved into\nthe world one after the other, without the assumption of Cuvier\u2019s\ncataclysms, became pure nonsense, and lost its foundation. It is\nevidently perfectly absurd to assume a distinct new creation of the\nwhole world of animals and plants at definite epochs, without the crust\nof the earth itself experiencing any considerable general revolution.\nAnd although this conception is most closely connected with Cuvier\u2019s\ntheory of catastrophes, still it prevailed when the latter had been\ncompletely destroyed and abandoned.\n\nIt was reserved for the great English naturalist, Charles Darwin, to\nremove this contradiction, and to show that the organic beings of the\nearth have a history as continuous and connected as the inorganic crust\nof the earth; that animals and plants have arisen from one another by as\ngradual a transmutation as that by which the varying forms of the\nearth\u2019s crust, the forms of the continents, and of the seas surrounding\nand separating them, have arisen out of earlier and quite different\nforms. In this respect we may truly say that in the domain of Zoology\nand Botany Darwin made the same progress as Lyell, his great countryman,\nin the domain of Geology. Both proved the _uninterrupted connection of\nthe historical development_, and demonstrated a gradual transmutation of\nthe different conditions succeeding one another.\n\nThe special merit of Darwin, as I have already remarked in a preceding\nchapter, is twofold. In the first place, he has treated the Theory of\nDescent, put forth by Lamarck and Goethe, in a much more comprehensive\nmanner, as a whole, and carried it out in a much more connected manner,\nthan had been done by any one of his predecessors. Secondly, he has\nestablished the causal foundation of this Theory of Descent by the\nTheory of Selection, which is peculiarly his own; that is, he has\ndemonstrated the acting _causes of the changes_ which the Theory of\nDescent simply stated, as _facts_. The Theory of Descent, introduced\ninto Biology in 1809, by Lamarck, asserts that all the different species\nof animals and plants are descended from a single or some few most\nsimple prototypes, produced by spontaneous generation. The Theory of\nSelection, established in 1859 by Darwin, shows us _why_ this must be\nso; it points out the acting causes in a manner with which Kant would\nhave been delighted, and indeed, in the domain of organic nature, Darwin\nhas become the Newton whose advent Kant thought himself entitled\nprophetically to deny.\n\nNow, before we approach Darwin\u2019s theory, it will perhaps be of interest\nto notice a few details as to the personal character of this great\nnaturalist, as to his life, and the way in which he was led to form his\ndoctrine. Charles Robert Darwin was born at Shrewsbury, on the Severn,\non the 12th of February, 1809; therefore, at present he is sixty-three\nyears old. In his seventeenth year (1825) he entered the University of\nEdinburgh, and two years later Christ\u2019s College, Cambridge. When\nscarcely twenty-two years old, in 1831, he was invited to take part in a\nscientific expedition which was sent out by England, in order to survey\naccurately the southernmost point of South America, and to examine\nseveral parts of the South Seas. This expedition, like many other\nvoyages of inquiry fitted out in a praiseworthy manner by England, had\nscientific objects, and at the same time was intended to solve practical\nproblems relating to navigation. The vessel, commanded by Captain\nFitzroy, appropriately bore the symbolic name of the _Beagle_. The\nvoyage of the _Beagle_, which lasted five years, was of the highest\nimportance to the full development of Darwin\u2019s genius; for in the very\nfirst year, when he set his foot on the soil of South America, the\noutline of the doctrine of descent dawned upon him. Darwin himself has\ndescribed this voyage in a work which is written in a very attractive\nstyle, and the perusal of which I strongly recommend to the reader. This\nbook of travel, which lies far above the usual average in interest, not\nonly shows in a very charming manner Darwin\u2019s amiable character, but we\ncan in many ways recognize the various steps by which he arrived at his\nconceptions. The result of the voyage was, first, a large scientific\nwork, the zoological and geological portion of which belong in a great\nmeasure to Darwin; and secondly, a celebrated work by him alone on Coral\nReefs, which in itself would have sufficed to secure to him a lasting\nreputation. It is well known that the islands in the South Seas consist\nfor the most part of coral reefs, and are surrounded by them. Formerly\nno satisfactory explanation could be given of their different and\nremarkable forms, and of their relation to those islands which are not\nformed of corals. It was reserved for Darwin to solve this difficult\nproblem, for together with the constructive action of the coral\nzoophytes, he assumed geological risings and depressions of the bottom\nof the sea to account for the origin of the different forms of reefs.\nDarwin\u2019s Theory of the Origin of Coral Reefs, like his later one as to\nthe Origin of Organic Species, is a theory which fully explains the\nphenomenon, and for this purpose assumes only the simplest natural\ncauses, without hypothetically supporting it with any unknown processes.\nAmong the remaining works of Darwin, I must not pass over his excellent\nmonograph on Cirrhipedia, a curious class of marine animals, which in\ntheir outward appearance resemble mussels, and were actually considered\nby Cuvier as Molluscs possessing two shells, while in truth they\nbelonged to the Crustacea (crabs).\n\nThe extraordinary hardships to which Darwin had been exposed during his\nvoyage in the _Beagle_ had injured his health to such a degree, that\nafter his return home he was obliged to withdraw from the restless\nturmoil of London life, and since then has lived in quiet retirement on\nhis estate at Down, near Bromley, in Kent. This seclusion from the\nrestless activity of the great city certainly exercised a beneficial\ninfluence upon Darwin, and it is probable that we owe to it, at least\npartially, the formation of the Theory of Selection. Undisturbed by the\nvarious engagements which in London would have wasted his strength, he\nwas enabled to concentrate his attention upon the great problem to\nwhich his mind had been turned during his voyage in the _Beagle_. In\norder to show what kind of observations during the voyage principally\ngave rise to the fundamental idea of the Theory of Selection, and in\nwhat manner he afterwards worked it out, I shall insert here a passage\nfrom a letter which he addressed to me on the 8th of October, 1864.\n\n\n_Letter from Charles Darwin to Haeckel, 8th October, 1864._\n\n\u201cIn South America three classes of facts were brought strongly before my\nmind. _Firstly_, the manner in which closely allied species replace\nspecies in going southward. _Secondly_, the close affinity of the\nspecies inhabiting the islands near South America to those proper to the\ncontinent. This struck me profoundly, especially the difference of the\nspecies in the adjoining islets in the Galopagos Archipelago. _Thirdly_,\nthe relation of the living Edentata and Rodentia to the extinct species.\nI shall never forget my astonishment when I dug out a gigantic piece of\narmour like that of the living armadillo.\n\n\u201cReflecting on these facts, and collecting analogous ones, it seemed to\nme probable that allied species were descended from a common parent. But\nfor some years I could not conceive how each form became so excellently\nadapted to its habits of life. I then began systematically to study\ndomestic productions, and after a time saw clearly that man\u2019s selective\npower was the most important agent. I was prepared, from having studied\nthe habits of animals, to appreciate the struggle for existence, and my\nwork in geology gave me some idea of the lapse of past time. Therefore,\nwhen I happened to read \u201cMalthus on Population,\u201d the idea of natural\nselection flashed on me. Of all the minor points, the last which I\nappreciated was the importance and cause of the principle of\ndivergence.\u201d\n\n\nDuring the leisure and retirement in which Darwin lived after his\nreturn, he occupied himself, as we see from this letter, first and\nspecially with the study of organisms in their cultivated state; that\nis, domestic animals and garden plants. This was undoubtedly the most\nlikely way to arrive at the Theory of Selection. In this, as in all his\nlabours, Darwin proceeded with extreme care and accuracy. With wonderful\ncaution and self-denial, he published nothing on this subject during a\nperiod of twenty-one years, from 1837 to 1858, not even a preliminary\nsketch of his theory, which he had written as early as 1844. He was\nalways anxious to collect still more certain experimental proofs, in\norder to be able to establish his theory in a complete form, and on the\nbroadest possible foundation of experience. While he was thus aiming at\nthe greatest possible perfection, which might perhaps have led him never\nto publish his theory at all, he was fortunately disturbed by a\ncountryman of his, who, independently of Darwin, had discovered the\nTheory of Selection, and in 1858 sent its outlines to Darwin himself,\nwith the request to hand them to Lyell for publication in some English\njournal. This was Alfred Wallace, one of the boldest and most\ndistinguished scientific travellers of modern times. For many years\nWallace had wandered alone in the wilds of the Sunda Islands, in the\ndense primitive forests of the Indian Archipelago; and during this close\nand comprehensive study of one of the richest and most interesting parts\nof the earth, with its great variety of animals and plants, he had\narrived at exactly the same general views regarding the origin of\norganic species as Darwin. Lyell and Hooker, both of whom had long known\nDarwin\u2019s work, now induced him to publish a short extract from his\nmanuscripts simultaneously with the manuscript sent him by Wallace. They\nappeared in the _Journal of the Linnean Society_, August, 1858.\n\nDarwin\u2019s great work \u201cOn the Origin of Species,\u201d in which the Theory of\nSelection is carried out in detail, appeared in November, 1859. Darwin\nhimself, however, characterizes this book (of which a fifth edition\nappeared in 1869, and the German translation by Bronn as early as\n1860)(1) as only a preliminary extract from a larger and more detailed\nwork, which is to contain a mass of facts in favour of his theory, and\ncomprehensive and experimental proofs. The first part of the larger work\npromised by Darwin appeared in 1868, under the title, \u201cThe Variations of\nAnimals and Plants in the State of Domestication,\u201d and has been\ntranslated into German by Victor Carus.(14) It contains a rich abundance\nof the most valuable evidence as to the extraordinary changes of organic\nforms which man can produce by cultivation and artificial selection.\nHowever much we are indebted to Darwin for this abundance of convincing\nfacts, still we do not by any means share the opinion of those\nnaturalists who hold that the Theory of Selection requires for its\nactual proof these further details. It is our opinion that Darwin\u2019s\nfirst work, which appeared in 1859, already contains sufficient proof.\nThe unassailable strength of his theory does not lie in the immense\namount of individual facts that may be adduced as proofs, but in the\nharmonious connection of all the great and general phenomena of organic\nnature, which agree in bearing testimony to the truth of the Theory of\nSelection.\n\nDarwin, at first, intentionally did not notice the important conclusion\nfrom his Theory of Descent, namely, the descent of the human race from\nother mammals. It was not till this highly important conclusion had been\ndefinitely established by other naturalists as the necessary sequel of\nthe doctrine of descent, that Darwin himself expressly endorsed it, and\nthereby completed his system. This was done in the highly interesting\nwork, \u201cThe Descent of Man, and Sexual Selection,\u201d which appeared as late\nas 1871, and has likewise been translated into German by Victor\nCarus.(48)\n\nThe careful study which Darwin devoted to _domestic animals and\ncultivated plants_ was of the greatest importance in establishing the\nTheory of Selection. The infinitely varied changes of form which man has\nproduced in these domesticated organisms by artificial selection are of\nthe very highest importance for a right understanding of animal and\nvegetable forms; and yet this study has, down to the most recent times,\nbeen most grossly neglected by zoologists and botanists. Without\nentering upon the discussion of the significance to be attached to the\nidea of species itself, they have filled not only bulky volumes, but\nwhole libraries, with descriptions of individual species, and with most\nchildish controversies as to whether these species are good, or\ntolerably good, and bad, or tolerably bad. If naturalists instead of\nspending their time on these useless fancies had duly studied cultivated\norganisms, and had examined the transmutation of the living forms,\ninstead of the individual dead ones, they would not have been led\ncaptive so long by the fetters of Cuvier\u2019s dogma. But as cultivated\norganisms are so extremely inconvenient to the dogmatic conception of\nthe permanence of species, naturalists to a great extent intentionally\ndid not concern themselves about them, and even celebrated naturalists\nhave often expressed the opinion that cultivated organisms, domesticated\nanimals and garden plants, are artificial productions of man, and that\ntheir formation and transformation could not decide anything about the\nnature of species and about the origin of the forms of species that live\nin a natural state.\n\nThis perverse view went so far that, for example, Andreas Wagner, a\nzoologist of Munich, quite seriously made the following ridiculous\nassertion:\u2014\u201cAnimals and plants in their wild state have been called\ninto being by the Creator as distinctly different and unchangeable\nspecies; but in the case of domestic animals and cultivated plants this\nwas not necessary, because he formed them from the beginning for the use\nof man. The Creator formed man out of a clod of earth, breathed the\nliving breath into his nostrils, and then created for him the different\nuseful domestic animals and garden plants, among which he thought well\nto save himself the trouble of distinguishing species.\u201d Unfortunately,\nAndreas Wagner does not tell us whether the _Tree of Knowledge_ in\nParadise was a \u201cgood\u201d wild species, or, as a cultivated plant, \u201cno\nspecies\u201d at all. As the Tree of Knowledge was placed by the Creator in\nthe centre of Paradise, we might be inclined to believe that it was a\nhighly favoured cultivated plant, and therefore no species at all. But\nsince, on the other hand, the fruit of the Tree of Knowledge was\nforbidden to man, and since many men, as Wagner himself clearly shows,\nhave never eaten of the fruit, it was evidently not created for the use\nof man, and therefore in all probability was a _real species!_ What a\npity Wagner has not given us any information about this important and\ndifficult problem!\n\nNow, however ridiculous this view may appear to us, it is only the\nlogical sequence of a false view (which is widely spread) of the special\nnature of cultivated organisms, and one may occasionally hear similar\nobjections from naturalists of great reputation. I must most decidedly,\nand at once, condemn this utterly false conception. It is the same\nperverseness which is committed by physicians who maintain that diseases\nare artificial productions, and not natural phenomena. It has been a\nwork of hard labour to combat this prejudice, and it is only in recent\ntimes that men have generally adopted the view that diseases are nothing\nbut natural changes of the organisms, or really natural phenomena of\nlife, which are produced by changed and abnormal conditions of\nexistence. Disease, therefore, is not a life beyond Nature\u2019s realm (vita\npr\u00e6ter naturam), as the early physicians used to say, but a natural life\nunder conditions which produce illness and threaten the body with\ndanger. Just in the same manner, cultivated organic forms are not\nartificial works of man, but natural productions which have arisen under\nthe influence of peculiar conditions of life. Man by his culture can\nnever directly produce a new organic form, but he can breed organisms\nunder new conditions of life, which are such as to influence and\ntransform them. All domestic animals and all garden plants are\noriginally descended from wild species, which have been transformed by\nthe peculiar conditions of culture.\n\nA thorough comparison of cultivated forms (races and varieties) with\norganisms not altered by cultivation (species and varieties), is of the\nutmost importance to the theory of selection. What is most surprising in\nsuch a comparison is the remarkably short time in which man can produce\na new form, and the high degree in which this form, produced by man, can\ndeviate from the original form. While wild animals and plants, one year\nafter another, appear to the zoologist and botanist approximately in the\nsame form, so as to have given rise to the false doctrine of the\nconstancy of species, domestic animals and garden plants, on the other\nhand, display the greatest changes within a few years. The perfection\nwhich gardeners and farmers have attained in the art of selection now\nenables them, in the space of a few years, arbitrarily to create\nentirely new animal and vegetable forms. For this purpose it is only\nnecessary to keep and propagate the organism under the influence of\nspecial conditions\u2014which are capable of producing new formations\u2014and\neven at the end of a few generations new species may be obtained, which\ndiffer from the original form in a much higher degree than so-called\ngood species in a wild state differ from one another. This fact is\nextremely important, and we cannot lay sufficient stress upon it. The\nassertion is not true that cultivated forms descended from one and the\nsame primary form do not differ from one another as much as wild animal\nand vegetable species differ among themselves. If we only make\ncomparisons, without prejudice, we can very easily perceive that a\nnumber of races or varieties which have been derived from a single\ncultivated form, within a short series of years, differ from one another\nin a higher degree than so-called good species (bon\u00e6 species), or even\ndifferent genera of one family, in the wild state.\n\nIn order to establish this extremely important fact as firmly as\npossible by experiments, Darwin decided to make a special study of the\nwhole extent of variation in form in a single group of domesticated\nanimals, and for this purpose he chose the _domestic pigeons_, which are\nin many respects especially suited for such a study. For a long time he\nkept on his estate all possible races and varieties of pigeons which he\nwas able to procure, and he was helped in this by rich contributions\nfrom all parts of the world. He also joined two London pigeon clubs, the\nmembers of which passionately, and with truly artistic skill, carry on\nthe breeding of the different forms of pigeons. Lastly, he formed\nconnections with some of the most celebrated pigeon-fanciers; so that he\ncould command the richest experimental material.\n\nThe art of, and fancy for, pigeon breeding is very ancient. Even more\nthan 3,000 years before Christ, it was carried on by the Egyptians. The\nRomans, under the emperors, laid out enormous sums upon the breeding of\npigeons, and kept accurate pedigrees of their descent, just as the Arabs\nkeep genealogical pedigrees of their horses, and the Mecklenburg\naristocracy of their own ancestors. In Asia, too, among the wealthy\nprinces, pigeon breeding was a very ancient fancy; in 1600, the court of\nAkber Khan possessed more than 20,000 pigeons. Thus in the course of\nseveral centuries, and in consequence of the various methods of breeding\npractised in the different parts of the world, there has arisen out of\none single originally tamed form, an immense number of different races\nand varieties, which in their most divergent forms are extremely\ndifferent from one another, and are often curiously characterized.\n\nOne of the most striking races of pigeons is the well-known fan-tailed\npigeon, which spreads its tail like the peacock, and carries a number of\n(from thirty to forty) feathers placed in the form of radii, while other\npigeons possess much fewer tail feathers\u2014generally twelve. We may here\nmention that the number of feathers on the tails of birds is considered\nby naturalists of great value as a systematic distinction, so that whole\norders can thereby be distinguished. For example, singing birds, almost\nwithout exception, possess twelve tail feathers; chirping birds\n(Strisores) ten, etc. Several races of pigeons, moreover, are\ncharacterized by a tuft of neck feathers, which form a kind of periwig;\nothers by grotesque transformation of their beaks and feet, by peculiar\nand often very remarkable decorations, as, for example, skinny lappets,\nwhich develop on the head; by a large crop, which is formed by the\ngullet being strongly inclined forward, etc. Remarkable, also, are the\nstrange habits which many pigeons have acquired; for example, the turtle\npigeons and the trumpeters with their musical accomplishments, the\ncarriers with their topographical instinct. The tumblers have the\nstrange habit of ascending into the air in great numbers, then turning\nover and falling down through the air as if dead. The ways and habits of\nthese endless races of pigeons\u2014the form, size, and colour of the\nindividual parts of their bodies, and their proportions, differ in a\nmost astonishing degree from one another; in a much higher degree than\nis the case with the so-called good species, or even with the perfectly\ndistinct genera, of wild pigeons. And what is of the greatest\nimportance, is the fact that these differences are not confined to the\nexternal form, but extend even to the most important internal parts;\nthere even occur great modifications of the skeleton and of the\nmuscular tissues. For example, we find great differences in the number\nof vertebr\u00e6 and ribs, in the size and shape of the gaps in the\nbreast-bones, in the size and shape of the merry-thought, in the lower\njaw, in the facial bones, etc. In short, the bony skeleton, which\nmorphologists consider a very permanent part of the body, and which\nnever varies to such an extent as the external parts\u2014shows such great\nchanges, that many races of pigeons might be described as special\ngenera, and this would doubtless be done if all these different forms\nhad been found in a wild and natural state.\n\nHow far the differences of the races of pigeons have been carried is\nbest shown by the fact that all pigeon breeders are unanimously of\nopinion that each peculiar or specially marked race of pigeons must be\nderived from a corresponding wild original species. It is true every one\nassumes a different number of original species. Yet Darwin has most\nconvincingly and acutely proved that all these pigeons, without\nexception, must be derived from a single wild primary species\u2014from the\nblue rock-pigeon (_Columba livia_). In like manner, it can be proved of\nmost of the domestic animals and cultivated plants, that all the\ndifferent races are descendants of a single original wild species which\nhas been brought by man into a cultivated condition.\n\nAn example similar to that of the domestic pigeons is furnished among\nmammals by our tame _rabbit_. All zoologists, without exception, have\nlong considered it proved that all its races and varieties are descended\nfrom the common wild rabbit, that is, from a single primary species. And\nyet the extreme forms of these races differ to such a degree from one\nanother, that every zoologist, if he met with them in a wild state,\nwould unhesitatingly designate them not only as an entirely distinct\n\u201cgood species,\u201d but even as species of entirely different genera of the\nLeporid family. Not only does the colour, length of hair, and other\nqualities of the fur of the different tame races of rabbits vary\nexceedingly, and form extremely broad contrasts, but, what is still more\nimportant, the typical form of the skeleton and its individual parts do\nso also, especially the form of the skull and the jaw (which is of such\nimportance in systematic arrangement); further, the relative proportion\nof the length of the ears, legs, etc. In all these respects the races of\ntame rabbits avowedly differ from one another far more than all the\ndifferent forms of wild rabbits and hares which are scattered over all\nthe earth, and are the recognized \u201cgood species\u201d of the genus _Lepus_.\nAnd yet, in the face of these clear facts, the opponents of the theory\nof development maintain that the wild species are not descended from a\ncommon prototype, although they at once admit it in the case of the tame\nraces. With opponents who so intentionally close their eyes against the\nclear light of truth, no further dispute can be carried on.\n\nWhile in this manner it appears certain that the domestic races of\npigeons, of tame rabbits, of horses, etc., notwithstanding the\nremarkable difference of their varieties, are descended in each case\nfrom but one wild, so-called \u201cspecies\u201d; yet, on the other hand, it is\ncertainly probable that the great variety of races of some of the\ndomestic animals, especially dogs, pigs, and oxen, must be ascribed to\nthe existence of several wild prototypes, which have become mixed. It\nis, however, to be observed that the number of these originally wild\nprimary species is always much smaller than that of the cultivated forms\nproceeding from their mingling and selection, and naturally they were\noriginally derived from a single primary ancestor, common to the whole\ngenus. In no case is each separate cultivated race descended from a\ndistinct wild species.\n\nIn opposition to this, almost all farmers and gardeners maintain, with\nthe greatest confidence, that each separate race bred by them must be\ndescended from a separate wild primary species, because they clearly\nperceive the differences of the races, and attach very high importance\nto the inheritance of their qualities; but they do not take into\nconsideration the fact that these qualities have arisen only by the slow\naccumulation of small and scarcely observable changes. In this respect\nit is extremely instructive to compare cultivated races with wild\nspecies.\n\nMany naturalists, and especially the opponents of the Theory of\nDevelopment, have taken the greatest trouble to discover some\nmorphological or physiological mark, some characteristic property,\nwhereby the artificially bred and cultivated races may be clearly and\nthoroughly distinguished from wild species which have arisen naturally.\nAll these attempts have completely failed, and have led only with\nincreasing certainty to the result, that such a distinction is\naltogether impossible. I have minutely discussed this fact, and\nillustrated it by examples in my criticism of the idea of species. (Gen.\nMorph. ii. 323-364.)\n\nI may here briefly touch on yet another side of this question, because\nnot only the opponents, but even a few of the most distinguished\nfollowers of Darwin\u2014for example, Huxley\u2014have regarded the phenomena of\n_bastard-breeding_, or _hybridism_, as one of the weakest points of\nDarwinism. Between cultivated races and wild species, they say, there\nexists this difference, that the former are capable of producing\nfruitful bastards, but that the latter are not. Two different cultivated\nraces, or wild _varieties of one species_, are said in all cases to\npossess the power of producing bastards which can fruitfully mix with\none another, or with one of their parent forms, and thus propagate\nthemselves; on the other hand, _two really different species_, two\ncultivated or wild _species_ of one genus, are said _never_ to be able\nto produce from one another bastards which can be fruitfully crossed\nwith one another, or with one of their parent species.\n\nAs regards the first of these assertions, it is simply refuted by the\nfact that there are organisms which do not mix at all with their own\nancestors, and therefore can produce no fruitful descendants. Thus, for\nexample, our cultivated guinea-pig does not bear with its wild Brazilian\nancestor; and again, the domestic cat of Paraguay, which is descended\nfrom our European domestic cat, no longer bears with the latter. Between\ndifferent races of our domestic dogs, for example, between the large\nNewfoundland dogs and the dwarfed lap-dogs, breeding is impossible, even\nfor simple mechanical reasons. A particularly interesting instance is\nafforded by the Porto-Santo rabbit (Lepus Huxleyi). In the year 1419, a\nfew rabbits, born on board ship of a tame Spanish rabbit, were put on\nthe island of Porto Santo, near Madeira. These little animals, there\nbeing no beasts of prey, in a short time increased so enormously that\nthey became a pest to the country, and even compelled a colony to remove\nfrom the island. They still inhabit the island in great numbers; but in\nthe course of four hundred and fifty years they have developed into a\nquite peculiar variety\u2014or if you will have it, into a \u201cgood\nspecies\u201d\u2014which is distinguished by a peculiar colour, a rat-like shape,\nsmall size, nocturnal life, and extraordinary wildness. The most\nimportant fact, however, is that this new species, which I call _Lepus\nHuxleyi_, no longer pairs with its European parent rabbit, and no longer\nproduces bastards with it.\n\nOn the other hand, we now know of numerous examples of fruitful genuine\nbastards; that is, of mixings that have proceeded from the crossing of\ntwo entirely different species, and yet propagate themselves with one\nanother as well as with one of their parent species. A number of such\nbastard species (species Hybrid\u00e6) have long been known to botanists; for\nexample, among the genera of the thistle (Cirsium), the laburnum\n(Cytisus), the bramble (Rubus), etc. Among animals also they are by no\nmeans rare, perhaps even very frequent. We know of fruitful bastards\nwhich have arisen from the crossing of two different species of a genus,\nas among several genera of butterflies (Zyg\u00e6na, Saturnia), the family of\ncarps, finches, poultry, dogs, cats, etc. One of the most interesting is\nthe hare-rabbit (Lepus Darwinii), the bastard of our indigenous hare and\nrabbit, many generations of which have been bred in France, since 1850,\nfor gastronomic purposes. I myself possess such hybrids, the products of\npure in-breeding, that is, both parents of which are themselves hybrids\nby a hare-father and a rabbit-mother. I possess them through the\nkindness of Professor Conrad, who has repeatedly made these experiments\nin breeding on his estate. The half-blood hybrid thus bred, which I name\nin honour of Darwin, appears to propagate itself through many\ngenerations by pure in-breeding, just as well as any genuine species.\nAlthough on the whole it is more like its mother (rabbit), still in the\nformation of the ears and of the hind-legs, it possesses distinct\nqualities of its father (hare). Its flesh has an excellent taste, rather\nresembling that of a hare, though the colour is more like that of a\nrabbit. But the hare (Lepus timidus) and the rabbit (Lepus cuniculus)\nare two species of the genus Lepus, so different that no systematic\nzoologist will recognize them as varieties of one species. Both species,\nmoreover, live in such different ways, and in their wild state entertain\nso great an aversion towards one another, that they do not pair so long\nas they are left free. If, however, the newly-born young ones of both\nspecies are brought up together, this aversion is not developed; they\npair with one another and produce the _Lepus Darwinii_.\n\nAnother remarkable instance of the crossing of different species (where\nthe two species belong even to different genera!) is furnished by the\nfruitful hybrids of sheep and goats which have for a long time been bred\nin Chili for industrial purposes. On what unessential circumstances in\nthe sexual mingling the fertility of the different species depend, is\nshown by the fact that he-goats and sheep in their mingling produce\nfruitful hybrids, while the ram and she-goat pair very rarely, and then\nwithout result. The phenomena of hybridism to which undue importance has\nbeen erroneously attributed are thus utterly unmeaning, so far as the\nidea of species is concerned. The breeding of hybrids does not enable\nus, any more than other phenomena, thoroughly to distinguish cultivated\nraces from wild species; and this circumstance is of the greatest\nimportance in the Theory of Selection.\n\n\n\n\nCHAPTER VII.\n\nTHE THEORY OF SELECTION (DARWINISM).\n\n\n   Darwinism (Theory of Selection) and Lamarckism (Theory of\n   Descent).\u2014The Process of Artificial Breeding.\u2014Selection\n   of the Different Individuals for After-breeding.\u2014The\n   Active Causes of Transmutation.\u2014Change connected with\n   Food, and Transmission by Inheritance connected with\n   Propagation.\u2014Mechanical Nature of these Two\n   Physiological Functions.\u2014The Process of Natural\n   Breeding: Selection in the Struggle for\n   Existence.\u2014Malthus\u2019 Theory of Population.\u2014The\n   Proportion between the Numbers of Potential and Actual\n   Individuals of every Species of Organisms.\u2014General\n   Struggle for Existence, or Competition to attain the\n   Necessaries of Life.\u2014Transforming Force of the Struggle\n   for Existence.\u2014Comparison of Natural and Artificial\n   Breeding.\u2014Selection in the Life of Man.\u2014Military and\n   Medical Selection.\n\n\nIt is, properly speaking, not quite correctly that the Theory of\nDevelopment, with which we are occupied in these pages, is usually\ncalled Darwinism. For, as we have seen from the historical sketch in the\nprevious chapters, the most important foundation of the Theory of\nDevelopment\u2014that is, the Doctrine of Filiation, or Descent\u2014had already\nbeen distinctly enunciated at the beginning of our century, and had been\ndefinitely introduced into science by Lamarck. The portion of the Theory\nof Development which maintains the common descent of all species of\nanimals and plants from the simplest common original forms might,\ntherefore, in honour of its eminent founder, and with full justice, be\ncalled _Lamarckism_, if the merit of having carried out such a principle\nis to be linked to the name of a single distinguished naturalist. On the\nother hand, the Theory of Selection, or breeding, might be justly called\n_Darwinism_, being that portion of the Theory of Development which shows\nus in what way and _why_ the different species of organisms have\ndeveloped from those simplest primary forms. (Gen. Morph. ii. 166.)\n\nIt is true we find the first trace of an idea of natural selection even\nforty years before the appearance of Darwin\u2019s work. For in the year 1818\nthere was published a paper \u201cOn a woman of the white race whose skin\npartly resembled that of a negro,\u201d which had been read before the Royal\nSociety as early as 1813. Its author, Dr. W. C. Wells, states that\nnegroes and mulattoes are distinguished from the white race by their\nimmunity from certain tropical diseases. On this occasion he remarks\nthat all animals have a tendency to change up to a certain degree, and\nthat farmers, by availing themselves of this tendency, and also by\nselection, improve their domestic animals; and then he adds, that what\nis done in this latter case \u201cby art, seems to be done with equal\nefficiency, though more slowly, by nature, in the formation of varieties\nof mankind fitted for the country which they inhabit. Of the accidental\nvarieties of man which would occur among the first few and scattered\ninhabitants of the middle regions of Africa, some one would be better\nfitted than the others to bear the diseases of the country. This race\nwould consequently multiply, while the others would decrease; not only\nfrom their inability to sustain the attacks of disease, but from their\nincapacity of contending with their more vigorous neighbours. The\ncolour of this vigorous race I take for granted, from what has been\nalready said, would be dark. But the same disposition to form varieties\nstill existing, a darker and a darker race would in the course of time\noccur; and as the darkest would be the best fitted for the climate, this\nwould at length become the most prevalent, if not the only race, in the\nparticular country in which it had originated.\u201d He then extends these\nsame views to the white inhabitants of colder climates. Although Wells\nclearly expresses and recognizes the principle of natural selection, yet\nit is applied by him only to the very limited problem of the origin of\nhuman races, and not at all to that of the origin of animal and\nvegetable species. Darwin\u2019s great merit in having independently\ndeveloped the Theory of Selection, and having brought it to complete and\nwell merited recognition, is as little affected by the earlier and long\nforgotten remark of Wells, as by some other fragmentary observations\nabout natural selection made by Patrick Mathew, and hidden in his book\non \u201cTimber for Shipbuilding, and the Cultivation of Trees,\u201d which\nappeared in 1831. The celebrated traveller, Alfred Wallace, who\ndeveloped the Theory of Selection independently of Darwin, and had\npublished it in 1858, simultaneously with Darwin\u2019s first contribution,\nlikewise stands far behind his greater and elder countryman in regard to\nprofound conception, as well as to extended application of the theory.\nIn fact Darwin, by his extremely comprehensive and ingenious development\nof the whole doctrine, has acquired a fair claim to see the theory\nconnected with his own name.\n\nThis Theory of Selection, Darwinism in its proper sense, to the\nconsideration of which we now turn our attention, rests essentially (as\nhas already been intimated in the last chapter) upon the comparison of\nthose means which man employs in the breeding of domestic animals and\nthe cultivation of garden plants, with those processes which in free\nnature, outside the cultivated state, lead to the coming into existence\nof new species and new genera. We must therefore, in order to understand\nthe latter processes, first turn to the artificial breeding by man, as\nwas, in fact, done by Darwin himself. We must inquire into the results\nto which man attains by his artificial breeding, and what means are\napplied in order to obtain those results; and we must then ask\nourselves, \u201cAre there in nature similar forces and causes acting\nsimilarly to those resorted to by man?\u201d\n\nFirst, in regard to artificial breeding, we start from the fact last\ndiscussed above, viz., that its products in some cases differ from one\nanother much more than the productions of natural breeding. It is a fact\nthat races or varieties often differ from one another in a much greater\ndegree and in much more important qualities than many so-called species,\nor \u201cgood species,\u201d\u2014nay, sometimes even more than so-called \u201cgood\ngenera\u201d in their natural state. Compare, for example, the different\nkinds of apples which the art of horticulture has derived from one and\nthe same original apple-form, or compare the different races of horses\nwhich their breeders have derived from one and the same original form of\nhorse, and it will be easily observed that the differences of the most\ndifferent forms are extremely important, and much more important than\nthe so-called \u201cspecific differences,\u201d which are referred to by\nzoologists and botanists when comparing wild forms for the purpose of\ndistinguishing several so-called \u201cgood species.\u201d\n\nNow, by what means does man produce this extraordinary difference or\ndivergence of several forms which are proved to be descended from the\nsame primary form? In order to answer this question, let us follow a\ngardener who desires to produce a new form of a plant, which is\ndistinguished by the beautiful colour of its flowers. He will first of\nall make a selection from a great number of plants which are seedlings\nfrom one and the same parent. He will pick out those plants which\nexhibit most distinctly the colour of flower he desires. The colour of\nflowers is a very changeable thing. Plants, for example, which as a rule\nhave a white flower, frequently show deviations into the blue or red.\nNow, supposing the gardener wishes to obtain the red colour in a plant\nusually producing white flowers, he will very carefully, from among the\nmany different individuals which are the descendants of one and the same\nseed-plant, select those which most distinctly show a reddish tint, and\nsow them exclusively, in order to produce new individuals of the same\nkind. He would cast aside and no longer cultivate the other seedlings\nwhich show a white or less distinct red colour. He will propagate\nexclusively the individual plants whose blossoms show the red most\nmarkedly, and he will sow the seeds produced by these selected plants.\nFrom the seedlings of this second generation, he will again carefully\nselect those in which the red, which is now visible in the majority of\nthem, is most distinctly displayed. If such a selection is carried on\nduring a series of six or ten generations, and if the flower which shows\nthe deepest red is most carefully selected, the gardener in the sixth or\ntenth generation will obtain the desired plants with flowers of a pure\nred.\n\nThe farmer wishing to breed a special race of animals, for example, a\nkind of sheep distinguished by particularly fine wool, proceeds in the\nsame manner. The only process applied in the improvement of wool\nconsists in this, that the farmer with the greatest care and\nperseverance selects from a whole flock of sheep those individuals which\nhave the finest wool. These only are used in breeding, and among the\ndescendants of these selected sheep, those again are chosen which have\nthe finest wool, etc. If this careful selection is carried on through a\nseries of generations, the selected breeding-sheep are in the end\ndistinguished by a wool which differs very strikingly from the wool of\nthe original parent, and this is exactly the advantage which the breeder\ndesired.\n\nThe differences of the individuals that come into consideration in this\nartificial selection are very slight. An ordinary unpractised man is\nunable to discover the exceedingly minute differences of individuals\nwhich a practised breeder perceives at the first glance. The business of\na breeder is not easy; it requires an exceedingly sharp eye, great\npatience, and an extremely careful manner of treating the organisms to\nbe bred. In each individual generation, the differences of individuals\nare perhaps not seen at all by the uninitiated; but by the accumulation\nof these minute differences during a series of generations, the\ndeviation from the original form becomes in the end very great. It\nbecomes so great that the artificially produced form may in the end\ndiffer far more from the original form than do two so-called \u201cgood\nspecies\u201d in their natural state. The art of breeding has now made such\nprogress, that man can often at discretion produce certain peculiarities\nin cultivated species of animals and plants. To practised gardeners and\nfarmers, you may give distinct commissions, and say, for example, I wish\nto have this species of plant with this or that colour, and with this or\nthat shape. Where breeding has reached the perfection which it has\nattained in England, gardeners and farmers are frequently able to\nfurnish to order the desired result within a definite period, that is,\nat the end of a number of generations. Sir John Sebright, one of the\nmost experienced English pigeon-breeders, could assert that in three\nyears he would produce any form of feather, but that he required six\nyears to obtain any desired form of the head and beak. In the process of\nbreeding the merino-sheep of Saxony, the animals are three times placed\non a table beside one another, and most carefully compared and studied.\nEach time only the best sheep with the finest wool are selected, so that\nin the end, out of a great multitude, there remain only some few\nanimals, but their wool is exquisitely fine, and only these last are\nused in breeding. We see, therefore, that the causes through which, in\nartificial breeding, great effects are produced, are unusually simple,\nand these great effects are obtained simply by accumulating the\ndifferences which in themselves are very insignificant, and become\nsurprisingly increased by a continually repeated selection.\n\nBefore we pass on to a comparison of this artificial with natural\nbreeding, let us see what natural qualities of the organisms are made\nuse of by the artificial breeder or cultivator. We can trace all the\ndifferent qualities which here come into play to physiological\nfundamental qualities of the organism, which are common to all animals\nand plants, and are most closely connected with the functions of\n_propagation_ and _nutrition_. These two fundamental qualities are\n_transmissivity_, or the capability of _transmitting by inheritance_,\nand _mutability_, or the capability of _adaptation_. The breeder starts\nfrom the fact that all the individuals of one and the same species are\ndifferent, though in a very slight degree, a fact which is as true of\norganisms in a wild as in a cultivated state. If you look about you in a\nforest consisting of only a single species of tree, for example of\nbeech, you will certainly not find in the whole forest two trees of this\nkind which are absolutely identical or perfectly equal in the form of\ntheir branches, the number of their branches and leaves, blossoms and\nfruits. Special differences occur everywhere, just as in the case of\nmen. There are no two men who are absolutely identical, perfectly equal\nin size, in the formation of their faces, the number of their hairs,\ntheir temperament, character, etc. The very same is true of individuals\nof all the different species of animals and plants. It is true that in\nmost organisms the differences are very trifling to the eye of the\nuninitiated. Everything here essentially depends on the exercise of the\nfaculty of discovering these often very minute differences of form. The\nshepherd, for example, knows every individual of his flock, solely by\naccurately observing their features, while the uninitiated are incapable\nof distinguishing at all the different individuals of one and the same\nflock. This fact of the individual difference is the extremely important\nfoundation on which the whole of man\u2019s power of breeding rests. If\nindividual differences did not exist everywhere, man would not be able\nto produce a number of different varieties or races from one and the\nsame original stock. We must, at the outset, hold fast the principle\nthat the phenomenon is quite universal; we must necessarily assume it\neven where, with the imperfect capabilities of our senses, we are unable\nto discover differences. Among the higher plants (the phanerogams, or\nflower-plants), where the individual stocks show such numerous\ndifferences in the number of branches or leaves, and in the formation of\nthe stem and branches, we can almost always easily perceive these\ndifferences. But this is not the case in the lower plants, such as\nmosses, alg\u00e6, fungi, and in most animals, especially the lower ones. The\ndistinction of all the individuals of one species is here, for the most\npart, extremely difficult or altogether impossible. But there is no\nreason for ascribing individual differences only to those organisms in\nwhich we can perceive them at once. We may, on the contrary, with full\ncertainty assume such individuality as a universal quality of all\norganisms, and we can do this all the more surely since we are able to\ntrace the mutability of individuals to the mechanical conditions of\nnutrition. We can show that by influencing nutrition we are able to\nproduce striking individual differences where they would not exist if\nthe conditions of nutrition had not been altered. The many complicated\nconditions of nutrition are never absolutely identical in two\nindividuals of a species.\n\nNow, just as we see that the mutability or capability of adaptation has\na causal connection with the general relations of nutrition in animals\nand plants, so too we find the second fundamental phenomenon of life,\nwith which we are here concerned, namely, the capability of\n_transmitting by inheritance_, to have a direct connection with the\nphenomenon of _propagation_. The second thing that a farmer or gardener\ndoes in artificial breeding, after he has selected, and has consequently\navailed himself of the mutability, is to endeavour to hold fast and\ndevelop the modified forms by Inheritance. He starts from the universal\nfact that children resemble their parents, that \u201cthe apple does not fall\nfar from the tree.\u201d This phenomenon of Inheritance has hitherto been\nscientifically examined only to a very small extent, which may partly\narise from the fact that the phenomenon is of such everyday occurrence.\nEvery one considers it quite natural that every species should produce\nits like; that a horse should not suddenly produce a goose, or a goose a\nfrog. We are accustomed to look upon these everyday occurrences of\nInheritance as self-evident. But this phenomenon is not so simply\nself-evident as it appears at first sight, and in the examination of\nInheritance the fact is very frequently overlooked that the different\ndescendants, derived from one and the same parents, are in reality\n_never_ quite identical, and also never absolutely like the parents, but\nare always slightly different. We cannot formulate the principle of\nInheritance, as \u201cLike produces like,\u201d but we must limit the expression\nto \u201cSimilar things produce similar things.\u201d The gardener, as well as the\nfarmer, avails himself of the fact of Inheritance in its widest form,\nand indeed with special regard to the fact that not only those qualities\nof organisms are transmitted by inheritance which they have inherited\nfrom _their_ parents but those also which they themselves have\n_acquired_. This is an important point upon which very much depends. An\norganism can transmit to its descendants not only those qualities of\nform, colour, and size which it has inherited from its parents, but it\ncan also transmit changes of these qualities, which it has acquired\nduring its own life through the influence of outward circumstances, such\nas climate, nourishment, training, etc.\n\nThese are the two fundamental qualities of animals and plants of which\nthe breeder must avail himself in order to produce new forms. The\ntheoretical principle of breeding is, indeed, extremely simple, but in\ndetail the practical application of this simple principle is difficult\nand immensely complicated. A thoughtful breeder, acting according to a\ndefinite plan, must understand the art of correctly estimating, in every\ncase, the general interaction between the two fundamental qualities of\nheirship and mutability.\n\nNow, if we examine the real nature of those two important properties of\nlife, we find that we can trace them, like all physiological functions,\nto physical and chemical causes, to the properties and the phenomena of\nmotion of those substances of which the bodies of animals and plants\nconsist. As we shall hereafter have to show in the more accurate\nconsideration of these two functions, the transmission by _Inheritance_,\nif we express ourselves quite generally, is essentially dependent upon\nthe material continuity and partial identity of the matter in the\nproducing and produced organism, the parents and the child. In every act\nof breeding a certain quantity of protoplasm or albuminous matter is\ntransferred from the parents to the child, and along with it there is\ntransferred the individually _peculiar molecular motion_. These\nmolecular phenomena of motion in the protoplasm, which call forth the\nphenomena of life, and are their active and true cause, differ more or\nless in all living individuals; they are of infinite variety.\n\n_Adaptation_, or transmutation is, on the other hand, essentially the\nconsequence of material influences, which the substance of the organism\nexperiences from the material surrounding it,\u2014in the widest sense of\nthe word from the _conditions_ of life. The external influences of the\nlatter are communicated to the individual parts of the body by the\nmolecular processes of nutrition. In every act of Adaptation the\nindividual molecular motion of the protoplasm, peculiar to each part,\ndisturbs and modifies the whole individual, or part of it, by\nmechanical, physical, or chemical influences. The innate, inherited\nvital actions of the protoplasm\u2014that is, the molecular phenomena of\nmotion of the smallest albuminous particles\u2014are therefore more or less\nmodified by it. The phenomenon of Adaptation, or transmutation, depends\ntherefore upon the material influence which the organism experiences\nfrom its surroundings, or its conditions of existence; while the\ntransmission by Inheritance is due to the partial identity of the\nproducing and produced organism. These are the real, simple, mechanical\nfoundations of the artificial process of breeding.\n\nNow Darwin asked himself, Does there exist a similar process of\nselection in nature, and are there forces in nature which take the place\nof man\u2019s activity in artificial selection? Is there a natural tendency\namong wild animals and plants which acts selectingly, in a similar\nmanner to the artificial selection practised by the designing will of\nman? All here depended upon the discovery of such a relation, and Darwin\nsucceeded in this so satisfactorily, that we consider his theory of\nselection completely sufficient to explain, mechanically, the origin of\nthe wild species of animals and plants. That relation which in free\nnature influences the forms of animals and plants, by selecting and\ntransforming them, is called by Darwin the \u201c_Struggle for Existence_.\u201d\n\nThe \u201cStruggle for Existence\u201d has rapidly become a watchword of the day.\nYet this designation is, perhaps, in many respects not very happily\nchosen, and the phenomena might probably have been more accurately\ndescribed as \u201c_Competition for the Means of Subsistence_.\u201d For under the\nname of \u201cStruggle for Life,\u201d many relations are comprehended which\nproperly and strictly speaking do not belong to it. As we have seen from\nthe letter inserted in the last chapter, Darwin arrived at the idea of\nthe \u201cStruggle for Existence\u201d from the study of Malthus\u2019 book \u201cOn the\nConditions and the Consequences of the Increase of Population.\u201d It was\nproved in that important work, that the number of human beings, on the\naverage, increases in a geometrical progression, while the amount of\narticles of food increase only in an arithmetical progression. This\ndisproportion gives rise to a number of inconveniences in the human\ncommunity, which cause among men a continual competition to obtain the\nnecessary means of life, which do not suffice for all.\n\nDarwin\u2019s theory of the struggle for life is, to a certain extent, a\ngeneral application of Malthus\u2019 theory of population to the whole of\norganic nature. It starts from the consideration that the number of\n_possible_ organic individuals which might arise from the germs\nproduced, is far greater than the number of _actual_ individuals which,\nin fact, do simultaneously live on the earth\u2019s surface. The number of\npossible or _potential individuals_ is given us by the number of the\neggs and organic germs produced by organisms. The number of these germs,\nfrom each of which, under favourable circumstances, an individual might\narise, is very much larger than the number of real or actual\n_individuals_\u2014that is, of those that really arise from these germs,\ncome into life, and propagate themselves. By far the greater number of\ngerms perish in the earliest stage of life, and it is only some favoured\norganisms which manage to develop, and actually survive the first period\nof early youth, and finally succeed in propagating themselves. This\nimportant fact is easily proved by a comparison of the number of eggs in\na given species with the number of individuals which exist of this\nspecies. These numerical relations show the most striking contrast.\nThere are, for example, species of fowls which lay great numbers of\neggs, and yet are among the rarest of birds; and the bird which is said\nto be the commonest (the most widely spread) of all, the stormy petrel\n(_Procellaria glacialis_), lays only a single egg. The relation is the\nsame in other animals. There are many very rare invertebrate animals,\nwhich lay immense quantities of eggs; and others again which produce\nonly very few eggs, and yet are among the commonest of animals. Take,\nfor example, the proportion which is observed among the human\ntape-worms. Each tape-worm produces within a short period millions of\neggs, while man, in whom these tape-worms are lodged, forms a far\nsmaller number of eggs, and yet fortunately there are fewer tape-worms\nthan human beings. In like manner, among plants there are many splendid\norchids, which produce thousands of seeds and yet are very rare, and\nsome kinds of asters (Composit\u00e6), which have but few seeds, are\nexceedingly common.\n\nThis important fact might be illustrated by an immense number of\nexamples. It is evidently, therefore, not the number of actually\nexisting germs which indicates the number of individuals which\nafterwards come into life and maintain themselves in life; but rather\nthe case is this, that the number of adult individuals is limited by\nother circumstances, especially by the relations in which the organism\nstands to its organic and inorganic surroundings. Every organism, from\nthe commencement of its existence, struggles with a number of hostile\ninfluences: it struggles against animals which feed on it, and to which\nit is the natural food, against animals of prey and parasites; it\nstruggles against inorganic influences of the most varied kinds, against\ntemperature, weather, and other circumstances; but it also struggles\n(and this is much the most important!), above all, against organisms\nmost like and akin to itself. Every individual, of every animal and\nvegetable species, is engaged in the fiercest competition with every\nother individual of the same species which lives in the same place with\nit. In the economy of nature the means of subsistence are nowhere\nscattered in abundance, but are very limited, and far from sufficient\nfor the number of organisms which might develop from the germs produced.\nTherefore the young individuals of most species of animals and\nvegetables must have hard work in obtaining the means of subsistence;\nthis necessarily causes a competition among them in order to obtain the\nindispensable supplies of life.\n\nThis great competition for the necessaries of life goes on everywhere\nand at all times, among human beings and animals as well as among\nplants; in the case of the latter this circumstance, at first sight, is\nnot so clearly apparent. If we examine a field which is richly sown with\nwheat, we can see that of the numerous young plants (perhaps some\nthousands) which shoot up on a limited space, only a very small\nproportion preserve themselves in life. A competition takes place for\nthe space of ground which each plant requires for fixing its root, a\ncompetition for sunlight and moisture. And in the same manner we find\nthat, among all animal species, all the individuals of one and the same\nspecies compete with one another to obtain these indispensable means of\nlife, or the conditions of existence in the wide sense of the word. They\nare equally indispensable to all, but really fall to the lot of only a\nfew\u2014\u201cMany are called, but few are chosen.\u201d The fact of the great\ncompetition is quite universal. You need only to cast a glance at human\nsociety, where this competition exists everywhere, and in all the\ndifferent branches of human activity. Here, too, a struggle is brought\nabout by the free competition of the different labourers of one and the\nsame class. Here too, as everywhere, this competition benefits the\nthing, or the work, which is the object of competition. The greater and\nmore general the competition, the more quickly improvements and\ninventions are made in the branch of labour, and the higher is the grade\nof perfection of the labourers themselves.\n\nThe position of the different individuals in this struggle for life is\nevidently very unequal. Starting from the inequality of individuals,\nwhich is a recognized fact, we must in all cases necessarily suppose\nthat all the individuals of one and the same species do not have equally\nfavourable prospects. Even at the beginning they are differently placed\nin this competition by their different strengths and abilities,\nindependently of the fact that the conditions of existence are\ndifferent, and act differently at every point of the earth\u2019s surface. We\nevidently have an infinite combination of influences, which, together\nwith the original inequality of the individuals during the competition\nfor the conditions of existence, favour some individuals and prejudice\nothers. The favoured individuals will gain the victory over the others,\nand while the latter perish more or less early, without leaving any\ndescendants, the former alone will be able to survive and finally to\npropagate the species. As, therefore, it is clear that in the struggle\nfor life the favoured individuals succeed in propagating themselves, we\nshall (even as the result of this relation) perceive in the next\ngeneration differences from the preceding one. Some individuals of this\nsecond generation, though perhaps not all of them, will, by inheritance,\nreceive the individual advantage by which their parents gained the\nvictory over their rivals.\n\nBut now\u2014and this is a very important law of inheritance\u2014if such a\ntransmission of a favourable character is continued through a series of\ngenerations, it is not simply transmitted in the original manner, but it\nis constantly increased and strengthened, and in a last generation it\nattains a strength which distinguishes this generation very essentially\nfrom the original parent. Let us, for example, examine a number of\nplants of one and the same species which grow together in a very dry\nsoil. As the hairs on the leaves of plants are very useful for receiving\nmoisture from the air, and as the hairs on the leaves are very\nchangeable, the individuals possessing the thickest hair on their leaves\nwill have an advantage in this unfavourable locality where the plants\nhave directly to struggle with the want of water, and in addition to\nthis have to compete with one another for the possession of what little\nwater there may be. These alone hold out, while the others possessing\nless hairy leaves perish; the more hairy ones will be propagated, and\ntheir descendants will, on the average, be more distinguished by their\nthick and strong hairs than the individuals of the first generation. If\nthis process is continued for several generations in one and the same\nlocality, there will arise at last such an increase of this\ncharacteristic, such an increase of the hairs on the surface of the\nleaf, that an entirely new species seems to present itself. It must here\nbe observed, that in consequence of the interactions of all the parts of\nevery organism, generally one individual part cannot be changed without\nat the same time producing changes in other parts. If, for instance, in\nour imaginary example, the number of the hairs on the leaves is greatly\nincreased, a certain amount of nourishment is thereby withdrawn from\nother parts; the material which might be employed to form flowers or\nseeds is diminished, and a smaller size of the flower or seed will then\nbe the direct or indirect consequence of the struggle for life, which in\nthe first place only produced a change in the leaves. Thus the struggle\nfor life, in this instance, acts as a means of selecting and\ntransforming. The struggle of the different individuals to obtain the\nnecessary conditions of existence, or, taking it in its widest sense,\nthe inter-relations of organisms to the whole of their surroundings,\nproduce mutations of form such as are produced in the cultivated state\nby the action of man\u2019s selection.\n\nThis agency will perhaps appear at first sight small and insignificant,\nand the reader will not be inclined to concede to the action of such\nrelations the weight which it in reality possesses. I must therefore\nfind space in a subsequent chapter to put forward further examples of\nthe immense and far-reaching power of transformation exhibited in\nnatural selection. For the present I will confine myself to simply\nplacing side by side the two processes of artificial and natural\nselection, and clearly explaining the agreement and the differences of\nthe two.\n\nBoth natural and artificial selection are quite simple natural,\nmechanical relations of life, which depend upon the _interaction_ of two\nphysiological functions, namely, on _Adaptation_ and _Inheritance_,\nfunctions which, as such, must again be traced to physical and chemical\nproperties of organic matter. The difference between the two forms of\nselection consists in this: in artificial selection the will of man\nmakes the selection according to a _plan_, whereas in natural selection,\nthe struggle for life (that universal inter-relation of organisms) acts\n_without a plan_, but otherwise produces quite the same result, namely,\na selection of a particular kind of individuals for propagation. The\nalterations produced by artificial selection are turned to the advantage\nof _those who make the selection_; in natural selection, on the other\nhand, to the advantage of the _selected organism_.\n\nThese are the most essential differences and agreements of the two modes\nof selection; it must, however, be further observed that there is\nanother difference, viz., in the duration of time required for the two\nprocesses of selection. Man in his artificial selection can produce very\nimportant changes in a very short time, while in natural selection\nsimilar results are obtained only after a much longer time. This arises\nfrom the fact that man can make his selection with much greater care.\nMan is able with the greatest nicety to pick out individuals from a\nlarge number, drop the others, and to employ only the privileged beings\nfor propagation, which is not the case in natural selection. In natural\nconditions, besides the privileged individuals which first succeed in\npropagating themselves, some few or many of the less distinguished\nindividuals will propagate themselves by the side of the former.\nMoreover, man can prevent the crossing of the original and the new form,\nwhich in natural selection is often unavoidable. If such a crossing,\nthat is, a sexual connection, of the new variety with the original forms\ntakes place, the offspring thereby produced generally returns to the\noriginal character. In natural selection, such a crossing can be avoided\nonly when the new variety by migration separates from the original and\nisolates itself.\n\nNatural selection therefore acts much more slowly; it requires much\nlonger periods than the artificial process of selection. But it is an\nessential consequence of this difference, that the product of artificial\nselection disappears much more easily, and that the new form returns\nrapidly to the earlier one, which is not the case in natural selection.\nThe new species arising from natural selection maintain themselves much\nmore permanently, and return much less easily to the original form, than\nis the case with products of artificial selection, and accordingly\nmaintain themselves during a much longer time than the artificial races\nproduced by man. But these are only subordinate differences, which are\nexplained by the different conditions of natural and artificial\nselection, and in reality are connected only with differences in the\nduration of time. The nature of the transformation and the means by\nwhich it is produced are entirely the same in both artificial and\nnatural selection. (Gen. Morph. ii. 248.)\n\nThe thoughtless and narrow-minded opponents of Darwin are never tired of\nasserting that his theory of selection is a groundless conjecture, or at\nleast an hypothesis which has yet to be proved. That this assertion is\ncompletely unfounded, may be perceived even from the outlines of the\ndoctrine of selection which have just been discussed. Darwin assumes no\nkind of unknown forces of nature, nor hypothetical conditions, as the\nacting causes for the transformation of organic forms, but solely and\nsimply the universally recognized vital activities of all organisms,\nwhich we term _Inheritance_ and _Adaptation_. Every naturalist\nacquainted with physiology knows that these two phenomena are directly\nconnected with the functions of propagation and nutrition, and, like all\nother phenomena of life, are purely mechanical processes of nature, that\nis, they depend upon the molecular phenomena of motion in organic\nmatter. That the interaction of these two functions effect a continual,\nslow transmutation of organic forms, is a necessary result of the\nstruggle for existence. But this, again, is no more a hypothetical\nrelation, nor one requiring a proof, than is the interaction of\nInheritance and Adaptation. The struggle for life is a mathematical\nnecessity, arising from the disproportion between the limited number of\nplaces in nature\u2019s household, and the excessive number of organic germs.\nThe origin of new species is moreover greatly favoured by the active or\npassive _migrations_ of animals and plants, which takes place everywhere\nand at all times, without being, however, entitled to rank as\n_necessary_ agents in the process of natural selection.\n\nThe origin of new species by natural selection, or, what is the same\nthing, by the interaction of Inheritance and Adaptation in the struggle\nfor life, is therefore a _mathematical necessity_ of nature which needs\nno further proof. Whoever, in spite of the present state of our\nknowledge, still seeks for _proofs_ for the Theory of Selection, only\nshows that he either does not thoroughly understand the theory, or is\nnot sufficiently acquainted with the biological facts\u2014has not the\nrequisite amount of experimental knowledge in Anthropology, Zoology, and\nBotany.\n\nIf, as we maintain, natural selection is the great active cause which\nhas produced the whole wonderful variety of organic life on the earth,\nall the interesting phenomena of _human life_ must also be explicable\nfrom the same cause. For man is after all only a most highly-developed\nvertebrate animal, and all aspects of human life have their parallels,\nor, more correctly, their lower stages of development in the animal\nkingdom. The whole history of nations, or what is called \u201cUniversal\nHistory,\u201d must therefore be explicable by means of \u201cnatural\nselection,\u201d\u2014must be a physico-chemical process, depending upon the\ninteraction of Adaptation and Inheritance in the struggle for life. And\nthis is actually the case. We shall give further proofs of this later\non.\n\nIt appears of interest here to remark that not only _natural_ selection,\nbut also _artificial_ selection exercises its influence in many ways in\nuniversal history. A remarkable instance of _artificial selection in\nman_, on a great scale, is furnished by the ancient Spartans, among\nwhom, in obedience to a special law, all newly-born children were\nsubject to a careful examination and selection. All those that were\nweak, sickly, or affected with any bodily infirmity, were killed. Only\nthe perfectly healthy and strong children were allowed to live, and they\nalone afterwards propagated the race. By this means, the Spartan race\nwas not only continually preserved in excellent strength and vigour, but\nthe perfection of their bodies increased with every generation. No doubt\nthe Spartans owed their rare degree of masculine strength and rough\nheroic valour (for which they are eminent in ancient history) in a\ngreat measure to this artificial selection.\n\nMany tribes also among the Red Indians of North America (who at present\nare succumbing in the struggle for life to the superior numbers of the\nwhite intruders, in spite of a most heroic and courageous resistance)\nowe their rare degree of bodily strength and warlike bravery to a\nsimilar careful selection of the newly-born children. Among them, also,\nall children that are weak or affected with any infirmity are\nimmediately killed, and only the perfectly strong individuals remain in\nlife, and propagate the race. That the race becomes greatly\nstrengthened, in the course of very many generations, by this artificial\nselection cannot in itself be doubted, and is sufficiently proved by\nmany well known facts.\n\nThe opposite of this artificial selection of the wild Redskins and the\nancient Spartans is seen in the individual selection which is\nuniversally practised in our modern military states, for the purpose of\nmaintaining standing armies, and which, under the name of _military\nselection_, we may conveniently consider as a special form of selection.\nUnfortunately, in our day, militarism is more than ever prominent in our\nso-called \u201ccivilization\u201d; all the strength and all the wealth of\nflourishing civilized states are squandered on its development; whereas\nthe education of the young, and public instruction, which are the\nfoundations of the true welfare of nations and the ennobling of\nhumanity, are neglected and mismanaged in a most pitiable manner. And\nthis is done in states which believe themselves to be the privileged\nleaders of the highest human intelligence, and to stand at the head of\ncivilization. As is well known, in order to increase the standing army\nas much as possible, all healthy and strong young men are annually\nselected by a strict system of recruiting. The stronger, healthier, and\nmore spirited a youth is, the greater is his prospect of being killed by\nneedle-guns, cannons, and other similar instruments of civilization. All\nyouths that are unhealthy, weak, or affected with infirmities, on the\nother hand, are spared by the \u201cmilitary selection,\u201d and remain at home\nduring the war, marry, and propagate themselves. The more useless, the\nweaker, or infirmer the youth is, the greater is his prospect of\nescaping the recruiting officer, and of founding a family. While the\nhealthy flower of youth dies on the battle-field, the feeble remainder\nenjoy the satisfaction of reproduction and of transmitting all their\nweaknesses and infirmities to their descendants. According to the laws\nof transmission by inheritance, there must necessarily follow in each\nsucceeding generation, not only a further extension, but also a more\ndeeply-seated development of weakness of body, and what is inseparable\nfrom it, a condition of mental weakness also. This and other forms of\nartificial selection practised in our civilized states sufficiently\nexplain the sad fact that, in reality, weakness of the body and weakness\nof character are on the perpetual increase among civilized nations, and\nthat, together with strong, healthy bodies, free and independent spirits\nare becoming more and more scarce.\n\nTo the increasing enervation of modern civilized nations, which is the\nnecessary consequence of military selection, there is further added\nanother evil. The progress of modern medical science, although still\nlittle able really to cure diseases, yet possesses and practises more\nthan it used to do the art of prolonging life during lingering, chronic\ndiseases for many years. Such ravaging evils as consumption, scrofula,\nsyphilis, and also many forms of mental disorders, are transmitted by\ninheritance to a great extent, and transferred by sickly parents to some\nof their children, or even to the whole of their descendants. Now, the\nlonger the diseased parents, with medical assistance, can drag on their\nsickly existence, the more numerous are the descendants who will inherit\nincurable evils, and the greater will be the number of individuals,\nagain, in the succeeding generation, thanks to that artificial \u201c_medical\nselection_,\u201d who will be infected by their parents with lingering,\nhereditary disease.\n\nIf any one were to venture the proposal, after the examples of the\nSpartans and Redskins, to kill, immediately upon their birth, all\nmiserable, crippled children to whom with certainty a sickly life could\nbe prophesied, instead of keeping them in life injurious to them and to\nthe race, our so-called \u201chumane civilization\u201d would utter a cry of\nindignation. But the same \u201chumane civilization\u201d thinks it quite as it\nshould be, and accepts without a murmur, that at the outbreak of every\nwar (and in the present state of civilized life, and in the continual\ndevelopment of standing armies, wars must naturally become more\nfrequent) hundreds and thousands of the finest men, full of youthful\nvigour, are sacrificed in the hazardous game of battles. The same\n\u201chumane civilization\u201d at present praises the abolition of capital\npunishment as a \u201cliberal measure!\u201d And yet capital punishment for\nincorrigible and degraded criminals is not only just, but also a benefit\nto the better portion of mankind; the same benefit is done by destroying\nluxuriant weeds, for the prosperity of a well cultivated garden. As by\na careful rooting out of weeds, light, air, and ground is gained for\ngood and useful plants, in like manner, by the indiscriminate\ndestruction of all incorrigible criminals, not only would the struggle\nfor life among the better portion of mankind be made easier, but also an\nadvantageous artificial process of selection would be set in practice,\nsince the possibility of transmitting their injurious qualities by\ninheritance would be taken from those degenerate outcasts.\n\nAgainst the injurious influence of artificial military and medical\nselection, we fortunately have a salutary counterpoise, in the\ninvincible and much more powerful influence of _natural selection_,\nwhich prevails everywhere. For in the life of man, as well as in that of\nanimals and plants, this influence is the most important transforming\nprinciple, and the strongest lever for progress and amelioration. The\nresult of the struggle for life is that, in the long run, that which is\nbetter, because more perfect, conquers that which is weaker and\nimperfect. In human life, however, this struggle for life will ever\nbecome more and more of an intellectual struggle, not a struggle with\nweapons of murder. The organ which, above all others, in man becomes\nmore perfect by the ennobling influence of natural selection, is the\n_brain_. The man with the most perfect understanding, not the man with\nthe best revolver, will in the long run be victorious; he will transmit\nto his descendants the qualities of the brain which assisted him in the\nvictory. Thus then we may justly hope, in spite of all the efforts of\nretrograde forces, that the progress of mankind towards freedom, and\nthus to the utmost perfection, will, by the happy influence of natural\nselection, become more and more certain.\n\n\n\n\nCHAPTER VIII.\n\nTRANSMISSION BY INHERITANCE AND PROPAGATION.\n\n\n   Universality of Inheritance and Transmission by\n   Inheritance.\u2014Special Evidences of the same.\u2014Human\n   Beings with four, six, or seven Fingers and\n   Toes.\u2014Porcupine Men.\u2014Transmission of Diseases,\n   especially Diseases of the Mind.\u2014Original\n   Sin.\u2014Hereditary Monarchies.\u2014Hereditary\n   Aristocracy.\u2014Hereditary Talents and Mental\n   Qualities.\u2014Material Causes of Transmission by\n   Inheritance.\u2014Connection between Transmission by\n   Inheritance and Propagation.\u2014Spontaneous Generation and\n   Propagation.\u2014Non-sexual or Monogonous\n   Propagation.\u2014Propagation by Self-Division.\u2014Monera and\n   Am\u0153b\u00e6.\u2014Propagation by the formation of Buds, by the\n   formation of Germ-Buds, by the formation of\n   Germ-Cells.\u2014Sexual or Amphigonous\n   Propagation.\u2014Formation of Hermaphrodites.\u2014Distinction\n   of Sexes, or Gonochorism.\u2014Virginal Breeding, or\n   Parthenogenesis.\u2014Material Transmission of Peculiarities\n   of both Parents to the Child by Sexual\n   Propagation.\u2014Difference between Transmission by\n   Inheritance in Sexual and in Asexual Propagation.\n\n\nThe reader has, in the last chapter, become acquainted with natural\nselection according to Darwin\u2019s theory, as the constructive force of\nnature which produces the different forms of animal and vegetable\nspecies. By natural selection we understand the interaction which takes\nplace in the struggle for life between the _transmission by inheritance_\nand the _mutability_ of organisms, between two physiological functions\nwhich are innate in all animals and plants, and which may be traced to\nother processes of life\u2014the functions of propagation and nutrition. All\nthe different forms of organisms, which people are usually inclined to\nlook upon as the products of a creative power, acting for a definite\npurpose, we, according to the Theory of Selection, can conceive as the\nnecessary productions of natural selection, working without a\npurpose,\u2014as the unconscious interaction between the two properties of\nMutability and Hereditivity. Considering the importance which\naccordingly belongs to these vital properties of organisms, we must\nexamine them a little more closely, and employ a chapter with the\nconsideration of Transmission by Inheritance. (Gen. Morph. ii. 170-191.)\n\nStrictly speaking, we must distinguish between Hereditivity\n(Transmissivity) and Inheritance (Transmission). Hereditivity is the\npower of transmission, the capability of organisms to transfer their\npeculiarities to their descendants by propagation. Transmission by\nInheritance, or Inheritance simply, on the other hand, denotes the\nexercise of the capability, the actual transmission.\n\nHereditivity and Transmission by Inheritance are such universal,\neveryday phenomena, that most people do not heed them, and but few are\ninclined to reflect upon the operation and import of these phenomena of\nlife. It is generally thought quite natural and self-evident that every\norganism should produce its like, and that children should more or less\nresemble their parents. Heredity is usually only taken notice of and\ndiscussed in cases relating to some special peculiarity, which appears\nfor the first time in a human individual without having been inherited,\nand then is transmitted to his descendants. It shows itself in a\nspecially striking manner in the case of certain diseases, and in\nunusual and irregular (monstrous) deviations from the usual formation of\nthe body.\n\nAmong these cases of the inheritance of monstrous deviations, those are\nspecially interesting which consist in an abnormal increase or decrease\nof the number five in the fingers or toes of man. It is not unfrequently\nobserved in families through several generations, that individuals have\nsix fingers on each hand, or six toes on each foot. Less frequent is the\nnumber of four or seven fingers or toes. The unusual formation arises at\nfirst from a single individual who, from unknown causes, is born with an\nexcess of the usual number of fingers and toes, and transmits these, by\ninheritance, to a portion of his descendants. In one and the same family\nit has happened that, throughout three, four, or more generations,\nindividuals have possessed six fingers and toes. In a Spanish family\nthere were no less than forty individuals distinguished by this excess.\nThe transmission of the sixth finger or toe is not permanent or enduring\nin all cases, because six-fingered people always intermarry again with\nthose possessing five fingers. If a six-fingered family were to\npropagate by pure in-breeding, if six-fingered men were always to marry\nsix-fingered women, this characteristic would become permanent, and a\nspecial six-fingered human race would arise. But as six-fingered men\nusually marry five-fingered women, and _vice vers\u00e2_, their descendants\nfor the most part show a very mixed numerical relation, and finally,\nafter the course of some generations, revert again to the normal number\nof five. Thus, for example, among eight children of a six-fingered\nfather and a five-fingered mother, two children may have on both hands\nand feet six fingers and toes, four children may have a mixed number,\nand two children may have the usual number of five on both hands and\nfeet. In a Spanish family, each child except the youngest had the number\nsix on both hands and feet; the youngest, only, had the usual number on\nboth hands and feet, and the six-fingered father of the child refused to\nrecognize the last one as his own.\n\nThe power of inheritance, moreover, shows itself very strikingly in the\nformation and colour of the human skin and hair. It is well known how\nexactly the nature of the complexion in many families\u2014for instance, a\npeculiar soft or rough skin, a peculiar luxuriance of the hair, a\npeculiar colour and largeness of the eyes\u2014is transmitted through many\ngenerations. In like manner, peculiar local growths or spots on the\nskin, the so-called moles, freckles, and other accumulations of pigment\nwhich appear in certain places, are frequently transmitted through\nseveral generations so exactly, that in the descendants they appear on\nthe same spots on which they existed in the parents. The porcupine men\nof the Lambert family, who lived in London last century, are especially\ncelebrated. Edward Lambert, born in 1717, was remarkable for a most\nunusual and monstrous formation of the skin. His whole body was covered\nwith a horny substance, about an inch thick, which rose in the form of\nnumerous thorn-shaped and scale-like processes, more than an inch long.\nThis monstrous formation of the outer skin, or epidermis, was\ntransmitted by Lambert to his sons and grandsons, but not to his\ngranddaughters. The transmission in this instance remained in the male\nline, as is often the case. In like manner, an excessive development of\nfat in certain parts of the body is often transmitted only in the\nfemale line. I scarcely need call to mind how exactly the characteristic\nformation of the face is transmitted by inheritance; sometimes it\nremains within the male, sometimes within the female line; sometimes it\nis blended in both.\n\nThe phenomena of transmission by inheritance of pathological conditions,\nespecially of the different forms of human diseases, are very\ninstructive and generally known. Diseases of the respiratory organs, the\nglands, and of the nervous system, are specially liable to be\ntransmitted by inheritance. Very frequently there suddenly appears in an\notherwise healthy family a disease until then unknown among them; it is\nproduced by external causes, by conditions of life causing disease. This\ndisease, brought about in an individual by external cause, is propagated\nand transmitted to his descendants, and some or all of them then suffer\nfrom the same disease. In case of diseases of the lungs, for instance in\nconsumption, this sad transmission by inheritance is well known, and it\nis the same with diseases of the liver, with syphilis, and diseases of\nthe mind. The latter are specially interesting. Just as peculiar\ncharacteristic features of man\u2014pride, ambition, frivolity, etc.\u2014are\ntransmitted to the descendants strictly by inheritance, so too are the\npeculiar abnormal manifestations of mental activity, which are usually\ncalled fixed ideas, despondency, imbecility, and generally \u201cdiseases of\nthe mind.\u201d This distinctly and irrefragably shows that the soul of man,\njust as the soul of animals, is a purely mechanical activity, the sum of\nthe molecular phenomena of motion in the particles of the brain, and\nthat it is transmitted by inheritance, together with its substratum,\njust as every other quality of the body is materially transmitted by\npropagation.\n\nWhen this exceedingly important and undeniable fact is mentioned, it\ngenerally causes great offence, and yet in reality it is silently and\nuniversally acknowledged. For upon what else do the ideas of \u201chereditary\nsin,\u201d \u201chereditary wisdom,\u201d and \u201chereditary aristocracy,\u201d etc., rest than\nupon the conviction that the _quality of the human mind_ is transmitted\nby propagation\u2014that is, by a purely _material_ process\u2014through the\nbody, from the parents to the descendants? The recognition of this great\nimportance of transmission by inheritance is shown in a number of human\ninstitutions, as for example, among many nations in the division into\ncastes, such as the castes of warriors, castes of priests, and castes of\nlabourers, etc. It is evident that the institution of such castes\noriginally arose from the notion of the great importance of hereditary\ndistinctions possessed by certain families, which it was presumed would\nalways be transmitted by the parents to the children. The institution of\nan hereditary aristocracy and an hereditary monarchy is to be traced to\nthe notion of such a transmission of special excellencies. However, it\nis unfortunately not only virtues, but also vices that are transmitted\nand accumulated by inheritance; and if, in the history of the world, we\ncompare the different individuals of the different dynasties, we shall\neverywhere find a great number of proofs of the transmission of\nqualities by inheritance, but fewer of transmissions of virtues than of\nvices. Look only, for example, at the Roman emperors, at the Julii and\nthe Claudii, or at the Bourbons in France, Spain, and Italy!\n\nIn fact, scarcely anywhere could we find such a number of striking\nexamples of the remarkable transmission of bodily and mental features by\ninheritance, as in the history of the reigning houses in hereditary\nmonarchies. This is specially true in regard to the diseases of the mind\npreviously mentioned. It is in reigning families that mental disorders\nare hereditary in an unusual degree. Thus Esquirol, distinguished for\nhis knowledge of mental diseases, proved that the number of insane\nindividuals in the reigning houses was, in proportion to the number\namong the ordinary population, as 60 to 1; that is, that disorders of\nthe brain occur 60 times more frequently in the privileged families of\nthe ruling houses than among ordinary people. If equally accurate\nstatistics were made of the hereditary nobility, the result would\nprobably be that here also we should find an incomparably larger\ncontingent of mental diseases than among the common, ignoble portion of\nmankind. This phenomenon can scarcely astonish us if we consider what\ninjury these privileged castes inflict upon themselves by their\nunnatural, one-sided education, and by their artificial separation from\nthe rest of mankind. By this means many dark sides of human nature are\nspecially developed and, as it were, artificially bred, and, according\nto the laws of transmission by inheritance, are propagated through\nseries of generations with ever-increasing force and dominance.\n\nIt is sufficiently obvious from the history of nations how in successive\ngenerations of many dynasties, for example, of the princes of Saxon\nThuringia and of the Medici, the noble solicitude for the most perfect\nhuman accomplishments in science and art were retained and transmitted\nfrom father to son; and how, on the other hand, in many other dynasties,\nfor centuries a special partiality for the profession of war, for the\noppression of human freedom, and for other rude acts of violence, have\nbeen hereditary. In like manner talents for special mental activities\nare transmitted in many families for generations, as, for instance,\ntalent for mathematics, poetry, music, sculpture, the investigation of\nnature, philosophy, etc. In the family of Bach there have been no less\nthan twenty-two eminent musicians. Of course the transmission of such\npeculiarities of mind depends upon the material process of reproduction,\nas does the transmission of mental qualities in general. In this case\nagain, the vital phenomenon, the manifestation of force (as everywhere\nin nature), is directly connected with definite relations in the\nadmixture of the material components of the organism. It is this\ndefinite proportion and molecular motion of matter which is transmitted\nby generation.\n\nNow, before we examine the numerous, and in some cases most interesting\nand important, laws of transmission by inheritance, let us make\nourselves acquainted with the actual nature of the process. The\nphenomena of transmission by inheritance are generally looked upon as\nsomething quite mysterious, as peculiar processes which cannot be\nfathomed by natural science, and the causes and actual nature of which\ncannot be understood. It is precisely in such a case that people very\ngenerally assume supernatural influences. But even in the present state\nof our physiology it can be proved with complete certainty that all the\nphenomena of inheritance are entirely natural processes, that they are\nproduced by mechanical causes, and that they depend on the material\nphenomena of motion in the bodies of organisms, which we may consider as\na part of the phenomena of propagation. All the phenomena of Heredity\nand the laws of Transmission by Inheritance can be traced to the\nmaterial process of _Propagation_.\n\nEvery organism, every living individual, owes its existence _either_ to\nan act of unparental or _Spontaneous Generation_ (Generatio Spontanea,\nArchigonia), or to an act of Parental Generation or _Propagation_\n(Generatio Parentalis, Tocogonia). In a future chapter we shall have to\nconsider Spontaneous Generation, or Archigony. At present we must occupy\nourselves with Propagation, or Tocogony, a closer examination of which\nis of the utmost importance for understanding transmission by\ninheritance. Most of my readers probably only know those phenomena of\nPropagation which are seen universally in the higher plants and animals,\nthe processes of Sexual Propagation, or Amphigony. The processes of\nNon-sexual Propagation, or Monogony, are much less generally known. The\nlatter, however, are far more suited to throw light upon the nature of\ntransmission by inheritance in connection with propagation.\n\nFor this reason, we shall first consider only the phenomena of\n_non-sexual_ or _monogonic propagation_ (Monogonia). This appears in a\nvariety of different forms, as for example, self-division, formation of\nbuds, the formation of germ-cells or spores (Gen. Morph. ii. 36-58). It\nwill be most instructive, first, to examine the propagation of the\nsimplest organisms known to us, which we shall have to return to later,\nwhen considering the question of spontaneous generation. These very\nsimplest of all organisms yet known, and which, at the same time, are\nthe simplest imaginable organisms, are the _Monera_ living in water;\nthey are very small living corpuscles, which, strictly speaking, do not\nat all deserve the name of organism. For the designation \u201corganism,\u201d\napplied to living creatures, rests upon the idea that every living\nnatural body is composed of organs, of various parts, which fit into\none another and work together (as do the different parts of an\nartificial machine), in order to produce the action of the whole. During\nlate years we have become acquainted with _Monera_, organisms which are,\nin fact, not composed of any organs at all, but consist entirely of\nshapeless, simple, homogeneous matter. The entire body of one of these\nMonera, during life, is nothing more than a shapeless, mobile, little\nlump of mucus or slime, consisting of an albuminous combination of\ncarbon. Simpler or more imperfect organisms we cannot possibly conceive.\n\nThe first complete observations on the natural history of a Moneron\n(Protogenes primordialis) were made by me at Nice, in 1864. Other very\nremarkable Monera I examined later (1866) in Lanzarote, one of the\nCanary Islands, and in 1867 in the Straits of Gibraltar. The complete\nhistory of one of these Monera, the orange-red _Protomyxa aurantiaca_,\nis represented in Plate I, and its explanation is given in the Appendix.\nI have found some curious Monera also in the North Sea, off the\nNorwegian coast, near Bergen. Cienkowski has described (1865) an\ninteresting Moneron from fresh waters, under the name of _Vampyrella_.\nBut perhaps the most remarkable of all Monera was discovered by Huxley,\nthe celebrated English zoologist, and called _Bathybius H\u00e6ckelii_.\n\u201cBathybius\u201d means, living in the deep. This wonderful organism lives in\nimmense depths of the ocean, which are over 12,000\u2014indeed, in some\nparts 24,000 feet below the surface, and which have become known to us\nwithin the last ten years, through the laborious investigations made by\nthe English. There, among the numerous Polythalamia and Radiolaria\nwhich inhabit the fine calcareous mud of these abysses, the Bathybius is\nfound in great quantities, sometimes in the shape of roundish, formless\nlumps of mucus, sometimes in the form of a network of mucus, covering\nfragments of stone and other objects. Small particles of chalk are\nfrequently embedded in these mucous gelatinous masses, and are, perhaps,\nproducts of their secretion. The entire body of this remarkable\nBathybius consists solely of shapeless plasma, or protoplasm, as in the\ncase of the other Monera\u2014that is, it consists of the same albuminous\ncombination of carbon, which in infinite modifications is found in all\norganisms, as the essential and never-failing seat of the phenomena of\nlife. I have given a detailed description and drawing of the Bathybius\nand other Monera in my \u201cMonographie der Moneren,\u201d 1870,(15) from which\nthe drawing in Fig. 9 is taken.\n\n[Illustration: Life history of a simplest organism. Pl. I.\n\nE. Haeckel del. _Prototmyxa aurantiaca._ Lagesse sc.]\n\nIn a state of rest most Monera appear as small globules of mucus or\nslime, invisible, or nearly so, to the naked eye; they are at most as\nlarge as a pin\u2019s head. When the Moneron moves itself, there are formed\non the upper surface of the little mucous globule, shapeless, fingerlike\nprocesses, or very fine radiated threads; these are the so-called false\nfeet, or pseudopodia. The false feet are simple, direct continuations of\nthe shapeless albuminous mass, of which the whole body consists. We are\nunable to perceive different parts in it, and we can give a direct proof\nof the absolute simplicity of the semi-fluid mass of albumen, for with\nthe aid of the microscope we can follow the Moneron as it takes in\nnourishment. When small particles suited for its nourishment\u2014for\ninstance, small particles of decayed organic bodies or microscopic\nplants and infusoria\u2014accidentally come into contact with the Moneron,\nthey remain hanging to the sticky semi-fluid globule of mucus, and here\ncreate an irritation, which is followed by a strong afflux of the mucous\nsubstance, and, in consequence, they become finally completely inclosed\nby it, or are drawn into the body of the Moneron by displacement of the\nseveral albuminous particles, and are there digested, being absorbed by\nsimple diffusion (endosmosis).\n\n[Illustration: FIG. 1.\u2014Propagation of the simplest organism, a Moneron,\nby self-division. _A._ The entire Moneron, a Protam\u0153ba. _B._ It falls\ninto two halves by a contraction in the middle. _C._ Each of the two\nhalves has separated from the other, and now represents an independent\nindividual.]\n\nJust as simple as the process of nutrition is the _propagation_ of these\nprimitive creatures, which in reality we can neither call animals nor\nplants. All Monera propagate themselves only in an asexual manner by\nmonogony; and in the simplest case, by that kind of monogony which we\nplace at the head of the different forms of propagation, that is, by\nself-division. When such a little globule, for example a Protam\u0153ba or\na Protogenes, has attained a certain size by the assimilation of foreign\nalbuminous matter, it falls into two pieces; a pinching in takes place,\ncontracting the middle of the globule on all sides, and finally leads to\nthe separation of the two halves (compare Fig. 1). Each half then\nbecomes rounded off, and now appears as an independent individual, which\ncommences anew the simple course of the vital phenomena of nutrition and\npropagation. In other Monera (Vampyrella), the body in the process of\npropagation does not fall into two, but into four equal pieces, and in\nothers, again (Protomonas, Protomyxa, Myxastrum), at once into a number\nof small globules of mucus, each of which again, by simple growth,\nbecomes like the parent body. Here it is evident that the process of\n_propagation is nothing but a growth of the organism beyond its own\nindividual limit of size_.\n\nThe simple method of propagation of the Moneron by self-division is, in\nreality, the most universal and most widely spread of all the different\nmodes of propagation; for by the same simple process of division,\n_cells_ also propagate themselves. Cells are those simple organic\nindividuals, a large number of which constitute the bodies of most\norganisms, the human body not excepted. With the exception of the\norganisms of the lowest order, which have not even the perfect form of a\ncell (Monera), or during life only represent a single cell (many\nProtista and single-celled plants), the body of every organic individual\nis composed of a great number of cells. Every organic cell is to a\ncertain degree an independent organism, a so-called \u201celementary\norganism,\u201d or an \u201cindividual of the first order.\u201d Every higher organism\nis, in a measure, a society or a state of such variously shaped\nelementary individuals, variously developed by division of labour.(39)\nOriginally every organic cell is only a single globule of mucus, like a\nMoneron, but differing from it in the fact that the homogeneous\nalbuminous substance has separated itself into two different parts, a\nfirmer albuminous body, the _cell-kernel_ (nucleus), and an external,\nsofter albuminous body, the _cell-substance_ or _body_ (protoplasma).\nBesides this, many cells later on form a third (frequently absent)\ndistinct part, inasmuch as they cover themselves with a capsule, by\nexuding an outer pellicle or _cell-membrane_ (membrana). All other forms\nof cells, besides these, are of subordinate importance, and are of no\nfurther interest to us here.\n\nEvery organism composed of many cells was originally a single cell, and\nit becomes many-celled owing to the fact that the original cell\npropagates itself by self-division, and that the new individual cells\noriginating in this manner remain together, and by division of labour\nform a community or a state. The forms and vital phenomena of all\nmany-celled organisms are merely the effect or the expression of all the\nforms and vital phenomena of all the individual cells of which they are\ncomposed. The egg, from which most animals and plants are developed, is\na simple cell.\n\n[Illustration: FIG. 2.\u2014Propagation of a single-celled organism,\nAm\u0153ba sph\u00e6rococcus, by self-division. _A._ The enclosed Am\u0153ba, a\nsimple globular cell consisting of a lump of protoplasm (_c_), which\ncontains a kernel (_b_) and a kernel speck (_a_), and is surrounded by a\ncell-membrane or capsule. _B._ The free Am\u0153ba, which has burst and\nleft the cyst or cell-membrane. _C._ It begins to divide by its kernel\nforming two kernels, and by the cell-substance between the two becoming\ncontracted. _D._ The division is completed by the cell-substance\nlikewise falling into two halves (_Da_ and _Db_).]\n\nThe single-celled organisms, that is, those which during life retain the\nform of a single cell, for example the Am\u0153b\u00e6, as a rule propagate\nthemselves in the simplest way by self-division. This process differs\nfrom the previously described self-division of the Moneron only in the\nfact that at the commencement the firmer cell-kernel (nucleus) falls\ninto two halves, by a pinching in at its middle. The two young kernels\nseparate from each other and act now as two distinct centres of\nattraction upon the surrounding softer albuminous matter, that is, the\ncell-substance (protoplasma). By this process finally the latter also\ndivides into two halves, and there now exist two new cells, which are\nlike the mother cell. If the cell was surrounded by a membrane, this\neither does not divide at all, as in the case of egg-cleavage (Fig. 3,\n4), or it passively follows the active pinching in of the protoplasm;\nor, lastly, every new cell exudes a new membrane for itself.\n\n[Illustration: FIG. 3.\u2014Egg of a mammal (a simple cell). _a._ The small\nkernel speck or nucleolus (the so-called germ-spot of the egg). _b._\nKernel or nucleus (the so-called germ-bladder of the egg). _c._\nCell-substance or protoplasm (the so-called yolk of the egg). _d._\nCell-capsule or membrane (membrane of the yolk) of the egg; called in\nmammals, on account of its transparency, Membrana pellucida.]\n\nThe non-independent cells which remain united in communities or states,\nand thus constitute the body of higher organisms, are propagated in the\nsame manner as are independent single-celled organisms, for example,\nAm\u0153ba (Fig. 2). Just as in that case, the cell with which most\nanimals and plants commence their individual existence, namely, the egg,\nmultiplies itself by simple division. When an animal, for instance a\nmammal (Fig. 3, 4), develops out of an egg, this process of development\nalways begins by the simple egg-cell (Fig. 3) forming an accumulation of\ncells (Fig. 4) by continued self-division. The outer covering, or cell\nmembrane, of the globular egg remains undivided. First, the cell-kernel\nof the egg (the so-called germinal vesicle) divides itself into two\nkernels, then follows the cell-substance (the yolk of the egg) (Fig. 4\n_A_). In like manner, the two cells, by continued self-division,\nseparate into four (Fig. 4 _B_), these into eight (Fig. 4 _C_), into\nsixteen, thirty-two, etc., and finally there is produced a globular mass\nof very numerous little cells (Fig. 4 _D_). These now, by further\nincrease and heterogeneous development (division of labour), gradually\nbuild up the compound many-celled organism. Every one of us, at the\ncommencement of our individual development, has undergone the very same\nprocess as that represented in Fig. 4. The egg of a mammal\u2014represented\nin Fig. 3, and its development in Fig. 4\u2014might as well be that of a\nman, as of an ape, dog, horse, or any other placental mammal.\n\n[Illustration: FIG. 4.\u2014First commencement of the development of a\nmammal\u2019s egg, the so-called \u201ccleavage of the egg\u201d (propagation of the\negg-cell by repeated self-division). _A._ The egg, by the formation of\nthe first furrow, falls into two cells. _B._ These separate by division\ninto four cells. _C._ The latter have divided into eight cells. _D._ By\nrepeated division a globular accumulation of numerous cells has\narisen.]\n\nNow, when one examines this simplest form of propagation, this\nself-division, it surely cannot be considered wonderful that the\nproducts of the division of the original organism should possess the\nsame qualities as the parental individual. For they are parts or halves\nof the parental organism, and the matter or substance in both halves is\nthe same, and as both the young individuals have received an equal\namount and the same quality of matter from the parent individual, one\ncan but consider it natural that the vital phenomena, the physiological\nqualities should be the same in both children. In fact, in regard to\ntheir form and substance, as well as to their vital phenomena, the two\nproduced cells can in no respect be distinguished from one another, or\nfrom the mother cell. They have _inherited_ from her the same nature.\n\nBut this same simple propagation by self-division is not only confined\nto simple cells\u2014it is the same also in the higher many-celled\norganisms; for example, in the coral zoophytes. Many of them which\nexhibit a high complexity of composition and organization, nevertheless,\npropagate themselves by simple division. In this case the whole\norganism, with all its organs, falls into two equal halves as soon as by\ngrowth it has attained a certain size. Each half again develops itself,\nby growth, into a complete individual. Here, again, it is surely\nself-evident that the two products of division will share the qualities\nof the parental organism, as they themselves are in fact halves of that\nparent.\n\nNext to propagation by division we come to propagation by the _formation\nof buds_. This kind of monogony is exceedingly widely spread. It occurs\nboth in the case of simple cells (though not frequently) and in the\nhigher organisms composed of many cells. The formation of buds is\nuniversal in the vegetable kingdom, less frequent in the animal kingdom.\nHowever, here also it occurs in the tribe of Plant-like Animals,\nespecially among the Coral Zoophytes, and among the greater portion of\nthe Hydroid Polyps very frequently, further also among some worms\n(Planarian Worms, Ring-Worms, Moss Animals, Tunicates). Most branching\nanimal-trees or colonies, which are exceedingly like branching plants,\narise like those plants, by the formation of buds.\n\nPropagation by the _formation of buds_ (Gemmatio) is essentially\ndistinguished from propagation by division, in the fact that the two\norganisms thus produced by budding are not of equal age, and therefore\nat first are not of equal value, as they are in the case of division. In\ndivision we cannot clearly distinguish either of the two newly produced\nindividuals as the parental, that is as the producer, because, in fact,\nboth have an equal share in the composition of the original parental\nindividual. If, on the other hand, an organism sends out a bud, then the\nlatter is the child of the former. The two individuals are of unequal\nsize and of unequal form. If, for instance, a cell propagates itself by\nthe formation of buds, we do not see the cell fall into two equal\nhalves, but there appears at one point of it a protuberance, which\nbecomes larger and larger, more or less separates itself from the\nparental cell, and then grows independently. In like manner we observe\nin the budding of a plant or animal, that a small local growth arises on\na part of the mature individual, which growth becomes larger and larger,\nand likewise more or less separates itself from the parental organism by\nan independence in its growth. The bud, after it has attained a certain\nsize, may either completely separate itself from the parental\nindividual, or it may remain connected with it and form a stock or\ncolony, whilst at the same time its life may be quite independent of\nthat of its parent. While the growth which starts the propagation, in\nthe case of self-division, is a total one affecting the whole body, it\nis in the formation of buds only partial, affecting merely a portion of\nthe parental organism. But here, also, the bud\u2014the newly-produced\nindividual which remains so long most directly connected with the\nparental organism, and which proceeds from it\u2014retains the essential\nqualities and the original tendency of development of its parent.\n\nA third mode of non-sexual propagation, that of the _formation of\ngerm-buds_ (Polysporogonia), is intimately connected with the formation\nof buds. In the case of the lower, imperfect organisms, among animals,\nespecially in the case of the Plant-like animals and Worms, we very\nfrequently find that in the interior of an individual composed of many\ncells, a small group of cells separates itself from those surrounding\nit, and that this small isolated group gradually develops itself into\nan individual, which, becomes like the parent, and sooner or later comes\nout of it. Thus, for example, in the body of the Fluke-worms\n(Trematodes) there often arise numerous little bodies consisting of many\ncells, that is _germ-buds_, or _polyspores_, which, at an early stage\nseparate themselves completely from the parent body, and leave it when\nthey have attained a certain stage of development.\n\nThe formation of germ-buds is evidently but little different from real\nbudding. But, on the other hand, it is connected with a fourth kind of\nnon-sexual propagation, which almost forms a transition to sexual\nreproduction, namely, the _formation of germ-cells_ (Monosporogonia),\nwhich is often briefly called formation of spores (sporogonia). In this\ncase it is no longer a group of cells, but a single cell, which\nseparates itself from the surrounding cells in the interior of the\nproducing organism, and which only becomes further developed after it\nhas come out of its parent. After this _germ-cell_, or monospore (or,\nbriefly, spore), has left the parental individual, it multiplies by\ndivision, and thus forms a many-celled organism, which by growth and\ngradual development attains the hereditary qualities of the parental\norganism. This occurs very generally among lower plants (Cryptogama).\n\nAlthough the formation of germ-cells very much resembles the formation\nof germ buds, it evidently and very essentially differs from the latter,\nand also from the other forms of non-sexual propagation which have\npreviously been mentioned, by the fact that only a very small portion of\nthe producing organism takes part in the propagation and, accordingly,\nin the transmission by inheritance. In the case of self-division, where\nthe whole organism falls into two halves, in the formation of buds,\nwhere a considerable portion of the whole body, already more or less\ndeveloped, separates from the producing individual, we easily understand\nthat the forms and vital phenomena should be the same in the producing\nand produced organism. It is much more difficult to understand in the\nformation of germ-buds, and more difficult still in the formation of\ngerm-cells, how this very small, quite undeveloped portion of the body,\nthis group of cells, or this single cell, not only directly takes with\nit certain parental qualities into its independent existence, but also\nafter its separation from the parental individual develops into a\nmany-celled body, and in this repeats the forms and vital phenomena of\nthe original producing organism. This last form of monogonic\npropagation\u2014that of the germ cells, or spore-formation\u2014leads us\ndirectly to a form of propagation which is the most difficult of all to\nexplain, namely, sexual propagation.\n\n_Sexual or amphigonic propagation_ (Amphigonia) is the usual method of\npropagation among all higher animals and plants. It is evident that it\nhas only developed, at a very late period of the earth\u2019s history, from\nnon-sexual propagation, and apparently in the first instance from the\nmethod of propagation by germ-cells. In the earliest periods of the\norganic history of the earth, all organisms propagated themselves in a\nnon-sexual manner, as numerous lower organisms still do, especially all\nthose which are at the lowest stage of organization, and which, strictly\nspeaking, can be considered neither as animals nor as plants, and which\ntherefore, as primary creatures, or Protista, are best excluded from\nboth the animal and vegetable kingdoms. In the case of the higher\nanimals and plants, the increase of individuals, as a rule, is at\npresent brought about in the majority of cases by sexual propagation.\n\nIn all the chief forms of non-sexual propagation mentioned above\u2014in\nfission, in the formation of buds, germ buds, and germ cells\u2014the\nseparated cell or group of cells was able by itself to develop into a\nnew individual, but in the case of sexual propagation the cell must\nfirst be fructified by another generative substance. The fructifying\nmale sperm must first mix with the female germ-cell (the egg) before the\nlatter can develop into a new individual. These two different\ngenerative substances, the male sperm and the female egg, are either\nproduced by one and the same individual hermaphrodite\n(Hermaphroditismus), or by two different individuals (sexual separation,\nGonochorismus) (Gen. Morph. ii. 58, 59).\n\nThe simpler and more ancient form of sexual propagation is through\ndouble-sexed individuals (Hermaphroditismus). It occurs in the great\nmajority of plants, but only in a minority of animals, for example, in\nthe garden snails, leeches, earth-worms, and many other worms. Every\nsingle individual among hermaphrodites produces within itself materials\nof both sexes\u2014eggs and sperm. In most of the higher plants every\nblossom contains both the male organ (stamens and anther) and the female\norgans (style and germ). Every garden snail produces in one part of its\nsexual gland eggs, and in another part sperm. Many hermaphrodites can\nfructify themselves; in others, however, copulation and reciprocal\nfructification of both hermaphrodites is necessary for causing the\ndevelopment of the eggs. This latter case is evidently a transition to\nsexual separation.\n\n_Sexual separation_ (Gonochorismus,) which characterizes the more\ncomplicated of the two kinds of sexual reproduction, has evidently been\ndeveloped from the condition of hermaphroditism at a late period of the\norganic history of the world. It is at present the universal method of\npropagation of the higher animals, and occurs, on the other hand, only\nin the minority of plants (for example, in many aquatic plants, _e.g._\nHydrocharis, Vallisneria; and in trees, _e.g._ Willows, Poplars). Every\norganic individual, as a non-hermaphrodite (Gonochoristus), produces\nwithin itself only one of two generative substances, either the male or\nthe female. The female individuals, both in animals and plants, produce\neggs or egg-cells. The eggs of plants in the case of flowering plants\n(Phanerogama), are commonly called \u201cembryo sacs\u201d; in the case of\nflowerless plants (Cryptogama), \u201cfruit spores.\u201d In animals, the male\nindividual secretes the fructifying sperm (sperma); in plants, the\ncorpuscles, which correspond to the sperm. In the Phanerogama, these are\nthe pollen grains, or flower-dust; in the Cryptogama, a sperm, which,\nlike that of most animals, consists of floating vibratile cells actively\nmoving in a fluid\u2014the zoosperms, spermatozoa, or sperm-cells.\n\nThe so-called _virginal reproduction_ (Parthenogenesis) offers an\ninteresting form of transition from sexual reproduction to the\nnon-sexual formation of germ-cells (which most resembles it); it has\nbeen demonstrated to occur in many cases among Insects, especially by\nSiebold\u2019s excellent investigations. In this case germ-cells, which\notherwise appear and are formed exactly like egg-cells, become capable\nof developing themselves into new individuals without requiring the\nfructifying seed. The most remarkable and most instructive of the\ndifferent partheno-genetic phenomena are furnished by those cases in\nwhich the same germ-cells, according as they are fructified or not,\nproduce different kinds of individuals. Among our common honey bees, a\nmale individual (a drone) arises out of the eggs of the queen, if the\negg has not been fructified; a female (a queen, or working bee), if the\negg has been fructified. It is evident from this, that in reality there\nexists no wide chasm between sexual and non-sexual reproduction, but\nthat both modes of reproduction are directly connected. The\nparthenogenesis of Insects must probably be regarded as a _relapse_ from\nthe sexual mode of propagation (possessed by the original parents of the\ninsects) to the earlier condition of non-sexual propagation. (Gen.\nMorph. ii. 86.) In any case, however, sexual reproduction, both in\nplants and animals, which seems such a wonderful process, has only\narisen at a later date out of the more ancient process of non-sexual\nreproduction. In both cases heredity is a necessary part of the\nphenomenon.\n\nIn all the different modes of propagation the essential point of the\nprocess is invariably a detachment of a portion of the parental organism\npossessing the capability of leading an individual, independent\nexistence. We may, therefore, in all cases expect, _\u00e0 priori_, that the\nproduced individuals\u2014which are, in fact, as is commonly said, \u201cthe\nflesh and blood\u201d of the parents\u2014will receive the vital characteristics\nand qualities of form which the parental individuals possess. It is\nsimply a larger or smaller quantity of the parental material, in fact of\nits albuminous protoplasm, or cell-substance, which passes to the\nproduced individual. But together with the material, its vital\nproperties\u2014that is, the molecular motions of the plasma\u2014are\ntransmitted, which then manifest themselves in its form. Inheritance by\nsexual breeding loses very much of the mysterious and wonderful\ncharacter which it at first sight possesses for the uninitiated, if we\nconsider the above-mentioned series of the different modes of\npropagation, and their connection one with another. It at first appears\nexceedingly wonderful that in the sexual propagation of man, and of all\nhigher animals, the small egg, the minute cell, often invisible to the\nnaked eye, is able to transfer to the produced organism all the\nqualities of the maternal organism, and, no less mysterious, that at\nthe same time the essential qualities of the paternal organism are\ntransferred to the offspring by means of the male sperm, which\nfructifies the egg-cell by means of a viscid substance in which minute\nthread-like cells or zoosperms move about. But as soon as we compare the\nconnected stages of the different kinds of propagation, in which the\nproduced organism separates itself more and more as a distinct growth\nfrom the parental individual, and more or less early enters upon its\nindependent career; as soon as we consider, at the same time, that the\ngrowth and development of every higher organism only depends upon the\nincrease of the cells composing it\u2014that is, upon their simple\npropagation by division\u2014it becomes quite evident that all these\nremarkable processes belong to one series.\n\nThe life of every organic individual is nothing but a connected chain of\nvery complicated material phenomena of motion. These motions must be\nconsidered as changes in the position and combination of the molecules,\nthat is, of the smallest particles of animated matter (of atoms placed\ntogether in the most varied manner). The specific, definite tendency of\nthese orderly, continuous, and inherent motions of life depends, in\nevery organism, upon the chemical mingling of the albuminous generative\nmatter to which it owes its origin. In man, as in the case of the higher\nanimals which propagate themselves in a sexual manner, the individual\nvital motion commences at the moment in which the egg-cell is fructified\nby the spermatic filaments of the seed, in which process both generative\nsubstances actually mix; and here the tendency of the vital motion is\ndetermined by the specific, or more accurately, by the individual\nnature of the sperm as well as of the egg. There can be no doubt as to\nthe purely mechanical material nature of this process. But here we stand\nfull of wonder and astonishment before the infinite and inconceivable\ndelicacy of this albuminous matter. We are amazed at the undeniable fact\nthat the simple egg-cell of the maternal organism, and a single paternal\nsperm-thread, transfer the molecular individual vital motion of these\ntwo individuals to the child so accurately, that afterwards the minutest\nbodily and mental peculiarities of both parents reappear in it.\n\nHere we stand before a mechanical phenomenon of nature of which Virchow,\nwhose genius founded the \u201ccellular pathology,\u201d says with full justice:\n\u201cIf the naturalist cared to follow the custom of historians and\npreachers, and to clothe phenomena, which are in their way unique, with\nthe hollow pomp of ponderous and sounding words, this would be the\nopportunity for him; for we have now approached one of those great\nmysteries of animal nature, which encircle the region of animal life as\nopposed to all the rest of the world of phenomena. The question of the\nformation of cells, the question of the excitation of a continuous and\nequable motion, and, finally, the questions of the independence of the\nnervous system and of the soul\u2014these are the great problems on which\nthe human mind can measure its strength.\u201d To comprehend the relation of\nthe male and female to the egg-cell is almost as much as to solve all\nthose mysteries. The origin and development of the egg-cell in the\nmother\u2019s body, the transmission of the bodily and mental peculiarities\nof the father to it by his seed, touch upon all the questions which the\nhuman mind has ever raised about man\u2019s existence. And, we add, these\nmost important questions are solved, by means of the Theory of Descent,\nin a purely mechanical and purely monistic sense!\n\nThere can then be no further doubt that, in the sexual propagation of\nman and all higher organisms, inheritance, which is a purely mechanical\nprocess, is directly dependent upon the material continuity of the\nproducing and produced organism, just as is the case in the simplest\nnon-sexual propagation of the lower organisms. However, I must at once\ntake this opportunity of drawing attention to an important difference\nwhich inheritance presents in sexual and non-sexual propagation. It is a\nfact long since acknowledged, that the individual peculiarities of the\nproducing organism are much more accurately transmitted to the produced\norganism by non-sexual than by sexual propagation. Gardeners have for a\nlong time made use of this fact in many ways. When, for instance, a\nsingle individual of a species of tree with stiff, upright branches\naccidentally produces down-hanging branches, a gardener, as a rule,\ncannot transmit this peculiarity by sexual, but only by non-sexual\npropagation. The twigs cut off such a weeping tree and planted as\ncuttings or slips, afterwards produce trees having likewise hanging\nbranches, as, for example, the weeping willows and beeches. Seedlings,\non the other hand, which have been reared out of the seed of such a\nweeping tree, generally have the original stiff and upright form of\nbranches possessed by their ancestors. The same may be observed in a\nvery striking manner in the so-called \u201ccopper-coloured trees,\u201d that is,\nvarieties of trees which are characterized by a red or reddish brown\ncolour of the leaves. Off-shoots from such copper-coloured trees (for\nexample, the copper beech), which have been propagated by cuttings in a\nnon-sexual manner, show the peculiar colour and nature of the leaves\nwhich distinguished the parental individual, while others reared from\nseeds of such a copper-coloured tree return to the green-coloured\ncondition of leaf.\n\nThis difference in inheritance will seem very natural when we consider\nthat the material connection between the producing and produced\nindividuals is much closer and lasts much longer in non-sexual than in\nsexual propagation. The special tendency of the molecular motion of life\ncan therefore fix itself much longer and more thoroughly in the filial\norganism, and be more strictly transmitted by non-sexual than by sexual\npropagation. All these phenomena, considered in connection, clearly\nprove that the transmission of bodily and mental peculiarities is a\npurely material and mechanical process. By propagation a greater or\nlesser quantity of albuminous particles, and together with them the\nindividual form of motion inherent in these molecules of protoplasm, are\ntransmitted from the parental organism to the offspring. As this form of\nmotion remains continuous, the more delicate peculiarities inherent in\nthe parental organism must sooner or later reappear in the filial\norganism.\n\n\n\n\nCHAPTER IX.\n\nLAWS OF TRANSMISSION BY INHERITANCE. ADAPTATION AND NUTRITION.\n\n\n   Distinction between Conservative and Progressive\n   Transmission by Inheritance.\u2014Laws of Conservative\n   Transmission: Transmission of Inherited\n   Characters.\u2014Uninterrupted or Continuous\n   Transmission.\u2014Interrupted or Latent\n   Transmission.\u2014Alternation of\n   Generations.\u2014Relapse.\u2014Degeneracy.\u2014Sexual\n   Transmission.\u2014Secondary Sexual Characters.\u2014Mixed or\n   Amphigonous Transmission.\u2014Hybrids.\u2014Abridged or\n   Simplified Transmission.\u2014Laws of Progressive\n   Inheritance: Transmission of Acquired\n   Characters.\u2014Adapted or Acquired Transmission.\u2014Fixed or\n   Established Transmission.\u2014Homochronous Transmission\n   (Identity in Epoch).\u2014Homotopic Transmission (Identity in\n   Part).\u2014Adaptation and Mutability.\u2014Connection between\n   Adaptation and Nutrition.\u2014Distinction between Indirect\n   and Direct Adaptation.\n\n\nIn the last chapter we considered Transmission by Inheritance, one of\nthe two universal vital activities of organisms, Adaptation and\nInheritance, which by their interaction produce the different species of\norganisms, and we have endeavoured to trace this very mysterious vital\nactivity to a more general physiological function of organisms, namely,\nto Propagation. This latter in its turn, like other vital phenomena of\nanimals and plants, depends on physical and chemical relations. It is\ntrue they appear at times exceedingly complicated, but can nevertheless\nin reality be traced to simple mechanical causes\u2014that is, to the\nrelations of attraction and repulsion in the particles or molecules\u2014in\nfact, to the motional phenomena of matter.\n\nNow, before we turn our attention to the second function, the phenomenon\nof Adaptation or Mutability, which counteracts the Transmission by\nInheritance, it seems appropriate first to cast one more glance at the\nvarious manifestations of Heredity, which we may perhaps even now\ndenominate the \u201c_laws of transmission by inheritance._\u201d Unfortunately,\nup to the present time very little has been done for this most important\nsubject, either in zoology or in botany, and almost all we know of the\ndifferent laws of inheritance is confined to the experiences of\ngardeners and farmers. It is not therefore to be wondered at, that on\nthe whole these exceedingly interesting and important phenomena have not\nbeen investigated with desirable scientific accuracy, or reduced to the\nform of scientific laws. Accordingly, what I shall relate of the\ndifferent laws of transmission are only some preliminary fragments taken\nout of the infinitely rich store which lies open to our inquiry.\n\nWe may first divide all the different phenomena of inheritance into two\ngroups, which we may distinguish as the transmission of _inherited_\ncharacters, and the transmission of _acquired_ characters; and we may\ncall the former the _conservative_ transmission, and the latter the\n_progressive_ transmission by inheritance. This distinction depends upon\nthe exceedingly important fact that the individuals of every species of\nanimals and plants can transmit to their descendants, not only those\nqualities which they themselves have inherited from their ancestors, but\nalso the peculiar, individual qualities which they have acquired during\ntheir own life. The latter are transmitted by progressive, the former\nby conservative inheritance. We have now first to examine the phenomena\nof _conservative inheritance_, that is, the transmission of such\nqualities as the organism has already received from its parents or\nancestors. (Gen. Morph. ii. 180.)\n\nAmong the phenomena of conservative inheritance we are first struck by\nthat which is its most general law, and which we may term the _law of\nuninterrupted or continuous transmission_. It is so universal among the\nhigher animals and plants, that the uninitiated might overestimate its\naction and consider it as the only normal law of transmission by\ninheritance. This law simply consists in the fact that among most\nspecies of animals and plants, every generation is, on the whole, like\nthe preceding\u2014that the parents are as like the grandparents as they are\nlike the children. \u201cLike produces like,\u201d as is commonly said, but more\naccurately \u201csimilar things produce similar things.\u201d For, in reality, the\ndescendants of every organism are never absolutely equal in all points,\nbut only similar in a greater or less degree. This law is so generally\nknown, that I need not give any examples of it.\n\nThe _law of interrupted or latent transmission_ by inheritance, which\nmight also be termed alternating transmission, is in a measure opposed\nto the preceding law. This important law appears principally active\namong many lower animals and plants, and manifests itself in contrast to\nthe former in the fact that the offspring are not like their parents,\nbut very dissimilar, and that only the third or a later generation\nbecomes similar to the first. The grandchildren are like the\ngrandparents, but quite unlike the parents. This is a remarkable\nphenomenon, and, as is well known, occurs also very frequently, though\nin a less degree, in human families. Every one of my readers doubtless\nknows some members of a family who, in this or that peculiarity, much\nmore resemble the grandfather or grandmother than the father or mother.\nSometimes it lies in bodily peculiarities, for example, features of\nface, colour of hair, size of body\u2014sometimes in mental qualities, for\nexample, temperament, energy, understanding\u2014which are transmitted in\nthis manner. This fact may be observed in domestic animals as well as in\nthe case of man. Among the domestic animals most liable to vary\u2014as the\ndog, horse, and ox\u2014breeders very frequently find that the product by\nbreeding resembles the grandparents far more than it does its own\nparental organism. If we express this general law and the succession of\ngenerations by the letters of the alphabet, then A = C = E, whilst\nB = D = F, and so on.\n\nThis very remarkable fact appears in a more striking way in the lower\nanimals and plants than in the higher, and especially in the well-known\nphenomenon of _alternation of generations_ (metagenesis). Here we very\nfrequently find\u2014for example, among the Planarian worms, sea-squirts or\nTunicates, Zoophytes, and also among ferns and mosses\u2014that the organic\nindividual in the first place produces, by propagation, a form\ncompletely different from the parental form, and that only the\ndescendants of this generation, again, become like the first. This\nregular change of generation was discovered by the poet Chamisso, on his\nvoyage round the world in 1819, among the _Salp\u00e6_, cylindrical\ntunicates, transparent like glass, which float on the surface of the\nsea. Here the larger generation, the individuals of which live isolated\nand possess an eye of the form of a horse-shoe, produce in a non-sexual\nmanner (by the formation of buds) a completely different and smaller\ngeneration. The individuals of this second smaller generation live\nunited in chains and possess a cone-shaped eye. Every individual of such\na chain produces, in a sexual manner (hermaphrodite) again, a non-sexual\nsolitary form of the first and larger generation. Among the Salp\u00e6,\ntherefore, it is always the first, third, and fifth generation, and in\nlike manner the second, fourth, and sixth generations, that are entirely\nlike one another. However, it is not always only one, but in other cases\na number of generations, which are thus leapt over; so that the first\ngeneration resembles the fourth and seventh, the second resembles the\nfifth and eighth, the third resembles the sixth and ninth, and so on.\nThree different generations alternate with one another; for example,\namong the neat _little sea-buoys_ (Doliolum), small tunicates closely\nrelated to the Salp\u00e6. In this case it is A = D = G, further, B = E = H,\nand C = F = I. Among the plant-lice (Aphides), each sexual generation is\nfollowed by a succession of from eight to ten or twelve non-sexual\ngenerations, which are like one another, but differ from the sexual\ngenerations. Then, again, a sexual generation reappears like the one\nlong before vanished.\n\nIf we further follow this remarkable law of latent or interrupted\ninheritance, and take into consideration all the phenomena appertaining\nto it, we may comprise under it also the well-known phenomena of\n_reversion_. By the term \u201creversion\u201d or \u201catavism\u201d we understand the\nremarkable fact known to all breeders of animals, that occasionally\nsingle and individual animals assume a form which has not existed for\nmany generations, but belongs to a generation which has long since\ndisappeared. One of the most remarkable instances of this kind is the\nfact that in some horses there sometimes appear singular dark stripes,\nsimilar to those of the zebra, quagga, and other wild species of African\nhorses. Domestic horses of the most different races and of all colours\nsometimes show such dark stripes; for example, a stripe along the back,\na stripe across the shoulders, and the like. The sudden appearance of\nthese stripes can only be explained by the supposition that it is the\neffect of a latent transmission, a relapse into the ancient original\nform, which has long since vanished, and was once common to all species\nof horses; the original form, undoubtedly, was originally striped like\nthe zebras, quaggas, etc. In like manner, certain qualities in other\ndomestic animals sometimes appear quite suddenly, which once marked\ntheir wild ancestors, now long since extinct. In plants, also, such a\nrelapse can be observed very frequently. All my readers probably know\nthe wild yellow toad-flax (Linaria vulgaris), a plant very common in our\nfields and hedges. Its dragon-mouthed yellow flower contains two long\nand two short stamens. But sometimes there appears a single blossom\n(Peloria) which is funnel-shaped, and quite regularly composed of five\nindividual and equal sections, with five corresponding stamens. This\nPeloria can only be explained as a relapse into the long since extinct\nand very ancient common form of all those plants which, like the\ntoad-flax, possess dragon-mouthed, two-lipped flowers, with two long and\ntwo short stamens. The original form, like the Peloria, possessed a\nregular five-spurred blossom, with five equal stamens, which only later\nand by degrees have become unequal (compare p. 17). All such relapses\nare to be brought under the law of interrupted or latent transmission,\nalthough the number of intervening generations may be enormous.\n\nWhen cultivated plants or domestic animals become wild, when they are\nwithdrawn from the conditions of cultivated life, they experience\nchanges which appear not only as adaptations to their new mode of life,\nbut partially also as relapses into the ancient original form out of\nwhich the cultivated forms have been developed. Thus the different kinds\nof cabbage, which are exceedingly different in form, may be led back to\nthe original form, by allowing them to grow wild. In like manner, dogs,\nhorses, heifers, etc., when growing wild, often revert more or less to a\nlong extinct generation. An immensely long succession of generations may\npass away before this power of latent transmission becomes extinguished.\n\nA third law of conservative transmission may be called the _law of\nsexual transmission_, according to which each sex transmits to the\ndescendants of the same sex peculiarities which are not inherited by the\ndescendants of the other sex. The so-called secondary sexual characters,\nwhich in many respects are of extraordinary interest, everywhere furnish\nnumerous examples of this law. Subordinate or secondary sexual\ncharacters are those peculiarities of one of the two sexes which are not\ndirectly connected with the sexual organs themselves; such characters,\nwhich exclusively belong to the male sex, are, for example, the antlers\nof the stag, the mane of the lion, and the spur of the cock. The human\nbeard, an ornament commonly denied to the female sex, belongs to the\nsame class. Similar characteristics by which the female sex is alone\ndistinguished are, for example, the developed breasts, with the\nlactatory glands of female mammals and the pouch of the female opossum.\nThe bodily size, also, and complexion, differs in female animals of many\nspecies from that of the male. All these secondary sexual qualities,\nlike the sexual organs themselves, are transmitted by the male organism\nonly to the male, not to the female, and _vice vers\u00e2_. Contrary facts\nare rare exceptions to the rule.\n\nA fourth law of transmission, which has here to be mentioned, in a\ncertain sense contradicts the last, and limits it, viz., the _law of\nmixed or mutual_ (amphigonous) _transmission_. This law tells us that\nevery organic individual produced in a sexual way receives qualities\nfrom both parents, from the father as well as from the mother. This\nfact, that personal qualities of each of the two sexes are transmitted\nto both male and female descendants, is very important, Goethe mentions\nit of himself, in the beautiful lines\u2014\n\n  \u201cVon Vater hab ich die Statur, des Lebens ernstes F\u00fchren\n   Von M\u00fctterchen die Frohnatur und Lust zu fabuliren.\u201d\n\n  \u201cFrom my father I have my stature and the serious tenour of my life,\n   From my mother a joyous nature and a turn for poetizing.\u201d\n\nThis phenomenon, I suppose, is so well-known to all, that I need not\nhere enter upon it. It is according to the different portions of their\ncharacter which father and mother transmit to their children, that the\nindividual differences among brothers and sisters are chiefly\ndetermined.\n\nThe very important and interesting phenomenon of _hybridism_ also\nbelongs to this law of mixed or amphigonous transmission. It alone,\nwhen rightly estimated, is quite sufficient to refute the prevailing\ndogma of the constancy of species. Plants, as well as animals, belonging\nto quite different species, may sexually mingle with one another and\nproduce descendants which in many cases can again propagate themselves,\nand that indeed either (more frequently) by mingling with one of the two\nparental species, or (more rarely) by pure in-breeding, hybrid mixing\nwith hybrid. The latter is well established, for example, in the hybrids\nof hares and rabbits (Lepus Darwinii, p. 147). The hybrids of a horse\nand a donkey, two different species of the same genus (Equus), are well\nknown. These hybrids differ according as the father or the mother\nbelongs to the one or the other species\u2014the horse or the donkey. The\nmule produced by a mare and a he-donkey has qualities quite different\nfrom those of the jinny (Hinnus), the hybrid of a horse and she-donkey.\nIn both cases the hybrid produced by the crossing of two different\nspecies is a mixed form, which receives qualities from both parents; but\nthe qualities of the hybrid are different, according to the form of the\ncrossing. In like manner, mulattoes produced by a European and a negress\nshow a different mixture of characters from the hybrids produced by a\nnegro with a European female. In these phenomena of hybrid-breeding, as\nwell as in the other laws of transmission previously mentioned, we are\nas yet unable to show the acting causes in detail; but no naturalist\ndoubts the fact that the causes are in all cases purely mechanical and\ndependent upon the nature of organic matter itself. If we possessed more\ndelicate means of investigation than our rude organs of sense and\nauxilliary instruments, we should be able to discover those causes, and\nto trace them to the chemical and physical properties of matter.\n\nAmong the phenomena of conservative transmission, we must now mention,\nas the fifth law, the _law of abridged or simplified transmission_. This\nlaw is very important in regard to embryology or ontogeny, that is in\nregard to the history of the development of organic individuals.\n_Ontogeny_, or the history of the development of individuals, as I have\nalready mentioned in the first chapter (p. 10), and as I subsequently\nshall explain more minutely, is nothing but a short and quick repetition\nof _Phylogeny_ dependent on the laws of transmission and\nadaptation\u2014that is, a repetition of the pal\u00e6ontological history of\ndevelopment of the whole organic tribe, or phylum, to which the organism\nbelongs. If, for example, we follow the individual development of a man,\nan ape, or any other higher mammal within the maternal body from the\negg, we find that the f\u0153tus or embryo arising out of the egg passes\nthrough a series of very different forms, which on the whole agrees\nwith, or at least runs parallel to, a series of forms which is presented\nto us by the historical chain of ancestors of the higher mammals. Among\nthese ancestors we may mention certain fishes, amphibians, marsupials,\netc. But the parallelism or agreement of these two series of development\nis never quite complete; on the contrary, in ontogeny there are always\ngaps and leaps which indicate the omission of certain stages belonging\nto the phylogeny. Fritz M\u00fcller, in his excellent work, \u201cF\u00fcr Darwin,\u201d(16)\nhas clearly shown in the case of the Crustacea, or crabs, that \u201cthe\nhistorical record preserved in the individual history of development is\ngradually obscured, in proportion as development takes a more and more\ndirect route from the egg to the complete animal.\u201d This process of\nobscuring and shortening is determined by the law of abridged\ntransmission, and I mention it here specially because it is of great\nimportance for the understanding of embryology, and because it explains\nthe fact, at first so strange, that the whole series of forms which our\nancestors have passed through in their gradual development are no longer\nvisible in the series of forms of our own individual development from\nthe egg.\n\nOpposed to the laws of the conservative transmission, hitherto\ndiscussed, are the phenomena of the transmission of the second series,\nthat is, the _laws of progressive transmission by inheritance_. As\nalready mentioned, they depend upon the fact that the organism transmits\nto its descendants not only those qualities which it has inherited from\nits own ancestors, but also a number of those individual qualities which\nit has acquired during its own lifetime. Adaptation is here seen to be\nconnected with transmission by inheritance (Gen. Morph. ii. 186).\n\nAt the head of these important phenomena of progressive transmission, we\nmay mention the _law of adapted or acquired transmission_. In reality it\nasserts nothing more than what I have said above, that in certain\ncircumstances the organism is capable of transmitting to its descendants\nall the qualities which it has acquired during its own life by\nadaptation. This phenomenon, of course, shows itself most distinctly\nwhen the newly acquired peculiarity produces any considerable change in\nthe inherited form. This is the case in the examples I mentioned in the\npreceding chapter as to transmission in general, in the case of the men\nwith six fingers and toes, the porcupine men, copper beeches, weeping\nwillows, etc. The transmission of acquired diseases, such as\nconsumption, madness, and albinism, likewise form very striking\nexamples. Albinoes are those individuals who are distinguished by the\nabsence of colouring matter, or pigments, in the skin. They are of\nfrequent occurrence among men, animals, and plants. In the case of\nanimals of a definite dark colour, individuals are not unfrequently born\nwhich are entirely without colour, and in animals possessing eyes, this\nabsence of pigment extends even to the eyes, so that the iris of the\neye, which is commonly of a bright or intense colour, is colourless, but\nappears red, on account of the blood-vessels being seen through it.\nAmong many animals, such as rabbits and mice, albinoes with white fur\nand red eyes are so much liked that they are propagated in great numbers\nas a special race. This would be impossible were it not for the law of\nthe transmission of adaptations.\n\nWhich of the changes acquired by an organism are transmitted to its\ndescendants, and which are not, cannot be determined _\u00e0 priori_, and we\nare unfortunately not acquainted with the definite conditions under\nwhich the transmission takes place. We only know in a general way that\ncertain acquired qualities are much more easily transmitted than others,\nfor example, more easily than the mutilations caused by accidents. These\nlatter are generally not transmitted by inheritance, otherwise the\ndescendants of men who have lost their arms or legs would be born\nwithout the corresponding arm or leg; but here, also, exceptions occur,\nand a race of dogs without tails has been produced by consistently\ncutting off the tails of both sexes of the dog during several\ngenerations. A few years ago a case occurred on an estate near Jena, in\nwhich by a careless slamming of a stable door the tail of a bull was\nwrenched off, and the calves begotten by this bull were all born without\na tail. This is certainly an exception; but it is very important to note\nthe fact, that under certain unknown conditions such violent changes are\ntransmitted in the same manner as many diseases.\n\nIn very many cases the change which is transmitted and preserved by\nadapted transmission is constitutional or inborn, as in the case of\nalbinism mentioned before. The change then depends upon that form of\nadaptation which we call the indirect or potential. A very striking\ninstance is furnished by the hornless cattle of Paraguay, in South\nAmerica. A special race of oxen is there bred which is entirely without\nhorns. It is descended from a single bull, which was born in 1770 of an\nordinary pair of parents, and the absence of horns was the result of\nsome unknown cause. All the descendants of this bull produced with a\nhorned cow were entirely without horns. This quality was found\nadvantageous, and by propagating the hornless cattle among one another,\na hornless race was obtained, which at present has almost entirely\nsupplanted the horned cattle in Paraguay. The case of the otter-sheep of\nNorth America forms a similar example. In the year 1791 a farmer, by\nname Seth Wright, lived in Massachusetts, in North America; in his\nnormally formed flock of sheep a lamb was suddenly born with a\nsurprisingly long body and very short and crooked legs. It was therefore\nunable to take any great leaps, and especially unable to leap across a\nhedge into a neighbour\u2019s garden\u2014a quality which seemed advantageous to\nthe owner, as the territories were divided by hedges. It therefore\noccurred to him to transmit this quality to other sheep, and by\ncrossing this ram with normally shaped ewes, he produced a whole race\nof sheep, all of which had the qualities of the father, short and\ncrooked legs and a long body. None of them could leap across the hedges,\nand they therefore were much liked and propagated in Massachusetts.\n\nA second law, which likewise belongs to the series of progressive\ntransmissions, may be called the _law of established or habitual\ntransmission_. It manifests itself in this, that qualities acquired by\nan organism during its individual life are the more certainly\ntransmitted to its descendants the longer the causes of that change have\nbeen in action, and that this change becomes the more certainly the\nproperty of all subsequent generations the longer the cause of change\nacts upon these latter also. The quality newly acquired by adaptation or\nmutation must be established or constituted to a certain degree before\nwe can calculate with any probability that it will be transmitted at all\nto the descendants. In this respect transmission resembles adaptation.\nThe longer a newly acquired quality has been transmitted by inheritance,\nthe more certainly will it be preserved in future generations. If,\ntherefore, for example, a gardener by methodical treatment has produced\na new kind of apple, he may calculate with the greater certainty upon\npreserving the desired peculiarity of this sort the longer he has\ntransmitted the same by inheritance. The same is clearly shown in the\ntransmission of diseases. The longer consumption or madness has been\nhereditary in a family the deeper is the root of the evil, and the more\nprobable it is that all succeeding generations will suffer from it.\n\nWe may conclude the consideration of the phenomena of inheritance with\nthe two very important laws of _homotopic_ and _contemporaneous\ntransmission by inheritance_. We understand by them the fact that\nchanges acquired by an organism during its life, and transmitted to its\ndescendants, appear in the same part of the body in which the parental\norganism was first affected by them, and that they also appear in the\noffspring at the same age as that at which they did so in the parent.\n\n_The law of contemporaneous or homochronous transmission_, which Darwin\ncalls the law of \u201ctransmission in corresponding periods of life,\u201d can\nbe shown very clearly in the transmission of diseases, especially of\nsuch as are recognized as very destructive, on account of their\nhereditary character. They generally appear in the organism of the child\nat the time corresponding with that in which the parental organism\ncontracted the disease. Hereditary diseases of the lungs, liver, teeth,\nbrain, skin, etc., usually appear in the descendants at the same period,\nor a little earlier than they showed themselves in the parental\norganism, or were contracted by it. The calf gets its horns at the same\nperiod of life as its parents did. In like manner the young stag\nreceives its antlers at the same period of life in which they appeared\nin its father or grandfather. In every one of the different sorts of\nvine the grapes ripen at the same time as they did in the case of their\nprogenitors. It is well known that the time of ripening varies greatly\nin the different sorts; but as all are descended from a single species,\nthis variation has been acquired by the progenitors of the several\nsorts, and has then been transmitted by inheritance.\n\nThe _law of homotopic transmission_, which is most closely connected\nwith the last mentioned law, and which might be called the law of\ntransmission in corresponding parts of the body, may also be very\ndistinctly recognized in pathological cases of inheritance. Large moles,\nfor example, or accumulations of pigment in several parts of the skin,\ntumours also, often appear during many generations, not only at the same\nperiod of life, but also in the same part of the skin. Excessive\ndevelopment of fat in certain parts of the body is likewise transmitted\nby inheritance. Above all, it is to be noted that numerous examples of\nthis, as well as of the preceding law, may be found everywhere in the\nstudy of embryology. Both the _law of homochronous and homotopic\ntransmission are fundamental laws of embryology, or ontogeny_. For these\nlaws explain the remarkable fact that the different successive forms of\nindividual development in all generations of one and the same species\nalways appear in the same order of succession, and that the variations\nof the body always take place in the same parts. This apparently simple\nand self-evident phenomenon is nevertheless exceedingly wonderful and\ncurious; we cannot explain its real causes, but may confidently assert\nthat they are due to the direct transmission of the organic matter from\nthe parental organism to that of the offspring, as we have seen above in\nthe case of the process of transmission in general, by a consideration\nof the details of the various modes of reproduction.\n\nHaving thus, then, considered the most important laws of Inheritance, we\nnow turn to the second series of phenomena bearing on natural selection,\nviz., to those of Adaptation or Variation. These phenomena, taken as a\nwhole, stand in a certain opposition to the phenomena of Inheritance,\nand the difficulty which arises in examining them consists mainly in\nthe two sets of phenomena being so completely intercrossed and\ninterwoven. We are but seldom able to say with certainty\u2014of the\nvariations of form which occur before our eyes\u2014how much is owing to\nInheritance, and how much to Adaptation. All characters of form, by\nwhich organisms are distinguished, are caused _either_ by Inheritance or\nby Adaptation; but as both functions are continually interacting with\neach other, it is extremely difficult for the systematic inquirer to\nrecognize the share belonging to each of the two functions in the\nspecial structure of individual forms. This is, at present, all the more\ndifficult, because we are as yet scarcely aware of the immense\nimportance of this fact, and because most naturalists have neglected the\ntheory of Adaptation, as well as that of Inheritance. The laws of\nInheritance, which we have just discussed, as well as the laws of\nAdaptation, which we shall consider directly, in reality form only a\nsmall portion of the phenomena existing in this domain, but which have\nnot as yet been investigated; and since every one of these laws can\ninteract with every other, it is clear that there is an infinite\ncomplication of physiological actions, which are at work in the\nconstruction of organisms.\n\nBut now, as to the phenomenon of variation or adaptation in general, we\nmust, as in the case of inheritance, view it as a quite universal,\nphysiological fundamental quality of all organisms, without\nexception\u2014as a manifestation of life which cannot be separated from the\nidea of organism. Strictly speaking, we must here also, as in the case\nof inheritance, distinguish between Adaptation itself and Adaptability.\nBy Adaptation (Adaptio), or Variation (Variatio), we understand the fact\nthat the organism, in consequence of influences of the surrounding\nouter world, assumes certain new peculiarities in its vital activity,\ncomposition, and form which it has not inherited from its parents; these\nacquired individual qualities are opposed to those which have been\ninherited, or, in other words, those which have been transmitted to it\nfrom its parents or ancestors. On the other hand, we call Adaptability\n(Adaptabilitas), or Variability (Variabilitas), the capability inherent\nin all organisms to acquire such new qualities under the influence of\nthe outer world. (Gen. Morph. ii. 191.)\n\nThe undeniable fact of organic adaptation or variation is universally\nknown, and can be observed at every moment in thousands of phenomena\nsurrounding us. But just because the phenomena of variation by external\ninfluences appear so self-evident, they have hitherto undergone scarcely\nany accurate scientific investigation. To them belong all the phenomena\nwhich we look upon as the results of contracting and giving up habits,\nof practice and giving up practices, or as the results of training, of\neducation, of acclimatization, of gymnastics, etc. Many permanent\nvariations brought about by causes producing disease, that is to say,\nmany diseases, are nothing but dangerous adaptations of the organism to\ninjurious conditions of life. In the case of cultivated plants and\ndomestic animals, variation is so striking and powerful that the breeder\nof animals and the gardener found their whole mode of proceeding upon\nit, or rather upon the interaction between these phenomena and those of\nInheritance. It is also well known to every one that animals and plants,\nin their wild state, are subject to variation. Every systematic treatise\non a group of animals or plants, if it were to be quite complete and\nexhaustive, ought to mention in every individual species the number of\nvariations which differ more or less from the prevailing or typical form\nof the species. Indeed, in every careful systematic special treatise one\nfinds, in the case of most species, mention of a number of such\nvariations, which are described sometimes as individual deviations, and\nsometimes as so-called races, varieties, degenerate species, or\nsubordinate species, and which often differ exceedingly from the\noriginal species, solely in consequence of the adaptation of the\norganism to the external conditions of life.\n\nIf we now endeavour to fathom the general causes of these phenomena of\nAdaptation, we arrive at the conclusion that in reality they are as\nsimple as the causes of the phenomena of Inheritance. We have shown that\nthe nature of the process of propagation furnishes the real explanation\nof the facts of Transmission by Inheritance, that is, the transmission\nof parental matter to the body of the offspring; and in like manner we\ncan show that the physiological function of _nutrition_, or _change of\nsubstance_, affords a general explanation of Adaptation or Variation.\nWhen I here point to \u201cnutrition\u201d as the fundamental cause of variation\nand adaptation, I take this word in its widest sense, and I understand\nby it the whole of the material changes which the organism undergoes in\nall its parts through the influences of the surrounding outer world.\nNutrition thus comprises not only the reception of actual nutritive\nsubstances and the influence of different kinds of food, but also, for\nexample, the action upon the organism of water and of the atmosphere,\nthe influence of sunlight, of temperature, and of all those\nmeteorological phenomena which are implied in the term \u201cclimate.\u201d The\nindirect and direct influence of the nature of the soil and of the\ndwelling-place also belong to it; and further, the extremely important\nand varied influence which is exercised upon every animal and every\nplant by the surrounding organisms, friends and neighbours, enemies and\nrobbers, parasites, etc. All these and many other very important\ninfluences, all of which more or less modify the organism in its\nmaterial composition, must be taken into consideration in studying the\nchange of substance which goes on in living things. Adaptation,\naccordingly, is the consequence of all those material variations which\nare produced in the change of substance of the organism by the external\nconditions of existence, or by the influences of the surrounding\nexternal world.\n\nHow very much every organism is dependent upon the whole of its external\nsurroundings, and changed by their alteration, is, in a general way,\nwell known to every one. Only think how much the human power of action\nis dependent upon the temperature of the air, or how much the\ndisposition of our minds depends upon the colour of the sky. Accordingly\nas the sky is cloudless and sunny, or covered with large heavy clouds,\nour state of mind is cheerful or dull. How differently do we feel and\nthink in a forest during a stormy winter night and during a bright\nsummer day! All the different moods of our soul depend upon purely\nmaterial changes of our brain, upon movements of molecular plasma, which\nare started through the medium of the senses by the different influences\nof light, warmth, moisture, etc. \u201cWe are a plaything to every pressure\nof the air.\u201d No less important and deeply influential are the effects\nproduced upon our mind and body by the different quality and quantity\nof food. Our mental activity, the activity of our understanding and of\nour imagination, is quite different accordingly as we have taken tea or\ncoffee, wine or beer, before or during our work. Our moods, wishes, and\nfeelings are quite different when we are hungry and when we are\nsatisfied. The national character of Englishmen and Gauchos, in South\nAmerica, who live principally on meat and food rich in nitrogen, is\nwholly different from that of the Irish, feeding on potatoes, and that\nof the Chinese, living on rice, both of whom take food deficient in\nnitrogen. The latter also form much more fat than the former. Here, as\neverywhere, the variations of the mind go hand in hand with the\ncorresponding transformations of the body; both are produced by purely\nmaterial causes. But all other organisms, in the same way as man, are\nvaried and changed by the different influences of nutrition. It is well\nknown that we can change in an arbitrary way the form, size, colour,\netc., of our cultivated plants and domestic animals, by change of food;\nthat, for example, we can take from or give to a plant definite\nqualities, accordingly as we expose it to a greater or less degree of\nsunlight and moisture. As these phenomena are generally widely known,\nand as we shall proceed presently to the consideration of the different\nlaws of adaptation, we will not dwell here any longer on the general\nfacts of variation.\n\nAs the different laws of transmission may be naturally divided into the\ntwo series of conservative and progressive transmission, so we may also\ndistinguish between two series of the laws of adaptation, first, the\nseries of laws of _indirect_, and secondly, the series of laws of\n_direct_ adaptation. The latter may also be called the laws of actual,\nand the former the laws of potential, adaptation.\n\nThe first series, comprising the phenomena of _indirect_ (potential)\nadaptation, has, on the whole, hitherto been little attended to, and\nDarwin has the merit of having directed special attention to this series\nof changes. It is somewhat difficult to place this subject clearly\nbefore the reader; I will endeavour to make it clear hereafter by\nexamples. Speaking quite generally, indirect or potential adaptation\nconsists in the fact that certain changes in the organism, effected by\nthe influence of nutrition (in its widest sense) and of the external\nconditions of existence in general, show themselves not in the\nindividual form of the respective organism, but in that of its\ndescendants. Thus, especially in organisms propagating themselves in a\nsexual way, the reproductive system, or sexual apparatus, is often\ninfluenced by external causes (which little affect the rest of the\norganism), to such a degree that its descendants show a complete\nalteration of form. This can be seen very strikingly in artificially\nproduced monstrosities. Monstrosities can be produced by subjecting the\nparental organism to certain extraordinary conditions of life, and,\ncuriously enough, such an extraordinary condition of life does not\nproduce a change of the organism itself, but a change in its\ndescendants. This cannot be called transmission by inheritance, because\nit is not a quality existing in the parental organism that is\ntransmitted by inheritance. It is, on the contrary, a change affecting\nthe parental organism, but not perceptible in it, that appears in the\npeculiar formation of its descendants. It is only the impulse to this\nnew formation which is transmitted in propagation through the egg of the\nmother or the sperm of the father. The new formation exists in the\nparental organism only as a possibility (potential); in the descendants\nit becomes a reality (actual).\n\nAs this very important and very general phenomenon had hitherto been\nentirely neglected, people were inclined to consider all the visible\nvariations and transformations of organic forms as phenomena of\nadaptation of the second series, that is, as phenomena of _direct_ or\nactual adaptation. The essence of this latter kind of adaptation\nconsists in the fact that the change affecting the organism (through\nnutrition, etc.) shows itself immediately by some transformation, and\ndoes not only make itself apparent in the descendants. To this class\nbelong all the well-known phenomena in which we can directly trace the\ntransforming influence of climate, food, education, training, etc., in\ntheir effects upon the individual itself.\n\nWe have seen how the two series of phenomena of progressive and\nconservative transmission, in spite of their difference in principle, in\nmany ways interfere with and modify each other, and in many ways\nco-operate with and cross each other. The same is the case, in a still\nhigher degree, in the two series of phenomena of indirect and direct\nadaptation, which are opposed to each other and yet closely connected.\nSome naturalists, especially Darwin and Carl Vogt, ascribe to the\nindirect or potential adaptation by far the more important and almost\nexclusive influence. But the majority of naturalists have hitherto been\ninclined to take the opposite view, and to attribute the principal\ninfluence to direct or actual adaptation. I consider this controversy,\nin the mean while, as almost useless. It is but seldom that we are in a\ncondition, in any individual case of variation, to judge how much of it\nbelongs to direct and how much to indirect adaptation. We are, on the\nwhole, still too little acquainted with these exceedingly important and\nintricate relations, and can only assert, in a general way, that the\ntransformation of organic forms is to be ascribed _either_ to direct\nadaptation alone, _or_ to indirect adaptation alone, or lastly, to the\nco-operation of both direct _and_ indirect adaptation.\n\n\n\n\nCHAPTER X.\n\nLAWS OF ADAPTATION.\n\n\n   Laws of Indirect or Potential Adaptation.\u2014Individual\n   Adaptation.\u2014Monstrous or Sudden Adaptation.\u2014Sexual\n   Adaptation.\u2014Laws of Direct or Actual\n   Adaptation.\u2014Universal Adaptation.\u2014Cumulative\n   Adaptation.\u2014Cumulative Influence of External Conditions\n   of Existence and Cumulative Counter-Influence of the\n   Organism.\u2014Free Will.\u2014Use and Non-use of\n   Organs.\u2014Practice and Habit.\u2014Correlative\n   Adaptation.\u2014Correlation of Development.\u2014Correlation of\n   Organs.\u2014Explanation of Indirect or Potential Adaptation\n   by the Correlation of the Sexual Organs and of the other\n   parts of the Body.\u2014Divergent Adaptation.\u2014Unlimited or\n   Infinite Adaptation.\n\n\nIn the last chapter we reduced into two groups the phenomena of\nAdaptation or Variation, which, in connection and interaction with the\nphenomena of Heredity, produce all the endless variety of forms in\nanimals and plants\u2014first, the group of indirect or potential, and\nsecondly, the group of direct or actual Adaptation. We shall occupy\nourselves with a closer examination of the different laws which we can\ndiscover in these two groups of the phenomena of variation. Let us first\ntake into consideration the remarkable and very important, although\nhitherto much neglected, phenomena of indirect variation.\n\n_Indirect or potential adaptation_ manifests itself, it will be\nremembered, in the striking and exceedingly important fact that organic\nindividuals experience transformations and assume forms in consequence\nof changes of nutrition which have not operated on them themselves, but\nupon their parental organism. The transforming influence of the external\nconditions of existence, of climate, of nutrition, etc., shows its\neffects here not directly in the transformation of the organism itself,\nbut indirectly in that of its descendants. (Gen. Morph. ii. 202.)\n\nAs the principal and most universal of the laws of indirect variation\nmust be mentioned _the law of individual adaptation_, or the important\nproposition that all organic individuals from the commencement of their\nindividual existence are unequal, although often very much alike. As a\nproof of this proposition, I may at once point to the fact, that in the\nhuman race in general all brothers and sisters, all children of the same\nparents, are unequal from their birth. No one will venture to assert\nthat two children at their birth are perfectly alike; that the size of\nthe individual parts of their bodies, the number of hairs on their\nheads, the number of cells composing their outer skins or epidermis, the\nnumber of blood-cells are the same in both children, or that both\nchildren have come into the world with the same abilities or talents.\nBut what more specially proves this law of individual difference, is the\nfact that in the case of those animals which produce several young ones\nat a time,\u2014for instance, dogs and cats,\u2014all the young of each birth\ndiffer from one another more or less strikingly in size and colour of\nthe individual parts of the body, or in strength, etc. Now this law is\nuniversal. All organic individuals from their beginning are\ndistinguished by certain, though often extremely minute, differences,\nand the cause of these individual differences, though in detail usually\nutterly unknown to us, depends partly or entirely on certain influences\nwhich the organs of propagation in the parental organism have undergone.\n\nA second law of indirect adaptation, which we shall call _the law of\nmonstrous or sudden adaptation_, is of less importance and less general\nthan the law of individual adaptation. Here the divergences of the\nchild-organism from the parental form are so striking that, as a rule,\nwe may designate them as monstrosities. In many cases they are produced,\nas has been proved by experiments, by the parental organism having been\nsubject to a certain treatment, and placed under peculiar conditions of\nnutrition; for example, when air and light are withdrawn from it, or\nwhen other influences powerfully acting upon its nutrition are changed\nin a certain way. The new condition of existence causes a strong and\nstriking modification of form, not directly of the organism itself, but\nonly of that of its descendants. The mode of this influence in detail we\ncannot discover, and we can only in a very general way detect a causal\nconnection between the abnormal formation of the child and a certain\nchange in the conditions of existence of its parents exerting a special\ninfluence upon the organs of propagation in the latter. The previously\nmentioned phenomenon of albinism probably belongs to this group of\nabnormal or sudden variations, also the individual cases of human beings\nwith six fingers and toes, the case of the hornless cattle, as well as\nthose of sheep and goats with four or six horns. The abnormal deviation\nin all these cases probably owes its origin to a cause which at first\nonly affected the reproductive system of the parental organism, the egg\nof the mother or the sperm of the father.\n\nA third curious manifestation of indirect adaptation may be termed _the\nlaw of sexual adaptation_. Under this name we indicate the remarkable\nfact that certain influences, which act upon the male organs of\npropagation only, affect the structure of the male descendants, and in\nlike manner other influences, which act upon the female organs of\npropagation only, manifest their effect only in the change of structure\nof the female descendants. This remarkable phenomenon is still very\nobscure, and has not as yet been investigated, but is probably of great\nimportance in regard to the origin of \u201csecondary sexual\ncharacteristics,\u201d to which we have already made allusion.\n\nAll the phenomena of sexual, monstrous, and individual adaptation, which\nwe may comprise under the name of the laws of _indirect or potential\nadaptation_, are as yet very little known to us in their real nature and\nin their deeper causal connection. Only this much we can at present\nmaintain with certainty, that numerous and important transformations in\norganic forms owe their existence to this process. Many and striking\nvariations of form solely depend on causes which at first only affect\nthe nutrition of the parental organism, and specially its organs of\npropagation. Evidently the relations in which the sexual organs stand to\nother parts of the body are of the greatest importance. We shall have\nmore to say of these presently, when we speak of the law of correlative\nadaptation. How powerfully the variations in the conditions of life and\nnutrition affect the propagation of organisms is rendered obvious by the\nremarkable fact that numerous wild animals which we keep in our\nzoological gardens, and exotic plants which are grown in our botanical\ngardens, are no longer able to reproduce themselves. This is the case,\nfor example, with most birds of prey, parrots, and monkeys. The\nelephant, also, and the animals of prey of the bear genus, in captivity\nhardly ever produce young ones. In like manner many plants in a\ncultivated state become sterile. The two sexes may indeed unite, but no\nfructification, or no development of the fructified germ, takes place.\nFrom this it follows with certainty that the changed mode of nutrition\nin the cultivated state is able completely to destroy the capability of\nreproduction, and therefore to exercise the greatest influence upon the\nsexual organs. In like manner other adaptations or variations of\nnutrition in the parental organism may cause, not indeed a complete want\nof descendants, but still important changes in their form.\n\nMuch better known than the phenomena of indirect or potential adaptation\nare those of _direct or actual adaptation_, to the consideration of\nwhich we now turn our attention. To them belong all those changes of\norganisms which are generally considered to be the results of practice,\nhabit, training, education, etc.; also those changes of organic forms\nwhich are effected directly by the influence of nutrition, of climate,\nand other external conditions of existence. As has already been remarked\nin direct or actual adaptation, the transforming influence of the\nexternal cause affects the form of the organism itself, and does not\nonly manifest itself in that of the descendants. (Gen. Morph. ii. 207.)\n\nWe may place _the law of universal adaptation_ at the head of the\ndifferent laws of direct or actual adaptation, because it is the chief\nand most comprehensive among them. It may be briefly explained in the\nfollowing proposition: \u201cAll organic individuals become unequal to one\nanother in the course of their life by adaptation to different\nconditions of life, although the individuals of one and the same species\nremain mostly very much alike.\u201d A certain inequality of organic\nindividuals, as we have seen, was already to be assumed in virtue of the\nlaw of individual (indirect) adaptation. But, beyond this, the original\ninequality of individuals is afterwards increased by the fact that every\nindividual, during its own independent life, subjects and adapts itself\nto its own peculiar conditions of existence. All different individuals\nof every species, however like they may be in their first stages of\nlife, become in the further course of their existence less like to one\nanother. They deviate from one another in more or less important\npeculiarities, and this is a natural consequence of the different\nconditions under which the individuals live. There are no two single\nindividuals of any species which can complete their life under exactly\nthe same external circumstances. The vital conditions of nutrition, of\nmoisture, air, light; further, the vital conditions of society, the\ninter-relations with surrounding individuals of the same or other\nspecies, are different in every individual being; and this difference\nfirst affects the functions, and later changes the form of every\nindividual organism. If the children of a human family show, even at the\nbeginning, certain individual inequalities which we may consider as the\nconsequence of individual (indirect) adaptation, they will appear still\nmore different at a later period of life, when each child has passed\nthrough different experiences, and has adapted itself to different\nconditions of life. The original difference of the individual processes\nof development, evidently becomes greater the longer the life lasts and\nthe more various the external conditions which influence the separate\nindividuals. This may be demonstrated in the simplest manner in man, as\nwell as in domestic animals and cultivated plants, in which the vital\nconditions may be arbitrarily modified. Two brothers, of whom one is\nbrought up as a workman and the other as a priest, develop quite\ndifferently in body as well as in mind; in like manner, two dogs of one\nand the same birth, of which one is trained as a sporting dog and the\nother chained up as a watch dog. The same observation may also readily\nbe made as to organic individuals in a natural state. If, for instance,\none carefully compares all the trees in a fir or beech forest, which\nconsists of trees of a single species, one finds that among all the\nhundreds or thousands of trees, there are not two individual trees\ncompletely agreeing in size of trunk and other parts, in the number of\nbranches, leaves, etc. Everywhere we find individual inequalities which,\nin part at least, are merely the consequences of the different\nconditions of life under which the trees have developed. It is true we\ncan never say with certainty how much of this dissimilarity in all the\nindividuals of every species may have originally been caused by indirect\nindividual adaptation, and how much of it acquired under the influence\nof direct or universal adaptation.\n\nA second series of phenomena of direct adaptation, which we may comprise\nunder _the law of cumulative adaptation_, is no less important and\ngeneral than universal adaptation. Under this name I include a great\nnumber of very important phenomena, which are usually divided into two\nquite distinct groups. Naturalists, as a rule, have distinguished,\nfirst, those variations of organisms which are produced directly by the\npermanent influence of external conditions (by the constant action of\nnutrition, of climate, of surroundings, etc.), and secondly, those\nvariations which arise from habit and practice, from accustoming\nthemselves to definite conditions of life, and from the use and non-use\nof organs. The latter influences have been set forth especially by\nLamarck as important causes of the change of organic forms, while the\nformer have for a very long time been recognized as such more generally.\n\nThe sharp distinction usually made between these two groups of\ncumulative adaptation, and which even Darwin still maintains, disappears\nas soon as we reflect more accurately and deeply upon the real nature\nand causal foundation of these two, apparently very different, series of\nadaptations. We then arrive at the conviction that in both cases there\nare always two different active causes to be dealt with: on the one hand\nthe _external influence_ or _action_ of adaptative conditions of life,\nand on the other hand the _internal reaction of the organism_ which\nsubjects and adapts itself to that condition of life. If cumulative\nadaptation is considered from the first point of view alone, and the\ntransforming actions of the permanent external conditions of life are\ntraced to those conditions solely, then the principal stress is laid\nunduly upon the external factor, and the necessary internal reaction of\nthe organism is not taken into proper consideration. If, on the other\nhand, cumulative adaptation is unjustly regarded solely in relation to\nits second factor, and the transforming action of the organism itself,\nits reaction against the external influences, its change by practice,\nhabit, use, or non-use of organs, is put into the foreground, then we\nforget that this reaction is first called into play by the action of\nexternal conditions of existence. Hence it seems that the distinction\nmade between these two groups lies only in the different manner of\nviewing them, and I believe that they can, with full justice, be\nconsidered as one. The most essential fact in these phenomena of\ncumulative adaptation is that the change of the organism which manifests\nitself first in the functions, and at a later period in the form, is the\nresult either of long enduring, or of often repeated, influences of an\nexternal cause. The smallest cause, by cumulation of its action, can\nattain the greatest results.\n\nThere are innumerable examples of this kind of direct adaptation. In\nwhatever direction we may examine the life of animals and plants, we\ndiscover on all hands evident and undeniable changes of this kind. Let\nme first mention some of those phenomena of adaptation occasioned\ndirectly by nutrition itself. Every one knows that the domestic animals\nwhich are bred for certain purposes can be variously modified, according\nto the different quantity and quality of the food given to them. If a\nfarmer in breeding sheep wishes to produce fine wool, he gives them\ndifferent food from what he would give if he wished to obtain good flesh\nor an abundance of fat. Choice race and carriage horses receive better\nfood than dray and cart horses. Even the bodily form of man\u2014for\nexample, the amount of fat\u2014is quite different according to his\nnutrition. Food containing much nitrogen produces little fat, that\ncontaining little nitrogen produces a great deal of fat. People who, by\nmeans of Banting\u2019s system, at present so popular, wish to become thin\neat only meat and eggs\u2014no bread, no potatoes. The important variations\nthat can be produced among cultivated plants, solely by changing the\nquantity and quality of nourishment, are well known. The same plant\nacquires an altogether different appearance, according as it is placed\nin a dry and warm place, exposed to the sunlight or placed in a cool\ndamp spot in the shade. Many plants, if transferred to the sea shore,\nget in a short space of time thick, fleshy leaves, and the same plants\nplaced in a particularly dry and hot locality get thin hairy leaves. All\nthese variations arise directly from the cumulative influence of changed\nnutrition.\n\nBut it is not only the quantity and quality of the articles of nutrition\nwhich affect and powerfully change and transform the organism, but it is\naffected also by all the other external conditions of existence, above\nall by its nearest organic surroundings, the society of friendly or\nhostile organisms. One and the same kind of tree develops itself quite\ndifferently in an open locality, where it is free on all sides, and in a\nforest where it must adapt itself to its surroundings, where it is\npressed on all sides by its nearest neighbours, and is forced to shoot\nupwards. In the former case, the branches of the tree spread widely out;\nin the latter, the trunk extends upwards, and the top of the tree\nremains small and contracted. How powerfully all these circumstances,\nand how powerfully the hostile or friendly influence of surrounding\norganisms, of parasites, etc., affect every animal and every plant, is\nso well known, that it appears superfluous to quote further examples.\nThe change of form, or transformation which is thereby effected, is\nnever solely the direct result of the external influence, but must\nalways be traced to the corresponding reaction, and to the activity of\nthe organism itself, which consists in contracting a habit, or practice,\nand in the use or non-use of organs. The fact that these latter\nphenomena, as a rule, have been considered distinct from the former, is\nowing first to the one-sided manner of viewing them already mentioned,\nand secondly to the wrong notion which has been formed as to the nature\nand the influence of the activity of the will in animals.\n\nThe activity of the will, which is the organ of habit, of practice, of\nthe use or non-use of organs among animals, is, like every other\nactivity of the animal soul, dependent upon material processes in the\ncentral nervous system, upon peculiar motions which emanate from the\nalbuminous matter of the ganglion cells, and the nervous fibres\nconnected with them. The will, as well as the other mental activities,\nin higher animals, in this respect is different from that of men only in\nquantity, not in quality. The will of the animal, as well as that of\nman, is never free. The widely spread dogma of the freedom of the will\nis, from a scientific point of view, altogether untenable. Every\nphysiologist who scientifically investigates the activity of the will in\nman and animals, must of necessity arrive at the conviction that _in\nreality the will is never free_, but is always determined by external or\ninternal influences. These influences are for the most part ideas which\nhave been either formed by Adaptation or by Inheritance, and are\ntraceable to one or other of these two physiological functions. As soon\nas we strictly examine the action of our own will, without the\ntraditional prejudice about its freedom, we perceive that every\napparently free action of the will is the result of previous ideas,\nwhich are based on notions inherited or otherwise acquired, and are\ntherefore, in the end, dependent on the laws of Adaptation and\nInheritance. The same also applies to the action of the will in all\nanimals. As soon as their will is considered in connection with their\nmode of life, in its relation to the changes which the mode of life is\nsubject to from external conditions, we are at once convinced that no\nother view is possible. Hence the changes of the will which follow the\nchanges of nutrition, and which, in the form of practice, habit, etc.,\nproduce variations in structure, must be reckoned among the other\nmaterial processes of cumulative adaptation.\n\nWhilst an animal\u2019s will is adapting itself to changed conditions of\nexistence by the acquisition of new habits, practices, etc., it not\nunfrequently effects the most remarkable transformations of the organic\nform. Numerous instances of this may be found everywhere in animal life.\nThus, for example, many organs in domestic animals are suppressed, when\nin consequence of a changed mode of life they cease to act. Ducks and\nfowls in a wild state fly exceedingly well, but lose this facility more\nor less in a cultivated state. They accustom themselves to use their\nlegs more than their wings, and in consequence the muscles and skeleton\nused in flying are essentially changed in their development and form.\nDarwin has proved this by a very careful comparative measurement and\nweighing of the respective parts of the skeleton in the different races\nof domestic ducks, which are all descended from the wild duck (_Anas\nboschas_). The bones of the wings in tame ducks are weaker, the bones of\nthe legs, on the other hand, are more strongly developed than in wild\nducks. In ostriches and other running birds which have become completely\nunaccustomed to fly, the consequence is that their wings are entirely\ncrippled and degenerate into mere \u201crudimentary organs\u201d (p. 12). In many\ndomestic animals, especially in many races of dogs and rabbits, we find\nthat in the cultivated state they have acquired pendulous ears. This is\nsimply a consequence of a diminished use of the auricular muscles. In a\nwild state these animals have to exert their ears very much in order to\ndiscover an approaching foe, and this is accompanied by a strong\ndevelopment of the muscular apparatus, which keeps the outer ears in an\nupright position, and by which they can turn them in all directions. In\na domestic state the same animals no longer require to listen so\nattentively, they prick up or turn their ears only a little; the\nauricular muscles cease to be used, gradually become weakened, and the\nears hang down flabbily, or become rudimentary.\n\nAs in these cases the function, and consequently the form also, of the\norgan becomes degenerated through disuse, so, on the other hand, it\nbecomes more developed by greater use. This is particularly striking if\nwe compare the brain, and the mental activity belonging to it, in wild\nanimals and those domestic animals which are descended from them. The\ndog and horse, which are so vastly improved by cultivation, show an\nextraordinary degree of mental development, in comparison with their\nwild original ancestors, and evidently the change in the bulk of the\nbrain, which is connected with it, is mainly determined by persistent\nexercise. It is also well known how quickly and powerfully muscles grow\nand change their form by continual practice. Compare, for example, the\narms and legs of a trained gymnast with those of an immovable book-worm.\n\nHow powerfully external influences affect the habits of animals and\ntheir mode of life, and in this way still further change their forms, is\nvery strikingly shown in many cases among amphibious animals and\nreptiles. Our commonest indigenous snake, the ringed snake, lays eggs\nwhich require three weeks\u2019 time to develop. But when it is kept in\ncaptivity, and no sand is strewn in the cage, it does not lay its eggs,\nbut retains them until the young ones are developed. The difference\nbetween animals producing living offspring and those laying eggs is here\neffaced simply by the change of the ground upon which the animal lives.\n\nThe water-salamanders, or tritons, which have been artificially made to\nretain their original gills, are extremely interesting in this respect.\nThe tritons are amphibious animals, nearly akin to frogs, and possess,\nlike the latter, in their youth external organs of\nrespiration\u2014gills\u2014with which they, while living in water, breathe the\nair dissolved in the water. At a later date a metamorphosis takes place\nin tritons, as in frogs. They leave the water, lose their gills, and\naccustom themselves to breathe with their lungs. But if they are\nprevented from doing this by being kept shut up in a tank, they do not\nlose their gills. The gills remain, and the water salamander continues\nthrough life in that low stage of development, beyond which its lower\nrelations, the gilled salamanders, or Sozobranchiata, never pass. The\ngilled salamander attains its full size, its sexual development, and\nreproduces itself without losing its gills.\n\nGreat interest was caused a short time ago, among zoologists, by the\naxolotel (Siredon pisciformis), a gilled salamander from Mexico, nearly\nrelated to the triton; it had already been known for a long time, and\nbeen bred on a large scale in the zoological garden in Paris. This\nanimal possesses external gills, like the young salamander, but retains\nthem all its life, like all other Sozobranchiata. This gilled salamander\ngenerally remains in the water, with its aquatic organs of respiration,\nand also propagates itself there. But in the Paris garden, unexpectedly\nfrom among hundreds of these animals, a small number crept out of the\nwater on to the dry land, lost their gills, and changed themselves into\ngill-less salamanders, which are not to be distinguished from a\nNorth-American genus of tritons (Amblystoma), and breathe only through\nlungs. In this exceedingly curious case we can directly follow the great\nstride from water-breathing to air-breathing animals, a stride which can\nindeed be observed every spring in the individual history of development\nof frogs and salamanders. Just as every separate frog and every separate\nsalamander transforms itself from an amphibious animal breathing through\ngills, at a later period into one breathing through lungs, so the whole\ngroup of frogs and salamanders have arisen from animals breathing\nthrough gills, and akin to the Siredon. The Sozobranchiata have remained\nup to the present day in that low stage of development. Ontogeny here\nexplains phylogeny; the history of the development of individuals\nexplains that of the whole group (p. 10).\n\nTo the law of accumulative adaptation there closely follows a third law\nof direct or actual adaptation, _the law of correlative adaptation_.\nAccording to this important law, actual adaptation not only changes\nthose parts of the organism which are directly affected by its\ninfluence, but other parts also not directly affected by it. This is the\nconsequence of organic solidarity, and especially of the unity of the\nnutrition existing among all the parts of every organism. If, for\nexample, the hairiness of the leaves increases in a plant by its being\ntransferred to a dry locality, then this change reacts upon the\nnutrition of other parts, and it may result in a shortening of the parts\nof the stalk, and produce a more contracted form of the whole plant. In\nsome races of pigs and dogs\u2014for example, in the Turkish dog\u2014which by\nadaptation to a warmer climate have more or less lost their hair, the\nteeth also have degenerated. Whales and Endentata (armadillos), which by\ntheir curious skin-covering are removed from the other mammals, also\nshow the greatest deviations in the formation of their teeth. Further,\nthose races of domestic animals (oxen and pigs) which have acquired\nshort legs have, as a rule, also a short and compact head. Among other\nexamples, the races of pigeons which have the longest legs are also\ncharacterized by the longest beaks. The same correlation between the\nlength of the legs and beaks is universal in the order of stilted-birds\n(Grallatores), in storks, cranes, snipe, etc. The correlations which\nthus exist between different parts of the organism are most remarkable,\nbut their real cause is unknown to us. In general, we can of course say,\nthe changes of nutrition affecting an individual part must necessarily\nreact on the other parts, because the nutrition of every organism is a\nconnected, centralized activity. But why just this or that part should\nexhibit this or that particular correlation is in most cases quite\nunknown to us. We know a great number of such correlations in nutrition;\nthey are especially seen in those changes of animals and plants which\ngive rise to an absence of pigment (noticed previously)\u2014in albinoes.\nThe want of the usual colouring matter goes hand in hand with certain\nchanges in the formation of other parts; for example, of the muscular\nand osseous system, consequently of organic systems which are not at all\nultimately connected with the system of the outer skin. Very frequently\nalbinoes are more feebly developed, and consequently the whole structure\nof the body is more delicate and weak than in coloured animals of the\nsame species. The organs of the senses and nervous system are in like\nmanner curiously affected when there is this want of pigment. White cats\nwith blue eyes are nearly always deaf. White horses are distinguished\nfrom coloured horses by their special liability to form sarkomatous\ntumours. In man, also, the degree of the development of pigment in the\nouter skin greatly influences the susceptibility of the organism for\ncertain diseases; so that, for instance, Europeans with a dark\ncomplexion, black hair, and brown eyes become more easily acclimatized\nto tropical countries, and are less subject to the diseases there\nprevalent (inflammation of the liver, yellow fever, etc.) than Europeans\nof white complexion, fair hair, and blue eyes. (Compare above, p. 150.)\n\nAmong these correlations in the formation of different organs, those are\nspecially remarkable which exist between the sexual organs and other\nparts of the body. No change of any part reacts so powerfully upon the\nother parts of the body as a certain treatment of the sexual organs.\nFarmers who wish to obtain an abundant formation of fat in pigs, sheep,\netc., remove the sexual organs by cutting them out (castration), and\nthis is indeed done to animals of both sexes. The result is an\nexcessive development of fat. The same is done to the singers in certain\nreligious corporations. These unfortunates are castrated in early youth,\nin order that they may retain their high boyish voices. In consequence\nof this mutilation of the genitals, the larynx remains in its youthful\nstage of development. The muscular tissues of the body remain at the\nsame time weakly developed, while below the skin an abundance of fat\naccumulates. But this mutilation also powerfully reacts upon the\ndevelopment of the nervous system, the energy of the will, etc., and it\nis well known that human castrates, or eunuchs, as well as castrated\nanimals, are utterly deficient in the special psychical character which\ndistinguishes the male sex. Man is a man, both in body and soul, solely\nthrough his male generative glands.\n\nThese most important and influential correlations between the sexual\norgans and the other parts of the body, especially the brain, are found\nequally in both sexes. This might be expected even _\u00e0 priori_, because\nin most animals the two kinds of organs develop themselves from the same\nfoundation, and at the beginning are not different. In man, as in the\nrest of the vertebrate animals, the male and female organs in the\noriginal state of the germ are entirely the same, and the differences of\nthe two sexes only gradually arise in the course of embryonic\ndevelopment (in man, in the ninth week of embryonic life), by one and\nthe same gland developing in the female as the ovary, and in the male as\nthe testicle. Every change of the female ovary, therefore, has a no less\nimportant reaction upon the whole female organism than every change of\nthe testicle has upon the male organism. Virchow has expressed the\nimportance of this correlation in his admirable essay on \u201cDas Weib und\ndie Zelle\u201d (\u201cWoman and the Cell\u201d), in the following words:\u2014\u201cWoman is\nwoman only by her sexual glands; all the peculiarities of her body and\nmind, of her nutrition and her nervous activity, the sweet delicacy and\nroundness of her limbs, the peculiar formation of the pelvis, the\ndevelopment of the breasts, the continuance of the high voice, that\nbeautiful ornament of hair on her head, with the scarcely perceptible\nsoft down on the rest of the skin\u2014then again, the depth of feeling, the\ntruth of her direct perceptions, her gentleness, devotion, and\nfidelity\u2014in short, all the feminine qualities which we admire and\nhonour in a true woman are but a dependence of the ovary. Take this\novary away, and the man-woman stands before us\u2014a loathly abortion.\u201d\n\nThe same close correlation between the sexual organs and the other parts\nof the body occurs among plants as generally as among animals. If one\nwishes to obtain an abundance of fruit from a garden plant, the growth\nof the leaves is curtailed by cutting off some of them. If, on the other\nhand, an ornamental plant with a luxuriance of large and beautiful\nleaves is desired, then the development of the blossoms and fruit is\nprevented by cutting off the flower buds. In both cases one system of\norgans develops at the cost of the others. Thus, also, most variations\nin the formation of leaves in wild plants result in corresponding\ntransformations of the generative parts or blossoms. The great\nimportance of this \u201ccompensation of development,\u201d of this \u201ccorrelation\nof parts,\u201d has been already set forth by Goethe, by Geoffroy St.\nHilaire, and other nature-philosophers. It rests mainly upon the fact\nthat direct or actual adaptation cannot produce an important change in a\nsingle part of the body, without at the same time affecting the whole\norganism.\n\nThe correlative adaptation between the reproductive organs and the other\nparts of the body deserves a very special consideration, because it is,\nabove all others, likely to throw light upon the obscure and mysterious\nphenomena of indirect or potential adaptation, which have already been\nconsidered. For just as every change of the sexual organs powerfully\nreacts upon the rest of the body, so on the other hand every important\nchange in another part of the body must necessarily more or less react\non the sexual organs. This reaction, however, will only become\nperceptible in the formation of the offspring which arise out of the\nchanged generative parts. It is, in fact, precisely those remarkable and\nimperceptible changes of the genital system (in themselves utterly\ninsignificant changes)\u2014changes of the eggs and the sperm\u2014brought about\nby such correlations, which have the greatest influence upon the\nformation of the offspring, and all the phenomena of indirect or\npotential adaptation previously mentioned may in the end be traced to\ncorrelative adaptation.\n\nA further series of remarkable examples of correlative adaptation is\nfurnished by the different animals and plants which become degenerated\nthrough parasitic life or parasitism. No other change in the mode of\nlife so much affects the shapes of organisms as the adoption of a\nparasitical life. Plants thereby lose their green leaves; as, for\ninstance, our native parasitical plants, Orobanche, Lathr\u00e6a, Monotropa.\nAnimals which originally have lived freely and independently, but\nafterwards adopt a parasitical mode of life on other animals or plants,\nin the first place cease to use their organs of motion and their organs\nof sense. The loss of this activity is succeeded by the loss of the\norgans themselves, and thus we find, for example, many crabs, or\ncrustacea, which in their youth possess a tolerably high degree of\norganization, viz., legs, antenn\u00e6, and eyes, in old age completely\ndegenerate, living as parasites, without eyes, without apparatus of\nmotion, and without antenn\u00e6. The lively, active form of youth, has\nbecome a shapeless, motionless lump. Only the most necessary organs of\nnutrition and propagation retain their activity; all the rest of the\nbody has degenerated. Evidently these complete transformations are, to a\nlarge extent, the direct consequences of cumulative adaption, of the\nnon-use and defective exercise of the organs, but a great portion of\nthem must certainly be attributed also to correlative adaptation.\n(Compare Plate X. and XI.)\n\nA seventh law of adaptation, the fourth in the group of direct\nadaptation, is _the law of divergent adaptation_. By this law we\nindicate the fact that parts originally formed alike have developed in\ndifferent ways under the influence of external conditions. This law of\nadaptation is extremely important for the explanation of the phenomenon\nof division of labour, or polymorphism. We can see this very easily in\nour own selves; for instance, in the activity of our two hands. We\nusually accustom our right hand to quite different work from that which\nwe give our left, and in consequence of the different occupation there\narises a different formation of the two hands. The right hand, which we\nuse much more than the left, shows a stronger development of the nerves,\nmuscles, and bones. The same applies to the whole arm. In most human\nbeings the bones and flesh of the right arm are, in consequence of their\nbeing more employed, stronger and heavier than those of the left arm.\nNow, as the special use of the right arm has been adopted and\ntransmitted by inheritance for thousands of years among Europeans, the\nstronger shape and size of the right arm have already become hereditary.\nP. Harting, an excellent Dutch naturalist, has shown by measuring and\nweighing newly-born children, that even in them the right arm is more\ndeveloped than the left.\n\nAccording to the same law of divergent adaptation, both eyes also\nfrequently develop differently. If, for example, a naturalist accustoms\nhimself always to use one eye for the microscope (it is better to use\nthe left), then that eye will acquire a power different from that of the\nother, and this division of labour is of great advantage. The one eye\nwill become more short-sighted, and better suited for seeing things near\nat hand; the other eye becomes, on the contrary, more long-sighted, more\nacute for looking at an object in the distance. If, on the other hand,\nthe naturalist alternately uses both eyes for the microscope, he will\nnot acquire the short-sightedness of the one eye and the compensatory\ndegree of long-sight in the other, which is attained by a wise\ndistribution of these different functions of sight between the two eyes.\nHere then again the function, that is the activity, of originally\nequally-formed organs can become divergent by habit; the function reacts\nagain upon the form of the organ, and thus we find, after a long\nduration of such an influence, a change in the more delicate parts and\nthe relative growth of the divergent organs, which in the end becomes\napparent even in their coarser outlines.\n\nDivergent adaptation can very easily be perceived among plants,\nespecially in creepers. Branches of one and the same creeping plant,\nwhich originally were formed alike, acquire a completely different form\nand extent, a completely different degree of curvature and diameter of\nspiral winding, according as they twine themselves round a thinner or a\nthicker bar. The divergent change of form of parts originally identical\nin form, which tending in different directions develop themselves under\ndifferent external conditions, can be distinctly demonstrated in many\nother examples. As this divergent adaptation interacts with progressive\ninheritance, it becomes the cause of a division of labour among the\ndifferent organs.\n\nAn eighth and last law of adaptation we may call _the law of unlimited\nor infinite adaptation_. By it we simply mean to express that we know of\nno limit to the variation of organic forms occasioned by the external\nconditions of existence. We can assert of no single part of an organism,\nthat it is no longer variable, or that if it were subjected to new\nexternal conditions it would not be changed by them. It has never yet\nbeen proved by experience that there is a limit to variation. If, for\nexample, an organ degenerates from non-use, this degeneration ends\nfinally in a complete disappearance of the organ, as is the case with\nthe eyes of many animals. On the other hand, we are able, by continual\npractice, habit, and the ever-increasing use of an organ, to bring it to\na degree of perfection which we should at the beginning have considered\nto be impossible. If we compare the uncivilized savages with civilized\nnations, we find among the former a development of the organs of\nsense\u2014sight, smell, and hearing\u2014such as civilized nations can hardly\nconceive of. On the other hand, the brain, that is mental activity,\namong more civilized nations is developed to a degree of which the wild\nsavages have no idea.\n\nThere appears indeed to be a limit given to the adaptability of every\norganism, by the \u201ctype\u201d of its tribe or phylum; that is, by the\nessential fundamental qualities of this tribe, which have been inherited\nfrom a common ancestor, and transmitted by conservative inheritance to\nall its descendants. Thus, for example, no vertebrate animal can acquire\nthe ventral nerve-chord of articulate animals, instead of the\ncharacteristic spinal marrow of the vertebrate animals. However, within\nthis hereditary primary form, within this inalienable type, the degree\nof adaptability is unlimited. The elasticity and fluidity of the organic\nform manifests itself, within the type, freely in all directions, and to\nan unlimited extent. But there are some animals, as, for example, the\nparasitically degenerate crabs and worms, which seem to pass even the\nlimit of type, and have forfeited all the essential characteristics of\ntheir tribe by an astonishing degree of degeneration. As to the\nadaptability of man, it is, as in all other animals, also unlimited, and\nsince it is manifested in him above all other animals, in the\nmodifications of the brain, there can be absolutely no limit to the\nknowledge which man in a further progress of mental cultivation may not\nbe able to exceed. The human mind, according to the law of unlimited\nadaptation, enjoys an infinite perspective of becoming ever more and\nmore perfect.\n\nThese remarks are sufficient to show the extent of the phenomena of\nAdaptation, and the great importance to be attached to them. The laws of\nAdaptation, or the facts of Variation caused by the influence of\nexternal conditions, are just as important as the laws of Inheritance.\nAll phenomena of Adaptation, in the end, can be traced to conditions of\nnutrition of the organism, in the same way as the phenomena of\nInheritance are referable to conditions of reproduction; but the latter,\nas well as the former, may further be traced to chemical and physical,\nthat is to mechanical, causes. According to Darwin\u2019s Theory of Selection\nthe new forms of organisms, the transformations which artificial\nselection produces in the state of cultivation, and which natural\nselection produces in the state of nature, arise solely by the\ninteraction of such causes.\n\n\n\n\nCHAPTER XI.\n\nNATURAL SELECTION BY THE STRUGGLE FOR EXISTENCE. DIVISION OF LABOUR AND\nPROGRESS.\n\n\n   Interaction of the Two Organic Formative Causes,\n   Inheritance and Adaptation.\u2014Natural and Artificial\n   Selection.\u2014Struggle for Existence, or Competition for\n   the Necessaries of Life.\u2014Disproportion between the\n   Number of Possible or Potential, and the Number of Real\n   or Actual Individuals.\u2014Complicated Correlations of all\n   Neighbouring Organisms.\u2014Mode of Action in Natural\n   Selection.\u2014Homochromic Selection as the Cause of\n   Sympathetic Colourings.\u2014Sexual Selection as the Cause of\n   the Secondary Sexual Characters.\u2014Law of Separation or\n   Division of Labour (Polymorphism, Differentiation,\n   Divergence of Characters).\u2014Transition of Varieties into\n   Species.\u2014Idea of Species.\u2014Hybridism.\u2014Law of Progress\n   or Perfectioning (Progressus, Teleosis).\n\n\nIn order to arrive at a right understanding of Darwinism, it is, above\nall, necessary that the two organic functions of _Inheritance and\nAdaptation_, which we spoke of in our last chapter, should be more\nclosely examined. If we do not, on the one hand, examine the purely\nmechanical nature of these two physiological activities, and the various\naction of their different laws, and if, on the other hand, we do not\nconsider how complicated the interaction of these different laws of\nInheritance and Adaptation must be, we shall not be able to understand\nhow these two functions, by themselves, have been able to produce all\nthe variety of animal and vegetable forms, which, in fact, they have.\nWe have, at least, hitherto been unable to discover any other formative\ncauses besides these two, and if we rightly understand the necessary and\ninfinitely complicated interaction of Inheritance and Adaptation, we do\nnot require to look for other unknown causes for the change of organic\nforms. These two fundamental causes are, as far as we can see,\ncompletely sufficient.\n\nEven long before Darwin had published his Theory of Selection, some\nnaturalists, and especially Goethe, had assumed the interaction of two\ndistinct formative tendencies\u2014a conservative or preserving, and a\nprogressive or changing formative tendency\u2014as the causes of the variety\nof organic forms. The former was called by Goethe the centripetal or\nspecifying tendency, the latter the centrifugal tendency, or the\ntendency to metamorphosis (p. 89). These two tendencies completely\ncorrespond with the two processes of Inheritance and Adaptation.\n_Inheritance_ is the _centripetal_ or _internal formative tendency_\nwhich strives to keep the organic form in its species, to form the\ndescendants like the parents, and always to produce identical things\nfrom generation to generation. _Adaptation_, on the other hand, which\ncounteracts inheritance, is the _centrifugal_ or _external formative\ntendency_, which constantly strives to change the organic forms through\nthe influence of the varying agencies of the outer world, to create new\nforms out of those existing, and entirely to destroy the constancy or\npermanency of species. Accordingly as Inheritance or Adaptation\npredominates in the struggle, the specific form either remains constant\nor changes into a new species. The degree of constancy of form in the\ndifferent species of animals and plants, which obtains at any moment,\nis simply the necessary result of the momentary predominance which\neither of these two formative powers (or physiological activities) has\nacquired over the other.\n\nIf we now return to the consideration of the process of selection or\nchoice, the outlines of which we have already examined, we shall be in a\nposition to see clearly and distinctly that both artificial and natural\nselection rest solely upon the interaction of these two formative\ntendencies. If we carefully watch the proceedings of an artificial\nselector\u2014a farmer or a gardener\u2014we find that only these two\nconstructive forces are used by him for the production of new forms. The\nwhole art of artificial selection rests solely upon a thoughtful and\nwise application of the laws of Inheritance and Adaptation, and upon\ntheir being applied and regulated in an artistic and systematic manner.\nHere the will of man constitutes the selecting force.\n\nThe case of natural selection is quite similar, for it also employs\nmerely these two organic constructive forces, these ingrained\nphysiological properties of Adaptation and Heredity, in order to produce\nthe different species. But the selecting principle or force, which in\n_artificial_ selection is represented by the conscious _will of man_\nacting for a definite purpose, consists in _natural_ selection of the\nunconscious _struggle for existence_ acting without a definite plan.\nWhat we mean by \u201cstruggle for existence\u201d has already been explained in\nthe seventh chapter. It is the recognition of this exceedingly important\nidentity which constitutes one of the greatest of Darwin\u2019s merits. But\nas this relation is very frequently imperfectly or falsely understood,\nit is necessary to examine it now more closely, and to illustrate by a\nfew examples the operation of the struggle for life, and the operation\nof natural selection _by means of_ the struggle for life (Gen. Morph.\nii. 231).\n\nWhen considering the struggle for life, we started from the fact that\nthe number of germs which all animals and plants produce is infinitely\ngreater than the number of individuals which actually come to life and\nremain alive for a longer or shorter time. Most organisms produce during\nlife thousands or millions of germs, from each of which, under\nfavourable circumstances, a new individual might arise. In most animals\nand plants these germs are eggs, that is cells, which for their\ndevelopment require sexual fructification. But among the Protista, the\nlowest organisms, which are neither animals nor plants, and which\npropagate themselves only in a non-sexual manner, the germ-cells, or\nspores, require no fructification. Now, in all cases the number of\nunsexual, as well as of sexual germs, is out of all proportion to the\nnumber of actually living individuals of every species.\n\nTaken as a whole, the number of living animals and plants on our earth\nremains always about the same. The number of places in the economy of\nnature is limited, and in most parts of the earth\u2019s surface these places\nare always approximately occupied. Certainly there occur everywhere and\nin every year fluctuations in the absolute and in the relative number of\nindividuals of all species. However, taken as a whole, these\nfluctuations are of little importance, and it is broadly the fact that\nthe total number of all individuals remains, on an average, almost\nconstant. There is a constant fluctuation, which depends on the fact\nthat in one year or another one or other series of animals and plants\npredominates, and that every year the struggle for life somewhat alters\ntheir relations.\n\nEvery single species of animals and plants would have densely peopled\nthe whole earth\u2019s surface in a short time, if it had not had to struggle\nagainst a number of enemies and hostile influences. Even Linn\u00e6us\ncalculated that if an annual plant only produced two seeds (and there is\nnot one which produces so few), it would have yielded in twenty years a\nmillion of individuals. Darwin has calculated of elephants, which of all\nanimals seem the slowest to increase, that in seven hundred and fifty\nyears the descendants of a single pair would amount to nineteen millions\nof individuals; this is supposing that every elephant, during its period\nof fertility (from the 30th to the 90th year), produced only three pairs\nof young ones, and survived itself to its hundredth year. In like manner\nthe increase of the number of human beings\u2014if calculated on the average\nproportion of births to population, and no hindrances to the natural\nincrease stood in the way\u2014would be such as to double the total in\ntwenty-five years. In every century the total number of men would have\nincreased sixteen-fold; whereas we know that the total number of human\nbeings increases but slowly, and that the increase of population is very\ndifferent in different countries. While European tribes spread over the\nwhole globe, other tribes or species of men every year draw nearer to\ntheir complete extinction. This is the case especially with the redskins\nof America, and with the copper-coloured natives of Australia. Even if\nthese races were to propagate more abundantly than the white Europeans,\nyet they would sooner or later succumb to the latter in the struggle for\nlife. But of all human individuals, as of all other organisms, by far\nthe majority perish at the earliest period of their lives. Of the\nimmense quantity of germs which every species produce, only very few\nactually succeed in developing, and of these few it is again only a very\nsmall portion which attain to the age in which they can reproduce\nthemselves (compare p. 161).\n\nFrom the disproportion between the immense excess of organic germs and\nthe small number of chosen individuals which are actually able to\ncontinue in existence beside one another, there follows of necessity\nthat universal struggle for life, that constant fight for existence,\nthat perpetual competition for the necessaries of life, of which I gave\na sketch in my seventh chapter. It is this struggle for life which\nbrings natural selection into play, which in its turn is made use of by\nthe interaction of the phenomena of Inheritance and Adaptation as a\nsifting agency, and which thus causes a continual change in all organic\nforms. In this struggle for acquiring the necessary conditions of\nexistence, those individuals will always overpower their rivals who\npossess any individual privilege, any advantageous quality, of which\ntheir fellow competitors are destitute. It is true we are able only in\nthe fewest cases (in those animals and plants best known to us) to form\nan approximate conception of the infinitely complicated interaction of\nthe numerous circumstances, all of which here come into combination.\nOnly think how infinitely varied and complicated are the relations of\nevery single human being to the rest of mankind, and in general, to the\nwhole of the surrounding outer world. But similar relations prevail also\namong all animals and plants which live together in one place. All\ninfluence one another actively or passively. Every animal and every\nplant struggles directly with a number of enemies, beasts of prey,\nparasitic animals, etc. Plants standing together struggle with one\nanother for the space of ground requisite for their roots, for the\nnecessary amount of light, air, moisture, etc. In like-manner, animals\nliving together struggle with one another for their food,\ndwelling-place, etc. In this most active and complicated struggle, any\npersonal superiority, however small, any individual advantage, may\npossibly decide the issue in favour of the one possessing it. This\nprivileged individual remains the victor in the struggle, and propagates\nitself, while its fellow-competitors perish before they succeed in\npropagating themselves. The personal advantage which gave it the victory\nis transmitted by inheritance to its descendants, and by a further\ndevelopment may become so strongly marked as to cause us to consider the\nlater generations as a new species.\n\nThe infinitely complicated correlations which exist between the\norganisms of every district, and which must be looked upon as the real\nconditions of the struggle for life, are mostly unknown to us, and are\nvery difficult to discover. We have hitherto been able to trace them\nonly to a certain point in individual cases, as in the example given by\nDarwin of the relations between cats and red clover in England. The red\nclover (_Trifolium pratense_), which in England is among the best fodder\nfor cattle, requires the visit of humming-bees in order to attain the\nformation of seeds. These insects, while sucking the honey from the\nbottom of the flower, bring the pollen in contact with the stigma, and\nthus cause the fructification of the flower, which never takes place\nwithout it. Darwin has shown by experiments, that red clover which is\nnot visited by humming-bees does not yield a single seed. The number of\nbees is determined by the number of their enemies, the most destructive\nof which are the field-mice. The more the field-mice predominate, the\nless the clover is fructified. The number of field-mice, again, is\ndependent upon the number of their enemies, principally cats. Hence in\nthe neighbourhood of villages and towns, where many cats are kept, there\nare plenty of bees. A great number of cats, therefore, is evidently of\ngreat advantage for the fructification of clover. This example may be\nfollowed still further, as has been done by Carl Vogt, if we consider\nthat cattle which feed on red clover are one of the most important\nfoundations of the wealth of England. Englishmen preserve their bodily\nand mental powers chiefly by making excellent meat\u2014roast beef and\nbeefsteak\u2014their principal food. The English owe the superiority of\ntheir brains and minds over those of other nations in a great measure to\ntheir excellent meat. But this is clearly indirectly dependent upon the\ncats, which pursue the mice. We may, with Huxley, even trace the chain\nof causes to those old maids who cherish and keep cats, and,\nconsequently, are of the greatest importance to the fructification of\nthe clover and to the prosperity of England. From this example we can\nsee that the further it is traced the wider is the circle of action and\nof correlation. We can with certainty maintain that there exist a great\nnumber of such correlations in every plant and in every animal, only we\nare not always able to point out and survey their concatenation as in\nthe last instance.\n\nAnother remarkable example of important correlations is the following,\ngiven by Darwin. In Paraguay, there are no wild oxen and horses, as in\nthe neighbouring parts of South America, both north and south of\nParaguay. This surprising circumstance is explained simply by the fact\nthat in that country a kind of small fly is very frequent, and is in the\nhabit of laying its eggs in the navel of newly-born calves and foals.\nThe newly-born animals die in consequence of this attack, and the small\ndeadly fly is therefore the cause of oxen and horses never becoming wild\nin that district. Supposing that this fly were destroyed by some\ninsect-eating bird, then these large mammals would grow wild in\nParaguay, as well as in the neighbouring parts of South America; and as\nthey would eat a quantity of certain species of plants, the whole flora,\nand, consequently again, the whole fauna of the country would become\nchanged. It is hardly necessary to state, that at the same time the\nwhole economy, and consequently the character, of the human population\nwould alter.\n\nThus the prosperity, nay, even the existence of whole populations can be\nindirectly determined by a single small animal or vegetable form in\nitself extremely insignificant. There are small coral islands whose\nhuman inhabitants live almost entirely upon the fruit of a species of\npalm. The fructification of this palm is principally effected by\ninsects, which carry the pollen from the male to the female palm trees.\nThe existence of these useful insects is endangered by insect-eating\nbirds, which in their turn are pursued by birds of prey. The birds of\nprey, however, often succumb to the attack of a small parasitical mite,\nwhich develops itself in millions in their feathers. This small,\ndangerous parasite, again, may be killed by parasitical moulds. Moulds,\nbirds of prey, and insects would in this case favour the prosperity of\nthe palm, and consequently of man; birds, mites, and insect-eating birds\nwould, on the other hand, endanger it.\n\nInteresting examples in relation to the change of correlations in the\nstruggle for life are furnished also by those isolated oceanic islands,\nuninhabited by man, on which at different times goats and pigs have been\nplaced by navigators. These animals become wild, and having no enemies,\nthey increase in number so excessively, that the rest of the animal and\nvegetable population suffer in consequence, and the island finally may\nbecome almost a waste, because there is insufficient food for the large\nmammals which increase too numerously. In some cases on an island thus\noverrun with goats and pigs, other navigators have let loose a couple of\ndogs, who enjoyed this superabundance of food, and they again increased\nso numerously, and made such havoc among the herds, that after several\nyears the dogs themselves lacked food, and they also almost died out.\nThe equilibrium of species continually changes in this manner in\nnature\u2019s economy, accordingly as one or another species increases at the\nexpense of the rest. In most cases the relations of different species of\nanimals and plants to one another are much too complicated for us to be\nable to follow them, and I leave it to the reader to picture to himself\nwhat an infinitely complicated machinery is at work in every part of the\nworld in consequence of this struggle. The impulses which started the\nstruggle, and which altered and modified it in different places, are in\nthe end seen to be the impulses of self-preservation\u2014in fact, the\ninstinct leading individuals to preserve themselves (the instinct of\nobtaining food), and the instinct leading them to preserve the species\n(instinct of propagation). It is these two fundamental instincts of\norganic self-preservation of which Schiller, the idealist (not Goethe,\nthe realist!) says:\n\n  \u201cMeanwhile, until philosophy\n   Sustains the structure of the world,\n   Her workings will be carried on\n   By hunger and by love.\u201d[4]\n\nIt is these two powerful fundamental instincts which, by their varying\nactivity, produce such extraordinary differences in species through the\nstruggle for life. They are the foundations of the phenomena of\nInheritance and Adaptation. We have, in fact, traced all phenomena of\nInheritance to propagation, all phenomena of Adaptation to nutrition, as\nthe two wider classes of material phenomena to which they belong.\n\nThe struggle for life in natural selection acts with as much selective\npower as does the will of man in artificial selection. The latter,\nhowever, acts according to a plan and consciously, the former without a\nplan and unconsciously. This important difference between artificial and\nnatural selection deserves especial consideration. For we learn by it to\nunderstand how _arrangements serving a purpose can be produced by\nmechanical causes acting without an object, as well as by causes acting\nfor an object_. The products of natural selection are arranged even more\nfor a purpose than the artificial products of man, and yet they owe\ntheir existence not to a creative power acting for a definite purpose,\nbut to a mechanical relation acting unconsciously and without a plan.\nIf we had not thoroughly considered the interaction of Inheritance and\nAdaptation under the influence of the struggle for life, we should not\nat first be inclined to expect such results from this natural process of\nselection as are, in fact, furnished by it. It may therefore be\nappropriate here to mention a few especially striking examples of the\nactivity of natural selection.\n\nLet us first take _Darwin\u2019s homochromic selection_ of animals, or the\nso-called \u201csympathetic selection of colours,\u201d into consideration.\nEarlier naturalists have remarked that numerous animals are of nearly\nthe same colour as their dwelling-place, or the surroundings in which\nthey permanently live. Thus, for example, plant-lice and many other\ninsects living on leaves are of a green colour. The inhabitants of the\ndeserts, the jerboa, or leaping mice, foxes of the desert, gazelles,\nlions, etc., are mostly of a yellow or yellowish-brown colour, like the\nsand of the desert. The polar animals, which live on the ice and snow,\nare white or grey, like ice and snow. Many of these animals change their\ncolour in summer and winter. In summer, when the snow partly vanishes,\nthe fur of these polar creatures becomes brownish-grey or blackish, like\nthe naked earth, while in winter it again becomes white. Butterflies and\ninsects which hover round the gay and bright flowers are like them in\ncolour. Now, Darwin explains this surprising circumstance quite simply\nby the fact that such colours as agree with the colour of the habitation\nare of the greatest use to the animals concerned. If these animals are\nanimals of prey, they will be able to approach the object of their\npursuit more safely and with less likelihood of observation, and, in\nlike manner, those animals which are pursued will be able to escape\nmore easily, if their colour is as little different as possible from\nthat of their surroundings. If therefore originally an animal species\nvaried so as to present cases of all colours, those individuals whose\ncolour most resembled the surroundings must have been most favoured in\nthe struggle for life. They remained more unobserved, maintained and\npropagated themselves, while those individuals or varieties differently\ncoloured died out.\n\nI have tried to explain, by the same sympathetic selection of colour,\nthe wonderful fact that the majority of pelagic animals\u2014that is, of\nthose which live on the surface of the open sea\u2014are bluish, or\ncompletely colourless and transparent, like glass and water itself. Such\ncolourless, glassy animals are met with in the most different classes.\nTo them belong, among fish, the Helmicthyid\u00e6, through whose crystalline\nbodies the words of a book can be read; among the molluscs, the finned\nsnails (Heteropods) and sea-butterflies, or whales-food (Pteropods);\namong worms, the Salp\u00e6, Alciope, and Sagitta; further, a great number of\npelagic crabs (Crustacea), and the greater part of the Medus\u00e6\nUmbrella-jellies, (Discomedus\u00e6); Comb-jellies, (Ctenophora). All of\nthese pelagic animals, which float on the surface of the ocean, are\ntransparent and colourless, like glass and like the water itself, while\ntheir nearest kin live at the bottom of the ocean, and are coloured and\nopaque like the inhabitants of the land. This remarkable fact, like the\nsympathetic colouring of the inhabitants of the earth, can be explained\nby natural selection. Among the ancestors of the pelagic glass-like\nanimals which showed a different degree of colourlessness and\ntransparency, those that were the most colourless and transparent must\nhave been most favoured in the active struggle for life which takes\nplace on the surface of the ocean. They were enabled to approach their\nprey the most easily unobserved, and were themselves least observed by\ntheir enemies. Hence they could preserve and propagate themselves more\neasily than their more coloured and opaque relatives; and finally, by\naccumulative adaptation and transmission by inheritance, through natural\nselection, in the course of many generations their bodies would attain\nthat degree of crystal-like transparency and colourlessness which we at\npresent admire in them. (Gen. Morph. ii. 242.)\n\nNo less interesting and instructive than homochromic selection is that\nspecies of natural selection which Darwin calls \u201c_sexual selection_,\u201d\nwhich explains the origin of the so-called \u201csecondary sexual\ncharacters.\u201d We have already mentioned these subordinate sexual\ncharacteristics, so instructive in many respects. They comprise those\npeculiarities of animals and plants which belong only to one of the two\nsexes, and which do not stand in any direct relation to the act of\npropagation itself (compare above, p. 244). Such secondary sexual\ncharacters occur in great variety among animals. We all know how\nstriking is the difference of the two sexes in size and colour in many\nbirds and butterflies. The male sex is generally the larger and more\nbeautiful. It often possesses special decorations or weapons; as for\nexample, the spur and comb of the cock, the antlers of the stag and\ndeer, etc. All these peculiarities of the two sexes have nothing\ndirectly to do with propagation itself, which is effected by the\n\u201cprimary sexual characters,\u201d or actual sexual organs.\n\nNow, the origin of these remarkable \u201csecondary sexual characters\u201d is\nexplained by Darwin simply by a choice or selection which takes place\nin the propagation of animals. In most animals the number of individuals\nof both sexes is unequal; either the number of the female or the number\nof the male individuals is greater, and, as a rule, when the season of\npropagation approaches, a struggle takes place between the rivals for\nthe possession of the animals of the other sex. It is well known with\nwhat vigour and vehemence this struggle is fought out among the higher\nanimals\u2014among mammals and birds\u2014especially among those of polygamous\nhabits. Among gallinaceous birds, where for one cock there are several\nhens, a severe struggle takes place between the competing cocks for as\nlarge a harem as possible. The same is the case with many ruminating\nanimals. Among stags and deer, for instance, at the period of rut,\ndeadly struggles take place between the males for the possession of the\nfemales. The secondary sexual character which here distinguishes the\nmales\u2014the antlers of stags and deer\u2014not possessed by the female, is,\naccording to Darwin, the consequence of that struggle. Here the motive\nand cause determining the struggle is not, as in the case of the\nstruggle for individual existence, self-preservation, but the\npreservation of the species\u2014propagation. There are numerous passive\nweapons of defence, as well as active weapons for attack. The lion\u2019s\nmane, not possessed by the female, is evidently such a weapon of\ndefence; it is an excellent means of protection against the bites which\nthe male lions try to inflict on each other\u2019s necks when fighting for\nthe females; consequently those males with the strongest manes have the\ngreatest advantage in the sexual struggle. The dewlap of the ox and the\ncomb of the cock are similar defensive weapons. Active weapons of\nattack, on the other hand, are the antlers of the stag, the tusks of\nthe boar, the spur of the cock, and the hugely developed pair of jaws in\nthe male stag-beetle; all are instruments employed by the males in the\nstruggle for the females, for annihilating or chasing away their rivals.\n\nIn the cases just mentioned, it is the bodily \u201cstruggle to the death\u201d\nwhich determines the origin of the secondary sexual characters. But,\nbesides these mortal struggles, there are other important competitions\nin sexual selection, which no less influence the structure of the\nrivals. These consist principally in the fact that the courting sex\ntries to please the other by external finery, by beauty of form, or by a\nmelodious voice. Darwin thinks that the beautiful voices of singing\nbirds have principally originated in this way. Many male birds carry on\na regular musical contest when they contend for the possession of the\nfemales. It is known of several singing birds, that in the breeding\nseason the males assemble in numbers round the females, and let their\nsongs resound before them, and that then the females choose the singers\nwho best please them for their mates. Among other songsters, individual\nmales pour out their songs in the loneliness of the forest in order to\nattract the females, and the latter follow the most attractive calls. A\nsimilar musical contest, though certainly less melodious, takes place\namong crickets and grasshoppers. The male cricket has on its belly two\ninstruments like drums, and produces with these the sharp chirping notes\nwhich the ancient Greeks curiously enough thought beautiful music. Male\ngrasshoppers, partly by using their hind-legs like the bow of a violin\nagainst their wing coverings, and partly by rubbing their wing coverings\ntogether, bring out tones which are, indeed, not melodious to us, but\nwhich please the female grasshoppers so much that they choose the male\nwho fiddles the best.\n\nAmong other insects and birds it is not song or, in fact, any musical\naccomplishment, but finery or beauty of the one sex which attracts the\nother. Thus we find that, among most gallinaceous birds, the cocks are\ndistinguished by combs on their heads, or by a beautiful tail, which\nthey can spread out like a fan; as for example, in the case of the\npeacock and turkey-cock. The magnificent tail of the bird of paradise is\nalso an exclusive ornament of the male sex. In like manner, among very\nmany other birds and very many insects, principally among butterflies,\nthe males are distinguished from the females by special colours or other\ndecorations. These are evidently the results of sexual selection. As the\nfemales do not possess these attractions and decorations, we must come\nto the conclusion that they have been acquired by degrees by the males\nin the competition for the females, which takes its origin in the\nselective discrimination of the females.\n\nWe may easily picture to ourselves, in detail, the application of this\ninteresting conclusion to the human community. Here, also, the same\ncauses have evidently influenced the development of the secondary sexual\ncharacters. The characteristics distinguishing the man, as well as those\ndistinguishing the woman, owe their origin, certainly for the most part,\nto the sexual selection of the other sex. In antiquity and in the Middle\nAges, especially in the romantic age of chivalry, it was the bodily\nstruggles to the death\u2014the tournaments and duels\u2014which determined the\nchoice of the bride; the strongest carried home the bride. In more\nrecent times, however, in our so-called \u201cpolished\u201d or \u201chighly\ncivilized\u201d society, competing rivals prefer to contend indirectly by\nmeans of musical accomplishments, instrumental performances and song, by\nbodily charms, natural beauty, or artificial decoration. But by far the\nmost important of these different forms of sexual selection in man is\nthat form which is the most exalted, namely, _psychical selection_, in\nwhich the mental excellencies of the one sex influence and determine the\nchoice of the other. The most highly intellectually developed types of\nmen have, throughout generations, when choosing a partner in life, been\nguided by her excellencies of soul, and have thus transmitted these\nqualities to their posterity, and they have in this way, more than by\nany other thing, helped to create the deep chasm which at present\nseparates civilized men from the rudest savages, and from our common\nanimal ancestors. In fact, both the part played by the prevalence of a\nhigher standard of sexual selection, and the part played by the due\ndivision of labour between the two sexes, is exceedingly important, and\nI believe that here we must seek for the most powerful causes which have\ndetermined the origin and the historical development of the races of\nman. (Gen. Morph. ii. 247.) As Darwin, in his exceedingly interesting\nwork, published in 1871, on \u201cThe Origin of Man and Sexual\nSelection,\u201d(48) has discussed this subject in the most masterly manner,\nand has illustrated it by most remarkable examples, I refer for further\ndetail to that work.\n\nBut now let us look again at two extremely important organic laws which\ncan be explained by the theory of selection, as necessary consequences\nof natural selection in the struggle for existence. I mean the law of\n_division of labour_, or _differentiation_, and the law of _progress_,\nor _perfecting_. When the phenomena due to these two laws first became\nknown, through observation of the historical development, the individual\ndevelopment, and the comparative anatomy of animals and plants,\nnaturalists were inclined to trace them to a direct creative influence.\nIt was supposed to be part of the plan of the Creator, acting for a\ndefinite purpose, in the course of time to develop the forms of animals\nand plants more and more variously, and to bring them more and more to a\nstate of perfection. We shall evidently make a great advance in the\nknowledge of nature if we reject this teleological and anthropomorphic\nconception, and if we can prove the two laws of Division of Labour and\nPerfecting to be the necessary consequences of natural selection in the\nstruggle for life.\n\nThe first great law which follows directly and of necessity from natural\nselection, is that of _separation_, or _differentiation_, which is\nfrequently called _division of labour_, or _polymorphism_, and which\nDarwin speaks of as _divergence of character_. (Gen. Morph. ii. 249.) We\nunderstand by it the general tendency of all organic individuals to\ndevelop themselves more and more diversely, and to deviate from the\ncommon primary type. The cause of this general inclination towards\ndifferentiation and the formation of heterogeneous forms from\nhomogeneous beginnings is, according to Darwin, simply to be traced to\nthe circumstance that the struggle for life between every two organisms\nrages all the more fiercely the nearer the relation in which they stand\nto one another, or the more nearly alike they are. This is an\nexceedingly important, and in reality an exceedingly simple relation,\nbut it is usually not duly considered.\n\nIt must be obvious to every one, that in a field of a certain size,\nbeside the corn-plants which have been sown, a great number of weeds\ncan exist, and, moreover, in places which could not have been occupied\nby corn-plants. The more dry and sterile places of the ground, in which\nno corn-plant would thrive, may still furnish sustenance to weeds of\ndifferent kinds; and such species and individuals of weeds will more\nreadily be able to exist in such conditions, in proportion as they are\nsuited to adapt themselves to the different parts of the ground. It is\nthe same with animals. It is evident that a much greater number of\nanimal individuals can live together in one and the same limited\ndistrict, if they are of various and different natures, than if they are\nall alike. There are trees (for example, the oak) on which a couple of\nhundred of different species of insects live together. Some feed on the\nfruits of the tree, others on the leaves, others again on the bark, the\nroot, etc. It would be quite impossible for an equal number of\nindividuals to live on this tree if all were of one species; if, for\nexample, all fed on the bark, or only upon the leaves. Exactly the same\nis the case in human society. In one and the same small town, only a\ncertain number of workmen can exist, even when they follow different\noccupations. The division of labour, which is of the greatest use to the\nwhole community, as well as to the individual workman, is a direct\nconsequence of the struggle for life, of natural selection; for this\nstruggle can be sustained more easily the more the activities, and\nhence, also, the forms of the different individuals deviate from one\nanother. The different function naturally produces its reaction in\nchanging the form, and the physiological division of labour necessarily\ndetermines the morphological differentiation, that is, the \u201cdivergence\nof character.\u201d(37)\n\nNow, I beg the reader again to remember that all species of animals and\nplants are variable, and possess the capability of adapting themselves\nto different places or to local relations. The varieties or races of\neach species, according to the laws of adaptation, deviate all the more\nfrom the original primary species, the greater the difference of the new\nconditions to which they adapt themselves. If we imagine these\nvarieties\u2014which have proceeded from a common primary form\u2014to be\ndisposed in the shape of a branching, radiating bunch, then those\nvarieties will be best able to exist side by side and propagate which\nare most distant from one another, which stand at the ends of the\nseries, or at the opposite sides of the bunch. Those forms, on the other\nhand, occupying a middle position\u2014presenting a state of\ntransition\u2014have the most difficult position in the struggle for life.\nThe necessaries of life differ most in the two extremes, in the\nvarieties most distant from one another, and consequently these will get\ninto the least serious conflict with one another in the general struggle\nfor life. But the intermediate forms, which have deviated less from the\noriginal primary form, require nearly the same necessaries of life as\nthe original form, and therefore, in competing for them, they will have\nto struggle most with, and be most seriously threatened by, its members.\nConsequently, when numerous varieties of a species live side by side on\nthe same spot of the earth, the extremes, or those forms deviating most\nfrom one another, can much more easily continue to exist beside one\nanother than the intermediate forms which have to struggle with each of\nthe different extremes. The intermediate forms will not be able to\nresist, for any length of time, the hostile influences which the extreme\nforms victoriously overcome. These alone maintain and propagate\nthemselves, and at length cease to be any longer connected with the\noriginal primary species through intermediate forms of transition. Thus\narise \u201cgood species\u201d out of varieties. Thus, then, the struggle for life\nnecessarily favours the general divergence of organic forms, that is,\nthe constant tendency of organisms to form new species. This fact does\nnot rest upon any mystic quality, or upon an unknown formative tendency,\nbut upon the interaction of Inheritance and Adaptation in the struggle\nfor life. As the intermediate forms, that is, the individuals in a state\nof transition, of the varieties of every species die out and become\nextinct, the process of divergence constantly goes further, and from the\nextremes forms develop which we distinguish as new species.\n\nAlthough all naturalists have been obliged to acknowledge the\nvariability and mutability of all species of animals and plants, yet\nmost of them have hitherto denied that the modification or\ntransformation of the organic form surpasses the original limit of the\ncharacters of the species. Our opponents cling to the\nproposition\u2014\u201cHowever far a species may exhibit deviations from its\nusual form in a collection of varieties, yet the varieties of it are\nnever so distinct from one another as two really good species.\u201d This\nassertion, which Darwin\u2019s opponents usually place at the head of their\narguments, is utterly untenable and unfounded. This will become quite\nclear as soon as we critically compare the various attempts to define\nthe idea of species. No naturalist can answer the question as to what is\nin reality a \u201cgenuine or good species\u201d (\u201cbona species\u201d); yet every\nsystematic naturalist uses this expression every day, and whole\nlibraries have been written on the question as to whether this or that\nobserved form is a species or a variety, whether it is a really good or\na bad species. The most general answer to this question used to be the\nfollowing: \u201cTo one species belong all those individuals which agree in\nall essential characteristics. Essential characteristics of species are\nthose which remain permanent or constant, and never become modified or\nvary.\u201d But as soon as a case occurred in which the characteristic\u2014which\nhad hitherto been considered essential\u2014did become modified, then it was\nsaid, \u201cThis characteristic is not essential to the species, for\nessential characteristics never vary.\u201d Those who argued thus evidently\nmoved in a circle, and the na\u00efvet\u00e9 with which this circular method of\ndefining species is laid down in thousands of books as an unassailable\ntruth, and is still constantly repeated, is truly astonishing.\n\nAll other attempts which have been made to arrive at a definite and\nlogical determination of the idea of organic \u201cspecies\u201d have, like the\nlast, been utterly futile, and led to no results. Considering the nature\nof the case, it cannot be otherwise. The idea of species is just as\ntruly a relative one and not absolute, as is the idea of variety, genus,\nfamily, order, class, etc. I have proved this in detail in the criticism\nof the idea of species in my \u201cGeneral Morphology\u201d (Gen. Morph. ii.\n323-364). I will waste no more time on this unsatisfactory discussion,\nand now only add a few words about the _relation of species to\nhybridism_. Formerly it was regarded as a dogma, that two good species\ncould never produce hybrids which could reproduce themselves as such.\nThose who thus dogmatized almost always appealed to the hybrids of a\nhorse and donkey, the mule and the hinny, which, truly enough, are\nseldom able to reproduce themselves. But the truth is that such\nunfruitful hybrids are rare examples, and in the majority of cases\nhybrids of two totally different species are fruitful and able to\nreproduce themselves. They can almost always fruitfully mix with one or\nother of the parent species, and sometimes also among themselves; and in\nthis way completely new forms can originate according to the laws of\n\u201cmixed transmission by inheritance.\u201d\n\nThus, in fact, _hybridism is a source of the origin of new species_,\ndistinct from the source we have hitherto considered\u2014natural selection.\nI have already spoken occasionally of these _hybrid species_ (species\nhybrid\u00e6), especially of the hare-rabbit (Lepus Darwinii), which has\narisen from the crossing of a male hare and a female rabbit; the\ngoat-sheep (Capra ovina), which has arisen from the pairing of a he-goat\nand ewe; also the different species of thistles (Cirsium), brambles\n(Rubus), etc. It is possible that many wild species have originated in\nthis way, as even Linn\u00e6us assumed. At all events, these hybrid species,\nwhich can maintain and propagate themselves as well as pure species,\nprove that hybridism cannot serve in any way to give an absolute\ndefinition to the idea of species.\n\nI have already mentioned (p. 47) that the many vain attempts to define\nthe idea of species theoretically have nothing whatever to do with the\npractical distinction of species. The extensive practical application of\nthe idea of species, as it is carried out in systematic zoology and\nbotany, is very instructive as furnishing an example of human folly.\nHitherto, by far the majority of zoologists and botanists, in\ndistinguishing and describing the different forms of animals and plants,\nhave endeavoured, above all things, to distinguish accurately kindred\nforms as so many \u201cgood species.\u201d However, it has been found scarcely\npossible, in any group, to make an accurate and consistent distinction\nof such \u201cgenuine or good species.\u201d There are no two zoologists, no two\nbotanists, who agree in all cases as to which of the nearly related\nforms of a genus are good species, and which are not. All authors have\ndifferent views about them. In the genus _Hieracium_, for example, one\nof the commonest genera of European plants, no less than 300 species\nhave been distinguished in Germany alone. The botanist Fries, however,\nonly admits 106, Koch only 52, as \u201cgood species,\u201d and others accept\nscarcely 20. The differences in the species of brambles (Rubus) are\nequally great. Where one botanist makes more than a hundred species, a\nsecond admits only about one half of that number, a third only five or\nsix, or even fewer species. The birds of Germany have long been very\naccurately known. Bechstein, in his careful \u201cNatural History of German\nBirds,\u201d has distinguished 367 species, L. Reichenbach 379, Meyer and\nWolff 406, and Brehm, a clergyman learned in ornithology, distinguishes\neven more than 900 different species.\n\nThus we see that here, and, in fact, in every other domain of systematic\nzoology and botany, the most arbitrary proceedings prevail, and, from\nthe nature of the case, must prevail. For it is quite impossible\naccurately to distinguish varieties and races from so-called \u201cgood\nspecies.\u201d _Varieties are commencing species._ The variability or\nadaptability of species, under the influence of the struggle for life,\nnecessitates the continual and progressive separation or differentiation\nof varieties, and the perpetual delimitation of new forms. Whenever\nthese are maintained throughout a number of generations by inheritance,\nwhilst the intermediate forms die out, they form independent \u201cnew\nspecies.\u201d The origin of new species by division of labour, or\nseparation, divergence, or differentiation of varieties, is therefore a\n_necessary consequence of natural selection_.(37)\n\nThe same kind of interest attaches to a second great law which we deduce\nfrom natural selection, and which is, indeed, closely connected with the\nlaw of Divergence, but in no way identical with it; namely, the law of\n_Progress_ (progressus), or _Perfecting_ (teleosis). (Gen. Morph. ii.\n257.) This great and important law, like the law of differentiation, had\nlong been empirically established by pal\u00e6ontological experience, before\nDarwin\u2019s Theory of Selection gave us the key to the explanation of its\ncause. The most distinguished pal\u00e6ontologists have pointed out the law\nof progress as the most general result of their investigations of fossil\norganisms. This has been specially done by Bronn, whose investigations\non the laws of construction(18) and the laws of the development(19) of\norganisms, although little heeded, are excellent, and deserve most\ncareful consideration. The general results of the law of differentiation\nand the law of progress, at which Bronn arrived by a purely mechanical\nhypothesis, and by exceedingly accurate, laborious, and careful\ninvestigations, are brilliant confirmations of the truth of these two\ngreat laws which we deduce as necessary inferences from the theory of\nselection.\n\nThe law of progress or of perfecting establishes the exceedingly\nimportant fact, on the ground of pal\u00e6ontological experience, that in\nsuccessive periods of this earth\u2019s history, a continual increase in the\nperfection of organic formations has taken place. Since that\ninconceivably remote period in which life on our planet began with the\nspontaneous generation of Monera, organisms of all groups, both\ncollectively as well as individually, have continually become more\nperfectly and highly developed. The steadily increasing variety of\nliving forms has always been accompanied by progress in organization.\nThe lower the strata of the earth in which the remains of extinct\nanimals and plants lie buried, that is, the older the strata are, the\nmore simple and imperfect are the forms which they contain. This applies\nto organisms collectively, as well as to every single large or small\ngroup of them, setting aside, of course, those exceptions which are due\nto the process of degeneration, which we shall discuss hereafter.\n\nAs a confirmation of this law I shall mention only the most important of\nall animal groups, the tribe of vertebrate animals. The oldest fossil\nremains of vertebrate animals known to us belong to the lowest class,\nthat of Fishes. Upon these there followed later more perfect Amphibious\nanimals, then Reptiles, and lastly, at a much later period, the most\nhighly organized classes of vertebrate animals, Birds and Mammals. Of\nthe latter only the lowest and most imperfect forms, without placenta,\nappeared at first, such as are the pouched animals (Marsupials), and\nafterwards, at a much later period, the more perfect mammals, with\nplacenta. Of these, also, at first only the lower kinds appeared, the\nhigher forms later; and not until the late tertiary period did man\ngradually develop out of these last.\n\nIf we follow the historical development of the vegetable kingdom we\nshall find the same law operative there. Of plants there existed at\nfirst only the lowest and most imperfect classes, the Alg\u00e6 or tangles.\nLater there followed the group of Ferns or Filicin\u00e6 (ferns, pole-reeds,\nscale-plants, etc.). But as yet there existed no flowering plants, or\nPhanerogama. These originated later with the Gymnosperms (firs and\ncycads), whose whole structure stands far below that of the other\nflowering plants (Angiosperms), and forms the transition from the group\nof fern-like plants to the Angiosperms. These latter developed at a\nstill later date, and among them there were at first only flowering\nplants without corolla (Monocotyledons and Monochlamyds); only later\nwere there flowering plants with a corolla (Dichlamyds). Finally, again,\namong these the lower polypetalous plants preceded the higher\ngamopetalous plants. The whole series thus constitutes an irrefutable\nproof of the great law of progressive development.\n\nNow, if we ask what is the cause of this fact, we again, just as in the\ncase of differentiation, come back to natural selection in the struggle\nfor life. If once more we consider the whole process of natural\nselection, how it operates through the complicated interaction of the\ndifferent laws of Inheritance and Adaptation, we shall recognize not\nonly divergence of character, but also the perfecting of structure to be\nthe direct and necessary result of it. We can trace the same thing in\nthe history of the human race. Here, too, it is natural and necessary\nthat the progressive division of labour constantly furthers mankind, and\nurges every individual branch of human activity into new discoveries and\nimprovements. This progress itself universally depends on\ndifferentiation, and is consequently, like it, a direct result of\nnatural selection in the struggle for life.\n\n\n\n\nCHAPTER XII.\n\nLAWS OF DEVELOPMENT OF ORGANIC TRIBES AND OF INDIVIDUALS. PHYLOGENY AND\nONTOGENY.\n\n\n   Laws of the Development of Mankind: Differentiation and\n   Perfecting.\u2014Mechanical Cause of these two Fundamental\n   Laws.\u2014Progress without Differentiation, and\n   Differentiation without Progress.\u2014Origin of Rudimentary\n   Organs by Non-use and Discontinuance of\n   Habit.\u2014Ontogenesis, or Individual Development of\n   Organisms.\u2014Its General Importance.\u2014Ontogeny, or the\n   Individual History of Development of Vertebrate Animals,\n   including Man.\u2014The Fructification of the Egg.\u2014Formation\n   of the three Germ Layers.\u2014History of the Development of\n   the Central Nervous System, of the Extremities, of the\n   Branchial Arches, and of the Tail of Vertebrate\n   Animals.\u2014Causal Connection and Parallelism of\n   Ontogenesis and Phylogenesis, that is of the Development\n   of Individuals and Tribes.\u2014Causal Connection of the\n   Parallelism of Phylogenesis and of Systematic\n   Development.\u2014Parallelism of the three Organic Series of\n   Development.\n\n\nIf man wishes to understand his position in nature, and to comprehend as\nnatural facts his relations to the phenomena of the world cognisable by\nhim, it is absolutely necessary that he should compare human with\nextra-human phenomena, and, above all, with animal phenomena. We have\nalready seen that the exceedingly important physiological laws of\nInheritance and Adaptation apply to the human organism in the same\nmanner as to the animal and vegetable kingdoms, and in both cases\ninteract with one another. Consequently, natural selection in the\nstruggle for life acts so as to transform human society, just as it\nmodifies animals and plants, and in both cases constantly produces new\nforms. The comparison of the phenomena of human and animal\ntransformation is especially interesting in connection with the laws of\ndivergence and progress, the two fundamental laws which, at the end of\nthe last chapter, we proved to be direct and necessary consequences of\nnatural selection in the struggle for life.\n\nA comparative survey of the history of nations, or what is called\n\u201cuniversal history,\u201d will readily yield to us, as the first and most\ngeneral result, evidence of a continually _increasing variety_ of human\nactivities, both in the life of individuals and in that of families and\nstates. This differentiation or separation, this constantly increasing\ndivergence of human character and the form of human life, is caused by\nthe ever advancing and more complete division of labour among\nindividuals. While the most ancient and lowest stages of human\ncivilization show us throughout the same rude and simple conditions, we\nsee in every succeeding period of history, among different nations, a\ngreater variety of customs, practices, and institutions. The increasing\ndivision of labour necessitates an increasing variety of forms\ncorresponding to it. This is expressed even in the formation of the\nhuman face. Among the lowest tribes of nations, most of the individuals\nresemble one another so much that European travellers often cannot\ndistinguish them at all. With increasing civilization the physiognomy of\nindividuals becomes differentiated, and finally, among the most highly\ncivilized nations, the English and Germans, the divergence in the\ncharacters of the face is so great that we very rarely mistake one face\nfor another.\n\nThe second great fundamental law which is obvious in the history of\nnations is the great law of progress or perfecting. Taken as a whole,\nthe history of man is the history of his _progressive development_. It\nis true that everywhere and at all times we may notice individual\nretrogressions, or observe that crooked roads towards progress have been\ntaken, which lead only towards one-sided and external perfecting, and\nthus deviate more and more from the higher goal of internal and enduring\nperfecting. However, on the whole, the movement of development of all\nmankind is and remains a progressive one, inasmuch as man continually\nremoves himself further from his ape-like ancestors, and continually\napproaches nearer to his own ideal.\n\nNow, if we wish to know what causes actually determine these two great\nlaws of development in man, namely, the law of divergence and the law of\nprogress, we must compare them with the corresponding laws of\ndevelopment in animals, and on a close examination we shall inevitably\ncome to the conclusion that the phenomena, as well as their causes, are\nexactly the same in the two cases. The course of development in man,\njust as in that of animals, being directed by the two fundamental laws\nof differentiation and perfecting, is determined solely by purely\nmechanical causes, and is solely the necessary consequence of natural\nselection in the struggle for life.\n\nPerhaps in the preceding discussion the question has presented itself to\nsome\u2014\u201cAre not these two laws identical? Is not progress in all cases\nnecessarily connected with divergence?\u201d This question has often been\nanswered in the affirmative, and Carl Ernst B\u00e4r, for example, one of the\ngreatest investigators in the domain of the history of development, has\nset forth the following proposition as one of the principal laws in the\nontogenesis of the animal body:\u2014\u201cThe degree of development (or\nperfecting) depends on the stage of separation (or differentiation) of\nthe parts.\u201d(20) Correct as this proposition may be on the whole, yet it\nis not universally true. In many individual cases it can be proved that\ndivergence and progress by no means always coincide. _Every progress is\nnot a differentiation, and every differentiation is not a progress._\n\nNaturalists, guided by purely anatomical considerations, had already set\nforth the law relating to progress in organization, that the perfecting\nof an organism certainly depends, for the most part, upon the division\nof labour among the individual organs and parts of the body, but that\nthere are also other organic transformations which determine a progress\nin organization. One, in particular, which has been generally\nrecognized, is the _numerical diminution of identical parts_. If, for\nexample, we compare the lower articulated animals of the crustacean\ngroup, which possess numerous pairs of legs, with spiders which never\nhave more than four pairs of legs, and with insects which always possess\nonly three pairs of legs, we find this law, for which a great number of\nexamples could be adduced, confirmed. The numerical diminution of pairs\nof legs is a progress in the organization of articulated animals. In\nlike manner the numerical diminution of corresponding vertebral joints\nin the trunk of vertebrate animals is a progress in their organization.\nFishes and amphibious animals with a very large number of identical\nvertebral joints are, for this very reason, less perfect and lower than\nbirds and mammals, in which the vertebral joints, as a whole, are not\nonly very much more differentiated, but in which the number of\ncorresponding vertebr\u00e6 is also much smaller. Further, according to the\nsame law of numerical diminution, flowers with numerous stamens are more\nimperfect than the flowers of kindred plants with a smaller number of\nstamens, etc. If therefore originally a great number of homogeneous\nparts exist in an organic body, and if, in the course of very many\ngenerations, this number be gradually decreased, this transformation\nwill be an example of perfecting.\n\nAnother law of progress, which is quite independent of differentiation,\nnay, even appears to a certain extent opposed to it, is the law of\n_centralization_. In general the whole organism is the more perfect the\nmore it is organized as a unit, the more the parts are subordinate to\nthe whole, and the more the functions and their organs are centralized.\nThus, for example, the system of blood-vessels is most perfect where a\ncentralized heart exists. In like manner, the dense mass of marrow which\nforms the spinal cord of vertebrate animals, and the ventral cord of the\nhigher articulated animals, is more perfect than the decentralized chain\nof ganglia of the lower articulated animals, and the scattered system of\nganglia in the molluscs. Considering the difficulty of explaining these\ncomplicated laws of progress in detail, I cannot here enter upon a\ncloser discussion of them, and must refer to Bronn\u2019s excellent\n\u201cMorphologischen Studien,\u201d and to my \u201cGeneral Morphology\u201d (Gen. Morph.\ni. 370, 550; ii. 257-266).\n\nJust as we have become acquainted with phenomena of progress, quite\nindependent of divergence, so we shall, on the other hand, very often\nmeet with divergencies which are not perfecting, but which are rather\nthe contrary, that is retrogressions or degenerations. It is easy to see\nthat the changes which every species of animal and plant experiences\ncannot always be improvements. But rather many phenomena of\ndifferentiation, which are of direct advantage to the organism itself,\nare yet, in a wider sense, detrimental, inasmuch as they lessen its\ngeneral capabilities. Frequently a relapse to simpler conditions of life\ntakes place, and by adaptation to them a divergence in a retrograde\ndirection. If, for instance, organisms which have hitherto lived\nindependently accustom themselves to a parasitical life, they thereby\ndegenerate or retrograde. Such animals, which hitherto had possessed a\nwell-developed nervous system and quick organs of sense, as well as the\npower of moving freely, lose these when they accustom themselves to a\nparasitical mode of life; they consequently retrograde more or less.\nThere the differentiation viewed by itself is a degeneration, although\nit is advantageous to the parasitical organism. In the struggle for life\nsuch an animal, which has accustomed itself to live at the expense of\nothers, by retaining its eyes and apparatus of motion, which are of no\nmore use to it, would only expend so much material uselessly; and when\nit loses these organs, then a great quantity of nourishment which was\nemployed for the maintenance of these parts, benefits other parts. In\nthe struggle for life between the different parasites, therefore, those\nwhich make least pretensions will have advantage over the others, and\nthis favours their degeneration.\n\nJust as this is found to be the case with the whole organism, so it is\nalso with the parts of the body of an individual organism. A\ndifferentiation of parts, which leads to a partial degeneration, and\nfinally even to the loss of individual organs, is, when looked at by\nitself, a degeneration, but yet may be advantageous to the organism in\nthe struggle for life. It is easier to fight when useless baggage is\nthrown aside. Hence we meet everywhere, in the more highly-developed\nanimal and vegetable bodies, processes of divergence, the essence of\nwhich is that they cause the degeneration, and finally the loss, of\nparticular parts. And at this point the most important and instructive\nof all the series of phenomena bearing upon the history of organisms\npresents itself to us, namely, that of _rudimentary or degenerate\norgans_.\n\nIt will be remembered that even in my first chapter I considered this\nexceedingly remarkable series of phenomena, from a theoretical point of\nview, as one of the most important and most striking proofs of the truth\nof the doctrine of descent. We designated as rudimentary organs those\nparts of the body which are arranged for a definite purpose and yet are\nwithout function. Let me remind the reader of the eyes of those animals\nwhich live in the dark in caves and underground, and which consequently\nnever can use them. In these animals we find real eyes hidden under the\nskin, frequently developed exactly as are the eyes of animals which\nreally see; and yet these eyes never perform any function, indeed\ncannot, simply for the reason that they are covered by an opaque\nmembrane, and consequently no ray of light falls upon them (compare\nabove, p. 13). In the ancestors of these animals, which lived in open\ndaylight, the eyes were well developed, covered by a transparent horny\ncapsule (cornea), and actually served the purpose of seeing. But as the\nanimals gradually accustomed themselves to an underground mode of life,\nand withdrew from the daylight and no longer used their eyes, these\nbecame degenerated.\n\nVery clear examples of rudimentary organs, moreover, are the wings of\nanimals which cannot fly; for example, the wings of the running birds,\nlike the ostrich, emeu, cassowary, etc., the legs of which have become\nexceedingly developed. These birds having lost the habit of flying, have\nconsequently lost the use of their wings; however, the wings are still\nthere, although in a crippled form. We very frequently find such\ncrippled wings in the class of insects, most members of which can fly.\n\nFrom reasons derived from comparative anatomy and other circumstances,\nwe can with certainty draw the inference that all insects now living\n(all dragon-flies, grasshoppers, beetles, bees, bugs, flies,\nbutterflies, etc.) have originated from a single common parental form,\nfrom a primary insect which possessed two well-developed pairs of wings,\nand three pairs of legs. Yet there are very many insects in which either\none or both pairs of wings have become more or less degenerated, and\nmany in which they have even completely disappeared. For example, in the\nwhole order of flies, or Diptera, the hinder pair of wings\u2014in the\nbee-parasites, or Strepsiptera, on the other hand, the fore pair of\nwings\u2014have become degenerated or entirely disappeared. Moreover, in\nevery order of insects we find individual genera, or species, in which\nthe wings have more or less degenerated or disappeared. The latter is\nthe case especially in parasites. The females have frequently no wings,\nwhereas the males have; for instance, in the case of glow-worms\n(Lampyris), Strepsiptera, etc. This partial or complete degeneration of\nthe wings of insects has evidently arisen from natural selection in the\nstruggle for life. For we find insects without wings living under\ncircumstances where flying would be useless, or even decidedly injurious\nto them. If, for example, insects living on islands fly about much, it\nmay easily happen that when flying they are blown into the sea by the\nwind, and if (as is always the case) the power of flying is differently\ndeveloped in different individuals, then those which fly badly have an\nadvantage over those which fly well; they are less easily blown into the\nsea, and remain longer in life than the individuals of the same species\nwhich fly well. In the course of many generations, by the action of\nnatural selection, this circumstance must necessarily lead to a complete\nsuppression of the wings. If this conclusion had been arrived at on\npurely theoretical grounds, we might be pleased to find its truth\nestablished by facts. For upon isolated islands the proportion of\nwingless insects to those possessing wings is surprisingly large, much\nlarger than among the insects inhabiting continents. Thus, for example,\naccording to Wollaston, of the 550 species of beetles which inhabit the\nisland of Madeira, 220 are wingless, or possess such imperfect wings\nthat they can no longer fly; and of the 29 genera which belong to that\nisland exclusively, no less than 23 contain such species only. It is\nevident that this remarkable circumstance does not need to be explained\nby the special wisdom of the Creator, but is sufficiently accounted for\nby natural selection, because in this case the hereditary disuse of the\nwings, the discontinuance of flying in the presence of dangerous winds,\nhas been very advantageous in the struggle for life. In other wingless\ninsects the want of wings has been advantageous for other reasons.\nViewed by itself, the loss of wings is a degeneration, but in these\nspecial conditions of life it is advantageous to the organism in the\nstruggle for life.\n\nAmong other rudimentary organs I may here, by way of example, further\nmention the lungs of serpents and serpent-like lizards. All vertebrate\nanimals possessing lungs, such as amphibious animals, reptiles, birds,\nand mammals, have a pair of lungs, a right and a left one. But in cases\nwhere the body is exceedingly thin and elongated, as in serpents and\nserpent-like lizards, there is no room for the one lung by the side of\nthe other, and it is an evident advantage to the mechanism of\nrespiration if only one lung is developed. A single large lung here\naccomplishes more than two small ones side by side would do; and\nconsequently, in these animals, we invariably find only the right or\nonly the left lung fully developed. The other is completely aborted,\nalthough existing as a useless rudiment. In like manner, in all birds\nthe right ovary is aborted and without function; only the left one is\ndeveloped, and yields all the eggs.\n\nI mentioned in the first chapter that man also possesses such useless\nand superfluous rudimentary organs, and I specified as such the muscles\nwhich move the ears. Another of them is the rudiment of the tail which\nman possesses in his 3\u20145 tail vertebr\u00e6, and which, in the human embryo,\nstands out prominently during the first two months of its development\n(compare Plates II. and III.). It afterwards becomes completely hidden.\nThe rudimentary little tail of man is an irrefutable proof of the fact\nthat he is descended from tailed ancestors. In woman the tail is\ngenerally by one vertebra longer than in man. There still exist\nrudimentary muscles in the human tail which formerly moved it.\n\nAnother case of human rudimentary organs, only belonging to the male,\nand which obtains in like manner in all male mammals, is furnished by\nthe mammary glands on the breast, which, as a rule, are active only in\nthe female sex. However, cases of different mammals are known,\nespecially of men, sheep, and goats, in which the mammary glands were\nfully developed in the male sex, and yielded milk as food for their\noffspring. I have already mentioned before (p. 12) that the rudimentary\nauricular muscles in man can still be employed to move their ears, by\nsome persons who have perseveringly practised them. In fact, rudimentary\norgans are frequently very differently developed in different\nindividuals of the same species; in some they are tolerably large, in\nothers very small. This circumstance is very important for their\nexplanation, as is also the other circumstance that generally in\nembryos, or in a very early period of life, they are much larger and\nstronger in proportion to the rest of the body than they are in fully\ndeveloped and fully grown organisms. This can, in particular, be easily\npointed out in the rudimentary sexual organs of plants (stamens and\npistil), which I have already mentioned. They are proportionately much\nlarger in the young flower-bud than in the mature flower.\n\nI have remarked (p. 15) that rudimentary or suppressed organs were the\nstrongest supports of the monistic or mechanical conception of the\nuniverse. If its opponents, the dualists and teleologists, understood\nthe immense significance of rudimentary organs, it would put them into a\nstate of despair. Their ludicrous attempts to explain that rudimentary\norgans were given to organisms by the Creator \u201cfor the sake of\nsymmetry,\u201d or \u201cas a formal provision,\u201d or \u201cin consideration of his\ngeneral plan of creation,\u201d sufficiently prove the utter impotence of\ntheir perverse conception of the universe. I must here repeat that, even\nif we knew absolutely nothing of the other phenomena of development, we\nshould be obliged to believe in the truth of the Theory of Descent,\nsolely on the ground of the existence of rudimentary organs. Not one of\nits opponents has been able to throw even a feeble glimmer of an\nacceptable explanation upon these exceedingly remarkable and important\nphenomena. There is scarcely any highly developed animal or vegetable\nform which has not some rudimentary organs, and in most cases it can be\nshown that they are the products of natural selection, and that they\nhave become suppressed by disuse. It is the reverse of the process of\nformation in which new organs arise from adaptation to certain\nconditions of life, and by the use of parts as yet incompletely\ndeveloped. It is true our opponents usually maintain that the origin of\naltogether new parts is completely inexplicable by the Theory of\nDescent. However, I distinctly assert that to those who possess a\nknowledge of comparative anatomy and physiology this matter does not\npresent the slightest difficulty. Every one who is familiar with\ncomparative anatomy and the history of development will find as little\ndifficulty about the origin of completely new organs as about the utter\ndisappearance of rudimentary organs. The disappearance of the latter,\nviewed by itself, is the converse of the origin of the former. Both\nprocesses are particular phenomena of differentiation, which, like all\nothers, can be explained quite simply and mechanically by the action of\nnatural selection in the struggle for life.\n\nThe infinitely important study of rudimentary organs and their origin,\nthe comparison of their pal\u00e6ontological and embryological development,\nnow naturally leads us to the consideration of one of the most important\nand instructive of all biological phenomena, namely, the parallelism\nwhich the phenomena of progress and divergence present to us in three\ndifferent series. When, in the last chapter, we spoke of perfecting and\ndivision of labour, we understood by those words progress and\nseparation, and those changes effected by them, which in the long and\nslow course of the earth\u2019s history have led to a continual variation of\nthe flora and fauna, to the origin of new and to the disappearance of\nancient species of animals and plants. Now, if we follow the origin, the\ndevelopment, and the life of every single organic individual, we meet\nwith exactly the same phenomena of progress and differentiation. The\nindividual development, or the _ontogenesis_ of every single organism,\nfrom the egg to the complete form is nothing but a growth attended by a\nseries of diverging and progressive changes. This applies equally to\nanimals, plants, and protista. If, for example, we consider the ontogeny\nof any mammal, of man, of an ape, or of a pouched animal, or if we\nfollow the individual development of any other vertebrate animal of\nanother class, we everywhere find essentially the same phenomena. Every\none of these animals develops itself originally out of a single cell,\nthe egg. This cell increases by self-division, and forms a number of\ncells, and by the growth of this accumulation of cells, by the divergent\ndevelopment of originally identical cells, by the division of labour\namong them, and by their perfecting, there arises the perfect organism,\nthe complicated composition of which excites our admiration.\n\nIt seems to me here indispensable to draw attention more closely to\nthose infinitely important and interesting processes which accompany\n_ontogenesis, or the individual development of organisms_, and\nespecially to that of vertebrate animals, man included. I wish\nespecially to recommend these exceedingly remarkable and instructive\nphenomena to the reader\u2019s most careful consideration, first, because\nthey are among the strongest supports of the Theory of Descent, and\nsecondly, because, considering their immense general importance, they\nhave hitherto been properly considered only by a few privileged persons.\n\nWe cannot indeed but be astonished when we consider the deep ignorance\nwhich still prevails, in the widest circles, about the facts of the\nindividual development of man and organisms in general. These facts, the\nuniversal importance of which cannot be estimated too highly, were\nestablished, in their most important outlines, even more than a hundred\nyears ago, in 1759, by the great German naturalist Caspar Friedriech\nWolff, in his classical \u201cTheoria Generationis.\u201d But, just as Lamarck\u2019s\nTheory of Descent, founded in 1809, lay dormant for half a century, and\nwas only awakened to new and imperishable life in 1859, by Darwin, in\nlike manner Wolff\u2019s Theory of Epigenesis remained unknown for nearly\nhalf a century; and it was only after Oken, in 1806 had published his\nhistory of the development of the intestinal tube, and after Meckel, in\n1812, had translated Wolff\u2019s work (written in Latin) on the same subject\ninto German, that Wolff\u2019s theory of epigenesis became more generally\nknown, and formed the foundation of all subsequent investigations of the\nhistory of individual development. The study of ontogenesis now received\na great stimulus, and soon there appeared the classical investigations\nof the two friends, Christian Pander (1817) and Carl Ernst B\u00e4r (1819).\nB\u00e4r, in his remarkable \u201cEntwickelungsgeschichte der Thiere,\u201d(20) worked\nout the ontogeny of vertebrate animals in all its important facts. He\ncarried out a series of such excellent observations, and illustrated\nthem by such profound philosophical reflections, that his work became\nthe foundation for a thorough understanding of this important group of\nanimals, to which, of course, man also belongs. The facts of embryology\nalone would be sufficient to solve the question of man\u2019s position in\nnature, which is the highest of all problems. Look attentively at and\ncompare the eight figures which are represented on the adjoining Plates\nII. and III., and it will be seen that the philosophical importance of\nembryology cannot be too highly estimated.\n\nWe may well ask, What do our so-called \u201ceducated\u201d circles, who think so\nmuch of the high civilization of the 19th century, know of these most\nimportant biological facts, of these indispensable foundations for\nunderstanding their own organism? How much do our speculative\nphilosophers and theologians know about them, who fancy they can arrive\nat an understanding of the human organism by mere guesswork or divine\ninspiration? What indeed do the majority of naturalists, not excepting\nthe majority of the so-called \u201czoologists\u201d (including the\nentomologists!), know about them?\n\nThe answer to this question tells much to the shame of the persons above\nindicated, and we must confess, willingly or unwillingly, that these\ninvaluable facts of human ontogeny are, even at the present day, utterly\nunknown to most people, or are in no way valued as they deserve to be.\nIt is in the face of such a condition of things as this that we see\nclearly upon what a wrong and one-sided road the much vaunted culture of\nthe 19th century still moves. Ignorance and superstition are the\nfoundations upon which most men construct their conception of their own\norganism and its relation to the totality of things; and these palpable\nfacts of the history of development, which might throw the light of\ntruth upon them, are ignored. It is true these facts are not calculated\nto excite approval among those who assume a thorough difference between\nman and the rest of nature, and who will not acknowledge the animal\norigin of the human race. That origin must be a very unpleasant truth to\nmembers of the ruling and privileged castes in those nations among which\nthere exists an hereditary division of social classes, in consequence of\nfalse ideas about the laws of inheritance. It is well known that, even\nin our day, in many civilized countries the idea of hereditary grades of\nrank goes so far, that, for example, the aristocracy imagine themselves\nto be of a nature totally different from that of ordinary citizens, and\nnobles who commit a disgraceful offence are punished by being expelled\nfrom the caste of nobles, and thrust down among the pariahs of \u201cvulgar\ncitizens.\u201d What are these nobles to think of the noble blood which flows\nin their privileged veins, when they learn that all human embryos, those\nof nobles as well as commoners, during the first two months of\ndevelopment, are scarcely distinguishable from the tailed embryos of\ndogs and other mammals?\n\nAs the object of these pages is solely to further the general knowledge\nof natural truths, and to spread, in wider circles, a natural conception\nof the relations of man to the rest of nature, I shall be justified if I\ndo not pay any regard to the widely-spread prejudice in favour of an\nexceptional and privileged position for man in creation, and simply give\nhere the embryological facts from which the reader will be able to draw\nconclusions affirming the groundlessness of those prejudices. I wish all\nthe more to entreat him to reflect carefully upon these facts of\nontogeny, as it is my firm conviction that a general knowledge of them\ncan only promote the intellectual advance, and thereby the mental\nperfecting, of the human race.\n\nAmidst all the infinitely rich and interesting material which lies\nbefore us in the ontogeny of vertebrate animals, that is, in the history\nof their individual development, I shall here confine myself to showing\nsome of those facts which are of the greatest importance to the Theory\nof Descent in general, as well as in its special application to man. Man\nis at the beginning of his individual existence a simple egg, a single\nlittle cell, just the same as every animal organism which originates by\nsexual generation. The human egg is essentially the same as that of all\nother mammals, and cannot be distinguished from the egg of the higher\nmammals. The egg represented in Fig. 5 might be that of a man or an ape\nas well as of a dog, a horse, or any other mammal. Not only the form and\nstructure, but even the size of the egg in most mammals is the same as\nin man, namely, about the 120th part of an inch in diameter, so that the\negg under favorable circumstances, with the naked eye, can just be\nperceived as a small speck. The differences which really exist between\nthe eggs of different mammals and that of man do not consist in the\nform, but in the chemical mixture, in the molecular composition of the\nalbuminous combination of carbon, of which the egg essentially consists.\nThese minute individual differences of all eggs, which depend upon\nindirect or potential adaptation (and especially upon the law of\nindividual adaptation), are indeed not directly perceptible to the\nexceedingly imperfect senses of man, but are cognisable through indirect\nmeans, as the primary causes of the difference of all individuals.\n\n[Illustration: FIG. 5.\u2014The human egg a hundred times enlarged. _a._ The\nkernel speck, or nucleolus (the so-called germinal spot of the egg).\n_b._ Kernel, or nucleus (the so-called germinal vesicle of the egg).\n_c._ Cell-substance, or protoplasm (so-called yolk of the egg). _d._\nCell-membrane (the yolk-membrane of the egg; in mammals, on account of\nits transparency, called zona pellucida). The eggs of other mammals are\nof the same form.]\n\nThe human egg is, like that of all other mammals, a small globular\nbladder, which contains all the constituent parts of a simple organic\ncell (Fig. 5). The most essential parts of it are the mucous\ncell-substance, or the protoplasma (_c_), which in an egg is called the\n\u201cyolk,\u201d and the cell-kernel, or nucleus (_b_), surrounded by it, which\nis here called by the special name of the \u201cgerminal vesicle.\u201d The latter\nis a delicate, clear, glassy globule of albumen, of about 1-600th part\nof an inch in diameter, and surrounds, a still smaller, sharply-marked,\nrounded granule (_a_), the kernel-speck, or the nucleolus of the cell\n(in the egg it is called the \u201cgerminal spot\u201d). The outside of the\nglobular egg-cell of a mammal is surrounded by a thick pellucid\nmembrane, the cell-membrane or yolk-membrane, which here bears the\nspecial name of zona pellucida (_d_). The eggs of many lower animals\n(for example of many Medus\u00e6) differ from this in being _naked_ cells, as\nthe outer covering, or cell-membrane, is wanting.\n\nAs soon as the egg (ovulum) of the mammal has attained its full\nmaturity, it leaves the ovary of the female, in which it originates, and\npasses into the oviduct, and through this narrow passage into the wider\npouch or womb (uterus). If, meanwhile, the egg is fructified by the male\nseed (sperm), it develops itself in this pouch into an embryo, and does\nnot leave it until perfectly developed and capable of coming into the\nworld at birth as a young mammal.\n\nThe variations of form and transformations which the fructified egg must\ngo through within the uterus before it assumes the form of the mammal\nare exceedingly remarkable, and proceed from the beginning in man, in\nprecisely the same way as in the other mammals. At first the fructified\negg of the mammal acts as a single-celled organism, which is about to\npropagate independently and increase itself; for example, an Am\u0153ba\n(compare Fig. 2, p. 188). In point of fact the simple egg-cell becomes\ntwo, by the process of cell-division which I have previously described.\nThere arise from the single germinal spot (the small kernel-speck of the\noriginal simple egg-cell) two new kernel-specks, and then in like\nmanner, out of the germinal vesicle (the nucleus), two new cell-kernels.\nThen, and not until then, does the globular protoplasma first separate\nitself by an equatorial furrow into two halves, in such a manner that\neach half encloses one of the two kernels, together with its\nkernel-speck. Thus the simple egg-cell, within the original cellular\nmembrane, has become two naked cells, each possessing its own kernel\n(Fig. 6).\n\n[Illustration: FIG. 6.\u2014First commencement of the development of a\nmammal\u2019s egg, the so-called \u201cyolk-cleavage\u201d (propagation of the egg-cell\nby repeated self-division). _A._ The egg, by the formation of the first\nfurrow, falls into two cells. _B._ These by division fall into four\ncells. _C._ These latter have fallen into eight cells. _D._ By continued\ndivision a globular mass of numerous cells has arisen.]\n\nThe same process of cell-division now repeats itself several times in\nsuccession. In this way, from two cells (Fig. 6 _A_) there arise four\n(Fig. 6 _B_); from four, eight (Fig. 6 _C_); from eight, sixteen; from\nthese, thirty-two, etc. Each time the division of the kernel-speck\nprecedes that of the kernel; this, again, precedes that of the\ncell-substance, or protoplasma. As the division of the latter always\ncommences with the formation of a superficial annular _furrow_, or\ncleft, the whole process is usually called the _furrowing of the egg_,\nor yolk-cleavage, and the products of it, that is, the cells arising\nfrom the continued halving, are called the _cleavage spheres_. However,\nthe whole process is nothing more than a simple, oft-repeated _division\nof cells_, and the products of it are actual, naked _cells_. Finally,\nthrough the continued division or \u201cfurrowing\u201d of the mammal\u2019s egg there\narises a mulberry-shaped ball, which is composed of a great number of\nsmall spheres, naked cells, containing kernels (Fig. 6 _D_). These cells\nare the materials out of which the body of the young mammal is\nconstructed. Every one of us has once been such a simple mulberry-shaped\nball, composed only of small equi-formal cells.\n\nThe further development of the globular lump of cells, which now\nrepresents the young body of the mammal, consists first in its changing\ninto a globular bladder, as fluid accumulates within it. This bladder is\ncalled the germ-bladder (vesicula blastodermica). Its wall is at first\ncomposed of merely equi-formal cells. But soon, at one point on the\nwall, arises a disc-shaped thickening, as the cells here increase\nrapidly, and this thickening is now the foundation of the actual body of\nthe germ or embryo, while the other parts of the germ-bladder serve only\nfor its nutrition. The thickened disc, or foundation of the embryo, soon\nassumes an oblong, and then a fiddle-shaped form, in consequence of its\nright and left walls becoming convex (Fig. 7, p. 304). At this stage of\ndevelopment in the first form of their germ or embryo, not only all\nmammals, including man, but even all vertebrate animals in\ngeneral\u2014birds, reptiles, amphibious animals, and fishes\u2014can either not\nbe distinguished from one another at all, or only by very unessential\ndifferences, such as the arrangement of the egg-coverings. In all the\nwhole body consists of nothing but a quite simple, oblong, oval, or\nviolin-shaped thin disc, which is composed of three closely connected\nmembranes or plates, lying one above another. Each of the three plates\nor layers of the germ consists simply of cells all exactly like one\nanother; but each layer has a different function in the building up of\nthe vertebrate animal body. Out of the upper or outer germ-layer arises\nsolely the outer skin (epidermis), together with the central parts of\nthe nervous system (spinal marrow and brain); out of the lower or inner\nlayer arises only the inner delicate skin (epithelium) which lines the\nwhole intestinal tube from the mouth to the anus, together with all the\nglands connected with it (lung, liver, salivary glands, etc.); out of\nthe middle germ-layer lying between the two others arise all the other\norgans, muscles, bones, blood-vessels. Now, the processes by which the\nvarious and exceedingly complicated parts of the fully-formed body of\nvertebrate animals arise out of such simple material\u2014out of the three\ngerm-layers composed only of cells\u2014are, in the first place, the\nrepeated division, and consequently the increase of cells; in the second\nplace, the division of labour or differentiation of these cells; and\nthirdly, the union of the variously developed or differentiated cells,\nfor the formation of the different organs. Thus arises the gradual\nprogress or perfecting which can be traced step by step in the\ndevelopment of the embryonic body. The simple embryonic cells, which are\nto constitute the body of the vertebrate animal, stand in the same\nrelation to each other as citizens who wish to found a state. Some take\nto one occupation, others to another, and work together for the good of\nthe whole. By this division of labour, or differentiation, and the\nperfecting (the organic progress) which is connected with it, it becomes\npossible for the whole state to accomplish undertakings which would have\nbeen impossible to the single individual. The whole body of the\nvertebrate animal, like every other many-celled organism, is a\nrepublican state of cells, and consequently it can accomplish organic\nfunctions which the individual cell, as a solitary individual (for\nexample, an Am\u0153ba, or a single-celled plant), could never perform.\n\nNo sensible person supposes that carefully devised institutions, which\nhave been established for the good of the whole, as well as for the\nindividual, in every human state, are the results of the action of a\npersonal and supernatural Creator, acting for a definite purpose. On the\ncontrary, every one knows that these useful institutions of organization\nin the state are the consequences of the co-operation of the individual\ncitizens and their common government, as well as of adaptation to the\nconditions of existence of the outer world. Just in the same way we must\njudge of the many-celled organism. In it also all the useful\narrangements are solely the natural and necessary result of the\nco-operation, differentiation, and perfecting of the individual\ncitizens\u2014the cells\u2014and by no means the artificial arrangements of a\nCreator acting for a definite purpose. If we rightly consider this\ncomparison, and pursue it further, we can distinctly see the perversity\nof that dualistic conception of nature which discovers the action of a\ncreative plan of construction in the various adaptations of the\norganization of living things.\n\nLet us pursue the individual development of the vertebrate animal body a\nfew stages further, and see what is next done by the citizens of this\nembryonic organism. In the central line of the violin-shaped disc, which\nis composed of the three cellular germ-layers, there arises a straight\ndelicate furrow, the so-called \u201cprimitive streak,\u201d by which the\nviolin-shaped body is divided into two equal lateral halves\u2014a right and\na left part or \u201cantimer.\u201d On both sides of that streak or furrow, the\nupper or external germ-layer rises in the form of a longitudinal fold,\nand both folds then grow together over the furrow in the central line,\nand thus form a cylindrical tube. This tube is called the marrow-tube,\nor medullary canal, because it is the foundation of the central nervous\nsystem, the _spinal marrow_ (medulla spinalis). At first it is pointed\nboth in front and behind, and it remains so for life in the lowest\nvertebrate animal, the brainless, skull-less Lancelet (Amphioxus). But\nin all other vertebrate animals, which we distinguish from the latter as\nskulled animals, or Craniota, a difference between the fore and hinder\nend of the marrow tube soon becomes visible, the fore end becoming\ndilated, and changing into a roundish bladder, the foundation of the\n_brain_.\n\nIn all Craniota, that is, in all vertebrate animals possessing skull and\nbrain, the brain, which is at first only the bladder-shaped dilatation\nof the anterior end of the spinal marrow, divides into five bladders\nlying one behind the other, four superficial, transverse in-nippings\nbeing formed. These _five brain-bladders_, out of which afterwards arise\nall the different parts of the intricately constructed brain, can be\nseen in their original condition in the embryo represented in Fig. 7. It\nis just the same whether we examine the embryo of a dog, a fowl, a\nlizard, or any other higher vertebrate animal. For the embryos of the\ndifferent skulled animals (at least the three higher classes of them,\nthe reptiles, birds and mammals) cannot be in any way distinguished at\nthe stage represented in Fig. 7. The whole form of the body is as yet\nexceedingly simple, being merely a thin, leaf-like disc. Face, legs,\nintestines, etc., are as yet completely wanting. But the five bladders\nare already quite distinct from one another.\n\n[Illustration: FIG. 7.\u2014Embryo of a mammal or bird, in which the five\nbrain-bladders have just commenced to develop. _v._ Fore brain. _z._\nTwixt brain. _m._ Mid brain. _h._ Hind brain. _n._ After brain. _p._\nSpinal-marrow. _a._ Eye-bladders. _w._ Primitive vertebr\u00e6. _d._\nSpinal-axis or notochord.]\n\nThe _first_ bladder, the _fore brain_ (_a_), is in so far the most\nimportant that it principally forms the hemispheres of the so-called\nlarger brain (cerebrum), that part which is the seat of the higher\nmental activities. The more these activities are developed in the series\nof vertebrate animals, the more do the two lateral halves of the fore\nbrain, or the hemispheres, grow at the expense of the other bladders,\nand overlap them in front and from above. In man, where they are most\nstrongly developed, agreeing with his higher mental activity, they\neventually almost entirely cover the other parts from above (compare\nPlates II. and III.) The _second_ bladder, the _twixt brain_ (_z_),\nforms that portion of the brain which is called the _centre of sight_,\nand stands in the closest relation to the eyes (_a_), which grow right\nand left out of the fore brain in the shape of two bladders, and later\nlie at the bottom of the twixt brain. The _third_ bladder, the _mid\nbrain_ (_m_), for the most part vanishes in the formation of the\nso-called _four bulbs_, a bossy portion of the brain, which is strongly\ndeveloped in reptiles and birds (Fig. _E_, _F_, Plate II.), whereas in\nmammals it recedes much more (Fig. _G_, _H_, Plate III.). The _fourth_\nbladder, the _hind brain_ (_h_), forms the so-called _little\nhemispheres_, together with the middle part of the _small brain_\n(cerebellum), a part of the brain as to the function of which the most\ncontradictory conjectures are entertained, but which seems principally\nto regulate the co-ordination of movements. Lastly, the _fifth_ bladder,\nthe _after brain_ (_n_), develops into that very important part of the\ncentral nervous system which is called the _prolonged marrow_ (medulla\noblongata). It is the central organ of the respiratory movements, and of\nother important functions, and an injury to it immediately causes death,\nwhereas the large hemispheres of the fore brain (or the organ of the\n\u201csoul,\u201d in a restricted sense) can be removed bit by bit, and even\ncompletely destroyed, without causing the death of the vertebrate\nanimal\u2014only its higher mental activities disappearing in consequence.\n\nThese five brain bladders, in all vertebrate animals which possess a\nbrain at all, are originally arranged in the same manner and develop\ngradually in the different groups so differently, that it is afterwards\nvery difficult to recognize the corresponding parts in the\nfully-developed brains. In the early stage of development which is\nrepresented in Fig. 7, it seems as yet quite impossible to distinguish\nthe embryos of the different mammals, birds, and reptiles, from one\nanother. But if we compare the much more developed embryos on Plates II.\nand III. with one another, we can clearly see an inequality in their\ndevelopment, and especially it will be perceived that the brain of the\ntwo mammals (_G_ and _H_) already strongly differ from that of birds\n(_F_) and of reptiles (_E_). In the two latter the mid brain\npredominates, but in the former the fore brain. Even at this stage the\nbrain of the bird (_F_) is scarcely distinguishable from that of the\ntortoise (_E_), and in like manner the brain of the dog (_G_) is as yet\nalmost the same as that of man (_H_). If, on the other hand, we compare\nthe brains of these four vertebrate animals in a fully developed\ncondition, we find them so very different in all anatomical particulars,\nthat we cannot doubt for a moment as to which animal each brain belongs.\n\nI have here explained the original equality, the gradual commencement,\nand the ever increasing separation or differentiation of the embryos in\nthe different vertebrate animals, taking the brain as a special example,\njust because this organ of the soul\u2019s activity is of special interest.\nBut I might as well have discussed in its stead the heart, or the liver,\nor the limbs, in short, any other part of the body, since the same\nwonder of creation is here ever repeated, namely, this, that all parts\nare originally the same in the different vertebrate animals, and that\nthe variations by which the different classes, orders, families, genera,\netc., differ and deviate from one another, are only gradually developed.\n\nThere are certainly few parts of the body which are so differently\nconstructed as the _limbs or extremities_ of the vertebrate animals.\nNow, I wish the reader to compare in Fig. _A-H_ on Plates II. and III.,\nthe four extremities (_bv_) of the embryos with one another, and he will\nscarcely be able to perceive any important differences between the human\narm (_H bv_), the wing of a bird (_F bv_), the slim foreleg of a dog (_G\nbv_), and the plump foreleg of the tortoise (_E bv_). In comparing the\nhinder extremities (_bh_) in these figures he will find it equally\ndifficult to distinguish the leg of a man (_H bh_), of a bird (_F bh_),\nthe hind-leg of a dog (_G bh_), and that of a tortoise (_E bh_). The\nfore as well as the hinder extremities are as yet short, broad\nlumps, at the ends of which the foundations of the five toes are placed,\nconnected as yet by a membrane. At a still earlier stage (Fig. _A-D_)\nthe five toes are not marked out at all, and it is quite impossible to\ndistinguish even the fore and hinder extremities from one another. The\nlatter, as well as the former, are nothing but simple roundish\nprocesses, which have grown out of the side of the trunk. At the very\nearly stage represented in Fig. 7 they are completely wanting, and the\nwhole embryo is a simple trunk without a trace of limbs.\n\n[Illustration: Pl. II. Germs or Embryos of four Vertebrates.\n\n_v._ Fore-brain. _z._ Twixt-brain. _m._ Mid-brain. _h._ Hind-brain. _n._\nAfter-brain. _w._ Spine. _r._ Spinal-cord.]\n\n[Illustration: Pl. III. Germs or Embryos of four Vertebrates.\n\n_na._ Nose. _a._ Eyes. _o._ Ear. _k{1} k{2} k{3}._ Gill-arches.\n_s._ Tail. _bv._ Fore-leg. _bh._ Hind-leg.]\n\nI wish especially to draw attention in Plates II. and III., which\nrepresents embryos in early stages of development (Fig. _A-D_)\u2014and in\nwhich we are not able to recognize a trace of the full-grown animal\u2014to\nan exceedingly important formation, which originally is common to all\nvertebrate animals, but which at a later period is transformed into the\nmost different organs. Every one surely knows the _gill-arches_ of fish,\nthose arched bones which lie behind one another, to the number of three\nor four, on each side of the neck, and which support the gills, the\nrespiratory organs of the fish (double rows of red leaves, which are\npopularly called \u201cfishes\u2019 ears.\u201d) Now, these gill-arches originally\nexist exactly the same in man (_D_), in dogs (_C_), in fowls (_B_), and\nin tortoises (_A_), as well as in all other vertebrate animals. (In Fig.\n_A-D_ the three gill-arches of the right side of the neck are marked\n_k{1} k{2} k{3}_). Now, it is only in fishes that these remain in\ntheir original form, and develop into respiratory organs. In the other\nvertebrate animals they are partly employed in the formation of the face\n(especially the jaw apparatus), and partly in the formation of the organ\nof hearing.\n\nFinally, when comparing the embryos on Plates II. and III., we must not\nfail to give attention again to the _human tail_ (_s_), an organ which,\nin the original condition, man shares with all other vertebrate animals.\nThe discovery of tailed men was long anxiously expected by many monistic\nphilosophers, in order to establish a closer relationship between man\nand the other mammals. And in like manner their dualistic opponents\noften maintained with pride that the complete want of a tail formed one\nof the most important bodily distinctions between men and animals,\nthough they did not bear in mind the many tailless animals which really\nexist. Now, man in the first months of development possesses a real tail\nas well as his nearest kindred, the tailless apes (orang-outang,\nchimpanzee, gorilla), and vertebrate animals in general. But whereas, in\nmost of them\u2014for example, the dog (_C_, _G_)\u2014in the course of\ndevelopment it always grows longer, in man (Fig. _D_, _H_) and in\ntailless mammals, at a certain period of development, it degenerates and\nfinally completely disappears. However, even in fully developed men, the\nremnant of the tail is seen in the three, four, or five tail vertebr\u00e6\n(vertebr\u00e6 coccyge\u00e6) as an aborted or rudimentary organ, which forms the\nhinder or lower end of the vertebral column (p. 289).\n\nMost persons even now refuse to acknowledge the most important deduction\nof the Theory of Descent, that is, the pal\u00e6ontological development of\nman from ape-like, and through them from still lower, mammals, and\nconsider such a transformation of organic form as impossible. But, I\nask, are the phenomena of the individual development of man, the\nfundamental features of which I have here given, in any way less\nwonderful? Is it not in the highest degree remarkable that all\nvertebrate animals of the most different classes\u2014fishes, amphibious\nanimals, reptiles, birds, and mammals\u2014in the first periods of their\nembryonic development cannot be distinguished at all, and even much\nlater, at a time when reptiles and birds are already distinctly\ndifferent from mammals, that the dog and the man are almost identical?\nVerily, if we compare those two series of development with one another,\nand ask ourselves which of the two is the more wonderful, it must be\nconfessed that _ontogeny_, or the short and quick history of development\nof the _individual_, is much more mysterious than _phylogeny_, or the\nlong and slow history of development of the _tribe_. For one and the\nsame grand change of form is accomplished by the latter in the course of\nmany thousands of years, and by the former in the course of a few\nmonths. Evidently this most rapid and astonishing transformation of the\nindividual in ontogenesis, which we can actually point out at any moment\nby direct observation, is in itself much more wonderful and astonishing\nthan the corresponding, but much slower and gradual transformation which\nthe long chain of ancestors of the same individual has gone through in\nphylogenesis.\n\nThe two series of organic development, the ontogenesis of the individual\nand the phylogenesis of the tribe to which it belongs, stand in the\nclosest causal connection with each other. I have endeavoured, in the\nsecond volume of the \u201cGeneral Morphology,\u201d(4) to establish this theory\nin detail, as I consider it exceedingly important. As I have there\nshown, _ontogenesis, or the development of the individual, is a short\nand quick repetition_ (recapitulation) _of phylogenesis, or the\ndevelopment of the tribe to which it belongs, determined by the laws of\ninheritance and adaptation_; by tribe I mean the ancestors which form\nthe chain of progenitors of the individual concerned. (Gen. Morph. ii.\n110-147, 371.)\n\nIn this intimate connection of ontogeny and phylogeny, I see one of the\nmost important and irrefutable proofs of the Theory of Descent. No one\ncan explain these phenomena unless he has recourse to the laws of\nInheritance and Adaptation; by these alone are they explicable. These\nlaws, which we have previously explained, are _the laws of abbreviated,\nof homochronic, and of homotopic inheritance_, and here deserve renewed\nconsideration. As so high and complicated an organism as that of man, or\nthe organism of every other mammal, rises upwards from a simple cellular\nstate, and as it progresses in its differentiation and perfecting it\npasses through the same series of transformations which its animal\nprogenitors have passed through, during immense spaces of time,\ninconceivable ages ago. I have already pointed out this extremely\nimportant parallelism of the development of individuals and tribes (p.\n10). Certain very early and low stages in the development of man, and\nthe other vertebrate animals in general, correspond completely in many\npoints of structure with conditions which last for life in the lower\nfishes. The next phase which follows upon this presents us with a change\nof the fish-like being into a kind of amphibious animal. At a later\nperiod the mammal, with its special characteristics, develops out of the\namphibian, and we can clearly see, in the successive stages of its later\ndevelopment, a series of steps of progressive transformation which\nevidently correspond with the differences of different mammalian orders\nand families. Now, it is precisely in the same succession that we also\nsee the ancestors of man, and of the higher mammals, appear one after\nthe other in the earth\u2019s history; first fishes, then amphibians, later\nthe lower, and at last the higher mammals. Here, therefore, the\nembryonic development of the individual is completely parallel to the\npal\u00e6ontological development of the whole tribe to which it belongs, and\nthis exceedingly interesting and important phenomenon can be explained\nonly by the interaction of the laws of Inheritance and Adaptation.\n\nThe example last mentioned, of the parallelism of the pal\u00e6ontological\nand of the individual developmental series, now directs our attention to\na third developmental series, which stands in the closest relations to\nthese two, and which likewise runs, on the whole, parallel to them. I\nmean that series of development of forms which constitutes the object of\ninvestigation in _comparative anatomy_, and which I will briefly call\nthe _systematic developmental series of species_. By this we understand\nthe chain of the different, but related and connected forms, which exist\n_side by side_ at any one period of the earth\u2019s history; as for example,\nat the present moment. While comparative anatomy compares the different\nforms of fully-developed organisms with one another, it endeavours to\ndiscover the common prototypes which underlie, as it were, the manifold\nforms of kindred genera, classes, etc., and which are more or less\nconcealed by their particular differentiation. It endeavours to make out\nthe series of progressive steps which are indicated in the different\ndegrees of perfection of the divergent branches of the tribe. To make\nuse again of the same particular instance, comparative anatomy shows us\nhow the individual organs and systems of organs in the tribe of\nvertebrate animals\u2014in the different classes, families, and species of\nit\u2014have unequally developed, differentiated, and perfected themselves.\nIt shows us how far the succession of classes of vertebrate animals,\nfrom the Fishes upwards, through the Amphibia to the Mammals, and here\nagain, from the lower to the higher orders of Mammals, forms a\nprogressive series or ladder. This attempt to establish a connected\nanatomical developmental series we may discover in the works of the\ngreat comparative anatomists of all ages\u2014in the works of Goethe,\nMeckel, Cuvier, Johannes M\u00fcller, Gegenbaur, and Huxley.\n\nThe developmental series of mature forms, which comparative anatomy\npoints out in the different diverging and ascending steps of the organic\nsystem, and which we call the systematic developmental series, is\nparallel to the pal\u00e6ontological developmental series, because it deals\nwith the _result_ of pal\u00e6ontological development, and it is parallel to\nthe individual developmental series, because this is parallel to the\npal\u00e6ontological series. If two parallels are parallel to a third, they\nmust be parallel to one another.\n\nThe varied differentiation, and the unequal degree of perfecting which\ncomparative anatomy points out in the developmental series of the\nSystem, is chiefly determined by the ever increasing variety of\nconditions of existence to which the different groups adapt themselves\nin the struggle for life, and by the different degrees of rapidity and\ncompleteness with which this adaptation has been effected. Conservative\ngroups which have retained their inherited peculiarities most\ntenaciously remain, in consequence, at the lowest and rudest stage of\ndevelopment. Those groups progressing most rapidly and variously, and\nwhich have adapted themselves to changed conditions of existence most\nreadily have attained the highest degree of perfection. The further the\norganic world developed in the course of the earth\u2019s history, the\ngreater must the gap between the lower conservative and the higher\nprogressive groups have become, as in fact may be seen too in the\nhistory of nations. In this way also is explained the historical fact,\nthat the most perfect animal and vegetable groups have developed\nthemselves in a comparatively short time to a considerable height, while\nthe lowest or most conservative groups have remained stationary\nthroughout all ages in their original simple stage, or have progressed,\nbut very slowly and gradually. The series of man\u2019s progenitors clearly\nshows this state of things. The sharks of the present day are still very\nlike the primary fish, which are among the most ancient vertebrate\nprogenitors of man, and the lowest amphibians of the present day (the\ngilled salamanders and salamanders) are very like the amphibians which\nfirst developed themselves out of fishes. So, too, the later ancestors\nof man, the Monotremata and Marsupials, the most ancient mammals, are at\nthe same time the most imperfect animals of the class which still exist.\n\nThe laws of inheritance and adaptation known to us are completely\nsufficient to explain this exceedingly important and interesting\nphenomenon, which may be briefly designated as the _parallelism of\nindividual, of pal\u00e6ontological, and of systematic development_. No\nopponent of the Theory of Descent has been able to give an explanation\nof this extremely wonderful fact, whereas it is perfectly explained,\naccording to the Theory of Descent, by the laws of Inheritance and\nAdaptation.\n\nIf we examine this parallelism of the three organic series of\ndevelopment more accurately, we have to add the following special\nqualifications. _Ontogeny_, or the history of the individual development\nof every organism (embryology and metamorphology), presents us with a\nsimple _unbranching_ or graduated chain of forms; and so it is with that\n_portion of phylogeny_ which comprises the pal\u00e6ontological history of\ndevelopment of the _direct ancestors only_ of an individual organism.\nBut _the whole of phylogeny_\u2014which meets us in the _natural system_ of\nevery organic tribe or phylum, and which is concerned with the\ninvestigation of the pal\u00e6ontological development _of all_ the branches\nof this tribe\u2014forms a _branching_ or tree-shaped developmental series,\na veritable pedigree. If we examine and compare the branches of this\npedigree, and place them together according to the degree of their\ndifferentiation and perfection, we obtain the tree-shaped, branching,\n_systematic developmental series of comparative anatomy_. Strictly\nspeaking, therefore, the latter is parallel to _the whole of phylogeny_,\nand consequently is only partially parallel to ontogeny; for ontogeny\nitself is parallel only to _a portion_ of phylogeny.\n\nAll the phenomena of organic development above discussed, especially the\nthreefold genealogical parallelism, and the laws of differentiation and\nprogress, which are evident in each of these three series of organic\ndevelopment, and, further, the whole history of rudimentary organs, are\nexceedingly important proofs of the truth of the Theory of Descent. For\nby it alone can they be explained, whereas its opponents cannot even\noffer a shadow of an explanation of them. Without the Doctrine of\nFiliation, the fact of organic development in general cannot be\nunderstood. We should therefore, for this reason alone, be forced to\naccept Lamarck\u2019s Theory of Descent, even if we did not possess Darwin\u2019s\nTheory of Selection.\n\n\n\n\nCHAPTER XIII.\n\nTHEORY OF THE DEVELOPMENT OF THE UNIVERSE AND OF THE EARTH. SPONTANEOUS\nGENERATION. THE CARBON THEORY. THE PLASTID THEORY.\n\n\n   History of the Development of the Earth.\u2014Kant\u2019s Theory\n   of the Development of the Universe, or the Cosmological\n   Gas Theory.\u2014Development of Suns, Planets, and\n   Moons.\u2014First Origin of Water.\u2014Comparison of Organisms\n   and Anorgana.\u2014Organic and Inorganic Substances.\u2014Degrees\n   of Density, or Conditions of Aggregation.\u2014Albuminous\n   Combinations of Carbon.\u2014Organic and Inorganic\n   Forms.\u2014Crystals and Formless Organisms without\n   Organs.\u2014Stereometrical Fundamental Forms of Crystals and\n   of Organisms.\u2014Organic and Inorganic Forces.\u2014Vital\n   Force.\u2014Growth and Adaptation in Crystals and in\n   Organisms.\u2014Formative Tendencies of Crystals.\u2014Unity of\n   Organic and Inorganic Nature.\u2014Spontaneous Generation, or\n   Archigony.\u2014Autogony and Plasmogony.\u2014Origin of Monera by\n   Spontaneous Generation.\u2014Origin of Cells from\n   Monera.\u2014The Cell Theory.\u2014The Plastid Theory.\u2014Plastids,\n   or Structural Units.\u2014Cytods and Cells.\u2014Four Different\n   Kinds of Plastids.\n\n\nIn our considerations hitherto we have endeavoured to answer the\nquestion, \u201cBy what causes have new species of animals and plants arisen\nout of existing species?\u201d We have answered this question according to\nDarwin\u2019s theory, that natural selection in the struggle for\nexistence\u2014that is, the interaction of the laws of Inheritance and\nAdaptation\u2014is completely sufficient for producing mechanically the\nendless variety of the different animals and plants, which have the\nappearance of being organized according to a plan for a definite\npurpose. Meanwhile the question must have already repeatedly presented\nitself to the reader, how did the first organisms, or that one original\nand prim\u00e6val organism arise, from which we derive all the others?\n\nThis question Lamarck(2) answered by the hypothesis of _spontaneous\ngeneration_, or _archigony_. But Darwin passes over and avoids this\nsubject, as he expressly remarks that he has \u201cnothing to do with the\norigin of the soul, nor with that of life itself.\u201d At the conclusion of\nhis work he expresses himself more distinctly in the following\nwords:\u2014\u201cI imagine that probably all organic beings which ever lived on\nthis earth descended from some primitive form, which was first called\ninto life by the Creator.\u201d Moreover, Darwin, for the consolation of\nthose who see in the Theory of Descent the destruction of the whole\n\u201cmoral order of the universe,\u201d appeals to the celebrated author and\ndivine who wrote to him, that \u201che has gradually learnt to see that it is\njust as noble a conception of the Deity to believe that he created a few\noriginal forms capable of self-development into other and needful forms,\nas to believe that he required a fresh act of creation to supply the\nvoids caused by the action of his laws.\u201d\n\nThose to whom the belief in a supernatural creation is an emotional\nnecessity may rest satisfied with this conception. They may reconcile\nthat belief with the Theory of Descent; for in the creation of a single\noriginal organism possessing the capability to develop all others out of\nitself by inheritance and adaptation, they can really find much more\ncause for admiring the power and wisdom of the Creator than in the\nindependent creation of different species.\n\nIf, taking this point of view, we were to explain the origin of the\nfirst terrestrial organisms, from which all the others are descended, as\ndue to the action of a personal Creator acting according to a definite\nplan, we should of course have to renounce all scientific knowledge of\nthe process, and pass from the domain of true science to the completely\ndistinct domain of poetical faith. By assuming a supernatural act of\ncreation we should be taking a leap into the inconceivable. Before we\ndecide upon this latter step, and thereby renounce all pretension to a\nscientific knowledge of the process, we are at all events in duty bound\nto endeavour to examine it in the light of a mechanical hypothesis. We\nmust at least examine whether this process is really so wonderful, and\nwhether we cannot form a tenable conception of a completely\nnon-miraculous origin of the first primary organism. We might then be\nable entirely to reject miracle in creation.\n\nIt will be necessary for this purpose, first of all, to go back further\ninto the past, and to examine the history of the creation of the earth.\nGoing back still further, we shall find it necessary to consider the\nhistory of the creation of the whole universe in its most general\noutlines. All my readers undoubtedly know that from the structure of the\nearth, as it is at present known to us, the notion has been derived, and\nas yet has not been refuted, that its interior is in a fiery fluid\ncondition, and that the firm crust, composed of different strata, on the\nsurface of which organisms are living, forms only a very thin pellicle\nor shell round the fiery fluid centre. We have arrived at this idea by\ndifferent confirmatory experiments and reasonings. In the first place,\nthe observation that the temperature of the earth\u2019s crust continually\nincreases towards the centre is in favour of this supposition. The\ndeeper we descend, the greater the warmth of the ground, and in such\nproportion, that with every 100 feet the temperature increases about one\ndegree. At a depth of six miles, therefore, a heat of 1500\u00b0 would be\nattained, sufficient to keep most of the firm substances of our earth\u2019s\ncrust in a molten, fiery, fluid state. This depth, however, is only the\n286th part of the whole diameter of the earth (1717 miles). We further\nknow that springs which rise out of a considerable depth possess a very\nhigh temperature, and sometimes even throw water up to the surface in a\nboiling state. Lastly, very important proofs are furnished by volcanic\nphenomena, the eruption of fiery fluid masses of stone bursting through\ncertain parts of the earth\u2019s crust. All these phenomena lead us with\ngreat certainty to the important assumption that the firm crust of the\nearth forms only quite a small fraction, not nearly the one-thousandth\npart of the whole diameter of the terrestrial globe, and that the rest\nis still for the most part in a molten or fiery fluid state.\n\nNow if, starting with this assumption, we reflect on the ancient history\nof the development of the globe, we are logically carried back a step\nfurther, namely, to the assumption that at an earlier date the whole\nearth was a fiery fluid body, and that the formation of a thin,\nstiffened crust on the surface was only a later process. Only gradually,\nby radiating its intrinsic heat into the cold space of the universe, has\nthe surface of the glowing ball become condensed into a thin crust.\nThat the temperature of the earth in remote times was much higher than\nit is now, is proved by many phenomena. Among other things, this is\nrendered probable by the equal distribution of organisms in remote times\nof the earth\u2019s history. While at present, as is well known, the\ndifferent populations of animals and plants correspond to the different\nzones of the earth and their appropriate temperature, in earlier times\nthis was distinctly not the case.\n\nWe see from the distribution of fossils in the remoter ages, that it was\nonly at a very late date, in fact, at a comparatively recent period of\nthe organic history of the earth (at the beginning of the so-called\nc\u00e6nolithic or tertiary period), that a separation of zones and of the\ncorresponding organic populations occurred. During the immensely long\nprimary and secondary periods, tropical plants, which require a very\nhigh degree of temperature, lived not only in the present torrid zone,\nunder the equator, but also in the present temperate and frigid zones.\nMany other phenomena also demonstrate a gradual decrease of the\ntemperature of the globe as a whole, and especially a late and gradual\ncooling of the earth\u2019s crust about the poles. Bronn, in his excellent\n\u201cInvestigations of the Laws of Development of the Organic World,\u201d has\ncollected numerous geological and pal\u00e6ontological proofs of this fact.\n\nThese phenomena and the mathematico-astronomical knowledge of the\nstructure of the universe justify the theory that, inconceivable ages\nago, long before the first existence of organisms, the whole earth was a\nfiery fluid globe. Now, this theory corresponds with the grand theory of\nthe origin of the universe, and especially of our planetary system,\nwhich, on the ground of mathematical and astronomical facts, was put\nforward in 1755 by our critical philosopher Kant,(22) and was later more\nthoroughly established by the celebrated mathematicians, Laplace and\nHerschel. This cosmogeny, or theory of the development of the universe,\nis now almost universally acknowledged; it has not been replaced by a\nbetter one, and mathematicians, astronomers, and geologists have\ncontinually, by various arguments, strengthened its position.\n\nKant\u2019s cosmogeny maintains that _the whole universe, inconceivable ages\nago, consisted of a gaseous chaos_. All the substances which are found\nat present separated on the earth, and other bodies of the universe, in\ndifferent conditions of density\u2014in the solid, semi-fluid, liquid, and\nelastic fluid or gaseous states of aggregation\u2014originally constituted\ntogether one single homogeneous mass, equally filling up the space of\nthe universe, which, in consequence of an extremely high degree of\ntemperature, was in an exceedingly thin gaseous or nebulous state. The\nmillions of bodies in the universe which at present form the different\nsolar systems did not then exist. They originated only in consequence of\na universal rotatory movement, or rotation, during which a number of\nmasses acquired greater density than the remaining gaseous mass, and\nthen acted upon the latter as central points of attraction. Thus arose a\nseparation of the chaotic primary nebula, or gaseous universe, into a\nnumber of rotating nebulous spheres, which became more and more\ncondensed. Our solar system was such a gigantic gaseous or nebulous\nball, all the particles of which revolved round a common central point,\nthe solar nucleus. The nebulous ball itself, like all the rest, in\nconsequence of its rotatory movement, assumed a spheroidal or a\nflattened globular form.\n\nWhile the centripetal force attracted the rotating particles nearer and\nnearer to the firm central point of the nebulous ball, and thus\ncondensed the latter more and more, the centrifugal force, on the other\nhand, always tended to separate the peripheral particles further and\nfurther from it, and to hurl them off. On the equatorial sides of the\nball, which was flattened at both poles, this centrifugal force was\nstrongest, and as soon as, by increase of density, it attained\npredominance over the centripetal force, a circular nebulous ring\nseparated itself from the rotating ball. This nebulous ring marked the\ncourse of future planets. The nebulous mass of the ring gradually\ncondensed, and became a planet, which revolved round its own axis, and\nat the same time rotated round the central body. In precisely the same\nmanner, from the equator of the planetary mass, as soon as the\ncentrifugal force gained predominance over the centripetal force, new\nnebulous rings were ejected, which moved round the planets as the latter\nmoved round the sun. These nebulous rings, too, became condensed into\nrotating balls. Thus arose the moons, only one of which moves round our\nearth, whilst four move round Jupiter, and six round Uranus. The ring of\nSaturn still shows us a moon in its early stage of development. As by\nincreasing refrigeration these simple processes of condensation and\nexpulsion repeated themselves over and over again, there arose the\ndifferent solar systems, the planets rotating round their central suns,\nand the satellites or moons moving round their planets.\n\nThe original gaseous condition of the rotating bodies of the universe\ngradually changed, by increasing refrigeration and condensation, into\nthe fiery fluid or molten state of aggregation. By the process of\ncondensation, a great quantity of heat was emitted, and the rotating\nsuns, planets, and moons, soon changed into glowing balls of fire, like\ngigantic drops of melted metal, which emitted light and heat. By loss of\nheat, the melted mass on the surface of the fiery fluid ball became\nfurther condensed, and thus arose a thin, firm crust, which enclosed a\nfiery fluid nucleus. In all essential respects our mother earth probably\ndid not differ from the other bodies of the universe.\n\nIn view of the object of these pages, it will not be of especial\ninterest to follow in detail the _history of the natural creation of the\nuniverse_, with its different solar and planetary systems, and to\nestablish it mathematically by the different astronomical and geological\nproofs. The outlines of it, which I have just mentioned, must be\nsufficient here, and for further details I refer to Kant\u2019s[5] \u201cGeneral\nHistory of Nature and Theory of the Heavens.\u201d(22) I will only add that\nthis wonderful theory, which might be called _the cosmological gas\ntheory_, harmonizes with all the general series of phenomena at present\nknown to us, and stands in no irreconcilable contradiction to any one of\nthem. Moreover, it is purely mechanical or monistic, makes use\nexclusively of the inherent forces of eternal matter, and entirely\nexcludes every supernatural process, every prearranged and conscious\naction of a personal Creator. Kant\u2019s Cosmological Gas Theory\nconsequently occupies a similar supreme position in _Anorganology_,\nespecially in _Geology_, and forms the crown of our knowledge in that\ndepartment, in the same way as Lamarck\u2019s Theory of Descent does in\n_Biology_, and especially in _Anthropology_. Both rest exclusively upon\nmechanical or unconscious causes (caus\u00e6 efficientes), in no case upon\nprearranged or conscious causes (caus\u00e6 finales). (Compare above, p.\n100-106.) Both therefore fulfil all the demands of a scientific theory,\nand consequently will remain generally acknowledged until they are\nreplaced by better ones.\n\nI will, however, not deny that Kant\u2019s grand cosmogeny has some weak\npoints, which prevent our placing the same unconditional confidence in\nit as in Lamarck\u2019s Theory of Descent. The notion of an original gaseous\nchaos filling the whole universe presents great difficulties of various\nkinds. A great and unsolved difficulty lies in the fact that the\nCosmological Gas Theory furnishes no starting-point at all in\nexplanation of the first impulse which caused the rotary motion in the\ngas-filled universe. In seeking for such an impulse, we are\ninvoluntarily led to the mistaken questioning about a \u201cfirst beginning.\u201d\nWe can as little imagine a _first beginning_ of the eternal phenomena of\nthe motion of the universe as of its final end.\n\nThe universe is unlimited and immeasurable in both space and time. It is\neternal, and it is infinite. Nor can we imagine a beginning or end to\nthe uninterrupted and eternal motion in which all particles of the\nuniverse are always engaged. The great laws of the _conservation of\nforce_(38) and the _conservation of matter_, the foundations of our\nwhole conception of nature, admit of no other supposition. The universe,\nas far as it is cognisable to human capability, appears as a connected\nchain of material phenomena of motion, necessitating a continual change\nof forms. Every form, as the temporary result of a multiplicity of\nphenomena of motion, is as such perishable, and of limited duration.\nBut, in the continual change of forms, matter and the motion inseparable\nfrom it remain eternal and indestructible.\n\nNow, although Kant\u2019s Cosmological Gas Theory is not able to explain the\ndevelopment of motion in the whole universe in a satisfactory manner,\nbeyond that gaseous state of chaos, and although many other weighty\nconsiderations may be brought forward against it, especially by\nchemistry and geology, yet we must on the whole acknowledge its great\nmerit, inasmuch as it explains in an excellent manner, by due\nconsideration of development, the whole structure of all that is\naccessible to our observation, that is, the anatomy of the solar\nsystems, and especially of our planetary system. It may be that this\ndevelopment was altogether different from what Kant supposes, and our\nearth may have arisen by the aggregation of numberless small meteorides,\nscattered in space, or in any other manner, but hitherto no one has as\nyet been able to establish any other theory of development, or to offer\none in the place of Kant\u2019s cosmogeny.\n\nAfter this general glance at the monistic cosmogeny, or the\nnon-miraculous history of the development of the universe, let us now\nreturn to a minute fraction of it, to our mother earth, which we left as\na ball flattened at both poles and in a fiery fluid state, its surface\nhaving condensed by becoming cooled into a very thin firm crust. The\ncrust, on first cooling, must have covered the whole surface of the\nterrestrial sphere as a continuous smooth and thin shell. But soon it\nmust have become uneven and hummocky; for, since during the continued\ncooling, the fiery fluid nucleus became more and more condensed and\ncontracted, and consequently the diameter of the earth diminished, the\nthin cold crust, which could not closely follow the softer nuclear mass,\nmust have fallen in, in many places. An empty space would have arisen\nbetween the two, had not the pressure of the outer atmosphere forced\ndown the fragile crust towards the interior, breaking it in so doing.\nOther unevennesses probably arose from the fact that, in different\nparts, the cooled crust during the process of refrigeration contracted\nalso itself, and thus became fissured with cracks and rents. The fiery\nfluid nucleus flowed up to the external surface through these cracks,\nand again became cooled and stiff. Thus, even at an early period there\narose many elevations and depressions, which were the first foundations\nof mountains and valleys.\n\nAfter the temperature of the cooled terrestrial ball had fallen to a\ncertain degree, a very important new process was effected, namely, the\n_first origin of water_. Water had until then existed only in the form\nof steam in the atmosphere surrounding the globe. The water could\nevidently not condense into a state of fluid drops until the temperature\nof the atmosphere had considerably decreased. Now, then, there began a\nfurther transformation of the earth\u2019s crust by the force of water. It\ncontinually fell in the form of rain, and in that form washed down the\nelevations of the earth\u2019s crust, filling the depressions with the mud\ncarried along, and, by depositing it in layers, it caused the extremely\nimportant neptunic transformations of the earth\u2019s crust, which have\ncontinued since then uninterruptedly, and which in our next chapter we\nshall examine a little more closely.\n\nIt was not till the earth\u2019s crust had so far cooled that the water had\ncondensed into a fluid form, it was not till the hitherto dry crust of\nthe earth had for the first time become covered with liquid water, that\nthe origin of the first organisms could take place. For all animals and\nall plants\u2014in fact, all organisms\u2014consist in great measure of fluid\nwater, which combines in a peculiar manner with other substances, and\nbrings them into a semi-fluid state of aggregation. We can therefore,\nfrom these general outlines of the inorganic history of the earth\u2019s\ncrust, deduce the important fact, that at a certain definite time life\nhad its beginning on earth, and that terrestrial organisms did not exist\nfrom eternity, but at a certain period came into existence for the first\ntime.\n\nNow, how are we to conceive of this origin of the first organisms? This\nis the point at which most naturalists, even at the present day, are\ninclined to give up the attempt at natural explanation, and take refuge\nin the miracle of an inconceivable creation. In doing so, as has already\nbeen remarked, they quit the domain of scientific knowledge, and\nrenounce all further insight into the eternal laws which have determined\nnature\u2019s history. But before despondingly taking such a step, and before\nwe despair of the possibility of any knowledge of this important\nprocess, we may at least make an attempt to understand it. Let us see if\nin reality the origin of a first organism out of inorganic matter, the\norigin of a living body out of lifeless matter, is so utterly\ninconceivable and beyond all experience. In one word, let us examine the\nquestion of _spontaneous generation, or archigony_. In so doing, it is\nabove all things necessary to form a clear idea of the principal\nproperties of the two chief groups of natural bodies, the so-called\ninanimate or inorganic, and the animate or organic bodies, and then\nestablish what is common to, and what are the differences between, the\ntwo groups. It is desirable to go somewhat carefully into the\n_comparison of organisms and anorgana_, since it is commonly very much\nneglected, although it is necessary for a right understanding of nature\nfrom the monistic point of view. It will be most advantageous here to\nlook separately at the three fundamental properties of every natural\nbody; these are matter, form, and force. Let us begin with _matter_.\n(Gen. Morph. iii.)\n\nBy chemistry we have succeeded in analysing all bodies known to us into\na small number of elements or simple substances, which cannot be further\ndivided, for example, carbon, oxygen, nitrogen, sulphur, and the\ndifferent metals: potassium, sodium, iron, gold, etc. At present we know\nabout seventy such elements or simple substances. The majority of them\nare unimportant and rare; the minority only are widely distributed, and\ncompose not only most of the anorgana, but also all organisms. If we\ncompare those elements which constitute the body of organisms with those\nwhich are met with in anorgana, we have first to note the highly\nimportant fact that in animal and vegetable bodies no element occurs but\nwhat can be found outside of them in inanimate nature. There are no\nspecial organic elements or simple organic substances.\n\nThe chemical and physical differences existing between organisms and\nanorgana, consequently, do not lie in their material foundation; they do\nnot arise from the different nature of the _elements_ composing them,\nbut from the different manner in which the latter are united by\nchemical _combination_. This different manner of combination gives rise\nto certain physical peculiarities, especially in density of substance,\nwhich at first sight seems to constitute a deep chasm between the two\ngroups of bodies. Inorganic or inanimate natural bodies, such as\ncrystals and the amorphous rocks, are in a state of density which we\ncall the firm or solid state, and which we oppose to the liquid state of\nwater and to the gaseous state of air. It is familiar to every one that\nthese three different degrees of density, or states of aggregation of\nanorgana, are by no means peculiar to the different elements, but are\nthe results of a certain degree of temperature. Every inorganic solid\nbody, by increase of temperature, can be reduced to the liquid or melted\nstate, and, by further heat, to the gaseous or elastic state. In the\nsame way most gaseous bodies, by a proper decrease of temperature can\nfirst be converted into a liquid state, and further, into a solid state\nof density.\n\nIn opposition to these three states of density of anorgana, the living\nbody of all organisms\u2014animals as well as plants\u2014is in an altogether\npeculiar fourth state of aggregation. It is neither solid like stone,\nnor liquid like water, but presents rather a medium between these two\nstates, which may therefore be designated as the firm-fluid or swollen\nstate of aggregation (viscid). In all living bodies, without exception,\nthere is a certain quantity of water combined in a peculiar way with\nsolid matter, and owing to this characteristic combination of water with\nsolid matter we have that soft state of aggregation, neither solid nor\nliquid, which is of great importance in the mechanical explanation of\nthe phenomena of life. Its cause lies essentially in the physical and\nchemical properties of a simple, indivisible, elementary substance,\nnamely, _carbon_ (Gen. Morph. i. 122-130).\n\nOf all elements, carbon is to us by far the most important and\ninteresting, because this simple substance plays the largest part in all\nanimal and vegetable bodies known to us. It is that element which, by\nits peculiar tendency to form complicated combinations with the other\nelements, produces the greatest variety of chemical compounds, and among\nthem the forms and living substance of animal and vegetable bodies.\nCarbon is especially distinguished by the fact that it can unite with\nthe other elements in infinitely manifold relations of number and\nweight. By the combination of carbon with three other elements, with\noxygen, hydrogen, and nitrogen (to which generally sulphur, and\nfrequently, also, phosphorus is added), there arise those exceedingly\nimportant compounds which we have become acquainted with as the first\nand most indispensable substratum of all vital phenomena, the albuminous\ncombinations, or albuminous bodies (protean matter).\n\nWe have before this (p. 185) become acquainted with the simplest of all\nspecies of organisms in the Monera, whose entire bodies when completely\ndeveloped consist of nothing but a semi-fluid albuminous lump; they are\norganisms which are of the utmost importance for the theory of the first\norigin of life. But most other organisms, also, at a certain period of\ntheir existence\u2014at least, in the first period of their life\u2014in the\nshape of egg-cells or germ-cells, are essentially nothing but simple\nlittle lumps of such albuminous formative matter, known as plasma, or\nprotoplasma. They then differ from the Monera only by the fact that in\nthe interior of the albuminous corpuscle the cell-kernel, or nucleus,\nhas separated itself from the surrounding cell-substance (protoplasma).\nAs we have already pointed out, the cells, with their simple attributes,\nare so many citizens, who by co-operation and differentiation build up\nthe body of even the most perfect organism; this being, as it were, a\ncell republic (p. 301). The fully developed form and the vital phenomena\nof such an organism are determined solely by the activities of these\nsmall albuminous corpuscles.\n\nIt may be considered as one of the greatest triumphs of recent biology,\nespecially of the theory of tissues, that we are now able to trace the\nwonder of the phenomena of life to these substances, and that we can\ndemonstrate the _infinitely manifold and complicated physical and\nchemical properties of the albuminous bodies to be the real cause of\norganic or vital phenomena_. All the different forms of organisms are\nsimply and directly the result of the combination of the different forms\nof cells. The infinitely manifold varieties of form, size, and\ncombination of the cells have arisen only gradually by the division of\nlabour, and by the gradual adaptation of the simple homogeneous lumps of\nplasma, which originally were the only constituents of the cell-mass.\nFrom this it follows of necessity that the fundamental phenomena of\nlife\u2014nutrition and generation\u2014in their highest manifestations, as well\nas in their simplest expressions, must also be traced to the material\nnature of that albuminous formative substance. The other vital\nactivities are gradually evolved from these two. Thus, then, the general\nexplanation of life is now no more difficult to us than the explanation\nof the physical properties of inorganic bodies. All vital phenomena and\nformative processes of organisms are as directly dependent upon the\nchemical composition and the physical forces of organic matter as the\nvital phenomena of inorganic crystals\u2014that is, the process of _their_\ngrowth and _their_ specific formation\u2014are the direct results of their\nchemical composition and of their physical condition. The _ultimate\ncauses_, it is true, remain in _both_ cases concealed from us. When gold\nand copper crystallize in a cubical, bismuth and antimony in a\nhexagonal, iodine and sulphur in a rhombic form of crystal, the\noccurrence is in reality neither more nor less mysterious to us than is\nevery elementary process of organic formation, every self-formation of\nthe organic cell. In this respect we can no longer draw a fundamental\ndistinction between organisms and anorgana, a distinction of which,\nformerly, naturalists were generally convinced.\n\nLet us secondly examine the agreements and differences which are\npresented to us in the _formation_ of organic and inorganic natural\nbodies (Gen. Morph. i. 130). Formerly the simple structure of the latter\nand the composite structure of the former were looked upon as the\nprincipal distinction. The body of all organisms was supposed to consist\nof dissimilar or heterogeneous parts, of instruments or organs which\nworked together for the purposes of life. On the other hand, the most\nperfect anorgana, that is to say, crystals, were supposed to consist\nentirely of continuous or homogeneous matter. This distinction appears\nvery essential. But it loses all importance through the fact that in\nlate years we have become acquainted with the exceedingly remarkable and\nimportant Monera.(15) (Compare above, p. 185.) The whole body of these\nmost simple of all organisms\u2014a semi-fluid, formless, and simple lump of\nalbumen\u2014consists, in fact, of only a single chemical combination, and\nis as perfectly simple in its structure as any crystal, which consists\nof a single inorganic combination, for example, of a metallic salt or of\na silicate of the earths and alkalies.\n\nAs naturalists believed in differences in the inner structure or\ncomposition, so they supposed themselves able to find complete\ndifferences in the external forms of organisms and anorgana, especially\nin the mathematically determinable crystalline forms of the latter.\nCertainly crystallization is pre-eminently a quality of the so-called\nanorgana. Crystals are limited by plane surfaces, which meet in straight\nlines and at certain measurable angles. Animal and vegetable forms, on\nthe contrary, seem at first sight to admit of no such geometrical\ndetermination. They are for the most part limited by curved surfaces and\ncrooked lines, which meet at variable angles. But in recent times we\nhave become acquainted, among Radiolaria(23) and among many other\nProtista, with a large number of lower organisms, whose body, in the\nsame way as crystals, may be traced to a mathematically determinable\nfundamental form, and whose form in its whole, as well as in its parts,\nis bounded by definite geometrically determinable planes and angles. In\nmy general doctrine of _Fundamental Forms, or Promorphology_, I have\ngiven detailed proofs of this, and at the same time established a\ngeneral system of forms, the ideal stereometrical type-forms, which\nexplain the real forms of inorganic crystals, as well as of organic\nindividuals (Gen. Morph. i. 375-574). Moreover, there are also perfectly\namorphous organisms, like the Monera, Am\u0153ba, etc., which change their\nforms every moment, and in which we are as little able to point out a\ndefinite fundamental form as in the case of the shapeless or amorphous\nanorgana, such as non-crystallized stones, deposits, etc. We are\nconsequently unable to find any essential difference in the external\nforms or the inner structure of anorgana and organisms.\n\nThirdly, let us turn to the _forces_ or the _phenomena of motion_ of\nthese two different groups of bodies (Gen. Morph. i. 140). Here we meet\nwith the greatest difficulties. The vital phenomena, known as a rule\nonly in the highly developed organisms, in the more perfect animals and\nplants, seem there so mysterious, so wonderful, so peculiar, that most\npersons are decidedly of opinion that in inorganic nature there occurs\nnothing at all similar, or in the least degree comparable to them.\nOrganisms are for this very reason called animate, and the anorgana,\ninanimate natural bodies. Hence, even so late as the commencement of the\npresent century, the science which investigates the phenomena of life,\nnamely physiology, retained the erroneous idea that the physical and\nchemical properties of matter were not sufficient for explaining these\nphenomena. In our own day, especially during the last ten years, this\nidea may be regarded as having been completely refuted. In physiology,\nat least, it has now no place. It now never occurs to a physiologist to\nconsider any of the vital phenomena as the result of a mysterious _vital\nforce_, of an active power working for a definite purpose, standing\noutside of matter, and, so to speak, taking only the physico-chemical\nforces into its service. Modern physiology has arrived at the strictly\nmonistic conviction that all of the vital phenomena, and, above all, the\ntwo fundamental phenomena of nutrition and propagation are purely\nphysico-chemical processes, and directly dependent on the material\nnature of the organism, just as all the physical and chemical qualities\nof every crystal are determined solely by its material composition. Now,\nas the elementary substance which determines the peculiar material\ncomposition of organisms is carbon, we must ultimately reduce all vital\nphenomena, and, above all, the two fundamental phenomena of nutrition\nand propagation to the properties of the carbon. _The\npeculiar-chemico-physical properties, and especially the semi-fluid\nstate of aggregation, and the easy decomposibility of the exceedingly\ncomposite albuminous combinations of carbon, are the mechanical causes\nof those peculiar phenomena of motion which distinguish organisms from\nanorgana, and which in a narrow sense are usually called \u201clife.\u201d_\n\nIn order to understand this \u201c_carbon theory_,\u201d which I have established\nin detail in the second book of my General Morphology, it is necessary,\nabove all things, closely to examine those phenomena of motion which are\ncommon to both groups of natural bodies. First among them is the\n_process of growth_. If we cause any inorganic solution of salt slowly\nto evaporate, crystals are formed in it, which slowly increase in size\nduring the continued evaporation of the water. This process of growth\narises from the fact that new particles continually pass over from the\nfluid state of aggregation into the solid, and, according to certain\nlaws, deposit themselves upon the firm kernel of the crystal already\nformed. From such an apposition of particles arise the mathematically\ndefinite crystalline shapes. In like manner the growth of organisms\ntakes place by the accession of new particles. The only difference is\nthat in the growth of organisms, in consequence of their semi-fluid\nstate of aggregation, the newly-added particles penetrate into the\ninterior of the organism (inter-susception), whereas anorgana receive\nhomogeneous matter from without only by apposition or an addition of new\nparticles to the surface. This important difference of growth by\ninter-susception and by apposition is obviously only the necessary and\ndirect result of the different conditions of density or state of\naggregation in organisms and anorgana.\n\nUnfortunately I cannot here follow in detail the various exceedingly\ninteresting parallels and analogies which occur between the formation of\nthe most perfect anorgana, the crystals, and the formation of the\nsimplest organisms, the Monera and their next kindred forms. For this I\nmust refer to a minute comparison of organisms and anorgana, which I\nhave carried out in the fifth chapter of my General Morphology (Gen.\nMorph. i. 111-160). I have there shown in detail that there exist no\ncomplete differences between organic and inorganic natural bodies,\nneither in respect to form and structure, nor in respect to matter and\nforce; and that the actually existing differences are dependent upon the\npeculiar nature of the _carbon_; and that there exists no insurmountable\nchasm between organic and inorganic nature. We can perceive this most\nimportant fact very clearly if we examine and compare the origin of the\nforms in crystals and in the simplest organic individuals. In the\nformation of crystal individuals, two different counteracting formative\ntendencies come into operation. The _inner constructive force_, or the\ninner formative tendency, which corresponds to the Heredity of\norganisms, in the case of the crystal is the direct result of its\nmaterial constitution or of its chemical composition. The form of the\ncrystal, so far as it is determined by this inner original formative\ntendency, is the result of the specific and definite way in which the\nsmallest particles of the crystallizing matter unite together in\ndifferent directions according to law. That independent inner formative\nforce, which is directly inherent in the matter itself, is directly\ncounteracted by a second formative force. The _external constructive\nforce_, or the external formative tendency, may be called Adaptation in\ncrystals as well as in organisms. Every crystal individual during its\nformation, like every organic individual, must submit and adapt itself\nto the surrounding influences and conditions of existence of the outer\nworld. In fact, the form and size of every crystal is dependent upon its\nwhole surroundings, for example, upon the vessel in which the\ncrystallization takes place, upon the temperature and the pressure of\nthe air under which the crystal is formed, upon the presence or absence\nof heterogeneous bodies, etc. Consequently, the form of every single\ncrystal, like the form of every single organism, is the result of the\ninteraction of two opposing factors\u2014the _inner_ formative tendency,\nwhich is determined by the chemical constitution of the _matter itself_,\nand of the _external_ formative tendency, which is dependent upon the\ninfluence of _surrounding_ matter. Both these constructive forces\ninteract similarly also in the organism, and, just as in the crystal,\nare of a purely mechanical nature and directly inherent in the substance\nof the body. If we designate the growth and the formation of organisms\nas a process of life, we may with equal reason apply the same term to\nthe developing crystal. The teleological conception of nature, which\nlooks upon organisms as machines of creation arranged for a definite\npurpose, must logically acknowledge the same also in regard to the\nforms of crystals. The differences which exist between the simplest\norganic individuals and inorganic crystals are determined by the _solid_\nstate of aggregation of the latter, and by the _semi-fluid_ state of the\nformer. Beyond that the causes producing form are exactly the same in\nboth. This conviction forces itself upon us most clearly, if we compare\nthe exceedingly remarkable phenomena of growth, adaptation, and the\n\u201ccorrelation of parts\u201d of developing crystals with the corresponding\nphenomena of the origin of the simplest organic individuals (Monera and\ncells). The analogy between the two is so great that, in reality, no\naccurate boundary can be drawn. In my General Morphology I have quoted\nin support of this a number of striking facts (Gen. Morph. i. 146, 156,\n158.)\n\nIf we vividly picture to ourselves this \u201c_unity of organic and inorganic\nnature_\u201d this essential agreement of organisms and anorgana in matter,\nform, and force, and if we bear in mind that we are not able to\nestablish any one fundamental distinction between these two groups of\nbodies (as was formerly generally assumed), then the question of\nspontaneous generation will lose a great deal of the difficulty which at\nfirst seems to surround it. Then the development of the first organism\nout of inorganic matter will appear a much more easily conceivable and\nintelligible process than has hitherto been the case, whilst an\nartificial absolute barrier between organic or animate, and inorganic or\ninanimate nature was maintained.\n\nIn the question of _spontaneous generation, or archigony_, which we can\nnow answer more definitely, it must be borne in mind that by this\nconception we understand generally the _non-parental generation of an\norganic individual_, the origin of an organism independent of a\nparental or producing organism. It is in this sense that on a former\noccasion (p. 183) I mentioned spontaneous generation (archigony) as\nopposed to parental generation or propagation (tocogony). In the latter\ncase the organic individual arises by a greater or less portion of an\nalready existing organism separating itself and growing independently.\n(Gen. Morph. ii. 32.)\n\nIn spontaneous generation, which is often also called original\ngeneration (generatio spontanea, \u00e6quivoca, primaria etc.), we must first\ndistinguish two essentially different kinds, namely, _autogeny_ and\n_plasmogeny_. By _autogeny_ we understand the origin of a most simple\norganic individual in an _inorganic formative fluid_, that is, in a\nfluid which contains the fundamental substances for the composition of\nthe organism dissolved in simple and loose combinations (for example,\ncarbonic acid, ammonia, binary salts, etc.). On the other hand, we call\nspontaneous generation _plasmogeny_ when the organism arises in an\n_organic formative fluid_, that is, in a fluid which contains those\nrequisite fundamental substances dissolved in the form of complicated\nand fluid combinations of carbon (for example, albumen, fat, hydrate of\ncarbon, etc.). (Gen. Morph. i. 174, ii. 33.)\n\nNeither the process of autogeny, nor that of plasmogeny, has yet been\ndirectly observed with perfect certainty. In early, and also in more\nrecent times, numerous and interesting experiments have been made as to\nthe possibility or reality of spontaneous generation. Almost all these\nexperiments refer not to autogeny, but to plasmogeny, to the origin of\nan organism out of already formed organic matter. It is evident,\nhowever, that this latter process is only of subordinate interest for\nour history of creation. It is much more important for us to solve the\nquestion, \u201cIs there such a thing as autogeny? Is it possible that an\norganism can arise, not out of pre-existing organic, but out of purely\ninorganic, matter?\u201d Hence we can quietly lay aside all the numerous\nexperiments which refer only to plasmogeny, which have been carried on\nvery zealously during the last ten years, and which for the most part\nhave had a negative result. For even supposing that the reality of\nplasmogeny were strictly proved, still autogeny would not be explained\nby it.\n\nThe experiments on autogeny have likewise as yet furnished no certain\nand positive result. Yet we must at the outset most distinctly protest\nagainst the notion that these experiments have proved the impossibility\nof spontaneous generation in general. Most naturalists who have\nendeavoured to decide this question experimentally, and who, after\nhaving employed all possible precautionary measures, under\nwell-ascertained conditions, have seen no organisms come into being,\nhave straightway made the assertion, on the ground of these negative\nresults: \u201cThat it is altogether impossible for organisms to come into\nexistence by themselves without parental generation.\u201d This hasty and\ninconsiderate assertion they have supported by the negative results of\ntheir experiments, which, after all, could prove nothing except that,\nunder these or those highly artificial circumstances created by the\nexperimenters themselves, no organism was developed. From these\nexperiments, which have been for the most part made under the most\nunnatural conditions, and in a highly artificial manner, we can by no\nmeans draw the conclusion that spontaneous generation in general is\nimpossible. The impossibility of such a process can, in fact, never be\nproved. For how can we know that in remote prim\u00e6val times there did not\nexist conditions quite different from those at present obtaining, and\nwhich may have rendered spontaneous generation possible? Indeed, we can\neven positively and with full assurance maintain that the general\nconditions of life in prim\u00e6val times must have been entirely different\nfrom those of the present time. Think only of the fact that the enormous\nmasses of carbon which we now find deposited in the primary coal\nmountains were first reduced to a solid form by the action of vegetable\nlife, and are the compressed and condensed remains of innumerable\nvegetable substances, which have accumulated in the course of many\nmillions of years. But at the time when, after the origin of water in a\nliquid state on the cooled crust of the earth, organisms were first\nformed by spontaneous generation, those immeasurable quantities of\ncarbon existed in a totally different form, probably for the most part\ndispersed in the atmosphere in the shape of carbonic acid. The whole\ncomposition of the atmosphere was therefore extremely different from the\npresent. Further, as may be inferred upon chemical, physical, and\ngeological grounds, the density and the electrical conditions of the\natmosphere were quite different. In like manner the chemical and\nphysical nature of the prim\u00e6val ocean, which then continuously covered\nthe whole surface of the earth as an uninterrupted watery sheet, was\nquite peculiar. The temperature, the density, the amount of salt, etc.,\nmust have been very different from those of the present ocean. In any\ncase, therefore, even if we do not know anything more about it, there\nremains to us the supposition, which can at least not be disputed, that\nat that time, under conditions quite different from those of to-day, a\nspontaneous generation, which now is perhaps no longer possible, may\nhave taken place.\n\nBut it is necessary to add here that, by the recent progress of\nchemistry and physiology, the mysterious and miraculous character which\nat first seems to belong to this much disputed and yet inevitable\nprocess of spontaneous generation, has been to a great extent, or almost\nentirely, destroyed. Not fifty years ago, all chemists maintained that\nwe were unable to produce artificially in our laboratories any\ncomplicated combination of carbon, or so-called \u201corganic combination.\u201d\nThe mystic \u201cvital force\u201d alone was supposed to be able to produce these\ncombinations. When, therefore, in 1828, W\u00f6hler, in G\u00f6ttingen, for the\nfirst time refuted this dogma, and exhibited pure \u201corganic\u201d urea,\nobtained in an artificial manner from a purely inorganic body (cyanate\nof ammonium), it caused the greatest surprise and astonishment. In more\nrecent times, by the progress of synthetic chemistry, we have succeeded\nin producing in our laboratories a great variety of similar \u201corganic\u201d\ncombinations of carbon, by purely artificial means\u2014for example alcohol,\nacetic acid, formic acid. Indeed, many exceedingly complicated\ncombinations of carbon are now artificially produced, so that there is\nevery likelihood, sooner or later, of our producing artificially the\nmost complicated, and at the same time the most important of all,\nnamely, the albuminous combinations, or plasma-bodies. By the\nconsideration of this probability, the deep chasm which was formerly\nand generally believed to exist between organic and inorganic bodies is\nalmost or entirely removed, and the way is paved for the conception of\nspontaneous generation.\n\nOf still greater, nay, the very greatest importance to the hypothesis of\nspontaneous generation are, finally, the exceedingly remarkable\n_Monera_, those creatures which we have already so frequently mentioned,\nand which are not only the simplest of all observed organisms, but even\nthe simplest of all imaginable organisms. I have already described these\nwonderful \u201c_organisms without organs_,\u201d when examining the simplest\nphenomena of propagation and inheritance. We already know seven\ndifferent genera of these Monera, some of which live in fresh water,\nothers in the sea (compare above, p. 184; also Plate I. and its\nexplanation in the Appendix). In a perfectly developed and freely motile\nstate, they one and all present us with nothing but a simple little lump\nof an albuminous combination of carbon. The individual genera and\nspecies differ only a little in the manner of propagation and\ndevelopment, and in the way of taking nourishment. Through the discovery\nof these organisms, which are of the utmost importance, the supposition\nof a spontaneous generation loses most of its difficulties. For as all\ntrace of organization\u2014all distinction of heterogeneous parts\u2014is still\nwanting in them, and as all the vital phenomena are performed by one and\nthe same homogeneous and formless matter, we can easily imagine their\norigin by spontaneous generation. If this happens through _plasmogeny_,\nand if plasma capable of life already exists, it then only needs to\nindividualize itself in the same way as the mother liquor of crystals\nindividualizes itself in crystallization. If, on the other hand, the\nspontaneous generation of the Monera takes place by true _autogeny_,\nthen it is further requisite that that plasma capable of life, that\nprim\u00e6val mucus, should be formed out of simpler combinations of carbon.\nAs we are now able artificially to produce, in our laboratories,\ncombinations of carbon similar to this in the complexity of their\nconstitution, there is absolutely no reason for supposing that there are\nnot conditions in free nature also, in which such combinations could\ntake place. Formerly, when the doctrine of spontaneous generation was\nadvocated, it failed at once to obtain adherents on account of the\ncomposite structure of the simplest organisms then known. It is only\nsince we have discovered the exceedingly important Monera, only since we\nhave become acquainted in them with organisms not in any way built up of\ndistinct organs, but which consist solely of a single chemical\ncombination, and yet grow, nourish, and propagate themselves, that this\ngreat difficulty has been removed, and the hypothesis of spontaneous\ngeneration has gained a degree of probability which entitles it to fill\nup the gap existing between Kant\u2019s cosmogony and Lamarck\u2019s Theory of\nDescent. Even among the Monera at present known there is a species which\nprobably, even now, always comes into existence by spontaneous\ngeneration. This is the wonderful _Bathybius H\u00e6ckelii_, discovered and\ndescribed by Huxley. As I have already mentioned (p. 184), this Moneron\nis found in the greatest depths of the sea, at a depth of between 12,000\nand 24,000 feet, where it covers the ground partly as retiform threads\nand plaits of plasma, partly in the form of larger or smaller irregular\nlumps of the same material.[6]\n\nOnly such homogeneous organisms as are yet not differentiated, and are\nsimilar to inorganic crystals in being homogeneously composed of one\nsingle substance, could arise by spontaneous generation, and could\nbecome the prim\u00e6val parents of all other organisms. In their further\ndevelopment we have pointed out that the most important process is the\nformation of a _kernel_ or _nucleus_ in the simple little lump of\nalbumen. We can conceive this to take place in a purely physical manner,\nby the condensation of the innermost central part of the albumen. The\nmore solid central mass, which at first gradually shaded off into the\nperipheral plasma, becomes sharply separated from it, and thus forms an\nindependent, round, albuminous corpuscle, the kernel; and by this\nprocess the Moneron becomes a _cell_. Now, it must have become evident\nfrom our previous chapters, that the further development of all other\norganisms out of such a cell presents no difficulty, for every animal\nand every plant, in the beginning of its individual life, is a simple\ncell. Man, as well as every other animal, is at first nothing but a\nsimple egg-cell, a single lump of mucus, containing a kernel (p. 297,\nFig. 5).\n\nIn the same way as the kernel of the organic cell arose in the interior\nor central mass of the originally homogeneous lump of plasma, by\nseparation, so, too, the first _cell-membrane_ was formed on its\nsurface. This simple, but most important process, as has already been\nremarked, can likewise be explained in a purely physical manner, either\nas a chemical deposit, or as a physical condensation in the uppermost\nstratum of the mass, or as a secretion. One of the first processes of\nadaptation effected by the Moneron originating by spontaneous generation\nmust have been the condensation of an external crust, which as a\nprotecting covering shut in the softer interior from the hostile\ninfluences of the outer world. As soon as, by condensation of the\nhomogeneous Moneron, a cell-kernel arose in the interior and a membrane\narose on the surface, all the fundamental parts of the unit were\nfurnished, out of which, by infinitely manifold repetition and\ncombination, as attested by actual observation, the body of higher\norganisms is constructed.\n\nAs has already been mentioned, our whole understanding of an organism\nrests upon the cell theory established thirty years ago by Schleiden and\nSchwann. According to it, every organism is either a simple cell or a\ncell-community, a republic of closely connected cells. All the forms and\nvital phenomena of every organism are the collective result of the forms\nand vital phenomena of all the single cells of which it is composed. By\nthe recent progress of the cell theory it has become necessary to give\nthe elementary organisms, that is, the \u201corganic\u201d individuals of the\nfirst order, which are usually designated as _cells_, the more general\nand more suitable name of _form-units_, or _plastids_. Among these\nform-units we distinguish two main groups, namely, the cytods and the\ngenuine cells. The _cytods_ are, like the Monera, pieces of plasma\nwithout a kernel (p. 186, Fig. 1). _Cells_, on the other hand, are\npieces of plasma containing a kernel or nucleus (p. 188, Fig. 2). Each\nof these two main groups of plastids is again divided into two\nsubordinate groups, according as they possess or do not possess an\nexternal covering (skin, shell, or membrane). We may accordingly\ndistinguish the following four grades or species of plastids, namely: 1.\n_Simple cytods_ (p. 186, Fig. 1 _A_); 2. _Encased cytods_; 3. _Simple\ncells_ (p. 188, Fig. 2 _B_); 4. _Encased cells_ (p. 188, Fig. 2 _A_).\n(Gen. Morph. i. 269-289.)\n\nConcerning the relation of these four forms of plastids to spontaneous\ngeneration, the following is the most probable:\u20141. The _simple cytods_\n(Gymnocytoda), naked particles of plasma without kernel, like the still\nliving Monera, are the only plastids which directly come into existence\nby spontaneous generation. 2. The _enclosed cytods_ (Lepocytoda),\nparticles of plasma without kernel, which are surrounded by a covering\n(membrane or shell), arose out of the simple cytods either by the\ncondensation of the outer layers of plasma or by the secretion of a\ncovering. 3. The _simple cells_ (Gymnocyta), or naked cells, particles\nof plasma with kernel, but without covering, arose out of the simple\ncytods by the condensation of the innermost particles of plasma into a\nkernel, or nucleus, by differentiation of a central kernel and\nperipheral cell-substance. 4. The _enclosed cells_ (Lepocyta), or\ntestaceous cells, particles of plasma with kernel and an outer covering\n(membrane or shell), arose either out of the enclosed cytods by the\nformation of a kernel, or out of the simple cells by the formation of a\nmembrane. All the other forms of form-units, or plastids, met with,\nbesides these, have only subsequently arisen out of these four\nfundamental forms by natural selection, by descent with adaptation, by\ndifferentiation and transformation.\n\nBy this _theory of plastids_, by deducing all the different forms of\nplastids, and hence, also, all organisms composed of them, from the\nMonera, we obtain a simple and natural connection in the whole series of\nthe development of nature. The origin of the first Monera by spontaneous\ngeneration appears to us as a simple and necessary event in the process\nof the development of the earth. We admit that this process, as long as\nit is not directly observed or repeated by experiment, remains a pure\nhypothesis. But I must again say that this hypothesis is indispensable\nfor the consistent completion of the non-miraculous history of creation,\nthat it has absolutely nothing forced or miraculous about it, and that\ncertainly it can never be positively refuted. It must be taken into\nconsideration that the process of spontaneous generation, even if it\nstill took place daily and hourly, would in any case be exceedingly\ndifficult to observe and establish with absolute certainty as such. With\nregard to the Monera, we find ourselves placed before the following\nalternative: _either_ they are actually directly derived from\npre-existing, or \u201ccreated,\u201d most ancient Monera, and in this case they\nwould have had to propagate themselves unchanged for many millions of\nyears, and to have maintained their original form of simple particles of\nplasma; _or_, the _present_ Monera have originated much later in the\ncourse of the organic history of the earth, by repeated acts of\nspontaneous generation, and in this case spontaneous generation may take\nplace now as well as then. The latter supposition has evidently much\nmore probability on its side than the former.\n\nIf we do not accept the hypothesis of spontaneous generation, then at\nthis one point of the history of development we must have recourse to\nthe miracle of a _supernatural creation_. The Creator must have created\nthe first organism, or a few first organisms, from which all others are\nderived, and as such he must have created the simplest Monera, or\nprim\u00e6val cytods, and given them the capability of developing further in\na mechanical way. I leave it to each one of my readers to choose between\nthis idea and the hypothesis of spontaneous generation. To me the idea\nthat the Creator should have in this one point arbitrarily interfered\nwith the regular process of development of matter, which in all other\ncases proceeds entirely without his interposition, seems to be just as\nunsatisfactory to a believing mind as to a scientific intellect. If, on\nthe other hand, we assume the hypothesis of spontaneous generation for\nthe origin of the first organisms, which in consequence of reasons\nmentioned above, and especially in consequence of the discovery of the\nMonera, has lost its former difficulty, then we arrive at the\nestablishment of an uninterrupted natural connection between the\ndevelopment of the earth and the organisms produced on it, and, in this\nlast remaining lurking-place of obscurity, we can proclaim the _unity of\nall Nature, and the unity of her laws of Development_ (Gen. Morph. i.\n164).\n\n\n\n\nCHAPTER XIV.\n\nMIGRATION AND DISTRIBUTION OF ORGANISMS. CHOROLOGY AND THE ICE-PERIOD OF\nTHE EARTH.\n\n\n   Chorological Facts and Causes.\u2014Origin of most Species in\n   one Single Locality: \u201cCentres of Creation.\u201d\u2014Distribution\n   by Migration.\u2014Active and Passive Migrations of Animals\n   and Plants.\u2014Means of Transport.\u2014Transport of Germs by\n   Water and by Wind.\u2014Continual Change of the Area of\n   Distribution by Elevations and Depressions of the\n   Ground.\u2014Chorological Importance of Geological\n   Processes.\u2014Influence of the Change of Climate.\u2014Ice or\n   Glacial Period.\u2014Its Importance to Chorology.\u2014Importance\n   of Migrations for the Origin of New Species.\u2014Isolation\n   of Colonists.\u2014Wagner\u2019s Law of Migration.\u2014Connection\n   between the Theory of Migration and the Theory of\n   Selection.\u2014Agreement of its Results with the Theory of\n   Descent.\n\n\nAs I have repeatedly said, but cannot too much emphasize, the actual\nvalue and invincible strength of the Theory of Descent does not lie in\nits explaining this or that single phenomenon, but in the fact that it\nexplains _all_ biological phenomena, that it makes _all_ botanical and\nzoological series of phenomena intelligible in their relations to one\nanother. Hence every thoughtful investigator is the more firmly and\ndeeply convinced of its truth the more he advances from single\nbiological observations to a general view of the whole domain of animal\nand vegetable life. Let us now, starting from this comprehensive point\nof view, survey a biological domain, the varied and complicated\nphenomena of which may be explained with remarkable simplicity and\nclearness by the theory of selection. I mean _Chorology_, or the theory\nof the _local distribution of organisms over the surface of the earth_.\nBy this I do not only mean the _geographical_ distribution of animal and\nvegetable species over the different parts and provinces of the earth,\nover continents and islands, seas, and rivers; but also their\n_topographical_ distribution in a _vertical_ direction, their ascending\nto the heights of mountains, and their descending into the depths of the\nocean. (Gen. Morph. ii. 286.)\n\nThe strange chorological series of phenomena which show the horizontal\ndistribution of organisms over parts of the earth, and their vertical\ndistribution in heights and depths, have long since excited general\ninterest. In recent times Alexander Humboldt(39) and Frederick Schouw\nhave especially discussed the geography of plants, and Berghaus and\nSchmarda the geography of animals, on a large scale. But although these\nand several other naturalists have in many ways increased our knowledge\nof the distribution of animal and vegetable forms, and laid open to us a\nnew domain of science, full of wonderful and interesting phenomena, yet\nChorology as a whole remained, as far as their labours were concerned,\nonly a desultory knowledge of a mass of individual _facts_. It could not\nbe called a science as long as the _causes_ for the explanation of these\nfacts were wanting. These causes were first disclosed by the theory of\nselection and its doctrine of the _migrations_ of animal and vegetable\nspecies, and it is only since the works of Darwin and Wallace that we\nhave been able to speak of an independent _science of Chorology_.\n\nIf all the phenomena of the geographical and topographical distribution\nof organisms are examined by themselves, without considering the gradual\ndevelopment of species, and if at the same time, following the customary\nsuperstition, the individual species of animals and plants are\nconsidered as forms independently created and independent of one\nanother, then there remains nothing for us to do but to gaze at those\nphenomena as a confused collection of incomprehensible and inexplicable\nmiracles. But as soon as we leave this low stand-point, and rise to the\nheight of the theory of development, by means of the supposition of a\nblood-relationship between the different species, then all at once a\nclear light falls upon this strange series of miracles, and we see that\nall chorological facts can be understood quite simply and clearly by the\nsupposition of a common descent of the species, and their passive and\nactive migrations.\n\nThe most important principle from which we must start in chorology, and\nof the truth of which we are convinced by due examination of the theory\nof selection, is that, as a rule, every animal and vegetable species has\narisen only _once_ in the course of time and only in _one_ place on the\nearth\u2014its so-called \u201ccentre of creation\u201d\u2014by natural selection. I share\nthis opinion of Darwin\u2019s unconditionally, in respect to the great\nmajority of higher and perfect organisms, and in respect to most animals\nand plants in which the division of labour, or differentiation of the\ncells and organs of which they are composed, has attained a certain\nstage. For it is quite incredible, or could at best only be an\nexceedingly rare accident, that all the manifold and complicated\ncircumstances\u2014all the different conditions of the struggle for life,\nwhich influence the origin of a new species by natural selection\u2014should\nhave worked together in exactly the same agreement and combination more\nthan once in the earth\u2019s history, or should have been active at the same\ntime at several different points of the earth\u2019s surface.\n\nOn the other hand, I consider it to be very probable that certain\nexceedingly imperfect organisms of the simplest structure, forms of\nspecies of an exceedingly indifferent nature, as, for example, many\nsingle-celled Protista, but especially the Monera, the simplest of them\nall, should have several times or simultaneously arisen in their\nspecific form in several parts of the earth. For the few and very simple\nconditions by which their specific form was changed in the struggle for\nlife may surely have often been repeated, in the course of time,\nindependently in different parts of the earth. Further, those higher\nspecific forms also, which have not arisen by natural selection, but by\n_hybridism_ (the previously-mentioned hybrid species, pp. 147 and 275),\nmay have repeatedly arisen anew in different localities. As, however,\nthis proportionately small number of organisms does not especially\ninterest us here, we may, in respect of chorology, leave them alone, and\nneed only take into consideration the distribution of the great majority\nof animal and vegetable species in regard to which the _single origin of\nevery species in a single locality_, in its so-called \u201ccentral point of\ncreation,\u201d can be considered as tolerably certain.\n\nEvery animal and vegetable species from the beginning of its existence\nhas possessed the tendency to spread beyond the limited locality of its\norigin, beyond the boundary of its \u201ccentre of creation,\u201d or, in other\nwords, beyond its _prim\u00e6val home_, or its natal place. This is a\nnecessary consequence of the relations of population and over-population\n(pp. 161 and 256). The more an animal or vegetable species increases,\nthe less is its limited natal place sufficient for its sustenance, and\nthe fiercer the struggle for life; the more rapid the _over-population_\nof the natal spot, the more it leads to _emigration_. These _migrations_\nare common to all organisms, and are the real cause of the wide\ndistribution of the different species of organisms over the earth\u2019s\nsurface. Just as men leave over-crowded states, so all animals and\nplants migrate from their over-crowded prim\u00e6val homes.\n\nMany distinguished naturalists, especially Lyell(11) and Schleiden, have\nbefore this repeatedly drawn attention to the great importance of these\nvery interesting migrations of organisms. The means of transport by\nwhich they are effected are extremely varied. Darwin has discussed these\nmost excellently in the eleventh and twelfth chapters of his work, which\nare exclusively devoted to \u201cgeographical distribution.\u201d The means of\ntransport are partly active, partly passive; that is to say, the\norganism effects its migration partly by free locomotion due to its own\nactivity, and partly by the movements of other natural bodies in which\nit has no active share.\n\nIt is self-evident that _active migrations_ play the chief part in\nanimals able to move freely. The more freely an animal\u2019s organization\npermits it to all move in directions, the more easily the animal species\ncan migrate, and the more rapidly it will spread over the earth.\n_Flying_ animals are of course most favoured in this respect, among\nvertebrate animals especially birds, and among articulated animals,\ninsects. These two classes, as soon as they came into existence, can\nhave more easily spread over the whole earth than any other animal, and\nthis fact partly explains the extraordinary uniformity of structure\nwhich characterizes these two great classes of animals. For, although\nthey contain an exceedingly large number of different species, and\nalthough the insect class alone is said to possess more different\nspecies than all other classes of animals together, yet all the\ninnumerable species of insects, and in like manner, also, the different\nspecies of birds, agree most strikingly in all essential peculiarities\nof their organization. Hence, in the class of insects, as well as in\nthat of birds, we can distinguish only a very small number of large\nnatural groups or orders, and these few orders differ but very little\nfrom one another in their internal structure. The orders of birds with\ntheir numerous species are not nearly as distinct from one another as\nthe orders of the mammalian class, containing much fewer species; and\nthe orders of insects, which are extremely rich in genera and species,\nresemble one another much more closely in their internal structure than\ndo the much smaller orders of the crab class. The general parallelism\nbetween birds and insects is also very interesting in relation to\nsystematic zoology; and the great importance of their richness in forms,\nfor scientific morphology, lies in the fact that they show us how,\nwithin the narrowest anatomical sphere, and without profound changes of\nthe essential internal organization, the greatest variety in external\nbodily forms can be attained. The reason of this is evidently their\nflying mode of life and their free locomotion. In consequence of this\nbirds, as well as insects, have spread very rapidly over the whole\nsurface of the earth, have settled in all possible localities\ninaccessible to other animals, and variously modified their specific\nform by superficial adaptation to particular local relations.\n\nNext to the flying animals, those animals, of course, have spread most\nquickly and furthest which were next best able to migrate, that is, the\nbest runners among the inhabitants of the land, and the best swimmers\namong the inhabitants of the water. However, the power of such active\nmigrations is not confined to those animals which throughout life enjoy\nfree locomotion. For the fixed animals also, such as corals, tubicolous\nworms, sea-squirts, lily encrinites, sea-acorns, barnacles, and many\nother lower animals which adhere to seaweeds, stones, etc., enjoy, at\nleast at an early period of life, free locomotion. They all migrate\nbefore they adhere to anything. Their first free locomotive condition of\nearly life is generally that of a \u201cciliated\u201d larva, a roundish, cellular\ncorpuscle, which, by means of a garb of movable \u201cflimmer-hairs,\u201d (Latin,\n\u201ccilia\u201d) swarms about in the water and bears the name of Planula.\n\nBut the power of free locomotion, and hence, also, of active migration,\nis not confined to animals alone, but many plants likewise enjoy it.\nMany lower aquatic plants, especially the class of the Tangles (Alg\u00e6),\nswim about freely in the water in early life, like the lower animals\njust mentioned, by means of a vibratile hairy coat, a vibrating whip, or\na covering of tremulous fringes, and only at a later period adhere to\nobjects. Even in the case of many higher plants, which we designate as\ncreepers and climbing plants, we may speak of active migration. Their\nelongated stalks and perennial roots creep or climb during their long\nprocess of growth to new positions, and by means of their widespread\nbranches they acquire new habitations, to which they attach themselves\nby buds, and bring forth new colonies of individuals of their species.\n\nInfluential as these active migrations of most animals and many plants\nare, yet alone they would by no means be sufficient to explain the\nchorology of organisms. _Passive migrations_ have ever been by far the\nmore important, and of far greater influence, in the case of most plants\nand in that of many animals. Such passive changes of locality are\nproduced by extremely numerous causes. Air and water in their eternal\nmotion, wind and waves with their manifold currents, play the chief\npart. The wind in all places and at all times raises light organisms,\nsmall animals and plants, but especially their young germs, animal eggs\nand plant seeds, and carries them far over land and seas. Where they\nfall into the water they are seized by currents or waves and carried to\nother places. It is well known, from numerous examples, how far in many\ncases trunks of trees, hard shelled fruits, and other not readily\nperishable portions of plants are carried away from their original home\nby the course of rivers and by the currents of the sea. Trunks of palm\ntrees from the West Indies are brought by the Gulf Stream to the British\nand Norwegian coasts. All large rivers bring down driftwood from the\nmountains, and frequently alpine plants are carried from their home at\nthe source of the river into the plains, and even further, down to the\nsea. Frequently numerous inhabitants live between the roots of the\nplants thus carried down, and between the branches of the trees thus\nwashed away there are various inhabitants which have to take part in the\npassive migration. The bark of the tree is covered with mosses, lichens,\nand parasitic insects. Other insects, spiders, etc., even small\nreptiles and mammals, are hidden within the hollow trunk or cling to the\nbranches. In the earth adhering to the fibres of the roots, in the dust\nlying in the cracks of the bark, there are innumerable germs of smaller\nanimals and plants. Now, if the trunk thus washed away lands safely on a\nforeign shore or on a distant island, the guests who had to take part in\nthe involuntary voyage can leave their boat and settle in the new\ncountry. A very remarkable kind of water-transport is formed by the\nfloating icebergs which annually become loosened from the eternal ice of\nthe Polar Sea. Although these cold regions are thinly peopled, yet many\nof their inhabitants, who were accidentally upon an iceberg while it was\nbecoming loosened, are carried away with it by the currents, and landed\non warmer shores. In this manner, by means of loosened blocks of ice\nfrom the northern Polar Sea, often whole populations of small animals\nand plants have been carried to the northern shores of Europe and\nAmerica. Nay, even polar foxes and polar bears have been carried in this\nway to Iceland and to the British Isles.\n\nTransport by air is no less important than transport by water in this\nmatter of passive migration. The dust covering our streets and roofs,\nthe earth lying on dry fields and dried-up pools, the light moist soil\nof forests, in short, the whole surface of the globe contains millions\nof small organisms and their germs. Many of these small animals and\nplants can without injury become completely dried up, and awake again to\nlife as soon as they are moistened. Every gust of wind raises up with\nthe dust innumerable little creatures of this kind, and often carries\nthem away to other places miles off. But even larger organisms, and\nespecially their germs, may often make distant passive journeys through\nthe air. The seeds of many plants are provided with light feathery\nprocesses, which act as parachutes and facilitate their flight in the\nair, and prevent their falling. Spiders make journeys of many miles\nthrough the air on their fine filaments, their so-called gossamer\nthreads. Young frogs are frequently raised by whirlwinds into the air by\nthousands, and fall down in a distant part as a \u201cshower of frogs.\u201d\nStorms may carry birds and insects across half the earth\u2019s\ncircumference. They drop in the United States, having risen in England.\nStarting from California, they only come to rest in China. But, again,\nmany other organisms may make the journey from one continent to another\ntogether with the birds and insects. Of course all parasites, the number\nof which is legion, fleas, lice, mites, moulds, etc., migrate with the\norganisms upon which they live. In the earth which often remains\nsticking to the claws of birds there are also small animals and plants\nor their germs. Thus the voluntary or involuntary migration of a single\nlarger organism may carry a whole small flora and fauna from one part of\nthe earth to another.\n\nBesides the means of transport here mentioned, there are many others\nwhich explain the distribution of animal and vegetable species over the\nlarge tracts of the earth\u2019s surface, and especially the general\ndistribution of the so-called cosmopolitan species. But these alone\nwould not nearly be sufficient to explain all chorological facts. How is\nit, for example, that many inhabitants of fresh water live in various\nrivers or lakes far away and quite apart from one another? How is it\nthat many inhabitants of mountains, which cannot exist in plains, are\nfound upon entirely separated and far distant chains of mountains? It\nis difficult to believe, and in many cases quite inconceivable, that\nthese inhabitants of fresh water should have in any way, actively or\npassively, migrated over the land lying between the lakes, or that the\ninhabitants of mountains in any way, actively or passively, crossed the\nplains lying between their mountain homes. But here geology comes to our\nhelp, as a mighty ally, and completely solves these difficult problems\nfor us.\n\nThe history of the earth\u2019s development shows us that the distribution of\nland and water on its surface is ever and continually changing. In\nconsequence of geological changes of the earth\u2019s crust, _elevations_ and\n_depressions_ of the ground take place everywhere, sometimes more\nstrongly marked in one place, sometimes in another. Even if they happen\nso slowly that in the course of centuries the seashore rises or sinks\nonly a few inches, or even only a few lines, still they nevertheless\neffect great results in the course of long periods of time. And\nlong\u2014immeasurably long\u2014periods of time have not been wanting in the\nearth\u2019s history. During the course of many millions of years, ever since\norganic life existed on the earth, land and water have perpetually\nstruggled for supremacy. Continents and islands have sunk into the sea,\nand new ones have arisen out of its bosom. Lakes and seas have slowly\nbeen raised and dried up, and new water basins have arisen by the\nsinking of the ground. Peninsulas have become islands by the narrow neck\nof land which connected them with the mainland sinking into the water.\nThe islands of an archipelago have become the peaks of a continuous\nchain of mountains by the whole floor of their sea being considerably\nraised.\n\nThus the Mediterranean at one time was an inland sea, when, in the place\nof the Straits of Gibraltar, an isthmus connected Africa with Spain.\nEngland, even during the more recent history of the earth, when man\nalready existed, has repeatedly been connected with the European\ncontinent and been repeatedly separated from it. Nay, even Europe and\nNorth America have been directly connected. The South Sea at one time\nformed a large Pacific Continent, and the numerous little islands which\nnow lie scattered in it were simply the highest peaks of the mountains\ncovering that continent. The Indian Ocean formed a continent which\nextended from the Sunda Islands along the southern coast of Asia to the\neast coast of Africa. This large continent of former times Sclater, an\nEnglishman, has called _Lemuria_, from the monkey-like animals which\ninhabited it, and it is at the same time of great importance from being\nthe probable cradle of the human race, which in all likelihood here\nfirst developed out of anthropoid apes. The important proof which Alfred\nWallace has furnished,(36) by the help of chorological facts, that the\npresent Malayan Archipelago consists in reality of two completely\ndifferent divisions, is particularly interesting. The western division,\nthe Indo-Malayan Archipelago, comprising the large islands of Borneo,\nJava, and Sumatra, was formerly connected by Malacca with the Asiatic\ncontinent, and probably also with the Lemurian continent just mentioned.\nThe eastern division, on the other hand, the Austro-Malayan Archipelago,\ncomprising Celebes, the Moluccas, New Guinea, Solomon\u2019s Islands, etc.,\nwas formerly directly connected with Australia. Both divisions were\nformerly two continents separated by a strait, but they have now for\nthe most part sunk below the level of the sea. Wallace, solely on the\nground of his accurate chorological observations, has been able in the\nmost acute manner to determine the position of this former strait, the\nsouth end of which passes between Balij and Lombok.\n\nThus, ever since liquid water existed on the earth, the boundaries of\nwater and land have eternally changed, and we may assert that the\noutlines of continents and islands have never remained for an hour, nay,\neven for a minute, exactly the same. For the waves eternally and\nperpetually break on the edge of the coast, and whatever the land in\nthese places loses in extent, it gains in other places by the\naccumulation of mud, which condenses into solid stone and again rises\nabove the level of the sea as new land. Nothing can be more erroneous\nthan the idea of a firm and unchangeable outline of our continents, such\nas is impressed upon us in early youth by defective lessons on\ngeography, which are devoid of a geological basis.\n\nI need hardly draw attention to the fact that these geological changes\nof the earth\u2019s surface have ever been exceedingly important to the\nmigrations of organisms, and consequently to their Chorology. From them\nwe learn to understand how it is that the same or nearly related species\nof animals and plants can occur on different islands, although they\ncould not have passed through the water separating them, and how other\nspecies living in fresh water can inhabit different enclosed\nwater-basins, although they could not have crossed the land lying\nbetween them. These islands were formerly mountain peaks of a connected\ncontinent, and these lakes were once directly connected with one\nanother. The former were separated by geological depressions, the latter\nby elevations. Now, if we further consider how often and how unequally\nthese alternating elevations and depressions occur on the different\nparts of the earth, and how, in consequence of this, the boundaries of\nthe geographical tracts of distribution of species become changed, and\nif we further consider in what exceedingly various ways the active and\npassive migrations of organisms must have been influenced by them, then\nwe shall be in a position to completely understand the great variety of\nthe picture which is at present offered to us by the distribution of\nanimal and vegetable species.\n\nThere is yet another important circumstance to be mentioned here, which\nis likewise of great importance for a complete explanation of this\nvaried geographical picture, and which throws light upon many very\nobscure facts, which, without its help, we should not be able to\ncomprehend. I mean the gradual _change of climate_ which has taken place\nduring the long course of the organic history of the earth. As we saw in\nour last chapter, at the beginning of organic life on the earth a much\nhigher and more equal temperature must have generally prevailed than at\npresent. The differences of zones, which in our time are so very\nstriking, did not exist at all in those times. It is probable that for\nmany millions of years but one climate prevailed over the whole earth,\nwhich very closely resembled, or even surpassed, the hottest tropical\nclimate of the present day. The highest north which man has yet reached\nwas then covered with palms and other tropical plants, the fossil\nremains of which are still found there. The temperature of this climate\nat a later period gradually decreased; but still the poles remained so\nwarm that the whole surface of the earth could be inhabited by\norganisms. It was only at a comparatively very recent period of the\nearth\u2019s history, namely, at the beginning of the tertiary period, that\nthere occurred, as it seems, the first perceptible cooling of the\nearth\u2019s crust at the poles, and through this the first differentiation\nor separation of the different zones of temperature or climatic zones.\nBut the slow and gradual decrease of temperature continued to extend\nmore and more within the tertiary period, until at last, at both poles\nof the earth, the first permanent ice caps were formed.\n\nI need scarcely point out in detail how very much this change of climate\nmust have affected the geographical distribution of organisms, and the\norigin of numerous new species. The animal and vegetable species, which,\ndown to the tertiary period, had found an agreeable tropical climate all\nover the earth, even as far as the poles, were now forced either to\nadapt themselves to the intruding cold, or to flee from it. Those\nspecies which adapted and accustomed themselves to the decreasing\ntemperature became new species simply by this very acclimatization,\nunder the influence of natural selection. The other species, which fled\nfrom the cold, had to emigrate and seek a milder climate in lower\nlatitudes. The tracts of distribution which had hitherto existed must by\nthis have been vastly changed.\n\nHowever, during the last great period of the earth\u2019s history, during the\nquaternary period (or diluvial period) succeeding the tertiary one, the\ndecrease of the heat of the earth from the poles did not by any means\nremain stationary. The temperature fell lower and lower, nay, even far\nbelow the present degree. Northern and Central Asia, Europe, and North\nAmerica from the north pole, were covered to a great extent by a\nconnected sheet of ice, which in our part of the earth seems to have\nreached the Alps. In a similar manner the cold also advancing from the\nsouth pole covered a large portion of the southern hemisphere, which is\nnow free from it, with a rigid sheet of ice. Thus, between these vast\nlifeless ice continents there remained only a narrow zone to which the\nlife of the organic world had to withdraw. This period, during which\nman, or at least the human ape, already existed, and which forms the\nfirst period of the so-called _diluvial epoch_, is now universally known\nas the _ice_ or _glacial period_.\n\nThe ingenious Carl Schimper is the first naturalist who clearly\nconceived the idea of the ice period, and proved the great extent of the\nformer glaciation of Central Europe by the help of the so-called\nboulders, or erratic blocks of stone, as also by the \u201cglacier tables.\u201d\nLouis Agassiz, stimulated by him, and considerably supported by the\nindependent investigations of the eminent geologist Charpentier,\nafterwards undertook the task of carrying out the theory of the ice\nperiod. In England, the geologist Forbes distinguished himself in this\nmatter, and also was the first to apply it to the theory of migrations\nand the geographical distribution of species dependent upon migration.\nAgassiz, however, afterwards injured the theory by his one-sided\nexaggeration, inasmuch as, from his partiality to Cuvier\u2019s theory of\ncataclysms, he endeavoured to attribute the destruction of the whole\nanimate creation then existing, to the sudden coming on of the cold of\nthe ice period and the \u201crevolution\u201d connected with it.\n\nIt is unnecessary here to enter into detail as to the ice period itself,\nand into investigations about its limits, and I may omit this all the\nmore reasonably since the whole of our recent geological literature is\nfull of it. It will be found discussed in detail in the works of\nCotta,(31) Lyell,(30) Vogt,(27) Zittel,(32) etc. Its great importance to\nus here is that it helps us to explain the most difficult chorological\nproblems, as Darwin has correctly perceived.\n\nFor there can be no doubt that this glaciation of the present temperate\nzones must have exercised an exceedingly important influence on the\ngeographical and topographical distribution of organisms, and that it\nmust have entirely changed it. While the cold slowly advanced from the\npoles towards the equator, and covered land and sea with a connected\nsheet of ice, it must of course have driven the whole living world\nbefore it. Animals and plants had to migrate if they wished to escape\nbeing frozen. But as at that time the temperate and tropical zones were\nprobably no less densely peopled with animals and plants than at\npresent, there must have arisen a fearful struggle for life between the\nlatter and the intruders coming from the poles. During this struggle,\nwhich certainly lasted many thousands of years, many species must have\nperished and many become modified and been transformed into new species.\nThe hitherto existing tracts of distribution of species must have become\ncompletely changed, and the struggle have been continued, nay, indeed,\nmust have broken out anew and been carried on in new forms, when the ice\nperiod had reached and gone beyond its furthest point, and when in the\npost-glacial period the temperature again increased, and organisms began\nto migrate back again towards the poles.\n\nIn any case this great change of climate, whether a greater or less\nimportance be ascribed to it, is one of those occurrences in the history\nof the earth which have most powerfully influenced the distribution of\norganic forms. But more especially one important and difficult\nchorological circumstance is explained by it in the simplest manner,\nnamely, the specific agreement of many of our Alpine inhabitants with\nsome of those living in polar regions. There is a great number of\nremarkable animal and vegetable forms which are common to these two far\ndistant parts of the earth, and which are found nowhere in the wide\nplains lying between them. Their migration from the polar lands to the\nAlpine heights, or _vice versa_, would be inconceivable under the\npresent climatic circumstances, or could be assumed at least only in a\nfew rare instances. But such a migration could take place, nay, was\nobliged to take place, during the gradual advance and retreat of the\nice-sheet. As the glaciation encroached from Northern Europe towards our\nAlpine chains, the polar inhabitants retreating before it\u2014gentian,\nsaxifrage, polar foxes, and polar hares\u2014must have peopled Germany, in\nfact all Central Europe. When the temperature again increased, only a\nportion of these Arctic inhabitants returned with the retreating ice to\nthe Arctic zones. Another portion of them climbed up the mountains of\nthe Alpine chain instead, and there found the cold climate suited to\nthem. The problem is thus solved in a most simple manner.\n\nWe have hitherto principally considered the _theory of the migrations_\nof organisms in so far as it explains the radiation of every animal and\nvegetable species from a single prim\u00e6val home, from a \u201ccentral point of\ncreation,\u201d and the dispersion of these species over a greater or less\nportion of the earth\u2019s surface. But these migrations are also of great\nimportance to the theory of development, because we can perceive in them\na very important means for the _origin of new species_. When animals and\nplants migrate they meet in their new home, in the same way as do human\nemigrants, with conditions which are more or less different from those\nwhich they have inherited throughout generations, and to which they have\nbeen accustomed. The emigrants must either submit and adapt themselves\nto these new conditions of life or they perish. By adaptation their\npeculiar specific character becomes the more changed the greater the\ndifference between the new and the old home. The new climate, the new\nfood, but above all, new neighbours in the forms of other animals and\nplants, influence and tend to modify the inherited character of the\nimmigrant species, and if it is not hardy enough to resist the\ninfluences, then sooner or later a new species must arise out of it. In\nmost cases this transformation of an immigrant species takes place so\nquickly under the influence of the altered struggle for life, that even\nafter a few generations a new species arises from it.\n\nMigration has an especial influence in this way on all organisms with\nseparate sexes. For in them the origin of new species by natural\nselection is always rendered difficult, or delayed, by the fact that the\nmodified descendants occasionally again mix sexually with the unchanged\noriginal form, and thus by crossing return to the first form. But if\nsuch varieties have migrated, if great distances or barriers to\nmigration\u2014seas, mountains, etc.\u2014have separated them from the old home,\nthen the danger of a mingling with the primary form is prevented, and\nthe isolation of the emigrant form, which becomes a new species by\nadaptation, prevents its breeding with the old stock, and hence prevents\nits return in this way to the original form.\n\nThe importance of migration for the isolation of newly-originating\nspecies and the prevention of a speedy return to the primary form has\nbeen especially pointed out by the philosophic traveller, Moritz Wagner,\nof Munich. In a special treatise on \u201cDarwin\u2019s Theory and the Law of the\nMigration of Organisms,\u201d(40) Wagner gives from his own rich experience a\ngreat number of striking examples which confirm the theory of migration\nset forth by Darwin in the eleventh and twelfth chapters of his book,\nwhere he especially discusses the effect of the complete isolation of\nemigrant organisms in the origin of new species. Wagner sets forth the\nsimple causes which have \u201clocally bounded the form and founded its\ntypical difference,\u201d in the following three propositions:\u20141. The\ngreater the total amount of change in the hitherto existing conditions\nof life which the emigrating individuals find on entering a new\nterritory, the more intensely must the innate variability of every\norganism manifest itself. 2. The less this increased individual\nvariability of organisms is disturbed in the peaceful process of\nreproduction by the mingling of numerous subsequent immigrants of the\nsame species, the more frequently will nature succeed, by\nintensification and transmission of the new characteristics, in forming\na new variety or race, that is, a commencing species. 3. The more\nadvantageous the changes experienced by the individual organs are to the\nvariety, the more readily will it be able to adapt itself to the\nsurrounding conditions; and the longer the undisturbed breeding of a\ncommencing variety of colonists in a new territory continues without its\nmingling with subsequent immigrants of the same species, the oftener a\nnew species will arise out of the variety.\n\nEvery one will agree with these three propositions of Moritz Wagner\u2019s.\nBut we must consider his view, that the migration and the subsequent\nisolation of the emigrant individuals is a _necessary_ condition for the\norigin of new species, to be completely erroneous. Wagner says, \u201cwithout\na long-enduring separation of colonists from their former species, the\nformation of a new race cannot succeed\u2014selection, in fact, cannot take\nplace. Unlimited crossing, unhindered sexual mingling of all individuals\nof a species will always produce uniformity, and drive varieties, whose\ncharacteristics have not been fixed throughout a series of generations,\nback to the primary form.\u201d\n\nThis sentence, in which Wagner himself comprises the main result of his\ninvestigations, he would be able to defend only if all organisms were of\nseparate sexes, if every origin of new individuals were possible only by\nthe mingling of male and female individuals. But this is by no means the\ncase. Curiously enough, Wagner says nothing of the numerous\nhermaphrodites which, possessing both the sexual organs, are capable of\nself-fructification, and likewise nothing of the countless organisms\nwhich are not sexually differentiated.\n\nNow, from the earliest times of the organic history of the earth, there\nhave existed thousands of organic species (thousands of which still\nexist) in which no difference of sex whatever exists, and, in fact, in\nwhich no sexual propagation takes place, and which exclusively reproduce\nthemselves in a non-sexual manner by division, budding, formation of\nspores, etc. All the great mass of Protista, the Monera, Am\u0153b\u00e6,\nMyxomycetes, Rhizopoda, etc., in short, all the lower organisms which we\nshall have to enumerate in the domain of Protista, standing midway\nbetween the animal and vegetable kingdoms, propagate themselves\n_exclusively in a non-sexual manner_. And this domain comprises a class\nof organisms which is one of the richest in forms, nay, even in a\ncertain respect the richest of all in forms, as all possible geometrical\nfundamental forms are represented in it. I allude to the wonderful class\nof the Rhizopoda, or Ray-streamers, to which the lime-shelled Acyttaria\nand the flint-shelled Radiolaria belong. (Compare chapter xvi.)\n\nIt is self-evident, therefore, that Wagner\u2019s theory is quite\ninapplicable to all these non-sexual organisms. Moreover, the same\napplies to all those hermaphrodites in which every individual possesses\nboth male and female organs and is capable of self-fructification. This\nis the case, for instance, in the Flat-worms, flukes, and tape-worms,\nfurther in the important Sack-worms (Tunicates), the invertebrate\nrelatives of the vertebrate animals, and in very many other organisms of\ndifferent groups. Many of these species have arisen by natural\nselection, without a \u201ccrossing\u201d of the originating species with its\nprimary form having been possible.\n\nAs I have already shown in the eighth chapter, the origin of the two\nsexes, and consequently sexual propagation in general, must be\nconsidered as a process which began only in later periods of the organic\nhistory of the earth, being the result of differentiation or _division\nof labour_. The most ancient terrestrial organisms can have propagated\nthemselves only in the simplest non-sexual manner. Even now all\nProtista, as well as all the countless forms of cells, which constitute\nthe body of higher organisms, multiply themselves only by non-sexual\ngeneration. And yet there arise here \u201cnew species\u201d by differentiation in\nconsequence of natural selection.\n\nBut even if we were to take into consideration the animal and vegetable\nspecies with separate sexes, in this case too we should have to oppose\nWagner\u2019s chief proposition, that \u201cthe _migration_ of organisms and their\nformation of colonies is the _necessary condition of natural\nselection_.\u201d August Weismann, in his treatise on the \u201cInfluence of\nIsolation upon the Formation of Species,\u201d(24) has already sufficiently\nrefuted that proposition, and has shown that even in one and the same\ndistrict one bi-sexual species may divide itself into several species by\nnatural selection. In relation to this question, I must again call to\nmind the great influence which _division of labour, or differentiation_,\npossesses, being one of the necessary results of natural selection. All\nthe different kinds of cells constituting the body of the higher\norganisms, the nerve cells, muscle cells, gland cells, etc., all these\n\u201cgood species,\u201d these \u201cbon\u00e6 species\u201d of elementary organisms, have\narisen solely by division of labour, in consequence of natural\nselection, although they not only never were locally isolated, but ever\nsince their origin have always existed in the closest local relations\none with another. Now, the same reasoning that applies to these\nelementary organisms, or \u201cindividuals of the first order,\u201d applies also\nto the many-celled organisms of a higher order which only at a later\ndate have arisen as \u201cgood species\u201d from among their fellows.\n\nWe are therefore of the same opinion as Darwin and Wallace, that the\nmigration of organisms and their isolation in their new home is a very\nadvantageous condition for the origin of new species; but we cannot\nadmit, as Wagner asserts, that it is a _necessary_ condition, and that\nwithout it no species can arise. Wagner sets up this opinion, \u201cthat\nmigration is a necessary condition for natural selection,\u201d as a special\n\u201c_law of migration_\u201d; but we consider it sufficiently refuted by the\nabove-mentioned facts. We have, moreover, already pointed out that in\nreality the origin of new species by natural selection is a\n_mathematical and logical necessity_ which, without anything else,\nfollows from the simple combination of three great facts. These three\nfundamental facts are\u2014the Struggle for Life, the Adaptability, and the\nHereditivity of organisms.\n\nWe cannot here enter into detail concerning the numerous interesting\nphenomena furnished by the geographical and topographical distribution\nof organic species, which are all wonderfully explained by the theory of\nselection and migration. For these I refer to the writings of Darwin,(1)\nWallace,(36) and Moritz Wagner,(40) in which the important doctrine of\nthe _limits of distribution_\u2014seas, rivers, and mountains\u2014is\nexcellently discussed and illustrated by numerous examples. Only three\nother phenomena must be mentioned here on account of their special\nimportance. First, the close relation of forms, that is, the striking\n\u201cfamily likeness\u201d existing between the characteristic local forms of\nevery part of the globe, and their extinct fossil ancestors in the same\npart of the globe; secondly, the no less striking \u201cfamily likeness\u201d\nbetween the inhabitants of island groups and those of the neighbouring\ncontinent from which the islands were peopled; lastly and thirdly, the\npeculiar character presented in general by the flora and fauna of\nislands taken as a whole.\n\nAll these chorological facts given by Darwin, Wallace, and\nWagner\u2014especially the remarkable phenomena of the limited local fauna\nand flora, the relations of insular to continental inhabitants, the wide\ndistribution of the so-called \u201ccosmopolitan species,\u201d the close\nrelationship of the local species of the present day with the extinct\nspecies of the same limited territory, the demonstrable radiation of\nevery species from a single central point of creation\u2014all these, and\nall other phenomena furnished to us by the geographical and the\ntopographical distribution of organisms, are explained in a simple and\nthorough manner by the theory of selection and migration, while without\nit they are simply incomprehensible. Consequently, in the whole of this\nseries of phenomena we find a new and weighty proof of the truth of the\nTheory of Descent.\n\n\n  [1]     The world is perfect save where Man\n          Comes in with his strife.\n\n  [2] Archebiosis (Bastian), Abiogenesis (Huxley).\n\n  [3]     Alle Glieder bilden sich aus nach ew\u2019gen Gesetzen,\n          Und die seltenste Form bewahrt im Geheimniss das Urbild.\n          Also bestimmt die Gestalt die Lebensweise des Thieres.\n          Und die Weise zu leben, sie wirkt auf alle Gestalten\n          M\u00e4chtig zur\u00fcck. So zeiget sich fest die geordnete Bildung,\n          Welche zum Wechsel sich neigt durch \u00e4usserlich wirkende Wesen.\n\n  [4]    \u201cEinstweilen bis den Bau der Welt\n          Philosophie zusammenh\u00e4lt,\n          Erh\u00e4lt sich ihr Getriebe\n          Durch Hunger und durch Liebe.\u201d\n\n  [5] \u201cAllgemeine Naturgeschichte und Theorie des Himmels.\u201d\n\n  [6] We must wait for fuller information on the subject of\n      Bathybius, at the hands of the naturalists of the _Challenger_\n      expedition, before accepting it finally as a distinct\n      organism.\u2014_Editor._\n\n\nEND OF VOL. I.\n\n\n\n\nWORKS OF PROFESSOR ERNST HAECKEL.\n\n\n   FREEDOM IN SCIENCE AND TEACHING. From the German of ERNST\n   HAECKEL. With a Prefatory Note by T. H. Huxley, F.R.S. 1\n   vol., 12mo.\n\n   THE EVOLUTION OF MAN. A Popular Exposition of the\n   Principal Points of Human Ontogeny and Phylogeny. From\n   the German of ERNST HAECKEL, Professor in the University\n   of Jena, author of \u201cThe History of Creation,\u201d etc. With\n   numerous Illustrations. In two vols., 12mo. Cloth. Price,\n   $5.00.\n\n_From the London Saturday Review._\n\n\u201cIn this excellent translation of Professor Haeckel\u2019s work, the English\nreader has access to the latest doctrines of the Continental school of\nevolution, in its application to the history or man. It is in Germany,\nbeyond any other European country, that the impulse given by Darwin\ntwenty years ago to the theory of evolution has influenced the whole\ntenor of philosophical opinion. 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APPLETON & CO., PUBLISHERS, 1, 3, & 5 BOND STREET, NEW YORK.","title":"The History of Creation, Vol. 1 (of 2): Or the Development of the Earth and its Inhabitants by the Action of Natural Causes","tradition":"philosophy-ethics","translated_text":null,"word_count":108708}