{"collection":"scripture-revelation","full_text_available":true,"graph_url":"https://unchartedknowledge.5gfusion.net/v2/api/page/gutenberg_46834/graph","html_url":"https://unchartedknowledge.5gfusion.net/v2/page/gutenberg_46834","id":"gutenberg_46834","license":"Public Domain (US)","rights_basis":"gutenberg_metadata_copyright_false","source":"gutenberg","source_url":"https://www.gutenberg.org/ebooks/46834","summary":null,"tags":["Category: Philosophy & Ethics","Category: Religion/Spirituality","Category: Science - Biology","Evolution (Biology)","Evolution (Biology) -- Religious aspects","Religion and science"],"text":"Transcriber's note: Italics text is denoted with _underscores_, boldface\ntext with =equals signs=. Other notes are at the end of this eBook.\n\n\n\n\n  EVOLUTION\n\n  ITS NATURE, ITS EVIDENCES, AND ITS\n  RELATION TO RELIGIOUS THOUGHT\n\n\n  BY\n  JOSEPH LE CONTE\n\n  AUTHOR OF \u201cRELIGION AND SCIENCE,\u201d ETC.\n  AND PROFESSOR OF GEOLOGY AND NATURAL HISTORY IN THE\n  UNIVERSITY OF CALIFORNIA\n\n  _SECOND EDITION, REVISED_\n\n  NEW YORK:\n  D. APPLETON AND COMPANY,\n  72 FIFTH AVENUE.\n  1897.\n\n\n\n\n  COPYRIGHT, 1888, 1891,\n  BY D. APPLETON AND COMPANY.\n\n\n\n\nPREFACE TO THE SECOND EDITION.\n\n\nThe three years which have elapsed since the publication of the first\nedition of this work have been years of great activity of thought on\nmany of the subjects treated therein. Some changes and additions seemed\ntherefore imperatively called for.\n\nFor example: There has sprung up recently among the foremost writers on\nevolution a warm discussion on the _factors_ of evolution, their number\nand relative importance. I have therefore added a chapter (Chap. III,\nPart II) on this subject--not, indeed, to discuss it fully (for this\nwould be impossible in the limits of a chapter), but to put the mind of\nthe reader in position to understand it and to judge for himself.\n\nAgain: Every reader of the first edition must have remarked that there\nare many fundamental religious questions which I have not touched at\nall in Part III. I had avoided these because my own mind was not yet\nfully clear. I regarded what I then wrote as only a little leaven\nin a very large lump. I was willing to wait and let it work. In the\nmean time it has worked in my own mind, and I hope in the minds of\nothers. I have therefore added two chapters to this part. In one I\nsimply carry out to their logical consequences the doctrine of the\nDivine Immanency. This brings up the questions of _First and Second\nCauses_; of _General and Special Providence_; of the _Natural and the\nSupernatural_; of _Mind vs. Mechanics in Nature_, etc., and shows the\nnecessary changes of view which are enforced by the theory of evolution.\n\nIn the other I take up very briefly \u201c_The Relation of Evolution to the\nDoctrine of the Christ_.\u201d In the discussion of this I restrain myself\nstrictly within the limits of the subject as stated above.\n\nThe only other important changes are in Chapter IV, Part III, \u201c_On the\nRelation of Man to Nature_.\u201d As I regard this as the most important\nchapter in the whole book, I have endeavored still further to enforce\nmy view of the origin of man\u2019s spirit, and especially to make it\nclearer by means of several additional illustrations.\n\n          JOSEPH LE CONTE.\n\n  BERKELEY, CAL., _July 1, 1891_.\n\n\n\n\nPREFACE TO THE FIRST EDITION.\n\n\nThe subject of the following work may be expressed in three questions:\nWhat is evolution? Is it true? What then? Surely, there are no\nquestions of the day more burning than these. Much has been written\non each of them, addressed to different classes of minds: some to\nthe scientific, some to the popular, and some to the religious and\ntheological; but nothing has yet appeared which covers the whole ground\nand connects the different parts together. Much, very much has been\nwritten, especially on the nature and the evidences of evolution, but\nthe literature is so voluminous, much of it so fragmentary, and most\nof it so technical, that even very intelligent persons have still very\nvague ideas on the subject. I have attempted to give (1) a very concise\naccount of what we mean by evolution, (2) an outline of the evidences\nof its truth drawn from many different sources, and (3) its relation to\nfundamental religious beliefs. I have determined, above all, to make\na book so small that it may be read through without much expense of\ntime and patience. But the subject is so large that in order to do so\nit was necessary to sacrifice all but what was most essential, and to\nforego all redundancy (the bane of so-called popular science) even at\nthe risk of baldness and obscurity. Nevertheless, I hope that the first\nand second parts will be found not only interesting to the intelligent\ngeneral reader, but even profitable to the special biologist. I have\ntried to make these parts as untechnical as possible, but I hope not\non that account the less scientific. For I am among these who think\nthat it is not necessary to be superficial in order to be popular--that\nscience may be adapted to the intelligent popular mind without ceasing\nto be science.\n\nThe third part seems to me still more important just now. There is\na deep and widespread belief in the popular mind, and even to some\nextent in the scientific mind, that there is something exceptional in\nthe doctrine of evolution as regards its relation to religious thought\nand moral conduct. Other scientific theories have required only some\nmodifications of religious conceptions, but this utterly destroys\nthe possibility of all religious belief by demonstrating a pure\nmaterialism. Now this, I believe, is a complete misconception. Thinking\nmen are fast coming to see this; some, indeed, have mistaken the\nchange for a reaction against evolution. It is a reaction not against\nevolution, but only against its materialistic implication. Evolution is\nmore and more firmly established every year. The tide of conviction is\none which knows no ebb. Some clear statement, in brief space, of its\ntrue relation to religious thought seems, therefore, very important at\nthis time.\n\nBERKELEY, CAL., _May, 1887_.\n\n\n\n\nCONTENTS.\n\n\n  PART I.\n\n  _WHAT IS EVOLUTION?_\n\n\n  CHAPTER I.\n\n  ITS SCOPE AND DEFINITION.\n\n  PAGE\n\n  _A type of evolution_--Development of an egg                         3\n\n  _Universality of evolution_--Pervades all nature and concerns\n      all departments of thought--One half of all science--\n      Illustrated (1) by human body, (2) by solar system, (3) by\n      society, (4) by earth, (5) by organic kingdom--The term\n      evolution usually, but not rightly, confined to this last        3\n\n  _Definition of evolution_--_I. Progressive change_--Shown in\n      the animal body, or the _Ontogenic_ series--In the animal\n      scale, or the _Taxonomic_ series--In the geological, or\n      _Phylogenic_ series--The three series similar, though not\n      identical                                                        8\n\n  _II. Change according to certain laws_--Three laws of succession\n      of organic forms                                                11\n\n  (_a_) _Law of differentiation_--Early forms are generalized;\n      afterwards separated into specialized forms--Illustrated\n      by fishes, by birds--Whole process of differentiation\n      illustrated by growth and branching of a tree                   11\n\n  (_b_) _Law of progress of the whole_--Mistake of confounding\n      evolution with upward progress--How far true, and how far\n      false--Illustrated by branching tree--Examples of this\n      mistake in the popular mind--In the scientific mind             13\n\n  (_c_) _Law of cyclical movement_--Shown in geological history--\n      Age of mollusks, fishes, reptiles, mammals, man--Illustrated\n      again by a branching tree--Increasing complexity as well as\n      height--Illustrated by diagram                                  16\n\n  _The above three laws are laws of evolution_--_Differentiation_\n      --Shown in the development of an egg, the type of evolution     19\n\n  _Progress of the whole_--Not progress of all parts--Shown in\n      the development of an egg                                       22\n\n  _Cyclical movement_--Less fundamental than other two--Shown in\n      Ontogeny of body, of mind--Increasing complexity--Necessity\n      of continued advance--Otherwise deterioration--All these\n      laws shown in progress of society---Differentiation shown--\n      Progress of the whole but not of all parts shown--Cyclical\n      movement shown--In social evolution, however, there is\n      another element, viz., conscious voluntary progress---This\n      kind of evolution contrasted with the other                     22\n\n  _III. Change by means of resident forces_--This is the point of\n      dispute--Sense in which we use term resident forces--Does\n      not touch question of origin of natural forces                  27\n\n  _The two views of the origin of organic forms briefly contrasted_\n      --As to whether natural or supernatural--As to variability,\n      definite or indefinite--As to change from one species to\n      another by transmutation or substitution--As to universality\n      of law of continuity                                            29\n\n\n  CHAPTER II.\n\n  THE RELATION OF LOUIS AGASSIZ TO THE THEORY OF EVOLUTION.\n\n  General misunderstanding on this subject--Necessary to give\n      sketch of history of the idea--Greeks, Lucretius, Swedenborg,\n      and Kant--First scientific presentation by Lamarck--General\n      character of Lamarck\u2019s views--Failed, and rightly so--Next,\n      Chambers\u2019s \u201cVestiges of Creation\u201d--Its general character--\n      Failed, and rightly so--Some think this unfortunate--Why\n      not so--An obstacle must be removed and a basis laid            32\n\n  _The obstacle removed_--Old views in regard to forces--\n      Correlation of forces established--But vital force considered\n      exception--Therefore living forms also supposed exception\n      to mode of origin of other forms--Then vital forces also\n      correlated--Therefore, _a priori_ probable that living forms\n      also correlated with other forms as to mode of origin--Thus\n      obstacle removed                                                35\n\n  _The basis laid_--Agassiz laid inductive _basis_ of evolution,\n      although he refused to build--He established the laws of\n      evolution and perfected the method of comparison--Importance\n      of method discussed--The method of _notation_--The method\n      of experiment--The difficulty of applying these to life\n      phenomena--Method of comparison shown--(1) In Taxonomic\n      series--(2) In Ontogenic series--(3) In Phylogenic series\n      --Cuvier the great worker by comparison in the Taxonomic\n      series--Agassiz in the Ontogenic and Phylogenic--Agassiz\n      also established the three laws of evolution given in previous\n      chapter--Thus he laid foundation--Why he did not build--\n      Supposed identity of evolution and materialism--The obstacle\n      being removed and the basis laid, when evolution again brought\n      forward it was universally accepted, because the world was\n      prepared--Place of Agassiz and Darwin compared--Formal\n      science _vs._ physical science--Illustrated by relation of\n      Kepler to Newton--Relation of Agassiz to time cosmos similar\n      to that of Kepler to space cosmos--So Darwin to Newton--\n      Some reflections on the above--Gravitation is the law of\n      space cosmos--Evolution of time cosmos--Of the divine\n      spheral music gravitation is the chordal harmony and evolution\n      the melody                                                      37\n\n\n  PART II.\n\n  _EVIDENCES OF THE TRUTH OF EVOLUTION._\n\n\n  CHAPTER I.\n\n  GENERAL EVIDENCES OF EVOLUTION AS A UNIVERSAL LAW.\n\n  _Evolution is continuity, causal relation, gradual becoming_\n      --Increasing acceptance of this idea--First accepted\n      for inorganic forms, mountains, continents and seas, rocks\n      and soils, earth as a whole, heavenly bodies--Therefore\n      acknowledged for all inorganics--Influence of geology in\n      bringing about this change--Organic forms: acknowledged\n      for individuals, true for classes, orders, families, genera\n      --Races and varieties also formed gradually--Artificial\n      species formed gradually--Examples of gradual changes in wild\n      species--Hyatt\u2019s researches--Other examples--Summing up\n      of general evidence--Sufficient ground for induction--\n      But evolution is not only inductively probable but certain,\n      axiomatic--It is the law of causation applied to forms, and\n      therefore a necessary truth                                     53\n\n\n  CHAPTER II.\n\n  SPECIAL PROOFS OF EVOLUTION.\n\n  _Introductory._\n\n  _Special proofs necessary_--Evolution, though certain, is not\n      yet accepted by the popular mind--Different departments from\n      which proofs are drawn                                          67\n\n  _Origin of new organic forms; the old view briefly stated_--\n      Necessary to give a brief statement of theories--Old view--\n      Permanency of specific types--Supernatural origin of species\n      --Centers of creation--Explanation of facts of geographical\n      distribution--Of geological distribution--Modification of\n      extreme view--Variability, but within limits--Illustrated       68\n\n  _The new view briefly stated_--Indefinite variability of organic\n      forms--Effect of environment on rigid forms--On plastic\n      forms--Taxonomic groups represent degrees of kinship            72\n\n  _Factors of evolution_--(1) Physical environment--(2) Use\n      and disuse of organs--(3) Natural selection--(4) Sexual\n      selection--(5) Physiological selection--Its necessity shown\n      --Its operation explained--Compared with natural selection\n      --Cause of variation unknown--Explanation of this is the\n      next great step in the theory of evolution                      73\n\n\n  CHAPTER III.\n\n  THE GRADES OF THE FACTORS OF EVOLUTION AND THE ORDER OF THEIR\n      APPEARANCE.\n\n  _Factors of evolution restated; their grades and the order of\n      their introduction shown_--Lamarckian factors, first\n      in order because they precede sexual reproduction--(1)\n      Environment--(2) Use and disuse--With sexual reproduction\n      selective factors introduced--(3) Natural selection--(4)\n      Physiological selection--(5) Sexual selection--With man\n      was introduced (6) the rational factor--In this process\n      two striking stages--viz., the introduction of sex and the\n      introduction of reason--Effect of each to hasten the steps of\n      evolution--The last by far the greater change                   81\n\n  _Contrast between organic and human evolution_--(1) The\n      meaning of term _fittest_ in each--(2) Destiny of the\n      weak and helpless in each--(3) The nature of evolutionary\n      transformation in each--(4) The law of strait and narrow way\n      applied in each--(5) Human evolution is a different kind and\n      on a higher plane                                               88\n\n  _Application to some questions of the day._\n\n  I. Neo-Darwinists, their position explained--Reasons for\n      dissenting--(_a_) Lamarckian factors preceded all others--\n      (_b_) Though now subordinate, they still underlie and condition\n      all other factors--(_c_) Shown by comparison of phylogeny\n      with ontogeny                                                   92\n\n  II. Human progress not identical with organic evolution--Mistake\n      of the materialists--But neither is it wholly different, as\n      some suppose                                                    96\n\n  III. Neo-Darwinism is fatal to hopes of human progress--Reason\n      may use freely Lamarckian factors, but can not use natural\n      selection in the same way as Nature does                        97\n\n\n  CHAPTER IV.\n\n  SPECIAL PROOFS FROM THE GENERAL LAWS OF ANIMAL STRUCTURE, OR\n      COMPARISON IN THE TAXONOMIC SERIES.\n\n  _General Principles._\n\n  _Analogy and homology_--Defined and illustrated by examples--\n      Wings and limbs--Lungs, gradual formation of, traced in the\n      Taxonomic series--Traced in the Ontogenic series--Examples\n      of homology in plants: tuber, cactus-leaf, acacia-leaf--\n      Definitions repeated and further explained--Common origin is\n      the only explanation of homology                                99\n\n  _Primary divisions of the animal kingdom_--True ground of such\n      divisions is ability to trace homology--We take examples\n      only from vertebrata and articulata--Compare to styles of\n      architecture--To machines--To branching stem                   107\n\n\n  CHAPTER V.\n\n  PROOFS FROM HOMOLOGIES OF THE VERTEBRATE SKELETON.\n\n  _Common general plan_--In several respects--Strongly suggestive of\n      common origin--Details of structure demonstrative of the same  111\n\n  _Special homology of vertebrate limbs_                             113\n\n  _Fore-limbs_--Comparison of fore-limbs of mammals, birds,\n      reptiles, and fishes, part for part--Gradual changes in\n      collar-bone and coracoid--In position of elbow--In bones\n      of forearm--In position of wrist--In the tread--The term\n      manus--Number of toes--Modifications for flight in various\n      animals--For swimming in whales and fishes                     113\n\n  _Hind-limbs_--Comparison of hind-limbs of several mammals--\n      Position of knee--Of heel--Plantigrade and digitigrade\n      --Degrees of the latter--Number of toes--General law in\n      regard to number of similar parts--Order of toe-dropping in\n      artiodactyles--In perissodactyles                              121\n\n  _Genesis of the horse_--Changes in foot-structure--Same true\n      of other parts of skeleton--Only natural explanation is\n      derivation--Nature compared with man in mode of working--\n      Angels--Griffins--Centaurs--Muscular and nervous systems\n      --Visceral organs                                              126\n\n\n  CHAPTER VI.\n\n  HOMOLOGIES OF THE ARTICULATE SKELETON.\n\n  _Illustrations from this type_--Plan of structure entirely\n      different--General plan of structure explained and\n      modifications shown--Shrimp--Modification of segments and\n      of appendages for various purposes: swimming, walking, eating,\n      sense--Illustrated by other crustaceans--By myriapods--\n      By marine worms--Crabs--Embryonic development of crabs--\n      insects--Modification of segments and appendages--Mouth\n      parts of insects                                               132\n\n  _Illustration of the law of differentiation_--Cells--Segments\n      --Individuals--Homologies in other departments of animals,\n      but these are less familiar--Between primary groups, homology\n      untraceable in adult forms--But these also probably connected\n      by common origin--Different views as to origin of vertebrates  144\n\n\n  CHAPTER VII.\n\n  PROOFS FROM EMBRYOLOGY, OR COMPARISON IN THE ONTOGENIC SERIES.\n\n  _Resemblance of the three series_--Frog, in Ontogeny passes\n      through main stages of Taxonomy and Phylogeny--Resemblance\n      only general--Many steps dropped out in Ontogeny               148\n\n  (1) _Ontogeny of tailless amphibians_--The frog: fish stage,\n      perennibranch stage, caducibranch stage, aneural stage--Same\n      stages in Phylogeny                                            150\n\n  (2) _Aortic arches_--Those of lizard described--Origin from\n      gill-arches of fish--Change from one to the other in Ontogeny\n      of a frog--Same changes in Phylogeny of lizard--Embryonic\n      condition of mammalian heart and vessels--Gradual change and\n      final condition in birds--In mammals--Gradual decrease in\n      number of aortic arches as we go up the vertebrate scale--\n      Cogency of the argument from aortic arches                     151\n\n  (3) _Vertebrate brain_--Fish brain--Brain of reptiles, birds,\n      mammals, man compared--Human brain passes through similar\n      stages--Changes in complexity of structure in Taxonomy--\n      Same changes in Ontogeny of mammals--Same in Phylogeny of\n      reptiles, birds, mammals                                       162\n\n  _Cephalization_--Explanation of, in body, in mind                  171\n\n  (4) _Fish-tails_--Homocercal and heterocercal--Vertebrated\n      and non-vertebrated--Order of change in Ontogeny--Same\n      in Phylogeny--Similar changes in birds\u2019 tails in Ontogeny\n      and Phylogeny--In other tailless animals--Examples from\n      articulates, insects, crustaceans, etc.                        172\n\n  _Illustration of the differentiation of the whole animal kingdom_\n      --Development of eggs of all kinds of animals--This a type\n      of changes in Phylogeny--Why Ontogeny repeats Phylogeny--\n      Law of acceleration                                            176\n\n  _Proofs from rudimentary and useless organs_--Examples from\n      whale: Teeth--Limbs--Hair--Olfactive organs--Examples\n      from man: muscles, c\u00e6cal appendage--Significance of useless\n      organs                                                         179\n\n\n  CHAPTER VIII.\n\n  PROOFS FROM GEOGRAPHICAL DISTRIBUTION OF ORGANISMS.\n\n  _Geographical faunas and floras_--Conditions which limit           183\n\n  _Temperature-regions_--Illustrated by plants--In latitude and\n      in elevation--Same in animal species                           184\n\n  _More perfect definition of regions_--Range of different\n      Taxonomic groups--Gradual shadings on borders of range--\n      Shadings out of individuals in number and vigor, but not in\n      specific character--As if centers of origin--Effect of east\n      and west barriers--Temperature regions repeated south of the\n      equator, but not species--As if centers of origin              186\n\n  _Continental faunas and floras_--Temperature zones continuous,\n      but not species--Reason: ocean barriers--As if centers\n      of origin--Polar regions: one. Why--Temperate zone--\n      Different species in different continents--Species of United\n      States and of Europe almost wholly different--As if origin\n      local--Exceptions--(1) Introduced species--(2) Hardy or\n      else wide-migrating species--(3) Alpine species--Tropical\n      zone of two continents still more different--Same true of\n      south temperate zone                                           188\n\n  _Subdivisions of continental faunas and floras_--Illustrated by\n      fauna and flora of United States                               191\n\n  _Special Cases_--Australia--Madagascar--Galapagos--River\n      mussels                                                        192\n\n  _Marine species_--Same principles applicable--Therefore organic\n      forms grouped in regions, sub-regions, provinces, etc.--\n      Primary regions according to Wallace--According to Allen       192\n\n  _Theory of the origin of geographical diversity_--Specific\n      centers of creation--Objections to. The element of time left\n      out--Progressive change in unlimited time, or evolution the\n      only rational explanation--This connects with geographical\n      changes in geological times, especially the Glacial epoch--\n      Geographical diversity in other times                          193\n\n  _Most probable view of the general process_--Last great period\n      of change was the Glacial epoch--This, therefore, is the key\n      to geographical distribution--Condition of things during the\n      Glacial epoch---In America--Changes in temperature--In\n      physical geography and in species--In Europe--Application\n      of principles                                                  196\n\n  (1) _Australia_--Characteristics of its fauna--Explanation\n      of--Isolation very early--Position of marsupials and\n      monotremes in the Taxonomic scale--Australia isolated before\n      the Tertiary--Effect of competition on evolution               200\n\n  (2) _Africa_--African region defined--Two groups of its\n      mammals, indigenes, and invaders--Effect of the invasion       204\n\n  (3) _Madagascar_--Characteristics of its fauna--Relation\n      to African indigenes--Separated before the invasion--\n      Significance of its lemurs                                     205\n\n  (4) _Island life_--Two kinds of islands--Defined and\n      illustrated by examples--(_a_) _Continental islands_--\n      General character of fauna--Illustrated by Madagascar,\n      New Zealand, British Islands, coast-islands of California\n      --Characteristics of the faunas of these explained--(b)\n      _Oceanic Islands_--Defined--Characteristics of faunas and\n      their origin                                                   207\n\n  (5) _Alpine species_--Characteristics of and their origin\n      explained--Migrations of Arctic species during Glacial times,\n      and their isolation on mountains                               215\n\n  _Objection_--Mode of change of species on borders of ranges--\n      Examples--Sweet-gum--Sequoia                                   217\n\n  _Answer_--Distribution of these forms in time, and their\n      migrations--They are remnants--Intermediate forms are extinct  219\n\n\n  CHAPTER IX.\n\n  PROOFS FROM VARIATION OF ORGANIC FORMS, ARTIFICIAL AND NATURAL.\n\n  _Limitation of the use of experiment in morphology_--Unconscious\n      experiments in breeding, and their results--Principles\n      involved--Inheritance, immediate and ancestral--Effect of\n      true breeding long continued--Method of selection illustrated\n      by diagram--Formation of a race--Process the same in nature\n      --Show selective effect of physical environment--Of organic\n      environment--Of migrations--Of unlimited time--Other\n      factors of change, and their effects shown in nature and in\n      domestication--Differences between artificial and natural\n      species                                                        222\n\n  _First difference, reversion_--The tendency to reversion\n      described--The reason explained--Illustrated by the case of\n      the pointer                                                    229\n\n  _Second difference, intermediate forms_--Reason is, these are\n      eliminated in nature                                           232\n\n  _Third difference, cross-fertility_--Natural species are usually\n      cross-sterile--Degrees of cross-sterility--Two bases of\n      species, morphological and physiological--Two kinds of\n      isolation, sexual repugnance and cross-sterility--Latter most\n      essential--Illustrated by plants and hermaphrodite animals--\n      Former only higher animals--Natural laws interfered with by\n      domestication--Illustrated by plants and animals               232\n\n  _Law of cross-breeding_--Effect of close breeding--Of crossing\n      varieties to a limit--The law investigated--Reproduction in\n      lowest organisms--Fission--Gemmation--Internal gemmation\n      --Sex introduced--Effect of, is funding of differences in\n      offspring and tendency to variation--Sexual and non-sexual\n      reproduction compared--Separation of sex elements--\n      Of sex-individuals--Introduction of sex-attraction--\n      Funding of greater differences in offspring--Crossing of\n      varieties--Diagram illustrating effect in vigor--Effect\n      also in plasticity--Application of these principles--\n      Necessity of sexual isolation to produce species--Origin of\n      cross-sterility and thus of species by Dr. Romanes\u2019s idea--\n      Why artificial varieties are cross-fertile--Geographical\n      species sometimes cross-fertile--Application of principles--\n      Absence of intermediate links in natural species explained--\n      Under what conditions such are found--Further explanation of\n      this point--Illustrated by a growing tree                      236\n\n  _Objection answered_--Intermediate links ought to be found fossil\n      --Answer (1) Imperfection of record. (2) The term species\n      indefinite. (3) Transitions between all other taxonomic groups\n      abundant. (4) Between species, also, both living and fossil\n      --Of fossil, Planorbis of Steinheim--Other examples--(5)\n      Why transition-forms are rare--Answer--Changes in every\n      department of nature are paroxysmal--Illustrated--So the\n      steps of evolution paroxysmal--Critical periods in evolution\n      --Causes of rapid advance--Apparent discontinuity between\n      species--(1) changes paroxysmal--(2) Brooks\u2019s idea--Male\n      sex is the progressive element--Illustrated by society--\n      Effect of prosperous times--Mrs. Treat\u2019s experiments--Hard\n      times produce excess of males, and therefore tend to diversity\n      --Summary                                                      248\n\n  _Objection_--Egyptian drawings and mummy plants, show no change\n      --Answer (1) Time too short. (2) We are now in time of slow\n      change. (3) All species don\u2019t change, most become extinct. (4)\n      Evolution is probably slower now than formerly--Reasons for\n      so thinking--Organic evolution approaching completion--\n      Other supposed objections                                      265\n\n  _Origin of beauty_--Explanation of, in higher animals--In\n      flowering plants--But in many cases we can\u2019t explain           269\n\n  _Incipient organs_--Difficulty of explaining--But these are\n      not objections to the _fact_ of evolution, but only to the\n      sufficiency of the present _theories_ of evolution. Therefore,\n      all discussion concerns special theories. The fact of evolution\n      is certain                                                     270\n\n\n  PART III.\n\n  _THE RELATION OF EVOLUTION TO RELIGIOUS THOUGHT._\n\n\n  CHAPTER I.\n\n  INTRODUCTORY.\n\n  _Evolution if true affects every department of thought_--What\n      will be its effect on religious beliefs?--Objection that\n      truth-seeker has nothing to do with effects--Answered          275\n\n  _Relation of the true and the good_                                277\n\n  _Relation of philosophy to life_--The three necessary elements\n      of a rational philosophy--Application to the case in hand--\n      And the subject of Part III justified--Exaggerated fears--\n      Different forms of the conflict of science and religion--(1)\n      Heliocentric theory--First effect and final result--(2) Law\n      of gravitation--Effect and result--(3) Antiquity of the\n      earth and cosmos--Effect and result--(4) Antiquity of man\n      --(5) Evolution                                                277\n\n\n  CHAPTER II.\n\n  THE RELATION OF EVOLUTION TO MATERIALISM.\n\n  _Supposed identity_--Tendency of the age--Evolution does not\n      differ in this regard from other laws of Nature--Absurdity\n      of identification illustrated in many ways--(1) Effect of\n      discovery of process of making--(2) Effect of new form of old\n      truth--(3) Manner in which vexed questions are settled and\n      rational philosophy found--Illustrated--A true philosophy\n      is a reconciliation of partial views--Three possible views\n      of origin of individuals and of species; two one-sided and\n      partial, and the third combining, reconciling, and therefore\n      rational--The only bar to speedy reconciliation is dogmatism\n      --Theological and scientific--The appropriate rebuke for\n      each--Therefore evolution does not differ from other laws in\n      regard to its relation to materialism--Nevertheless, great\n      changes in our traditional beliefs impending--Main changes\n      are notions concerning God, Nature, and man, in their relations\n      to one another                                                 284\n\n\n  CHAPTER III.\n\n  THE RELATION OF GOD TO NATURE.\n\n  The issue in regard to this relation stated--The growth of the\n      issue described--The old view of direct relation--The\n      effect of science and the resulting view--The compromise--\n      Destroyed by evolution--The issue forced--The alternative\n      view--Immanence of Deity--This view explained--Objection\n      of idealism--Answered--It is not subjective idealism--\n      Objection of pantheism--Answer deferred--Objection that the\n      view is incompatible with practical life--Answered             297\n\n\n  CHAPTER IV.\n\n  THE RELATION OF MAN TO NATURE.\n\n  _The two extreme views in this regard_--They are views from\n      different points, psychical and material--The latter very\n      productive in modern times--But many fear the final effect--\n      Reconciliation is possible--Scientific materialism has two\n      branches--_Physiological branch_ explained--Conclusion--\n      Answer--Relation of psychic to brain changes is inscrutable\n      --The mystery illustrated--Outside and inside view--\n      Different from other phenomena in this regard                  304\n\n  _Evolution branch_--Close relation of man to animals--Therefore\n      must extend immortal spirit to animals--to plants--to all\n      existence, and thus identify immortality with conservation\n      of force--Embryonic series--Where did spirit enter?--\n      Evolution series--Where did spirit enter?--Answer--\n      Derived from Nature--The true view of origin stated--Show\n      that it is not in discord with other phenomena of evolution\n      --The five planes of matter and of force--The change from\n      one to another not gradual now nor in the evolution of natural\n      forces--Consecutive births into higher forms--Every step\n      of these changes taking place now--Relation of these facts\n      to immortality--The process briefly stated--Omnipresent\n      divine energy individuated to separate entity in man--Anima\n      of animals is spirit in embryo--Came to birth in man--\n      Illustrated in other ways--(1) By more or less completed\n      water-drop--(2) By submergence and emergence--(3) By\n      planet birth--(4) By physical birth--(5) By grades of\n      organic individuality--(6) By the body as an instrument of\n      communication between two worlds--Self-consciousness the sign\n      of spirit-individuality--Any animal conscious of self would\n      be immortal--Similar changes in passing from animals to man\n      in all other departments of psychic activity--Objection that\n      other changes of energy not permanent; answered--Our view\n      of origin compared with alternative views--Plato\u2019s view--\n      Orthodox view                                                  311\n\n  _Some general conclusions_--(1) Two series of changes,\n      brain-changes and mind-changes--The initiative in animals\n      --In man--(2) Justification of term \u201c_vital principle_\u201d\n      --Becomes entity in man--(3) This view is a complete\n      reconciliation of realism and nominalism--(4) No meaning in\n      Nature without spirit--And no meaning in geological history\n      without derivative origin of spirit--Material evolution finds\n      its goal in man, psychic evolution in the divine man           327\n\n\n  CHAPTER V.\n\n  THE RELATION OF GOD TO MAN.\n\n  _Question of revelation_--Difficulty of the subject--Operation\n      of divine spirit on spirit of man more direct than on Nature\n      --This is revelation--This is no violation of law, but\n      operation by higher law--Term supernatural is relative--\n      Illustrated--There is but one kind of revelation, and this to\n      all men in different degrees--Always imperfect, and therefore\n      must be tried by reason                                        331\n\n\n  CHAPTER VI.\n\n  THE OBJECTION, THAT THE ABOVE VIEW IMPLIES PANTHEISM, ANSWERED.\n\n  _The objection stated and the general answer_--In deepest\n      questions single lines of thought lead to extreme views--Must\n      follow other lines--These lead to personality                  335\n\n  (1) Exact character of relation of God and of necessary law to\n      man\u2019s freedom is inscrutable                                   338\n\n  (2) On the inside of brain-changes we find personality--So on\n      the inside of natural phenomena must also be person--In\n      either case science studies the outside only--In Nature\n      all is mechanics on the outside, but all is mind on the\n      inside--Thought behind brain-changes compels belief in same\n      behind natural phenomena--Law of infinite expansion--\n      Illustrated by ideas of Space and Time--So also with idea\n      of self--Infinite person inconceivable, but contrary is more\n      inconceivable--Illustrated by ideas of Space and Time          338\n\n  (3) Idea of _Causation_ and of _Force_--Derived from _within_\n      --Steps of the evolution of this idea--Final result is one\n      infinite personal will--Expansion of idea of causal nexus\n      between phenomena to the idea of one infinite cause            342\n\n  (4) Idea of _design_ also originates _within_--Ineradicable, but\n      changes form--Expands to infinity--Same change produced by\n      science in all our notions concerning God--Same in our sense\n      of _mystery_--Same in our notions concerning _creation_--\n      Same in our conceptions of _design_--Thus, self-consciousness\n      behind brain-changes compels belief in God behind Nature--The\n      closeness of connection in the one case necessitates closeness\n      of connection in the other--Every material change in Nature\n      caused by a mental change behind Nature                        345\n\n\n  CHAPTER VII.\n\n  SOME LOGICAL CONSEQUENCES OF THE DOCTRINE OF THE DIVINE IMMANENCY.\n\n  Religious thought subject to the law of evolution; three main\n      stages                                                         351\n\n  I. _Conception of God_--The three stages shown--(1)\n      Anthropomorphism--(2) Absentee landlordism--(3) Immanence      351\n\n  II. _Question of First and Second Causes_--The three stages shown\n      here--(1) All is First Cause but man-like--(2) Distinction\n      of first and second causes introduced--(3) Identification of\n      these                                                          354\n\n  III. _General and Special Providence_--The same three stages\n      shown and the same outcome--viz., identification               355\n\n  IV. _Natural and the supernatural_--The same stages and the same\n      final identification--Question of miracles                     355\n\n  V. _Question of design or mind in Nature_--The same three stages\n      and the same solution shown here--Confusion in the minds of\n      modern writers                                                 357\n\n  VI. _Question of mode of creation_--Old and new views contrasted   358\n\n\n  CHAPTER VIII.\n\n  RELATION OF EVOLUTION TO THE IDEA OF THE CHRIST.\n\n  Comparison of organic with human evolution--The idea of the first\n      is _man_, of the second is the _Christ_--Definition of the\n      Christ as _ideal man_--The Christ ought to differ from us\n      in a superhuman way--Shown by several illustrations--The\n      Christ, as ideal man, a true object of rational worship--The\n      ideal of organic evolution comes _at the end_--Ideal of human\n      evolution must come _in the course_--Objection that there are\n      many partial ideals answered--Relative vs. absolute moral\n      ideal.                                                         360\n\n\n  CHAPTER IX.\n\n  THE RELATION OF EVOLUTION TO THE PROBLEM OF EVIL.\n\n  The difficulty of the problem--The light on it by evolution--\n      Evil must be based on the constitution of Nature and therefore\n      universal--Some of its forms                                   365\n\n  (1) _Physical evil in animal kingdom_--Condition of organic\n      evolution is struggle with an apparently inimical environment\n      --In its course it seems evil--Looking back from the end it\n      is good.                                                       365\n\n  (2) _Physical evil in relation to man_--Necessary condition\n      of social evolution is also struggle with a seeming evil\n      environment--But looking back from the end this evil is also\n      seen to be good--Without it man would never have emerged from\n      animality.                                                     366\n\n  (3) _Organic evil--Disease_--This also is the necessary\n      condition of acquisition of knowledge of organic Nature--In\n      the course of evolution it seems evil, but from the end it is\n      seen to be good--In the physical world, laws of Nature are\n      beneficent in their general operation, and only evil in their\n      specific operation through our ignorance.                      367\n\n  (4) _Moral evil--Moral disease_--Difference between this\n      and other forms of evil--Can this also be transmuted into\n      good?--This is only the highest form of evil, and therefore\n      subject to the same laws of evolution--Here also elevation\n      comes only through knowledge and power, and these only through\n      struggle with apparent evil--In course it seems evil,\n      looking back from end it is seen to be good to the race--\n      In all, therefore, the individual is sacrificed to the race,\n      but impossible here--A way of escape found in the nature of\n      a moral being--In this case not only final victory for the\n      race, but also within the power of the individual--In this\n      case success is in proportion to honest effort in right spirit\n      --Roots, of evil in the necessary law of evolution--It is\n      the necessary condition of all progress--Without it a moral\n      being is impossible--From philosophic point of view things\n      are not good and evil, but only higher and lower--All things\n      good in their places--Evil is discord--Good is due relation\n      --Action and reaction of higher and lower is the necessary\n      condition of true virtue                                       369\n\n\n\n\nPART I.\n\n_WHAT IS EVOLUTION?_\n\n\n\n\nCHAPTER I.\n\nITS SCOPE AND DEFINITION.\n\n\n=A Type of Evolution.=--Every one is familiar with the main facts\nconnected with the development of an egg. We all know that it begins as\na microscopic germ-cell, then grows into an egg, then organizes into\na chick, and finally grows into a cock; and that the whole process\nfollows some general, well-recognized law. Now, this process is\nevolution. It is more--it is _the_ type of all evolution. It is that\nfrom which we get our idea of evolution, and without which there would\nbe no such word. Whenever and wherever we find a process of change\nmore or less resembling this, and following laws similar to those\ndetermining the development of an egg, we call it evolution.\n\n_Universality of Evolution._--Evolution as a _process_ is not\nconfined to one thing, the egg, nor as a doctrine is it confined\nto one department of science--biology. The process pervades the\nwhole universe, and the doctrine concerns alike every department of\nscience--yea, every department of human thought. It is literally one\nhalf of all science. Therefore, its truth or falseness, its acceptance\nor rejection, is no trifling matter, affecting only one small corner\nof the thought-realm. On the contrary, it affects profoundly the\nfoundations of philosophy, and therefore the whole domain of thought.\nIt determines the whole attitude of the mind toward Nature and God.\n\nI have said evolution constitutes one half of all science. This may\nseem to some a startling proposition. I stop to make it good.\n\nEvery system of correlated parts may be studied from two points of\nview, which give rise to two departments of science, one of which--and\nthe greater and more complex--is evolution. The one concerns changes\nwithin the system by action and reaction between the parts, producing\nequilibrium and stability; the other concerns the progressive movement\nof the system, as a whole, to higher and higher conditions--the\nmovement of the point of equilibrium itself, by constant slight\ndisturbance and readjustment of parts on a higher plane, with more\ncomplex inter-relations. The one concerns the laws of sustentation of\nthe system, the other the laws of evolution. The one concerns things as\nthey are, the other the process by which they become so. Now, Nature\nas a whole is such a system of correlated parts. Every department and\nsub-department of Nature, whether it be the solar system or the earth,\nor the organic kingdom, or human society, or the human body, is such a\nsystem of correlated parts, and is therefore subject to evolution. We\ncan best make this thought clear by examples:\n\n1. Take, then, the _human body_. This complex and beautiful system\nof correlated and nicely-adjusted parts may be studied in a state of\nmaturity and equilibrium, in which all the organs and functions by\naction and reaction co-operate to produce perfect stability, health,\nand physical happiness. This study is physiology. Or else the same may\nbe studied in a state of progressive change. Now, we perceive that the\nstability is never perfect--the point of equilibrium is ever moving. By\nthe ever-changing number and relative power of the co-operating parts\nthe equilibrium is ever being disturbed, only to be readjusted on a\nhigher plane, with still more beautiful and complex inter-relations.\nThis is growth, development, evolution. Its study is called embryology.\n2. Take another example--_the solar system_. We may study sun, planets,\nand satellites in their mutual actions and reactions, co-operating to\nproduce perfect equilibrium, stability, beautiful order, and musical\nharmony. This is the ideal of physical astronomy as embodied in\nLaplace\u2019s \u201cM\u00e9canique C\u00e9leste.\u201d Or we may study the same in its origin\nand progressive change. Now, we perceive that equilibrium and stability\nare never absolutely perfect, but, on the contrary, there is continual\ndisturbance with readjustment on a higher plane--continual introduction\nof infinitesimal discord, only to enhance the grandeur and complexity\nof the harmonic relations. This is the nebular hypothesis--the theory\nof the development of the solar system. It is cosmogony; it is\nevolution. 3. Again: _society_ may be studied in the mutual play of\nall its social functions so adjusted as to produce social equilibrium,\nhappiness, prosperity, and good government. This is social statics.\nBut equilibrium and stability are never perfect. Permanent social\nequilibrium would be social stagnation and decay. Therefore, we must\nstudy society also in its onward movement--the equilibrium ever\ndisturbed, only to be readjusted on a higher plane with more and more\ncomplexly inter-related parts. This is dynamics--social progress. It\nis evolution. 4. Again: the _earth_, as a whole, may be studied in\nits present forms, and the mutual action of all its parts--lands and\nseas, mountains and valleys, rivers, gulfs, and bays, currents of air\nand ocean--and the manner in which all these, by action and reaction,\nco-operate to produce climates and physical conditions such as we now\nfind them. This is physical geography. Or, we may study the earth\nin its gradual progress toward its present condition--the changes\nwhich have taken place in all these parts, and consequent changes in\nclimate; in a word, the gradual process of becoming what it now is.\nThis is physical geology--it is evolution. 5. Lastly, we may study\nthe whole _organic kingdom_ in its entirety as we now find it--the\nmutual relation of different classes, orders, genera, and species to\neach other and to external conditions, and the action and reaction\nof these in the struggle for life--the geographical distribution of\nspecies and their relation to climate and other physical conditions,\nthe whole constituting a complexly adjusted and permanent equilibrium.\nThis is a science of great importance, but one not yet distinctly\nconceived, much less named.[1] Or, we may study the same in its gradual\nprogressive approach, throughout all geological times, toward the\npresent condition of things, by continual changes in the parts, and\ntherefore disturbance of equilibrium and readjustment on a higher plane\nwith more complex inter-relations. This is development of the organic\nkingdom. In the popular mind it is, _par excellence_, evolution.\n\nWe might multiply examples without limit. There are the same two\npoints of view on all subjects. As already said, in the one we are\nconcerned with things as they are; in the other, with the process\nby which they became so. This \u201claw of becoming\u201d in all things--this\nuniversal law of progressive inter-connected change--may be called the\nlaw of continuity. We all recognize the universal relation of things,\ngravitative or other, in space. This asserts the universal causal\nrelation of things in _time_. This is the universal law of evolution.\n\nBut it has so happened that in the popular mind the term evolution\nis mostly confined to the development of the organic kingdom, or\nthe law of continuity as applied to this department of Nature. The\nreason of this is that this department was the last to acknowledge\nthe supremacy of this law; this is the domain in which the advocates\nof supernaturalism in the realm of Nature had made their last stand.\nBut it is wholly unphilosophical thus to limit the term. If there be\nany evolution, _par excellence_, it is evolution of the individual or\nembryonic development. This is the clearest, the most familiar, and\nmost easily understood, and therefore the type of evolution. We first\ntake our idea of evolution from this form, and then extend it to other\nforms of continuous change following a similar law. But, since the\npopular mind limits the term to development of the organic kingdom, and\nsince, moreover, this is now the battleground between the advocates\nof continuity and discontinuity--of naturalism and supernaturalism in\nthe _realm of Nature_--what we shall say will have reference chiefly\nto this department, though we shall illustrate freely by reference to\nother forms of evolution.\n\n\nDEFINITION OF EVOLUTION.\n\nEvolution is (1) continuous _progressive change_, (2) _according to\ncertain laws_, (3) and by means of _resident forces_. It may doubtless\nbe defined in other and perhaps better terms, but this suits our\npurposes best. Embryonic development is the type of evolution. It\nwill be admitted that this definition is completely realized in this\nprocess. The change here is certainly continuously progressive; it is\naccording to certain well-ascertained laws; it is by forces (vital\nforces) resident in the egg itself. Is, then, the process of change\nin the organic kingdom throughout geologic times like this? Does it\ncorrespond to the definition given above? Does IT also deserve the\nname of evolution? We shall see.\n\nI. =Progressive Change.=--Every individual animal body--say man\u2019s--has\nbecome what it now is by a gradual process. Commencing as a microscopic\nspherule of living but apparently unorganized protoplasm, it gradually\nadded cell to cell, tissue to tissue, organ to organ, and function to\nfunction; thus becoming more and more complex in the mutual action of\nits correlated parts, as it passed successively through the stages of\ngerm, egg, embryo, and infant, to maturity. This ascending series of\ngenetically connected stages is called the embryonic or _Ontogenic_\nseries.[2]\n\nThere is another series the terms of which are coexistent, and which,\ntherefore, is not in any sense a genetic or development series, but\nwhich it is important to mention, because to some degree similar to\nand illustrative of the last. Commencing with the lowest unicelled\nmicroscopic organisms, and passing up to the animal scale, _as it now\nexists_, we find a series of forms similar, though not identical, with\nthe last. Here, again, we find cell added to cell, tissue to tissue,\norgan to organ, and function to function, the animal body becoming more\nand more complex in structure, in the mutual action of its correlated\nparts, and the mutual action with the environment, until we reach the\nhighest complexity of structure and of internal and external relations\nonly in the highest animals. This ascending series may be called\nthe natural history series; or, the classification or _Taxonomic\nseries_.[3] The terms of this series are, of course, not genetically\nconnected; at least, not directly so connected. In what way they are\nconnected, and how the series comes to be similar to the last, we shall\nsee by-and-by.\n\nFinally, there is still a third series, the grandest and most\nfundamental of all, but only recently recognized, and therefore\nstill imperfectly known. Commencing with the earliest organisms,\nthe very dawn of life, in the very lowest rocks, and passing onward\nand upward through Eozoic, Pal\u00e6ozoic, Mesozoic, Cenozoic, to the\nPsychozoic or present time, we again find first the lowest forms,\nand then successively forms more and more complex in structure, in\nthe interaction of correlated parts and in interaction with the\nenvironment, until we reach the most complex internal and external\nrelations, and therefore the highest structure only in the present\ntime.[4] This series we will call the geological or _phylogenic_\nseries.[5] According to the evolution theory, the terms of _this_\nseries also are genetically connected. It is, therefore, an evolution\nseries. Furthermore, it is the most fundamental of the three series,\nbecause it is the _cause_ of the other two. The Ontogenic series is\nlike it because it is a brief recapitulation, through heredity, as it\nwere from memory, of its main points. The Taxonomic series is like\nit because the _rate_ of advance along different lines was different\nin every degree, and therefore every stage of the advance is still\nrepresented in a general way among existing forms. Some of these points\nwill be explained more fully in future chapters, in connection with the\nevidences of the truth of evolution.\n\nIt will be admitted, then, that we find _progressive change_ in organic\nforms throughout geological times. This is the first point in the\ndefinition of evolution.\n\nII. =Change according to Certain Laws.=--We have shown continuously\nprogressive change in organic forms during the whole geologic history\nof the earth, similar in a general way to that observed in embryonic\ndevelopment. We wish now to show that the _laws of change_ are similar\nin the two cases. What, then, are the laws of succession of organic\nforms in geologic times? I have been accustomed to formulate them thus:\n_a._ The law of differentiation; _b._ The law of progress of the whole;\n_c._ The law of cyclical movement.[6] We will take up these and explain\nthem successively, and then, afterward, show that they are also the\nlaws of embryonic development, and therefore the laws of evolution.\n\n_a._ =Law of Differentiation.=--It is a most significant fact, to\nwhich attention was first strongly directed by Louis Agassiz, that\nthe earliest representatives of any group, whether class, order, or\nfamily, were not what we would now call typical representatives of\nthat group; but, on the contrary, they were, in a wonderful degree,\nconnecting links; that is, that along with their distinctive classic,\nordinal, or family characters they possessed also other characters\nwhich connected them closely with other classes, orders, or families,\nnow widely distinct, without connecting links or intermediate forms.\nFor example: The earliest vertebrates were fishes, but not typical\nfishes. On the contrary, they were fishes so closely connected by many\ncharacters with amphibian reptiles, that we hardly know whether to\ncall some of them reptilian fishes, or fish-like reptiles. From these,\nas from a common vertebrate stem, were afterward separated, by slow\nchanges from generation to generation, in two directions, the typical\nfishes and the true reptiles. So, also, to take another example, the\nfirst birds were far different from typical birds as we now know them.\nThey were, on contrary, birds so reptilian in character, that there\nis still some doubt whether bird-characters or reptilian characters\npredominate in the mixture, and therefore whether they ought to be\ncalled reptilian birds or bird-like reptiles. From this common stem,\nthe more specialized modern reptiles branched off in one direction and\ntypical birds in another, and intermediate forms became extinct; until\n_now_, the two classes stand widely apart, without apparent genetic\nconnection. This subject will be more fully treated hereafter, and\nother examples given. These two will be sufficient now to make the idea\nclear.\n\nSuch early forms combining the characters of two or more groups,\nnow widely separated, were called by Agassiz _connecting_ types,\n_combining_ types, _synthetic_ types, and sometimes _prophetic_ types;\nby Dana, _comprehensive_ types; and by Huxley, _generalized_ types.\nThey are most usually known now as _generalized_ types, and their\nwidely-separated outcomes _specialized_ types. Thus, in general, we may\nsay that the widely-separated groups of the present day, when traced\nback in geological times, approach one another more and more until they\nfinally unite to form common stems, and these in their turn unite to\nform a common trunk. From such a common trunk, by successive branching\nand rebranching, each branch taking a different direction, and all\ngrowing wider and wider apart (differentiation), have been gradually\ngenerated all the diversified forms which we see at the present day.\nThe last leafy ramifications--flower-bearing and fruit-bearing--of this\ntree of life, are the fauna and flora of the present epoch. The law\nmight be called a law of ramification, of specialization of the parts,\nand diversification of the whole.\n\n_b._ =Law of Progress of the Whole.=--Many imagine that progress is\nthe one law of evolution; in fact, that evolution and progress are\ncoextensive and convertible terms. They imagine that in evolution the\nmovement must be upward and onward in all parts; that degeneration\nis the opposite of evolution. This is far from the truth. There\nis, doubtless, in evolution, progress to higher and higher planes;\nbut not along every line, nor in every part; for this would be\ncontrary to the law of differentiation. It is only progress of the\nwhole organic kingdom in its entirety. We can best make this clear\nby an illustration. A growing tree branches and again branches _in\nall directions_, some branches going upward some sidewise, and some\ndownward--anywhere, everywhere, for light and air; but the whole tree\ngrows ever taller in its higher branches, larger in the circumference\nof its outstretching arms, and more diversified in structure. Even\nso the tree of life, by the law of differentiation, branches and\nrebranches continually in all directions--some branches going upward\nto higher planes (progress), some pushing horizontally; neither rising\nnor sinking, but only going farther from the generalized origin\n(specialization); some going downward (degeneration), anywhere,\neverywhere, for an unoccupied place in the economy of Nature, but the\nwhole tree grows ever higher in its highest parts, grander in its\nproportions, and more complexly diversified in its structure.\n\nIt may be well to pause here a moment to show how this mistaken\nidentification of evolution with progress alone, without modification\nby the more fundamental laws of differentiation, has given rise to\nmisconceptions in the popular and even in the scientific mind. The\nbiologist is continually met with the question, \u201cDo you mean to say\nthat any one of the invertebrates, such, for instance, as a spider,\nmay eventually, in the course of successive generations, become a\nvertebrate, or that a dog or a monkey is on the highway to become a\nman?\u201d By no means. There is but one straight and narrow way to the\nhighest in evolution as in all else, and few there be that have found\nit--in fact, probably two or three only at every step. The animals\nmentioned above have diverged from that way. In their ancestral\nhistory, they have missed the golden opportunity, if they ever had it.\nIt is easy to go on in the way they have chosen, but impossible to get\nback on the ascending trunk-line. To compare again with the growing\ntree, only one straight trunk-line leads upward to the terminal bud. A\nbranch once separated must grow its own way, if it grow at all.\n\nOf the same nature is the mistake of some extreme evolutionists,\nsuch as Dr. Bastian and Professor Haeckel, and of nearly all\nanti-evolutionists, viz., that of imagining that the truth of\nevolution and that of spontaneous generation must stand or fall\ntogether. On the contrary, _if_ life did _once_ arise spontaneously\nfrom any lower forces, physical or chemical, by natural process,\n_the conditions necessary for so extraordinary a change could hardly\nbe expected to occur but once in the history of the earth_. They\nare, therefore, _now_, not only unreproducible, but unimaginable.\nSuch golden opportunities do not recur. Evolution goes only onward.\nTherefore, the impossibility of the derivation of life from non-life\n_now_, is no more an argument against such a derivation _once_, than\nis the hopelessness of a worm ever becoming a vertebrate _now_, an\nargument against the derivative origin of vertebrates. Doubtless if\nlife were now extinguished from the face of the earth, it could not\nagain be rekindled by any natural process known to us; but the same is\nprobably true of every step of evolution. If any class--for example,\nmammals--were now destroyed, it could not be re-formed from any other\nclass now living. It would be necessary to go back to the time and\nconditions of the separation of this class from the reptilian stem.\nTherefore, the falseness of the doctrine of abiogenesis,[7] so far from\nbeing any argument against evolution, is exactly what a true conception\nof evolution and knowledge of its laws would lead us to expect.\n\n_c._ =Law of Cyclical Movement.=--The movement of evolution has ever\nbeen onward and upward, it is true, but not at uniform rate in the\nwhole, and especially in the parts. On the contrary, it has plainly\nmoved in successive cycles. The tide of evolution rose ever higher and\nhigher, without ebb, but it nevertheless came in successive waves,\neach higher than the preceding and overborne by the succeeding. These\nsuccessive cycles are the dynasties or reigns of Agassiz, and ages\nof Dana; the reign of mollusks, the reign of fishes, of reptiles,\nof mammals, and finally of _man_. During the early Pal\u00e6ozoic times\n(Cambrian and Silurian) there were no vertebrates.[8] But never in\nthe history of the earth were mollusks of greater size, number, and\nvariety of form than then. They were truly the rulers of these early\nseas. In the absence of competition of still higher animals, they had\nthings all their own way, and therefore grew into a great monopoly of\npower. In the later Pal\u00e6ozoic (Devonian) fishes were introduced. They\nincreased rapidly in size, number, and variety; and being of higher\norganization they quickly usurped the empire of the seas, while the\nmollusca dwindled in size and importance, and sought safety in a less\nconspicuous position. In the Mesozoic times, reptiles, introduced a\nlittle earlier,[9] finding congenial conditions and an unoccupied\nplace above, rapidly increased in number, variety, and size, until\nsea and land seem to have swarmed with them. Never before or since\nhave reptiles existed in such numbers, in such variety of form, or\nassumed such huge proportions; nor have they ever since been so\nhighly organized as then. They quickly became rulers in every realm\nof Nature--rulers of the sea, swimming reptiles; rulers of the land,\nwalking reptiles; and rulers of the air, flying reptiles. In the\nunequal contest, fishes therefore sought safety in subordination.\nMeanwhile mammals were introduced in the Mesozoic, but small in size,\nlow in type (marsupials), and by no means able to contest the empire\nwith the great reptiles. But in the Cenozoic (Tertiary) the conditions\napparently becoming favorable for their development, they rapidly\nincreased in number, size, variety, and grade of organization, and\nquickly overpowered the great reptiles, which almost immediately sank\ninto the subordinate position in which we now find them, and thus\nfound comparative safety. Finally, in the Quaternary, appeared man,\ncontending doubtfully for a while, with the great mammals, but soon (in\nPsychozoic) acquiring mastery through superior intelligence. The huge\nand dangerous mammals were destroyed and are still being destroyed; the\nuseful animals and plants were preserved and made subservient to his\nwants; and all things on the face of the earth are being readjusted to\nthe requirements of his rule. In all cases it will be observed that\nthe rulers were such because, by reason of strength, organization, and\nintelligence, they were fittest to rule. There is always room at the\ntop. To illustrate again by a growing tree: This successive culmination\nof higher and higher classes may be compared to the flowering and\nfruiting of successively higher and higher branches. Each uppermost\nbranch, under the genial heat and light of direct sunshine, received in\nabundance by reason of position, grew rapidly, flowered, and fruited;\nbut quickly dwindled when overshadowed by still higher branches, which,\nin their turn, monopolized for a time the precious sunshine.\n\nBut observe, furthermore: when each ruling class declined in\nimportance, it did not perish, but continued in a subordinate position.\nThus, the whole organic kingdom became not only higher and higher in\nits highest forms, but also more and more complex in its structure and\nin the interaction of its correlated parts. The whole process and its\nresult is roughly represented in the accompanying diagram, Fig. 1, in\nwhich A B represents the course of geological time and the curve, the\nrise, culmination, and decline of successive dominant classes.\n\n[Illustration:\n\n  MOLLUSCS--Silurian.\n  FISHES--Devon. and Carb.\n  REEPTILES--Mesozoic.\n  MAMMALS--Tert\u2019y and Quat.\n  MAN--Present.\n\nFIG. 1.]\n\n\nTHE ABOVE THREE LAWS ARE LAWS OF EVOLUTION.\n\nThese three laws we have shown are distinctly recognizable in the\nsuccession of organic forms in the geological history of the earth.\nThey are, therefore, undoubtedly the _general laws of succession_. Are\nthey also laws of evolution? Are they also discoverable in embryonic\ndevelopment, the type of evolution? They are, as we now proceed to show:\n\n=Differentiation.=--In reproduction the new individual appears: 1.\nAs a _germ_-cell--a single microscopic living cell. 2. Then, by\ngrowth and multiplication of cells, it becomes an _egg_. This may be\ncharacterized as an aggregate of _similar_ cells, and therefore is\nnot yet differentiated into tissues and organs. In other words, it\nis not yet visibly organized; for organization may be defined as the\npossession of different parts, performing different functions, and\nall co-operating for one given end, viz., the life and well-being of\nthe organism. 3. Then commences the really characteristic process of\ndevelopment, viz., _differentiation_ or diversification. The cells\nare at first all alike in form and function, for all are globular in\nform, and each performs all the functions necessary for life. From\nthis common point now commences development in _different directions_,\nwhich may be compared to a branching and rebranching, with more and\nmore complex results, according as the animal is higher in the scale\nof organization and advances toward a state of maturity. First, the\ncell-aggregate (egg) separates into three distinct layers of cells,\ncalled ecto-blast, endo-blast, and meso-blast. These by further\ndifferentiation form the three fundamental groups of organs and\nfunctions, viz., the _nervous system_, the _nutritive system_, and the\n_blood system_: the first presiding over the exchange of _force_ or\ninfluence, by action and reaction with the environment, and between the\ndifferent parts of the organism; the second presiding over the exchange\nof _matter_ with the environment, by absorption and elimination; the\nthird presiding over exchanges of matter between different parts of\nthe organism. The first system of functions and organs may be compared\nto a system of telegraphy, foreign and domestic; the second to foreign\ncommerce; the third to an internal carrying-trade. Following out any\none of these groups in higher animals, say the nervous system, it\nquickly differentiates again into two sub-systems, viz., cerebro-spinal\nand ganglionic, each having its own distinctive functions, which we\ncan not stop to explain. Then the cerebro-spinal again differentiates\ninto voluntary and reflex systems. All of these have meanwhile\nseparated into sensory and motor centers and fibers. Then, taking\nonly the sensory fibers, these again are differentiated into five\nspecial senses, each having a wholly different function. Then, finally,\ntaking any one of these, say the _sense of touch_ or feeling, this\nagain is differentiated into many kinds of fibers, each responding to\na different impression, some to heat, others to cold, still others\nto pressure, etc. We have taken the nervous system; but the same\ndifferentiation and redifferentiation takes place in all other systems,\nand is carried to higher and higher points according to the position in\nthe scale of the animal which is to be formed.\n\nOr, to vary the mode of presentation a little, the cells of the\noriginal aggregate, commencing all alike, immediately begin to take on\ndifferent forms, in order to perform different functions. Some cells\ntake on a certain form and aggregate themselves to form a peculiar\ntissue which we call muscle, and which does nothing else, can do\nnothing else, than contract under stimulus. Another group of cells\ntake on another peculiar form and aggregate themselves to form another\nand very different tissue, viz., nervous tissue, which does nothing\nand can do nothing but carry influence back and forth between the\ngreat external world and the little world of consciousness within.\nStill another group of cells take still another form and aggregate\nto form still another tissue, viz., the _epithelial_, whose only\nfunction is to absorb nutritive and eliminate waste matters. Thus, by\ndifferentiation of form and limitation of function, or division of\nlabor, the different parts of the organism are bound more and more\nclosely together by mutual dependence, and the whole becomes more and\nmore distinctly individuated, and separation of parts becomes more and\nmore a mutilation, and finally becomes impossible without death. This\nprocess, as already said, reaches its highest point only in the later\nstages of development of the highest animals.\n\n=Progress.=--The _law of progress_ is, of course, admitted to be a\nlaw of ontogeny; but observe here, also, it is true only of the whole\nand not necessarily of all the parts, _except from the point of view\nof the whole_. Thus, for example, starting all from a common form or\ngeneralized type, some cells _advance_ to the dignity of brain-cells,\nwhose function is somehow connected with the generation or at least\nthe manifestation of thought, will, and emotion; other cells _descend_\nto the position of kidney-cells, whose sole function is the excretion\nof urine. But here, also, the highest cells are successively higher,\nand the whole aggregate is successively nobler and more complex. It\nis again a branching and rebranching, in every direction, some going\nupward, some downward, some horizontally, anywhere, everywhere, to\nincrease the complexity of relations internal and external, and\ntherefore to elevate the plane of the whole.\n\n=Cyclical Movement.=--Lastly, the law of cyclical movement is also a\nlaw of ontogeny and therefore of evolution. This law, however, is less\nfundamental than the other two, and is, therefore, less conspicuous in\nthe ontogenic than in the phylogenic series. It is conspicuous only in\nthe later stages of ontogeny, and in other higher kinds of evolution,\nsuch as social evolution. For example, in the ontogenic development of\nthe body and mind from childhood to manhood we have plainly successive\nculminations and declines of higher and higher functions. In bodily\ndevelopment we have culminating first the _nutritive_ functions, then\nthe _reproductive_ and _muscular_, and last the _cerebral_. In mental\ndevelopment we have culmination first of the receptive and retentive\nfaculties in childhood, then of imaginative and \u00e6sthetic faculties\nin youth and young manhood; then of the reflective and elaborative\nfaculties--the faculties of productive work in mature manhood; and,\nfinally, the moral and religious sentiments in old age. The first\ngathers and stores materials; the second vivifies and makes them\nplastic building materials; the third uses them in actual constructive\nwork--in building the temple of science and philosophy; and the fourth\ndedicates that temple only to noblest purposes.\n\nObserve here, also, that when each group of faculties culminates and\ndeclines, it does not perish, but only becomes subordinate to the next\nhigher dominant group, and the whole psychical organism becomes not\nonly higher and higher in its highest parts, but also more and more\ncomplex in its structure and in the interaction of its correlated parts.\n\nObserve, again, the necessity laid upon us by this law--the necessity\nof continued evolution to the end. Childhood, beautiful childhood,\ncan not remain--it must quickly pass. If, with the decline of its\ncharacteristic faculties, the next higher group characteristic of youth\ndo not increase and become dominant, then the glory of life is already\npast and deterioration begins. Have we not all seen sad examples of\nthis? Youth, glorious youth, must also pass. If the next higher group\nof reflective and elaborative faculties do not arise and dominate, then\nprogressive deterioration of character commences here--thenceforward\nthe whole nature becomes coarse, as we so often see in young men,\nor else shrivels and withers, as we so often see in young women.\nFinally, manhood, strong and self-relying manhood, must also pass. If\nthe moral and religious sentiments have not been slowly growing and\ngathering strength all along, and do not now assert their dominance\nover the whole man, then commences the final and saddest decline of\nall, and old age becomes the pitiable thing we so often see it. But,\nif the evolution have been normal throughout; if the highest moral and\nreligious nature have been gathering strength through all, and now\ndominates all, then the psychic evolution rises to the end--then the\ncourse of life is like a wave rising and cresting only at the moment\nof its dissolution, or, like the course of the sun, if not brightest\nat least most glorious in its setting. And thus--may we not hope?--the\nglories of the close of a well-spent life become the pledge and\nharbinger of an eternal to-morrow?\n\nWe have thus far illustrated the three laws of succession of organic\nforms by ontogeny, because this is the type of evolution; but they\nmay be illustrated also by other forms of evolution. Next to the\ndevelopment of the individual, undoubtedly the _progress of society_\nfurnishes the best illustration of these laws.\n\nCommencing with a condition in which each individual performs all\nnecessary social functions, but very imperfectly; in which each\nindividual is his own shoemaker and tailor, and house-builder and\nfarmer, and therefore all persons are socially alike; as society\nadvances, the constituent members begin to diverge, some taking on\none social function and some another, until in the highest stages of\nsocial organization this diversification or division and subdivision\nof labor reaches its highest point, and each member of the aggregate\ncan do perfectly but one thing. Thus, the social organism becomes\nmore and more strongly bound together by mutual dependence, and\nseparation becomes mutilation. I do not mean to say that this extreme\nis desirable, but only that an approach to this is _a_ natural law of\nsocial development. _Is not this the law of differentiation?_\n\nSo also _progress_ is here, as in other forms of evolution--a _progress\nof the whole_, but not necessarily of every part. Some members of\nthe social aggregate advance _upward_ to the dignity of statesmen,\nphilosophers, and poets; some advance _downward_ to the position\nof scavengers and sewer-cleansers.[10] But the highest members are\nprogressively higher, and the whole aggregate is progressively grander\nand more complex in structure and functions.\n\nSo, again, the _law of cyclical movement_ is equally conspicuous here.\nSociety everywhere advances, not uniformly, but by successive waves,\neach higher than the last; each urged by a new and higher social\nforce, and embodying a new and higher phase of civilization. Again:\nas each phase declines, its characteristic social force is not lost,\nbut becomes incorporated into the next higher phase as a subordinate\nprinciple, and thus the social organism as a whole becomes not only\nhigher and higher, but also more and more complex in the mutual\nrelations of its interacting social forces.\n\nLet us not be misunderstood, however. There is undoubtedly in social\nevolution something more and higher than we have described, but which\ndoes not concern us here, except to guard against misconstruction.\nThere is in society a _voluntary progress_ wholly different from the\nevolution we have been describing. In _true_ or material evolution\nnatural law works for the betterment of the whole utterly regardless\nof the elevation of the individual, and the individual contributes to\nthe advance of the whole quite unconsciously while striving only for\nhis own betterment. This unconscious evolution by natural law inherited\nfrom the animal kingdom is conspicuous enough in society, especially in\nits early stages, but we would make a great mistake if we imagined, as\nsome do, that this is all. Besides the unconscious evolution by natural\nlaws, _inherited from below_, there is a higher evolution, _inherited\nfrom above_, indissolubly connected with man\u2019s spiritual nature--a\nconscious, voluntary striving of the best members of the social\naggregate for the betterment of the whole--a conscious, voluntary\nstriving both of the individual and of society toward a recognized\n_ideal_. In the one kind of evolution the fittest are those most in\nharmony with the environment, and which therefore always survive; in\nthe other, the fittest are those most in harmony with the ideal, and\nwhich often do not survive. The laws of this free voluntary progress\nare little understood. They are of supreme importance, but do not\nspecially concern us here. We will speak of it again in another chapter.\n\nThe three laws above mentioned might be illustrated equally well by all\nother forms of evolution. We have selected only those which are most\nfamiliar. They may, therefore, be truly called the laws of evolution.\nWe have shown that they are the laws of succession of organic forms.\n\n=III. Change by Means of Resident Forces.=--Thus far in our argument\nI suppose that most well-informed men will raise no objection. It\nwill be admitted, I think, even by those most bitterly opposed to\nthe theory of evolution, that there has been throughout the whole\ngeological history of the earth an onward movement of the organic\nkingdom to higher and higher levels. It will be admitted, also, that\nthere is a grand and most significant resemblance between the course\nof development of the organic kingdom and the course of embryonic\ndevelopment--between the laws of succession of organic forms and the\nlaws of ontogenic evolution. But there is another essential element in\nontogenic evolution. It is that the _forces_ or causes of evolution\nare _natural_; that they reside in the thing developing and in the\nreacting environment. This we know is true of embryonic development; is\nit true also of the geologic succession of organic forms? It is true of\nontogeny; is it true also of phylogeny? If not, then only by a metaphor\ncan we call the process of change in the organic kingdom throughout\ngeological history an evolution. This is the point of discussion, and\nnot only of discussion, but, alas! of heated and even angry dispute.\nThe field of discussion is thus narrowed to this third point only.\n\nBefore stating the two opposite views of the cause of evolution, it\nis necessary to remind the reader that when the evolutionist speaks\nof the forces that determine progressive changes in organic forms\nas _resident_ or _inherent_, all that he means, or ought to mean,\nis that they are resident in the same sense as all natural forces\nare resident; in the same sense that the vital forces of the embryo\nare resident in the embryo, or that the forces of the development of\nthe solar system according to the nebular or any other cosmogonic\nhypotheses are resident in that system. In other words, they mean only\nthat they are _natural_, not supernatural. This does not, of course,\ntouch that deeper, that deepest of all questions, viz., the essential\n_nature and origin of natural forces_; how far they are independent\nand self-existent, and how far they are only modes of divine energy.\nThis is a question of philosophy, not of science. This question is\nbriefly discussed in another place (Part III, Chap. III); it does not\nimmediately concern us here.\n\n=The Two Views briefly Contrasted.=--As already stated, all will admit\na grand resemblance between the stages of embryonic development and\nthose of the development of the organic kingdom. This was first brought\nout clearly by Louis Agassiz, and is, in fact, the greatest result\nof his life-work. All admit, also, that the embryonic development is\na natural process. Is the development of the organic kingdom also a\nnatural process? All biologists of the present day contend that it\nis; all the old-school naturalists, with Agassiz at their head, and\nall anti-evolutionists of every school, contend that it is not. We\ntake Agassiz as the type of this school, because he has most fully\nelaborated and most distinctly formulated this view. As formulated by\nhim, it has stood in the minds of many as an alternative and substitute\nfor evolution.\n\nAccording to the evolutionists, all organic forms, whether species,\ngenera, families, orders, classes, etc., are variable, and, if external\nconditions favor, these variations accumulate in one direction and\ngradually produce new forms, the intermediate links being usually\ndestroyed or dying out. According to Agassiz, the higher groups,\nsuch as genera, families, orders, etc., are indeed variable by the\nintroduction of new species, but species are the ultimate elements of\nclassification, and, like the ultimate elements of chemistry, are\nunchangeable; and, therefore, the speculations of the evolutionist\nconcerning the transmutation of species are as vain as were the\nspeculations of the alchemists concerning the transmutation of\nmetals--that the origin of man, for example, from any lower species\nis as impossible as the origin of gold from any baser metal. Both\nsides admit frequent change of species during geological history, but\none regards the change as a change by gradual _transmutation_ of one\nspecies _into_ another through successive generations and by _natural_\nprocess, the other as change by _substitution_ of one species _for_\nanother by direct supernatural _creative act_. Both admit the gradual\ndevelopment of the organic kingdom as a whole through stages similar\nto those of embryonic development; but the one regards the whole\nprocess as natural, and therefore strictly comparable to embryonic\ndevelopment, the other as requiring frequent special interference of\ncreative energy, and therefore comparable rather to the development\nof a building under the hand and according to the preconceived plan\nof an architect--a plan, in this case, conceived in eternity and\ncarried out consistently through infinite time. It is seen that the\nessential point of difference is this: The one asserts the variability\nof species (if conditions favor, and time enough is given) without\nlimit; the other asserts the permanency of specific forms, or their\nvariability only within narrow limits. The one asserts the origin\nof species by \u201c_descent with modifications_\u201d; the other, the origin\nof species by \u201c_special act of creation_.\u201d The one asserts the law\nof continuity (i. e., that each stage is the natural outcome of the\nimmediately preceding stage) in this, as in every other department of\nNature; the other asserts that the law of continuity (i. e., of cause\nand effect) does not hold in this department; that the links of the\nchain of changes are discontinuous, the connection between them being\nintellectual, not physical.\n\nSo much for sharp contrasting characterization of the two views,\nnecessary for clear understanding of much that follows. We will have\nto give them more fully hereafter when we take up the evidences of\nevolution in Part II.\n\n\n\n\nCHAPTER II.\n\nTHE RELATION OF LOUIS AGASSIZ TO THE THEORY OF EVOLUTION.\n\n\nIn order to clear up the conception of evolution, it is necessary\nto give a brief history of the idea, and especially to explain the\nrelation of Louis Agassiz to that theory. This is the more necessary,\nbecause there is a deep and wide-spread misunderstanding on this\nsubject, and thus scant justice has been done our great naturalist,\nespecially by the English and Germans; and also because this relation\nis an admirable illustration of an important principle in scientific\nphilosophy.\n\nLike all great ideas, we find the first germs of this in Greek\nphilosophy, in the cosmic speculations of Thales and Pythagoras.\nNext (about 100 B. C.) we find it more clearly expressed by the Roman\nthinker, Lucretius, in his great philosophic poem entitled \u201cDe Rerum\nNatura.\u201d After a dormancy of nearly eighteen centuries it next emerges\nwith still more clearness in the theological speculations of Swedenborg\nand the philosophical speculations of Kant. All these we pass over with\nbare mention, because these thinkers approached the subject from the\nphilosophic rather than the scientific side--in the metaphysical rather\nthan the scientific spirit.\n\nThe first serious attempt at scientific presentation of the subject was\nby the celebrated naturalist, Lamarck, in a work entitled \u201cPhilosophie\nZo\u00f6logique,\u201d published in 1809. It is not necessary, in this rapid\nsketch, to give a full account of Lamarck\u2019s views. Suffice it to say\nthat the essential idea of evolution, viz., the indefinite variability\nand the derivative origin of species, was insisted on with great\nlearning and skill, and illustrated by many examples. With Lamarck,\nthe factors of evolution or causes of change of organic forms were--1.\nModification of organs in function and therefore in structure, by a\nchanging environment--external factor; and, 2. Modification of organs\nby _use_ and _disuse_--internal factor. In both cases the modifications\nare inherited and increased from generation to generation, without\nlimit. This second factor seems to have taken, in the mind of Lamarck,\nthe somewhat vague and transcendental form of aspiration or upward\nstriving of the animal toward higher conditions. These are acknowledged\nto-day as true factors of evolution, but the distinctively Darwinian\nfactor, viz., \u201cdivergent variation and natural selection,\u201d was not then\nthought of. The publication of Lamarck\u2019s views produced a powerful\nimpression, but only for a little while. Pierced by the shafts of\nridicule shot by nimble wits of Paris, and crushed beneath the heavy\nweight of the authority of Cuvier, the greatest naturalist and\ncomparative anatomist of that or perhaps of any time, it fell almost\nstill-born. I believe it was best that it should thus perish. Its birth\nwas premature; it was not fit to live. The world was not yet prepared\nfor a true scientific theory. Nevertheless, the work was not without\nits effect upon some of the most advanced thinkers of that time; upon\nSaint-Hilaire and Comte in France, and upon Goethe and Oken in Germany.\nIt was good seed sown and destined to spring up and bear fruit in\nsuitable environment; but not yet.\n\nThe next attempt worthy of attention in this rapid sketch is that\nof Robert Chambers, in a little volume entitled \u201cVestiges of a\nNatural History of Creation,\u201d published in 1844. It was essentially a\nreproduction of Lamarck\u2019s views in a more popular form. It was not a\ntruly scientific work nor written by a scientific man. It was rather an\nappeal from the too technical court of science to the supposed wider\nand more unprejudiced court of popular intelligence. It was therefore\nfar more eloquent than accurate; far more specious than profound.\nIt was, indeed, full of false facts and inconsequent reasonings.\nNevertheless, it produced a very strong impression on the thinking,\npopular mind. But _it_ also quickly fell, pierced by keen shafts of\nridicule, and crushed beneath the heavy weight of the authority of all\nthe most prominent naturalists of that time, with Agassiz at their\nhead. The question for the time seemed closed. I believe, again, it was\nbest so, for the time was not yet fully ripe.\n\nI know full well that many think with Haeckel that biology was kept\nback half a century by the baneful authority of Cuvier and Agassiz;\nbut I can not think so. The hypothesis was contrary to the facts\nof science _as then known and understood_. It was conceived in the\nspirit of baseless speculation, rather than of cautious induction; of\nskillful elaboration rather than of earnest truth-seeking. Its general\nacceptance would have debauched the true spirit of science. I repeat\nit: the time was not yet ripe for a scientific theory. The ground\nmust first be cleared and a solid foundation built; an insuperable\n_obstacle_ to hearty rational acceptance must first be removed, and an\ninductive _basis_ must be laid.\n\n=The Obstacle removed.=--The obstacle in the way of the acceptance\nof the derivative origin of species was the then prevalent _notion\nconcerning the nature of life_. We must briefly sketch the change which\nhas taken place in the last forty years in our ideas on this subject.\n\nUntil about forty years ago, the different forces of Nature, such\nas gravity, electricity, magnetism, light, heat, chemical affinity,\netc., were supposed to be entirely distinct. The realm of Nature was\ndivided up into a number of distinct and independent principalities,\neach subject to its own sovereign force and ruled by its own petty\nlaws. About that time it began to be evident, and is now universally\nacknowledged, that all these forces are but different _forms_ of one,\nuniversal, omnipresent energy, and are transmutable unto one another\nback and forth without loss. This is the doctrine of correlation of\nforces and conservation of energy, one of the grandest ideas of modern\ntimes. But _one_ force seemed still to be an exception. Life-force\nwas still believed to be a peculiar, mysterious principle or entity,\nstanding above other forces and subordinating them; not correlated\nwith, not transmutable unto, nor derivable from, other and lower\nforces, and therefore in some sense supernatural. Now, if this be true\nof living _forces_, it is perfectly natural, yea, almost necessary,\nto believe that living _forms_ are wholly different from other forms\nin their origin. New forms of dead matter may be derived, but new\nliving forms are _underived_. Other new forms come by natural process,\nnew organic forms by supernatural process. The conclusion was almost\nunavoidable. But soon vital force also yielded to the general law of\ncorrelation of natural forces. Vital forces are also transmutable into\nand derivable from physical and chemical forces. Sun-force, falling on\nthe green leaves of plants, is absorbed and converted into vital force,\ndisappears as _light_ to reappear as _life_. The amount of life-force\ngenerated is measured by the amount of light extinguished. The same\nis true of animal life. As in the steam-engine the locomotive energy\nis derived from the fuel consumed and measured by its amount, so in\nthe animal body, the animal heat and animal force are derived from and\nmeasured by the food and tissue consumed by combustion. Thus, vital\nforce may be regarded as so much force withdrawn from the general fund\nof chemical and physical forces, to be again refunded without loss at\ndeath. This obstacle is, therefore, now removed. If vital force falls\nin the same category as other natural forces, there is no reason why\nliving forms should not fall into the same category in this regard\nas other natural forms. If new forms of dead matter are derived from\nold forms by modification, according to _physical_ laws, there is no\nreason why new living forms should not also be derived from old forms\nby modification according to _physiological_ laws. Thus, at last, the\nobstacle was removed--the ground was cleared.\n\n=The Basis laid.=--But Science is not content with removal of _a\npriori_ objections. She must also have positive proofs. The ground\nmust not only be cleared, but a true inductive basis of facts, and\nespecially of laws and methods, must be laid. _This was the life-work\nof Agassiz._ Yes, as strange as it may seem to some, it is nevertheless\ntrue that the whole inductive basis, upon which was afterward built\nthe modern theory of evolution, was laid by Agassiz, although he\nhimself persistently refused to build upon it any really scientific\nsuperstructure. It is plain, then, that all attempts at building\nprevious to Agassiz\u2019s work must, of necessity, have resulted in an\nunsubstantial structure--an edifice built on sand, which could not\nand ought not to stand. I must stop here in order to explain somewhat\nfully this important point, and thus to give due credit to the work of\nAgassiz.\n\nThe title of any scientist to greatness must be determined, not so much\nby the multitude of new facts he has discovered as by the new laws he\nhas established, and especially by the new methods he has inaugurated\nor perfected. Now, I think it can be shown that to Agassiz, more\nthan to any other man, is due the credit of having _established the\nlaws of succession of living forms_ in the geological history of the\nearth--laws upon which must rest any true theory of evolution. Also,\nthat to him, more than to any other man, is due the credit of having\n_perfected the method_ (method of comparison) by the use of which alone\nbiological science has advanced so rapidly in modern times. This is\nhigh praise. I wish to justify it. I begin with the method.\n\nScientific methods bear the same relation to _intellectual progress_\nthat tools, instruments, machines, mechanical contrivances of\nall sorts, bear to _material progress_. They are intellectual\n_contrivances_--indirect ways of accomplishing results far too hard\nfor bare-handed, unaided intellectual strength. As the civilized man\nhas little or no advantage over the savage in bare-handed strength of\nmuscle, and the enormous superiority of the latter in accomplishing\nmaterial results is due wholly to the use of mechanical contrivances\nor machines; even so, in the higher sphere of intellect, the scientist\nmakes no pretension to the possession of greater unaided intellectual\nstrength than belongs to the uncultured man, or even perhaps to the\nsavage. The amazing intellectual results achieved by science are due\nwholly to the use of intellectual contrivances or scientific methods.\nAs in the lower sphere of material progress the greatest benefactors of\nthe race are the inventors or perfecters of new mechanical contrivances\nor _machines_, so also in the higher sphere of intellectual progress\nthe greatest benefactors of the race are the inventors or perfecters of\nnew intellectual contrivances or _methods of research_.\n\nTo illustrate the power of methods, and the necessity of their use,\ntake the case of the _method of notation_, so characteristic of\nmathematics, and take it even in its simplest and most familiar form:\nNine numeral figures, having each a value of its own, and another\ndependent upon its position; a few letters, _a_ and _b_, and _x_ and\n_y_, connected by symbols, + and-and =: that is all. And yet, by the\nuse of this simple contrivance, the dullest school-boy accomplishes\nintellectual results which would defy the utmost efforts of the\nunaided strength of the greatest genius. And this is only the simplest\ntool-form of this method. Think of the results accomplished by the use\nof the more complex machinery of the higher mathematics!\n\nTake next the method of experiment so characteristic of physics and\nchemistry. The phenomena of the external world are far too complex and\nfar too much affected by disturbing forces and modifying conditions to\nbe understood at once by bare, unaided intellectual insight. They must\nfirst be simplified. The physicist, therefore, contrives artificial\nphenomena under ideal conditions. He removes one complicating condition\nafter another, one disturbing cause and then another, watching\nmeanwhile the result, until finally the necessary condition and the\ntrue cause are discovered. On this method rests the whole fabric of the\nphysical and chemical sciences.\n\nBut when we rise still higher, viz., into the plane of life, the\nphenomena of Nature become still more complex and difficult to\nunderstand directly; and yet just here, where we are the most powerless\nwithout some method, our method of experiment almost wholly _fails\nus_. The phenomena of life are not only far more complex than those\nof dead matter, but the conditions of life are so nicely adjusted,\nthe equilibrium of forces so delicately balanced, that, when we\nattempt to introduce our clumsy hands in the way of experiment, we\nare in danger of overthrowing the equilibrium, of destroying the\nconditions of the experiment, viz., life; and then the whole problem\nfalls immediately into the domain of chemistry. What shall we do?\nIn this dilemma we find that Nature herself has already prepared\nfor us, ready to hand, an elaborate series of simplified conditions\nequivalent to experiments. The phenomena of life are, indeed, far too\ncomplex to be at once understood--the problem of life too hard to be\nsolved--in the higher animals; but, as we go down the animal scale,\ncomplicating conditions are removed one by one, the phenomena of life\nbecome simpler and simpler, until in the lowest microscopic cell or\nspherule of living protoplasm we finally reach the simplest possible\nexpression of life. The equation of life is reduced to its simplest\nterms, and now, if ever, we begin to understand the true value of the\nunknown quantity. This is the natural history series, or _Taxonomic_\nseries, already spoken of on page 10. Again, Nature has prepared, and\nis now preparing daily before our eyes, another series of gradually\nsimplified conditions. Commencing with the mature condition of one of\nthe higher animals--for example, man--and going backward along the\nline of individual history through the stages of infant embryo, egg\nand germ, we find again the phenomena of life becoming simpler and\nsimpler, until we again reach the simplest conceivable condition in\nthe single microscopic cell or spherule of living protoplasm. This, as\nalready explained, is the embryonic or _Ontogenic_ series. Again, that\nthere be no excuse for man\u2019s ignorance of the laws of life, Nature has\nprepared still another series; and this the grandest of all, for it is\nthe cause of both the others. Commencing with the plants and animals of\nthe present epoch, and going back along the track of geological times,\nthrough Cenozoic, Mesozoic, Pal\u00e6ozoic, Eozoic, to the very dawn of\nlife--the first syllable of recorded time--and we find again a series\nof organic forms growing simpler and simpler, until, if we could find\nthe very first, we would undoubtedly again reach the simplest condition\nin the lowest conceivable forms of life. This, as we have already seen,\nis the geologic or evolution, or _Phylogenic_ series. We have already\nexplained these three series, only in this connection it suits our\npurpose to take the terms backward.\n\nNow, it is by _comparison_ of the terms of each of these series going\nup and down, and watching the first appearance, the growth, and the\nperfecting of tissues, organs, functions, and by the comparison of\nthe three series with one another term by term--I say it is wholly\nby comparison of this kind that biology has in recent times become a\ntrue inductive science. This is the \u201c_method of comparison_.\u201d It is\nthe great method of research in all those departments which can not be\nreadily managed by the method of experiment. It has already regenerated\nbiology, and is now applied with like success in sociology under the\nname of _historic method_. Yes; anatomy became scientific only through\ncomparative anatomy, physiology through comparative physiology, and\nembryology through comparative embryology. May we not add, sociology\nwill become truly scientific only through comparative sociology, and\npsychology through comparative psychology?\n\nNow, while it is true that this method, like all other methods, has\nbeen used, from the earliest dawn of thought, in a loose and imperfect\nway, yet it is only in very recent times that it has been organized,\nsystematized, perfected, as a true scientific method, as a great\ninstrument of research; and the prodigious recent advance of biology is\ndue wholly to this cause. Now, among the great leaders of this modern\nmovement, Agassiz undoubtedly stands in the very first rank. I must try\nto make this point plain, for it is by no means generally understood.\n\nCuvier is acknowledged to be the great founder of comparative anatomy.\nHe it was that first perfected the method of comparison, but comparison\nonly in one series--the _Taxonomic_. Von Baer and Agassiz added to\nthis comparison in the ontogenic series also, and comparison of\nthese two series with each other, and therefore the application of\nembryology to the classification of animals. If Von Baer was the\nfirst announcer, Agassiz was the first great practical worker by this\nmethod. Last and most important of all, in its relation to evolution,\nAgassiz added _comparison in the geologic or phylogenic series_. The\none grand idea underlying Agassiz\u2019s whole life-work was the essential\nidentity of the three series, and therefore the light which they must\nshed on one another. The two guiding and animating principles of his\nscientific work were--1. That the embryonic development of one of the\nhigher representatives of any group repeated in a general way the\nterms of the Taxonomic series in the same group, and therefore that\nembryology furnished the key to a true classification; and, 2. That the\nsuccession of forms and structure in geological times in any group is\nsimilar to the succession of forms and structure in the development of\nthe individual in the same group, and thus that embryology furnishes\nalso the key to geological succession. In other words, during his\nwhole life, Agassiz insisted that the laws of embryonic development\n(ontogeny) are also the laws of geological succession (phylogeny).\nSurely this is the foundation, the only solid foundation, of a true\ntheory of evolution. It is true that Agassiz, holding as he did the\ndoctrine of permanency of specific types, and therefore rejecting the\ndoctrine of the derivative origin of species, did not admit the causal\nor natural relation of phylogenic succession to embryonic succession\nand taxonomic order as we now believe it--it is true that for him the\nrelation between the three series was an intellectual not a physical\none--consisted in the preordained plans of the Creator, and not in\nany genetic connection or inherited property; but evidently the first\nand greatest step was the discovery of the relation itself, however\naccounted for. The rest was sure to follow.\n\nBut more. Not only did Agassiz establish the essential identity of the\ngeologic and embryonic succession, the general similarity of the two\nseries, phylogenic and ontogenic, but he also announced and enforced\nall the formal laws of geologic succession (i. e., of evolution), as\nwe now know them. These, as already stated and illustrated, are the\nlaw of differentiation, the law of progress of the whole, and the law\nof cyclical movement, although he did not formulate them in these\nwords. No true inductive evidence of evolution was possible without\nthe knowledge of these laws, and for this knowledge we are mainly\nindebted to Agassiz. He well knew also that they were the laws of\nembryonic development and therefore of evolution; but he avoided the\nword evolution, as implying the derivative origin of species, and\nused instead the word _development_, though it is hard to see in what\nthe words differ. Thus, it is evident that Agassiz laid the whole\nfoundation of evolution, solid and broad, but refused to build any\nscientific structure on it; he refused to recognize the legitimate, the\nscientifically necessary outcome of his own work. Nevertheless, without\nhis work a scientific theory of evolution would have been impossible.\nWithout Agassiz (or his equivalent), there would have been no Darwin.\n\nThere is something to us supremely grand in this refusal of Agassiz to\naccept the theory of evolution. The opportunity to become the leader of\nmodern thought, the foremost man of the century, was in his hands, and\nhe refused, because his religious, or, perhaps better, his philosophic\nintuitions, forbade. To Agassiz, and, indeed, to all men of that time,\nto many, alas! even now, evolution is materialism. But materialism is\nAtheism. Will some one say, the genuine Truth-seeker follows where she\nseems to lead _whatever be the consequences_? Yes; whatever be the\nconsequences to one\u2019s self, to one\u2019s opinions, prejudices, theories,\nphilosophies, but not to _still more certain truth_. Now, to Agassiz,\nas to all genuine thinkers, the existence of God, like our own\nexistence, is more certain than any scientific theory, than anything\ncan possibly be made by proof. From his standpoint, therefore, he was\nright in rejecting evolution as conflicting with still more certain\ntruth. The mistake which he made was in imagining that there was any\nsuch conflict at all. But this was the universal mistake of the age. A\nlesser man would have seen less clearly the higher truth and accepted\nthe lower. A greater man would have risen above the age, and seen that\nthere was no conflict, and so accepted both. All thinking men are\ncoming to this conclusion now, but none had done so then.\n\nNow, then, at last, the obstacle of supernaturalism in the realm of\nNature having been removed by the establishment of the doctrine of\ncorrelation of natural forces, and the extension of this doctrine\nto embrace also life-force; and now also a broad and firm basis of\ncarefully-observed facts and well-established laws of succession\nof organic forms having been laid by Agassiz, when again, for the\nthird time, the doctrine of origin of species \u201cby derivation with\nmodifications\u201d was brought forward by Darwin in a far more perfect\nform, with more abundant illustrative materials, and with a new\nand most potent factor of modification--viz., divergent variations\nand natural selection--it found the scientific world already fully\nprepared, and anxiously waiting. I say _anxiously_ waiting--for the\nsupposed supernatural origin of species had been the one exception\nto the otherwise universal law of cause and effect, or the law of\ncontinuity. It was therefore in open contradiction to the whole drift\nof scientific thought for five hundred years. Is it any wonder,\nthen, that the derivative origin of species was welcomed with joy by\nthe scientific world? For five hundred years, scientific thought,\nlike a rising tide which knows no ebb, had tended thitherward with\never-increasing pressure, but kept back by the one supposed fact of\nthe supernatural origin of species. Darwin lifted the gate, and the\nin-rushing tide flooded the whole domain of thought.\n\nWhat, then, is the place of Agassiz in biological science? What is the\nrelation of Agassiz to Darwin--of Agassizian development to Darwinian\nevolution? I answer, it is the relation of formal science to physical\nor causal science. Agassiz advanced biology to the _formal_ stage;\nDarwin carried it forward, to some extent at least, to the _physical_\nstage. All true inductive sciences in their complete development pass\nthrough these two stages. Science in the one stage treats of the _laws_\nof phenomena; in the other, of the _causes_ or explanation of these\nlaws. The former must precede the latter, and form its foundation;\nthe latter must follow the former, and constitute its completion. The\nchange from the one to the other is always attended with prodigious\nimpulse to science.\n\nTo illustrate: Until Kepler, astronomy was little more than\nan accumulation of disconnected facts concerning celestial\nmotions--abundant materials, but no science; piles of brick and stone,\nbut no building. Kepler reduced this chaos to beautiful order and\nmusical harmony by the discovery of the three great laws which bear his\nname, and therefore he has been justly called the legislator of the\nheavens--_the lawgiver of space_. But, had he been asked the _cause_\nof these beautiful laws, he could only have answered, \u201cThe _first\ncause_--the direct will of the Deity.\u201d A good answer and a true, but\nnot scientific; because it places the question beyond the domain of\nscience, which deals only with second or physical causes. But Newton\ncomes forward and gives a _physical cause_. He shows that all these\nbeautiful laws are the necessary result of gravitation; and thus\nastronomy becomes a physical science. So, until Agassiz, the facts\nof geological succession of organic forms were in a state of lawless\nconfusion. Agassiz by establishing the three great laws of succession,\nwhich ought to bear his name, reduced this chaos to order and beauty;\nand, therefore, he might justly be called the legislator of geological\nhistory--the _lawgiver of time_. But, when asked the cause of these\nlaws, he could only answer, and did indeed answer, \u201cThe plans of the\nCreator.\u201d A noble answer and true, but not scientific. Darwin now comes\nforward and gives, partly at least, the cause of these laws. He shows\nthat all these beautiful laws are explained by the doctrine of \u201corigin\nof species by derivation with modifications\u201d; that these laws are\nnot ultimate, but derivative from more fundamental laws of life; and\nthus biology is advanced one step, at least, toward the causal stage.\nNewton and Darwin substituted second causes for first cause--natural\nfor supernatural. They each in his own department broke the bonds of\nsupernaturalism in the domain of Nature.\n\nOne more important reflection: There are two, and only two, fundamental\nconditions of material existence--_space_ and _time_. There are,\ntherefore, two, and only two, cosmoses--space-cosmos and time-cosmos.\nThese have been redeemed from confusion and reduced to law and order\nand beauty--changed from chaos to cosmos--by science. For this result\nwe are chiefly indebted, in the one case, to Kepler and Newton; in the\nother, to Agassiz and Darwin. The universal law, in the one cosmos, is\nthe _law of gravitation_; in the other, the _law of evolution_. Traced\nby analysis to its deepest roots of philosophic truth, the one law\nmay be called the divine mode of sustentation; the other, the divine\nprocess of creation.\n\nOr again: we have all heard of the \u201cmusic of the spheres\u201d--a beautiful\nand significant name used by the old thinkers for the divine order of\nthe universe--a music heard not by human ear, but only by the attentive\nhuman spirit. Harmonic relation apprehended by _reason_ we call _Law_,\nand its embodiment Science; the same apprehended by the imagination\nand \u00e6sthetic sense, we call _Beauty_, and its embodiment _Art_,\n_music_. Now, in music there are two kinds of harmony, simultaneous\nand consecutive--chordal harmony and melody. These must be combined\nto produce the grandest effect. So in cosmic order, too, there are\ntwo kinds of harmonic relation--the _co-existent in space_ and the\n_consecutive in time_. The law of gravitation expresses the universal\nharmonic inter-relation of _objects_ co-existent in space, the law of\nevolution, the universal harmonic relation of _forms_ successive in\ntime. Of the divine spheral music, the one is the chordal harmony, the\nother the consecutive harmony or melody. Combined they form the divine\nchorus which \u201cthe morning stars sang together.\u201d\n\n\n\n\nPART II.\n\n_EVIDENCES OF THE TRUTH OF EVOLUTION._\n\n\n\n\nCHAPTER I.\n\nGENERAL EVIDENCES OF EVOLUTION AS A UNIVERSAL LAW.\n\n\nLet us again remind the reader that evolution means, first of all,\n_continuity_. The law of evolution, although it doubtless means much\nmore, means, first of all, a law of continuity, or _causal relation\nthroughout Nature_. It means that, alike in every department of Nature,\neach state or condition grew _naturally_ out of the immediately\npreceding. In a word, it means that, in the course of Nature, nothing\nappears suddenly and without natural cause, but, on the contrary,\neverything is the natural and usually the gradual outcome of a previous\ncondition. This is _now_ admitted by every one in regard to _nearly_\neverything: evolutionists apply it to the whole course of Nature.\nI said this is _now_ admitted by every one in regard to _nearly_\neverything; but this has not always been so. The world has come to its\npresent position on this subject only by a very gradual process. Let\nus then trace rapidly the history of the gradual change, for it will\nprepare us for much that follows.\n\nThere was a time (and that not many decades ago) when all things, the\norigin of which transcends our ordinary experience, were supposed to\nhave originated suddenly and without natural process--to have been made\nat once, out of hand. There was a time when, for example, mountains\nwere supposed to have been made at once, with all their diversified\nforms, of beetling cliffs and thundering waterfalls, or gentle slopes\nand smiling valleys, just as we now find them. But _now_ we know that\nthey have become so only by a very gradual process, and are still\nchanging under our very eyes. In a word, they have been formed by a\n_process of evolution_. We know now the date of mountain-births; we\ntrace their growth, maturity, decay, and death; and find even, as it\nwere, the fossil bones of extinct mountains in the crumpled strata\nof their former places. There was a time when continents and seas,\ngulfs, bays, and rivers, were supposed to have originated at once,\nsubstantially as we now see them. _Now_, we know that they have been\nchanging throughout all geological time, and are still changing. Not,\nhowever, change back and forth in any direction indifferently and\nwithout goal, but gradual change from less perfect to more perfect\ncondition, with more and more complex inter-relations--i. e., by a\n_process of evolution_. We are able now, though still imperfectly,\nto trace some of the stages of this evolution. There was a time when\nrocks and soils were supposed to have been always rocks and soils; when\nsoils were regarded as an original clothing made on purpose to hide the\nrocky nakedness of the new-born earth. God clothed the earth so, and\nthere an end. _Now_ we know that rocks rot down to soils; soils are\ncarried down and deposited as sediments; and sediments re-consolidate\nas rocks--the same materials being worked over and over again, passing\nthrough all these stages many times in the history of the earth. In\na word, there was a time when it was thought that the earth with\nsubstantially its present form, configuration, and climate, was made\nat once out of hand, as a fit habitation for man and animals. _Now_\nwe know that it has been changing, preparing, becoming what it is by\na slow process, through a lapse of time so vast that the mind sinks\nexhausted in the attempt to grasp it. It has become what it now is\nby a _process of evolution_. The same change of view has taken place\nconcerning the origin of all the heavenly bodies. We may, therefore,\nconfidently generalize--we may assert without fear of contradiction\nthat _all inorganic forms_, without exception, have originated by a\nprocess of evolution.\n\nThe proof of all this we owe to geology--a science born of the present\ncentury. This science establishes the law of _universal continuity_ of\nevents, through infinite _time_, as astronomy does that of _universal\ninter-relation_ of objects through infinite _space_. How great the\nchange these two sciences have made in the realm of human thought!\nUntil the birth of modern astronomy the intellectual _space-horizon_\nof the human mind was bounded substantially by the dimensions of\nour earth; sun, moon, and stars, being but inconsiderable bodies\ncirculating at a little distance about the earth, and for our behoof.\nAstronomy was then but the geometry of the curious lines traced by\nthese wandering fires on the concave blackboard of heaven. With the\nfirst glance through a telescope the phases of Venus and the satellites\nof Jupiter, revealed clearly to the mind the existence of other\nworlds besides and like our own. In that moment the idea of _infinite\nspace_, full of worlds like our own, was for the first time completely\nrealized, and became thenceforward the heritage of man. In that moment\nthe _intellectual horizon of man was infinitely extended_. So also\nuntil the birth of geology, about the beginning of the present century,\nthe intellectual _time-horizon_ of the human mind was bounded by six\nthousand years. The discovery about that time of vertebrate remains,\nall wholly different from those now inhabiting the earth, revealed\nthe existence of other time-faunas, besides our own and the idea of\ninfinite time, of which the life of humanity is but an epoch, was\nborn in the mind of man; and again the intellectual horizon of man\nwas infinitely extended. These two are the grandest ideas, and their\nintroduction the grandest epochs, in the intellectual history of man.\nWe have long ago accepted and readjusted our mental furniture to the\nrequirements of the one, but the necessary readjustment to the other is\nnot yet complete.\n\nAll inorganic forms, then, it is admitted, have come by evolution. But\nhow is it with organic or living forms? Let us see.\n\nEvery one knows, because it is within the limits of ordinary\nexperience, that every _individual_ organism _now_ originates and\ngradually becomes what we see it, by a natural process--that is, by\nevolution. If, then, there be any exception, it must be only the _first\nof each kind_. But what kind? There are many kinds of kinds; classes,\norders, families, genera, species, varieties. Now, many of these kinds\ncan be shown to have become what we see them by a gradual process\nsimilar, at least, to evolution. Take for example, classes. The class\nof fishes and the class of reptiles are _now_ widely distinct and\nhave little in common except a vertebrate structure; but, as already\nshown, page 12, this extreme difference has not always existed. On\nthe contrary, the earliest representatives of these two classes so\nmerged into one another that each seemed either. From this common stock\nthe two classes were gradually separated, each going its own way and\nbecoming more and more widely distinct even to the present day. There\ncan be no doubt, therefore, that _these two classes_, as we now know\nthem, _have become_ what they are by a gradual process. Again: In the\nwhole realm of Nature there is not a class more distinctly separate\nfrom every other and without intermediate links than birds. But this\nhas not always been so. They have gradually become so. The earliest\nbirds were so reptilian in structure and appearance that if we could\nsee them now we would be in doubt whether we should call them birds or\nreptiles. Birds have gradually separated themselves from the reptilian\nstem, becoming more and more bird-like from age to age, until now, at\nlast, the two classes are wholly separated and the intermediate links\ndestroyed. So far as external characters are concerned, birds may be\nsaid to have finally and wholly released themselves from entangling\nalliance with any other class.\n\nClasses, then, it will be admitted, have undoubtedly become what we\nnow know them by a very gradual process following laws identical (as\nwe have already seen, page 19) with the laws of evolution. Shall we\ntry orders? Of the class Mammalia there are two well-recognized and\nwidely-distinct _orders_, viz., the Carnivores and the Herbivores. We\nall know how widely diverse these are in form, in structure, in habits,\nand in food. Has it always been so? Have these been made so at once?\nBy no means. They have gradually become so. The earliest mammals were\nneither the one nor the other distinctively. They were _omnivores_,\ncompletely intermediate in food, habits, form, and structure. From this\ncommon stock the two orders have gradually separated, the carnivores\nbecoming more and more adapted to one mode of life and the herbivores\nto another, by a process following the laws of evolution, as already\nexplained. Shall we try _families_ and _genera_? Marsh and Huxley have\nshown us how completely the horse family (_Equid\u00e6_) and the horse-genus\n(_Equus_) illustrate the process of gradual becoming and the law of\nevolution. Under their guidance, we see that the earliest traceable\nancestor of the horse family, before it was distinctively a horse\nfamily at all, had on the fore-foot five toes in the Lower Eocene,\nfour toes in the Upper Eocene, and three toes in the Miocene; then we\nsee the two side-toes shortening up more and more in the Pliocene and\nbecoming rudimentary splints, leaving only one toe in the Quaternary\nand present epochs. Thus, the side-splints in the foot of the modern\nhorse tell the story of its three-toed ancestry. Similar gradual\nchanges are clearly traceable in size, shape, structure of limbs, of\nteeth, and of brain. In all respects the members of the horse family\nhave become more and more horse-like in the course of time.\n\nThis subject will be taken up and more fully illustrated, under the\nhead of special evidences, in a subsequent chapter. We here touch it\nonly sufficiently to illustrate this universal law of gradual becoming.\n\nWe have taken only a few examples, but the same is undoubtedly true of\nall Taxonomic groups _above species_. Passing over these last for the\nmoment, we take next _races_ and _varieties_. These smaller groups are\nadmitted by all to be formed by a natural process, because not only\ncan we make them artificially, but all the intermediate links may be\nfound in Nature. So we have only _species_ remaining. Yes; species are\nimagined by the old-school naturalist and by the anti-evolutionist of\nto-day as the _ultimate elements_ of Taxonomy. This, then, is the _last\nditch_ upon which the defense of supernaturalism in the realm of Nature\nis made. \u201cOther groups,\u201d they say, \u201cmay have gradually become what they\nnow are by the successive introduction of specific forms according\nto a preordained plan which is well expressed by the formal laws of\nevolution. But _species_ are without transition forms. _They_ come in\nsuddenly, remain unchanged while they continue, and finally pass out\nsuddenly, so far as specific characters are concerned. New species come\nin their places by direct act of creation--by _substitution_, not by\ntransmutation.\u201d This, then, is the last intrenchment. Can we give any\ngood evidence of gradual formation of species? I believe we can.\n\nFirst, then, it is admitted that we can easily make varieties and\nraces artificially. We will not _now_ describe the process; we are all\nfamiliar with the results, viz., the varieties of domestic animals\nand of useful and ornamental plants; the extremely different breeds\nof horses, cattle, sheep, dogs, pigeons, etc.; of wheat, cabbages,\nturnips; of roses, dahlias, etc., etc. No one will doubt that the\nextreme varieties of any of these, say greyhound and pug, if wild,\nwould be called distinct species, or even distinct genera. We do not\ncall them so, for two reasons: first, because we see them made; and,\nsecond, because we find all intermediate links between them; and the\nusual definition of species is that they can not be made, and they have\nno intermediate links. Thus, then, the question is narrowed down to\n_wild species_. They say: \u201cWe take our stand on these\u201d (surely a very\nnarrow ground for so broad a philosophy). \u201cWe defy you to show gradual\nformation with intermediate links.\u201d\n\nNow, in fact, by diligent search such intermediate links between\nwell-recognized species have been found in some cases, especially in\nbirds, on account of their great power of dispersal. Certain forms\nhave long been known from widely-separated regions, and universally\nregarded as distinct species, as distinct as any. Then, by minute\nexaminations of intermediate regions, a complete series of intermediate\nforms has been picked up. This has occurred not only in one case but in\nmany cases, and not in birds only but in many other classes--examples\nincrease with our increasing knowledge.[11] The only answer to such\nevidence is that _these are not true species_. Now, see the fallacy\nlurking here! They define species as ultimate elements of taxonomy, as\ndistinct and without intermediate links, and then require us to find\nsuch intermediate links; and, finally, when with infinite pains some\nsuch links are found, they say: \u201cOh! I see; we were mistaken; they are\nonly varieties!!\u201d It is true that naturalists, when intermediate links\nare found, usually put all together as one species, but this they do\npurely for the sake of clearness of definition and description. It is\nfreely admitted by the evolutionist that species are _now_ usually\ndistinct and without intermediate links, these having been destroyed in\nthe struggle for life. This will be fully explained in another chapter.\nIt is also freely admitted that although intermediate links must have\nexisted at one time, their remains are rarely found. The reason of\nthis will also be explained hereafter. Nevertheless, in some cases, as\nalready seen, we do find them still existing. Now, we add that in some\ncases, where they no longer exist, we find them in the form of fossil\nremains. The most remarkable example of this is found in the gradual\nchanges in the forms of Planorbis in the fresh-water deposits of\nSteinheim, as shown by the admirable researches of Hyatt.[12] We shall\ndiscuss these also more fully in another place. Now, if there be any\nsuch links at all, however rare, then every objection to the derivative\norigin of species is removed.\n\nPerhaps it may be well to make bare mention of another kind of\nevidence, viz., the actual change of species under the eyes, by\nthe action of change of environment. The different species of the\ngenus _Artemia_ (a low form of crustacean) live in brine-pools. By\nconcentrating the brine of such a pool, one species (_A. salina_)\nhas been observed to change in successive generations into another\n(_A. Muhlhausenii_), and the latter back again to the former by slow\nfreshening.[13] Again: The siredon and the amblystoma have always,\nuntil recently, been regarded as not only distinct species, but\ndistinct genera of amphibians. Siredon was supposed to be a permanent\ngill-breather, while amblystoma becomes by metamorphosis a pure\nair-breather. Now, however, it is known that the former may change into\nthe latter. But the most curious part of the life-history of these\nanimals, is that if water be abundant the siredon reproduces freely,\nand remains indefinitely a gill-breather; but if the water dries up\nit changes into the lung-breathing amblystoma. We do not give this\nas examples of change of species, for the change is in the individual\nlife, and therefore in the nature of metamorphosis, but as evidence\nof the power of physical conditions in modifying the development of\norganic forms and therefore of the manner in which gill-breathers were\nprobably transformed into air-breathers.\n\nTo sum up: 1. All _inorganic_ forms, without exception, have become\nwhat we find them by a natural process--i. e., by evolution. 2. All\n_organic_ or living forms within the _limits of observation_, i. e.,\nevery living thing, has become what we now see, by a gradual, natural\nprocess--i. e., by evolution. 3. All taxonomic groups, except species,\nhave undoubtedly become what we now see them by a gradual process,\nfollowing the laws of evolution, and therefore presumably by a natural\nprocess of evolution. 4. By artificial means, breeds, races, etc., very\nsimilar, at least in many respects, to species, are seen to arise by\na gradual natural process--i. e., by evolution. 5. In some instances,\nat least, natural species are observed to pass into one another by\nintermediate links in such wise that we are forced to conclude that\nthey have been formed by a natural process.\n\nMay we not, then, safely generalize, and make the law universal? Is\nnot this a sufficient ground for confident induction? Even though\nsome facts are still inexplicable, is that a sufficient reason for\nwithholding assent to a theory which explains so much? In all induction\nwe first establish a law provisionally from the observation of a\ncomparatively few facts, and then extend it over a multitude of facts\nnot included in the original induction. If it explains these also,\nthe law is verified. The law of gravitation was first based on the\nobservation of a few facts, and then verified by its explanation of\nnearly all the facts of celestial motion. There are some outstanding\nfacts of celestial motion still unexplained, but we do not, therefore,\ndoubt the law of gravitation. The same principle applied in biology\nought to establish the law of evolution, for it also explains all\nthe facts of biology as no other law can. But inductive evidence\ndiffers from other kinds of evidence in one respect, which, in fact,\nconstitutes its strength to the scientific, but its weakness to the\npopular mind. It is a kind of circumstantial evidence, but its force\ndoes not consist in a few strong circumstances easily appreciated,\nsuch as strike the popular mind, and force conviction, but rather in a\nmultitude of small circumstances, each by itself insignificant, but all\ntogether pointing to one conclusion and demanding one explanation. Such\nevidence is, indeed, overwhelming, but only to the mind that masters\nit. The evidence for the law of gravitation is literally the whole\nscience of astronomy. So also the evidence for the law of evolution\nis the whole science of biology. Neither of these laws can be proved\nin a debating society, but only by a course of study. In the one case\nthe law has been universally accepted--not, however, on evidence, for\nthere are few indeed who appreciate the evidence, but on the authority\nof scientific unanimity. In the other case there has not yet been time\nenough for the already established unanimity to have its full effect.\n\nThus much, we believe, will be generally admitted as a very moderate\nclaim. Evolution is certainly a legitimate induction from the facts\nof biology. But we are prepared to go much further. We are confident\nthat evolution is _absolutely certain_. Not, indeed, evolution as a\nspecial theory--Lamarckian, Darwinian, Spencerian--for these are all\nmore or less successful modes of explaining evolution; nor evolution\nas a school of thought, with its following of disciples--for in this\nsense it is still in the field of discussion--but evolution as a law\nof derivation of forms from previous forms; evolution as a law of\ncontinuity, as a universal law of becoming. In this sense it is not\nonly certain, it is axiomatic. It is only necessary to conceive it\nclearly, to see that it is a necessary truth. This may seem paradoxical\nto some. I stop to justify it.\n\nPhysical phenomena we all admit follow one another in unbroken\nsuccession, each derived from a preceding, and giving origin to a\nsucceeding. We call this the law of causation, and say that it is\naxiomatic. We might call it a law of derivation. So also organic\n_forms_ follow one another in continuous chain, each derived from a\npreceding and giving origin to a succeeding. We call this a law of\nderivation. We might call it a _law of causation_, and say that it too\nis axiomatic. The origins of new phenomena are often obscure, even\ninexplicable, but we never think to doubt that they have a natural\ncause; for so to doubt is to doubt the validity of reason, and the\nrational constitution of Nature. So also the origins of new organic\n_forms_ may be obscure or even inexplicable, but we ought not on that\naccount to doubt that they had a natural cause, and came by a natural\nprocess; for so to doubt is also to doubt the validity of reason, and\nthe rational constitution of organic Nature. The law of evolution\nis naught else than the scientific or, indeed, the rational mode of\nthinking about the origin of things in every department of Nature. In\na word, it is naught else than the law of necessary causation applied\nto _forms_ instead of phenomena. Evolution, therefore, is no longer\na school of thought. The words _evolutionism_ and _evolutionist_\nought not any longer to be used, any more than _gravitationism_ and\n_gravitationist_; for the law of evolution is as certain as the law of\ngravitation. Nay, it is far more certain. The nexus between _successive\nevents in time_ (causation) is far more certain than the nexus between\n_coexistent objects in space_ (gravitation). The former _is a necessary\ntruth_, the latter is usually classed as a contingent truth. I have\nused and may continue to use the term evolutionist, but if so it is\nonly in deference to the views of many intelligent persons, who do not\nyet see the certainty of the law.\n\n\n\n\nCHAPTER II.\n\nSPECIAL PROOFS OF EVOLUTION.\n\n_Introductory._\n\n\nIt will be seen from the preceding chapter that we regard the law of\nevolution in its wider sense, viz., the derivative origin of all forms,\norganic or other, as axiomatic, and therefore requiring no further\nproof. Among scientific men there is no longer any discussion of the\ntruth of this law, but only of the theories of the causes of the law.\nWe believe that to the scientific mind there is no other rational mode\nof looking at the subject of origin of organic forms. To such a mind,\ntherefore, all that follows is but the deductive application of that\nlaw in the explanation of the phenomena of organic Nature. But it takes\ntime for the popular mind to readjust itself to new and revolutionary\ntruth. Many minds, even among the most intelligent, have not yet\naccepted this as the only rational mode of thought. Many men require\nfurther _special proofs_ of the derivative origin of organic forms.\nEven to those who accept evolution, these proofs will be interesting\nas illustrations of such origin. We will attempt to bring out these\nproofs under several heads, the most important of which are: 1. Proofs\nfrom morphology, or the general laws of animal structure; 2. Proofs\nfrom embryology; 3. Proofs from geographical distribution of organic\nforms; and, 4. Proofs from artificial breeding. The subject is so vast\nthat all we can do is to touch lightly only the most salient points\nunder each of these heads; for, as we have already said, the evidence\nis really nothing less than the whole science of biology. Preparatory\nto this, however, it is necessary to bring out a little more fully than\nbefore (page 29), though still only in outline, the two antagonistic\nviews, which may be called the old and the new, or the natural and the\nsupernatural, of the origin of new organic forms, especially species.\n\n=Origin of New Organic Forms; the Old View briefly stated.=--According\nto the old-school naturalists, species are the ultimate elements of\ntaxonomy: genera, families, orders, etc., may gradually change their\ncharacter from age to age, by the introduction of new species; but\nspecies were supposed to be substantially _permanent_. It was necessary\nto have some unit for convenience of description and classification,\nand this was found to be the best because most stable. As in nearly\nall cases of beliefs, this doctrine was held at first somewhat\nloosely, as a provisional and convenient view--as a good working\nhypothesis--but gradually, under pressure of controversy, became more\nstrictly formulated, and, as it were, hardened into a scientific\ndogma, especially in the hands of Agassiz. According to this view,\nthe first pair or pairs of each specific kind originated we know not\nhow, but certainly _at once in its present form_ in full perfection,\nand, therefore, presumably by _direct creative_ act of Deity; and then\nafterward by the law of generation continued to produce others of the\nsame pattern indefinitely. Moreover, the first one or more pairs of\neach kind multiplied and spread abroad in every direction, _each from\nits own center of origin_, as far as physical conditions and struggle\nfor life with other species would allow. This idea explains tolerably\nwell the geographical distribution of species as we now find it. For\nexample, species on different continents are widely different, because\nthose on each have originated independently where we now find them, and\nspread in all directions as far as physical conditions would allow, but\ncould not reach other continents because of the ocean-barrier. That\nthis is the only reason they are not there, is shown by the fact that,\nif they are carried there, they usually do perfectly well. Even on the\nsame continent, for the same reason, species may be very different\nif separated by impassable barriers such as high mountain-chains or\nby climate. But wherever one group of species, originating in one\nplace, comes in contact on the margin of their range with another\ngroup of species originating in another place, we see no evidence of\n_transmutation_ of one form _into_ another, but only _substitution_ of\none fully-formed species _for_ another equally fully formed. Therefore,\nwe must conclude that physical conditions may limit the range of a\nspecies, but can not transmute it into another. Thus, to say the least,\nmany of the facts of geographical distribution are well explained\nby this idea of creative origin in specific centers and subsequent\npermanence of specific form. We say _many_ of the facts; we will show\nhereafter that _not all_ can be thus explained.\n\nBut the main question is not of geographical but of geological\ndistribution; not distribution in space, but succession in time.\nSpecies do not continue forever. On the contrary, they have changed\nmany times in the course of geological history. As conditions become\nunfavorable, species die out or become extinct, and others take their\nplace and carry forward the life and development of the organic\nkingdom. Now, how do they change? According to this school of thought,\nhere also, as in geographical distribution, they are not transmuted\nbut replaced; here also physical conditions may destroy a species,\nbut can not transform it into another. As species die out, others are\ncreated at once, out of hand and fully formed in their place; but in\naccordance with a preordained plan consistently carried out and working\never toward higher and higher conditions. Thus, life is continued on\nthe earth by the alternation of supernatural and natural processes; by\nthe alternate use of direct and indirect action of Deity: direct in\nthe introduction of first pairs, indirect through the natural process\nof reproduction in the continuance and multiplication of the species.\nEach species is made according to a pattern in the Divine mind, on a\nsort of intellectual die, and then continues to reproduce a succession\nof individuals of the same pattern as if struck from the same die\nuntil the die is broken or worn out. Another die is made, of another\npattern, and individuals are struck from this; and so on, throughout\nthe whole geological history of the organic kingdom. Only, we must\nadd that the successive dies are made to follow one another according\nto a plan which is expressed by the three laws already given on page\n11. Thus, the origin of individuals is natural, the origin of species\nsupernatural; the making of dies is supernatural, the coinage is\nnatural.\n\nWe have stated this view in a too extreme form, in order to make it\nclearer. We now, therefore, proceed to qualify somewhat. Specific types\nwere held, by writers of this school of thought, to be _substantially_\nbut not absolutely unchangeable. Successive individuals of the same\nspecies were admitted to be not exactly alike. Such slight differences\nwere called _varieties_. It was admitted, indeed, that species\nvaried, but it was believed that such variations in any direction\nwere strictly limited in amount. A species may be compared to a right\ncylinder standing on end. As such a cylinder may be tilted slightly\nin one direction or another, without overthrowing its equilibrium,\nthe cylinder tending ever to right itself and return to its original\nposition, so a species may be varied slightly in one direction or\nanother without destroying its integrity, the species tending ever to\nreturn to its normal or typical form. But as the cylinder, if pushed\ntoo far from its normal position, is overthrown, so also a species,\nif pressed too far in the way of variation from its typical form, is\ndestroyed, but not changed into another species. As cylinders may be\nmore or less rigid, depending upon the breadth of their bases, so also\nsome species are more rigidly set in their typical form, and some are\nmore plastic to influences causing variations, but in all cases there\nis a limit to the amount of oscillation consistent with integrity.\n\n=The New View briefly stated.=--According to Darwin, and all biologists\nof the present day, species are variable _without limit_, if only the\ncauses of change are constant and slow enough in their operation,\nand the time long enough. A species must be in harmony with its\nenvironment, for this is the condition of its existence. Now, if the\nenvironment change, the species must _tend_ to change slowly from\ngeneration to generation, so as to readjust its relations in harmony\nwith the changing environment. If the change of environment be slow,\nthe readjustment may be successful, and the species will change\ngradually into another form, so different that it will be called\na different species, especially if the intermediate gradations be\ndestroyed. If the change in the environment be too rapid, many species,\nespecially the more rigid, will be destroyed, while the more plastic\nmay survive by modification. Thus, at every step in the evolution\nof the organic kingdom, some species have died without issue, while\nothers have saved themselves by changing into new forms in harmony\nwith the new environment. Comparing to a growing tree, some branches\novershadowed die, while others push on for light, forming new lateral\nbuds, and dividing as they grow. By continued divergent change species\ngradually become genera, genera families, etc. Thus, varieties,\nspecies, genera, families, orders, classes, etc., are only different\ndegrees of differences formed all in the same way. Varieties are only\ncommencing species, species commencing genera, and so on. There is\nno making and wearing out of dies, and making of new ones; the whole\nprocess is a natural one--the whole series is genetically connected. In\na perfect classification varieties, species, genera, families, orders,\nclasses, etc., are only different _degrees of blood-kinship_.\n\nSo much may be regarded as certain, and out of the field of discussion\namong biologists of the present day. It is only in defining this\nprocess more accurately, and especially in the _theory of the causes_\nor _factors_ of evolution, that there are still difference and\ndiscussion. The most probable view on this subject we now proceed to\ngive.\n\n=Factors of Evolution.=--The causes of change or adaptive modification,\nor the factors of evolution, are at least _four_ well known, and\nprobably many more still unknown: 1. The physical environment--heat and\ncold, dryness and moisture--affects function of organs, and function\naffects structure, and both changed function and changed structure are\ninherited by offspring, and so increased from generation to generation,\nbecoming greater without limit. 2. Increased _use_ or _disuse_ of\norgans enforced or permitted by change in the environment, physical\nor organic, or both, induces change in form, size, and structure of\nthe organs; and this change is inherited by the offspring, and so\nfrom generation to generation small differences are integrated until\nthey become great without limit. These two factors were recognized\nby Lamarck. 3. \u201cNatural selection,\u201d or \u201csurvival of the fittest,\u201d\namong divergent varieties of offspring. This is the distinctive\nDarwinian factor. In the two preceding factors the change is during\nthe _individual lifetime_, and reproduction is supposed to transmit\nit unchanged to the offspring. In this factor, on the contrary,\nthe form and structure are supposed to remain unchanged during the\nindividual life, but for some unknown cause there are slight variations\nin different directions (divergent) in the offspring from the same\nparents. Now, when we remember that by reproduction the number of\nindividuals tends to increase by geometrical progression, and that\nin each generation only a very few (on an average only two from all\nthe offspring of one pair) can survive, it is evident that among\nthese divergent varieties those will most likely survive which are\nmost in harmony with the external environment, and which possess the\nmost efficient organs of defense or of escape, or for food-taking.\nThe surviving offspring, therefore, will be on the average better in\nthese respects than their parents. It matters not how little better,\nfor the integration of even infinitesimal improvements from generation\nto generation will eventually produce any required amount of change.\n4. To the above Darwin has added also \u201c_sexual selection_.\u201d In\n_natural_ selection there is struggle of _all_ for _food_, or _means\nof living_. In sexual selection there is a struggle among the _males_\nfor possession of the _female_, and the _means of procreation_. The\none is connected with the nutritive appetite, the other with the\nreproductive appetite. This mode of selection acts in two ways, by the\nlaw of battle and the law of attractiveness. The strongest or the most\nattractive males alone, or mainly, leave offspring, which, of course,\ninherit their peculiarities; and these are increased indefinitely\nby integration through successive generations, thus increasing the\nstrength or the beauty. Of these two laws, the law of battle is most\nconspicuous among mammals, and the law of attractiveness among birds.\nIt is evident that this factor can not operate among many lower animals\nwhich are hermaphroditic, nor among plants.\n\nOf these acknowledged factors of evolution, the first two were known\nto Lamarck and the older evolutionists. The third and fourth are\ndistinctively Darwinian. According to Darwin, while all these are\noperative, the third is the most powerful; but Spencer accords this\ndistinction to the Lamarckian factors. Many American zo\u00f6logists take\nthe same view.\n\nSuch until very recently were all the recognized factors of evolution.\nBut, within the past year (1886) has taken place, it seems to us,\nthe most important advance in the theory of evolution since Darwin.\nIt is the suggestion by Mr. Catchpool,[14] and afterward the more\nfull elaboration by Dr. Romanes, of another factor, which he calls\n\u201c_physiological selection_.\u201d[15]\n\nThe great objections to the sufficiency of the theory of evolution,\nas left by Darwin, were twofold: 1. While natural selection accounts\ncompletely for the formation of _useful_ structures or adaptive\nmodifications, and therefore for differences characterizing classes,\norders, families, and even genera--for these are all adaptive--it\ncan not so completely account for those constituting species; for\nthese consist mostly of _trivial_ differences in coloration, relative\nproportion of parts, which are of _no perceivable use_ in the struggle\nfor life, and therefore could not be preserved and integrated by\nnatural selection. Therefore, according to Romanes, natural selection\nis a theory of origin of adaptive structures rather than of origin of\nspecies. Comparing to a growing tree, once admit lateral buds started,\nand natural selection completely accounts for the growth in different\ndirections, and therefore for the profuse ramification; but the origin\nof the lateral buds is not explained.\n\n2. The second difficulty is as follows: Such commencing differences as\nconstitute varieties and species not only would not be preserved and\nintegrated by natural selection unless useful, but would immediately\nbe _swamped by cross-breeding_ with the parental form. But, as the\nwhole divergence commences in varieties, evidently it could not\ncommence at all unless this cross-breeding be in some way prevented.\nThis may, indeed, be done, without the assumption of any new factor\nof evolution, by _migration_; and, hence, migration must be regarded\nas an important agent in the creation of new forms, not only by the\neffect of a new environment, but also by prevention of the swamping of\ncommencing species by cross-breeding with the parental form; but in a\ncrowded locality, without outlet for migration (the very conditions\nmost favorable for severe competitive struggle, and therefore for\nmost potent operation of natural selection; and therefore, also,\naccording to Darwin, for profuse diversification), commencing varieties\ncould not pass into species, because swamped by cross-breeding.\nOnce the divergence reaches the point of cross-sterility--i. e., of\nspecies--then, indeed, by true breeding, characters, even though not\nuseful, may be preserved. But how is it to commence?\n\nThis difficulty has been severely felt by all Darwinists. It seems to\nus that it is largely met by Dr. Romanes. According to Romanes, no\norgan is so subject to varietal changes as the _reproductive_, and\nthese in no respect so much as in degrees of fertility. Unfortunately,\nthese changes are not visible, and must be judged of only by the\nresults. It is not uncommon, for example, to find sterility between\nindividuals (sexual incompatibility) who are both of them perfectly\nfertile with other individuals. Similarly, cross-sterility, partial\nor complete, is not uncommon between varieties or races, as Mr.\nDarwin has long ago noticed. It very generally, as we know, occurs\nbetween, and, in fact, is constantly used as a test of, species. Now,\nthis cross-sterility with parent stock, which we find so constant a\ncharacter of species, and which, therefore, must _have commenced as a\npartial cross-sterility_ in varieties, is it _antecedent or consequent\nto other variations_? It has been usual to suppose it consequent\nto a certain amount of divergence, viz., that which constitutes,\nor at least approaches, species. But, according to Romanes, it is\n_antecedent_. Among many other variations, this is that one which\noriginates species, because it prevents reversion by cross-breeding\nwith the parent stock, and insures true breeding with its own kind.\nIn a word, it sexually isolates the species. Suppose, then, a species\nmultiplying indefinitely in one locality: trivial variations of many\nkinds, and in many directions, occur among the offspring. These are\nmerged by cross-breeding into the original type, which, therefore,\nremains unchanged. But, from time to time, among these variations\nthere occur some affecting the reproductive organs in such wise as to\nproduce partial or complete cross-sterility with the parent form. This\nis the beginning of a new species. It breeds true with its own kind,\nand therefore all the associated variations external and visible, and\ntherefore constituting species, although trivial and of no use in the\nstruggle for life, are preserved.\n\nThis view completely accounts for the cross-fertility of artificial\nbreeds equivalent in other respects to species; for cross-sterility\nis not an end aimed at by the breeder, it being easy to prevent\ncross-breeding, if desired, by artificial isolation. But, if this view\nbe true, species from widely-different geographical regions ought also\nto be often cross-fertile, because, having been formed by geographical\nisolation, sexual isolation was not a necessary factor in their\nformation. This point deserves testing by careful observation.\n\nIt may be, and has been, objected to Dr. Romanes\u2019s claims, that this is\nno new factor; that physiological selection is only a form of natural\nselection. This objection, it seems to us, is little more than a play\nupon words. It certainly is selection, and by a _natural_ process,\nand therefore in some sense a natural selection, but not in the sense\nof Darwin. It is not a selection of individuals _fittest to survive_;\nfor cross-fertile individuals are as fit to survive as individuals,\nthough not as species, as are cross-sterile. Natural selection is\nintent only on preserving the best individuals; physiological selection\non preserving the kind. Natural selection continues the direction of\nprogress unchanged; physiological makes new directions.\n\nIn addition to all these factors of _organic_ evolution, there is still\nanother far higher factor characteristic of man alone. This is the\n_conscious, voluntary co-operation of the thing evolving--the spirit\nof man--in the work of its own evolution_. This may be called the\n_rational factor_. This, the most important factor of human evolution,\nis usually ignored by writers on evolution--either as non-existent,\nor else as lying beyond the domain of science. We will emphasize its\nimportance by taking it up more fully in the next chapter.\n\nIt will be observed that Darwin and his followers take divergent\nvariations of offspring simply as a known fact, upon which natural\nselection operates to produce progressive modification; and, as the\ncause of variation in offspring is wholly unknown, such variations are\noften spoken of as fortuitous. But, of course, it is well understood\nthat nothing in Nature is really fortuitous. They may, however, for\nall purposes of natural selection be thus regarded until we know\ntheir cause. It is evident, then, that if we, with Darwin, take\nnatural selection, as the most important known factor, the really most\nimportant cause of evolution is the _cause_ of varieties. This is the\n_unknown_ fundamental factor. As Darwin reduced Agassiz\u2019s three formal\nlaws of succession to more general laws of life, and thus made one\nimportant step in the advance of biological science, so he who shall\nexplain the _cause_ of divergent variation will make another important\nstep by reducing the phenomena to still more general and fundamental\nlaws of life.\n\nIn conclusion, let me again impress upon the reader that all the doubt\nand discussion, above described, as to the factors of evolution, is\nentirely aside from the truth of evolution itself, concerning which\nthere is no difference of opinion among thinkers.\n\n\n\n\nCHAPTER III.\n\nTHE GRADES OF THE FACTORS OF EVOLUTION AND THE ORDER OF THEIR\nAPPEARANCE.\n\n\nWe have given in the previous chapter six factors of evolution--viz.:\n1. _Pressure of the environment._ 2. _Use and disuse of parts._\n3. _Natural selection._ 4. _Sexual selection._ 5. _Physiological\nselection._ 6. _Reason._ Let us now compare these as to their grade in\nthe scale of energy and as to the order of their introduction.\n\nThe first two or the Lamarckian factors are the lowest in position,\nthe most fundamental and universal, and therefore the first in\nthe order of appearance. They precede all other factors, and were\ndoubtless for a long time _the only ones in operation_. For, observe,\nall the selective factors--i. e., those of Darwin and Romanes--are\nconditioned on reproduction; for the changes produced by these are\nnot in the individual during life, but in the offspring at birth.\nAnd not only so, but the operations of these factors are further\nconditioned on _sexual modes_ of reproduction; for all the non-sexual\nmodes of reproduction--as, for example, by fissure and by budding--are\nbut slight modifications of growth, and the resulting multitude of\norganisms may be regarded as in some sense _only an extension of the\nfirst individual_. Of course, therefore, the identical characters of\nthe first individual are continued indefinitely, except in so far\nas they are modified in successive generations by the effect of the\nenvironment and by use and disuse--i. e., by the Lamarckian factors.\nIn sexual generation, on the contrary, the characters of two diverse\nindividuals are funded in a common offspring; and the same continuing\nthrough successive generations, it is evident that the inheritance in\neach individual offspring is infinitely multiple. Now, the _tendency\nto variation_ in offspring _is in proportion to the multiplicity of\nthe inheritance_: for among the infinite number of slightly differing\ncharacters, as it were, offered for inheritance in each generation,\nsome individuals will inherit more of one and some more of another\ncharacter. In a word, sexual reproduction by multiple inheritance\n_tends to variation of offspring, and thus furnishes material for\nnatural selection_.[16]\n\nThus, then, I repeat, all the selective factors are absolutely\ndependent on sexual modes of reproduction. But there was a time when\nthis mode of reproduction did not yet exist.[17] The sexual modes\ndeveloped out of non-sexual modes. If these non-sexual preceded sexual\nmodes of reproduction, it is evident that at first only Lamarckian\nfactors could operate. Evolution was then carried forward wholly\nby changes in the individual produced by environment and by use and\ndisuse (acquired characters), inherited and increased by integration\nthrough successive generations indefinitely. It is probable, therefore,\nthat the _rate_ of evolution was at first comparatively slow; unless,\nindeed, as seems probable, the _earliest_ forms _were then_ and the\n_lowest_ forms _are now_ more plastic under the influence of physical\nconditions than are the present higher forms. Doubtless, now, in the\nhigher animals and plants, the Darwinian factors are by far the most\npotent; for, among plants, where we can use these factors separately,\nif we wish to _make_ varieties, we propagate by seeds (sexual\nreproduction); but, if we wish to preserve varieties, we propagate by\nbuds and cuttings (non-sexual reproduction).\n\nI have taken the two Lamarckian factors together, and showed that they\npreceded the Darwinian. But even in the two Lamarckian factors there is\na difference in grade. Undoubtedly the lowest, the most fundamental,\nand therefore the first introduced, was _pressure of the physical\nenvironment_. For use and disuse of organs implies some degree of\nvolition and voluntary motion, and therefore already some advance in\nthe scale of evolution.\n\nWith the introduction of sex another entirely different and higher\nfactor was introduced, viz., _natural selection_, or selection of\nthe fittest individuals of a varying progeny. We have already seen\nhow sexual generation produces variation of offspring, and how this\nfurnishes materials for natural selection. As soon, therefore, as this\nform of generation was evolved, this higher factor came into operation\nand immediately assumed control; while the previous factors became\nsubordinate, though still underlying, conditioning, and modifying the\nactivity of the higher. The result was an immediate increase in the\nrate of evolution. It is very worthy of note that it is in the higher\nanimals, such as birds and mammals, in which we have only the highest\nforms of sexual reproduction, where the diversity of characters of\nthe two sexes funded in the offspring is the greatest, and where,\ntherefore, the variation in offspring is also greatest and natural\nselection most active; it is precisely among these that the Lamarckian\nfactors are most feeble, because, during the most plastic period of\nlife, the offspring is removed from the influence of the physical\nenvironment, and from use and disuse by its inclosure within the womb,\nor within a large egg surrounded with abundant nutriment. Development\nis already well advanced before Lamarckian factors can operate at all.\n\nNext, I suppose, physiological selection, or Romanes\u2019s factor, came\ninto operation. After the introduction of sex, it became necessary that\nthe individuals of some varieties should be isolated in some way, so\nas to prevent the swamping of varietal characters, as fast as formed,\nin a common stock, by _cross-breeding_. In very low forms, with slow\nlocomotion, such isolation might easily take place accidentally. Even\nin higher forms, changes in physical geography or accidental dispersion\nby winds and currents would often produce geographical isolation,\nand thus, by preventing crossing with the parent stock, secure the\nformation of new species from such isolated varieties. But, in order\nto insure in all cases the preservation of commencing species, _sexual\nisolation_, or partial or complete infertility of some varieties\nwith other varieties and with the parent stock, was introduced, as\nI suppose, later. The process by which this takes place has already\nbeen explained. According to Romanes, natural selection alone, with\ncross-breeding, tends to _monotypal_ evolution; isolation of some kind\nis necessary for polytypal evolution. The tree of evolution, under\nthe influence of natural selection alone, grows, palm-like, from its\n_terminal bud_; isolation of varieties was necessary for the starting\nof _lateral buds_, and thus for the profuse ramification which is its\nmost conspicuous character.\n\nNext, I suppose, was introduced _sexual selection_, or contest among\nthe males, by battle or by display, for possession of the females,\nand the success of the strongest or the most attractive; and the\nperpetuation and increase of these superior qualities of strength\nand beauty in the next generation. This, I suppose, was later,\nbecause connected with a higher development of the psychical nature.\nThis is especially true where splendor of color or beauty of song\ndetermines the selection. As might be supposed, therefore, this factor\nis operative only among the highest animals, especially birds and\nmammals.[18]\n\nNext and last, and only with the appearance of _Man_, another entirely\ndifferent and far higher factor was introduced, viz., _conscious,\nvoluntary co-operation_ in the work of his own evolution--a conscious,\nvoluntary striving to _attain an ideal_. We have called this a factor,\nbut it is much more than a mere factor, co-ordinate with other factors.\nIt is, rather, a different kind of evolution. It is evolution on\na higher plane and by another nature. As _physical_ Nature works\n_unconsciously_, using certain factors, so _spiritual_ nature works\n_consciously_, co-operating and using the same factors. At first this\nfactor, if we still call it so, was extremely feeble. In the early\nstages of his progress, man, like other animals, was largely urged\non by forces of organic evolution, unknowing and uncaring whither\nhe tended. But more and more, as civilization advances, this higher\nand distinctively human factor becomes more and more dominant, until\nnow, in civilized communities, it takes control of evolution. Reason,\ninstead of Nature, now assumes control, though still using the methods\nand factors of Nature. This _free_, self-determined evolution of the\nrace, in order to distinguish it from the _necessary_ evolution of the\norganic kingdom, we call progress.\n\nNow, in this whole process we observe two striking stages. The one is\nthe introduction of sex, the other is the introduction of reason.[19]\nThey may be compared to two equally striking stages in the development\nof the _individual_. As the _ontogenic_ evolution receives fresh\nimpulse at the moment of fertilization, so the evolution of the organic\nkingdom receives fresh impulse at the moment of introduction of sex. As\nin ontogenic evolution the individual at birth enters upon a new and\nhigher plane, in which it co-operates in its own _physical_ growth,\nso the organic kingdom, with the introduction of man, enters upon a\nnew and higher plane, in which man co-operates in the physical and\n_spiritual_ growth of the race. With sex three new and higher factors\nwere introduced, and these immediately assumed control and quickened\nthe rate of evolution. With reason another and infinitely higher factor\nis introduced, which, in its turn, assumes control, and not only again\nquickens the rate, but elevates the whole plane of evolution. Moreover,\nthis voluntary, rational factor not only takes control itself, but\ntransforms all other factors and uses them in a new way and for its own\nhigher purposes.\n\nThis last is by far the greatest change which has ever occurred in\nthe history of evolution. In organic evolution Nature operates by\nnecessary law without the conscious voluntary co-operation of the thing\nevolving. In human progress man voluntarily co-operates with Nature in\nthe work of evolution, and even assumes to take the process mainly into\nhis own hands. Organic evolution is by _necessary_ law, human progress\nby _free_ or at least by freer law. Organic evolution is by a _pushing_\nupward and onward from _below_ and _behind_, human progress by a\n_drawing_ upward and onward from above and in front by the attractive\nforce of ideals. In a word, organic evolution is by the law of _force_,\nhuman evolution by the law of _love_.\n\nIt may be well to stop a moment and show briefly some of the\ndifferences between organic and human evolution--differences which are,\nof course, wholly the result of the introduction of this new factor:\n\n1. In organic evolution \u201c_the fittest_\u201d are those most in harmony\nwith the physical environment, and therefore they survive. In human\nevolution _the fittest_ are those most in harmony with _the ideal_, and\noften, especially in the early stages, when the race is still largely\nunder the dominion of organic factors, they do not survive, because\nnot in harmony with the social environment. But, although the fittest\nindividuals may indeed perish, the _ideal_ survives in the race and\nwill eventually triumph.\n\n2. In organic evolution the weak, the sick, the helpless, the unfit\nin any way perish and _ought to perish_, because this is the most\nefficient way of strengthening the _blood_ or _physical nature_ of the\nspecies, and thus of carrying forward evolution. In human evolution\nthe weak, the helpless, the sick, the old, the unfit in any way are\nsustained and _ought to be sustained_, because sympathy, love, pity,\nstrengthen the _spirit_ or _moral nature_ of the race. But let us\nremember that in this material world of ours and during this earthly\nlife the spirit or moral nature is conditioned on the physical nature;\nand, therefore, in all our attempts to help the weak we must be careful\nto avoid poisoning the blood and weakening the physical vigor of the\nrace by inheritance. This gravest of social problems, viz., How shall\nwe obey the higher law of love and mutual help without weakening the\n_blood_ of the race by inheritance and the spirit of the race by\nremoving the necessity of self-help?--this problem, I believe, can and\nwill be solved by a _rational education_, physical, mental, and moral.\nI only allude to this. It is too wide a field to follow up here.\n\n3. In organic evolution the bodily _form_ and _structure_ must\ncontinually change in order to keep in harmony with the ever-changing\nenvironment. In other words, organic evolution is by continual change\nof species, genera, families, etc. There must be continual evolution\nof new forms by modification. In human evolution, on the contrary, and\nmore and more as civilization advances, man modifies the environment so\nas to bring it into harmony with himself and his wants, and therefore\nthere is no necessity of change of bodily form and structure or\nmaking of new species of man. Human evolution is not by modification\nof _form_--new species; but by modification of spirit--new planes of\nactivity, _higher character_. And the spirit is modified and character\nelevated, not by _pressure_ of an _external physical environment_, but\nby the _attractive_ force of an _internal spiritual ideal_.\n\n4. The way of evolution toward the highest--i. e., from protozoan\nto man and from lowest man to the ideal, the divine man--is a very\n_straight and narrow way_, and few there be that find it. In the\ncase of organic evolution it is so straight and so narrow that any\ndivergence therefrom is fatal to upward movement toward man. Once get\noff the track, and it is _impossible_ to get on again. No living form\nof animal is on its way _manward_, or can by any possibility develop\ninto man. They are all gone out of the way. There is none going right;\nno, not one. The organic kingdom developing through all geological\ntimes may be compared to a tree whose trunk is deeply buried in the\nlowest strata, whose great limbs were separated in early geological\ntimes, whose secondary branches diverged in middle geological times,\nand whose extreme twiglets, and also its graceful foliage, its\nbeautiful flowers, and luscious fruits, are the fauna and flora of\nthe present day. But this tree of evolution is an _excurrent stem_,\ncontinuous through the clustering branches to the terminal shoot--man.\nOnce leave the stem as a branch, and it is easy to continue growing in\nthe direction chosen, but impossible to get back on the straight upward\nway to the highest. In human evolution, whether individual or racial,\nthe same law holds, but with a difference. If individual or race gets\noff the straight, narrow way toward the highest--the divine ideal--it\nis hard, very hard to get back on the track. Hard, I say, but _not_\nimpossible, because man\u2019s conscious voluntary effort is the chief\nfactor in his own evolution. By virtue of self-activity, through the\nuse of reason and co-operation in the work of evolution, man alone of\nall created things is able to rectify an error of direction and return\nagain to the deserted way.\n\n5. In organic evolution, when a higher factor appears, it immediately\nassumes control, and previous lower factors sink into a subordinate\nposition, though still underlying and conditioning the higher. But in\nhuman evolution, the higher rational factor, when it comes in with\nman, not only assumes control, but transforms all other factors and\nuses them in a new way and for its own higher purposes. In fact, as\nalready said, it is much more than a mere factor. It determines a\nnew kind of evolution--evolution on a new and higher plane though,\nindeed, underlaid and conditioned by the laws of organic evolution. As\n_external physical_ Nature uses many factors to carry forward organic\nevolution, so the _internal spiritual_ nature, characteristic of man\nalone, uses these same factors in a new way to carry forward human\nevolution or progress. Thus, for example, one organic factor--the\nenvironment--is modified or even totally changed so as to effect\nsuitably the human organism. This is _hygiene_. Again, use and\ndisuse--another factor--is similarly transformed. The various organs of\nthe body and faculties of the mind are deliberately used in such wise\nand degree (determined by reason) as to produce the highest efficiency\nof each part and the greatest strength and beauty of the whole. This\nis _education_--physical, mental, moral. So also the selective factors\nare similarly transformed, and _natural_ selection becomes _rational_\nselection. We all know how this method is applied to domestic animals\nand cultivated plants in the formation of useful or beautiful\nvarieties. Why should it not be applied also to the improvement of our\nrace in the selection of our mates in marriage, or in the selection of\nour teachers, our law-makers, our rulers? Alas! how little even yet\ndoes reason control our selection in these matters! How largely are we\nyet under the law of organic evolution!\n\n_Application of these principles to some questions of the day_:\n\nI. Evolution, as a law of derivation of organic forms from previous\nforms by descent with modifications, as already shown, is as certain\nas the law of gravitation. This question has passed beyond the realm\nof doubtful discussion; but the causes, the factors, the details of\nthe process of evolution are still under discussion. Both Darwin and\nSpencer, the two great founders of the theory of evolution in its\nmodern form, acknowledge and insist on at least four factors, viz., the\ntwo Lamarckian and the two distinctively Darwinian. The only difference\nbetween them is in the relative importance of the two sets: Spencer\nregarding the former and Darwin the latter as the more potent. But in\nthese latest times there has arisen a class of biologists, including\nsome of highest rank, such as Wallace, Weismann, and Lankester, who\nout-Darwin Darwin himself in their exaltation of the most distinctive\nDarwinian factor, viz., natural selection. They try to show that\nnatural selection is the sole and sufficient cause of evolution; that\nchanges in the individual, whether as the effect of the environment or\nby use and disuse of organs, are not inherited at all; that Lamarck was\nwholly wrong; that Darwin (in connection with Wallace) was the sole\nfounder of the true theory of evolution; and, finally, that Darwin\nhimself was wrong only in making any terms whatever with Lamarck. This\nview has been called _Neo-Darwinism_.\n\nPerhaps the reasons for this view have been most strongly put by\nWeismann, and are based partly on experiments, but mainly on his\ningenious and now celebrated theory of the immortality of germ-plasm.\nThe animal body consists of two kinds of cells wholly different in\nfunction--somatic cells and germ-cells, including in this last the\nsexual elements both male and female. Somatic cells are specially\nmodified for the various functions of the body; germ-cells are\nwholly unmodified. The somatic cells are for the conservation of\nthe _individual_ life, the germ-cells for the conservation of the\n_species_. In the development of the egg the germ-cell multiplies\nitself into a cell-aggregate, and then most of the resulting multitude\nof cells are modified in various ways to form the tissues and organs\nof the body--somatic cells; but a few are reserved and put aside\nin an unmodified form in the sexual organs as germ-cells, to again\nproduce ova which again divide into somatic and germ-cells, and so on\nindefinitely. Now, according to Weismann, inheritance is only through\n_germ-cells_, while the environment affects only the _somatic cells_.\nTherefore changes produced by the environment can not be inherited.\nSexual modes of generation were introduced for the purpose of producing\nvariability in progeny, and thus furnishing material for natural\nselection, as this was the only means of evolutionary advance. Weismann\nmade many experiments on animals, especially by mutilation, to show\nthat somatic changes are not inherited.\n\nA full discussion of this question would be unsuitable in a work like\nthis. We will therefore content ourselves with making three brief\nremarks:\n\n_a._ If the views presented in the early part of this chapter are true,\nthen the Lamarckian factors must be true factors, _because there was\na time when there were no others_. They were therefore necessary, at\nleast to start the process, even if no longer necessary at present.\n\n_b._ But if these factors were ever operative, _they must be so\nstill_, though possibly in a subordinate degree. A lower factor is\nnot abolished, but only becomes subordinate to a higher when the\nlatter is introduced. Thus it may well be that Lamarckian factors are\ncomparatively feeble at the present time and among living species,\nespecially of the higher animals, and yet not absent altogether. In the\nearliest stages of evolution there was a _complete identification of\ngerm-cells and somatic cells_--of the individual with the species. In\nsuch cases, of course, any effect of the environment must be inherited\nand increased from generation to generation. But the differentiation\nof the germ and somatic cells was not all at once, nor is their\nsympathetic relation completely severed. It was a _gradual process_,\nand therefore the effect of the environment _on the germ-cells through\nthe somatic cells_ continued, though in decreasing degree, and still\ncontinues. The differentiation in the higher animals is now so complete\nthat germ-cells are probably not at all affected by changes in somatic\ncells, unless these changes are _long continued in the same direction,\nand are not antagonized by natural selection_.\n\n_c._ It is a general principle of evolution that the _law of the whole\nis repeated with modifications in the part_. This is a necessary\nconsequence of the unity of Nature. We ought to expect, therefore,\nand do find, that the order of the use of the factors of evolution is\nthe same in the evolution of the _organic kingdom_, in the evolution\nof _each species_, and in the evolution of _each individual_. In all\nthese the physical factors are at first powerfully operative; these\nbecome subordinate to organic factors, and these, in their turn, to\npsychical and rational factors. Therefore, as the individual in its\nearly stages--i. e., in embryo and infancy--is peculiarly plastic\nunder the influence of the physical environment, and afterward becomes\nmore and more independent of these; so a species when first formed is\nmore plastic under the influences of Lamarckian factors, and afterward\nbecomes more rigid to the same. And so also the organic kingdom was\nat first more plastic under Lamarckian factors, and has become less\nso in the present species, especially in the higher animals. The\nprincipal reason of this, as we have already seen, is the increasing\ndifferentiation of germ and somatic cells, and the removal of the\nformer to the interior, where they are more and more protected from\nexternal influence.\n\nII. Some evolutionists--the materialistic--insist on making human\nevolution identical in all respects with organic evolution. This, we\nhave shown, is not true. The very least that can be said is that a\nnew and far more potent factor is introduced with man, which modifies\ngreatly the process. But we may claim much more, viz., that evolution\nis here on a different and higher plane. The factors of organic\nevolution are, indeed, still present, and condition the whole process;\nbut they are not left to be used by Nature alone. On the contrary, they\nare used in a new way and for higher purposes--by reason.\n\nBut by a revulsion from the materialistic extreme some have gone to the\nopposite extreme. They would place human progress and organic evolution\nin violent antagonism, as if subject to entirely different and even\nopposite laws; but we have also shown that, although the distinctive\nhuman factor is indeed dominant, yet it is underlaid and conditioned by\nall the lower factors; that these lower factors are still necessary as\nthe agents used by reason.\n\nIII. We have already given the views of Weismann and Wallace, and some\nreasons for not accepting them; but there is one important aspect\nnot yet touched. There are some logical consequences of these views\nwhen applied to human evolution which seem to us nothing less than a\n_reductio ad absurdum_. This brings into view still another contrast\nbetween organic evolution and human progress.\n\nIn organic evolution, when the struggle for life is fierce and pitiless\nas it is now among the higher animals, natural selection is undoubtedly\nby far the most potent factor. It is at least conceivable (though\nnot probable) that at the present time organic evolution might be\ncarried on mainly or even wholly by this factor alone; but in human\nevolution, especially in civilized communities, this is impossible.\nIf Weismann and Wallace be right, then alas for all our hopes of race\nimprovement--physical, mental, and moral!--for natural selection will\nnever be applied by man to himself as it is by Nature to organisms. His\nspiritual nature forbids. Reason may freely use the Lamarckian factors\nof environment and of use and disuse, but is debarred the unscrupulous\nuse of natural selection _as its only method_. As this is an important\npoint, we must explain.\n\nAll enlightened schemes of physical culture and hygiene, although\ndirected primarily to secure the strength, the health, and the\nhappiness of the _present generation_, yet are sustained and\nennobled by the conviction that the improvement of the individuals\nof each generation enters by inheritance into the gradual physical\nimprovement of the race. All our schemes of education, intellectual\nand moral, though certainly intended mainly for the improvement\nof the individual, are glorified by the hope that the race also is\nthereby gradually elevated. It is true that these hopes are usually\nextravagant; it is true that the _whole_ improvement of one generation\nis not carried over by inheritance into the next; it is true,\ntherefore, that we can not by education raise a lower race up to the\nplane of a higher in a few generations or even in a few centuries: but\nthere must be at least a small residuum, be it ever so small, carried\nforward from each generation to the next, which, accumulating from age\nto age, determines the slow evolution of the race. Such are the hopes\non which all noble efforts for race-improvement are founded. Are all\nthese hopes baseless? They are so if Weismann and Wallace are right. If\nit be true that reason must direct the course of human progress, and\nif it be true also that selection of the fittest in the organic sense\nis the only method which can be used by reason, then the dreadful law\nof pitiless destruction of the weak, the helpless, the sick, the old,\nmust with Spartan firmness be voluntarily and deliberately carried out.\nAgainst such a course we instinctively revolt with horror, because\ncontrary to the law of our spiritual nature.\n\nBut the use by reason of the Lamarckian factors is not attended with\nany such revolting consequences. All our hopes of race-improvement,\ntherefore, are strictly conditioned on the efficacy of these\nfactors--i. e., on the fact that useful changes, determined by\neducation in each generation, are to some extent inherited and\naccumulated in the race.\n\n\n\n\nCHAPTER IV.\n\nSPECIAL PROOFS, TAKEN FROM THE GENERAL LAWS OF ANIMAL STRUCTURE, OR\nFROM COMPARISON IN THE TAXONOMIC SERIES.\n\n_General Principles._\n\n\n=Analogy and Homology.=--In biology those organs or parts in different\nanimals are said to be _analogous_ which, however different their\norigin, have a general similarity of form and especially of function;\nwhile those are called _homologous_ which, however different their\ngeneral appearance, and however different their function, yet may,\nby close examination and extensive comparison, be shown to be\nmodifications of one another--to be, in fact, originally the same part\nmodified for different purposes. In the former the parts compared look\nand behave as if they were the same, but are not; in the latter they\nlook and behave entirely differently, but are, in fact, the same part\nin disguise.\n\nWe can best make this plain by examples. The wing of a bird and\nthe wing of a butterfly are analogous organs. They have the same\nfunction--i. e., flying; and this function necessitates the same\ngeneral form of a flat plane. But they are not at all homologous; they\nare not at all the same organ or part. They certainly have never been\nformed one out of the other by modification. But the wing of a bird,\nthe fore-paw of a reptile or mammal, the wing of a bat, and the arm and\nhand of a man, though so different in form and function, are homologous\nparts. On close examination they are found to have the same general\nstructure, to be composed of essentially the same pieces, although they\nare so greatly modified in order to adapt them to different functions,\nthat the general or superficial resemblance is now lost. Their\nstructure is precisely such as it would be if they had all originated\nfrom some archetypal fore-limb by modifications in different directions\nof its several parts. By extensive comparison in the taxonomic and\nontogenic series, all the intermediate gradations between these extreme\nmodifications may be picked up.\n\n[Illustration: FIG. 2.--Lepidosiren.]\n\nAnother example. The lungs of a mammal and the gills of a fish are\nanalogous organs, since they have the same function of a\u00ebration of the\nblood. But they are not at all homologous: they are not built on the\nsame plan; by no effort of the mind can we imagine that the former\ncould have come out of the latter by modification. On the contrary,\nwe have positive proof that it did not so come. But there is an organ\nin the fish which is homologous with the mammalian lung, viz., the\nair-bladder, or swim-bladder. We know it--1. Because we can trace in\nthe taxonomic series all the gradations from the one to the other. In\nmost fishes the air-bladder is wholly cut off from the gullet, and\nonly very feebly supplied with blood. It is used and can be used only\nfor flotation. In others, as the gar-pike, the swim-bladder is quite\nvascular and opens by a tube into the throat. Through this opening\nair is gulped down from time to time into the bladder, and again\nfrom time to time expelled. In other words, this fish supplements\nits gill-breathing by an imperfect lung-breathing. We have here\nthe beginning of a lung. In still other fishes, viz., the Dipnoi\n(_lepidosiren_ and _ceratodus_, Fig. 2), the air-bladder becomes a\nmore perfect lung--i. e., a very vascular sacculated sac; and there is\nnot only an opening into the throat, but also from the throat to the\nsnout. In other words, we have for the first time _nostrils_. These\nfishes completely combine gill-breathing with lung-breathing. The step\nfrom these to the lowest amphibian reptiles is so small, that some have\nclassed the lepidosiren among amphibians instead of fishes. The siredon\nor axolotl of New Mexico, the necturus or menobranchus of our Northern\nlakes, and the siren of our Southern swamps, have both gills and lungs,\nand breathe both air and water; but the lung is very imperfect, being\nonly a sacculated sac, like the air-bladder of the ceratodus and\nlepidosiren. No one doubts that the air-breathing organ of an amphibian\nis a true lung; yet we have traced all the gradations between it and\nthe air-bladder of a fish. We conclude, therefore, that if there be\nany such thing as transmutation of organic forms, the lung of higher\nanimals must have been formed by the process above described.[20]\n\nBut we know it still more certainly--2. Because we can trace the change\nfrom the one to the other in the ontogenic series. In the life-history\nof the individual we can actually see the one thing change into the\nother. The frog, as is well known, when first hatched, is a tadpole. It\nhas no legs, but locomotes by means of a vertically-expanded tail. It\nhas no lungs, but breathes water instead of air, by means of gills. It\nis in all respects, therefore, a fish, and would be classed as such if\nit remained in this condition. But it does not; it gradually loses its\ntail and gills, and acquires legs and lungs, and breathes air only. Now\nin this change whence came the lungs? From the gills by modification?\nNo; but from an organ similar in character and position to the\nair-bladder of a ceratodus, or a lepidosiren. This organ has gradually\ndeveloped into a lung. The steps of the change are briefly as follow:\nFirst, the breathing is wholly water-breathing by gills. Next, by the\ndevelopment of this other organ, it is partly water-breathing by\ngills, and partly air-breathing by lungs. Lastly, the gills gradually\ndry up, and the lungs develop more and more, until the breathing is\nwholly by lungs.\n\nWe have dwelt somewhat upon this example, because it is an excellent\nexample of what we mean by homology, and also because we will have\noccasion to use it again. But so important, for all that follows in\nthis part, is a clear idea on the subject of homology, that it will be\nbest to familiarize the mind of the reader with it by means of a few\nexamples drawn from plants.\n\nA potato is analogous to a root--a tuberous root like that of a\ndahlia or a sweet-potato--but is not at all homologous with these.\nOn the contrary, it is homologous with a stem. It is essentially an\nunderground, leafless branch, which has thickened enormously at the\npoint by accumulation of starch. The evidence of this is found in\nthe fact that it has rudimentary leaves (scales) arranged in regular\nspiral order of phylotaxis, each with its axillary bud (eyes). It is\nstill more clearly shown by the fact that buds above-ground which, if\nlet alone, would form leafy branches, may be made to become tubers by\ncovering them with earth or dead leaves, and thus excluding the light;\nand, conversely, underground buds which, if let alone, would form\ntubers, may be made to grow into leafy branches by exposing them to the\nlight.\n\nTake another example: The broad, flat, elliptical, green masses so\ncharacteristic of the cactus family, and usually called their leaves,\nare indeed _analogous_ to leaves in color, form, and function; for\nthey are green and flat, and assimilate carbonic acid and water (CO2\nand H2O) like leaves. But they are not, in truth, leaves, but modified\nstems, for they have the essential structure of stems, with their\npith, wood, medullary rays, and bark, and may be traced through all\ngradations into the ordinary cylindrical form of stems. Where are\ntheir leaves, then? Their spines are their abortive leaves. These\nare arranged spirally like leaves, and bear buds in their axils like\nleaves. They are, in truth, leaves, modified to perform the function of\ndefensive armor; while their function has been delegated to the stem\nflattened for this purpose.\n\n[Illustration:\n\n  FIG. 3.--A branch of young acacia, showing change from one form of\n      leaf to the other; _a_, _b_, _c_, _d_, successive stages of\n      change; _l_, _s_, leaf stalk which gradually changes into the\n      blade in _c_, _d_, and _e_.\n]\n\nOne more example: The acacias, of which there are fifteen to twenty\nspecies in California, introduced from Australia, form two groups\nhaving extremely different styles of leaves. We will call them the\nfeather-leaved and the simple-leaved acacias. In the former, the leaves\nare very finely bipinnate, and the general aspect of the foliage is\nextremely feathery and graceful. In the latter the leaves are simple,\novate, and, curiously enough, set on edge; and the general aspect\nof the tree is therefore rather stiff. It seems at first incredible\nthat leaves so different and aspects so diverse should belong to\nplants of the same genus. But a little close examination shows that,\nas usual, the botanists are right and the popular judgment wrong.\nThe plumose-leaf is the normal leaf-form for this genus. The simple\nleaf is not only abnormal, but in a homological sense is not a\nleaf at all--i. e., it does not correspond to the part called the\n_blade_ in ordinary simple leaves of other trees. In the seedling of\nthe simple-leaved acacias, and sometimes for a considerable time in\nthe young tree, the leaves are all plumose. As the tree matures it\ngradually changes its dress and puts on its _toga virilis_. The gradual\nchange from the one form to the other may easily be traced in the same\ntree, and even often in the same branch (Fig. 3). The steps of the\nchange (_a_, _b_, _c_, and _d_) are shown in the following figure,\ndrawn from nature. It is seen, by bare inspection of the figure, that\nthe so-called leaf, _d_, of the simple-leaved acacias, is really the\nvertically-expanded leaf-stalk, _l_, _s_, the true leaf or blade being\nwholly aborted. The whole structure of this so-called leaf is different\nfrom that of a true blade. For example, its style of ribbing is\nparallel, its position is edgewise to the sky, its palisade cells are\non both sides alike, etc. To emphasize this difference, botanists call\nsuch an apparent leaf a _phyllodium_, or phyllode.\n\nAfter these illustrations we now repeat the definitions in different\nwords. Analogy has reference to _general resemblance_ of form\ndetermined by _similarity of function_, however different the origins\nof the parts compared may be. Homology has reference to _community\nof origin_, however obscured to the superficial observer such common\norigin may be by modifications necessary to adapt to different\nfunctions. Observe, then, there are two ideas here which must be kept\ndistinct. One is common origin, always shown by deep-lying, essential\nidentity of structure; the other is adaptive modification for function.\nOrgans of the most diverse origin may resemble by adaptive modification\nfor the same function. This is analogy. Organs of the same origin\nmay assume very different appearance by adaptive modifications for\ndifferent functions. This is homology. In the latter case, which is\nthe one that concerns us, a profound study of essential structure\nand structural relations to other parts, and especially extensive\ncomparison in the taxonomic and ontogenic series, will usually\ndetect the homology, or common origin, in spite of the obscurations\nproduced by adaptive modifications. It is seen, also, that analogy is\na superficial resemblance, easily detected by the popular eye, and\ntherefore embodied in popular language; while homology is a deep-seated\nand essential resemblance, detected often only by profound study and\nextensive comparison. Now, one of the strongest proofs of the truth\nof evolution is taken from the homologies of animal structure. Common\norigin completely explains homology. Every other explanation is\ntranscendental, and therefore unscientific.\n\n=Primary Divisions of the Animal Kingdom.=--Now, the animal kingdom\nconsists of several primary divisions, called sub-kingdoms or\ndepartments. The animals in these groups differ so essentially from\none another in their _plan of structure_, that it is difficult, if\nnot impossible, to trace any structural relation between them--to\nimagine how the members of one could have been derived from those of\nanother--or conceive the common stem from which they all separated.\nIn other words, it is impossible, in the present state of knowledge,\nto trace homology with any certainty from one group to another. But\nwithin the limits of each primary group the homology is easy. Some\nnaturalists--Agassiz and Cuvier--have made four or five of these\nprimary groups. Some--Huxley--have made eight. Some make nine or\nten.[21] We will not trouble ourselves to settle this question; for\nall agree to make _vertebrata_ and _articulata_ or _arthropoda_ two of\nthem, and all our illustrations will be drawn from these. Other groups\nare too unfamiliar to the general reader to serve our purpose.\n\nNow, as already stated, homology can not be traced with any certainty\nbetween the primary groups, but within the limits of each group it may\nbe traced with ease and beauty. Analogy, however, being connected with\nfunction, and function being universal, can be traced throughout the\nanimal kingdom. While, therefore, it is probable, nay, almost certain,\nthat all animals have had a common origin, we can not yet trace these\ngreat departments by homology to that common origin. But the common\norigin of each department is quite clear. For example, the structure of\nall vertebrate animals is precisely such as would be the case if all\ncame from one primal vertebrate, variously modified to adapt to various\nmodes of life. Also, the structure of all arthropods is precisely\nsuch as would be if all came from one primal arthropod, which, from\ngeneration to generation, became gradually modified in different\ndirections, in order to adapt itself to various modes of life. But\nbetween arthropods and vertebrates we can not yet clearly see a common\norigin, although there doubtless was such.\n\nThese great departments may, therefore, be compared to _natural\nstyles of animal architecture_. As there are various styles of human\narchitecture--Oriental, Egyptian, Greek, Gothic--each of which may be\nvariously modified to adapt it to all the different purposes for which\nbuildings are made, without destroying, though perhaps obscuring, the\nintegrity of the style; so the different primary groups or departments\nmay be regarded as different styles of animal structure, each of which\nmay be and has been modified in many ways to adapt it to various habits\nand modes of life, obscuring but not destroying the general style.\nOr they may be compared to natural _machines_. As a steam-engine, by\nmodification, may be adapted to many kinds of purposes, obscuring,\nperhaps, but not destroying the essential identity of structure;\neven so the vertebrate machine by modification may be, and has been,\nadapted to many kinds of purposes, and thus become a swimming-machine,\na crawling-machine, a flying-machine, a running-and leaping-machine,\nwithout destroying, although obscuring, the essential identity of\nstructure. As in architecture, \u00e6sthetic principles of form may be\ntraced through each style, but not from style to style, while the\nmechanical principles of construction run through all alike; so also\nin animal architecture, the laws of form and styles of structure are\ntraceable with ease only within the limits of each primary group,\nwhile the laws of function are traceable through all groups alike.\nOr, again, and finally: Each of these departments may be compared\nto a _tree_, with branches, twigs, and spray, all obviously coming\nfrom one common stem, but each stem seems separate. They are, indeed,\nprobably, themselves only great branches of one common trunk, but their\nconnection is too remote and obscure to be made out clearly by means\nof homology. Other evidences, however, drawn from other sources, as we\nshall see hereafter, are not wholly wanting.\n\n\n\n\nCHAPTER V.\n\nPROOFS FROM HOMOLOGIES OF THE VERTEBRATE SKELETON.\n\n\nThe proposition to be established here is, that all vertebrates\nhave not only a common general plan of structure, but an essential\nidentity even in detail, although this identity is obscured by adaptive\nmodifications. We will try to show first a common general plan, and\nthen, taking parts most familiar to the general reader, will show\nessential identity even in detail.\n\n=Common General Plan.=--1. All vertebrate animals, and none other, have\nan _internal_ jointed skeleton worked by muscles on the _outside_.\nAs we shall see hereafter, the relation of skeleton and muscle in\narthropods is exactly the reverse.\n\n2. In all vertebrates, and in none other, the axis of this skeleton\nis a jointed backbone (vertebral column) inclosing and protecting the\nnervous centers (cerebro-spinal axis). These, therefore, may well be\ncalled back-boned animals.\n\n3. All vertebrates, and none other, have a number of their anterior\nvertebral joints enlarged and consolidated into a box to form the\nskull,[22] in order to inclose and protect a similar enlargement of\nthe nervous center, viz., the brain; and also usually, but not always,\na number of posterior joints, enlarged and consolidated to form the\npelvis, to serve as a firm support to the hind-limbs.\n\n4. All vertebrates, and none other, have two cavities, inclosed\nand protected by the skeleton, viz., the neural cavity above, and\nthe visceral or body cavity below, the vertebral column; so that a\ncross-section of the body is diagrammatically represented by Fig. 4.\n\n[Illustration:\n\n  FIG. 4.--Diagram cross-section through the body of a vertebrate,\n      showing the relation of skeleton to the cavities. _n_, neutral\n      cavity; _v_, visceral cavity; _c_, centrum of vertebra.\n]\n\n5. All vertebrates, with few exceptions, and no other animals, have\ntwo and only two pair of limbs. The exceptions are of two kinds,\nviz.: _a_, some lowest fishes, amphioxus and lampreys, which probably\nrepresent the vertebrate condition before limbs were acquired; and _b_,\ndegenerate forms like snakes and some lizards, which have lost their\nlimbs by disuse.\n\nSo much concerns the general plan of skeletal structures, and is\nstrongly suggestive of--in fact, is inexplicable without--common\norigin. But much more remains which is not only suggestive, but\ndemonstrative of such origin. By extensive comparison in the taxonomic\nand ontogenic series, the whole vertebrate structure in all its\ndetails in different animals may be shown to be modifications one\nof another. Sometimes a piece is enlarged, sometimes diminished, or\neven becomes obsolete; sometimes several pieces are consolidated into\none; but, in spite of all these obscurations, corresponding parts may\nusually be made out. This is the main subject of this chapter.\n\n=Special Homology of Vertebrate Limbs.=--It would lead us much too far\ninto unfamiliar technicalities to take up the whole skeleton. We select\nthe limbs, both because their general structure is more familiar, and\nbecause in them the two fundamental ideas of essential identity and of\nadaptive modification are both admirably illustrated. The reason of\nthis is, that it is by the limbs that the organism chiefly reacts on\nthe environment, and is modified by it.\n\n=Fore-limbs.=--In the accompanying figures (Figs. 5-18) we have\nrepresented, side by side, the fore-limbs of many vertebrates, taken\nfrom all the classes--mammals, birds, reptiles, and fishes. For\nconvenience of comparison, the corresponding parts are similarly\nlettered in all. Also, in order to identify easily certain important\ncorresponding segments, we have drawn through them a continuous\ndotted line. In man, nearly all the parts are present, and his limbs,\ntherefore, may be taken as a term of comparison; for man\u2019s structure,\nexcept his brain, is far less modified than that of many animals.\n\nNote, then, the following points: 1. The collar-bone (clavicle) is\nassociated with wide separation of the shoulders, and the free use of\nthe fore-limb for prehension or for flight, but is gradually lost in\nproportion as the fore-limb is brought nearer together and used for\nsupport, because it is no longer wanted. I say _gradually_, for all\nthe steps of the passing away may be found. The useless rudimentary\ncondition is not uncommon.\n\n[Illustration:\n\n  FIGS. 5-9.--5. Fore-limb of man. 6. Dog 7. Hog. 8. Sheep. 9. Horse.\n      _sc_, scapula; _c_, coracoid; _a_, _b_, two bones of fore-arm.\n      (Taken from various sources and grouped.)\n]\n\n[Illustration:\n\n  FIGS. 10-13.--10. Fore-limb of bat. 11. Bird. 12. Arch\u00e6opteryx.\n      13. Pterodactyl. (Lettered as in previous figures;\n      grouped from various sources.)\n]\n\n2. The coracoid (_c_), it is seen, is a small, beak-like process\nof the blade-bone (scapula) in man and mammals; but in birds (Fig.\n11) and reptiles (Figs. 14, 18) it is a separate bone as large as\nthe blade-bone itself, jointed with the latter at the shoulder and\nwith the breast-bone (sternum) in front, thus making together a\nstrong shoulder-girdle for the attachment of the fore-limb. This was\nundoubtedly the condition in the original or earliest walking animal,\nviz., reptiles. It was inherited and retained by birds, because\nnecessary for powerful action of the wings in flight. In mammals\nit gradually dwindled and became united with the blade-bone as a\nprocess. In one mammal, the lowest and most reptilian living--the\nornithorhynchus--the coracoid is much like that of reptiles--a large,\nflat bone, separated from the blade-bone and articulated with the\nbreast-bone. It is a significant fact that, in the mammalian embryo,\nit is first developed as a separate bone and afterward united with the\nscapula.\n\n[Illustration: FIGS. 14-17.--14. Fore-limb of turtle. 15. Mole. 16.\nWhale. 17. Fish.]\n\n3. In man, monkeys, bears, and some other mammals, the limb is fairly\nfree from the body and the elbow half-way down the limb; while in\nherbivores (Figs. 8, 9), such as the horse, ox, and deer, etc., the\nelbow is high on the side of the body, and the limb is free only\nfrom the elbow downward. Perhaps in these cases most observers do\nnot recognize it as an elbow at all. All gradations between these\nextremes are easily traced. The free condition of the limb is evidently\nthe original one, the condition in herbivores being an extreme\nmodification associated with another modification mentioned under 5.\n\n4. In man and in many mammals, and in all reptiles and birds, there are\ntwo bones in the forearm (radius and ulna). In the more specialized\nforms of hoofed animals (ungulates), such as horse and ruminants (Figs.\n8, 9), there is apparently but one. Two is the normal and original\nnumber; but one of them, the ulna, has gradually become smaller and\nsmaller, and finally is reduced to a short splint, and consolidated\nwith the radius as a process extending backward to form the point\nof the elbow. In the horse family every step of this reduction and\nconsolidation may be traced in the course of its geological history.\n\n[Illustration: FIG. 18.--Mosasaur.]\n\n5. The _wrist_ of many mammals and all birds differs in structure from\nthat of man, chiefly in containing a smaller number of bones. The\nnormal number, as in man, seems to be eight. The decrease takes place\nmainly by consolidation of two or more into one. In such cases usually\nthe embryo will show the bones still separate, thus revealing the\nancestral condition. Again, the _position_ of the wrist is noteworthy.\nIn man, monkeys, the bear family, and several other mammalian families,\nand in all reptiles, the hand bends forward at the wrist, so that\nthe tread is on the whole palm (palmigrade). But, in all the most\nspecialized mammals, the wrist can not bend in this direction, and\ntherefore this joint can not be brought to the ground. The tread is\ntherefore on the toes (digitigrade), and the wrist is high up above\nthe ground. In the horse (Fig. 9), the ox, and many other mammals, for\nexample, the wrist is so high that it is not usually recognized as a\nwrist, and is often called the _fore-knee_. Now, homologous parts ought\nto have the same _scientific_ name; but to use the word \u201c_hand_\u201d in\nthe case of lower animals might produce confusion and misconception.\nTherefore it has been agreed among comparative anatomists to use\ninstead the Latin word \u201c_manus_\u201d for all that corresponds, in any\nanimal, to the hand of man--i. e., all from the wrist downward.\nThe manus of a horse is about fifteen inches long. The manus of a\npterodactyl, such as that found by Marsh in the cretaceous strata of\nthe West, with an expanse of wings of twenty-five feet, was probably\nnot less than seven or eight feet long.\n\n6. The number of palm-bones (metapodal) and toes deserves special\nnotice. In fishes, and in some extinct swimming reptiles, these are\nor were very numerous, but in the earliest land-animals they became\nfive. This is the number now in nearly all reptiles, and in all the\nmore generalized mammals. It may be called the normal number for a\nwalking animal. In very many mammals, such, for example, as the dog\nfamily, they are reduced to four, though the fifth often remains as a\nuseless, rudimentary splint and dew-claw (Fig. 6), thus showing the\nprocess of dwindling in the ancestry. In hoofed animals the process of\ngradual diminution is shown even in existing forms, and still better in\nextinct forms. Confining ourselves, now, only to existing forms, in the\nelephant there are five palm-bones and toes, and in the hippopotamus\nthere are four, all functional. In the hog (Fig. 7) there are still\nfour, but two are behind the others and much smaller, and do not touch\nthe ground--are not functional unless in soft ground. In the cow, deer,\netc., the palm-bones are reduced to two, and these are consolidated\ninto _one_ (canon-bone), and the toes are reduced to two efficient and\ntwo useless rudiments. In the sheep and the goat (Fig. 8) these useless\nrudiments are dropped, and there are two only. Finally, in the horse\n(Fig. 9), the _toes_ are reduced to one, although the palm-bones are\nstill three, two of them, however, being reduced to rudimentary splints.\n\nHow is it with birds? Have these also palm-bones and fingers? Yes,\nin birds (Fig. 11) there are three palm-bones and three fingers (the\nfourth and fifth being wanting); one of them--the thumb--is free, and\nsometimes carries a claw. In the earliest known and most reptilian\nbird, the arch\u00e6opteryx (Fig. 12), all the three fingers are free, have\nthe full number of joints, and all of them carry claws. In the embryo\nof living birds the fingers are all free, as in the arch\u00e6opteryx.\n\n[Illustration: FIG. 19.--Restoration of Rhamphorhynchus phyllurus\n(after Marsh). One-seventh natural size.]\n\n7. Observe, finally, as an admirable illustration of different\nadaptative modifications for the same purpose--flight--the structure\nof the manus of flying animals. In the bat (Fig. 10), the flat\nflying-plane is made by enormous elongation of the palm-bones and\nfinger-bones, their wide separation and the stretching of a thin\nmembrane between them. In the pterosaurs, or extinct flying reptiles\n(Fig. 13), one finger only is greatly enlarged and elongated, and\nthe flying-membrane is stretched between it and the hind-leg (Fig.\n19), while the other three fingers are free and provided with claws.\nIf it be asked which finger is it that is so greatly enlarged in\nthis animal, we answer, it is the _little finger_. In birds, on\nthe contrary, the manus is consolidated to the last degree, to\nform a strong basis for attachments for the quills which form the\nflying-plane, and which are themselves extreme modifications of the\nscales of reptiles. But throughout all these extreme modifications the\nsame essential structure is detectable.\n\nIt is perhaps unnecessary to dwell upon the still greater modifications\nof limbs for swimming, as in the whale (Fig. 16), the ichthyosaur,\nmosasaur (Fig. 18), and the fish (Fig. 17). A careful inspection of the\nfigures, after what we have said, will be sufficient to explain them.\nIn the fish alone the upper segments of the limb, viz., shoulder-girdle\nand humerus, are wanting, not being yet introduced, and the manus is\nnot yet differentiated into palm-bones and fingers, and the fingers\nare indefinitely multiplied. All these characters are indications of\nlow position in the scale of evolution. The earliest vertebrates were\nfishes. Limbs were not yet completely formed. In embryos of higher\nanimals, also, the outer segments are first formed.\n\n=Hind-Limbs.=--Figs. 20 to 24 represent, in a similar way, the\nhind-limbs of several animals--in this case all mammals. As before,\ncorresponding parts are similarly lettered, and a dotted line is\ncarried through certain prominent parts, especially the knee, heel,\ninstep, and toes. By careful inspection the figures explain themselves.\nNevertheless, it will be well to draw special attention to several of\nthe more important points:\n\n[Illustration: FIGS. 20-24.--20. Hind-limb of man. 21. Monkey. 22. Dog.\n23. Sheep. 24. Horse.]\n\n1. See, then, the position of the knee. The thigh-bone in man, monkeys,\nbears, and several other families of mammals, and all reptiles, is free\nfrom the body, and the knee is far removed and half-way down the limb\n(Figs. 20, 21). This is undoubtedly the original and normal condition\nof land-animals. But in all the more highly specialized and swifter\nanimals the knee is brought nearer and nearer to the body, until, in\nthe swiftest of all, such as the ruminants and the horse (Figs. 23,\n24), it is high up on the side of the body, in the middle of what is\nusually called the thigh but which really includes the thigh and the\nupper part of the lower leg or shank.\n\n2. See, again, the position of the heel. In man, monkey, bear, and many\nother mammals, and all _living_ reptiles, the heel is on the ground,\nthe tread is on the whole foot, plantigrade; while in all the more\nspecialized and agile animals, and especially in the swiftest of all,\nsuch as the horse, the deer, etc., the heel is high in the air, and the\ntread is digitigrade.\n\n3. Observe, again: there are two degrees of digitigradeness. The one\nwe find in carnivorous or clawed digitigrades, the other in herbivores\nor hoofed digitigrades. In the one the tread is on the whole length of\nthe toes to the balls, as in man when he _tip-toes_; in the other the\n_tread is on the tip of the last joint alone_. All that in any animal\ncorresponds to the foot of a man--i. e., from the hamstring and heel\ndownward--is called, in comparative anatomy, the \u201c_pes_.\u201d The pes,\nor foot of a horse, is eighteen inches long. It is easy to see what\nspring and activity this mode of treading gives to an animal. Think how\nhelpless a horse would be if he trod on the whole foot, heel down!\n\n4. Observe, again, the number of toes. In the process of specialization\nthere is a tendency for these to become fewer and stronger.[23] The\nnormal number, as already seen, is five. All the earliest mammals,\nand many orders of mammals still living, have five; but in the most\nspecialized orders, such as the ungulates or hoofed animals, they\nwere steadily reduced in number in the course of evolution. In the\nelephant there are still five, in the hippopotamus there are four, in\nthe rhinoceros three, in the goat two, in the horse one. Still more\nthe order of the dropping is regular. If an animal have but four toes,\nit is usually the first, or great toe, or thumb, that is wanting, or\nmay be rudimentary. If, as in the rhinoceros, there are only three,\nthen No. 5, or little toe, is also wanting, and the existing toes are\nNos. 2, 3, and 4. If an animal has only two toes, as the goat, these\nare Nos. 3 and 4; and if only one, as the horse, it is the third or\nmiddle toe. Or, to put it more definitely: hoofed animals are divided\ninto two groups, even-toed (artiodactyl) and odd-toed (perissodactyl).\nThe even-toed may have four, as in the hippopotamus; or two, as in the\ngoat. The odd-toed may have three, as in the rhinoceros; or but one, as\nin the horse. Now, both of these orders came by differentiation, far\nback in the Eocene Tertiary, from a five-toed plantigrade ancestor.\nAfter dropping No. 1 (thumb or great toe) it is not yet decided, so far\nas number of toes is concerned, whether the resulting four-toed animal\nshall become artiodactyl or perissodactyl. If the former, then the\ntwo side-toes (Nos. 2 and 5) become shortened up, as in the hog; then\nrudimentary, as in the ox and deer; and finally pass away entirely, as\nin the goat. If, on the other hand, the four-toed animal is on the line\nof perissodactyl evolution, it becomes first a three-toed animal by\ndropping No. 5. Now, the two side-toes (Nos. 2 and 4) shorten up more\nand more, and the middle toe increases in size, until finally, in the\nmodern horse, only the greatly enlarged middle toe (No. 3) remains.\nWe look with wonder and admiration at the _danseuse_ pirouetting on\nthe point of one toe. The horse is performing this feat all the time.\nYes, the one toe of a horse has all the three joints like ours. The\ncoffin-bone is the last joint, and the hoof is the nail.\n\n[Illustration: _a b c d e f g_\n\n  Equus: Quaternary and Recent.\n\n  Pliohippus: Pliocene.\n\n  Protohippus: Lower Pliocene.\n\n  Miohippus: Miocene.\n\n  Mesohippus: Lower Miocene.\n\n  Orohippus: Eocene.\n\n  FIG. 25.--Diagram illustrating gradual changes in the horse family.\n      Throughout _a_ is fore-foot; _b_, hind-foot; _c_, fore-arm; _d_,\n      shank; _e_, molar on side-view; _f_ and _g_, grinding surface of\n      upper and lower molars (after Marsh).\n]\n\n=Genesis of the Horse.=--Every step of this process on the\nperissodactyl line may be traced in the history of the genesis of\nthe horse. The beautiful form and structure of this animal were not\nmade at once, but by a slow process of integration of small changes\nfrom generation to generation, and from epoch to epoch of the earth\u2019s\nhistory. The horse (as in fact did all ungulates) came from a five-toed\n_plantigrade_ ancestor, but we are not able to trace the direct line\nof genesis quite so far. The earliest stage that we can trace with\ncertainty, in this line of descent, is found in the eohippus of Marsh.\nThis was a small animal, no bigger than a fox, with three toes behind\nand four serviceable toes in front, with an additional fifth palm-bone\n(splint), and perhaps a rudimentary fifth toe like a dew-claw. This was\nin early Eocene times. Then, in later Eocene, came the orohippus, which\ndiffers from the last chiefly in the disappearance of the rudimentary\nfifth toe and splint. (See Fig. 25.) Next, in the Miocene, came the\nmesohippus and miohippus. These were larger animals (about the size of\na sheep), and had three serviceable toes all around; but in the former\nthe rudiment of a fourth splint in the fore-limb yet remained. Then,\nin the Miocene, came the protohippus and pliohippus. These were still\nlarger animals, being about the size of an ass. In the former the two\nside-toes were shortening up and the middle toe becoming larger. In\nthe latter the two side-toes have become splints. Lastly, only in\nthe Quaternary comes the genus _Equus_, or true horse. The size of the\nanimal is become greater, the middle toe stronger, the side-splints\nsmaller; but in the side-splints of the modern horse we have still\nremaining the evidence of its three-toed ancestor.\n\nSimilar gradual changes may be traced in the two leg-bones, which\nhave gradually consolidated into one; in the teeth, which have become\nprogressively longer and more complex in structure, and therefore a\nbetter grinder; in the position of the heel and wrist, which have\nbecome higher above-ground; in the general form, which has become\nmore graceful and agile; and, lastly, in the brain, which has become\nprogressively larger and more complex in its convolutions--to give\ngreater battery-power, to make a more powerful dynamo--to work the\nimproved skeletal machine. See, then, how long it has taken Nature to\nproduce that beautiful finished article we call the horse!\n\n       *       *       *       *       *\n\nWe have taken only limbs as examples of what is true of the whole\nskeleton. To the superficial observer the bodies of animals of\ndifferent classes seem to differ fundamentally in plan--to be entirely\ndifferent machines, made each for its own purposes, at once, out of\nhand. Extensive comparison, on the contrary, shows them to be the same,\nalthough the essential identity is obscured by adaptive modifications.\nThe simplest, in fact the only scientific, explanation of the phenomena\nof vertebrate structure is the idea of a primal vertebrate, modified\nmore and more through successive generations by the necessities of\ndifferent modes of life.\n\nSee, then, in conclusion, the difference between man\u2019s mode of working\nand Nature\u2019s. A man having made a steam-engine, and desiring to use it\nfor a different purpose from that for which it was first designed and\nused, will nearly always be compelled to add new parts not contemplated\nin the original machine. Nature rarely makes new parts--never, if\nshe can avoid it--but, on the contrary, adapts an old part to the\nnew function. It is as if Nature were not free to use any and every\ndevice to accomplish her end, but were conditioned by her own plans\nof structure; as, indeed, she must be according to the derivation\ntheory. For example: In early Devonian times fishes were the only\nrepresentatives of the vertebrate type of structure. The vertebrate\nmachine was then a _swimming-machine_. In the course of time, when all\nwas ready and conditions were favorable, reptiles were introduced.\nHere, then, is a new function--that of locomotion on land. We want a\n_walking-machine_. Shall we have a new organ for this new function? No:\nthe old swimming-organ is modified so as to adapt it for walking. Time\nwent on, until the middle Jurassic, and birds were introduced. Here\nis a new and wonderful function, that of flying in the air. We want a\n_flying-machine_. We know how man would have done this; for we have\nthe result of his imagination in angels of Christian art and griffins\nof Greek mythology. He would have added wings to already existing\nparts, and this would have necessitated the alteration of the whole\nplan of structure, both skeletal and muscular. Nature only modifies\nthe fore-limbs for this new purpose. If we must have wings, we must\nsacrifice fore-legs. We can not have both without violating the laws of\nmorphology. Finally, ages again passed, and, when time was fully ripe,\nman was introduced. Now we want some part to perform a new and still\nmore wonderful function. We want a _hand_, the willing and efficient\nservant of a rational mind. We know, again, how man would have done\nthis, for we have the result in the centaurs of Greek mythology, in\nwhich man\u2019s chest, and arms, and head are added to the body of a\nquadruped. But natural laws must not be violated, even for man. If we\nwant hands, we must sacrifice feet. Again, therefore, the fore-limbs\nare modified for this new and exquisite function. Thus, in the fin of\na fish, the fore-paw of a reptile or a mammal, the wing of a bird, and\nthe arm and hand of a man, we have the same part, variously modified\nfor many purposes.\n\nMany other illustrations might be taken from the skeleton and from\nother systems, especially the muscular and nervous. But in the\nmuscular system the modifications have been so extreme that homology\nis much more difficult to trace, and therefore requires more extensive\nknowledge than we yet possess, and more extended comparison than has\nyet been attempted. It has been traced with some success through\nmammals, and probably will be through air-breathing vertebrates--i. e.,\nalso through birds, reptiles, and amphibians; but to trace it through\nfishes seems almost hopeless. In the case of the nervous system, and\nespecially of the brain, it is again distinct; but this had better be\ntaken up under another head, viz., proofs from ontogeny, Chapter VI.\n\nIn the visceral organs homology is very plain, in fact too plain.\nThere is not modification enough in most cases even to obscure it,\nbecause function is the same in all animals. These organs do not,\ntherefore, furnish good illustrations of that essential identity in the\nmidst of adaptive modification which constitutes the argument for the\nderivative origin of structure. It is the organs of _animal life_ that\nshow this most perfectly, because it is these that take hold on the\nenvironment and are modified by it. There are, however, a few striking\nillustrations to be found among the visceral organs, especially the\nblood-system. This, however, had better also be deferred to the chapter\non ontogeny.\n\n\n\n\nCHAPTER VI.\n\nHOMOLOGIES OF THE ARTICULATE SKELETON.\n\n\nWe have taken the vertebrate skeleton first, only because this\ndepartment is most familiar. But in reality, the most beautiful\nillustrations of essential identity of structure in the midst of\ninfinite diversity of adaptive modification for different functions\nand habits of life, and therefore of common origin from a primal form,\nare found in the department of articulates. I use the old Cuvierian\ndepartment _articulata_, rather than the more modern _arthropods_,\nbecause the former includes worms also. Now, whether worms should\nbe thus included with arthropods, or deserve a whole department to\nthemselves it matters not for our purposes. It is generally admitted\nthat arthropods probably descended from marine worms. They all have\nthe same general plan of skeletal structure. It will suit my purpose,\ntherefore, to regard worms as the lowest form of jointed animals.\n\nHere, then, we have an entirely different plan of structure--a\ndifferent style of architecture and different mechanical principles\nof machinery. Instead of a skeleton within and muscles acting on the\noutside, we have the skeleton on the outside, and muscles acting from\nwithin. Instead of two cavities, a neural and visceral, the skeleton\nforms but one cavity, in which all organs are inclosed and protected.\nInstead of finding the nerve-axis on the dorsal aspect of the body, we\nfind it on the ventral aspect.\n\n[Illustration:\n\n  FIG. 26.--Diagram section across an arthropod, showing the inclosing\n      skeleton-ring and a pair of jointed appendages, _n_, nervous\n      center; _v_, viscera; _b_, blood system.\n]\n\nTake any articulate animal, for example, a shrimp, a centiped, or\na beetle. Cut it across the body, and look at the end (Fig. 26).\nWe see a ring of bone (chitin) inclosing all the organs (nervous\nsystem _n_, blood system _b_, and visceral system _v_), and a pair\nof jointed appendages, perhaps legs, on each side. Now imagine these\nparts repeated in a linear series. The rings repeated make a hollow,\njointed tube or barrel, the appendages repeated make a continuous row\nof appendages on each side. Now this is exactly what we actually\nfind. The whole articulate skeleton is ideally made up of a series\nof such repeated rings and appendages, modified according to the\nposition in the series, and the uses to which they are put. And then\nthe whole articulate department is made up of such articulate animals\nagain modified according to place in the scale of articulates. The\nmodification in the lower forms is slight, and therefore the identity\nof the repeated parts is obvious; but as we go up the scale, and\nthe number and complexity of the functions increase, the adaptive\nmodification becomes greater and greater, until finally it so obscures\nthe essential identity, that it requires the most extensive comparison\nin the taxonomic series and in the ontogenic series, to pick up the\nintermediate links and establish the fact of common origin. In a word,\nwhether they so originated or not, it is certain that the structure of\narticulate animals is exactly such as would be the case if all these\nanimals were genetically connected, and came originally from a primal\nform something like one of the lower crustaceans, or, perhaps, a marine\nworm.\n\n[Illustration: FIG. 27.--Shrimp (Pal\u00e6monetes vulgaris).]\n\n[Illustration: FIG. 28.--External anatomy of the lobster (after\nKingsley).]\n\nIt will be best to take an example from about the middle of the\nscale, where the two elements, viz., essential identity and adaptive\nmodification, are somewhat evenly balanced, and both traceable with\nease and certainty. Take, then, a cray-fish, a lobster, or a shrimp.\nThis animal (Fig. 27) has twenty or twenty-one rings and pairs of\njointed appendages. The rings are some of them diminished, some\nof them increased in size. Sometimes several are consolidated;\nsometimes several are partially or wholly aborted. The appendages\nare modified in shape and size, according to their position, so as\nto make them swimming-appendages (swimmerets), walking-appendages\n(legs), eating-appendages (jaws), and sense-appendages (antenn\u00e6). For\nexample, in the abdominal region, or so-called tail, we have seven\nsegments, all being perfect movable rings, each with its pair of\njointed appendages, except the last, or _telson_. The appendages of the\nfirst ring (Fig. 28, B) are specially modified in the male as organs\nof copulation (B\u2032). The next four pairs are modified for swimmerets\n(D\u2032) and for use as holders of the eggs in the female. The appendages\nof the sixth ring (G) are broad and paddle-shaped, and, together with\nthe telson or seventh ring (H), form the powerful terminal swimmer.\nGoing, now, to the cephalo-thorax: in this either a large number of\nsegments (thirteen or fourteen) are consolidated above to form the\nupper shell or carapace; or else, as is more probable, two or three\nof the anterior segments have enlarged and grown backward over, and\nat the expense of the others, to form this shell. At any rate, it is\ncertain that the carapace is formed of the dorsal portions of a number\nof segments consolidated together. Below, however, the segments are\nall distinct, and have each its own pair of appendages. For example,\ngoing forward in this region, the five next pairs of appendages are\ngreatly enlarged and very strong, and serve the purpose of locomotion.\nThey are _walking-appendages_. The next two or three pairs are smaller\nand somewhat modified, but not so much as to obscure their essential\nsimilarity to legs. Like legs, they are many-jointed, and like legs,\ntoo, they have gills attached to them. They are called maxillipeds, or\njaw-feet. They are used like hands to gather food and carry it to the\nmouth. They are _gathering-appendages_. Then follow three or four pairs\nstill more modified, and used for mastication. They are called maxill\u00e6\nand mandibles. They are _eating-appendages_. Then follow two pairs,\nlong, many-jointed, with the same kind of curious hinge-joints, which\nwe have in the legs, undoubtedly homologous with all the others, but\nused for an entirely different purpose, and specially modified for that\npurpose. They are the antenn\u00e6. They are delicate organs of touch and\nof hearing, for the ear is situated in the basal joint of the anterior\npair. Last of all, there is still another pair, jointed and movable, on\nthe ends of which are situated the eyes. These last three, therefore,\nare _sense-appendages_. Some writers make this last pair special\norgans, not homologous with appendages.\n\n[Illustration: FIG. 29.--Appendages of a prawn (after Cuvier).]\n\n[Illustration: FIG. 30.--Appendages of Nebalia.]\n\nFor the sake of greater distinctness, we give the whole series of these\nappendages in one of the higher forms, viz., the prawn (Palemon, Fig.\n29, and in one of the lower forms, Nebalia, Fig. 30).\n\n[Illustration: FIG. 31.--Vibilia, an amphibod crustacean (after Milne\nEdwards).]\n\nThat these are really homologous parts is further shown by the fact\nthat in the case of other crustaceans, such as limulus, the same\nappendages, i. e., the appendages of the same body segments, which in\nthe cases before mentioned are used as feet, become swimmers, while\nthe appendages corresponding to jaw-feet become walkers; and even what\ncorresponds to antenn\u00e6 or sense-appendages, may, as in branchippus,\nbecome powerful claspers. Finally, in all the lowest crustaceans, the\nidentity is evident, because all the segments and their appendages are\nmuch alike in form and function (Fig. 31).\n\n[Illustration: FIG. 32.--Lithobius forcipatus (after Carpenter).]\n\nWe have taken examples from near the middle of the articulate scale,\nbecause, as already stated, both the essential identity and the\nadaptive modifications are easily traced. If we go downward in the\nscale, the structure becomes more and more generalized, and the rings\nand appendages become more and more alike (Fig. 31), until in the most\ngeneralized forms we have only a series of similar rings, with similar\npairs of appendages, except some necessary modifications to form the\nhead and tail. This is well shown in the centiped (Fig. 32), and still\nbetter in marine worms (Fig. 33). In some marine worms the slight\nmodification to form the head takes place under our very eyes. These\noften multiply by dividing themselves into two. When they do so, they\nmake a new head and new tail by slight modification of segments and\nappendages (Fig. 33).\n\n[Illustration: FIG. 33.--Syllis prolifera.]\n\nIf, on the other hand, we go up the scale, we find adaptive\nmodifications obscuring more and more the simple and obvious identity\nof parts, until finally the identity can not be recognized without\nextensive comparison in the taxonomic series and study of embryonic\nconditions. In crabs--which is a higher form than cray-fish--the tail\nor abdomen seems to be wanting, but is only very small and bent under\nthe body and thus concealed. In all essential respects the structure is\nprecisely like the cray-fish. In fact, in the embryo, we trace the one\nform into the other; for the crab is at first a long-tailed crustacean\n(Fig. 34).\n\n[Illustration: FIG. 34.--Development of Carcinus m\u0153nas. A, zo\u00e6a stage;\nB, megalopa stage; C, final state (after Couch).]\n\nInsects are the highest form of articulates. In these, therefore, we\nfind the modification is still greater than in crustaceans, though even\nhere the ring-and-appendage structure is plain enough in most cases.\n\nOne of the best evidences of high grade among animals is the gathering\nof the segments into distinct groups, and especially the distinctness\nof the _head_ as one of these groups. In worms and lower crustaceans\nthere is no grouping at all, the skeleton being a continuous series\nof joints, only slightly modified at the anterior and posterior\nextremities. In the higher crustacea, and in spiders and scorpions,\nthey are grouped into two regions, viz., cephalo-thorax and abdomen.\nIn insects they are grouped into three very distinct regions--head,\nthorax, and abdomen. In insects, therefore, we find for the first\ntime the head distinctly separated from the rest of the body. This\nis an evidence of high grade, because it shows the dominance of\nhead-functions.\n\n[Illustration:\n\n  FIG. 35.--External anatomy of Caloptenus spretus, the head and thorax\n      disjointed; up, uropatagium; _f_, furcula; _c_, cercus (drawn by\n      J. T. Kingsley).\n]\n\nThe insect, such, for example, as a grasshopper, consists of seventeen\nor eighteen segments (Fig. 35). Of these, four belong to the head,\nthree to the thorax, and about ten to the abdomen. Those of the abdomen\nare all separated and movable; those of the thorax and head are more or\nless consolidated. The appendages of the head-segments become antenn\u00e6\nand jaw-parts, i. e., mandibles--maxill\u00e6 and labium; the appendages\nof the thorac-segments become legs (the wings are not homologous with\nappendages), while those of the abdomen are aborted. The steps of the\ngradual consolidation on the one hand, and the abortion on the other,\nmay be traced in the embryo or larva--i. e., in the caterpillar or the\ngrub of a bee or a beetle. In the caterpillar, for example, there is\nno grouping into three regions, there is no consolidation, and all the\nsegments have appendages. Again, the almost infinite variety in the\nmouth-parts among insects, brought about by adaptive modifications for\nbiting, for piercing, and for sucking, and yet the essential identity\nof all to the more simple and generalized structure of the grasshopper,\nis an admirable illustration of the same principle. But to dwell upon\nthese minor points would carry us too far.\n\n=Illustration of the Law of Differentiation.=--We have here, in the\nmodifications of segments and appendages of articulates, an admirable\nillustration of the most fundamental law of evolution, viz., the law of\ndifferentiation. As we have already seen (page 21), perhaps the most\nbeautiful and certainly the most fundamental illustration of this law\nis found in the development of cell-structure. Commencing in the lowest\nanimals, and in the earliest embryonic stages of the higher animals,\nfrom a condition in which all are alike, the _cells_ as we go upward\nquickly diverge into different forms to produce different tissues and\nperform different functions. Here, then, we have a perfect example of\nessential identity and adaptive modification. It is the very best type\nof differentiation. So also skeletal _segments_, commencing, in the\nlowest articulates and in earliest embryonic stages of the higher, all\nalike, as we go upward in either series, begin immediately to diverge\nin various directions (divergent variation), taking different forms to\nsubserve different uses. Here, again, therefore, is an illustration\nof the law of differentiation. Lastly, in the articulate department,\ncommencing with the lowest forms and earliest embryonic conditions,\nand we may add earliest geological times, and going up either series\nfrom generalized forms very much alike, the _individuals_ are gradually\ndifferentiated into many special forms, in order to adapt them to\nthe diversified modes of life actually found in nature. Thus cells,\nsegments, individuals, are all alike affected by this most fundamental\nlaw.\n\nWe have taken our illustrations from only the two departments of\nvertebrata and articulata, because these are the most familiar to the\nreader, and also have been most carefully studied. We have shown that\nthe general structure of all vertebrates is precisely what it would\nbe if they all had come from one primal vertebrate form, and that\nof all articulates what it would be if all had come from one primal\narticulate form. The only _natural_ explanation, and, therefore, the\nonly scientific explanation of this, is that _they were really thus\nderived_. The same kind of evidence may be drawn from the study of\nother departments, but to pursue the subject any further in this\ndirection would carry us beyond the limits which we have assigned. We\ndesire only to explain the nature, not to give all, of the evidence.\nThe examples given will be sufficient for the purposes of illustration.\nThe whole proof is nothing less than the whole science of comparative\nanatomy.\n\nVertebrates, then, were derived from a primal vertebrate, articulates\nfrom a primal articulate, and so for other departments. But whence were\nthese _primals_ derived? Are there any intermediate links between, any\ndeeply concealed common plan of structure underlying these primary\ngroups, showing a common origin? It must be confessed that, in their\n_mature_ condition, there seems to be but little evidence of such.\nThese primary groups seem to be built on different plans, to be\nfundamentally of different styles of architecture. Therefore Darwin,\nin the true spirit of inductive caution--that true scientific spirit\nwhich keeps strictly within the limits of evidence--commences with four\nor five distinct primal kinds, from which by divergent variation all\nanimals were descended. Nevertheless, the truly scientific biologist\nmust ever strongly incline to believe that these also came from some\n_primal animal_, and even that both animals and plants were derived\nfrom some primal form of _living thing_; that as, in the taxonomic\nseries, the animal and vegetal kingdoms in their lowest forms merge\nundistinguishably into one another; as in the ontogenic series the\nanimal and plant germ are one, so also in the phylogenic series the\nearliest organisms were simply living things, but not distinctively\nanimal nor vegetal. Science, therefore, whose mission is to trace\norigins as far back as possible, must ever strive to find connecting\nlinks between the primary groups. Some such have been supposed to\nhave been discovered. Some find the origin of vertebrates among the\nmolluscoids (ascidians); some find the origins of both vertebrates and\narticulates among marine worms (annelids). This point is still too\ndoubtful to be dwelt upon here. It may be that we seek in vain for such\nconnecting links among existing forms. It may well be that the point of\nseparation of these great primary groups (unless we except vertebrates)\nwas far lower even than these low forms. Both phylogeny and ontogeny\nseem to indicate this. In the earliest fauna known, the primordial (for\nif there was life in the arch\u00e6an it was not yet differentiated into a\nfauna), all the great departments, except the vertebrates, seem to\nhave been represented. In embryonic development, too, the point of\nconnection or even of similarity, between the great departments, is\nfound, as we shall see hereafter, only in the earliest stages--i. e.,\nlower down than any but the lowest existing forms, viz., the protozoa.\n\n\n\n\nCHAPTER VII.\n\nPROOFS FROM EMBRYOLOGY, OR COMPARISON IN THE ONTOGENIC SERIES.\n\n\nIt is a curious and most significant fact that the successive stages of\nthe development of the _individual_ in the higher forms of any group\n(ontogenic series) resemble the stages of increasing complexity of\ndifferentiated structure in ascending the animal scale in that group\n(taxonomic series), and especially the forms and structure of animals\nof that group in successive geological epochs (phylogenic series). In\nother words, the individual higher animal in embryonic development\npasses through temporary stages, which are similar in many respects to\npermanent or mature conditions in some of the lower forms in the same\ngroup. To give one example for the sake of clearness: The frog, in its\nearly stages of embryonic development, is essentially a fish, and if\nit stopped at this stage would be so called and classed. But it does\nnot stop; for this is a temporary stage, not a permanent condition.\nIt passes through the fish stage and through several other temporary\nstages, which we shall explain hereafter, and onward to the highest\ncondition attained by amphibians. Now, if we could trace perfectly\nthe successive forms of amphibians, back through the geological epochs\nto their origin in the Carboniferous, the resemblance of this series\nto the stages of the development of a frog would doubtless be still\ncloser. Surely this fact, if it be a fact, is wholly inexplicable\nexcept by the theory of derivation or evolution. The embryo of a\nhigher animal of any group passes _now_ through stages represented by\nlower forms, because in its evolution (phylogeny) its ancestors _did\nactually have these forms_. From this point of view the ontogenic\nseries (individual history) is a brief recapitulation, as it were, from\nmemory, of the main points of the philogenic series, or family history.\nWe say brief recapitulation of the _main_ points, because many minor\npoints are dropped out. Even some main points of the earliest stages of\nthe family history may be dropped out of this sort of inherited memory.\n\nThis resemblance between the three series must not, however, be\nexaggerated. Not only are many steps of phylogeny, especially in\nits early stages, dropped out in the ontogeny, but, of course, many\nadaptive modifications for the peculiar conditions of embryonic life\nare added. But it is remarkable how even these--for example the\numbilical cord and placenta of the mammalian embryo--are often only\nmodifications of egg-organs of lower animals, and not wholly new\nadditions. It is the similarity in spite of adaptive modifications that\nshows the family history.\n\nWe will now illustrate by a few striking examples.\n\nWe can not do better than to take, again, as our first example, the\ndevelopment of tailless amphibians, and dwell a little more upon it:\n\n=1. Ontogeny of Tailless Amphibians.=--It is well known that the\nembryo or larva of a frog or toad, when first hatched, is a legless,\ntail-swimming, water-breathing, gill-breathing animal. It is\nessentially a fish, and would be so classed if it remained in this\ncondition. The fish retains permanently this form, but the frog passes\non. Next, it forms first one pair and then another pair of legs;\nand meanwhile it begins to breathe also by lungs. At this stage it\nbreathes equally by lungs and by gills; i. e., both air and water.\nNow, the lower forms of amphibians, such as siredon, menobranchus,\nsiren, etc., retain permanently this form, and are therefore called\n_perennibranchs_, but the frog still passes on. Then the gills\ngradually dry up as the lungs develop, and they now breathe wholly by\nlungs, but still retain the tail. Now this is the permanent, mature\ncondition of many amphibians, such as the triton, the salamander, etc.,\nwhich are therefore called _caducibranchs_, but the frog still passes\non. Finally, it loses the tail, or rather its tail is absorbed and its\nmaterial used in further development, and it becomes a perfect frog,\nthe highest order (_anoura_) of this class.\n\nThus, then, in ontogeny the fish goes no further than the fish stages.\nThe perennibranch passes through the fish stage to the perennibranch\namphibian. The caducibranch takes first the fish-form, then the\nperennibranch-form, and finally the caducibranch-form, but goes no\nfurther. Last, the anoura takes first the fish-form, then that of the\nperennibranch, then that of the caducibranch, and finally becomes\nanoura. This is shown in the diagram, which must be read upward, line\nby line.\n\n[Illustration:\n\n  FISH.      PERENNIBRANCH.     CADUCIBRANCH.      ANOURA.\n                                                     ^\n  FISH.      PERENNIBRANCH.     CADUCIBRANCH.--------^\n                                     ^\n  FISH.      PERENNIBRANCH-----------^\n                   ^\n  FISH.------------^\n\nDiagram showing the stages of development of amphibians. (To be read\nupward.)]\n\nNow, this is undoubtedly the order of succession of forms in geological\ntimes--i. e., in the phylogenic series. This series is indicated by\nthe arrows in the diagram. Fishes first appeared in the Devonian\nand Upper Silurian in very reptilian or rather amphibian forms.\nThen in the Carboniferous, fishes still continuing, there appeared\nthe lowest--i. e., most fish-like--forms of amphibians. _These were\nundoubtedly perennibranchs._ In the Permian and Triassic higher forms\nappeared, which were certainly caducibranch. Finally, only in the\nTertiary, so far as we yet know, do the highest form (anoura) appear.\nThe general similarity of the three series is complete. If we read the\ndiagram horizontally, we have the ontogenic series; if diagonally with\nthe arrows, we have both the taxonomic and the phylogenic series.\n\n=2. Aortic Arches.=--But some will, perhaps, say that these stages\nin the ontogeny are only examples of adaptive modifications--like\nmodifications for like conditions of life--and had better be accounted\nfor in this way, without reference to family history. We will,\ntherefore, take another example, which can not be thus accounted\nfor--an example in which there is no possible use _now_ for the\npeculiar form or structure which we find. For this purpose we take the\ncase of the _course of circulation in vertebrates_.\n\n[Illustration: FIG. 36.--Showing heart and outgoing blood-vessels of a\nlizard (after Owen). The arrows show the course of the blood.]\n\n[Illustration: FIG. 37.--A, heart and gill-arches of a fish; B, one\narch, with fringe (after Owen); H, the heart.]\n\nIf one examines the large vessels _going out_ from the heart of a\nlizard, he will find _six aortic arches_--i. e., three on each side.\nThese all unite below to form the one descending abdominal aorta. This\nis shown in the accompanying figure (Fig. 36), in which _a a\u2032 a\u2033_ and\n_b b\u2032 b\u2033_ are the six arches. Now, there is no conceivable use in\nhaving so many aortic arches. We know this, because there is but one in\nbirds and mammals, and the circulation is as effective, nay, much more\neffective in these than in reptiles. The explanation of this anomaly is\nrevealed at once as soon as we examine the circulation of a _fish_,\nwhich is shown in the accompanying figure (Fig. 37). The multiplication\nof the aortic arches is here, of course, necessary, for they are the\n_gill-arches_. The whole of the blood passes through these arches, to\nbe a\u00ebrated in the gill-fringes. The use of this peculiar structure is\nhere obvious enough. If a lizard were ever a fish, and afterward turned\ninto a lizard, changing its gill-respiration for lung-respiration,\nthen, of course, the useless gill-arches would remain to tell the\nstory. Now, although a lizard never was a fish, in its _individual_\nhistory or ontogeny, it was a fish in its family history or phylogeny,\nand therefore it yet retains, by heredity, this curious and _useless_\nstructure as evidence of its ancestry.\n\n[Illustration: FIG. 38.]\n\n[Illustration: FIG. 39.\n\n  FIGS. 38, 39.--Diagrams showing the change of the course of blood\n      in the development of a frog. 38. The tadpole stage. 39. The\n      mature condition. H, heart; G G\u2032 G\u2033, external gills; _g g\u2032 g\u2033_,\n      internal gills; _c c_, connecting branches in the tadpole; _p p_,\n      pulmonary branches.\n]\n\nThat this is the true explanation is demonstrated by the fact that in\namphibians this very change actually takes place before our eyes in\nthe _individual history_. We have already seen that the individual\nfrog, in its tadpole state, is a gill-breather. It has therefore its\ngill-arches (Fig. 38), three on each side, like a fish, and for the\nsame reason, viz., the a\u00ebration of the blood. But when its gills dry\nup and lung-respiration is established, its now useless gill-arches\nstill remain as aortic arches, to attest their previous condition (Fig.\n39). Now, the lizard undoubtedly came from an air-breathing, tailed\namphibian, and therefore inherited this form of arterial distribution.\nIn both lizard and amphibian the ultimate cause is an origin from\nfishes, in which such arches are obviously necessary. The diagrams,\nFigs. 38 and 39, are illustrations somewhat idealized, showing the\nmanner in which the change actually takes place in air-breathing\namphibians. Fig. 38 represents the tadpole stage, and Fig. 39 the\nmature condition. In the former the gills are mostly external, G G\u2032,\netc., but also internal, _g g\u2032_, as in the fish. Observe in this\ncondition the small connecting vessels, _c c\u2032_. When the external gills\ndry up, these are enlarged, and the whole of the blood passes through\nthem, as shown in Fig. 39. It is seen, also, in Fig. 38, that a small\nbranch, _p_, goes from the lower gill-arches to the yet rudimentary\nlung, _l_. When the gill-fringes have disappeared, the whole of the\nblood of the lower arch goes through the now enlarged pulmonary branch\nto the lungs, L, now in full activity, and the remainder of this arch\ndisappears, as shown by the dotted lines in Fig. 39.\n\nThe change which actually took place in the family history of the\nlizard probably differed from the above only in being more simple, the\ngills being only internal like the fish. The external gills complicate\nthe process a little in the case of the frog, but the principle is\nprecisely the same.\n\nAs already explained (pages 82-85), the large gap between fishes and\nreptiles, as regards mode of respiration, is completely filled both\nin the taxonomic series--i. e., in ganoids, dipnoi, and the mature\ncondition of the different orders of amphibians--and in the ontogeny\nof the higher amphibians. Now, we add that the same is true of the\narterial distribution. We have just traced the change in the ontogeny\nof the frog, but the steps of the same change are traceable in passing\nfrom the typical fish (teleosts), through dipnoi and amphibians to\nreptiles. Thus, again, the phylogeny, the taxonomy, and the ontogeny,\nare in complete accord.\n\nBut the argument for evolution does not stop here. If birds and\nmammals have come from reptiles, and therefore from fishes, we may\nexpect to find some evidences of the same kind still lingering in\nthe great arteries. And such we do find. It is a most curious and\nsignificant fact that, in the early embryonic condition of birds and\nmammals, including man himself, we find on each side of the neck\nseveral gill-slits, each with its gill-arch, and therefore _several\naortic arches on each side_, precisely similar to what we have already\ndescribed. These arches are subsequently, some of them, obliterated;\nsome modified to form the one aortic arch, and some of them still more\nmodified to form the other great arteries coming from the heart to\nsupply the head and forelimbs.\n\n[Illustration:\n\n  FIG. 40.--Diagram of mammalian heart. _a_, aorta; _p_, pulmonary\n      artery; _scs\u2032c\u2032_, subclavium on each side; _cc\u2032_, carotids on\n      each side.\n]\n\n[Illustration: FIG. 41.--Ideal diagram representing the primitive\naortic arches (after Rathke).]\n\nThis is so beautiful and convincing an example, and one so generally\nunfamiliar, to even intelligent persons, not especially acquainted with\nbiology, that it is best to explain it more fully. In Fig. 40 we give\na mammalian heart and outgoing vessels, very slightly modified, so as\nto suggest the process of change. In Fig. 41 we give an ideal diagram\nrepresenting the primitive aortic arches as they exist in the embryo of\nmammals, birds, and reptiles. It represents, also, substantially, the\narches as they exist in the _mature_ condition in the most reptilian\nfishes (dipnoi) and in some sharks, except that in these the arches\nare of course furnished with gill-fringes. We will use this figure,\ntherefore, to represent both the embryonic condition of air-breathing\nvertebrates and the mature condition of some fishes. The place of\nthe heart is indicated by the dotted circle. Fig. 36, on page 134,\nshows what these arches become in reptiles (lizard). It is seen that\nthe two upper arches on each side are obliterated, as indeed they\nalready are in some teleost fishes. Fig. 42 shows what they become in\nbirds. The two upper arches are, of course, obliterated. The others\nare all modified, each in a manner which may be readily understood\nby comparison with Fig. 41. Finally, Fig. 43 shows what they become\nin mammals and in man. In the bird (Fig. 42) the first pair of arches\nbecome the two pulmonary arteries as they do also in the lizard. The\nsecond pair become on the right side (left of the diagram) the aortic\narch, on the left side (right of the diagram) the left subclavian,\n_s\u2032c\u2032_ (the right subclavian, _sc_, is a branch of the aortic arch).\nThe third pair become carotids, _cc_, while the fourth and fifth, as\nalready said, are aborted. In the mammal (Fig. 43), on the left side\n(right of the diagram) the first arch becomes the pulmonary artery,\n_p_. In the f\u0153tus the continuation of this arch forms the ductus\narteriosus, which is afterward obliterated, as shown in the dotted\nline. The second arch becomes the aortic arch, the third the left\nexterior carotid. On the right side (left of the diagram) the first\narch becomes aborted; the second, the right subclavian, _sc_ (the\n_left_ subclavian, _s\u2032c\u2032_, is a branch of the aortic arch); and the\nthird, the right carotid. Nos. 4 and 5, on both sides, as usual, are\naborted.\n\n[Illustration: FIG. 42.--Modified for bird.]\n\n[Illustration: FIG. 43.--Modified for mammal.]\n\n[Illustration: FIG. 44.--Lancelet (Amphioxus lanceolatus). Magnified\ntwo and one-half times.]\n\nSee, then, the gradual process of change through the whole vertebrate\ndepartment. In the lowest of all vertebrates, if vertebrate it may\nbe called (for what corresponds to its backbone is an unjointed,\nfibrous cord), the amphioxus or lancelet (Fig. 44), there are about\nforty gill-arches on each side. As we rise in the scale of fishes\nthese are reduced in number. In the lamprey, there are seven; in the\nsharks, usually five; in ordinary fishes (teleosts), there are four or\nsometimes only three on each side, the others being aborted. Thus far\nthe change is only by diminution of number in accordance with a law\nuniversal in biology, that decrease in the number of identical organs\nis evidence of advance in the grade of organization, provided that it\nbe associated with more perfect structure of the organ. The further\nchange is one of adaptive modification. In some reptiles (lizard) the\nthree gill-arches on each side all retain the form of aortic arches;\nin some reptiles only two retain this form. In birds and mammals only\none arch is retained, in the form of aortic arch, the others being\nmodified to form the great outgoing vessels of the heart, or else\naborted. It may be well to observe that in birds the one aortic arch\nturns to the right, while in mammals it turns to the left. This is\npositive evidence that mammals could not have come from birds, nor\n_vice versa_. They both came from reptiles, and, of the many reptilian\narches, a right one was retained by the bird branch, and a left one by\nthe mammalian.\n\nIn all the figures illustrating this subject, we have left out the\ngreat _incoming_ vessels or veins, because we are not here concerned\nwith them, they not being transformed gill-arches.\n\nLast of all, it may be well to stop a moment to show the cogency of\nthis evidence. If it were a question of the origin of some structure\nnot only useful (for all structures selected by Nature must be useful)\nbut the _best imaginable_, like the eye or the ear, for example; then,\nif _we examined only the highest form_ or _the finished article_, there\nare two ways in which it is possible to explain the adaptive structure.\nWe may either suppose that it was made at once out of hand, by some\nintelligent contriver; or else that it was slowly made by a process\nof evolution, becoming more and more perfect by a selection of only\nthe most perfect from generation to generation. But in the case of the\nsix aortic arches of the lizard, we are shut up to the one explanation\nonly, viz., by slow process of evolution. One arch is all that is\nnecessary, as is plainly shown by the use of only one in the more\nperfect circulation of birds and mammals. If the thing were done out\nof hand, unconditioned by the previous structure in fishes, to have\nmade six was surely but a bungling piece of work.\n\n[Illustration: FIG. 45.--Fish-brain. A, side view; B, top view.]\n\n[Illustration: FIG. 46.--Reptile-brain. A, side view; B, top view.]\n\n[Illustration: FIG. 47.--Bird-brain. A, side view; B, top view.]\n\n[Illustration: FIG. 48.--Mammal-brain. A, top view; B, side view.]\n\n[Illustration: FIG. 49.--Man\u2019s brain. A, side view; B, top view.]\n\n=3. Vertebrate Brain.=--Another excellent example is the structure of\nthe vertebrate brain. The brain of an average fish is represented in\nFig. 45. It consists of four or five swellings, or ganglia, strung\nalong, one beyond another. Commencing behind, these are, first, the\nmedulla, _m_; then the cerebellum, _cb_; then the optic lobes, _ol_;\nthen the cerebrum and thalamus combined, _cr_; and last, the olfactive\nlobes, _of_. Of these, it will be observed, the optic lobe is the\nlargest in the brain of the fish (Fig. 45). In the brain of the reptile\n(Fig. 46) we have the same serial arrangement, of the same parts,\nonly that the cerebrum has now become the dominant part instead of\nthe optic lobes. In the average bird (Fig. 47) the cerebrum has grown\nso large that it extends backward, and partly covers the optic lobes.\nIn the lower mammals (marsupials), the brain is much the same in this\nrespect, as in birds--i. e., the cerebrum only partly covers the optic\nlobes, so that, looked at from above, the whole series of ganglia are\nstill visible. But in the average mammal (Fig. 48) the cerebrum is so\nenlarged that it covers entirely the optic lobes and encroaches on the\ncerebellum behind and the olfactive lobes in front. In some monkeys,\nindeed, the cerebellum is nearly or even quite covered. Finally, in\nman (Fig. 49), the cerebrum has grown so enormously that it covers\nevery other part and completely conceals them from view when the brain\nis looked at from above. In front it not only covers but has grown far\nbeyond the olfactive lobes; behind it extends beyond and overhangs the\ncerebellum; on the sides it overhangs and covers all. Looked at from\nabove, nothing is seen but this great ganglion. The ideal section (Fig.\n50) represents all these stages diagrammatically in one figure. After\nwhat has been said, the figure will be readily understood.\n\n[Illustration: FIG. 50.--Ideal section showing all the above stages.]\n\n[Illustration: FIG. 51.--Sub-fish Stage. _th_, thalamus; _ol_, optic\nlobe; _m_, medulla.]\n\n[Illustration:\n\n  FIG. 52.--Fish-stage. _of_, olfactive lobe; _cr_, cerebrum; _th_,\n      thalamus; _ol_, optic lobe; _cb_, cerebellum; _m_, medulla.\n]\n\n[Illustration: FIG. 53.--Reptile-stage.]\n\nNow, it is a most remarkable fact that substantially these same\nstages, which are permanent conditions in the taxonomic series, are\npassed through as transient stages in the embryonic development of the\nhuman brain, and in the order given above. The very early condition\nof the human brain is represented in Fig. 51. It is evidently nothing\nmore than the intercranial continuation of the spinal cord, enlarged\na little into three swellings or ganglia. These are the early\nrepresentatives of the medulla, the optic lobes, and the thalamus;\nwhich last may be regarded as the basal and most fundamental part of\nthe cerebrum. This stage may be regarded as lower than that of the\nordinary fish. I have called it, therefore, the _sub-fish stage_.\nThe cerebellum is a subsequent outgrowth from the medulla, as is\nthe cerebrum and olfactive lobes from the thalamus. Fig. 52 may be\nsaid, therefore, to represent fairly the fish-stage. Henceforward the\nprincipal growth is in the cerebrum and cerebellum, both of which are\nsubsequent outgrowths of the original simple ganglia, the medulla, and\nthe thalamus. The cerebrum especially increases steadily in relative\nsize, first becoming larger than but not covering the optic lobes (Fig.\n53). This represents the reptilian stage. Next, by further growth,\nit covers partly the optic lobes (Fig. 54). This may be called the\nbird-stage. Then it covers wholly the optic lobes, and encroaches on\nthe cerebellum behind and olfactive lobes in front (Fig. 55). This is\nthe mammalian stage. Finally, it covers and overhangs all, and thus\nassumes the human stage (Fig. 56).\n\n[Illustration:\n\n  FIG. 54.--Bird-stage. _of_, olfactive lobe; _cr_, cerebrum; _th_,\n      thalamus; _ol_, optic lobe; _cb_, cerebellum; _m_, medulla.\n]\n\n[Illustration: FIG. 55.--Mammalian stage.]\n\n[Illustration: FIG. 56.--Human stage.]\n\nWe have spoken thus far only of relative _size_; but progressive\nchanges take place also in complexity of structure--i. e., in the\ndepth and number of convolutions of the cerebrum and cerebellum. The\ncerebrums of fish, of reptile, bird, and lower mammals are smooth.\nAbout the middle of the mammalian series it begins to be convoluted.\nThese convolutions become deeper and more numerous as we go upward in\nthe scale, until they reach the highest degree in the human brain.\nThe object of these inequalities is to increase the surface of gray\nmatter--i. e., the extent of the force-generating as compared with\nthe force-transmitting part of the brain, or battery as compared with\nconducting-wire. Now, in embryonic development the human brain passes\nalso through these stages of increasing complexity of organization.\nHere also the ontogenic is similar to the taxonomic series.\n\nNow, why should this peculiar order be observed in the building of the\nindividual brain? We find the answer, the only conceivable scientific\nanswer to this question, in the fact that _this is the order of the\nbuilding of the vertebrate brain by evolution_ throughout geological\nhistory. We have already seen that fishes were the only vertebrates\nliving in the Devonian times. The first form of brain, therefore, was\nthat characteristic of that class. Then reptiles were introduced;\nthen birds and marsupials; then true mammals; and, lastly, man. The\ndifferent styles of brains characteristic of these classes were,\ntherefore, successively made by evolution from earlier and simpler\nforms. In phylogeny this order was observed because these successive\nforms were necessary for perfect adaptation to the environment at each\nstep. In taxonomy we find the same order, because, as already explained\n(page 11), every stage of advance in phylogeny is still represented\nin existing forms. In ontogeny we have still the same order,\nbecause ancestral characteristics are inherited, and family history\nrecapitulated in the individual history.\n\n[Illustration: FIG. 57.--A, brain of extinct Ichthyornis; B, modern\ntern.]\n\n[Illustration: FIG. 58.--A, brain of Eocene dinoceras; B, Miocene\nbrontothere; C, modern horse.]\n\nBut not only is this order found in the evolution of the whole\nvertebrate department, but something of the same kind is found also\nin the evolution of _each class_. The earliest reptiles, the earliest\nbirds, and the earliest mammals had smaller and less perfectly\norganized brains than their nearest congeners of the present day.\nThis is shown in the accompanying figures (Figs. 57 and 58). To\ncarry out one example more perfectly: In the history of the horse\nfamily, in connection with the changes of skeletal structure already\ndescribed (page 108), we have also corresponding changes in the\nsize and structure of the brain; _pari passu_ with the improvement\nof the mechanism we have also increased engine-power and increased\nmuscular energy and therefore increased activity and grace. The brain\nof a modern horse, though not very large, is remarkable for the\ncomplexity of its convolutions. The great energy, activity, and nervous\nexcitability of the horse are the result of this structure.\n\n=Cephalization.=--Thus, in going up the phylogenic, the taxonomic,\nor the ontogenic series, we find a gradual process of development\nheadward, brainward, cerebrumward; or, more generally, we might say\nthat in all organic evolution we find an increasing dominance of the\nhigher over the lower, and of the highest over all. For example, in\nthe lowest plane of either series we find first the different systems\nimperfectly or not at all differentiated. Then, as differentiation\nof these progress, we find an increased dominance of the highest\nsystem--the _nervous system_; then in the nervous system, the\nincreasing dominance of its highest part--the _brain_; then in the\nbrain the increasing dominance of its highest ganglion--the _cerebrum_;\nand, lastly, in the cerebrum the increasing dominance of its highest\nsubstance--the exterior gray matter--as shown by the increasing number\nand depth of the convolutions. This whole process may be called\n_cephalization_.\n\nShall the process stop here? When evolution is transferred from the\nanimal to the human plane, from the physiological to the psychical,\nfrom the involuntary and necessary to the voluntary and free, shall not\nthe same law hold good? Yes! all social evolution, all culture, all\neducation, whether of the race or the individual, must follow the same\nlaw. All _psychical advance is a cephalization_--i. e., an increasing\ndominance of the higher over the lower and of the highest over all; of\nthe mind over the body, and in the mind of the higher faculties over\nthe lower; and, finally, the subordination of the whole to the highest\nmoral purpose.\n\n[Illustration: FIG. 59.--Homocercal tail-fin. A, form; B, structure.]\n\n[Illustration: FIG. 60.--Heterocercal or vertebrated tail-fin. A, form;\nB, structure.]\n\n=4. Fish-Tails.=--Still another and last example: It has long been\nnoticed that there are among fishes two styles of tail-fins. These\nare the even-lobed, or homocercal (Fig. 59), and the uneven-lobed,\nor heterocercal (Fig. 60). The one is characteristic of ordinary\nfishes (teleosts), the other of sharks and some other orders. In\n_structure_ the difference is even more fundamental than in _form_.\nIn the former style the backbone stops abruptly in a series of short,\nenlarged joints, and thence sends off rays to form the tail-fin\n(Fig. 59, B); in the latter the backbone runs through the fin to its\nvery point, growing slenderer by degrees, and giving off rays above\nand below from each joint, but the rays on the lower side are much\nlonger (Fig. 60, B). This style of fin is, therefore, _vertebrated_,\nthe other _non-vertebrated_. Figs. 59 and 60 show these two styles in\nform and structure. But there is still another style found only in the\nlowest and most generalized forms of fishes. In these the tail-fin is\nvertebrated and yet symmetrical. This style is shown in Fig. 61, A and\nB.\n\n[Illustration: FIG. 61.--Vertebrated but symmetrical fin. A, form; B,\nstructure.]\n\nNow, in the development of a teleost fish (Fig. 58), as has been shown\nby Alexander Agassiz,[24] the tail-fin is first like Fig. 61; then\nbecomes heterocercal, like Fig. 60; and, finally, becomes homocercal\nlike Fig. 59. Why so? Not because there is any special advantage in\nthis succession of forms; for the changes take place either in the egg\nor else in very early embryonic states. The answer is found in the\nfact that _this is the order of change in the phylogenic series_. The\nearliest fish-tails were either like Fig. 61 or Fig. 60; never like\nFig. 59. The earliest of all were almost certainly like Fig. 61; then\nthey became like Fig. 60; and, finally, only much later in geological\nhistory (Jurassic or Cretaceous), they became like Fig. 59. This order\nof change is still retained in the embryonic development of the last\nintroduced and most specialized order of existing fishes. The family\nhistory is repeated in the individual history.\n\n[Illustration: FIG. 62.--Tail of the Arch\u00e6opteryx.]\n\n[Illustration: FIG. 63.--Tail of a modern bird.]\n\nSimilar changes have taken place in the form and structure of birds\u2019\ntails. The earliest bird known--the Jurassic Arch\u00e6opteryx--had a long\nreptilian tail of twenty-one joints, each joint bearing a feather on\neach side, right and left (Fig. 62). In the typical modern bird, on the\ncontrary, the tail-joints are diminished in number, shortened up, and\nenlarged, and give out long feathers, fan-like, to form the so-called\ntail (Fig. 63). The Arch\u00e6opteryx\u2019 tail is _vertebrated_, the typical\nbird\u2019s _non-vertebrated_. This shortening up of the tail did not take\nplace at once, but gradually. The Cretaceous birds, intermediate in\ntime, had tails intermediate in structure. The Hesperornis of Marsh\nhad twelve joints. At first--in Jurassic--the tail is fully a half\nof the whole vertebral column. It then gradually shortens up until it\nbecomes the aborted organ of typical modern birds. Now, in embryonic\ndevelopment, the tail of the modern typical bird _passes through all\nthese stages_. At first the tail is nearly one half the whole vertebral\ncolumn; then, as development goes on, while the rest of the body grows,\nthe growth of the tail stops, and thus finally becomes the aborted\norgan we now find. The ontogeny still passes through the stages of the\nphylogeny. The same is true of all tailless animals. The frog is tailed\nin the larval condition, because its ancestors were tailed amphibians.\nEven man himself is endowed with a much more considerable tail, viz.,\neight or nine joints, in his early embryonic condition.[25]\n\nWe have taken all our examples from vertebrates, but quite as many\nand as good examples might be found among articulates. Insects, in\nthe larval state, are worm-like in form. Hence it is probable that\nthe earliest progenitors of this class were worm-like. Again, some\ninsects have aquatic larv\u00e6. The progenitors of these--in fact, of\nall insects--were probably aquatic. Crabs, in a larval condition, are\nlong-tailed, and we know that the long-tailed crustaceans (Macrourans)\npreceded the short-tailed (Brachyourans). Water-breathing animals\npreceded air-breathers; the same is true in the ontogeny of the frog,\nof many insects, and, we might add, even of mammals. For the breathing\nof the _f\u0153tus in utero_ is essentially by exposure of f\u0153tal blood\nto the oxygenated blood of the mother in a sort of _gill-fringes_\n(placental tufts). But why should we multiply examples? The whole of\nembryology, in every department, is made up of examples of the same law.\n\n=Illustration of the Differentiation of the Whole Animal\nKingdom.=--Finally, the law of differentiation in the evolution of\nthe whole animal kingdom may be well illustrated by means of the\ndifferent directions taken in the development of the eggs of all the\nvarious kinds of animals. Suppose, then, we have one thousand eggs,\nrepresenting all the different departments, classes, orders, families,\netc., of animals. Many of these may doubtless be identified by form\nor size, or some other superficial character, as the eggs of this or\nthat animal, _but structurally they are all alike_. At first, i. e.,\nas germ-cells, they all represent the _earliest condition_ of life on\nthe earth, and the _lowest forms_ of life _now_. If we now watch their\ndevelopment, we find that some remain in this first condition without\nfurther change. These we set aside. They are _Protozoa_. The remainder\ncontinue to develop, but at first it would be impossible to say to\nwhich of the several departments or primary groups they each belonged.\nThen, by cell-multiplication, the original single cell becomes a\ncell-aggregate. It may be compared now to a compound protozoan, such\nas Foraminifera. The cell-aggregate then differentiates into layers,\nand forms, in fact, a two-layered sac called a gastrula. This is the\nstructure of some of the lowest c\u0153lenterates, such as the hydra. Thus\nfar all seem to go together. But now, for the first time, the primary\ngroups are declared. If it be a vertebrate, for example, the most\nfundamental characters--the cerebro-spinal axis, the vertebral column,\nand the double cavity, neural and visceral, are outlined. Suppose,\nnow, we set aside all other departments, and fix our attention on the\nvertebrates. At first we could not tell which were mammals, birds,\nreptiles, or fishes; but after a while the classes are declared. We\nnow set aside all other classes and watch the mammals. After a while\nthe order declares itself. We select the ungulates. Then the family is\ndeclared, say the _Equid\u00e6_; then the genus, _Equus_; and, lastly, the\nspecies, _Caballus_.[26]\n\nThe same would be true if we followed any other line of development,\nwhether in vertebrates or in any other department. Observe, then, that,\nin following any one line as we have done, there is an increasing\nspecialization, and, if we followed all the lines, an increasing\ndifferentiation, like the branching and rebranching of a tree. Now,\nthis is the type and illustration of what took place in the development\nof the animal kingdom. We conclude that the animal kingdom appeared\nfirst as Protozoa, then as living cell-aggregates or compound\nprotozoans, then as gastrula or two-layered sacs with oral opening.\nThen the great primary departments, unless we except the vertebrates,\ncommenced to separate. This took place before the primordial period;\nfor in the primordial fauna we have all the departments, except\nvertebrates, already declared. This completely explains why it is that\nwe are able to trace homology only within the limits of each primary\ngroup.\n\nBut the question has doubtless already occurred to the thoughtful\nreader, \u201cWhy should the steps of the phylogeny be repeated in the\nontogeny?\u201d The general answer is doubtless to be found in the law of\nheredity--that wonderful law, so characteristic of living things. We\nhave compared it to a brief recapitulation from memory--the minor\npoints, especially if they be also early, dropping out. But can we\nnot explain it further? It is probable that we find a more special\nexplanation in \u201c_the law of acceleration_,\u201d first brought forward by\nProf. Cope. By the law of heredity each generation repeats the form and\nstructure of the previous, and in the order in which they successively\nappeared. But there is a tendency for each successively-appearing\ncharacter to appear a little earlier in each successive generation;\nand by this means time is left over for the introduction of still\nhigher _new_ characters. Thus, characters which were once adult are\npushed back to the young, and then still back to the embryo, and thus\nplace and time are made for each generation to push on still higher.\nThe law of acceleration is a sort of young-Americanism in the animal\nkingdom. If our boys acquire knowledge and character similar to that of\nadults of a few generations back, they will have time while still young\nand plastic to press forward to still higher planes.\n\n=Proofs from Rudimentary and Useless Organs.=--These have to a large\nextent been anticipated under previous heads. The tails of birds and\nthe gill-arches of reptiles are rudimentary. The finger-bones of a\nwhale\u2019s paddle or a turtle\u2019s flipper may be regarded as useless, at\nleast so far as the exact number of constituent pieces is concerned;\nfor an extended surface, without visible joints or separate fingers, is\nall that is seen, and apparently all that is required. The splint-bones\nof a horse\u2019s foot or the dew-claws of a dog\u2019s foot are certainly\nuseless. We have already, in speaking of modifications of structure and\nof embryonic conditions, given many examples of this kind, but it may\nbe well to add some striking examples with this special point in view.\n\nIf different orders of existing mammals were indeed made by gradual\nmodification of some generalized primal form, then it is evident that\nthese useless remnants of once useful parts would be most common in\nthe most highly modified forms. Now, of all mammals, the whales are\nperhaps the most modified or changed from the original mammalian\nform--so much modified, in fact, that the popular eye scarcely\nrecognizes them as mammals at all. Here, then, we might expect, and do\nindeed find, many examples:\n\n1. The baleen whales have no teeth, and no use for them. They have\ninstead a wonderful armature of fringed whalebone plates (baleen),\nby means of which they gather their food.[27] Yet the embryo of\nthe whale has a full set of rudimentary teeth deeply buried in the\njawbone, and formed in the usual way characteristic of mammalian\nteeth--i. e., by an infolding of the epithelial surface of the\ngum--_but the teeth are never cut_; in fact, they reach their highest\ndevelopment in mid-embryonic life, and are again absorbed. Why, then,\nthis waste of developmental energy? Why should teeth be formed only\nto be reabsorbed without being cut? The only conceivable answer is,\nbecause the ancestors of the whale, before the family of whales was\nfairly established, had teeth which were gradually, from generation to\ngeneration, aborted, because no longer used, the baleen plates having\ntaken their place. If whales were made at once out of hand as we now\nsee them, is it conceivable that these useless teeth would have been\ngiven them?\n\n2. Again, many whales have rudimentary pelvic bones, but no hind-limbs.\nWhy should there be pelvic bones, when the sole object of these bones\nis to act as a basis for hind-limbs? In some whales, for example the\nright whale, there are also rudiments of hind-legs, but these are\nburied beneath the skin and flesh, and therefore, of course, wholly\nuseless. The only explanation of these facts is that the ancestors of\nall the whales before they had become whales were quadrupeds, which\nafterward took to the water, and little by little the hind-legs, for\nwant of use, dwindled away to the useless remnants which we now find.\n\n3. Again, whales seem to be hairless, yet rudimentary hairs are\nfound in the skin. Their organs of smell are rudimentary, but made\non the pattern of those of mammals, not of fishes--i. e., they are\nair-smelling, not water-smelling organs. From all these, as well as\nmany other facts, it is evident that the whales descended in early\nTertiary times from some marsh-loving, powerful-tailed, short-legged,\nscant-haired quadruped by modifications gradually induced by increasing\naquatic habits.\n\nExamples of such rudimentary organs might be multiplied without limit.\nAs might be expected, some are found even in man. Such, for example,\nare the muscles for moving the ear, necessary in animals but useless\nin man, and therefore rudimentary. Similarly useless in man are the\nscalp-muscle, used by animals to erect the crest or bristles on the\nhead, and the skin-muscle of the neck and chest, used by animals\nfor shaking the skin of those parts. Most persons have lost the\npower of using these. For my part I can use them all--ear-muscles,\nscalp-muscle, skin-muscle--but they serve no useful purpose.\n\nAgain, and finally, in man and many mammals we find a slender,\nworm-like appendage about three inches long, attached to the c\u00e6cum of\nthe large intestine. Anatomists and physiologists, under the influence\nof that philosophy which maintains that every part of the fearfully\nand wonderfully made human frame was _directly_ contrived to subserve\nsome useful purpose, have puzzled themselves to find the use of this.\nIt probably has no use; on the contrary, it is a continual source of\ndanger. If the human body had been made at once out of hand, it would\nnot have been there. How came it, then? It is the rudimentary remnant\nof an organ--a greatly enlarged c\u00e6cum--which has served, and in some\nmammals still serves, a useful purpose. All these cases are survivals;\nthey are organs which, like many customs in society, have outlived\ntheir usefulness, but still continue by heredity.\n\nBut why multiply examples? All along the track of evolution organs\nbecome useless by changes in the habits of their possessors. They are\nnot, however, shed or dropped bodily at once. No; they are _retained\nby heredity_, but _dwindle by disuse_, more and more, until they pass\naway entirely. But even when they are entirely gone in the adult, they\nare often found still lingering in the embryo. They are among the\nmost obvious and convincing proofs of the origin of organic forms by\nderivation.\n\n\n\n\nCHAPTER VIII.\n\nPROOFS FROM GEOGRAPHICAL DISTRIBUTION OF ORGANISMS.\n\n\nIt is well known that the kinds of organisms found in widely-separated\ncountries differ more or less conspicuously. The traveler in Australia\nor in Africa finds all, the traveler in Europe nearly all, the animals\nand plants wholly different from those he has been accustomed to see\nat home. Even the visitor from the Atlantic to the Pacific coast, if\nhe observes at all, will find nearly all organisms strange to him.\nThe facts of geographical diversity of organisms are so numerous and\ncomplex that, at first sight, they seem utterly lawless. Only recently\nthis subject has been redeemed from chaos and reduced to something like\norder and law by the light thrown upon it by the theory of evolution.\nWe will give, in very brief outline, the most important facts, and then\nshow how they may be explained.\n\n=Geographical Faunas and Floras.=--The group of animals and plants\ninhabiting any locality, whether peculiar to that locality or not,\nis called, in popular language, its fauna and flora. But, in a true\nscientific sense, a fauna and flora is a _natural_ group of animals\nand plants in one place, _differing_ more or less conspicuously\nfrom other groups in other places, and _separated from them by\nphysico-geographical boundaries, or by physical conditions of some\nkind._ The members of such a group can only exist in certain harmonic\nrelations with external conditions, and with one another. These\nrelations with one another are often complex and nicely adjusted,\nso that change in one term is propagated through the whole series\nof terms, giving rise often to the most unexpected results, until\nfinally a new equilibrium is established. Thus, the destruction of\ncertain insectivorous birds, in mere wanton sport, may give rise to the\nmultiplication of insect pests, and this to the destruction of certain\nkinds of plants, and this to the diminution of certain herbivores, and\nthis in its turn to the disappearance of certain carnivores. It is well\nknown that the introduction of rabbits into New Zealand and Australia\nhas produced the most unexpectedly disastrous effect upon certain\ncrops, on account of the absence of the fierce and active carnivores\nwhich keep in check their excessive multiplication in Europe.\n\nNow, among the physical conditions which limit faunas and floras, and\nseparate them from each other, the most important and universal is\ntemperature.\n\n=Temperature-Regions.=--If we travel from equator to pole, we pass\nthrough mean temperatures varying from 80\u00b0 to 0\u00b0. This gives rise\nto a very regular zonal arrangement of plant-forms: 1. We have\nfirst a region in which palms and palm-like forms are abundant and\ncharacteristic, and which therefore may be called the region of palms.\nIt corresponds with the tropic zone. 2. We next have a region in which\nhard-wood foliferous trees are most abundant and characteristic;\nfirst mostly evergreens and then deciduous trees, and therefore may\nbe called the region of hard-wood forests. This corresponds with the\ntemperate-zone. 3. Then we find a region characterized predominantly by\npines and pine-like trees and birches, and may be called the region of\npines. This is the sub-Arctic region. 4. Then a region without trees,\nbut only shrubs and summer plants. This is the Arctic region. 5. And,\nfinally, an almost wholly plantless region of perpetual ice--the polar\nregion.\n\nThese regions are determined wholly by temperature, and therefore, in\ngoing up a mountain-slope to snowy summits, we pass through similar\nregions in smaller space. For example, in going from sea-level to\nthe summits of the Sierra, 14,000 to 15,000 feet high, we commence\nin a region of predominantly hard-wood trees; but at 3,000 feet the\nforests become almost wholly coniferous, at 11,000 to 12,000 feet the\nvegetation becomes shrubby, and at 13,000 feet we reach perpetual snow.\n\nWe have taken plants first, because these, being fixed to the soil and\nincapable of voluntary seasonal migrations, are more strictly and\nsimply limited by temperature--i. e., the arrangement of different\nkinds in zones is more simple and conspicuous. But the same rule\nholds also for animals. In passing from equator to pole, animal kinds\nalso change frequently, so that there are many temperature-faunas in\nwhich the animals are all very different. In both animals and plants,\nspecies, genera, families, etc., are limited by temperature. These are\nfamiliar facts; we recall them to the reader in order that we may base\nthereon a clearer definition of these limits.\n\n=More Perfect Definition of Regions.=--1. The area over which any form\nspreads is called its _range_. Now, the range of a species is more\nrestricted than that of a genus, because, when a species is limited by\ntemperature, another species of the same genus may carry on the genus.\nFor the same reason the range of a family is usually greater than that\nof a genus, and so on for higher classification-groups. For example,\npines range on the slopes of the Sierra from about 2,000 feet to\n11,000 feet, but not the same species. In ascending, we meet first the\nnut-pine (_Pinus Sabiniana_), then the yellow-pine (_P. ponderosa_),\nthen the sugar-pine (_P. Lambertiana_), then the tamarack-pine (_P.\ncontorta_), and last, the _Pinus flexilis_, etc.\n\n[Illustration: FIG. 64.]\n\n2. Where two contiguous temperature-regions come in contact, there is\nno sharp line between; on the contrary, they _shade gradually_, almost\nimperceptibly, into one another, the ranges of species overlapping and\ninterpenetrating, and the two species coexisting on the borders of\ntheir ranges. This is represented by the diagram (Fig. 64), in which\nthe horizontal lines represent the north and south ranges of species of\ntwo groups, A and B, separated by the dotted line.\n\n3. Species also pass out gradually on the borders of these ranges and\nothers come in gradually, so _far as number and vigor of individuals\nare concerned_. If _a a\u2032_ and _b b\u2032_ (Fig. 65) represent the north\nand south range of two species, and _b a\u2032_ their overlap or area of\ncoexistence, then the height of the curves A and B will represent the\nnumber and vigor of the individuals in different parts of the range.\n\n[Illustration: FIG. 65.]\n\n4. While, therefore, there is a shading of contiguous groups into each\nother by overlap of species-ranges; while there is also a gradual\npassing out of species so far as number and vigor of individuals\nis concerned, yet, in _specific characters_ we observe usually no\nsuch gradation. Species seem to come in on one border with all their\nspecific characters perfect, remain substantially unchanged throughout\ntheir range, and pass out on the other border, still the same species.\nIn other words, one species takes the place of another, usually by\n_substitution_, not by _transmutation_. It is _as if_ species had\noriginated, no matter how, each in its own region, and had spread\nin all directions as far as physical conditions and struggle with\nother species would allow. This important subject will be more fully\ndiscussed later.\n\n5. We have thus far spoken of species as limited by temperature alone,\nbut they are limited also by _barriers_. If, then, there be an east and\nwest barrier, such as a high mountain-range, or a wide sea or desert,\nthere will be no shading or gradation of any kind, because the barrier\nprevents overlapping, interpenetration, and struggle on the margins.\nFor example: The species north and south of the Himalayas, or north\nand south of Sahara, are widely different. It is, again, _as if_ they\noriginated each where we find them and spread as far as they could, but\nthe physical barrier prevented mingling and shading.\n\n6. There are temperature-regions south as well as north of the equator.\nNow, although the climatic conditions are quite similar, the species of\ncorresponding temperature-regions north and south are wholly different.\nIt is, again, as if they originated where we find them, and were kept\nseparate by the barrier of tropical heat between. If carried over, they\noften do perfectly well.\n\n\n_Continental Faunas and Floras._\n\nIf the land-surfaces were continuous all around the globe, there is\nlittle doubt that each temperature region with its characteristic\nspecies would also be substantially continuous. There would, it is\ntrue, be some local variations dependent upon soil and humidity,\netc., but substantially the same species would exist all around.\nThe distribution would be almost wholly zonal. But the intervening\noceans are complete barriers to continental species. Hence we ought to\nexpect, and do find, that the faunas and floras of different continents\nare almost totally different. Each apparently originated on its own\ncontinent, and did not spread to other continents, only because they\ncould not get there. It is necessary to explain this in more detail.\n\n[Illustration: FIG. 66.--Polar projection of the earth. 1, tropical; 2,\ntemperate; 3, sub-arctic; 4, arctic; 5, polar regions.]\n\nFig. 66 represents a polar view of the earth, showing the eastern and\nwestern continents, and the five temperature zones already described.\nNow, if we examine the species in each region, commencing at the pole,\nwe find that those of Nos. 5 and 4 are almost identical all around.\nThe reason is obvious. The continents come close together there, with\nice-connection if not land-connection all around. There is but one\ncircumpolar region. But, as soon as we come down to No. 3 and No. 2,\nthe species on the two continents are nearly all different, because\nthere is an impassable barrier between, either in the form of ocean\nor of Arctic cold. For example, the animals and plants inhabiting the\nUnited States are almost wholly different from those in Europe, not\nonly in species, but even largely in genera and to some extent in\nfamilies. There are some exceptions to this rule, but these are of the\nkind which prove the rule, or rather the principle on which the rule\nis founded. These exceptions are mainly of three kinds: 1. _Introduced\nspecies._--All our weeds, many garden-plants, and many animal pests are\nof this kind. They were not found here when America was discovered,\nonly because they could not get here; for, when brought here, they\ndo so well that they often overrun the country and dispossess the\nnative species, as we ourselves have done the Indians. 2. _Hardy or\nelse wide-migrating species._--Hardy species have wide range; they\nmay belong to No. 4 as well as No. 3. If so, they range down to No. 3\non both continents. Migrating birds, such as ducks and geese, etc.,\nbreed in summer in No. 4, and migrate southward in winter on both\ncontinents from the common circumpolar ground. 3. _Alpine species._--It\nis a curious fact that species on tops of snowy mountains in temperate\nregions of the two continents are wonderfully similar, though so\ncompletely isolated. We are not yet prepared to discuss this point.\nWe shall do so later. Suffice it to say now that it can be completely\nexplained.\n\nIn region No. 1 the continental diversity is still greater. Not only\nspecies and genera, but whole families and even orders, are peculiar\nto each continent. The great pachyderms--elephant, rhinoceros,\nhippopotamus--are peculiar to the Eastern; the edentates--sloths and\narmadillos--to the Western. The humming-birds, those gems of the\nforests, of which there are over four hundred species, and the whole\ncactus family, are peculiar to America, while the tailless monkeys are\nequally characteristic of the Eastern Continent.\n\nThe continents do not come together again toward the south, and,\ntherefore, as might be expected, the great difference between the two\npersists to the southern points. The faunas of the southern points of\nSouth America, Africa, and Australia are very different.\n\n=Subdivisions of Continental Faunas and Floras.=--Besides the\nsubdivisions of continental faunas, north and south, determined\nby temperature as already explained, if there be in any continent\nan impassable barrier running north and south, there will be a\ncorresponding difference in the species on the two sides, east and\nwest. We give but one example: The North American Cordilleras or Rocky\nMountains, with their high ranges and desert plains, constitute a very\ngreat barrier between the eastern and western portions of the United\nStates. Hence, we find an extraordinary difference between the species\ninhabiting California and those found in the eastern portion of the\ncountry. Speaking generally, all the species and many of the genera are\npeculiar. The exceptions, too, are significant. Leaving out introduced\nspecies, of which there are many, they are mostly strong-winged or\nwidely-migrating birds, such as the turtle-dove, the turkey-buzzard,\nthe bald eagle, and, of course, many water-birds.\n\n=Special Cases.=--If any body of land is widely separated from\nall other lands by deep seas, we invariably find a corresponding\npeculiarity of its species. Thus, the species inhabiting Australia and\nMadagascar are perhaps the most peculiar in the world. We do not dwell\nfurther on these, because we will discuss them hereafter. There is a\nlittle group of very small islands--the Galapagos--about six hundred\nmiles off the western coast of South America, and surrounded on all\nsides by deep sea. These islands are stocked with a collection of\ncurious animals not found elsewhere on the surface of the earth; but\namong them are no mammals at all. We might multiply examples without\nlimit. Even the rivers emptying in the same sea sometimes have each\nits peculiar species of mussels. In the Altamaha River there are\nseveral species of unios--such, for instance, as the wonderful spinous\nunio--not found elsewhere. How came they there? Howsoever they may have\ncome there, they are now kept isolated there by barriers of land and of\nsalt water.\n\nMany other curious details will come up in our discussion of the origin\nof diversity.\n\n=Marine Species.=--Precisely the same principles apply here; but\ndiversity in the case of marine species is perhaps less marked, and\ncertainly less general, because of the universal oceanic connection.\nOpen-sea species are therefore almost universal. But many marine\nspecies are confined to shallow water, and therefore to shore-lines.\nThe species on the two shores of the same ocean, or the two coasts of\nthe same continent, are different, being isolated east and west by\nbarriers of deep sea or of land, and north and south by temperature.\nAlso about isolated lands, like Australia and Madagascar, the species\nare peculiar.\n\nThus, then, species, genera, etc., are limited in every direction;\nnorth and south by temperature, and in all directions by barriers,\nin the form of oceans, deserts, and mountain-chains. Add to these,\npeculiar climates and soils, and we see that, from this point of view,\nthe whole surface of the earth may be divided and sub-divided into\nregions, sub-regions, provinces, etc. It would carry us too far to\nexplain the primary and secondary divisions adopted by Mr. Wallace, and\nthe somewhat different ones suggested by Mr. Allen. Our main object is\nto discuss the _cause_ of this diversity, and especially to show the\nlight shed upon it by the theory of evolution. We have only given a\nsketch of the facts sufficient for this purpose.\n\n\n_Theory of the Origin of Geographical Diversity._\n\nIt will be observed that all along we have assumed a sort of\nprovisional theory. We have said in every case, it is _as if_ organic\nforms originated where we find them, and have gone thence wherever\nthey could--as far in every direction as physical conditions and\nstruggle with competing species would allow. This view has been\nformulated as the \u201ctheory of specific centers of origin.\u201d There would\nbe less objection to this as a first provisional theory did it not\nassume a supernatural _mode_ of origin. But, in the minds of those\nwho hold it, it has usually assumed expressly or tacitly the form of\n\u201c_specific centers of creation_,\u201d thus implying the immutability of\nspecific types and the supernaturalism of specific origin (page 68). In\nthis latter or usual form it completely fails to account for the facts\ngiven above. For, if this were the mode of origin, each species ought\nin every case to be perfectly adapted to its own environment, and to no\nother. But, on the contrary, introduced species often flourish better\nthan in their own country, and better than the natives of their new\nhomes. In the less objectionable form of \u201cspecific centers of origin,\u201d\nwithout defining the mode of origin, it accounts well for many of the\nmore obvious facts of geographical diversity, as it _now_ exists, but\nnot all. According to this view, the amount of diversity ought to be in\nstrict proportion to the completeness of isolation, or impassableness\nof the separating barriers; but this is not _exactly_ true. There is\nanother element, not yet mentioned, which is just as important as\nimpassableness, but which until recently has been left entirely out\nof account. This is the element of _time_--the amount of time since\nthe barrier was set up, or during which it has continued to exist.\nThese two elements, it is true, are closely connected with each other;\nfor, since all changes in physical geography have taken place very\nslowly--since barriers in the form of mountain-ranges and seas have\nincreased by slow process of growth--it is evident that impassableness\nis, to some extent, a measure of time. But they are by no means in\nstrict proportion. The one or the other may predominate.\n\nNow, this time-element connects geographical distribution with changes\nof physical geography and climate in _geological_ times, and especially\nwith the _latest_ of these changes, viz., those occurring during the\n_Glacial epoch_. During that remarkable epoch extraordinary changes\nof climate, from extreme Arctic rigor to great mildness, enforced\nwide migrations of species southward and northward; while concomitant\nchanges of physical geography, by elevation of the earth\u2019s crust over\nwide areas, opened highways between previously-isolated continents,\npermitting migrations in various directions, and by subsequent\ndepression again isolating the migrated species in their new homes.\nIt is evident, then, that the recognition of the element of almost\nunlimited time at once introduces into the question of geographical\ndistribution the _idea of evolution_. If the study of geographical\ndistribution, as _it now exists_, and as a part of science of physical\ngeography, gave rise naturally to the theory of \u201cspecific centers of\norigin,\u201d the study of the same, in connection with geological time,\nand as a part of geological science, now demands its explanation by the\ntheory of evolution.\n\nIt must be borne in mind, then, that geographical diversity of\norganisms is not a question of the present epoch only. There has\nbeen geographical diversity in every previous geological epoch; it\nis, therefore, a question of geology as well as of biology. It is\nprobable, however, that diversity has increased with the course of\ngeological times, and is greater now than ever before. In other words,\nin the evolution of the organic kingdom, the law of differentiation\nhas prevailed here, as in other departments of biology. A clear\nstatement of the causes of the _present_ distribution of organisms\nmust embrace also the causes of geographical diversity _generally_.\nWe give, therefore, at once a brief statement of what seems to us the\nmost probable view, and shall then proceed to show how it explains the\npresent distribution.\n\n=Most Probable View of the General Process.=--Bearing in mind, then,\nthis time-element, the phenomena of geographical diversity are best\nexplained by the following suppositions: 1. A gradual progressive\nmovement (evolution) of the organic kingdom, marching, as it were,\nabreast, at equal rate along the whole line--i. e., in all parts of\nthe earth, and throughout all geological times, under the action of\nall the forces or factors, and following all the laws, of evolution\nalready explained (pages 19 and 73). If this were all, there would be\nno _geographical_ diversity, although _organic diversity_ might be\nas great as it is now. There would be differentiation of forms and\nstructure everywhere, but no differentiation of groups in different\nlocalities. 2. Under the influence of different conditions in\ndifferent places, more or less isolated from one another by climatic\nor physical barriers, the onward movement (evolution) of organic\nforms takes different directions and different rates, and gives rise\nto local groups, which become more and more differentiated, without\nlimit as time goes on. This element, acting by itself throughout all\ngeological times, would ere this have produced an extreme geographical\ndiversity, such as does not anywhere exist. 3. From time to time, at\nlong intervals, extensive changes of physical geography and climate,\nproduced by crust elevations, partly enforce by change of temperature,\nand partly permit by opening of gateways, extensive migrations and\ndispersals of species, by which mingling and struggle for life and\nfinal readjustment takes place, and extreme diversity is prevented.\nSuch mingling of different faunas and floras on the same ground,\nand the severe struggle for life that thus ensues, and the survival\nof the fittest in many directions, are, as already shown, among the\nmost powerful factors of evolution. They tend to _increase organic_\ndiversity, but to _diminish geographical_ diversity. 4. At the close\nof such great periods of change as indicated in the last, by contrary\nmovement of the earth-crust--i. e., subsidence--new barriers are set up\nand new isolations are produced, and the process of divergence again\ncommences and increases steadily so long as the barriers continue to\nexist.\n\nNow, the last of these periods of great changes and extensive\nmigrations, and subsequent isolations, was the Glacial epoch. It was\nthis epoch, therefore, which mainly determined the present geographical\ndistribution of species. Thus, the present distribution is a key to the\ndirections of the last great migrations, and therefore to the nature of\nthe changes in physical geography and climate which then occurred; and,\nconversely, the character of these changes, determined in other ways,\n_furnishes the only key to the present distribution of species_.\n\nBefore applying the foregoing principles in the explanation of special\ncases, it may be well to give a very brief outline of the condition of\nthings during the Glacial epoch.\n\nIn America, during this epoch, by increasing cold the southern margin\nof the great northern ice-sheet crept slowly southward, until it\nreached the latitude of about 38\u00b0 to 40\u00b0. Arctic species were thus\ndriven southward slowly, from generation to generation, until they\noccupied the whole of the United States, as far as the shores of\nthe Gulf, while temperate species were forced still farther south,\ninto Central and South America. This period of extreme rigor and\nsouthward migration was followed by a period of great mildness,\nduring which the ice and its accompanying Arctic conditions retreated\nnorthward, followed by Arctic species. More than one advance and\nretreat, apparently, occurred during this time. Again, during the\nsame time, brought about by northern elevation, there was broader\nconnection than now exists between North and South America, and free\nmigrations between, in both directions, enforced by extreme changes\nin temperature. Also, during this or previous time, there were broad\nconnections between North America and Asia, in the region of Behring\nStrait, and between America and Europe, in high-latitude regions, and\nextensive migrations of faunas and floras between were thus permitted.\nThe necessary result of all these migrations of species, partly\nenforced by changes of climate, partly permitted by opening of gateways\nsince closed, was exceptionally rapid changes in organic forms. This\nwas the result of two causes: First, the severer pressure of a changing\nphysical environment; and, second, a severer struggle for life between\nthe natives and the invaders.\n\nIn Europe, during the same time and from similar causes, there were at\nleast three or four different faunas struggling together for mastery\non the same soil. First, there were the Pliocene indigenes, who had,\nif any, pre-emption right to the soil; second, invaders from Arctic\nregions, driven southward by increasing cold; third, invaders from\nAsia, permitted by the removal of the old sea-barrier which once\nextended from the Black Sea to the Arctic, and of which the Caspian and\nAral are existing remnants, and thus opening a gateway for migration\nwhich has remained open ever since; fourth, invaders from Europe and\nAsia into Africa, and sometimes back again into Europe, by opening\nof gateways through the Mediterranean, which have been since closed.\nOne of these highways was through Gibraltar, and one from Italy to\nAfrica through Sicily. As in America, so here, in even greater degree,\nthe severe pressure of changing environment and the severe struggle\nfor life produced rapid changes of organic forms. Many species were\ndestroyed; others saved themselves by modifications adapted more\nperfectly to the changed conditions. There is little doubt that\nman came into Europe with the Asiatic invasion, and was one of the\nprincipal agents of change, especially in the way of destruction of\nmany old forms.\n\nSuch is a very brief outline of the last great geological change and\nits general results. Being the last, this one has left the strongest\nand most universal impress on the _present_ geographical distribution.\nBut similar changes by crust oscillations, if not also by extreme\nchanges of climate, have repeatedly occurred in geological times, and\nsome of the most remarkable geographical faunas and floras are the\nresult of these earlier geological changes. We will now give a few\nexamples illustrating these principles:\n\n1. _Australia_ is undoubtedly more peculiar in its fauna and flora than\nany other known country. Not only are all its species peculiar, not\nfound elsewhere on the face of the earth, but its genera, its families,\nand even many of its orders of animals and plants, are also peculiar.\nThese facts are so familiar that it is unnecessary to dwell on them.\nI need only mention, among plants, the whole of the simple-leaved\nacacias, already mentioned on page 86, of which there are so many\nspecies, and the whole family of the eucalyptids, of which there are\nseveral hundred species. Among animals I need mention only the order\nof monotremes, or egg-laying mammals, and nearly the whole order of\nmarsupials, or pouched animals, of which there are over two hundred\nspecies. On the other hand, the true typical mammals are entirely\nabsent, with the exception of a few bats and a few rats, which have\nevidently been accidentally introduced from abroad.\n\nAnother very noteworthy fact, which must be taken in connection with\nthe last, is that Australian forms are far less advanced in the race of\nevolution than those of any other country--i. e., that many old forms\nwhich have long ago become extinct elsewhere are still retained there.\nA few examples will suffice. The marsupials just mentioned are an old\nform once universally distributed, but now nearly extinct everywhere,\nexcept in Australia; the cestracion, or Port Jackson shark, and the\nceratodus, are Pal\u00e6ozoic and Mesozoic forms retained only in Australia.\n\nWhat is the explanation of these remarkable facts? We find the\nsufficient answer in the fact that Australia has been long isolated\nfrom all other countries. While geographical changes in geological\ntimes have mingled more or less the organic forms of other countries,\nand the sharp struggle for life has produced more rapid advance and\nthe production of many new and higher forms better armed for the\nbattle of life, Australia has remained isolated from competition, and\ntherefore comparatively unprogressive.\n\nCan we tell when Australia was finally isolated? Approximately we can.\nThe class of mammals is divided into two groups, which differ widely\nfrom each other; so widely, that they are called sub-classes. These\nare placental mammals, or true typical mammals, and non-placental or\nreptilian mammals. The non-placentals include only the marsupials and\nthe monotremes (ornithorhyncus and echidna). The monotremes actually\nlay eggs and incubate them. In the marsupials the embryo has no\nplacental connection with the mother, and is born in a very imperfect\ncondition, utterly unfit for independent life, and placed in the pouch\n(marsupium), and _permanently_ attached there to the teat until it is\ncapable of independent life; after which only it voluntarily nurses\nlike other new-borns. In other words, the gestation commenced in the\nwomb is completed in the pouch. The uterine gestation in the opossum\nis only seventeen days, while the marsupial gestation is about two\nand a half months. In a kangaroo seven feet high in sitting position\nthe embryo at birth is only one inch long--a pink, hairless, almost\namorphous mass. The monotremes are pure oviparous animals, like birds\nand reptiles. The marsupials might well be called _semi-oviparous_.\nIn pure egg-layers the whole embryonic development is outside of the\nbody; in pure young-bearers the whole is within the body; in marsupials\nit is partly within and partly without. Now--1. The monotremes are\nfound nowhere but in Australia and the neighboring New Guinea. 2. The\nmarsupials are also all confined to the Australian region, except a few\noppossums in America. 3. There are some two hundred and thirty species\nof non-placentals in the Australian region. 4. As already said, there\nare no true mammals at all in Australia, except a few bats and rats\nwhich have come accidentally from abroad. 5. But non-placentals existed\nabundantly in _Mesozoic times everywhere_, both in Europ-Asia and in\nAmerica, while true mammals did not appear at all on the surface of\nthe earth until the _Tertiary_, when they almost immediately became\nvery abundant everywhere, except in Australia. _Evidently, therefore,\nAustralia was isolated before the Tertiary._ The enormous difference\nbetween its fauna and flora and those of other countries is due to\nat least three things: 1. So long an isolation necessarily produced\ngreat divergence of forms. This alone, however, would not affect the\n_grade of organization_. 2. Saved from wide migrations, and especially\ninvasions from Eurasia, the great field of competitive struggle, it was\nleft far behind in the race of evolution. Hence many of its forms are\narchaic; its mammalian fauna, for instance, is still in the Mesozoic\nstage. 3. Its distance from other large continents is so great that\naccidental colonization has been very slight, only extending to a few\nbats and a few rats.\n\nI stop a moment to insist on the effect of competitive struggle in\ndeveloping organic forms strong for the battle of life. Of all the\ncontinents, Eurasia has been the scene of most frequent geological\nchanges, and therefore the arena of fiercest competitive struggle\nthrough wide and frequent migrations. Eurasian species, therefore, are\nthe strongest of all. They have conquered wherever they have gone.\nSpecies in isolated regions are usually the weakest. The great moas\nand the dodo could not have continued to exist unless protected in a\nsort of bomb-proof. Kangaroos would now be quickly exterminated by the\nintroduction of fierce Eurasian carnivores.\n\n2. _Africa._--The fauna of that part of Africa north of Sahara is\nessentially Mediterranean--i. e., a sub-group of the Eurasian. Sahara,\nrather than the Mediterranean Sea, is the true intercontinental\nbarrier. The true African region, therefore, is south of Sahara. Now,\naccording to Mr. Wallace, whom I mainly follow here, the true African\nmammalian fauna consists of two very different groups of animals. The\none is a group of very small, curious animals, mostly low forms of\ninsectivores and lemurs, very peculiar to this region, though more\nresembling those of Madagascar than of any other region; the other\nis a group of large and powerful animals which dominate the region.\nThese latter are similar to, though not identical with, those which\ninhabited Eurasia in Pliocene times. The great carnivores, pachyderms,\nand ruminants of the region are examples of this group. Now, the\nexplanation of these facts is as follows: The indigenes of Africa are\nthe animals of the first group. Africa, in Tertiary times, was isolated\nfrom the great field of combat, Eurasia, and therefore its animals were\nsmall, of low grade, and peculiar. During later Tertiary (Pliocene)\ntimes, then, Africa was inhabited by animals of the first group, while\nEurasia was dominated by animals of the second group. These two groups\nwere then separated by the Desert of Sahara, or else by a sea in that\nregion. Some time during the Glacial epoch geographical changes removed\nthis barrier, and climatic changes drove the Eurasian animals southward\ninto Africa, where, finding congenial climate, they took possession\nof the continent, dominating the feebler natives. Subsequently they\nwere isolated there by the formation of the desert, and the process\nof divergence commenced, and has gone on to the formation of many\nnew forms. Meanwhile the change, partly by extinction and partly by\nmodification, has gone on still more rapidly in Eurasia, but in a\ndifferent direction. Hence, Africa is regarded as one of the primary\nfaunal regions.\n\n3. _Madagascar._--This, next to the Australian, is probably the most\npeculiar faunal region known. There is probably not a single mammalian\nspecies found there which is known to occur anywhere else. It is\nremarkable also as the principal home of that strange, generalized,\nancient form of monkeys--the lemurs. And yet its animals, though\nvery different, have a distant resemblance to those of Africa; not,\nhowever, to the present dominant type, but to those we have called\nthe indigenes. Not one of the northern invaders is found there. The\nobvious conclusion from these facts is, that Madagascar was formerly\nunited with Africa, and both were occupied by the same mammalian fauna\n(which may be called African indigenes, although they were considerably\ndifferent from their descendants of the present day), but became\nseparated before the northern invasion. The effect of this invasion\nwas to hasten the steps of change in the indigenous fauna of Africa,\npartly by extermination, partly by modification, while the isolated\nportion in Madagascar went on at the usual slow rate of change in\nisolated regions. The time since the separation (which was certainly\nduring the Tertiary period) has been sufficiently long to produce very\ngreat divergence in both, but _especially in the African indigenes_. In\nthe fauna of Madagascar, therefore, we have a nearer approach to the\noriginal fauna of both. On account of this long isolation, we have here\nmany ancient types which are extinct elsewhere. The lemurs are such an\nancient type. These are a wonderfully-generalized type of monkeys--a\nconnecting link between monkeys and other mammals, especially\ninsectivores. As might be supposed, from the law of differentiation,\nalready explained (page 11), they are the earliest form, the\nprogenitors, of monkeys. In fact, in early Tertiary times, they were\nfound not only in Africa and Madagascar, but all over the earth, as the\nonly representatives of the monkey family. The true monkeys were not\nintroduced until the mid-Tertiary. In Eurasia and in America (which at\nthat time was probably connected with Eurasia) wide migrations and\nfrequent conflicts of faunas produced comparatively rapid evolution\nof new and higher forms, while in isolated Africa old types continued\nuntil the invasion. Madagascar was spared this invasion, and therefore\nold types are still preserved there. At present, at least three\nquarters of all lemurs are confined to Madagascar, although a few\nspecies are still found in Africa and in the great East Indian islands.\n\n4. =Island-Life.=--Mr. Wallace has divided islands into two kinds,\ncontinental and oceanic islands. The division is undoubtedly a good\none, although we may not always be able to refer an example with\ncertainty to the one or the other class. _Continental_ islands are\nthose on the borders of continents, and separated from the latter\nonly by _shallow water_. _Oceanic_ islands are those, usually very\nsmall, found in the midst of the ocean, with abyssal depth all about.\nContinental islands may be regarded as appendages to the neighboring\ncontinent--as outliers of continents separated by submergence, and\nhave, in fact, been thus formed. Oceanic islands have been formed\ngeologically recently by volcanic action building up from the\nsea-bottom. Continental islands have a continental structure--i. e.,\nthey are composed of stratified as well as of igneous rocks. Their\nstructure is a record of geological history, like that of the\nneighboring continent. Oceanic islands are composed wholly of volcanic\nrocks; or, if there be any stratified rocks, these are only of the most\nrecent date. As examples of continental islands we have New Zealand\nas an appendage of Australia, the great East Indian (Borneo, Java,\nSumatra, etc.) and the Japanese Islands, etc., as appendages of Asia;\nthe British Islands, appendages of Europe; the West Indian Islands,\nappendages of America; Madagascar, an appendage of Africa, etc., etc.\nAs examples of oceanic islands we have the Azores and Bermudas in the\nAtlantic, and the Polynesian islands in mid-Pacific.\n\n_a. Continental Islands._--Now, the fauna of continental islands, as\nmight be expected from the mode of origin of these islands, is similar\nto, though not identical with, that of the neighboring continent; the\namount of difference being in proportion to the _length of time since_\nthey were separated and the _width of the separation_. _Madagascar_,\nfor example, has been long separated from its parent continent, and by\na wide and deep channel. Its fauna, therefore, differs greatly from\nthat of Africa, although resembling it more than that of any other\ncountry. The separation of _New Zealand_ from Australia has been not\nquite so long, and the divergence, therefore, is not so great. These\ntwo will be sufficient illustrative examples of long separation, and\ntherefore of great differentiation of forms.\n\n[Illustration: FIG. 67.--Map of outline of coast of Western Europe, if\nelevated 600 feet (after Lyell).]\n\nOn the other hand, the British Isles are an excellent example of\ncomparatively recent separation. These isles have probably been several\ntimes united and separated from Europe, but we are here concerned only\nwith the more recent. They are now separated from the continent and\nfrom one another only by shallow seas. An elevation of less than six\nhundred feet--geologically a very small change--would bare the bottoms\nof the Irish and English Channels and the North Sea, and connect these\nislands with one another and with the continent (Fig. 67). Now, it is\nwell known that there were during the Glacial epoch, and subsequently,\nseveral oscillations of level sufficient to connect and separate\nthese islands. In the mid-Glacial epoch the British Islands, by\nsubmergence, were nearly obliterated, being reduced to an archipelago\nof small islets representing the high mountains of Wales and Scotland.\nThe Pliocene fauna and flora were, therefore, largely exterminated.\nDuring the close of that epoch they were elevated above the present\ncondition and broadly connected with the continent (Fig. 67), and the\nnewly-exposed land was taken possession of by European species, man\namong the number. Still later--i. e., at the beginning of the present\nepoch--the islands by subsidence were again separated, but not widely,\nfrom the continent. This is the condition now. What, then, was the\nresult? 1. The fauna and flora of the British Isles are substantially\nthe same, but _less rich_ in species than that of Continental Europe,\nsome of the European species being wanting. This shows that the last\nconnection was not a long one; the colonization had not been completed\nbefore re-isolation. 2. This poverty of species is more conspicuous in\nIreland, because colonization is progressive in space as well as in\ntime. Some species had not reached so far when Ireland was re-isolated\nfrom England. The conspicuous absence of snakes, for example, is thus\naccounted for. There is, we all know, another theory to account for\nthis, but we prefer the natural one. 3. The difference between British\nand European fauna and flora is very small, it is true, but there is\nsome difference, varietal if not specific. The reason is, that the time\nsince separation is too small to produce much divergence, and the width\nof the existing barriers not great enough to prevent colonization by\naccidental causes.\n\nThe continental islands of the southern coast of Asia are good examples\nof an intermediate condition as to the length of time since separation,\nand of the consequent degree of differentiation of the faunas and\nfloras.\n\n_Coast-Islands of California._--We give one more example, and dwell\nupon it a little, because it occurs on our own coast.\n\nThe recent studies of Mr. E. L. Greene on the flora of the islands off\nthe coast of California have brought to light some facts which are an\nadmirable illustration of the principles laid down above.\n\nOn looking at a good map of California, any one will observe eight\nor ten islands, some of them of considerable size, strung along the\ncoast from Point Conception southward, and separated from the mainland\nby a sound twenty to thirty miles wide. They are in structure true\ncontinental islands--outliers of the mainland separated by a subsidence\nof a few hundred feet. Moreover, the date of their separation is known.\nThey were certainly connected with the mainland during the later\nPliocene and early Quaternary, for bones of the mammoth, characteristic\nof that time, have been found on one of them.[28] They were therefore\nseparated during the Glacial epoch.\n\nThe main peculiarities of the flora of these islands are the following:\n\n1. Out of nearly three hundred species of plants gathered by Mr.\nGreene, about fifty are wholly peculiar to these islands. 2. Of the\nremaining two hundred and fifty species, nearly all are distinctively\nCalifornian. In other words, the distinctively Californian forms are\nvery abundant, while the common American forms are rare--i. e., the\nisland flora is distinctively Californian, with many peculiar species\nadded.\n\nI explain these facts as follows: The whole coast-region of California\nis geologically very recent, having emerged from the sea as late as\nthe beginning of the Pliocene epoch. As soon as emerged it was of\ncourse colonized from adjacent parts. Since that time its peculiar\nflora has been formed by gradual modification. The environment has been\nsufficiently peculiar, the isolation sufficiently complete, and the\ntime sufficiently long, to make a very distinct group of organisms. It\nis one of Mr. Wallace\u2019s primary divisions of the Ne-arctic region.\n\nDuring late Pliocene and early Quaternary times, as already said, the\nislands were still a part of the mainland, and the whole was occupied\nby the same species, viz., the distinctively Californian species\nnow found in both, together, as I suppose, with the peculiar island\nspecies. During the oscillations of the glacial times the islands were\nseparated by subsidence of the continental margin. Simultaneously with\nthis subsidence, or subsequently thereto, came the invasion of northern\nspecies, driven southward by glacial cold. Then came the mingling of\ninvaders with natives, the struggle for mastery, the extermination\nof many forms--viz., the peculiar island species--and the slight\nmodification of others, and the final result is the California flora\nof to-day. But the island flora was spared this invasion by isolation.\nTherefore the invading species are mostly wanting, the distinctive\nisland species were saved, and the result is the island flora of\nto-day. The island flora, therefore, somewhat nearly represents the\nPliocene indigenes of both.\n\nIt will be observed that this case is somewhat like that of Madagascar,\nbut with a characteristic difference. In the case of Madagascar, the\nseparation has been long. The extreme peculiarity of its fauna is the\nresult partly of progressive divergence and partly of many forms saved\nby isolation. In the case of the coast-islands of California, the time\nhas not been long enough for any great divergence by modification. The\npeculiarity of its species is due almost wholly to species saved by\nisolation.[29]\n\n_b. Oceanic Islands._--We have seen that faunas and floras of\ncontinental islands are somewhat similar to those of the neighboring\ncontinent, though with varying degrees of difference--the amount of\ndifference, or divergence by evolution, being in proportion to the\namount of time and the impassableness of the separating barriers. But\noceanic islands have never been connected with any continent. They\nare new land formed in the midst of the ocean by volcanic action.\nWhen they first appeared they were, of course, without inhabitants\nof any kind, animal or vegetal. How were they peopled? We answer by\n_waifs_ from here and there--by _castaways from other lands_. The\ndominance of particular kinds will depend on the direction of winds\nand currents, bringing from some lands more than others, and upon the\nkinds of animals or seeds of plants most liable to be successfully\ncarried across wide seas. Their faunas and floras, therefore, are\ncharacterized by a mixture of species resembling, though not usually\nidentical with, those of various lands, with a predominance of those\nof some one land, and by the singular and complete absence of mammals\nand amphibians, these being unlikely to be transported by floating\ntimber, as are small reptiles and insects, etc. Among mammals, however,\nthere is a significant exception in favor of bats, the reason being\nboth their power of flight and their habit of concealment in hollow\ntrees, etc. To this explanation, however, we must add that divergence\nby isolation will meanwhile go on in proportion to time. The Azores,\nfor example, have been peopled from Europe, Africa, and America, but\nmostly from Europe, on account of the prevailing winds and currents\nbeing favorable to colonization from that direction. There are many\ncurious peculiarities in the species, however, because colonization is\nvery slow, and divergent variation has been going on _pari passu_. The\nBermudas, on the other hand, have been colonized mainly from America,\nbecause of the current of the Gulf Stream.\n\nThese few examples are sufficient for our purpose, which is only to\nillustrate the causes of geographical distribution. If any one desires\nto pursue this interesting subject, we would refer him to that most\nfascinating book, Mr. Wallace\u2019s \u201cIsland-Life.\u201d\n\n5. =Alpine Species.=--These afford an admirable illustration of the\nfact that in isolated faunas and floras the amount of difference is\nproportioned not only to the completeness of isolation, but also and\nmainly to the _time of isolation_.\n\nIt is well known that Alpine species--i. e., those species inhabiting\nthe region bordering the perpetual snow of lofty mountains--are very\nsimilar to one another, even in the most distant localities, where\ntheir isolation from one another is as complete as possible; as, for\nexample, in the high Alps of Europe, the high mountains of Colorado\nand California. Why is this? We find the key to this mystery in the\nadditional fact that _they are similar also to Arctic species_. A\nsomewhat full explanation is here necessary.\n\nDuring Miocene times, magnolias and taxodiums (bald cypress),\nlike those in forests and swamps of Carolina and Louisiana, and\nsequoias and libocedrus like those now in California, and many other\ntemperate-region forms of plants, grew abundantly in Greenland,\nand northward certainly to 75\u00b0 north latitude. At that time there\ncould not have been any perpetual polar ice, and therefore no Arctic\nspecies, unless on _high mountains in polar regions_. In Pliocene\ntimes perpetual polar ice, and therefore Arctic species, probably\ncommenced to appear. As the cold of the Glacial epoch came on and\nincreased in severity, the polar ice extended southward as a general\nice-sheet, until it reached in America 40\u00b0 and in Europe about 50\u00b0\nnorth latitude. In the United States its margin can be traced as\na distinct moraine through Long Island, middle New Jersey, middle\nPennsylvania; thence, less distinctly, following the Ohio River,\ncrossing the Mississippi; thence following the Missouri, on its south\nside, into Montana. By the increasing cold, Arctic species were driven\nslowly southward, generation after generation, until they occupied\nthe whole of the United States to the Gulf, and the whole of Europe\nto the Mediterranean. As these species on the two continents came\nfrom a _common home_ in polar regions, they were similar to one\nanother, except in so far as some slight divergent modification may\nhave been produced during their southward travel. When the glacial\nrigor declined, and the ice-sheet gradually retreated to its present\nposition, Arctic species, following the snow-edge, went also northward,\non both continents, to their present home in polar regions. But there\nwas an alternative way of migration left open which was embraced by\ncertain plants and insects. While on both continents most individuals\nwent northward, some of them went upward, following the snow-edge into\nhigh mountains, and were left _stranded there_. Thus it has come to\npass that the plants and insects of high mountains in temperate regions\nof different continents, though so widely separated and impassably\nisolated, are extremely similar to one another. But, though similar,\nthey are rarely identical. The time has been long enough for some but\nnot very great divergent modification. It is impossible to conceive a\nmore beautiful illustration of the principles we have been trying to\nenforce.\n\n       *       *       *       *       *\n\nThus, then, undoubtedly all the phenomena of geographical distribution\nof species are most rationally explained on the principle of slow\nevolution--changes, different in different places, and increasing with\nthe time of isolation and its completeness.\n\n=Objection.=--The only objection which can be raised against this\nview is the manner in which contiguous geographical faunas and floras\npass into one another when they are _limited not by barriers but\nby temperature_. In passing from equator to poles, over continuous\nland, we of course pass through many successive faunas and floras,\nlimited wholly or mainly by temperature. Now, if species are indeed\nindefinitely modifiable, then on the borders of contiguous faunas or\nfloras, where one species disappears and another closely allied but\nadapted to a colder temperature takes its place, the one species (say\nthe anti-evolutionists) ought to be gradually _transmuted_ into the\nother, so that all the gradations may be traced. But this is certainly\nnot usually the fact. On the contrary, a species may indeed pass out\ngradually, and another come in gradually, so far as _number and vigor\nof individuals are concerned_; but, in _specific character_, they\nmay be said, usually at least, to come in suddenly, with all their\ncharacters perfect, remain unchanged throughout their whole range, and\npass out suddenly at its borders. Another species takes its place,\noverlapping in range and coexisting on the borders of both; this also\ncontinues unchanged, as far as it goes, and so on. The change from one\nfauna to another is apparently not by _transmutation_ of one species\n_into_ another by gradations, but by _substitution_ of one perfect\nspecies _for_ another perfect species. As a broad general statement,\nthe condition of things is precisely such as would be the case if\nspecific types were substantially immutable by physical conditions, but\nwere originated in some inscrutable way (created) in the regions where\nwe now find them, and have spread in every direction as far as physical\nconditions and struggle with other species would allow them--their\nranges therefore interpenetrating and overlapping one another on their\nborders.\n\nTwo characteristic examples will make our meaning clear. There is not\na more characteristic tree known than the sweet-gum, or liquidambar.\nThis tree grows from the borders of Florida to the shores of the\nGreat Lakes. It may indeed be most numerous and vigorous somewhere in\nthe middle region, and may die out gradually in number and vigor of\nindividuals on the borders of its range, but in specific character it\nis substantially the same throughout, easily recognizable by its dense\nwood, its winged bark, its five-starred leaf, its spinous burr, and its\nfragrant gum. Physical conditions may diminish its number and vigor,\nand limit its extension, but seem powerless to essentially modify its\nspecific character. It seems to give up its life rather than change its\nnature.\n\nAnother striking example: The sequoias (redwood and big-tree) are\nentirely confined to California, and there are only two species now\nexisting, viz., the redwood (_S. sempervirens_) of the Coast Ranges,\nand the big-tree (_S. gigantea_) of the Sierra Nevada. Doubtless they\nare most numerous and vigorous somewhere in the middle of their range,\nand die out gradually in number and vigor on the borders north and\nsouth, being replaced there by other genera better adapted to the\nphysical conditions; but in specific character they remain essentially\nunchanged throughout. They are everywhere the same--easily recognizable\nby wood, bark, leaf, and burr. Both in this case, and in the previous\none of the sweet-gum, it is as if they were created perfect in their\npresent localities, and have spread in all directions as far as\nphysical conditions and the struggle with other competing species would\nallow; but physical conditions seem powerless to change them into any\nother species by adaptive modification.\n\n=Answer.=--We have, we believe, stated the objection fairly. The\nanswer is, that the elements of _time_ and of _migrations_ have not\nbeen taken into the account. In fact, this objection was conceived and\nformulated before the idea of geological time was fully assimilated by\nthe human mind, and our theories of origin adjusted to it. If these\nspecies did indeed originate where we now find them, and _in the\npresent geological epoch_, the argument might at least be entertained;\nbut this is not the fact. We know something of the geological history\nof all these species, and the history of the migrations of some of\nthem. We know that sweet-gums were abundant and of _many species_ in\nthe United States in Tertiary times, and all have become extinct except\nthis remnant. Whatever of modifications there were must be looked\nfor at or about the time of its origin in Tertiary times, not now.\nSpecies, like individuals, are plastic only when young. This one has\nalready become rigid, and all the more so as it is a remnant widely\nseparated from other species. For competition is strongest and most\neffective with nearest allies. Present species are mostly isolated\nremnants--terminal twiglets of the tree of life. Twiglets are of course\nwidely separated at their visible ends. Their points of union with\nother twiglets must be sought below.\n\nIn the case of the sequoias, we know something also of the history of\ntheir migrations. In Miocene times they were abundant, and of many\nspecies in circumpolar regions. Some twenty-four species of fossil\nsequoias are known, fourteen of which are Tertiary. By the cold of\nthe Glacial epoch they were driven slowly southward, both in America\nand in Europe--in America as far as Southern California. After the\nGlacial epoch, and the return of temperate conditions, they doubtless\nattempted to go northward again; but these great changes were too much\nfor them; they were wholly exterminated in Europe, and nearly so in\nAmerica. A few were left stranded high up on the slopes of the Sierra\nNevada, and on the cool, moist slopes of the Coast Ranges. The species\nnow in California are not identical with those found in the Miocene\nstrata of Greenland; but the difference is only what we might expect\nafter such extensive migrations and such long and severe struggle for\nlife. Further, it is noteworthy that the Miocene species fall into two\ngroups, viz., the yew-like leaved and the cypress-like leaved. These\nare represented to-day in California, the one by the redwood, the other\nby the big-tree. They are evidently direct descendants of the Miocene\nspecies, though somewhat modified.\n\nBut it will be objected that there ought to be some cases of\ntransitional forms showing transmutation--in fact, there ought to\nbe some cases of species now forming under our eyes. There are, we\nbelieve, examples of such cases. But intermediate forms are not likely\nto be maintained long, especially if migrations occur to give rise to\nsevere conflict of forms. In that case the intermediate forms are soon\neliminated, and species become distinct. This important point will be\ndiscussed more fully in the next chapter.\n\n\n\n\nCHAPTER IX.\n\nPROOFS FROM VARIATION OF ORGANIC FORMS, ARTIFICIAL AND NATURAL.\n\n\nAs already stated, page 40, the use of the method of experiment in\nthe field of biology is, unfortunately, very limited. Nevertheless,\nit is already beginning to be used more and more in the department\nof physiology, and may be used also, to a limited extent, in the\ndepartment of morphology. It is true that direct _scientific_\nexperiments, for the express purpose of producing permanent\nmodifications of form, and thus testing the theory of evolution, are of\ncomparatively little value as yet, because the all-important element\nof time is wanting. The steps of evolution are so slow, and the time\nnecessary to produce any sensible effect is usually so great, that, in\ncomparison, man\u2019s individual lifetime is almost a vanishing quantity.\nBut, from time immemorial, experiments have been _unconsciously_\nmade by man on domestic animals and food-plants, which bear directly\non this subject. All domestic animals and food-plants, and many\nornamental flowering plants, have been subjected for ages to a process\nof artificial selection acting upon natural variation of offspring.\nAs wild species are modified, we believe, indefinitely by divergent\nvariation and _natural_ selection, so domestic species are modifiable\ncertainly largely, perhaps indefinitely, by divergent variation\nand _artificial_ selection by man. We all know the extraordinary\nmodifications which have thus been gradually brought about in domestic\nanimals, such as dogs, horses, sheep, pigeons, etc.; in food-plants,\nas cereal grains, garden-vegetables, etc., and in ornamental plants,\nas roses, dahlias, pinks, etc. We can only give very briefly the\nprinciples of the process by which these extreme modifications are\nproduced, referring the reader to works specially devoted to this\nsubject for more complete accounts.\n\nLet it be borne in mind, then (_a_), that inheritance is not only\nfrom the immediate parents, but from the whole line of ancestry. The\ninheritance from the immediate parents is, doubtless, usually greater\nthan from any other _one_ term of the ancestral series--the effect on\nthe offspring of any previous generation becomes, doubtless, less and\nless as the distance from the offspring increases--yet the _sum_ of\nthe ancestral inheritance is far greater than the immediate parental.\nLet it also be borne in mind (_b_) that true breeding from one form\nfor many generations creates a fund of heredity in that form, and thus\ntends to produce fixity, rigidity, or permanence in that form.\n\n[Illustration: FIG. 68.]\n\nNow, the method of producing artificial breeds, sometimes consciously,\nsometimes unconsciously, is, briefly, as follows: Suppose it be\ndesired to obtain a variety of an animal, say a dog, having a\ncertain character. We start from a common type, _a_ (Fig. 68). If\nthis type were allowed to breed naturally, the slight divergent\nvariation of offspring represented by the radiating lines would\nneutralize one another by interbreeding, the individual differences\nwould be \u201c_pooled_\u201d in a common stock, and the species would remain\nsubstantially constant. But if among all these slightly divergent\nvarieties we select one, _b_, which seems in the right direction, and\nruthlessly destroy all the others (indicated by crossing them out by\nthe circular line), and breed this variety, _b_, only, we shall get\nagain a number of divergent varieties. It may be that the larger number\nof these will be backward, in the direction of the original type _a_,\non account of the ancestral heredity in that direction, but some will\nagain be in the desired direction. Let all the varieties other than\nthe desired one, but especially the backward-going or reverting ones,\nbe again destroyed, and the one kind only selected which seems to be\nin the right direction, viz., _c_. As we push the form thus from\ngeneration to generation in the desired direction, especially if we\nattempt to hasten too much the process, the resistance to movement--if\nI may use the expression--in that direction becomes greater and greater\n(shown by the decreasing distances between the successive points of\ndivergence, _a_, _b_, _c_, _d_, etc.), and the tendency to reversion\nbecomes stronger (shown by the greater number and length of the\nbackward-going lines), until finally it is almost impossible to push\nany farther. We will suppose that _x_ is such a limit. But if, now,\nwe breed true on the point _x_, destroying the reversions or backward\nvariations for many generations, we will gradually accumulate a fund\nof ancestral heredity on this point which increases with every added\ngeneration, until finally the tendency to reversion becomes small. The\nvariety _breeds true_ without further interference, or with only very\ngeneral superintendence. Such a permanent variety is called a _race_.\nAfter a race is firmly established for a sufficient length of time,\nand the tendency to reversion is lost, it may itself become a new\npoint of departure for the formation of new varieties or races, in the\nsame or other directions. Thus, during even the brief history of man,\nhave been formed races of the different domestic animals, and useful\nand ornamental plants, differing so greatly from each other that, if\nfound in the wild state, they would unhesitatingly be called different\nspecies, or even in some cases different genera.\n\nNow, if art can vary form so greatly, and in so short time, why may\nnot Nature in limitless time? If art by artificial selection, why not\nNature by natural selection? Nature is as rigid in selection and as\nruthless in destruction: why may we not expect similar or even much\ngreater results? The process is similar in the two cases--i. e.,\nselection among varieties in offspring, only that the selection\nis natural instead of artificial, and the process is so slow that\nthere is little tendency to reversion in the latter case. Suppose,\nthen, we have a gradually changing physical environment, or climate.\nAmong the divergent varieties of any species in each generation,\nthose would be preserved which are most in accordance with the new\nclimate, and the others would perish. This is natural selection, or\nsurvival of the fittest. Add to this the effect of the change in\nthe organic environment. All species are modified by the changing\nphysical environment; but these modified species again all affect\none another in the competitive struggle for life, and the strongest\nor swiftest, or most cunning, survive (natural selection). Add to\nthis, again, the struggle among the males for possession of the\nfemales--for reproductive opportunities--by which only the strongest\nand most courageous, or the most beautiful and attractive, leave\nprogeny which inherit their peculiarities (sexual selection). Add to\nthese, finally, _migrations_, voluntary among higher and involuntary\ndispersals among lower animals and plants, and the consequent mingling\nof faunas and floras--the migrations subjecting them to great change\nof environment, both physical and organic, and the mingling producing\nfiercer struggle for life--and we have in powerful operation many\ncauses of modification. Add, I say, all these causes of modification\ntogether, and then make the process slow and continuous through\nunlimited time, and where is the limit to the degree of change?\nCommencing in any species, from any point of departure, there are\nformed first slight modifications which would be called varieties; then\nthese modifications, continuing in the same direction, form races;\nthese races by wider separation become species, and species in their\nturn become genera, etc. Comparing, again, to a growing tree, varieties\nare swelling buds; when they grow into twigs, they are species; when\nthey branch again into different species, the branching stem becomes a\ngenus, etc.\n\nWe have thus far spoken only of the various forms of one factor, viz.,\nthe Darwinian factor of selection, whether natural or artificial.\nWe have dwelt upon this one, because the natural and the artificial\nprocesses are so similar, and the artificial is so controllable. But\nthere are other factors in operation, in art as well as in nature. We\nhave already spoken (p. 73) of other factors of natural change. We\nhave shown how changing physical environment affects _function_, and\nfunction affects _form and structure_, and how these slight changes are\nintegrated by heredity through many generations. We have also shown how\n_use_ or _disuse_ increases or diminishes the size and change the form\nof parts, and these changes, also, however slight, are integrated by\nheredity.\n\nNow, these factors are operative also in domestication of animals\nand cultivation of plants. No environment is so new and peculiar as\ndomestication and cultivation. The soil and temperature in plants,\nfood and housing of domesticated animals, tend to change form and\nstructure of the offspring, although in a way which it is difficult\nintelligently to control, and thus are prolific of varieties from\nwhich to select. In fact, they often give rise to great and unexpected\nmodifications, called sports, which form points of departure for new\nvarieties and races. Now, in nature, not only are all these causes\nand factors of change in constant operation, but they act together in\na peculiarly complex way. All the members of a fauna and flora, and\nthe physical environment of any locality, constitute together a most\ncomplex and delicately adjusted system of correlated parts. A change in\none part is propagated through the whole system; also, a change in one\nfactor affects all other factors. When we add to this the large amount\nof time, in comparison with individual human life and observation,\nnecessary to produce visible change of form, we can easily understand\nwhy the process is still imperfectly understood, although the _fact_ is\ncertain.\n\nBut it will be asked, Are there, then, no differences between the\nartificially made extreme varieties equivalent, so far as difference\nof form is concerned, to species, and real natural species? There\nare. If there were not, there would never have been any doubt about\nthe derivative origin of natural species. But if it be asked, Are not\nthese differences fundamental, and therefore fatal to the argument for\nevolution derived from this source? we answer, we think not. We will\ndeal frankly and fairly with these differences.\n\n=First Difference, Reversion.=--The strong tendency of artificial\nvarieties to reversion, even during the process of formation, and\nespecially their complete reversion to the original type if the hand\nof man be withdrawn--i. e., if left to themselves, or become wild--is\nsupposed to show an essential difference between such varieties,\nhowever extreme, and true species--is supposed, in fact, to prove an\nindestructible permanency of specific types. Nature disowns these\nartificial forms, and as it were brands them with bastardy. Not only\nso, she strives ever to destroy them. The supporting hand of man is\nnecessary to sustain them. Left to themselves and to Nature, they\nquickly revert to the original type. If all the extreme varieties of\ndogs, from the greyhound and Newfoundland, on the one hand, to the\nterrier and lap-dog on the other, were turned loose on an isolated\nisland, uninhabited by man but full of other animals, and left there\nto shift for themselves--and the island were visited again after a\nlapse of a hundred or a thousand years--it is probable that a uniform\nspecies, something like to, though perhaps not identical with, the\nwolf, would be found. They would have reverted to the original or\nnearly the original wild type from which they were produced by\ndomestication. All or nearly all that was done by man would have been\nundone by Nature. This reversion is one test of species.\n\nBut the reason of this tendency to reversion is obvious: First, the\ntime was too short, the rate of change was too rapid, in the artificial\nformation of these varieties. There was not time enough to accumulate\na fund of heredity on each successive stage of the change. Therefore\nthe form is unstable and the tendency to revert is strong. Compare the\nfleeting days and the hurrying impatience of man with the infinite time\nand the divine patience of Nature! But mere instability is not the\nprincipal cause of reversion. Secondly, in the case of artificial forms\nin a wild state, _natural selection compels reversion_. Every species\nin a wild state must of course be in harmony with the environment. But\nartificially made forms are in harmony with the artificial environment\nof domestication, but not with the environment of nature. In nature\nthe fittest survive, but artificial breeds are not fit to survive in a\nstate of nature. They are therefore quickly destroyed in the struggle\nfor life, or must be modified. Nature immediately begins to select\nthe fittest, and gradually in the course of time produces one or more\nuniform species, similar to that from which they came, or perhaps to\nwhat they would have been by this time if left to the operation of\nnatural causes under the conditions supposed. But natural species, if\nthey are formed, as the derivationists suppose, by the operation of\nnatural causes, can not revert unless the conditions revert; for the\nsame causes which operated to produce, still continue to operate to\nkeep, the species. Take an example:\n\nThe form, the habits, and the instincts of the pointer have been made\nby a slow process of artificial selection of divergent varieties of\noffspring, and by training of individuals continued and its effects\naccumulated through many generations. But this form and these habits\nand instincts, so laboriously produced, would be quickly destroyed by\nNature. The pointer, left to himself, must either change or become\nextinct, because not adapted to the wild state. Such instincts and\nhabits would not only be of no use, but would be incompatible with\nsuccess in the struggle for life. But suppose for a moment that these\nhabits and instincts were useful to the animal in a wild state;\nevidently they would be instantly seized upon by natural selection,\nand not only perpetuated but intensified until a very distinct species\nwould be produced. The same is true of all other races of dogs. If the\nNewfoundland, the greyhound, and the pug were all turned loose in a\nforest, and if each of these kinds were admirably adapted to some place\nin the economy of Nature--for some special mode of food-getting without\ncorresponding disabilities in other directions (as must be the case\nif made by natural selection)--there can be no doubt they would each\nsurvive, and their characters intensified; intermediate forms would\ndisappear (for reasons which we shall see presently), and we would\nsoon have three distinct species, or perhaps we would even call them\ndistinct genera.\n\n=Second Difference, Intermediate Forms.=--Natural species are\ndistinct--marked out with hard and fast lines--while artificially-made\nraces, even though in their typical forms they differ as much or more\nthan natural species, shade into one another by insensible gradations.\nIn answer and explanation of this difference we remark: If species or\nmodified forms of any kind, whether natural or artificial, are made by\nnatural causes, and not at once out of hand by supernatural creation,\nthen of course there must have been gradations in the process of\nmaking. Now, in the artificial case, the whole process as well as the\nresult lies within the limits of observation, while in the natural case\nonly the final result. But it will be asked, Why are the gradations\nnot seen also in the final result? We answer, because the intermediate\nforms are eliminated in the struggle for life, and not reproduced by\ncross-breeding. If artificial races always bred true--i. e., without\ncrossing, as natural species do--they would probably soon be as\nsharply demarked. Cross-breeding is the great cause of the shadings\nbetween domestic races. This brings me to the third and most important\ndifference.\n\n=Third Difference, Cross-Fertility.=--Artificially-made races breed\nfreely and without repugnance with one another, and the offspring\nof such cross-breeding is indefinitely fertile. Natural species\nwill not usually unite with one another, being prevented by sexual\nrepugnance and other causes. Or, if they do sexually unite, there is\neither no offspring, or else the offspring is sterile, and therefore\nthe intermediate form dies out in the first generation; or else the\noffspring is imperfectly fertile, and therefore the intermediate form\nis eliminated in a few generations, and the species remain distinct;\nor else the offspring is more fertile with the parent stocks, and\ntherefore revert to the parent stocks, and still the species remain\ndistinct. Such infertile, or imperfectly fertile, offspring--the result\nof crossing of species--are called hybrids.\n\nThis is regarded as a most important test of true species, as\ncontrasted with varieties or races. There are two bases on which\nspecies may be founded. Species may be based on _form_, morphological\nspecies; or they may be based on _reproductive functions_,\nphysiological species. By the one method a _certain amount of\ndifference_ of form, structure, and habit, _constitutes species_;\naccording to the other, if the two kinds breed freely with each other\nand the offspring is indefinitely fertile, the kinds are called\nvarieties, but if they do not they are called species. The two tests,\nhowever, do not always accord. Every now and then we find undoubted\nmorphological species which may be crossed and produce indefinitely\nfertile offspring. Yet it is certainly true that species are usually\ncross-sterile, while varieties, whether natural or artificial, are\ncross-fertile.\n\nIn explanation of this important difference, let it be observed that\nthere are here two things which must be kept distinct in the mind,\nalthough they are, doubtless, closely allied--viz., sexual repugnance\n(psychological element) and cross-sterility (physiological element).\nThe former is found, of course, only in the higher animals, where\nfertilization is _voluntary_. The latter is universal among all\nliving things. This latter, therefore, is the more fundamental and\nessential element, and the former may be regarded as its psychical\nsign in the higher animals. It is of this latter, therefore--i. e.,\ncross-sterility--that we shall speak mainly.\n\nSuppose, then, we have growing together in the same locality many\nspecies of pines or oaks, or other anemophilous trees. The whole air\nis filled with the pollen of many species, and every germ-cell must\nreceive many kinds of male cells, and yet there are no hybrids, but,\non the contrary, the species remain distinct. So also in case of\nhermaphrodite animals, where the fertilization is involuntary; many\naquatic species are found together in the same locality, and the water\nis filled with sperm-cells of many different species. Many kinds of\nsperm-cells must fall on each germ-cell, and yet there are no hybrids;\nthe species remain distinct. In all such cases we must suppose that\nthere is, among the different kinds of male cells, a struggle for the\npossession of the germ or female cell, or a sort of sexual selection by\nthe female cell among the competing male cells, and the fittest--the\nmost in accord; i. e., those of the same species--prevail. This is\nuniversal. But in the higher animals, in addition to the prepotency\nof male cells of the same species, and comparative infertility in\ncase of union of those of different species, sexual attraction and\nsexual repugnance contribute to the same result, and species are thus\ndoubly separated. Thus sexual selection is of two kinds: selection of\nindividuals for union (psychical), and selection of sperm-cells for\nfertilization (physiological). The one kind is usually the sign of the\nother--attraction the sign of fertility, and repugnance of sterility.\n\nBut in the domestic state it is all otherwise. Free competition between\nindividuals or between cells is not allowed. Thus, for example, among\nplants, crossings may be forced and hybrids made in gardens which would\nnever occur in Nature. The florist prevents fertilization in the same\nkind and compels fertilization of a different kind. If male cells of\nthe same kind were allowed to compete, the result would be different.\nDoubtless the same method would succeed in many lower animals. So also\nin higher animals free competition and sexual selection for union are\noften not allowed, and therefore animals of different species, such as\nthe horse and the ass, unite, which would not do so if they were free\nto select as in the wild state. These two are widely distinct species,\nsometimes even called genera, and therefore the offspring is infertile;\nbut two closely allied species, such as two species of wolf, or of the\nfox, in a domestic state would probably not only unite but produce\nindefinitely fertile offspring. In fact, it is almost certain that the\ndog was made by a mixture of several species of wolf, most, perhaps\nall, of them now extinct.[30] On the other hand, it is not at all\ncertain that the extreme varieties of dogs have not passed the limit\nof greatest attraction, and therefore of greatest cross-fertility, and\nthat, if allowed free choice, as in Nature, they would not breed true,\nor tend to breed true, with their own kind, and intermediate kinds die\nout in the struggle for life.\n\n=Law of Cross-breeding.=--Before going any further in this discussion,\nit is necessary to bring out another point of extreme importance in the\nformation of varieties, both natural and artificial--a point which I\nbelieve throws light upon the very significance of sex itself--I refer\nto the effect of cross-breeding.\n\nIt is a curious and most significant fact that different varieties,\nboth natural and artificial, are, up _to a certain limit_, not only\ncross-fertile and cross-attractive, but even more so than individuals\nof the same variety. Long experience has shown that very close breeding\nof the same variety for a long time fixes the _kind_ but _weakens_ the\n_stock_, especially in fertility, while judicious crossing of varieties\nstrengthens the stock, increasing its fertility, and especially\nproducing _plasticity_ or _variability_. Therefore breeders, if they\nwish to preserve a valuable variety, breed close; but, if they wish to\nmake new varieties, cross-breed. But we have already seen that species\nare usually cross-sterile. Therefore there must be some regular law of\nincrease to a maximum, and again decrease to zero. It is this law that\nI now wish to investigate.\n\nIn the lowest animals and plants multiplication of individuals and\nthe continuance of the kind are independent of sex, and therefore\nin such there may be no sex at all. The sexual elements are not yet\ndifferentiated. An individual divides itself into two; each grows to\nthe original size and again divides into two, and so on, it may be\nindefinitely. In this lowest form of reproduction the individual is\nsacrificed to the kind, or else we may regard the kind as an extension\nof the individual, and reproduction as a modification of growth. But\nthere are other sexless modes of reproduction, found in nearly all\nplants and many lower animals, in which the individuality is not\nsacrificed. The next step in the ascending scale is reproduction by\n_budding_. In this case a bud is formed which grows into a perfect\nindividual, and may remain attached to the parent stalk, forming\ntogether a compound individual, as in most plants and many lower\nanimals, such as the coral; or it may separate and assume independent\nlife, as in some plants and many lower animals. In still other animals,\nas in many hydrozoa, the budding function is relegated to a special\npart, which thus becomes a reproductive _organ_. The next step is the\nplacing of the budding organ, for greater safety, in an _interior\ncavity_. This is the case with aphids. Now, why would not this be an\nexcellent mode of reproduction for all animals, man included? Why\nwas sex introduced at all? There are very sufficient reasons, of\nmany kinds, which may come up later; but the fundamental reason, in\nconnection with evolution, is _the funding of individual differences\nin a common offspring, thereby giving to the offspring a tendency to\ndivergent variation_.\n\nNow, _non-sexual_ reproduction is _absolute true breeding_. The law\nof like producing like is absolute. Heredity is all-powerful, and\ntendency to variation is _nil_. These modes of reproduction are in\nfact but a modification of growth and an extension of the individual.\nEvolution-changes in animals produced in this way only must be very\nslow, since the most powerful factor of evolution, viz., natural\nselection among divergent varieties of offspring, would be wanting.\nIn the earliest times, therefore, before sex was yet declared,\nwe may imagine that physical environment was the great and only\nfactor of change. Sexual reproduction introduces the new element of\nvariation of offspring from which Nature makes her selections; and\nthis element of variation is apparently the result of the union of\n_diverse_ individuals, and the funding of these differences in a common\noffspring, and thus a double inheritance of individual characteristics\nfrom the parents and a multiple inheritance of the same from the\nancestry. See, then, with this end in view, the pains Nature has\ntaken to make the difference between the uniting individuals and the\ndiversity of inheritance by the offspring as great as possible, and\nyet the gradual way in which she has accomplished it. As already said,\nthe lowest form of reproduction is that by _fission_. Next comes\nbudding in _any_ part indifferently. Next comes the relegation of the\nbudding function to a particular part. This is the first appearance\nof a reproductive _organ_. Next comes the placing of this organ, for\ngreater safety, within. Thus far all is non-sexual reproduction--all\na modification of growth--an extension of the individual, like the\npropagation of plants by cuttings and by buds. Then comes sexual\nreproduction in its lowest forms.\n\nIt may be well to stop here, to show the entire difference between this\nand non-sexual modes. The latter, we have seen, is only a modification\nof growth, an extension of the individual. Now, sexual reproduction\nis the opposite of all this. Growth is a constant multiplication of\ncells. One cell is ever becoming two similar cells--or, if we call them\nindividuals, one individual is ever becoming two similar individuals.\nBut in sexual reproduction we have an exactly reverse process. Reduced\nto its simplest terms, sexual reproduction is the fusion of _two\ndiverse_ cells, sperm-cell and the germ-cell, to form _one_ cell,\nthe ovule--literally, a diverse twain forming one flesh. In its\nhigher forms it is the union of diverse _individuals_ to bring about\nthe same result. Instead of one cell becoming two, it is two cells\nbecoming one; instead of one individual becoming two in the offspring,\nit is two individuals becoming one in the offspring. But this great\nchange was not brought about at once, but only in the most gradual\nmanner. First, the sexual elements--sperm-cell and germ-cell--are\nseparated, but _in the same organ_. Then the organs--spermary and\novary--are separated, but in the _same individual_. This is the\ncondition of self-fertilizing hermaphroditism so common among plants\nand lower animals. Then comes cross-fertilizing hermaphroditism; and\nNature takes much pains and uses many ingenious devices to prevent\nself-fertilization and insure cross-fertilization. Now, for the\nfirst time, we have slight individual differences funded in a common\noffspring. Then, in order to absolutely forbid self-fertilization, and\nat the same time allow greater differences in the crossing individuals\nthan could be attained in hermaphroditic individuals, the sex organs\nare separated in _different individuals_, and fertilization can\nonly take place by _voluntary union_. Then, to insure the union of\nsuitable individuals, and forbid the ban between unsuitable, there are\nintroduced sexual attraction and repulsion. Then, last of all, the\ndifference between the two sex-individuals becomes greater and greater\nas we go up. It is conspicuous only in vertebrates and some insects,\nand very conspicuous only in birds and mammals.\n\nWe see, then, as we go up the taxonomic, and undoubtedly also the\nphylogenic series, that there is a cross-breeding of more and\nmore diverse individuals, a funding of more and more divergent\ncharacteristics in a common offspring. Why is this? I answer, for the\nsake of _better results in the offspring_. This is abundantly shown\nby direct experiment. In hermaphroditic plants in which there may\nbe either self-fertilization or else cross-fertilization with other\nindividuals of the same species, the latter produces better results in\nnumber and vigor of offspring. But there are other advantages, more\ndifficult to prove but none the less certain, and of the greatest\nimportance in evolution: First, as already stated, complexity of\ninheritance, like complexity of composition in a chemical substance,\ngives instability to the embryo, and thus liability to variation in the\noffspring; and this in its turn furnishes the material for selection\nof the fittest. Again, it seems to me that there is a direct tendency\nto improve the offspring by a sort of struggle in the embryo among the\nvarious qualities inherited from both sides, and a survival of the best\nand strongest--a sort of pre-potency of strong qualities.\n\nCan divergence of uniting individuals and the funding of diverse\ncharacteristics go any further? It may. The differences of the uniting\nindividual may be still further increased, and the resulting offspring\nstill further improved by the cross-breeding of different varieties\nof the same species, for we thus add varietal differences to sexual\ndifferences in the uniting individuals. It is well known that too\nclose breeding, or consanguineous breeding, or breeding in and in, as\nit is variously called, if continued long, has a bad effect on the\noffspring, weakening the stock, while judicious crossing of varieties\nwithin certain limits of difference has a good effect, strengthening\nthe stock and increasing its fertility. It probably does so in two\nways: one direct, by funding many diverse qualities from both sides,\nand the survival in the offspring of the strongest and best; the other\nindirect, by giving _plasticity_, instability to the embryo, and\nvariability to the offspring, and therefore abundant material for the\noperation of selection, either by man or by Nature. We said, \u201cwithin\ncertain limits of difference.\u201d If the difference is extreme, as in\nextreme varieties and races, then the effect becomes again bad, and\nmore and more so as the limit of specific difference is approached;\nat which limit at last Nature shuts down and forbids the bans. Thus,\nthen, there is in cross-breeding a regular law of effect, increasing to\na maximum and again decreasing, which may be graphically represented\nby a curve (Fig. 69). In this figure the horizontal line represents\nthe ordinary level of the type; distances on this line represent\ndifferences, individual, varietal, or specific; ordinates above or\nbelow represent the effect, good or bad, of crossing. Thus s s\u2032\nrepresent two species, and the line between represents their specific\ndifferences; _r r\u2032_ represent different races or permanent varieties;\n_v v\u2032_ two strong varieties; _d d\u2032_ ordinary individual differences; _c\nc\u2032_ close resembling or consanguineous individuals. The undulating line\nrepresents the effect of crossing these various kinds. It is seen that\n\u201cin-and-in breeding,\u201d _c c\u2032_, produces bad effect (negative ordinates);\nbreeding of ordinary individual differences, _d d\u2032_, keeps the stock at\nthe ordinary level--in its typical form; crossing two strong varieties,\n_v v\u2032_, produces maximum good effect (positive ordinates); crossing\ndecided races produces again bad effects, which become infinitely bad\nas we approach species, S S\u2032.[31]\n\n[Illustration: FIG. 69.]\n\nIt is generally admitted that long-continued very close breeding has a\nbad effect. Even in plants, Darwin has shown that cross-fertilization\nhas better effect than self-fertilization, this last being of course\nthe closest possible breeding. But it is probable that the principal\nbad effect is not on the stock but _on the process of evolution_. Very\nclose breeding weakens the stock, ordinary breeding of individual\ndifferences maintains the stock at the ordinary level and fixes it.\nCross-breeding of varieties strengthens the stock, and also (and this\nis its main advantage) produces plasticity in the stock, gives rise\nto strong divergent variations, or even sports, and thus becomes a\nmain agent in evolution. It is probable, moreover, that the higher\nthe function the more sensitive is it to these effects of breeding.\nTherefore, the effect is greater in man than in any other animal. It is\ntrue that many have doubted the bad effect of close breeding in man,\nand have brought forward formidable statistics to substantiate their\nposition; but these doubtless take no account of the most important\nfunction, the psychic, and especially the most important element in\nevery function, so far as evolution or progress is concerned, viz.,\n_plasticity_ or capability of progressive improvement. The tendency\nof consanguineous breeding, or even the breeding of persons of like\ncharacter and experiences, as in an isolated community, is, if not to\ndeteriorate the physique, at least to fix, stereotype the character,\nand thus to check social progress. Contrarily, the crossing of\nvarieties of the same race seems not only to strengthen but, by the\ndiverse inheritance, to produce plasticity of character and capacity\nfor progress. But the difference between the primary races seems too\ngreat for crossing with advantage. Some degree of sexual repugnance\nwhich undoubtedly exists between the primary races is the psychical\nsign of this fact.[32]\n\nIf, now, we go back to what we said before taking up this subject of\nthe effect of cross-breeding, we at once see that there is an apparent\nflaw in all our reasonings. If close in-and-in breeding produced\nbetter and more numerous offspring than cross-breeding between slight\nvarieties, then, indeed, such varieties would be preserved, and\nincrease in divergence from generation to generation until they became\nspecies. Or, in any case, if, in any way, divergence could reach the\npoint of extreme varieties or races, or what are called sub-species,\nthen commencing cross-sterility would complete the separation, and thus\nform true species. But how can the process of progressive divergence\nbegin, when slight varieties are even more fertile by cross-breeding\nthan by close breeding? Is it not evident that, with every generation,\nthe slight varieties would cross-breed with one another and with the\nparent stock, and thus all varietal differences would be funded into\na common stock, and the type would be preserved unchanged? This, as\nalready pointed out (p. 76), has always been the chief difficulty\nin the way of imagining how varieties can grow into species; and\nthe difficulty is _only increased_ by our discussion of the law of\ncross-breeding. Now, just here, Dr. Romanes\u2019s most important and\nprolific idea comes to our help, and, as it seems to us, completely\nsolves the difficulty.\n\nAccording to Dr. Romanes, no organ is so subject to variation as\nthe reproductive, and this in no respect so much as in degrees and\nkinds of fertility--we might almost say so subject to freaks of\ncross-sterility. Now, suppose we start with any well-defined species\nin a state of nature. With every generation there are many slightly\ndivergent individual varieties, some greater and some less; but these\nare all immediately swamped by crossing with one another and with the\nparent stock, and the species remains unchanged. But suppose among\nthese divergent variations there arise, from time to time, some which\naffect the reproductive organs in such wise that the variety, though\nperfectly fertile with its own kind, is infertile, or imperfectly\nfertile, with other varieties, and especially with the parent stock.\nThe change may be only in the _time_ of flowering in plants, or season\nof heat in animals, or it may be actual infertility in sexual union.\nRight here we have the beginning of a new species. The variety is\nsexually isolated from the parent stock by cross-sterility, and\ntherefore all its peculiarities, however trivial, are preserved by\ntrue breeding. Cross-breeding is necessary to make species, but true\nbreeding preserves them. Cross-breeding tends ever to make varieties,\nbut immediately destroys them again. This constant forming and\nswamping, separating and again merging of varieties, like mixing of\ndough, makes the whole mass (stock) more and more plastic and subject\nto variety. This plasticity finally gives rise to varieties of the kind\nwhich produces species by sexual isolation. By continued merging the\ncentrifugal forces continually increase, but are continually repressed\nby crossing, until finally varieties break away to form species.\n\nNow it is easy to see, from this point of view, why artificial\nvarieties are cross-fertile. It is because in artificial breeding we\nare intent only on making varieties in form, size, color, etc., and not\nat all on making any characterized by cross-sterility with the parent\nstock. Cross-sterility with the parent stock, or with other varieties,\nwould be of no advantage, because we control the breeding, and can\nbreed true if we desire. Sexual isolation is not necessary, because\nwe can use physical isolation. On the contrary, such cross-sterility\nwould be a positive disadvantage to the breeder, by limiting the range\nof his experiments just where they would be most prolific in making\nnew varieties. Hence, as might be expected, all domestic varieties are\ncross-fertile, unless it be the extreme varieties, which may, in some\ninstances, have passed the limit of greatest fertility.\n\nIf this idea be true, then species which have originated in the same\nlocality ought to be always cross-sterile, but species which have\ngrown up apart, in widely separated geographical regions, ought to be\nsometimes cross-fertile, because they were isolated by physical not by\nsexual barriers. Such, Dr. Romanes thinks, is a fact. It is, however,\na very important point, which ought to be carefully investigated. We\nsay \u201c_sometimes_.\u201d It is probable that most geographical species also\nare cross-sterile; for, although the isolation by cross-sterility of\nslight varieties be the main cause of the origin of species, yet a\nspecies formed by isolation of any other kind will gradually become\ncross-sterile with other species. Although cross-sterility be the main\ncause of divergence, yet divergence beyond a certain limit, however\ncaused, will bring about cross-sterility, because the reproductive\norgans will partake of the general change going on in every part.\n\n=Application.=--Suppose, then, a species breeding naturally in a wild\nstate. Individual varieties are constantly being formed and again\nfunded back into the common stock by cross-breeding. If the varieties\nthus formed be decided, the cross-breeding will strengthen the stock,\nand especially will preserve and increase its plasticity or tendency to\nvariation. Finally, among the widely divergent varieties there is one\naffecting the reproductive organs of several individuals in such wise\nthat they are infertile, or imperfectly fertile, with the parent stock,\nthough perfectly fertile among themselves. These form a new species,\nwhich continue to increase indefinitely.\n\n=Objection answered.=--This view completes the answer to an objection\nwhich is often made to evolution: \u201cIf natural species are formed by\ntransmutation, why is it we do not find intermediate links? Why is not\norganic nature made up only of individual forms, shading insensibly\ninto each other in such wise that classification becomes a mere device\nto handle more conveniently complex material? Why is it that groups,\nespecially species, are marked out with hard and fast lines?\u201d We\nhave heretofore answered this by saying that intermediate forms are\neliminated. So they are, but how? Dr. Romanes\u2019s idea of physiological\nselection largely answers this. It is by the funding of _ordinary_\nvarieties into a common parental stock by crossing, and separating\n_specific_ varieties by cross-sterility. Thus the organic field is\nbroken up into points about which variations oscillate. As every mass\nof matter, when closely examined, is found to consist of aggregations\nabout centers of _cohesive_ attraction as discrete granules or\ncrystals, and only exceptionally do we find a homogeneous vitreous\nstructure; even so organic forms aggregate about points of _sexual_\nattraction, and the whole mass consists of discrete species, and only\nexceptionally--i. e., in domestication--do we find insensible shadings.\nNow, species are the smallest aggregate of individuals, as granules\nare of molecules. Species are more distinctly marked out by hard and\nfast lines than are other taxonomic groups only because they are the\n_last_, going downward, that are cross-sterile--because right here is\nthe change from cross-sterility to cross-fertility.\n\nIf this view be true, then in _the same locality_ species ought to be\nalways distinct and without shadings. If we find shadings at all, it\nought to be in intermediate geographical regions, where isolation is\nnot sexual but physical. Now, this is exactly what we find to be the\nfact. _Innumerable examples of such intermediate forms in intermediate\ngeographical regions_ are now known, especially among birds and\nreptiles, and examples have so increased in modern times, by closer\nstudy, that naturalists, especially ornithologists, have been compelled\nto resort to a trinomial nomenclature in order to designate these\ngeographical sub-species.[33]\n\nIf any further explanation is necessary, it will probably be found in\nthe following suggestions:\n\n1. The number of individual varieties constantly being formed is\nalmost infinite, but the number of places in nature is very limited.\nNow, among the infinite number of slight individual varieties formed\nwith every generation, the competitive struggle will be severest\nbetween those most nearly alike, because they are competitors for the\n_same_ place. Only one kind succeeds, viz., the fittest. Intermediate\nforms are, therefore, exactly those which are eliminated in the most\nwholesale way. 2. Add to this the fact that, as soon as divergence,\nfrom whatsoever cause, reaches a certain point, sexual repugnance\nor cross-sterility, or both, come in to perpetuate and increase the\nseparation already commenced. 3. Add to this, again, that migrations\nin higher animals, and involuntary dispersals in lower animals and\nin plants, and the mingling together of different faunas and floras,\nproduces a still fiercer struggle for life, especially between natives\nand invaders, and thus great numbers of forms are destroyed; all but\nthe fittest are weeded out, and therefore the distinctness of the\nremainder is greatly increased. Periods of great changes of physical\ngeography and of climate, and therefore of wide and general migrations,\nare also periods of great weedings-out of unfit forms. Thus it\nhappens that existing faunas and floras are little else than isolated\n_remnants_.\n\nTo illustrate, again, by a growing tree: If all the buds of a tree\nlived and grew, they would soon become so numerous that they would\ntogether form a solid hemispherical mass, like a coral-head, with no\nroom between for leaf or light or air. But ninety-nine one-hundredths\nof buds die in the struggle for light and air, and therefore the\nsurvivors are distinct growing points, widely separated from each\nother. Species are such extreme, but separated, twiglets of the tree of\nlife.\n\n=Objection.=--But it will be objected, again: The twig-_points_\nare, indeed, separate, but the twigs themselves must meet somewhere\nlower down, where they began to grow. Intermediate links may be\nwanting _now_, but they must, of course, have existed once--i. e., in\nprevious geological times, and therefore ought to be found fossil. In\ndistribution in space or geographically, organic kinds may be marked\noff by hard-and-fast lines, but, if their derivative origin be true,\nin their distribution in _time_ or geologically, there ought to be\nmany examples of insensible shadings between them. In fact, if we\nonly had all the extinct forms, the organic kingdom, taken as a whole\nand throughout all time, ought to consist not of species at all, but\nsimply of individual forms, shading insensibly into each other, like\nthe colors of the spectrum, and our classification ought to be a mere\nmatter of convenience, having no counterpart in nature. But this is\nnot the fact. On the contrary, the law of distribution in time is\napparently similar in this respect to the law of distribution in space,\nalready given (page 169). As in the case of _contiguous_ geographical\nfaunas, the change is apparently by _substitution_ of one species _for_\nanother, and not by _transmutation_ of one species _into_ another.\nSo also in _successive_ geological faunas, the change seems rather\nby substitution than by transmutation. In both cases species seem to\ncome in suddenly, with all their specific characters perfect, remain\nsubstantially unchanged as long as they last, and then die out and\nare replaced by others. Certainly this looks much like immutability\nof specific forms, and supernaturalism of specific origin. We have,\nwe believe, satisfactorily explained this in the case of geographical\ndistribution (page 201), but how can we explain it in the case of\ngeological distribution?\n\n=Answer.=--1. The reason for this, given by Darwin and other\nevolutionists, is the extremely fragmentary character of the geological\nrecord. If the existing faunas and floras are but isolated remnants,\nthe rest having been _destroyed_ by migrations and conflicts, how\nmuch more are fossil faunas and floras but fragmentary remnants, the\nrest having been _lost_, partly because never preserved, and partly\nby destruction of the record! If from this cause existing species are\nwidely separated, how much more ought we to expect to find fossil\nspecies distinct and widely separated!\n\nThis is undoubtedly in most cases a true and sufficient answer, yet we\nthink the fragmentariness of the geological record has been overstated.\nWhile it is true that there are many and wide gaps in the record; while\nit is true, also, that even where the record is continuous many forms\nmay not have been preserved, yet there are some cases, especially\nin the Tertiary fresh-water deposits, where the record is not only\ncontinuous for hundreds of feet in thickness, but the abundance of\nlife was very great, and the conditions necessary for preservation\nexceptionally good. In such cases the number of fossil species found\non each horizon seems to be as great as in existing faunas over equal\nspace. The record in these cases seems to be continuous and without\nbreak, and crowded with fossil forms; and yet, although the species\nchange greatly, and perhaps many times, in passing from the lowest to\nthe highest strata, we do not usually, it must be acknowledged, find\nthe gradual transitions we would naturally expect, if the change were\neffected by gradual transformations. The incompleteness of the record,\ntherefore, although a true and important cause, is not the whole cause.\n\nIn further and completer answer to this greatest of all objections, we\nwill throw out the following suggestions:\n\n2. We must remember that considerable latitude is allowed by the\nanti-derivationists to _variation of species;_ so much so, indeed, that\nit is often difficult to draw the line between well-marked varieties\nand closely-allied species. Now, according to the derivationist,\nthese strong varieties, breeding usually true, are naught else than\ncommencing species.\n\n3. On every side and everywhere, both in existing faunas and in fossil\nforms, but especially in the latter, we find innumerable examples of\ntransitions, or intermediate forms, between all the _higher groups_,\nsuch as genera, families, orders, and classes. It is, in fact, by means\nof these that the great law of differentiation from generalized types\nhas been established. It is, therefore, only between _species_ that\nsuch intermediate forms are rare.\n\n4. But even between species such intermediate forms, though rare, have\nbeen pointed out, both in existing and in extinct faunas. But the\nopposition contend that, in all such cases, the previously supposed\nspecies are only varieties. We have already (page 61) spoken of the\nobvious fallacy involved in this position. Species are first defined\nas forms distinct and without intermediate links, and then we are\nchallenged to find such links; and when, with much labor, we find them,\nthey say the supposed species are not species, but only varieties.\nBut there are some cases in which this subterfuge will not do. There\nare cases in which the transitions are between forms so extreme that\nthey can not, by any stretch of the term, be called varieties. We will\nselect and dwell upon but one striking example, viz., the fossil forms\nof the Tertiary fresh-water deposits of Steinheim.\n\nIn W\u00fcrtemberg, near the little village of Steinheim, are found certain\nstrata of sand and lime, which are evidently deposits from a small\nlake of Tertiary times. The deposits are extremely rich in fossil\nshells, especially of the different species of the genus _Planorbis_.\nAs the deposits seem to have been continuous for ages, and the fossil\nshells very abundant, this seemed to be an excellent opportunity to\ntest the theory of derivation. With this end in view, they have been\nmade the subject of exhaustive study by Hilgendorf in 1866,[34] and by\nHyatt in 1880.[35] In passing from the lowest to the highest strata\nthe species change greatly and many times, the extreme forms being so\ndifferent that were it not for the intermediate forms they would be\ncalled not only different species but different genera. And yet the\ngradations are so insensible that the whole series is nothing less\nthan a demonstration, in this case at least, of origin of species by\nderivation with modifications. The accompanying plate of successive\nforms (Fig. 70), which we take from Prof. Hyatt\u2019s admirable memoir,\nwill show this better than any mere verbal explanation. It will be\nobserved that, commencing with four slight varieties--probably sexually\nisolated varieties--of one species, each series shows a gradual\ntransformation as we go upward in the strata--i. e., onward in time.\nSeries I branches into three sub-series, in two of which the change of\nform is extreme. Series IV is remarkable for great increase in size\nas well as change in form. In the plate we give only selected stages,\nbut in the fuller plates of the memoir, and still more in the shells\nthemselves, the subtilest gradations are found.\n\n[Illustration: FIG. 70.--Transformations of Planorbis (after Hyatt).\n\n  _Series IV._ 1, Pl. levis: Undorf. 2, Pl. Steinheimensis;\n      3, tenuis-Steinheimensis; 4, tenuis; 5, discoideus; 6,\n      trochiformis-discoideus; 7, trochiformis: Steinheim.\n\n  _Series III._ 8, Pl. levis: Undorf. 9, Pl. oxystomus; 10, supremus;\n      11, supremus var. turrita: Steinheim.\n\n  _Series II._ 12, Pl. levis: Undorf. 13, Pl. crescens-parvus; 14, 15,\n      crescens: Steinheim.\n\n  _Series I._ _Sub-series 3._ 16, Pl. levis: Undorf. 17, Pl.\n      minutus-levis; 18, minutus; 19, 20, triquetrus: Steinheim.\n      _Sub-series 2._ 21, Pl. minutus; 22, 23, denudatus-minutus; 24,\n      denudatus var. distortus: Steinheim. _Sub-series 1._ 25, Pl.\n      costatus-minutus; 26, costatus; 27, 28, costatus var--: Steinheim.\n\n  The specimens from Undorf all belong to an older Tertiary period than\n      that at Steinheim.\n]\n\nThis case is striking, partly because it is a very favorable one,\nbut mainly because it has been so carefully studied. There can be no\ndoubt that equally careful study would reveal the same transition\nin many other cases. Nor are such transitions confined to the lower\nforms of life, though they are probably more abundant there. According\nto Cope, the nicest gradations may be traced between some of the\nextinct mammalian species so abundant in the Tertiary deposits of the\nWest--especially between the species of the extinct generalized\nfamily of _Oredontid\u00e6_[36] The same is probably true of the many\nextinct species of the horse family.\n\nIt is interesting to observe that the details of the process of change\nin the forms of _Planorbis_ are in accord with Dr. Romanes\u2019s views.\nThe change does not seem to have been uniform but somewhat paroxysmal.\nThe forms seem to remain stable for a long time, and then a few break\ninto several different forms, while the more rigid die out. It is as if\ncross-breeding had kept the type true, but at the same time increased\nits tendency to variation, until finally one or more varieties became\nsexually isolated and thus formed new species.\n\n5. But still the question remains: Why are transitional forms _rare_ in\nall cases, especially between species--so rare that they are eagerly\nsought and highly prized? I believe that the true reason of this is\nthat _the steps of evolution are not always uniform_.\n\nNearly all evolutionists have assumed and even insisted on uniformity,\nas the opposite of catastrophism and of supernaturalism, and therefore\nas essential to the idea of evolution. They say that the constancy of\nthe action of the forces of change necessitates the uniformity of the\nrate of change. But, in fact, this is not always nor even usually true.\nCauses or forces are constant, but phenomena everywhere and in every\ndepartment of Nature are _paroxysmal_. The forces producing storms\nand lightning, and volcanoes and earthquakes, are or may be constant;\nyet the phenomena are in the highest degree paroxysmal. Wherever in\nnature we have a constant force and a strong resistance, we find more\nor less paroxysmal action. For this reason the wind blows in puffs,\nthe friction of wind on water produces waves, water running in small\npipes issues in pulses. The reason is obvious, as may be seen by\nthe following examples: Suppose lifting forces within the earth are\nresisted by crust-rigidity. The forces accumulate uniformly until the\nresistance gives way, and suddenly we have an earthquake. Water running\nwith great resistance in small pipes is checked, but soon accumulates\nadditional force, which overcomes the resistance, only to be again\nchecked, and so on, and therefore runs in pulses. Now, the course of\nevolution of the whole earth may be likened to such a current; there\nare forces of movement and forces of resistance--progressive forces\nand conservative forces. The progressive force is accumulative, the\nresisting force is constant. Thus, in all evolution or history,\nwhether of the earth or of society, there are periods of comparative\nquiet, during which the forces of change are gathering strength, and\nperiods of revolution or rapid change, during which these forces show\nthemselves in conspicuous effects.\n\nNow, that there have been such periods of rapid revolutionary change\nin the history of the earth, there can be no doubt. The history of the\nearth is marked by periods of comparative quiet, during which life was\nexceptionally abundant and prosperous, and change of organic forms\nslow and uniform--separated by periods of disturbance, revolution,\nrapid changes of physical geography and climate, and consequently of\ncomparatively rapid and sweeping changes in organic forms. These form\nthe division-lines between great eras of the earth\u2019s history, and\nare always marked by extensive unconformity of the strata, showing\nthe changes of physical geography above spoken of, and by apparently\nsudden and sweeping change in life-forms, showing the great changes of\nclimate and other physical conditions. Unfortunately, in all cases of\nunconformity of strata, there is, of course, a break in the continuity\nof the record; and when the unconformity is very general a portion of\nthe record may be irrecoverably lost. The consequence is, that there is\nan apparent break also in the continuity of life-forms. It looks, at\nfirst sight, like wholesale extermination of old and recreation of new\nforms. But undoubtedly the break in the continuity of life is apparent\nonly, as is shown by the loss in the record. If we could recover the\nwhole record, as indeed we sometimes do, we should find in all cases\nthat there is no break in the continuity of evolution, but only more\nrapid rate of change at these times. But to this cause of rapid rate\nof progress--i. e., change of physical environment--we must add change\nof organic environment induced by the physical. We have already seen\n(p. 179) that extensive changes in physical geography and climate are\nalways accompanied by wide migrations and dispersals of species, the\nmingling of faunas and floras, and the severer struggle for life,\nand the sweeping weeding-out of all but the fittest, and the change\nof these latter, making them still fitter. These two causes of rapid\nchange, viz., change of climate and migrations, together with the loss\nof record, we believe completely account for those sweeping changes,\nnot only of species but even of genera, families, and orders which\ncharacterize the passage from one great era to another.\n\nBut this does not yet explain the apparent discontinuity between\n_consecutive_ species in the same locality in continuous, conformable\nstrata, or the rarity of transitional forms when one species takes the\nplace of another in an apparently continuous record. In such continuous\ndeposits the successive faunas do indeed gradate insensibly into one\nanother, but apparently as in contiguous geographical regions (p. 200)\nby substitution, not by transmutation. How shall we explain this?\n\nOn this point I throw out some suggestions: 1. In the modification of\nspecies, too, as well as in other progressive changes, we may imagine\ntwo forces operating, one progressive, the other conservative--the\none external, the other internal. The external progressive force\nconsists of all the factors of change already mentioned, the internal\nconservative is the law of heredity, of like producing like. A changing\nenvironment tends continually and increasingly to change of organisms,\nbut change is resisted by heredity, which tends to adhere, within\nnarrow limits, to the same form. But since the external force or\ntendency to change increases constantly--since the discord between the\nenvironment and the organism becomes ever greater, there must come a\ntime when either the species is destroyed, or else the resistance of\nheredity gives way, and rapid change takes place. The alternative is\npresented to the species to transform or perish; and in one or perhaps\nin two or three generations we have an amount of change which, under\nother circumstances, might take a hundred generations to accomplish.\nThese rapid changes are in fact exactly what in artificial varieties\nwe call sports. We do not know all the conditions which determine\nsports in domestication, and still less what determines large and\nwidely-divergent variations, and therefore rapid origin of many\ndivergent species, in geological history. But one thing seems probable,\nviz., that, when a species begins to change, it continues to change\neasily and in many directions. When resistance gives way it takes some\ntime, many generations, for heredity to gather force again. Hence,\nyoung species are plastic, fluent, because heredity, on any one point,\nhas not yet accumulated. But as soon as a stable form is again reached,\nthen, by accumulating a fund of heredity, the form tends to become more\nand more rigid, until often it becomes too rigid to yield to modifying\ninfluences, and therefore becomes extinct. By far the greater number\nof species do thus become extinct and leave no progeny, while the few\nmore plastic forms are modified in several directions, and the number\nof forms may, after a little time, be undiminished or even increased.\n\n2. As to the _cause_ of rapid changes of form during revolutionary\nor critical periods in the earth\u2019s history, Brooks has introduced\nan idea which is very suggestive, and deserves serious attention.\nWe have above spoken of the progressive element as external. Brooks\nregards both elements as internal, and represented by the two sexes.\nThe male represents the progressive, the female the conservative\nelement. The one tends to divergent variation, the other to fixity\nof type by heredity. I think we will all admit that, as a general\nrule, in man (and probably all the higher animals) the male is more\nhighly differentiated into many divergent forms--the female is more\nlike the type-form of the species. In man, the male is certainly more\ndiversified in form, in expression, and in character. If they have the\nkeenest ear for musical pitch, they are also most often music-deaf;\nif they have the sharpest perception of color, they are also most\noften color-blind; if among them we find the brightest intellects, we\nalso find the dullest and most stupid; if there are among them more\ngeniuses, so, also, there are more cranks. The same is also, probably,\ntrue of other animals, in proportion to their grade of organization.\nThe operation of these two equally necessary elements is well shown\nin every advancing society. The initiative of every movement, in all\ndirections, good or bad, is determined by the male; the conservation\nof whatever balance of good there may be, seems to be mainly by the\nfemale. The male tries all things, the female holds fast that which\nis good. By the one society gains a little in each generation; by the\nother the gain is conserved and made a new point of departure. The one\nis ever building hastily a scaffolding and platform; the other ever\nconsolidating into a permanent structure. Now, according to Brooks,\nwhat is true in the plane of social progress is true also in the lower\nplane of organic evolution. In sexual union, and in the resulting\noffspring, the sperm-cell is the element which tends to divergent\nvariation, and the germ-cell to fixity of type, through heredity. In\nartificial breeding, then, we ought to make new varieties by proper use\nof the sire; we ought to preserve them true by proper management of the\ndam.\n\nBut, again, it is believed that in many lower animals, especially\ninsects, the high-feeding of the mother, and consequent good condition\nof the ovum, tends to the production of female offspring. It seems\nalmost certain that, in butterflies, the sex is not yet declared\nin the caterpillar stage. According to the careful experiments of\nMrs. Treat,[37] if the caterpillars be well fed, they become female\nbutterflies; but, if poorly fed, they make males. One purpose of this\nprovision of Nature is, doubtless, to provide for the greater draught\non the vitality of the female in reproduction.\n\nNow for the application. In good times in the history of a species,\nwhen everything is prosperous, external conditions are favorable, and\nfood is abundant, females are in excess, and individuals are greatly\nmultiplied. Under these conditions, evolution would be slow and\nuniform. But in _bad_ times in the history of a species, when external\nconditions were unfavorable, not only would there be excess of males,\nbut these, through the influence of the changing environment, as well\nas through the dominance of the male element, would be more than\nusually varied in character. Among the strongly divergent varieties\nthus formed, the fittest--i. e., those most in accord with the changing\nenvironment--would survive and leave offspring partaking of their\ncharacter. We have already repeatedly said that the severer pressure of\na rapidly-changing environment determines correspondingly rapid changes\nin organic forms. It may do so in many ways; but, according to Brooks,\none of the most important ways is by determining an excess of the male\nelement.\n\nIn brief, then, the causes of rarity of transitional forms among\nfossils are--1. The change being, for the reasons given, comparatively\nrapid, the _number of generations_ between consecutive species are\nfew, perhaps only one. 2. Times of rapid change are also times of\nunfavorable conditions, and therefore the number of _individuals_\nin each generation is small, and all the smaller--in Brooks\u2019s\nview--because of the fewness of females. When we remember that fossils\nare but a small fraction of the actual faunas and floras of the\ntime, surely these two causes go far toward explaining the rarity of\nlinks between _species_. 3. Add to these the existence of periods of\nwide-spread changes in physical geography and climate, and consequent\nwide migrations and dispersals of species, and we sufficiently account\nfor those sweeping changes in species, genera, families, and orders,\nwhich mark the limits of the great eras, and which are made still more\nabrupt, and apparently supernatural, by the loss of record at these\ntimes.[38]\n\n=Objection.=--There is still one more objection which will be made. We\nhave drawings of plants, animals, and men, by Egyptian artists, who\nlived at least three thousand years ago, and the species of the one and\nthe races of the other are still the same. Still better, we have among\nthe wrappings of Egyptian mummies the very plants themselves, leaves\nand flowers perfectly preserved, and even colors almost perfect. Yet\nthe species are exactly the same as grow in Egypt to-day. If species\nare made by gradual transmutation, surely there ought to have been some\nchange in three thousand years.\n\n=Answer=.--It may be well to note that this apparent permanence is true\nof _races_ of men as well as of _species_ of animals and plants. But\nthe very men who insist on permanence of species are equally insistent\non the variability of varieties and races. The objection, therefore,\nproves too much. We shall not insist on this, however, because as\nderivationists we regard races as naught else than commencing species,\nand therefore subject to the same laws. We are not striving for triumph\nin debate, but only for truth. The true answer will, we believe, be\nfound among the following suggestions:\n\n1. Three thousand years seems a long time in human history, but in\ngeological history it is but a day. This, the usual answer, is no doubt\na true one, but hardly, we think, sufficient. When we remember the\nenormous change which has taken place in faunas and floras since the\nend of the Tertiary, if change still continues at the same rate, surely\nit ought to be distinctly perceptible in three thousand years.\n\n2. But we must remember that such changes are usually more or less\nparoxysmal; not, indeed, so sudden as to break the continuity of life,\nbut far more rapid at some times than at others. The last critical\nor revolutionary period of rapid change was the Glacial epoch. Since\nthat time--i. e., during the human period--a new equilibrium has been\nestablished, and the changes in organic forms have been very slow.\n\n3. Remember, again, that in evolution _all_ species do not change. On\nthe contrary, most become rigid, and either remain unchanged, almost\nindefinitely, or else die out and leave no descendants. Only the more\nplastic forms change into other species, but usually into several\nother species, and thus the number of forms may be undiminished, even\nthough the larger number of old forms leave no descendants. It is true,\ntherefore, of this as well as of other epochs, that the greater number\nof species are permanent.\n\n4. It is not impossible--indeed, it is in exact accordance with the\nlaws of evolution--that organic forms are more permanent now than\never before. Evolution is a growth; the forces of growth must exhaust\nthemselves. Evolution proceeds by constant differentiation and\nspecialization, but extreme specialization always arrests evolution.\nIn ontogenic evolution, for example, cell-structure becomes more\nand more specialized, but also thereby more and more rigid, and,\nwhen specialization is complete, evolution stops, and cell-forms are\npermanent. It is this which limits the cycle of every evolution. So is\nit precisely with evolution of the organic kingdom, except that the\ncycle is much longer. Here, also, every step is by specialization, and\nyet specialization fixes the form, and finally arrests the advance on\nthat line. Thus, throughout the whole geological history of the earth,\nthe larger number of forms, by specialization, become rigid and perish,\nwhile the fewer, more generalized, and more plastic forms take up the\nmarch and carry it forward a step, only to be themselves specialized\nand fixed. If we compare, again, to a tree: each twig finishes its\ngrowth, flowers, fruits, and dies; other buds take up the growth and\ncarry it forward. By specialization the highest condition of a certain\nform of life is attained, but other possibilities are shut off. Extreme\nspecialization is the flowering and fruiting--the end and completion\nof twig-life. Now, obviously, this specialization and respecialization\ncan not go on forever. When it is complete in every direction it must\ncease, and forms become permanent, or else perish. When it flowers it\nmust die.\n\nNow, is not the advent of man in many ways a sign of the completeness\nof organic evolution? Certain it is that with man there begins an\nentirely new form of evolution. Certain it is that with man evolution\nis transferred from the organic to the social plane, from the material\nto the psychical. Certain it is that the forces, the conditions\nand results of this evolution, are wholly different from those of\nthe other. In organic evolution the organism must conform to the\nenvironment; in human evolution the environment is made to conform to\nthe wants of the organism. The one is unconscious and involuntary,\npassive under the dominating laws of Nature; the other is conscious,\nvoluntary progress toward an ideal, _by the use_, among other means,\nof the laws of Nature. The one is by change of external form--i. e.,\nchange of species--the other by change of brain-structure. Now, does\nnot the commencing of the cycle of this new evolution imply the\nclosing of that of the old? The two may overlap somewhat now, but it\nis evident that, when the cycle of human evolution culminates, when\nhighly civilized man shall have taken possession of the whole earth,\nthe whole organic kingdom must be readjusted to his wants. All organic\nforms must be either domesticated or destroyed. Organic forms will no\nlonger be modified by natural but wholly by artificial selection.\n\n       *       *       *       *       *\n\nThere are many other supposed objections which have been urged, but\nthese are mostly not objections to evolution, but only to some _special\ntheory_ of evolution--Darwinian, Spencerian, Lamarckian, or other.\n\n=Origin of Beauty=.--For example, it has been urged that natural\nselection can only account for _useful_ structures; but _beauty_ is\nas universal and as conspicuous in nature as _use_. In many cases\nDarwin has shown that beauty is useful, and in such cases it is, of\ncourse, seized upon by selection and intensified. Thus, the gorgeous\ncoloring of birds and insects is largely due to sexual selection.\nBeauty is attractive, and therefore the most beautiful prevail in\nsecuring reproductive opportunities. This character is, therefore,\nperpetuated in the offspring, and intensified from generation to\ngeneration. But, of course, this can apply only to higher animals,\nin which the sexes are separate and sexual union voluntary. It can\nnot apply to self-fertilizing hermaphrodites; and yet in these, also,\nwe often find the most gorgeous coloring. Again, Darwin has very\ningeniously and successfully explained the case of the beauty and\nfragrance of flowers of hermaphroditic plants by another principle,\nviz., that of _insect-selection_. Insects are attracted by the most\nshowy and fragrant flowers, and thus become the means of carrying\npollen from flower to flower, insuring fertilization, and especially\ncross-fertilization. The most beautiful and fragrant flowers are most\ncertain to be fertilized, and thus beauty and fragrance become useful\nto the plant, and therefore are selected and intensified.\n\nThese and many other cases of beauty may doubtless be explained by\nshowing that it is useful; but beauty which is without any use can\nnot be explained by natural selection. Now, as already said, the\nmost gorgeous beauty is lavishly distributed even among the lowest\nanimals, such as marine shells and polyps, where no such explanation\nis possible. The process by which such beauty is originated and\nintensified is wholly unknown to us.\n\n=Incipient Organs=.--Again, Mivart has drawn attention to another\ndifficulty in the way of natural selection as an explanation even of\nuseful organs. Darwin does not, of course, attempt to account for the\n_origin_ of varieties. As we have already seen, he assumes divergent\nvariation of offspring as the necessary material on which natural\nselection operates. He who shall explain the origin of varieties will\nhave made another great step in completing the theory of evolution. But\nnot only does not natural selection explain the _origin_ of varieties,\nbut neither can it explain the _first steps_ of advance toward\nusefulness. An organ must be already useful before natural selection\ncan take hold of it to improve it. It can not make it useful, but only\n_more useful_. For example, if fins commenced as buds from the trunk,\nit is difficult to see how they could be of any use, and therefore\nhow they could be improved by natural selection until they were of\nconsiderable size, and especially until muscles were developed to move\nthem. Until that time they would seem to be a hindrance to be removed\nby natural selection, instead of a use to be preserved and improved. It\nwould seem that many organs must have passed through this _incipient\nstage_, in which their use was prospective.\n\nMuch that is very interesting might be said on these and similar points\nof difficulty, but all this lies entirely aside from the scope of\nthis work. As already said, these are not objections to evolution or\nderivation, but only to _Darwinism_, or any other special theory, as a\n_sufficient explanation_ of the process of evolution. They only show\nthat we do not yet fully understand this process; that there are still\nother and perhaps greater factors of evolution than is yet dreamed of\nin our philosophy.\n\nIn the foregoing chapters on special evidences, and especially in the\nlast two, the reader will observe many points of doubt, discussion, and\ndifference of opinion. Let it not be concluded on that account that the\n_law of evolution_ is still in the region of uncertainty. It can not be\ntoo strongly insisted on that the fact of evolution as a universal law\nmust be kept distinct from the causes, the factors, the conditions, the\nprocesses, of evolution. The former is certain, the latter are still\nimperfectly understood.\n\n\n\n\nPART III.\n\n_THE RELATION OF EVOLUTION TO RELIGIOUS THOUGHT._\n\n\n\n\nCHAPTER I.\n\nINTRODUCTORY.\n\n\nFrom what has preceded, the reader will perceive that we regard the\nlaw of evolution as thoroughly established. In its most general\nsense, i. e., as a law of continuity, it is a necessary condition of\nrational thought. In this sense it is naught else than the universal\nlaw of necessary causation applied to forms instead of phenomena. It\nis not only as certain as--it is far more certain than--the law of\ngravitation, for it is not a contingent, but a necessary truth like the\naxioms of geometry. It is only necessary to conceive it clearly, to\naccept it unhesitatingly. The consensus of scientific and philosophical\nopinion is already well-nigh, if not wholly, complete. If there are\nstill lingering cases of dissent among thinking men, it is only because\nsuch do not yet conceive it clearly--they confound it with some special\nform of explanation of evolution which they, perhaps justly, think not\nyet fully established. We have sometimes in the preceding pages used\nthe words evolutionist or derivationist; they ought not to be used any\nlonger. The day is past when evolution might be regarded as a school\nof thought. We might as well talk of gravitationist as of evolutionist.\n\nIf, then, evolution as a law be certain, if, moreover, it is a law\naffecting not only one part of Nature--the organic kingdom--and one\ndepartment of science--biology--but the whole realm of Nature and every\ndepartment of science, yea, every department of thought, changing our\nwhole view of Nature and modifying our whole philosophy, the question\npresses upon us, \u201cWhat will be its effect on religious belief, and\ntherefore on moral conduct?\u201d This is a question of gravest import.\nTo answer it, however imperfectly, is the chief object of this work.\nExcept for this, it would probably never have been undertaken. All that\ngoes before is subsidiary to this.\n\nBut I will doubtless be met at the very threshold by an objection\nfrom the scientific side. Some will say--because it is the fashion\nnow to say--that as simple, honest truth-seekers, we have nothing to\ndo with its effect on religion and on life. They say we must follow\nTruth wherever she leads, utterly regardless of what may seem to us\nmoral consequences. This I believe is a grave mistake, the result of a\nreaction, and on the whole a wholesome and noble reaction, against the\nfar more common mistake of sacrificing truth to a supposed good. But\nthe reaction, as in most other cases, has gone much too far. There is\na true _philosophic_ ground of justification for the reluctance with\nwhich even honest truth-seekers accept a doctrine which seems harmful\nto society. Effect on life is, and ought to be, an important element\nin _our estimate of the truth of any doctrine_. It is necessary for me\nto show this, in order to justify this part of my work.\n\n=Relation of the True and the Good.=--There is a necessary and\nindissoluble connection between truth and usefulness. We all at once\nadmit this connection in one direction. We all admit that a truth must\neventually have its useful application. It may not be _now_, nor in ten\nyears, nor in a century, nor even in a millennium, but some time in the\nfuture it will vindicate its usefulness. No truth is trivial or useless\nin its relation to human life, for man is a part of Nature, and his\nlife must be in accordance with the laws of Nature. Every one admits\nthis, but not every one admits the converse proposition, viz., that\nwhatever doctrine or belief, in the long run and throughout the history\nof human advancement, has tended to the betterment of our race, must\nhave in it an element of truth by virtue of which it has been useful;\nfor man\u2019s good can not be in conflict with the laws of Nature. Also,\nwhatever in the long run and in the final outcome tends to the bad in\nhuman conduct, ought to be received, even by the honest truth-seeker,\nwith distrust as containing essential error. The reason of this will\nnow be further explained.\n\n=Relation of Philosophy to Life.=--There are three primary divisions\nof our psychical nature, viz., sensuous, intellectual, and volitional\nor moral. There are three corresponding primary processes necessary\nto make a complete rational and satisfactory philosophy: (1) There\nis first the _instreaming_ of the external world through the senses,\nas impressions. These we call facts or phenomena. (2) The elaboration\nof these facts within, by the _intellect_, into a compact, consistent\nstructure. This we call knowledge. (3) The outgoing of this knowledge\nby the _will_ into the world as right or wise conduct. Now these three\nare all equally necessary. All these three portions of our complex\nnature are equally urgent to be satisfied.[39] But, unfortunately,\nscientific workers are too apt to think only 1 and 2 necessary--that\ntrue facts elaborated into consistent theory are all we need care for.\nTheologians and metaphysicians, on the other hand, seem to think only 2\nand 3 necessary. They elaborate a theory consistent in all its parts,\nexquisitely woven in beautiful and delicate pattern, and apparently\nsatisfactory in its application to the right conduct of life, but are\nless careful to inquire whether it is in harmony with facts derived\nfrom the senses. But, we repeat, all three are equally necessary. The\nfirst gathers the materials, the second constructs the edifice, the\nthird, by _use_, by practical application, _tests_ whether it be a fit\nbuilding to live in, whether it is constructed on sound architectural\nprinciples. The tendency of the olden time was to neglect the first,\nthe tendency of the present time is to neglect the third. But we repeat\nwith stronger emphasis that this third element is equally necessary.\nAll admit that successful application in art is the surest test of\nthe truth of science. Now, social conduct is the art corresponding to\nour philosophy of life, and therefore is the sure test of its truth.\nIt follows, therefore, that unless all these three primary divisions\nof our nature are satisfied by any doctrine, there must result an\nineradicable confusion and discord in our psychical nature, and\ncordial acceptance is not only impossible but irrational. We insist\nupon this the more because it has become the fashion in these latter\ndays of dominance of science, to say that to inquire into effects on\nsociety is inconsistent with the scientific spirit, and unworthy of the\nhonest truth-seeker. But, observe, I am speaking of effects on society\nonly as a _test of truth_. I would not swerve a hair\u2019s breadth from\nabsolute devotion to truth. It is necessary, indeed, to inquire into\neffects on society, but we must inquire only in the patient spirit\ncharacteristic of the truth-seeker. Whatever is really true will surely\nvindicate itself by its beneficence, if we will only wait patiently for\nfinal results. Evolution is no exception to this universal truth. It\nwill surely vindicate its beneficence, but we must wait yet a little\nwhile--not very long.\n\nSo much it was necessary to say in justification of the inquiry which\nconstitutes this third part of our work. But, after this justification,\nthe question returns with additional emphasis, \u201cWhat will be the effect\nof the universal acceptance of the law of evolution on religious\nthought, and through this on the right conduct of life?\u201d\n\nThere can be no doubt that evolution, as a law affecting all science\nand every department of Nature, must fundamentally affect the whole\nrealm of thought, and profoundly modify our traditional views of\nNature, of God, and of man. There can be no doubt that we are now on\nthe eve of a great revolution. But, as in all great revolutions, so\nin this, the first fears as to its effects are greatly exaggerated.\nTo many, both friends and foes of Christianity, evolution seems to\nsweep away the whole foundation, not only of Christianity, but of all\nreligion and morals, by demonstrating a universal materialism. Many are\nready to cry out in anguish, \u201cYe have taken away our gods, what have we\nmore? Ye have destroyed our dearest hopes and noblest aspirations, what\nmore is left worth living for?\u201d But I think all who are at all familiar\nwith the history of the so-called conflict between religion and science\nwill admit this is not the first time this cry has been raised against\nscience. They have heard this danger-cry so often that they begin\nto regard it as little more than a wolf-cry--scientific wolf in the\nreligious fold. It may not be amiss, then, to stop a moment to trace\nrapidly the main points of this conflict--to discuss the various forms\nof this scientific wolf.\n\nFirst, then, it came in the form of the _heliocentric theory of\nthe planetary system_. We once thought the earth the center of the\nuniverse, and so firm that it can not be moved. But science shows that\nit moves about the sun, and spins unceasingly on its axis. Every one\nhas heard of the terror of the sheep produced by this discovery, and\nthe nearly tragic results to the bold scientist. But now we look back\nwith wonder that there should have been any trouble at all. Would any\nChristian now consent to give up the grand conceptions of Nature and\nof God thus opened to the human mind--the idea of infinite space full\nof worlds, of which our earth is one, moving in silent harmony as in a\nmystic dance? Verily, this wolf has proved itself a harmless, nay, a\nvery noble beast, and lies down in peace with the lambs.\n\nNext, it came in the shape of the _law of gravitation_, as sustentation\nof the cosmos by law and resident forces. The effect of this on\nreligious thought was even more profound, though less visible on the\nsurface, because only perceived by the most intelligent. It seemed\nat that time to remove God from the course of Nature. This was the\nreal ground of the skepticism of the last century, and also the real\nmotive of Voltaire\u2019s ardent advocacy of Newton\u2019s views before these\nwere generally accepted in France. But now, who would give up this\ngrand idea--this conception of law pervading infinite space--the same\nlaw which controls the falling of a stone guiding also the planetary\norbs in their fiery courses? This is indeed the divine spheral music,\ninaudible but to the ear of science, accompanying the celestial dance.\n\nNext, it came in the form of the _antiquity of the earth_ and of the\ncosmos. The earth which we had fondly thought made specially for us\nabout six thousand years ago; sun, moon, and stars, which we had vainly\nimagined shone only for our behoof--these, science tells us, existed\nand each performed its due course inconceivable ages before there was a\nman to till the ground or contemplate the heavens. Some of my readers\nmay still remember the horror, the angry dispute which followed the\npromulgation of these facts. But now, who would consent to give up the\nnoble conception of infinite time thus opened to the human mind and\nbecome forever the heritage of man?\n\nNext, it came in the form of the _antiquity of man_. It is probable,\nnay, certain, that man has inhabited the earth far longer than we had\npreviously supposed we had warrant for believing. The controversy on\nthis question and the dread of its result has indeed not yet entirely\nsubsided. Some timid people still look askance at this wolf, but I\nthink all intelligent people accept it and find it harmless.\n\nNext, and last, it comes now in the form of _evolution_--of the origin\nof all things, even of organic forms, by _derivation_--of _creation\nby law_. We are even now in the midst of the terror created by this\ndoctrine. But what is evolution but law throughout infinite time? The\nsame law which now controls the development of an egg has presided\nover the creation of worlds. Infinite space and the universal law\nof gravitation; infinite time and the universal law of evolution.\nThese two are the grandest ideas in the realm of thought. The one is\nuniversal sustentation, the other universal creation, by law. There is\none law and one energy pervading all space and stretching through all\ntime. Our religious philosophy has long ago accepted the one, but has\nnot yet had time to readjust itself completely to the other. A few more\nyears, and Christians will not only accept, but love and cherish this\nalso for the noble conceptions it gives of Nature and of God.\n\nBut some will exclaim, \u201cNoble conceptions of God, say you! Why, it\nutterly obliterates the idea of God from the mind. All other conflicts\nwere for outworks--this strikes at the citadel. All others required\nonly readjustment of claims, rectification of boundaries betwixt\nscience and religion--this requires nothing less than unconditional\nsurrender. Evolution is absolute materialism, and materialism is\nincompatible with belief in God, and therefore with religion of any\nkind whatsoever!\u201d Before proceeding any further, it becomes necessary\nto remove this difficulty out of the way.\n\n\n\n\nCHAPTER II.\n\nTHE RELATION OF EVOLUTION TO MATERIALISM.\n\n\nIt is seen in the sketch given in the previous chapter that, after\nevery struggle between theology and science, there has been a\nreadjustment of some beliefs, a giving up of some notions which really\nhad nothing to do with religion in a proper sense, but which had\nbecome so _associated_ with religious belief as be to confounded with\nthe latter--a giving up of some line of defense which ought never to\nhave been held because not within the rightful domain of theology at\nall. Until the present the whole difficulty has been the result of\nmisconception, and Christianity has emerged from every struggle only\nstrengthened and purified, by casting off an obstructing shell which\nhindered its growth. But the present struggle seems to many an entirely\ndifferent and far more serious matter. To many it seems no longer\na struggle of theology, but of essential religion itself--a deadly\nlife-and-death struggle between religion and materialism. To many,\nboth skeptics and Christians, evolution seems to be synonymous with\nblank materialism, and therefore cuts up by the roots every form of\nreligion by denying the existence of God and the fact of immortality.\nThat the enemies of religion, if there be any such, should assume and\ninsist on this identity, and thus carry over the whole accumulated\nevidence of evolution as a demonstration of materialism, although\nwholly unwarranted, is not so surprising; but what shall we say of the\nincredible folly of her friends in admitting the same identity!\n\nA little reflection will explain this. There can be no doubt that there\nis at present a strong and to many an overwhelming tendency toward\nmaterialism. The amazing achievements of modern science; the absorption\nof intellectual energy in the investigation of external nature and\nthe laws of matter have created a current in that direction so strong\nthat of those who feel its influence--of those who do not stay at\nhome, shut up in their creeds, but walk abroad in the light of modern\nthought--it sweeps away and bears on its bosom all but the strongest\nand most reflective minds. Materialism has thus become a fashion of\nthought; and, like all fashions, must be guarded against. This tendency\nhas been created and is now guided by science. Just at this time it is\nstrongest in the department of biology, and especially is evolution its\nstronghold. This theory is supposed by many to be simply demonstrative\nof materialism. Once it was the theory of gravitation which seemed\ndemonstrative of materialism. The sustentation of the universe by law\nseemed to imply that Nature operates itself and needs no God. That time\nis passed. Now it is evolution and creation by law. This will also\npass. The theory seems to many the most materialistic of all scientific\ndoctrine only because it is the _last_ which is claimed by materialism,\nand the absurdity of the claim is not yet made clear to many.\n\nThe truth is, there is no such necessary connection between evolution\nand materialism as is imagined by some. There is no difference in this\nrespect between evolution and any other law of Nature. In evolution,\nit is true, the last barrier is broken down, and the whole domain of\nnature is now subject to law; but it is only _the last_; the march\nof science has been in the same direction all the time. In a word,\nevolution is not only not identical with materialism, but, to the deep\nthinker, it has not added a feather\u2019s weight to its probability or\nreasonableness. Evolution is one thing and materialism quite another.\nThe one is an established law of nature, the other an unwarranted and\nhasty inference from that law. Let no one imagine, as he is conducted\nby the materialistic scientist in the paths of evolution from the\ninorganic to the organic, from the organic to the animate, from the\nanimate to the rational and moral, until he lands, as it seems to him,\nlogically and inevitably, in universal materialism--let no such one\nimagine that he has walked all the way in the domain of science. He\nhas stepped across the boundary into the domain of philosophy. But,\non account of the strong tendency to materialism and the skillful\nguidance of his leaders, there seems to be no such boundary; he does\nnot distinguish between the inductions of science and the inferences\nof a shallow philosophy; the whole is accredited to science, and the\nfinal conclusion seems to carry with it all the certainty which belongs\nto scientific results. The fact that these materialistic conclusions\nare reached by some of the foremost scientists of the present day adds\nnothing to their probability. In a question of science, viz., the law\nof evolution, their authority is deservedly high, but in a question\nof philosophy, viz., materialism, it is far otherwise. If the pure\nscientists smile when theological philosophers, unacquainted with the\nmethods of science, undertake to dogmatize on the subject of evolution,\nthey must pardon the philosophers if they also smile when the pure\nscientists imagine that they can at once solve questions in philosophy\nwhich have agitated the human mind from the earliest times. I am\nanxious to show the absurdity of this materialistic conclusion, but I\nshall try to do so, not by any labored argument, but by a few simple\nillustrations.\n\n1. It is curious to observe how, when the question is concerning a\nwork of Nature, we no sooner find out how a thing is made than we\nimmediately exclaim: \u201cIt is not made at all, it became so of itself!\u201d\nSo long as we knew not how worlds were made, we of course concluded\nthey must have been created, but so soon as science showed _how_ it\nwas probably done, immediately we say we were mistaken--they were not\nmade at all. So also, so long as we could not imagine how new organic\nforms originated, we were willing to believe they were created, but,\nso soon as we find that they originated by evolution, many at once say,\n\u201cWe were mistaken; no creator is necessary at all.\u201d Is this so when the\nquestion is concerning a work of man? Yes, of one kind--viz., the work\nof the magician. Here, indeed, we believe in him, and are delighted\nwith his work, until we know how it is done, and then all our faith\nand wonder cease. But in any honest work it is not so; but, on the\ncontrary, when we understand how it is done, stupid wonder is changed\ninto intellectual delight. Does it not seem, then, that to most people\nGod is a mere wonder-worker, a chief magician. But the mission of\nscience is to show us how things are done. Is it any wonder, then, that\nto such persons science is constantly destroying their superstitious\nillusions? But if God is an honest worker, according to reason--i. e.,\naccording to law--ought not science rather to change gaping wonder into\nintelligent delight--superstition into rational worship?\n\n2. Again, it is curious to observe how an _old truth_, if it come only\nin a _new form_, often strikes us as something unheard of, and even\nas paradoxical and almost impossible. A little over thirty years ago\na little philosophical toy, the gyroscope, was introduced and became\nvery common. At first sight, it seems to violate all mechanical laws,\nand set at naught the law of gravitation itself. A heavy-brass wheel,\nfour to five inches in diameter, at the end of a horizontal axle, six\nor eight inches long, is set rotating rapidly, and then the free end\nof the axis is supported by a string or otherwise. The wheel remains\nsuspended in the air while slowly gyrating. What mysterious force\nsustains the wheel when its only point of support is at the end of\nthe axle, six or eight inches away? Scientific and popular literature\nwere flooded with explanations of this seeming paradox. And yet it was\nnothing new. The boy\u2019s top, that spins and leans and will not fall,\nalthough solicited by gravity, so long as it spins, which we have seen\nall our lives without special wonder, is precisely the same thing.\n\nNow, evolution is no new thing, but an old familiar truth; but,\ncoming now in a new and questionable shape, lo, how it startles\nus out of our propriety! Origin of forms by evolution is going on\neverywhere about us, both in the inorganic and the organic world. In\nits more familiar forms, it had never occurred to most of us that it\nwas a scientific refutation of the existence of God, that it was a\ndemonstration of materialism. But now it is pushed one step farther\nin the direction it has always been going--it is made to include also\nthe origin of species--only a little change in its form, and lo, how\nwe start! To the deep thinker, now and always, there is and has been\nthe alternative--materialism or theism. God operates Nature or Nature\noperates itself; but evolution puts no new phase on this old question.\nFor example, the origin of the individual by evolution. Everybody knows\nthat every one of us individually became what we now are by a slow\nprocess of evolution from a microscopic spherule of protoplasm, and yet\nthis did not interfere with the idea of God as our individual maker.\nWhy, then, should the discovery that the species (or first individuals\nof each kind) originated by evolution destroy our belief in God as the\ncreator of species?\n\n3. It is curious and very interesting to observe the manner in which\nvexed questions are always finally settled, if settled at all. All\nvexed questions--i. e., questions which have tasked the powers of\nthe greatest minds age after age--are such only because there is\na real truth on both sides. Pure, unmixed error does not live to\nplague us long. Error, when it continues to live, does so by virtue\nof a germ of truth contained. Great questions, therefore, continue\nto be argued _pro_ and _con_ from age to age, because each side\nis in a sense--i. e., from its own point of view--true, but wrong\nin excluding the other point of view; and a true solution, a true\nrational philosophy, will always be found in a view which combines and\nreconciles the two partial, mutually excluding views, showing in what\nthey are true and in what they are false--explaining their differences\nby transcending them. This is so universal and far-reaching a principle\nthat I am sure I will be pardoned for illustrating it in the homeliest\nand tritest fashion. I will do so by means of the shield with the\ndiverse sides, giving the story and construing it, however, in my own\nway. There is, apparently, no limit to the amount of rich marrow of\ntruth that may be extracted from these dry bones of popular proverbs\nand fables by patient turning and gnawing.\n\nWe all remember, then, the famous dispute concerning the shield,\nwith its sides of different colors, which we shall here call white\nand black. We all remember how, after vain attempts to discover the\ntruth by dispute, it was agreed to try the scientific method of\ninvestigation. We all remember the surprising result. Both parties to\nthe dispute were right and both were wrong. Each was right from his\npoint of view, but wrong in excluding the other point of view. Each\nwas right in what he asserted, and each wrong in what he denied. And\nthe complete truth was the combination of the partial truths and the\nelimination of the partial errors. But we must not make the mistake of\nsupposing that truth consists in _compromise_. There is an old adage\nthat truth lies in the middle between antagonistic extremes. But it\nseems to us that this is the place of _safety_, not of truth. This is\nthe favorite adage, therefore, of the timid man, the time-server, the\nfence-man, not the truth-seeker. Suppose there had been on the occasion\nmentioned above one of these fence-philosophers. He would have said:\n\u201cThese disputants are equally intelligent and equally valiant. One side\nsays the shield is white, the other that it is black, now truth lies\nin the middle; therefore, I conclude the shield is gray or neutral\ntint, or a sort of pepper-and-salt.\u201d Do we not see that he is the only\nman who has no truth in him? No; truth is no heterogeneous mixture of\nopposite extremes, but a stereoscopic combination of two surface views\ninto one solid reality.\n\nNow, the same is true of all vexed questions, and I have given this\ntrite fable again only to apply it to the case in hand.\n\nThere are three possible views concerning the origin of organic forms\nwhether individual or specific. Two of these are opposite and mutually\nexcluding; the third combining and reconciling. For example, take the\nindividual. There are three theories concerning the origin of the\nindividual. The first is that of the pious child who thinks that he was\nmade very much as he himself makes his dirt-pies; the second is that\nof the street-gamin, or of Topsy, who says: \u201cI was not made at all,\nI growed\u201d; the third is that of most intelligent Christians--i. e.,\nthat we were made by a process of evolution. Observe that this latter\ncombines and reconciles the other two, and is thus the more rational\nand philosophical. Now, there are also three exactly corresponding\ntheories concerning the origin of species. The first is that of many\npious persons and many intelligent clergymen, who say that species were\nmade at once by the Divine hand _without natural process_. The second\nis that of the materialists, who say that species were not made at all,\nthey were derived, \u201cthey growed.\u201d The third is that of the theistic\nevolutionists, who think that they were _created_ by a process of\nevolution--who believe that making is not inconsistent with growing.\nThe one asserts the divine agency, but denies natural process; the\nsecond asserts the natural process, but denies divine agency; the third\nasserts _divine agency by natural process_. Of the first two, observe,\nboth are right and both wrong; each view is right in what it asserts,\nand wrong in what it denies--each is right from its own point of view,\nbut wrong in excluding the other point of view. The third is the only\ntrue rational solution, for it includes, combines, and reconciles the\nother two; showing wherein each is right and wherein wrong. It is the\ncombination of the two partial truths, and the elimination of the\npartial errors. But let us not fail to do perfect justice. The first\ntwo views of origin, whether of the individual or of the species, are\nindeed both partly wrong as well as partly right; but the view of the\npious child and of the Christian contains by far the more essential\ntruth. Of the two sides of the shield, theirs is at least the whiter\nand more beautiful.\n\nBut, alas! the great bar to a speedy settlement of this question and\nthe adoption of a rational philosophy is not in the head but in the\nheart--is not in the reason but in pride of opinion, self-conceit,\ndogmatism. The rarest of all gifts is a truly tolerant, rational\nspirit. In all our gettings let us strive to get this, for _it_\nalone is true wisdom. But we must not imagine that all the dogmatism\nis on one side, and that the theological. Many seem to think that\ntheology has a \u201c_pre-emptive right_\u201d to dogmatism. If so, then modern\nmaterialistic science has \u201c_jumped the claim_.\u201d Dogmatism has its roots\ndeep-bedded in the human heart. It showed itself first in the domain\nof theology, because there was the seat of power. In modern times it\nhas gone over to the side of science, because here now is the place of\npower and fashion. There are _two dogmatisms_, both equally opposed\nto the true rational spirit, viz., the old theological and the new\nscientific. The old clings fondly to old things, only because they\nare old; the new grasps eagerly after new things, only because they\nare new. True wisdom and true philosophy, on the contrary, tries all\nthings both old and new, and holds fast only to that which is good and\ntrue. The new dogmatism taunts the old for credulity and superstition;\nthe old reproaches the new for levity and skepticism. But true wisdom\nperceives that they are both equally credulous and equally skeptical.\nThe old is credulous of old ideas and skeptical of new; the new is\nskeptical of old ideas and credulous of new. Both deserve the unsparing\nrebuke of all right-minded men. The appropriate rebuke for the old\ndogmatism has been already put in the mouth of Job in the form of a\nbitter sneer: \u201cNo doubt ye are the people, and wisdom shall _die_ with\nyou.\u201d The appropriate rebuke for the new dogmatism, though not put into\nthe mouth of any ancient prophet, ought to be uttered--I will undertake\nto utter it here. I would say to these modern materialists, \u201cNo doubt\nye are the men, and wisdom and true philosophy were _born_ with you.\u201d\n\nLet it be observed that we are not here touching the general question\nof the personal agency of God in operating Nature. This we shall take\nup hereafter. All that we wish to insist on now is that the process and\nthe law of evolution does not differ in its relation to materialism\nfrom all other processes and laws of Nature. If the sustentation of\nthe universe by the law of gravitation does not disturb our belief in\nGod as the sustainer of the universe, there is no reason why the origin\nof the universe by the law of evolution should disturb our faith in God\nas the creator of the universe. If the law of gravitation be regarded\nas the Divine mode of sustentation, there is no reason why we should\nnot regard the law of evolution as the Divine process of creation. It\nis evident that if evolution be materialism, then is gravitation also\nmaterialism; then is every law of Nature and all science materialism.\nIf there be any difference at all, it consists only in this: that, as\nalready said, here is the _last_ line of defense of the supporters of\nsupernaturalism in the realm of Nature. But being the last line of\ndefense--the last ditch--it is evident that a yielding here implies\nnot a mere shifting of line, but a change of base; not a readjustment\nof details only, but a _reconstruction of Christian theology_. This, I\nbelieve, is indeed necessary. There can be little doubt in the mind of\nthe thoughtful observer that we are even now on the eve of the greatest\nchange in traditional views that has taken place since the birth of\nChristianity. But let no one be greatly disturbed thereby. For as then,\nso now, change comes not to destroy but to fulfill all our dearest\nhopes and aspirations; as then, so now, the germ of living truth has,\nin the course of ages, become so encrusted with meaningless traditions\nwhich stifle its growth, that it is necessary to break the shell to set\nit free; as then, so now, it has become necessary to purge religious\nbelief of dross in the form of trivialities and superstitions. This\nhas ever been and ever will be the function of science. The essentials\nof religious faith it does not, it can not, touch, but it purifies and\nennobles our conceptions of Deity, and thus elevates the whole plane of\nreligious thought.\n\nIt will not, of course, be expected of me to give, even in briefest\noutline, a system of reconstructed Christian thought. Such an attempt\nwould be wholly unbecoming. Time, very much time, and the co-operation\nof many minds, bringing contributions from many departments of thought,\nis necessary for this. In a word, it can only itself come by a gradual\nprocess of evolution. But from the point of view of science some very\nfundamental changes in traditional views are already plain. Of these\nthe most fundamental and important are our ideas concerning God,\nNature, and man in their relations to one another. These will form the\nsubject of the next three chapters.\n\n\n\n\nCHAPTER III.\n\nTHE RELATION OF GOD TO NATURE.\n\n\nWe have already said that evolution does not differ essentially from\nother laws of Nature in its bearing on religious belief. It only\nreiterates and enforces with additional emphasis what Science, in all\nits departments, has been saying all along. The difficulties in the\nway of certain traditional views have pressed with ever increasing\nforce upon the thoughtful mind ever since the birth of modern science.\nAll along, an issue has been gathering, but put off from time to time\nby compromise, until now, at last, the issue is forced upon us and\ncompromise is exhausted. The issue (let us look it squarely in the\nface) is: Either God is far more closely related with Nature, and\noperates it in a more direct way than we have recently been accustomed\nto think, or else (mark the alternative) Nature operates itself and\nneeds no God at all. There is no middle ground tenable.\n\nLet us trace rapidly the growth of this issue. The old idea and the\nmost natural to the religious mind was the direct agency of God in\nevery event and phenomenon of Nature. This view is nobly expressed\nin the noblest literature in the world--in the Hebrew and Christian\nScriptures: \u201cHe looketh on the earth and it trembleth. He toucheth\nthe hills and they smoke.\u201d \u201cHe maketh his sun to rise on the evil and\non the good, and sendeth his rain on the just and on the unjust.\u201d But\nnow comes Science and explains all these phenomena by natural laws and\nresident forces, and we all accept her explanation. Thus, one by one\nthe phenomena of Nature are explained by the operation of resident\nforces according to natural laws, until the whole course of Nature,\nas we now know it, has been, or will be, or conceivably may be, thus\nexplained.\n\nThus has gradually grown up, without our confessing it, a kind of\nscientific polytheism--one great Jehovah, perhaps, but with many agents\nor sub-gods, each independent, efficient, and doing all the real work\nin his own domain. The names of these, our gods, are gravity, light,\nheat, electricity, magnetism, chemical affinity, etc., and we are\npractically saying: \u201cThese be your gods, O Israel, which brought you\nout of the land of Egyptian darkness and ignorance. These be the only\ngods ye need fear, and serve, and study the ways of.\u201d\n\nWhat, then, is practically the notion which most people seem to have of\nthe relation of Deity to Nature? It is that of a great master-mechanic\nfar away above us and beyond our reach, who once upon a time, long\nago, and once for all, worked, created matter, endowed it with\nnecessary properties and powers, constructed at once out of hand this\nwonderful cosmos with its numberless wheels within wheels, endowed\nit with forces, put springs in it, wound it up, set it a-going, and\nthen--_rested_. The thing has continued to go of itself ever since.\nHe might have not only rested but _slept_, and the thing would have\ngone of itself. He might not only have slept but _died_, and still\nthe thing would have continued to go of itself. But, no, I forget.\nHe must not sleep or die, for the work is not absolutely perfect.\nThere are some things too hard even for Him to do in this masterful,\ngod-like way. There are some things which even He can not do except in\na \u2019prentice-like, man-like way. The hand must be introduced from time\nto time to repair, to rectify, to improve, especially to introduce new\nparts, such as new organic forms.\n\nSuch was the state of the compromise until twenty-five years ago.\nNature is sufficient of itself for its _course_ and continuance, but\nnot for _origins_ of at least _some_ new parts. Such was the state of\nthe compromise until Darwin and the theory of evolution. But, now,\neven this poor privilege of occasional interference is taken away.\nNow, origins, as well as courses, are reduced to resident forces\nand natural law. Now, Nature is sufficient of itself, not only for\nsustentation, but also for creation. Thus, Science has seemed to push\nHim farther and farther away from us, until now, at last, if this view\nbe true, evolution finishes the matter by pushing Him entirely out of\nthe universe and dispensing with Him altogether. This, of course, is\nmaterialism. But this is no new view now brought forward for the first\ntime by evolution. On the contrary, evolution only finishes what\nscience has been doing all along.\n\nSee, then, how the issue is forced. Either Nature is sufficient of\nitself and wants no God at all, or else this whole idea, the history\nof which we have been tracing, is radically false. We have here given\nby science either a demonstration of materialism or else a _reductio\nad absurdum_. Which is it? I do not hesitate a moment to say it is a\nreductio ad absurdum. And I believe that evolution has conferred an\ninestimable benefit on philosophy and on religion by forcing this issue\nand compelling us to take a more rational view.\n\nWhat, then, is the alternative view? It is the utter rejection with\nBerkeley and with Swedenborg of the independent existence of matter\nand the real efficient agency of natural forces. It is the frank\nreturn to the old idea of direct divine agency, but in a new, more\nrational, less anthropomorphic form. It is the bringing together\nand complete reconciliation of the two apparently antagonistic and\nmutually excluding views of _direct agency_ and _natural law_. Such\nreconciliation we have already seen is the true test of a rational\nphilosophy. It is the belief in a God not far away beyond our reach,\nwho once long ago enacted laws and created forces which continue of\nthemselves to run the machine we call Nature, but a God _immanent_,\na God resident _in_ Nature, at all times and in all places directing\nevery event and determining every phenomena--a God in whom in the most\nliteral sense not only we but all things have their being, in whom all\nthings consist, through whom all things exist, and without whom there\nwould be and could be nothing. According to this view the phenomena of\nNature are naught else than objectified modes of divine thought, the\nforces of Nature naught else than different forms of one omnipresent\ndivine energy or will, the laws of Nature naught else than the regular\nmodes of operation of that divine will, invariable because He is\nunchangeable. According to this view the law of gravitation is naught\nelse than the mode of operation of the divine energy in sustaining\nthe cosmos--the divine method of sustentation; the law of evolution\nnaught else than the mode of operation of the same divine energy in\noriginating and developing the cosmos--the divine method of creation;\nand Science is the systematic knowledge of these divine thoughts and\nways--a rational system of natural theology. In a word, according to\nthis view, there is no real efficient force but spirit, and no real\n_independent_ existence but God.\n\nBut some will object that this is pure _Idealism_. Yes, but far\ndifferent from what usually goes under that name. The ideal philosophy\nas usually understood regards the external world as having no real\nobjective existence outside of _ourselves_--as objectified mental\nstates of the _observer_--as literally such stuff as dreams are made\nof--as a mere phantasmagoria of trooping shadows having no real\nexistence but in the mind of the dreamer, and each dreamer makes his\nown world. Not so in the idealism above presented. According to _this_\nthe external world is the objectified modes, not of the mind of the\nobserver, but of the mind of God. According to this, the external world\nis not a mere unsubstantial figment or dream, but for _us_ a very\nsubstantial objective reality surrounding us and conditioning us on\nevery side.\n\nAgain, it will be objected that this is pure _Pantheism_. Again, we\nanswer \u201cyes.\u201d Call it so if you like, but far different from what goes\nunder that name, far different from the pantheism which sublimates\nthe personality of the Deity into all-pervading unconscious force,\nand thereby dissipates all our hopes of personal relation with him.\nProperly understood, we believe this view completely reconciles the\ntwo antagonistic and mutually excluding views of impersonal pantheism\nand anthropomorphic personalism, and is therefore more rational than\neither. The discussion of this most important point can only come up\nafter the next chapter, because the argument for the personality of\nDeity is derived, not from without by the study of Nature, but from\nwithin in our own consciousness. We therefore put off its discussion\nfor the present.\n\nBut, finally, some will object, \u201cWe can not live and work effectively\nunder such a theory unless, indeed, we escape through pantheism.\u201d It\nmay, alas! be true that this view brings us too near Him in our sense\nof spiritual nakedness and shortcoming. It may, indeed, be that we can\nnot live and work in the continual realized presence of the Infinite.\nIt may, indeed, be that we must still wear the veil of a practical\nmaterialism on our hearts and minds. It may, indeed, be that in our\npractical life and scientific work we must still continue to think\nof natural forces as efficient agents. But, if so, let us at least\nremember that this attitude of mind must be regarded only as our\nordinary work-clothes--necessary work-clothes it may be of our outer\nlower life--to be put aside when we return _home_ to our inner higher\nlife, religious and philosophical.\n\n\n\n\nCHAPTER IV.\n\nTHE RELATION OF MAN TO NATURE.\n\n\nThere are two widely distinct views concerning the relation of man\nto Nature; the one as old as the history of human thought, the other\nonly now urged upon us by modern science. According to the one, man\nis the counterpart and equivalent of Nature. He alone has--in fact\nis--an immortal spirit, and therefore he belongs to a world of his\nown. According to the other, man is but a part, a very insignificant\npart of Nature, and connected in the closest way with all other parts,\nespecially with the animal kingdom. He has no world of his own, nor\neven kingdom of his own: he belongs to the animal kingdom. In that\nkingdom he has no department of his own: he is a vertebrate. In the\ndepartment of vertebrates he has no privileged class of his own: he is\na mammal. In the class of mammals he has no titled order of his own:\nhe is a primate, and shares his primacy with apes. It is doubtful if\nhe may enjoy the privacy of a family of his own--the Hominid\u00e6--for the\nstructural differences between man and the anthropoid apes are probably\nnot so great as between the sheep family and the deer family.\n\nNow it is evident that these two are only views from different points,\npsychical and structural. From the psychical point of view it is simply\nimpossible to exaggerate the wideness of the gap that separates man\nfrom even the highest animals. From this point of view man must be\nset over as an equivalent, not only to the whole animal kingdom, but\nto the whole of Nature besides. From the structural point of view,\non the contrary, it is impossible to exaggerate the closeness of the\nconnection. Man\u2019s body is identified with all Nature in its chemical\nconstituents, with the body of all animals in its functions, with all\nvertebrates, especially mammals, in its structure. Bone for bone,\nmuscle for muscle, ganglion for ganglion, almost nerve-fiber for\nnerve-fiber, his body corresponds with that of the higher animals.\nWhether he was derived from lower animals or not, certain it is that\nhis structure even in the minutest details is precisely such as it\nwould be if he were thus derived by successive slight modifications.\n\nNow, of these two views, the latter has been in recent times enormously\nproductive in increasing our knowledge. Anatomy has become truly\nscientific only through comparative anatomy; physiology through\ncomparative physiology; embryology through comparative embryology.\nSociology is fast following in the same line, and becoming scientific\nthrough comparative sociology. Is not the same true also of psychology?\nWill not psychology become truly scientific only through comparative\npsychology, i. e., by the study of the spirit of man in relation to\nwhat corresponds to it in lower animals? But this view and this method,\nwhen pushed to what seems to many their logical conclusion, end in\nidentification of man with mere animals, of spirit with mere physical\nand chemical forces, immortality with mere conservation of energy,\nand thus leads to blank and universal materialism. Thus, while it\nincreases our knowledge, it destroys our hopes. Is there any escape?\nThere is. The two extreme views given above are not irreconcilable. As\nalready said, they are only views from different points, and therefore,\nalthough both true, are equally one-sided and partial, and a true and\nrational philosophy, in this as in all other cases of vexed questions,\nis found only in a higher view, which combines and reconciles these\nmutually excluding extremes. Can we find such a view? I think we can.\n\nLet us first, however, trace some of the stages of this scientific\nmaterialism. There are two main branches of the argument for\nmaterialism: one derived from _brain-physiology_, the other from\n_evolution_. As we wish to be perfectly fair, we will present and even\npress the argument in both these directions, although the latter alone\nbears directly on the subject in hand.\n\nIn recent times, physiology has made great and, to many, startling\nadvances in the direction of connecting mental phenomena with\nbrain-changes. Physiologists have established the correlation of\nvital with chemical and physical forces,[40] and probably in some\nsense, at least, of mental with vital forces. They have proved, in\nevery act of perception, first a physical change in a nerve-terminal,\nthen a propagated thrill along a nerve-fiber, and then a resulting\nchange, physical or chemical, in the brain; and in every act of\nvolition, a change first in a brain-cell, then, a return thrill along\na nerve-fiber, and a resulting contraction of a muscle. Even the\nvelocity of the transmission to and fro has been measured, and the\ntime necessary to produce brain-changes estimated. They have also\nestablished the existence of physical and chemical changes in the\nbrain corresponding to every change of mental state, and with great\nprobability an exact quantitative relation between these changes of\nbrain and the corresponding changes of mind. In the near future they\nmay do more: they may localize all the different faculties and powers\nof the mind, each in its several place in the brain, and thus lay the\nfoundations of a truly scientific phrenology. In the far-distant future\nwe may possibly do much more. We may connect each kind of mental state\nwith a different and distinctive kind of brain-change. We may find, for\nexample, a right-handed rotation of atoms associated with _love_, and\na left-handed rotation associated with _hate_, or a gentle sideways\noscillation associated with _consciousness_, and a vertical pounding\nassociated with _will_. Now, suppose all this, and even much more, be\ndone in the way of associating, both in degree and in kind, mental\nchanges with brain-changes. What then? \u201cWhy,\u201d say the materialists,\n\u201cwe thereby identify _mind_ with _matter_, mental forces with material\nforces. Thought, emotion, consciousness and will become products of the\nbrain, in the same sense as bile is a product of the liver, or urea a\nproduct of the kidneys.\u201d\n\nSuch is, in brief, the argument. Now, the answer: We may do all\nwe have supposed and much more. We may push our knowledge in this\ndirection as far as the boldest imagination can reach, and even\nthen we are no nearer the solution of this mystery of the relation\nof brain-changes and mental changes than we are now. Even then it\nwould be impossible for us to conceive _how_ brain-changes produce\nmental changes or _vice versa_. Physical changes in sense-organs,\ntransmitted along nerve-fibers, determine changes in brain-substance.\nSo much is intelligible. But now there appear--how it is impossible\nto imagine--consciousness, thought, emotion, etc.--phenomena of an\nentirely different order, belonging to an entirely different world. So\ndifferent, that it is impossible to imagine the nature of the nexus\nbetween, or to construe the one in terms of the other. Brain-cells are\nagitated and thought appears: Aladdin\u2019s lamp is rubbed, and the genie\nappears. There is just as much intelligible causal relation between the\ntwo sets of phenomena in the one case as in the other.\n\nNow, this mystery is not of the nature of those which disappear under\nthe light of knowledge. On the contrary, science only brings it out in\nsharper relief, and emphasizes its absolute unsolvableness. Suppose\nan absolutely perfect knowledge, perfect in degree, but human in kind.\nSuppose an ideally perfect science--a science which has so completely\nsubdued its domain, and reduced it to such perfect simplicity, that\nthe whole cosmos may be expressed in a single mathematical formula--a\nformula which, worked out with plus signs, would give every phenomenon\nand event which shall ever occur in the future, and with minus signs\nevery phenomenon and event which has ever occurred in the past. Surely,\nthis is an ideally perfect science. Yet, even to such a science, the\nrelation of brain-changes to mental states would be as great a mystery\nas now. It would even come out in stronger relief, because so many\nother apparent mysteries would disappear. Like the essential nature of\nmatter or the ultimate cause of force, this relation lies evidently\nbeyond the domain of science. It requires some other _kind_ of\nknowledge than human to understand it.\n\nBut materialists insist so much on the identity of brain-physiology\nwith psychology, that even at the risk of tediousness we will multiply\nillustrations in order, if possible, to make this point still clearer.\nSuppose, then, we exposed the brain of a living man in a state of\nintense activity. Suppose, further, that our senses were absolutely\nperfect, so that we could see every change, of whatever sort, taking\nplace in the brain-substance. What would we see? Obviously nothing but\nmolecular changes, physical and chemical; for to the outside observer\nthere is absolutely nothing else there to see. But the subject of\nthis experiment sees nothing of all this. His experiences are of a\ndifferent order, viz., consciousness, thought, emotions, etc. Viewed\nfrom the _outside_, there is--there can be--nothing but motions; viewed\nfrom the _inside_, nothing but thought, etc.--from the one side, only\n_physical_ phenomena; from the other side, only _psychical_ phenomena.\nIs it not plain that, from the very nature of the case, it must ever\nbe so? Certain vibrations of brain molecules, certain oxidations with\nthe formation of carbonic acid, water, and urea on the one side,\nand there appear on the other sensations, consciousness, thoughts,\ndesires, volitions. There are, as it were, two sheets of blotting-paper\npasted together. The one is the brain, the other the mind. Certain\nink-scratches or blotches, _utterly meaningless_ on the one, soak\nthrough and appear on the other as _intelligible writing_, but how we\nknow not, and can never hope to guess. But when the paste dissolves,\n_shall the writing remain_? We shall see.\n\nBut some will object. There is nothing specially strange and unique\nin all this, for the same mystery underlies the essential nature of\nall kinds of force and matter, and therefore all phenomena. True\nenough, but with this difference. Physical and chemical forces and\nphenomena are indeed incomprehensible in their essential nature; but\nonce accept their existence, and all their different forms are mutually\nconvertible, construable in terms of each other and all in terms of\nmotion. But it is impossible by any stretch of the imagination to\nthus construe mental forces and mental phenomena. It may, indeed, be\nimpossible to conceive _how came_ the plane of material existence, but,\nstanding on that plane, all phenomena fall into intelligible order. But\nthere is another plane above this one, having no intelligible relation\nwith it. We must climb up and stand on this before its phenomena fall\ninto intelligible order. In a word, material forces and phenomena are,\nindeed, a mystery, but only of the _first order_. But mental and moral\nforces and phenomena are a mystery even from the standpoint of the\nother, and are therefore a mystery of the _second order_--a mystery\nwithin a mystery.\n\nWe repeat, then, with additional emphasis after this examination, that\nwe can not imagine between physical and psychical phenomena a relation\nof cause and effect _in the same sense_ in which we use these terms\nin physical science, although in some sense there is doubtless such a\nrelation. If man were the only animal we had to deal with, there would\nbe no standing ground left for materialism. But there is still another\ndifficulty which sticks deeper. It is that suggested by the _law of\nevolution_ and enforced by the _comparative method_.\n\n=Relation of Man to Animals.=--Man, we say, is endowed with, _is_, in\nfact, an immortal spirit. What is spirit? We know things only by their\nphenomena; what are the phenomena of spirit? Consciousness, will,\nintelligence, memory, love, hate, fear, desire--surely these are some\nof them. But has not a dog or a monkey all these? Pressed with this\ndifficulty, some have indeed felt compelled to accord immortal spirit\nto higher animals. But we can not stop here. If to these, then also to\nall animals; for we have here only a sliding scale without break. Can\nwe stop now and make it coextensive with sentiency? No; for the lowest\nanimals and lowest plants merge into each other so completely that no\none can draw the line between them with certainty. We must extend it to\nplants also. Shall we stop here and make immortal spirit coextensive\nwith life? We can not; for life-force is certainly correlated with,\ntransmutable into, and derivable from, physical and chemical forces. We\nmust extend it into dead nature also. Therefore, everything is immortal\nor none. Our boasted immortality by continued extension becomes\nthinner and thinner until it evaporates into thin air. It becomes\nnaught else than _conservation of energy_, and not, as we had hoped,\nconservation of _self-conscious personality_. This may be interesting\nas a scientific fact; but of what value to us personally is a continued\nexistence of our spiritual forces as heat, light, electricity, or\nany other form of unconscious force? Thus, then, if once we pass the\ngap between man and the higher animals, there is no possibility of a\nstopping-place anywhere.\n\nSuch is the difficulty presented by comparison in the _taxonomic_\nseries. Take now the _embryonic_ series. Each one of us, individually,\nwas formed gradually by a process of evolution, from a microscopic\nspherule of protoplasm undistinguishable in structure from the lowest\nforms of protozoal life. Now, in this gradual process of evolution,\nwhere did immortal spirit come in? Was it in the germ-cell? Then why\ndeny it to the protozoan? Was it at the quickening, or at the birth,\nor at the moment of first self-consciousness, or at some later period\nof capacity of abstract thought? Again, when it did come in, was it\nsomething superadded or did it grow out of something already existing\nin the embryo or the infant?\n\nOr take the _evolution series_ from protozoan to man. This we have\nalready seen is similar in outline to the other two. Now, in the\ngradual evolution of the animal kingdom throughout all geological time,\nterminating in man, when did immortal spirit come in? Did it enter with\nlife, or with sentient life, or somewhere in the ascending scale of\nanimals, or with the advent of man? If with man, was it some new thing\nadded at once out of hand, or did it grow out of something already\nexisting in animals?\n\nThis last, we are persuaded, is the only tenable view--the only view\nthat can effect that reconciliation between the two extreme, mutually\nexcluding views now usually held, which, as already seen, is the true\ntest of a rational philosophy. I believe that the spirit of man _was_\ndeveloped out of the _anima_ or conscious principle of animals, and\nthat this, again, was developed out of the lower forms of life-force,\nand this in its turn out of the chemical and physical forces of Nature;\nand that at a certain stage in this gradual development, viz., with\nman, it _acquired_ the property of immortality precisely as it now,\nin the individual history of each man at a certain stage, acquires\nthe capacity of abstract thought. This is, in brief, the view which I\nwish to enforce. The reader must understand, however, that this is _my\nown view_ only, a view for which I have earnestly contended for twenty\nyears. It appeals, therefore, not to authority, but only to reason. I\nwish now to present it as briefly as possible.\n\nFirst, then, I would draw attention to the fact that there is nothing\nwholly exceptional in such transformation with the sudden appearance of\nnew powers and properties; but, on the contrary, it is in accordance\nwith many analogies in the lower forces, and therefore _a priori_\nnot only credible but probable. For example, force and matter may\nbe said to exist _now_ on several distinct planes raised one above\nanother. There is a sort of taxonomic scale of force and matter. These\nare, 1, the plane of elements; 2, the plane of chemical compounds;\n3, the plane of vegetal life; 4, the plane of animal life; and 5,\nthe plane of rational and, as we hope, immortal life. Each plane has\nits own appropriate force and distinctive phenomena. On the first\noperates physical forces, producing physical phenomena only--for the\noperation of chemical affinity immediately raises matter to the next\nplane. On the second plane operates, in addition to physical, also\nchemical forces, producing all those changes by action and reaction,\nthe study of which constitutes the science of chemistry. On the\nthird plane, in addition to the two preceding forces, with their\ncharacteristic phenomena, operates also life-force, producing the\ndistinctive phenomena characteristic of living things. On the fourth\nplane, in addition to all lower forces and their phenomena, operates\nalso a higher form of life-force characteristic of animals, producing\nthe phenomena characteristic of sentient life, such as sensation,\nconsciousness, and will. On the fifth plane, in addition to all the\npreceding forces and phenomena, we have also the forces and phenomena\ncharacteristic of rational and moral life.\n\nNow, although there are doubtless great differences of level on each\nof these planes, yet there is a very distinct break between each.\nAlthough there are various degrees of the force characteristic of each,\nyet the difference between the characteristic forces is one of kind\nas well as of degree. Although energy by transmutation may take all\nthese different forms, and thus does now circulate up and down through\nall these planes, yet the passage from one plane upward to another is\nnot a gradual passage by sliding scale, but _at one bound_. When the\nnecessary conditions are present, a new and higher form of force at\nonce appears, _like a birth_ into a higher sphere. For example, when\nhydrogen and oxygen are brought together under proper conditions, water\nis born--a new thing with new and wholly unexpected properties and\npowers, entirely different from those of its components. When CO2, H2O,\nand NH3 are brought together under suitable conditions, viz., in the\ngreen leaves of plants, in the presence of sunlight, living protoplasm\nis then and there born, a something having entirely new and unexpected\npowers and properties. It is no gradual process but sudden, like birth\ninto a higher sphere.\n\nNow, there is not the least doubt that the same is true of the order\nand manner of the _first appearance_ of the natural forces in the\nphylogenic series. In the history of the evolution of the cosmos,\nthe forces of Nature have appeared successively and suddenly when\nconditions became favorable. There was a time in the history of the\nearth when only physical forces existed, chemical affinity being held\nin abeyance by the intensity of the heat.[41] By gradual cooling,\nchemical affinity at a certain stage came into being--was born, a\nnew form of force, with new and peculiar phenomena, though doubtless\nderived from the preceding. Ages upon ages passed away until the\ntime was ripe and conditions were favorable, and life appeared--a\nnew and higher form of force, producing a still more peculiar group\nof phenomena, but still, as I believe, derived from the preceding.\nAges upon ages again passed away, during which this life-force\ntook on higher and higher forms--in the highest foreshadowing and\nsimulating reason itself--until finally, when the time was fully ripe\nand conditions were exceptionally favorable, spirit, self-conscious,\nself-determining, rational, and moral, appeared--a new and still higher\nform of force, but still, as I am persuaded, derived from the preceding.\n\nNow, that these forces are really of derivative origin is proved by the\nfact that we see every step of this process taking place daily under\nour very eyes. I pass over the conversion of physical into chemical\nforce because this is admitted on all hands. I begin, therefore, with\nvital force. Sunlight falling on green leaves disappears as light\nand reappears as life--is consumed in doing the work of decomposing\nCO2, H2O, and NH3, and the C, H, O, and N thus set free from\nprevious combination unite to form living protoplasm.[42] Again, in\nthe embryonic history of every animal we see the next change take\nplace--i. e., the emergence of the psychic out of the vital. In the\ngerm-cell, in the egg, and even in the early stages of the embryo,\nthere is no distinctive animal life--i. e., no consciousness, nor\nvolition, nor response of any kind to stimulus. At a certain stage\ndistinctive animal or psychic life appears. We call it quickening.\nMaterials for psychology are now present for the first time. In man\nalone, and that only some time after physical birth, we see the last\nchange. The new-born child has animal life only. The emergence of\nself-consciousness--a change so wonderful that it may well be called\nthe birth of spirit--takes place only at the age of two to three years.\nNow for the first time we have phenomena distinctive of humanity.\n\nBut some will ask, \u201cHow is this consistent with immortality?\u201d In\nanswer, let me again remind the reader that with every new form of\nforce, with every new birth of the universal energy into a higher\nplane, there appear new, unexpected, and, previous to experience,\nwholly unimaginable properties and powers. This last birth is of course\nno exception. Why may not immortality be one of these new properties?\nBut this point is so important that we must treat it more fully.\n\nRemember, then, the view of the relation of God to Nature, already\nexplained. Remember that the forces of Nature are naught else than\ndifferent forms of the one omnipresent Divine energy. Remember that, as\njust shown, this Divine omnipresent energy has taken on successively\nhigher and higher forms in the course of cosmic time. Now this upward\nmovement has been wholly by _increasing individuation_, not only\nof matter, but also _of force_. This universal Divine energy, in a\ngeneralized condition, _unindividuated_, diffused, pervading all\nNature, is what we call physical and chemical force. The same energy in\nhigher form, individuating matter, and itself individuated, but only\nyet very imperfectly, is what we call the life-force[43] of plants. The\nsame energy, more fully individuating matter and itself more fully\nindividuated, but not completely, we call the _anima_ of animals. This\nanima, or animal soul, as time went on, was individuated more and more\nuntil it resembled and foreshadowed the spirit of man. Finally, still\nthe same energy, completely individuated as a separate entity and\ntherefore self-conscious, capable of separate existence and therefore\nimmortal, we call the spirit of man.\n\nAccording to this view, the vital principle of plants and the anima\nof animals are but different stages of the development of spirit in\nthe womb of Nature: _in man at last it came to birth_. In plants and\nanimals it was in deep embryo sleep--in the latter, quickened, indeed,\nbut not viable--still unconscious of self, incapable of independent\nlife, with physical, umbilical connection with Nature; but now at last\nin man, separated from Nature, capable of independent life, born into\na new and higher plane of existence. Separated, but not wholly: Nature\nis no longer _gestative_ mother, but still _nursing_ mother of spirit.\nAs the _organic embryo_ at birth reaches independent _material_ or\n_temporal_ life, even so _spirit embryo_ by birth attains independent\n_spiritual_ or _eternal_ life.\n\nAlthough birth is its truest correspondence and best illustration, yet\nwe may vary the illustration in many ways:\n\n1. Nature may be likened to a level water-surface. This represents\nunindividuated physical and chemical force. On this surface some\nindividuating force pulls up a portion of the water into a _commencing_\ndrop. This represents the condition of spirit in plants. Or by greater\nforce the surface may be lifted higher into a nipple-like eminence\n_simulating a drop_, or even into an almost complete drop with only\na neck-like connection with the general surface. This represents the\ncondition of spirits in the higher animals. In all these cases, even\nthough the drop be nearly completed, if we remove the individuating\nor lifting force, the commencing drop is immediately drawn back by\ncohesion and refunded into the general watery surface. But, once\ncomplete the drop, and there is no longer any tendency to revert, even\nthough the lifting force is removed. This represents the condition of\nspirit in man.\n\n2. Or Nature may, again, be likened to a water-surface beneath which\nthe anima of animals is deeply and tranquilly submerged, wholly\nunknowing of any higher, freer world above. In man spirit emerges above\nthe surface into a higher world, looks down on Nature beneath him,\naround on other emerged spirits about him, and upward to the Father of\nall spirits above him. Emerged, but not wholly free--head above, but\nnot yet foot-loose.\n\n3. Or, again: As a planet must break away from physical, cohesive\nconnection with the central sun (planet-birth) in order to enter into\nhigher gravitative relations, which thenceforward determine all its\nmovements in beautiful harmony; as the embryo must break away from\nphysical umbilical connection with the mother in order to enter into\nhigher spiritual bonds of love, which thenceforward determine all\ntheir mutual relations--even so spirit must break away from physical\nand material connection with the forces of Nature, which are but the\nomnipresent Divine energy, in order thereby to enter into higher\nrelations of filial love to God and brotherly love to man.\n\n4. As the new-born child differs little in grade of physical\norganization from the mature but unborn embryo, but at the moment\nof birth there is a sudden and complete change, not so much in the\ngrade of organization but in the whole plane of existence--a change\nabsolutely necessary for further advance, for another cycle of life;\neven so at the moment of the origin of man, howsoever this may have\nbeen accomplished, there may have been no great change in the _grade_\nof _psychical_ structure, but yet a complete change in the _plane_ of\npsychical life--a change absolutely necessary for further advance, for\nanother cycle of evolution. In both cases there is a sudden entrance\ninto a new world, the sudden appearance of a new creature with entirely\ndifferent capacities--a passing out of an old world, a waking up in\na new and higher. According to this view, man alone is a _child_ of\nGod, capable of separate spirit-life--separate but not yet wholly\nindependent of Nature. As already said, Nature is no longer gestative\nmother, but still nursing mother of spirit--we are weaned only by\ndeath.\n\n5. Or, again: As in passing up the _organic_ scale, we find all grades\nof completeness of organic individuality, an increasing individuation\nof bodily form which completes itself as a perfect organic individual\nonly in the higher animals, so, also, in passing up the _dynamic_\nscale, force or energy is individuated more and more until the process\nreaches completeness as a spirit-individual or dynamic individual--a\nperson only in man. _Organic_ individuality completes itself in\nanimals. _Psychic_ individuality only in man.\n\n6. One more illustration and the last. The animal body may be likened\nto an exquisitely adjusted instrument of communication between two\nworlds--the material world without and the spiritual world within. The\nkey-boards of this marvelous instrument are the nerve-terminals of the\nsense-organs in contact with the material world, and the brain-cells\nin touch with the spirit-world. External Nature plays on the one by\nsensation and determines changes in spirit. Spirit plays on the other\nby will and muscular contraction, and determines changes in external\nNature. Now, in animals spirit is fast asleep or at most dreaming, or\neven perhaps somnambulistic, but at least unconscious of _self_, and\nacts only by stimulus--only responds in some sense automatically as\nsleepers do. In man spirit is wide awake and may respond automatically\nlike animals, or may choose not to respond at all. Moreover, it acts\nfreely in its own domain--the world of ideas--_without external\nstimulus_; or of its own free-will may _initiate_ changes in the\nexternal world. With God all phenomena commence at the _spirit-end_.\nIn animals all commence at the _matter-end_, and by automatic response\nterminate in the same. Man alone lives in both worlds, partakes of both\nnatures, and acts according to either method.\n\nThe more we reflect on this subject, the more we shall be convinced\nthat completed spirit individuality explains, as nothing else can, all\nthat is characteristic of man. It is this which constitutes person, or\nthe self-acting ego. It is this which constitutes self-consciousness,\nfree-will, and moral responsibility. And out of these, again, grows,\nthe recognition of relations to other moral beings and to God, and\ntherefore ethics and religion. Out of these, also, grows the capacity\nof indefinite voluntary progress. This also means separate life,\nspirit-viability, or immortality. Self-consciousness especially seems\nto me the simplest sign of separate entity or spirit-individuality,\nand its appearance among psychical phenomena _the very act of\nspirit-birth_. We may imagine man to have emerged ever so gradually\nfrom animals: in this gradual development the moment he became\nconscious of self, the moment he turned his thoughts inward in wonder\nupon himself and on the mystery of his existence as separate from\nNature, that moment marks the birth of humanity out of animality.\nAll else characteristic of man followed as a necessary consequence.\nI am quite sure that, if any animal, say a dog or a monkey, could be\neducated up to the point of self-consciousness (which, however, I am\nsure is impossible), that moment _he_ (no longer _it_) would become a\nmoral responsible being, and all else characteristic of moral beings\nwould follow. At that moment would come personality, immortality,\ncapacity of voluntary progress; and science, philosophy, religion,\nwould quickly follow.\n\nWe have emphasized self-consciousness as the most fundamental sign of\nspirit-individuality; but a difference of exactly the same kind is\nfound running through the whole gamut of human faculties as compared\nwith corresponding faculties in animals. As animal consciousness is\nrelated to human self-consciousness, so exactly is animal will to human\nfree-will, animal intelligence to human reason, animal sign-language to\nrational grammatical speech of man, constructive art of animals to true\nrational progressive art of man. In every one of these the resemblance\nis great, but the difference is immense, and not only in degree but\nalso in kind. In every case it is like shadow and substance, promise\nand fulfillment, or, still better, it is like embryo and child. The\nchange from one to the other is like to a birth into a higher sphere,\nthe beginning of another cycle of evolution. We would like to follow\nthis idea out in detail, but it would lead us beyond the scope of this\nwork. Those who desire to do so we would refer to an article by the\nauthor on the \u201cPsychical Relation of Man to Animals.\u201d[44]\n\nBut it will be objected that there are other births of energy from\nlower to higher condition; but such births do not insure continued\nexistence in the higher condition. In the gradual evolution of energy\ndescribed on page 316, when a portion rises from physical to chemical,\nfrom chemical to vital, or from vital to sentient, it does not remain\never after in the higher condition--there is no immortality on the\nhigher plane. On the contrary, all these lower forms of energy are\ncontinually ascending and descending; transformation is downward as\nwell as upward. Why should there be an exception in this last birth?\nIn these successive upward metamorphoses of energy why should the last\nonly be permanent? I answer: Because it reaches at last its final goal,\nviz., complete individuation, as free, self-acting spirit; it reaches\nagain the spiritual plane from which it sprang, and becomes thereby\na partaker of the Divine nature; because it comes at last into moral\nrelations with the absolute--the Divine--and therefore above the plane\nof shifting changes. If the scale of energy be likened to a ladder with\nmany rounds, reaching from the plane of matter to the plane of spirit,\nthen so long as energy is on the ladder it ascends and descends; but,\nonce it reaches the plane of free spirit, it is in a wholly new world\nin which eternal ascent is the law.\n\nPerhaps I can best bring out the reasonableness of my view by comparing\nit with other possible alternative views.\n\nThere are three possible views as to the nature, the origin,\nand the destiny of the human spirit: (1.) That it pre-existed\nalways--uncreated, underived, eternal, both ways--backward as well\nas forward. Therefore, as it never began, so it will never end. It\nis _immortal of its own right_. This is substantially the view of\nPlato, of Leibnitz, and perhaps some other philosophers. (2.) That\nit is derived from God _directly_--created at once _without natural\nprocess_; that at the moment of creation of the first man Adam, and\nat some unknown time and in some inscrutable way in the history of\neach individual, it was _injected into the body from the outside_,\nand at the same time _endowed_ with immortality. This, I take it, is\nthe orthodox view. (3.) That it was indeed derived from God, but not\ndirectly; created indeed, but only by natural process of evolution;\nthat it indeed pre-existed, but only as embryo in the womb of Nature,\nslowly developing through all geological times, and finally coming\nto birth as _living_ soul in man. Thus it _attains_ immortality at a\ncertain stage of development, viz., at spirit-birth. This is the view I\nhave striven to enforce.\n\nI hold up these three views: Which is the more rational? The view of\nPlato--that of self-existent, uncreated, eternal spirit--I think few\nwill entertain at this time of the world\u2019s day. The usual orthodox\nview I have shown is surrounded with insuperable difficulties; is\nwholly unscientific and irrational. What is there left but the view\npresented above? Plato is right in asserting pre-existence, but wrong\nin denying creation. The usual view is right in asserting creation, but\nwrong in denying natural process. The view I have presented asserts\npre-existence in embryo and creation by natural process. It therefore\ncombines and reconciles the two extreme views, and is more rational\nthan either.\n\n=Some General Conclusions.=--There are still two or three thoughts so\nclosely connected with what we have already said that we can not pass\nthem over:\n\n1. We have seen that every mental state corresponds with a particular\nbrain state, and every mental change with a brain change. We have,\ntherefore, here, two series, physical and psychical, corresponding\nwith each other, term for term. For every change in the one there is\na corresponding change in the other, both in kind and amount. Now, is\nnot this the test of the relation of cause and effect? It certainly is.\nYes, there must be a causal relation here, even though we are not able\nto understand the nature of the causal nexus. But which is cause and\nwhich effect? If the view above presented be correct, then in animals\n_brain changes_ are in all cases the _cause_ of psychical phenomena.\nIn man alone, and only in his higher activities, _psychic_ changes\nprecede and determines brain changes. In man alone brain changes\nare determined not only by external but by _internal_ impressions.\nMan alone perceives not only objects--_material things_--but also\nrelations and properties _abstracted_ from the objects, i. e., _ideal\nthings_; and, moreover, not only relations between objects, but also\nrelations between relations or ideas. In man alone there is an inner\nworld--microcosm--the _things_ of which are _thoughts_, ideas, etc.\nThis _self-acting power_ of spirit on _the things of itself_, instead\nof merely reacting as played upon by external nature, is characteristic\nof man, and is a necessary result and a sign of severance, partial at\nleast, of physical bond with Nature.\n\n2. Again, I have used the term vital _principle_. I must justify it.\nI know full well that it is the fashion to ridicule the term as a\nremnant of an old superstition which regards vital force as a sort of\nsupernatural entity unrelated to other forces of Nature. No one has\nstriven more earnestly than myself to establish the correlation of\nvital with physical and chemical forces;[45] and yet, if the view above\npresented be true, there is a _kind_ of justification even for the\nterm vital _principle_--much more, vital _force_. There is a kind of\nreason and true insight in the personification of the forces of Nature,\nand especially of vital force. All forces, by progressive dynamic\nindividuation, are on the way toward entity or personality, but fully\nattain that condition only in man.\n\n3. Again, to perceive relations and properties abstracted from material\nthings, to form abstract or general ideas, to form not only _per_cepts\nbut also _con_cepts, is admitted to be a characteristic of man--a\ncharacteristic on which all our science and philosophy rest. From time\nimmemorial the vexed question has been debated, \u201cHave such abstract\nor general ideas any _real_ existence, or are they mere _names_ of\nfigments of the mind?\u201d This is the famous question of _realism_ and\n_nominalism_. Now, if our view be correct, then there is one most\nfundamental abstraction, viz., _self_, which is indeed a _reality_.\nSelf-consciousness is the direct recognition of the one reality,\nspirit, of which all others are the sign and shadow--the true reality\nwhich underlies and gives potency to all abstractions or ideas. Do\nwe not find in this view, then, the foundation of a true realism, or\nrather a complete reconciliation of realism and nominalism?\n\n4. Thus, then, Nature, through the whole geological history of the\nearth, was gestative mother of spirit, which, after its long embryonic\ndevelopment, came to birth and independent life and immortality in man.\nIs there any conceivable meaning in Nature without this consummation?\nAll evolution has its beginning, its course, its end. Without\nspirit-immortality this beautiful cosmos, which has been developing\ninto increasing beauty for so many millions of years, when its\nevolution has run its course and all is over, would be precisely as if\nit had never been--an idle dream, an idiot tale signifying nothing. I\nrepeat: Without spirit-immortality the cosmos has no meaning. Now mark:\nIt is equally evident that, _without this gestative method of creation\nof spirit_, the whole geological history of the earth previous to man\nwould have no meaning. If man\u2019s spirit were made at once out of hand,\nwhy all this elaborate preparation by evolution of the organic kingdom?\nThe whole evolution of the cosmos through infinite time is a gestative\nprocess for the birth of spirit--a divine method of the creation of\nspirits.\n\nThus, again, man is born of Nature into a higher nature. He therefore\nalone is possessed of two natures--a lower, in common with animals,\nand a higher, peculiar to himself. The whole mission and life-work of\nman is the progressive and finally the complete dominance, both in the\nindividual and in the race, of the higher over the lower. The whole\nmeaning of sin is the humiliating bondage of the higher to the lower.\nAs the _material_ evolution of Nature found its goal, its completion,\nand its significance in man, so must man enter immediately upon a\nhigher _spiritual_ evolution to find its goal and completion and its\nsignificance in the ideal man--the Divine man. As spirit, unconscious\nin the womb of Nature, continued to develop by _necessary_ law until\nit came to birth and independent life in man, so the new-born spirit\nof man, both in the individual and in the race, must ever strive by\n_freer_ law to attain, through a newer birth, unto a higher life.\n\n\n\n\nCHAPTER V.\n\nTHE RELATION OF GOD TO MAN.\n\n\nIn the two preceding chapters we have discussed the relation of God\nto Nature and of man to Nature. There is still another relation, if\npossible, of still more vital importance to us, viz., the _relation of\nGod to man_. This, of course, introduces the question of revelation--a\nsubject which I approach with some reluctance. I feel I am treading\non holy ground, and must do so with shoes removed. If it be asked,\nHow is evolution concerned with the subject of revelation? I answer\nEvolution emphasizes and enforces the reign of law taught by all\nscience, and makes it at last _universal_. Many conclude, therefore,\nthat, if evolution be true, a belief in the possibility of any form\nof revelation is irrational. I do not think this follows, and I will\ngive my reasons. I do so, however, very briefly, because we are not yet\nready to formulate our views except in the most general way.\n\nIf man be indeed something more than a higher species of animal; if\nman\u2019s spirit be indeed a spark of Divine energy individuated to the\npoint of self-consciousness and recognition of his relation to God; if\nspirit embryo, developing in the womb of Nature through all geological\ntime, came to birth and independent spirit-life in man, and thus man\nalone is a _child of God_ as well as a product of Nature--if all this\nbe true, then it is evident that this wholly _new_ relation requires\nalso a wholly different mode of Divine operation. If God operates on\nNature only by regular processes, which we call _natural laws_, then he\n_must_ operate on spirit in a different and a more direct way, and this\nwe call _revelation_. If to the student of Nature it is inconceivable\nthat He should operate on Nature except by natural laws (for this is\nthe name we give to His chosen mode of operation there), then to the\nstudent of theology it is equally inconceivable, if our view of man\nbe true, that He should not operate on spirit in some more direct and\nhigher way, i. e., by revelation.\n\nBut some will ask, Is not this a palpable violation of law? I think\nnot. All divine operations are, must be, according to reason, i. e.,\naccording to law. The operation of the divine on the human spirit,\ni. e., revelation, must therefore be according to law, but a higher\nlaw than that which governs Nature, and, therefore, from _the point\nof view of Nature_, supernatural. There is nothing wholly unique in\nthis. Life is a higher form of force than the physical and chemical.\nLife-phenomena are therefore super-physical, and if we confined the\nterm Nature to dead Nature they would be supernatural. So the free,\nself-determined acts of spirit on spirit, even of the spirit of man\non the spirit of man, much more of the Spirit of God on the spirit\nof man, may be according to law, and yet from the natural point of\nview be supernatural. It is true that, in the complex of phenomena,\nmaterial and spiritual inextricably woven together, which go to make\nup human life, Science must ever strive to reduce as much as possible\nto material laws, for this is her domain, and she is bound to extend\nit; but, if our view of man be true, there will always remain a\nlarge residuum of phenomena--a whole world of phenomena--which will\nnever yield, because clearly beyond her domain. Standing on the\nlower material plane, these phenomena are wholly super-material, and\ntherefore incomprehensible from the material point of view. We must\nrise and stand on the higher plane before these also are reduced to\nlaw, but a higher law than that operating on the lower plane. If,\ntherefore, science insists on banishing the supernatural from the realm\nof Nature, theology may reasonably insist on its necessity, _in this\nsense_, in the realm of morals and religion.\n\nIf, then, the direct influence of the Spirit of God on the spirit of\nman be what we call revelation, then there is evidently no other kind\nof revelation possible; and, furthermore, such revelation is given to\nall men in different degrees. It is given to all men as conscience;\nin greater measure to all great and good men as clearer perception of\nrighteousness; in pre-eminent measure to Hebrew prophets and Christian\napostles; but supremely and perfectly to Jesus alone. But there is, and\nin the nature of things there can be, _no test of truth but reason_.\nWe _must_ fearlessly, but honestly and reverently, try all things,\neven revelations, by this test. We must not regard, as so many do,\nthe spirit of man as the passive amanuensis of the Spirit of God.\nRevelations to man must of necessity partake of the imperfections of\nthe medium through which it comes. As pure water from heaven, falling\nupon and filtering through earth, must gather impurities in its course\ndiffering in amount and kind according to the earth, even so the pure\ndivine truth, filtering through man\u2019s mind, must take imperfections\ncharacteristic of the man and of the age. Such filtrate must be\nredistilled in the alembic of reason to separate the divine truth from\nthe earthy impurities.\n\n\n\n\nCHAPTER VI.\n\nTHE OBJECTION, THAT THE ABOVE VIEW IMPLIES PANTHEISM, ANSWERED.\n\n\nIt will be observed that the views presented in the last three\nchapters are closely connected with one another, and all conditioned\non the \u201cRelation of God to Nature,\u201d urged in Chapter III. Now it will\ndoubtless be objected to this view, especially as applied in Chapter IV\non the \u201cRelation of Man to Nature,\u201d that it is naught else than pure\npantheism; that it destroys completely the personality of Deity, and\nwith it all our hopes of communion with him, and all our aspirations of\nlove and worship toward him; that, according to this view, God becomes\nonly the soul or animating principle of Nature, operating everywhere\nbut unconsciously like the vital principle of an organism; that the\nwhole cosmos becomes in fact a great organism, developing under the\noperation of _resident_ force according to _necessary_ law, only that\n_we_ apotheosize this omnipresent force and call it God; and finally,\nthat God is naught else than an abstraction, created like other\nabstractions or general ideas wholly by the human mind, and having no\nobjective existence. Furthermore, it will be said, that according to\nthis view, this omnipresent unconscious energy individuates itself by\nnecessary law of evolution more and more until it reaches, _for the\nfirst time in man_, self-consciousness and immortality, and thus that\nman himself is the only self-conscious immortal being in existence, and\ntherefore the only being worthy of reverence and worship. Thus, this\nview leads to humanity-worship or rather to _self-worship_.\n\nI feel the full force of this objection. I answer it as follows: I\nfreely admit that, following up this scientific line of thought alone,\nwe are carried strongly in the direction of pantheism. But there is\nnothing strange or exceptional in this. In all the deepest questions,\nsingle lines of thought inevitably carry us to extreme one-sided views.\nThis seems to be the necessary result of the essentially two-fold\nnature of man, self-conscious spirit in a material body, the relation\nbetween which is, and must ever be, inscrutable. On this account\nthere is and must be a fundamental antithesis in human philosophy,\ni. e., two lines of thought, the material and spiritual, which lead\nto two apparently irreconcilable views.[46] We have already seen\nthat a rational philosophy, whenever we are able to reach such, is\nalways found in a higher and more comprehensive view, which includes,\ncombines, and reconciles two one-sided, partial, and mutually excluding\nviews. But spirit and matter, or mind and brain, or God and Nature,\nis _the_ fundamental antithesis which underlies and is the cause of\nall other lesser antitheses. This antithesis, therefore, is absolutely\nfundamental, and therefore forever irreconcilable. We must accept\nboth sides, even though we can not clearly perceive the nature of\ntheir relation. We must be content with compromise where we can not\neffect complete reconciliation. We must frankly acknowledge that the\nantagonism is apparent only, and the result of the limitation of our\nfaculties, and believe that, if we could only rise to a high enough\npoint of view, like all other antitheses, this also would disappear in\na rational philosophy.\n\nNow, to apply these principles. No one, we admit, can form a clear\nconception of how immanence of Deity is consistent with personality,\nand yet we must accept both, because we are irresistibly led to each\nof these by different lines of thought. Science, following one line of\nthought, uncorrected by a wider philosophy, is naturally led toward the\none extreme of pantheistic immanence; the devout worshiper, following\nthe wants of his religious nature, is naturally led toward the other\nextreme of anthropomorphic personality. The only rational view is to\naccept both immanence and personality, even though we can not clearly\nreconcile them, i. e., immanence without pantheism, and personality\nwithout anthropomorphism. We have already seen in the third chapter,\nhow following the scientific line of thought, we are logically driven\nto immanence. We wish now to show how, following another line of\nthought, we are as logically driven to personality. On this most\ndifficult subject, however, all we are prepared to do is to throw out\nsome brief suggestions, in the hope that they may be carried out more\nperfectly by some thoughtful reader; scatter some seed-thoughts, in the\nhope that, falling haply on good soil, they may spring up and bear more\nfruit than I have been able to produce.\n\n1. In the gradual individuation of the universal Divine energy\ndescribed in Chapter IV, there must of course be a corresponding growth\nof a kind of independent self-activity which reaches completeness\nin man, and in fact constitutes what we call self-consciousness\nand free will. The exact nature of the relation of Deity or of the\ngeneral forces of Nature to this gradually individuated portion, I do\nnot undertake to define. And how this idea of partial self-activity\ncomports with the absoluteness of Deity we can not clearly understand.\nBut this fact need not specially disturb us here; for this is only one\nbranch of the wider question of the moral agency of man in relation to\nthe absolute sovereignty of God, or the freedom of man in relation to\nnecessary law in Nature.\n\n2. =Personality behind Nature.=--We have already shown that, if the\nbrain of a living, thinking man were exposed to the scrutiny of an\noutside observer with absolutely perfect senses, all that he would\nor could possibly see would be molecular motions, physical and\nchemical. But the subject himself, the thinking, self-conscious spirit,\nwould experience and observe by introspection only consciousness,\nthought, emotion, etc. On the _outside_, only physical phenomena;\non the _inside_ only psychical phenomena. Now, _must not the same\nbe necessarily true of Nature also?_ Viewed from the outside by the\nscientific observer, nothing is seen, nothing can be seen, there is\nnothing else to be seen, but motions, material phenomena; but behind\nthese, on the other side, on the _inside_, must not there be in this\ncase also psychical phenomena, consciousness, thought, will; in a word,\n_personality_?[47] In the only place where we do get behind physical\nphenomena, viz., in the brain, we find psychical phenomena. Are we not\njustified, then, in concluding that in all cases the psychical lies\nbehind the physical? The human brain is a wonderful instrument, by\nmeans of which, in some inscrutable way, viz., in our own experience,\nwe do get behind, on the other side, on the inside of some material\nphenomena, and in so far become partakers of the Divine nature. But\nbehind other phenomena of Nature we may never hope to penetrate either\nby observation or experience, but only in dim way by highest reason.\nScience, even in the case of the brain, can not pass from the one kind\nof phenomena to the other. If she would study the _inside_ she must\nabandon the _outside_--she must abandon the microscope and take to\nintrospection. If she would study the phenomena of the higher platform,\nshe must leave the lower and climb up and stand on the higher. If this\nbe true of the brain where the two kinds of phenomena are brought\nso close together, how much more is it true of the phenomena of the\ncosmos. We can never hope, either by observation or by experience,\nto pass beyond the veil. We must abandon the methods of science and\nreach it, if at all, in some other way. Not the clear-sighted but the\npure-hearted shall see God in Nature.\n\nThus, then, we see that our own self-conscious personality behind\nbrain phenomena compels us to accept consciousness, will, thought,\npersonality behind Nature. Now I assert that, once get this abstract\nidea in the mind, and by a necessary law of thought it gradually\nexpands without limit, and eventually reaches the form of infinite\nconsciousness, will, thought, etc., and therefore of an infinite\nperson. This law of indefinite expansion may be illustrated by\nthe ideas of space and time. The animal, and, indeed, the infant,\nunderstands space and time only in their relation to itself, but has\nnot yet abstracted these from their contents. This comes only with\nthe birth of self-conscious personality. But, so soon as the abstract\nidea of space is acquired, by a necessary law of mental activity\nit expands without limit, and finally becomes the idea of infinite\nspace. Similarly, so soon as the idea of time as abstracted from its\ncontents is conceived, it inevitably expands without limit and grows\ninto the idea of infinite time. So is it precisely with the idea of\nself-conscious personality. The animal or the very young child is\nindeed conscious of its body and of external objects in their mutual\nrelations, but not of self, as abstracted from its contents. The\nanimal never attains it, the child does. Now, so soon as this idea of\nself-conscious personality--of a spiritual entity underlying material\nphenomena--appears, by a necessary law of mental activity it expands\nwithout limit, and inevitably reaches the idea of an infinite self, an\ninfinite person, God, behind the phenomena of Nature.\n\nBut some will object that this idea of infinite personality\nis inconceivable. True enough; but _the opposite is far more\ninconceivable_. The ideas of infinite space and infinite time are\nalso inconceivable, yet we must accept them, because the idea of all\nspace or all time being limited is still more inconceivable; for\nif we think of space or time as limited, immediately there comes\nthe question, \u201cWhat is there beyond the limit?\u201d There is therefore\nthis wide difference between these two inconceivables: the one is\nso only in the sense of transcending the power of our mind, but the\nother is unthinkable, self-contradictory, absurd. So also is it with\nself-conscious personality. The idea of an infinite self, i. e., God,\nis indeed inconceivable, but only in the sense of transcending our\npower of comprehension; but the idea of the consciousness behind the\ncosmos as being limited or finite is more than inconceivable, it is\nunthinkable, self-contradictory, absurd; for immediately comes the\nquestion, \u201cWhat is there beyond which limits it?\u201d To the Greek mind\nZeus was limited; therefore of necessity came also the idea of Fate,\nsuperior to and limiting Zeus himself. To them, therefore, Fate was the\nreal God--the absolute.\n\n3. _Divine Personality._--I have used the word personality as\nexpressing the nature of God. But let me not be misunderstood. I\nwell know we can not conceive clearly of an infinite, unconditioned\npersonality. Deeply considered, it seems nothing short of a\ncontradiction in terms. All I insist on is this: In our view of the\nnature of God, the choice is not between personality and something\n_lower_ than personality, viz., an _unconscious force_ operating\nNature by _necessity_, as the materialists and pantheists would have\nus believe; but between personality as we know it in ourselves and\nsomething inconceivably _higher_ than personality. Language is so\npoor that we are obliged to represent even _our_ mental phenomena by\nphysical images. How much more, then, the Divine nature by its human\nimage! Self-conscious personality is the highest thing we know or can\nconceive. We offer him the very best and truest we have when we call\nhim a Person; even though we know that this, our best, falls far short\nof the infinite reality.\n\n4. =Cause in Nature.=--We have thus far spoken only or principally\nof self-consciousness, but the same precisely is true of another\nessential attribute of personality, viz., _free-will_. Every one\nadmits causative force or forces operating in Nature. Science has shown\nthat all the different kinds of force are but different forms of one\nomnipresent energy. Now, looking abroad on Nature from the outside,\nthis omnipresent energy seems to modern science as simply resident,\ninherent in matter itself, and therefore as operating unconsciously\nand by necessity. But the question occurs, \u201cWhence did we get the idea\nof force, energy, _causation_?\u201d I answer unhesitatingly: We get it\nnot from without by observation of Nature, but from within through\nconsciousness; not from the outside view, but from, the inside view of\nphenomena. We can not conceive of phenomena without force, of effects\nwithout cause, because we are intensely conscious of being ourselves\nthrough our wills an active cause of external phenomena. If we were\nmerely passive observers, not active causers of changes in the external\nworld, then these external phenomena would seem to us merely to shift\nand change and succeed each in a certain order. We might note the\norder and determine the laws of sequence, and thus form a science;\nbut it would never enter into our minds to imagine any causal or\ndynamical nexus between them. In the mind of such passive observer,\nbut not doer--thinker, but not worker--would be completely realized\nthe only thorough-going and consistent materialistic philosophy,\ni. e., a philosophy in which, like Comte\u2019s, cause and force have no\nplace--are in fact banished as a superstition from science. But the\nclear consciousness of essential energy, of causative force within, the\ncertainty that we ourselves, through our wills and by the conscious\nexertion of force do determine changes in the external world, compels\nus to attribute all changes to causative force of some kind, and\nnaturally enough, until the interference of science, to a personal will\nlike our own. Thus by a necessary law we project our internal states\ninto external Nature.\n\nBut see now the steps of evolution of this idea. At first, i. e.,\nin the uncultured races, and also in childhood, external forces\ntake the form of a personal will like our own residing in _each\nobject_, and controlling its phenomena as our wills control our bodily\nmovements (fetichism). Then, as culture advances, it takes next\nthe form of several personal wills controlling each the phenomena\nof a different department of Nature (polytheism). Finally, in the\nhighest stage of culture, it takes the form of one personal will\ncontrolling the phenomena of the whole cosmos (monotheism). To the\nreligious but unscientific mind in all these stages the personal\nwill is anthropomorphic. But we have already seen (Chapter III) how\nanthropomorphism has been driven by science from one department after\nanother, until now at last by evolution it is driven out of Nature\nentirely, and to those following this line of thought alone, the\nphenomena of Nature are relegated to forces inherent in matter, and\noperating by laws necessary and fatal; and not only so, but material\nforces are made to invade even the realm of consciousness, and reduce\nthis also to material laws. Thus the savage _e_jects his own conscious\npersonal will into every separate object of Nature; the modern\nmaterialist _in_jects material forces into the realm of consciousness.\nBut, as already seen, a rational philosophy admits these two antithetic\nviews, and strives to combine and reconcile them. This reconciliation,\nas far as it is possible for us, is found in a personal will immanent\nin Nature, and determining directly all its phenomena.\n\nThus it is evident that the idea of a causal nexus between successive\nphenomena is a primary conception, and therefore ineradicable and\ncertain. Even from the purest evolution point of view it must be true,\nfor, if man\u2019s mind grew out of the forces of Nature, this idea must\nrepresent a fact in Nature. Also, analysis shows that all causative\nforce originates in _will_. Lastly, culture and reason, by a necessary\nlaw of expansion, carry us upward to the conception of one infinite\nsustaining and creative will. Science may sometimes obscure but can\nnot destroy this idea. Evolution, which was supposed by some to have\ndestroyed it for ever, has only temporarily obscured it in the minds\nof the unreflecting, by the supposed identity of evolution with\nmaterialism. From this temporary eclipse it now emerges with still\ngreater clearness and far greater nobleness. For, observe: All the\neffects known to us in Nature are finite; therefore a personal will,\nwhich determines these _separately_ by successive acts, as we do, must\nalso be finite like ourselves. But a will, which by _one eternal_ act\never-doing, never done, determines the evolution and the sustentation\nof an infinite cosmos, must itself be infinite. Thus only in the\ndoctrine of universal evolution do we rise to a just conception of God\nas an infinite cause.\n\n5. =Design in Nature.=--As the idea of _cause_ and force is related\nto _will_, so precisely is the idea of _design_ related to _thought_.\nWe get this also, not from without, but from within. Adaptation of\nmeans to ends is in our experience the result of thought, and we can\nnot conceive it to result otherwise. The effect of science can not be\nto destroy this primary conception--which, indeed, like all primary\nconceptions, is ineradicable, and already more certain than anything\ncan be made by proof--but only to exalt and purify our conceptions\nof the designer. For, observe: In any case of _adaptive_ structure,\nwhether in the animal body or in planetary relations, the evidence of\ndesign is not in the materials, but in the _use_ of the materials; not\nin the _parts_, but in the _adjustment_ of the parts for a purpose.\nDesign, purpose, adjustment, _adaptation_, are not material things,\nbut relations or intellectual things, and therefore perceivable only\nby thought, and conceivable only as the result of thought. It is\nsimply impossible to talk about such adaptive structures without using\nlanguage which implies design. The very word \u201c_adaptive_\u201d implies it.\nIt is impossible even to think of such structures without implicitly\nassuming intelligence as the cause. It makes no particle of difference\n_how_ the material originated, or whether it ever originated at all;\nit matters not whether the adaptation was done at once out of hand,\nor whether by slow process of modification; it matters not whether\nthe adaptive modification was brought about by a process of natural\nselection, or by pressure of a physical environment; whether without\nlaw or according to law. The removal of the result from man-like\ndirectness of separate action can not destroy the idea of design,\nbut only modify our conception of the Designer. What science, and\nespecially evolution, destroys, therefore, is not the idea of design,\nbut only our low anthropomorphic notions of the mode of working of the\nDesigner.\n\nPrecisely the same change takes place here under the influence of\nscience as has taken place in all our notions concerning God. The\nuncultured savage sees a _separate_ god in every object. As culture\nadvances, his gods become fewer and nobler, until, in the most advanced\nstates, man recognizes but one infinite God, the creator and sustainer\nof all. God is still in every phenomenon, but no longer as a separate\nGod, but only as the separate manifestation of the One. Thus culture\ntakes away our gods, but only to compel us to seek him in nobler forms\nuntil we reach the only true God. But, even after the conception of the\none God is reached, how many seem to regard him as altogether such a\none as ourselves; but science shows us that his ways are not like our\nways, nor his ends as our ends. Thus science, more than all other kinds\nof culture, simplifies while it infinitely ennobles and purifies our\nconceptions of Deity.\n\nAgain, the same change takes place in our sense of _mystery_. I\nsuppose most people imagine that it is the special mission of science\nto destroy all mystery. Many seem to think that superstition, or even\nreligion, is inseparably connected with ignorance and mystery, and\nall must disappear together before the light of science. But not so.\nThere is only a gradual progressive change--an evolution in the form of\nmystery as well as in the form of religion. To the savage everything is\na _separate_ mystery. The function of science is, indeed, to destroy\nthese separate mysteries, by explaining them; but, in doing so, it only\nreduces them to fewer and grander mysteries, and these again to still\nfewer and grander, until, in an ideally perfect science, all separate\nand partial mysteries are swallowed up in the one all-embracing\ninfinite mystery--the mystery of existence. There is still mystery\nin each object, but no longer a separate mystery--only a separate\nmanifestation of the one overwhelming mystery.\n\nOr, again, and finally: The same change occurs in our ideas of\n_creation_. At first every object is a separate creation--a\nmanufacture. With advancing science these separate, creative acts\nbecome fewer and nobler, until now, at last, in evolution, all\nare embraced and swallowed up in _one eternal_ act of creation--a\nnever-ceasing procession of the divine energy. Every object is still a\ncreation, but not a separate creation--only a separate manifestation of\nthe one continuous creative act.\n\nNow, precisely the same change must take place in our conception of\ndesign in Nature. To the uncultured there is a distinct and separate\ndesign in every separate work of Nature. But, as science advances, all\nthese distinct, separate, petty, man-like designs are merged into fewer\nand grander designs, until, finally, in evolution at last, we reach\nthe conception of the one infinite, all-embracing design, stretching\nacross infinite space, and continuing unchanged through infinite time,\nwhich includes and predetermines and absorbs every possible separate\ndesign. There is still design in everything, but no longer a separate\ndesign--only a separate manifestation of the one infinite design.\n\nThus, then, our own self-consciousness and will and thought give rise,\nnecessarily, to the conception of an infinite self-consciousness, will,\nand thought--i. e., God. The necessity to believe in self-conscious\nspirit behind bodily phenomena compels us to believe also in an\ninfinite self-conscious spirit behind cosmic phenomena. Looking at the\noperations of this ever-active spirit, whether in the one case or the\nother, _from the outside_, it looks like unconscious energy inherent\nin matter itself, and therefore like necessity, or fate. But, looked\nat from the inside _in the one case_, the brain, we perceive only\nself-conscious, free activity of spirit. Therefore, we are compelled\nto acknowledge in the other case, the cosmos, also, the same source\nof all activity, the same cause of all phenomena. We are compelled to\nacknowledge an infinite immanent Deity behind phenomena, but manifested\nto us on the outside as an all-pervasive energy. But some portion of\nthis all-pervasive energy again individuates itself more and more, and\ntherefore acquires more and more a kind of independent self-activity\nwhich reaches its completeness in man as self-consciousness and\nfree-will. We said, \u201c_a kind of_ independent self-activity.\u201d How this\ncomports with the absoluteness of God we can not understand, any more\nthan we can understand how it comports with invariable law in Nature.\nWe simply accept them both as primary truths, even though we can never\nhope to reconcile them completely, because we can not understand the\nexact nature of the relation of spirit to matter. We can not look at\nthe outside and the inside at the same time. If we could understand\nthe relation of psychical phenomena to brain-changes, then might\nwe hope to understand far more perfectly than now the relation of\nGod to Nature. But as in the one case, the brain, although we can\nnot understand the _nature_ of the relation, yet we are sure of the\nintimacy of the connection of the two series, psychical and physical,\nterm for term; so in the other case, the cosmos, although we can not\nunderstand the exact _nature_, we are sure of the intimacy of the\nconnection, _term for term_--every material phenomenon and event with a\ncorresponding psychical phenomenon as its cause.\n\n\n\n\nCHAPTER VII.\n\nSOME LOGICAL CONSEQUENCES OF THE DOCTRINE OF THE DIVINE IMMANENCY.\n\n\nThe doctrine of the Divine immanency carries with it the solution of\nmany vexed questions. In fact, in its light these questions simply pass\nout of view as no longer having any significance. Several of these\nquestions have been alluded to in an indirect way in the previous\nchapter and in Chapter III. We take them up distinctly here, and show\ntheir relation to evolution.\n\nReligious thought, like all else, is subject to a law of evolution,\nand therefore passes through regular stages. Of these stages, three\nare very distinct and even strongly contrasted. They correspond in\na general way to the three stages of Comte, which he has misnamed\nthe _theological_, the _metaphysical_, and the _positive_. We will\nillustrate by many examples.\n\n\nI. _Conception of God._\n\nThis, the most fundamental conception of all religion, has passed from\na gross anthropomorphism to a true spiritual theism, and the change\nis largely due to science and especially to the theory of evolution.\nThere are three main stages in the history of this change: (1.) The\nfirst is a _low_ anthropomorphism. God is altogether such a one as\nourselves, but larger and stronger. His action on Nature, like our\nown, is _direct_; his will is wholly man-like, capricious and without\nlaw. (2.) The second is still anthropomorphism, but of a nobler sort.\nGod is not _altogether_ like ourselves. He is man-like; yes, but\nalso _king-like_. He is _not_ present in Nature, but sits enthroned\nabove Nature in solitary majesty. He acts on Nature, not directly but\nindirectly, through physical forces and natural laws. He is an absentee\nlandlord governing his estate by means of appointed agents, which are\nthe natural forces and laws established in the beginning. He interferes\npersonally and by direct action only occasionally, to initiate\nsomething new or to rectify something going wrong. This idea culminated\nand found the clearest expression in the eighteenth century, and was\nthe necessary result of the scientific ideas then prevalent, viz.,\nideas of pre-established _stability_ of cosmic order and _fixedness_ of\norganic types. God was the great _artificer_, the great _architect_,\nworking, as it were, on foreign material and conditioned by its nature.\nHe established all things as they are in the beginning, and they have\ncontinued so ever since.\n\nThis conception still lingers in the religious mind, and is in fact the\nprevailing one now. It is a great advance on the preceding, but, alas!\nit removes God beyond the reach of our love. He is the architect of\nworlds, the artificer of the eye, the sovereign ruler of the universe,\nbut not our Father. We are his creatures, his subjects, but not his\nchildren.\n\n(3.) The third and last stage in this development is true spiritual\ntheism. God is immanent, resident in Nature. Nature is the house\nof many mansions in which he ever dwells. The forces of Nature are\ndifferent forms of his energy acting directly at all times and in\nall places. The laws of Nature are the modes of operation of the\nomnipresent Divine energy, invariable because he is perfect. The\nobjects of Nature are objectified, externalized--materialized states\nof Divine consciousness, or Divine thoughts objectified by the Divine\nwill. In this view we return again to _direct_ action, but in a nobler,\na spiritual, Godlike form. He is again brought very near to every one\nof us and restored to our love, for in him we live and move and have\nour being. In him all things consist, by him all things exist. This\nview has been held by noble men in all times, especially by the early\nGreek fathers, but is now verified and well-nigh demonstrated by the\ntheory of evolution. No other view is any longer tenable.\n\nThe idea of God is of course the most fundamental of all religious\nideas, and a change in this carries with it many other changes. Some of\nthese necessary outcomes, especially the nature, the origin, and the\ndestiny of the human spirit, and its relation to the Divine spirit, I\nhave already treated in previous chapters. But there are others which\nflow so directly and obviously that they may be presented in brief\nspace.\n\n\nII. _Question of First and Second Causes._\n\nAmong the most obvious of these is the question of first and second\ncauses. This distinction, I suppose, did not exist in early thought.\nAs a popular view, it was mainly due to the physical science of the\neighteenth century. It was a necessary corollary of the idea of God\nas the great architect sitting outside of Nature and acting on Nature\nas on foreign material. According to this view, God is the original\nand primary cause of all things; but he _delegates_ his power to\n_secondary_ forces, such as gravity, heat, electricity, etc., which\nare therefore the immediate causes of phenomena. I believe that most\npersons hold this view still. But it is now being displaced by the\nidea of God immanent or resident in Nature as already explained. This\nview is a complete _identification_ of first and second causes. All\ncauses are mere modes of the first cause. They seem to us secondary,\nnecessary, and unconscious only because they act according to\ninvariable law. But law itself is only the mode of operation of a\nperfect will. Thus we have the same three stages of evolution here\nalso: (1.) First, all is first cause, direct, man-like, capricious,\nlawless. (2.) Then the first cause acts king-like, indirectly by many\nappointed agents subject to pre-enacted laws. These agents or secondary\ncauses directly determine all natural phenomena. (3.) Lastly, come the\ncomplete combination and reconciliation of these two. All is by first\ncause and direct action, like the first. All is by invariable law like\nthe second, the law being only the mode of operation of a perfect will.\n\n\nIII. _Question of General and Special Providence._\n\nSo also providence, general and special, is only another phase of the\nsame question and solved in the same way. At first all is _special_\nprovidence--the result of caprice or favoritism and without law. Then\nall or nearly all is general providence operating by invariable law;\nbut from time to time the general law is broken through for special\npurposes when necessary. Is not this the prevailing view now? Lastly,\nthese two must be combined and reconciled in a third. All is alike\ngeneral and special: general--i. e., according to law; special--i. e.,\nby direct action. There is no real distinction between the two. The\ndistinction vanishes in the light of a higher view.\n\n\nIV. _The Natural and the Supernatural._\n\nIn precisely the same category falls the question of the natural and\nthe supernatural. The same three stages are evident here also, and the\nsame solution: 1. First all is supernatural and lawless, and Nature is\nviewed with stupid wonder and abject fear. 2. Then Nature is reduced to\nmechanical laws and made subject to man. Wonder and fear give place to\nindifference and even perhaps to contempt. We practically live without\nGod in the world. It requires, now, _miracles_ or a violent breaking\nthrough of law in order to startle us out of our stupidity and awaken\nin us a sense of the Divine presence. 3. But we must come lastly to a\nhigher philosophy. We must recognize that all is natural and all is\nsupernatural according as we view it, but none more than another. All\nis natural--i. e., according to law; but all is supernatural--i. e.,\nabove Nature, as we usually regard Nature, for all is permeated with\nthe immediate Divine presence. Wonder in the contemplation of Nature\nreturns, or rather exalted reverence and rational worship are given\nin place of open-mouthed wonder and superstitious fear. Once clearly\nconceive the idea of God permeating Nature and determining directly all\nits phenomena according to law, and the distinction between the natural\nand the supernatural disappears from view, and with it disappears also\nthe necessity of miracles as _we usually understand miracles_. In fact,\nthe word as we usually understand it has no longer any meaning.\n\nI must stop a moment to explain, lest I be misunderstood; and to\nenforce, lest it be thought I speak lightly.\n\nMiracle, in the sense of violation of law, is simply impossible,\nbecause law is the expression of the essential nature and perfection\nof God. It is as impossible for God to perform a miracle in this sense\nas it is for him to lie, and for the same reason, viz., that it is\ncontrary to his essential nature. In what sense, then, is a miracle\npossible? I answer, only as an occurrence or a phenomenon _according to\na law higher than any we yet know_. If we define Nature as phenomena\ngoverned by physical and chemical laws and forces, then life becomes\nsupernatural and miraculous--because higher than Nature as we define\nit. If we reduce the phenomena of life to law and include these\nalso in our definition of Nature but limit it there, then the free,\nself-determined phenomena of reason become supernatural because above\nour definition of Nature. There may well be still other and higher\nmodes of Divine activity, the law of which we do not and may never\nunderstand. These are above our present definition of Nature, and\ntherefore to us supernatural or miraculous. But, even if miracles in\nthe ordinary sense were possible, is it not evident that the ordinary\nprocesses of Nature are far more wonderful, more truly Godlike, than\nany such miracle?\n\n\nV. _Question of Design in Nature._\n\nSo, again, the question of design or purpose or mind in Nature is\nsimilarly solved. It has been said, it is continually now being\nsaid, that evolution has destroyed forever the teleological view\nof Nature--i. e., the idea of design in Nature. Yes, if we mean\nthe man-like, cabinet-making, watch-making design of Paley and\nolder writers--a separate petty design for each separate object. It\nhas indeed destroyed this, but only to replace it by a far nobler\nconception--a truly Godlike design, a design embracing all space and\nrunning through all time, including and absorbing all possible separate\ndesigns and predetermining them by a universal law of evolution.\n\nOr the same question may be put in another way as \u201cMind _vs._\nMechanics in Nature.\u201d In the evolution of thought on this subject at\nfirst all was _mind_, but lawless, capricious, like our own. Then\none department after another of Nature was reduced to mechanical,\nphysical, necessary law, until all have been or will be or conceivably\nmay be thus reduced, and mind seems driven out of Nature entirely.\nThe friends of religion in despair cry out for at least some small\ncorner left for mind. Thus I find in recent numbers of an English\nscientific periodical, \u201cNature,\u201d a discussion concerning mind as _one_\nof the factors of evolution.[48] Is it not amusing, if it were not\nso sad?--God the Divine mind as _one of the factors_ of evolution!\nThe true solution is very simple. All is mind or none; so also all\nis mechanics or none. It _is all mind through mechanics_. It is all\nmechanics from the outside; it is all mind from the inside. To science\nall is mechanics; to theology all is mind. It is the duty of philosophy\nto reconcile these two opposites by the higher view that mechanics is\nbut the mode of operation of the Divine mind. There is only one form of\nevolution, viz., human progress, in which mind--but the _human_, not\nthe Divine mind--is _one_ of the factors of evolution. But to think and\nspeak thus of God in relation to Nature is to place him on the human\nplane. It is gross anthropomorphism.[49]\n\n\nVI. _Question of the Mode of Creation._\n\nI might multiply examples almost without limit, of questions the\nsolution of which depends on this one of the relation of God to Nature.\nI give one more--Creation.\n\nThe creation of the universe _at once_--in the beginning--out of\nnothing--and then _rest ever since_. This old anthropomorphic idea is\nnow replaced by that of continuous creation--unhasting, unresting,\nby an eternal process of evolution. For if the universal law of\ngravitation is the Divine mode of sustentation of the universe, the no\nless universal law of evolution is the Divine process of creation.\n\n\n\n\nCHAPTER VIII.\n\nTHE RELATION OF EVOLUTION TO THE IDEA OF THE CHRIST.\n\n\nWhat think ye of Christ? This is indeed in many ways a test-question,\nand we ought frankly to meet it. I have feared heretofore to touch this\nquestion. I now only throw out some brief suggestions--scatter some\nseed-thoughts. Does Evolution have anything to say on this also? I\nthink it does. This I proceed to show:\n\nAs organic evolution reached its goal and completion in _man_, so human\nevolution must reach its goal and completion in the _ideal man_--i. e.,\nthe Christ. According to this view, the Christ is the ideal man, and\ntherefore--(mark the necessary implication)--and therefore the Divine\nman. We are all as men (as contradistinguished from brutes)--we are\n_all_, I say, _sons of God_; the Christ is the well-beloved Son. We\nare _all_ in the image of God; he is the express and _perfect image_.\nWe are all partakers in various degrees of the Divine nature; in him\nthe Divine nature is completely realized. It is not necessary that the\nideal man--the Christ--should be perfect in knowledge or in power; on\nthe contrary, he must grow in wisdom and in stature, like other men;\nbut he must be _perfect in character_. _Character is essential spirit._\nAll else, even knowledge, is only environment for its culture. In the\ndazzling light of modern science we are apt to forget this. Character\nis the _attitude_ of the human spirit toward the Divine Spirit. If I\nshould add anything to this definition, I would say it is spiritual\n_attitude_ and spiritual _energy_. In the Christ this attitude must be\nwholly right; the harmony--the union with the Divine--must be perfect.\nThis perfect union gives, of necessity, also fullness of spiritual\nenergy.\n\nNow, I wish to show that, although the Christ as thus defined must\nbe human--yes, even more intensely human than any one of us--yet by\nthe law of evolution we ought to expect him to differ from us in an\ninconceivable degree, and especially in a superhuman way. This I do by\na series of illustrations.\n\nWe have said that the Christ is the ideal and therefore the Divine\nman--that he is the goal and completion of humanity. But in evolution\na goal is not only a completion of one stage, but also the beginning\nof another and higher stage--on a higher plane of life with new and\nhigher capacities and powers _unimaginable from any lower plane_. Let\nme illustrate:\n\n1. As man is the ideal--the goal and completion of animal evolution,\nand yet is he also a birth into a higher plane of life--the spiritual;\nso the Christ, the ideal man, may be only the goal and completion of\nhuman evolution, and yet is he also a birth into a new and higher\nplane--_the Divine_.\n\n2. As the human spirit pre-existed in embryo in animals, slowly\ndeveloping through all geological times, until it came to birth and\nimmortality in man, so the Divine spirit is in embryo in man in various\ndegrees of development, and comes to birth and completion of Divine\nlife in the Christ.\n\n3. As animals reached, finally, _conscious relations_ with God in\nman, even so man reaches _union_ with God in the Christ. As man, the\nideal animal, is a union of the _animal_ with the _spiritual_; so the\nChrist, the ideal of human evolution, is a union of the _human_ and the\n_Divine_.\n\n4. Finally: As with the appearance of man there were introduced new\npowers and properties unimaginable from the animal point of view, and\ntherefore from that point of view seemingly supernatural--i. e., above\ntheir nature--so with the appearance of the Christ we ought to expect\nnew powers and properties unimaginable from the human point of view,\nand therefore to us seemingly supernatural--i. e., _above our nature_.\n\nThe Christ as defined above--i. e., as the _ideal man_--is undoubtedly\na true object of rational worship. There are two and only two\nfundamental moral principles, viz., love to God and love to man. Both\nof these must be embodied in a rational worship. The one must be\nembodied in the worship of an Infinite Spirit--God; the other in the\nworship of the ideal man--the Christ.\n\nBut some one will object that, admitting all this, it is impossible\nthat the goal, the ideal, should appear until the _end of the course_\nof evolution. To him I answer: This is indeed true of animal evolution,\nbut not of human evolution. We have already seen (see p. 88 _et seq._)\nthat there is an essential difference in this regard between these\ntwo kinds of evolution. In addition to all the factors of organic\nevolution, in human progress there is a new and higher factor added,\nwhich immediately takes precedence of all others. This factor is _the\nconscious voluntary co-operation of the human spirit in the work of its\nown evolution_. The method of this new factor consists essentially in\nthe formation, and especially in the _voluntary pursuit, of ideals_. In\norganic evolution _species_ are transformed by the _environment_. In\nhuman evolution _character_ is transformed by _its own ideal_. Organic\nevolution is by _necessary_ law--human evolution is by voluntary\neffort, i. e., by _free_ law. Organic evolution is _pushed_ onward and\nupward from behind and below. Human evolution is _drawn_ upward and\nforward from above and in front by the attractive force of ideals. Thus\nthe ideal of organic evolution can not appear until the end; while the\nattractive ideals of human evolution _must_ come--whether only in the\nimagination or realized in the flesh--but must come somehow _in the\ncourse_. The most powerfully attractive ideal ever presented to the\nhuman mind, and, therefore, the most potent agent in the evolution of\nhuman character, is _the Christ_. This ideal must come--whether in the\nimagination or in the flesh I say not, but--must come somehow _in the\ncourse_ and not at the end. At the end the whole human race, drawn\nupward by this ideal, must reach the fullness of the stature of the\nChrist.\n\nBut it will be again objected that all ideals are relative and\ntemporary; that we are in fact drawn onward and upward by many\nsuccessive ideals, one beyond another, in the course. Ideals are but\nmile-stones which we put successively behind us while we press on to\nanother; they are successive rounds of an infinite ladder which we put\nsuccessively beneath us while we rise higher. This one also we shall\neventually put behind us and pass on.\n\nTo this I have two answers: Admitted that in many ways such is the\ncourse of progress; but who has been able to reach this ideal and\nconceive a higher? When this one is reached and completely realized in\nour personal character, it will be time enough to propose another.\n\nAgain, it is true that in many ways we have advanced and are still\nadvancing by the use of partial ideals; but this use of partial and\nrelative ideals is itself in only a temporary stage of evolution. At\na certain stage we catch glimpses of the _absolute_ moral ideal. Then\nour gaze becomes fixed, and we are thenceforward drawn upward forever.\nThe human race has already reached a point when the absolute ideal of\ncharacter is attractive. This Divine ideal can never again be lost to\nhumanity.\n\n\n\n\nCHAPTER IX.\n\nTHE RELATION OF EVOLUTION TO THE PROBLEM OF EVIL.\n\n\nThe problem of evil has tasked the power and baffled the skill of the\ngreatest thinkers in every age. It would be folly in me to imagine that\nI can solve it. Its complete solution is probably impossible in the\npresent state of science. Yet I can not doubt that on this, as on every\nimportant question relating to man, the theory of evolution will throw\nnew and important light. All I can hope to do is to throw out some\nbrief suggestions on the subject.\n\nIf evolution be true, and especially if man be indeed a product of\nevolution, then what we call evil is not a unique phenomenon confined\nto man, and the result of an accident, but must be a great fact\npervading all nature, and a part of its very constitution. It must have\nexisted in all time in different forms, and subject like all else to\nthe law of evolution. Let us, then, trace rapidly some of the steps of\nthis evolution.\n\n1. _External Physical Evil in the Animal Kingdom._--As already seen in\nprevious chapters, the necessary condition of evolution of the organic\nkingdom is a _struggle_ for life--a conflict on every side, with a\nseemingly _inimical_ environment and a survival of only the strongest,\nthe swiftest, or the most cunning--in a word, the fittest. Now, suppose\nthe course of organic evolution finished in the introduction of man,\nand from this vantage-ground we look back over the course and consider\nits result. Shall we call that evil which was the necessary condition\nof the progressive elevation which culminated so gloriously? Evil\ndoubtless it seemed to the individual, struggling animal, but is this\nworthy to be weighed in comparison with the evolution of the whole\norganic kingdom until it culminated in man? Is it not rather a _good_\nin disguise? I suppose human arrogance may be willing enough to admit\nit in _this_ case, where animals only are sufferers.\n\n2. _Physical Evil in Relation to Man._--But organic evolution,\ncompleted in man, was immediately transferred to a higher plane, and\ncontinued as social evolution; material evolution is transformed into\npsychical evolution; unconscious evolution, according to _necessary_\nlaw, to conscious voluntary progress toward a recognized goal, and\naccording to a _freer_ law. But in this transformation the fundamental\nconditions of evolution do not change. Man also is surrounded on every\nside with what at first seems to him an _evil environment_, against\nwhich he must ever struggle or perish. Heat and cold, tempest and\nflood, volcanoes and earthquakes, savage beasts and still more savage\nmen. What is the remedy--the only conceivable remedy? Knowledge of\nthe laws of Nature, and thereby acquisition of power over Nature. But\nincreasing knowledge and power are equivalent to progressive elevation\nin the scale of psychical being. This conflict with what seems an evil\nenvironment is, therefore, the necessary condition of such elevation.\nIt is not too much to say that, without this condition, except for this\nnecessity for struggle, man could never have emerged out of animality\ninto humanity, or, having thus emerged, would never have risen above\nthe lowest possible stage. Now suppose, again, this ideal to have been\nattained--suppose knowledge of physical laws and power over physical\nforces to be complete--suppose physical nature completely subdued,\nput beneath our feet, and subject to our will, and, from the high\nintellectual position thus attained, we look back over the whole ground\nand consider the result. Shall that be called evil which was obviously\nthe necessary condition for attaining our then elevated position? Evil\nit doubtless seemed to the individuals who fell, and still seems to us\nwho now suffer, by the way in the conflict; but is physical discomfort\nor even physical death of the individual to be weighed in comparison\nwith the psychical elevation of the individual, and especially of the\nrace? Evidently, then, physical evil even in the case of man is only\n_seeming_ evil, but _real_ good.\n\n3. _Organic Evil--Disease._--But there is a more dreadful form of evil\nthan that which results from _external_ physical nature--an evil far\nmore subtle and difficult to understand, and therefore to conquer.\nI mean _internal_ organic evil--disease in its diversified forms\nand with its attendant weakness and suffering, inscrutable often in\nits causes, insidious in its approaches, contagious, infectious,\nspreading from house to house, carrying suffering and death in its\ncourse, and leaving sorrow and desolation behind. Is there any remedy\nwhich can transmute this evil into good? There is. It is again\nknowledge--knowledge of the laws, and power over the forces, of\n_organic nature_. Is it not evident that complete knowledge of the laws\nof health and the causes of disease would put this evil also under our\nfeet? Is it not evident that a perfect knowledge of the laws of health,\nand a perfect living according to these laws, would so entirely subdue\nthis evil that men would no longer die except by natural decay or by\naccident? Is it not evident, also, that the race will not attain this\nknowledge unless it be forced upon us by the necessity of avoiding the\ndread evil of disease?\n\nNow suppose, again, this ideal attained, suppose this dread evil\nsubdued by complete knowledge, and again from our elevated intellectual\nposition we look back over the ground. Shall we call that evil which\nwas the necessary condition of our intellectual elevation? Evil,\ndoubtless, it seems to us individuals who have suffered and are still\nsuffering through our ignorance; but is such individual suffering or\neven individual death to be weighed against the psychical elevation of\nthe individual and evolution of the race? Ought not the individual to\nbe willing to suffer thus much vicariously for the race? Is not this\nseeming evil also a _real_ good?\n\nMay we not, then, confidently generalize? May we not say that all\nphysical evil is good in its general effect--that every law of Nature\nis beneficent in its general operation, and, if sometimes evil in\nits specific operation, is so only through our ignorance? Partly\nby survival of the fittest, and partly by intelligence, man, like\nother animals, brings himself in accord with the laws of Nature, and\nthus appropriates the good and avoids the evil, and Nature becomes\nbeneficent only. But, also unlike any other animal, man by rational\nknowledge makes the laws of Nature his servants, and uses them for his\nown purposes, thus increasing his power and elevating the plane of his\nlife.\n\n4. _Moral Evil._--But there is still another form of evil, the most\ndreadful of all. This one may be called _the_ evil, in some sense, _the\nonly evil_. It is that of which all other forms are but the shadows\ncast backward and downward along the course of evolution and on lower\nstages of existence. This consummation of all evil is _sin_--_moral\ndisease_--more dreadfully contagious and deadly than any organic\ndisease. What shall we say now? Is there any rational explanation of\nthis evil? Is there any possible-reason or excuse for an all-wise,\nall-powerful Ruler afflicting man alone of all His creatures with this\ngreatest of all evils? In all other cases, the individual and the race\nsacrifice themselves for a time _physically_ for the sake of final\nspiritual elevation; but this _is spiritual debasement_. In all other\ncases, there is a sacrifice in the _course_ in order to attain the\n_goal_, but this is a missing of the goal itself. Is there any view\nwhich mitigates this evil, any philosophic alchemy which can transmute\nthis evil into good? Age after age the human mind has prostrated\nitself in helpless paralysis before this problem. Most thinkers have\nbeen content to say, \u201cThou hast ordered it so. Thou art good. It must\nbe right.\u201d But many, and among them some of the best minds, have\nsaid, \u201cEither God is not all-good, or else not all-wise, or else not\nall-powerful, or else there is no God at all.\u201d Does evolution shed any\nlight on this dread problem? I believe it does.\n\nWe have said that all other evils are but shadows of this one, cast\nbackward and downward on earlier stages of evolution and lower forms of\nexistence. But from the evolution point of view these earlier and lower\nforms of evil are rather to be regarded as _fore_shadowings of the\nreality to come. They are but earlier and lower stages of the evolution\nof the _same thing_--embryonic conditions of the now full-grown evil.\nIf so, then the same law must apply here also, though, as we shall see,\nwith a difference. Here, also, the individual as well as the race finds\nhimself surrounded by what seems an evil environment, against which\nhe must struggle. The spirit of man is inclosed and conditioned by a\nlower environment, which he must subdue or perish. Here, then, is again\na deadly conflict: \u201ca law in the members warring against the law of\nthe spirit, and bringing it into captivity\u201d; a law of selfism warring\nagainst the law of love, and bringing it into subjection; solicitations\nto debasement on the one hand, and solicitations to wrong others on the\nother. How shall it be overcome? What is the remedy? Again I answer,\nKnowledge of and conformity to the _laws of the moral world_. But, as\nin other cases, so in this: this knowledge of and conformity to law,\nwhich is the true goal of humanity, will not be attained unless it is\nforced upon us by necessity and in self-defense--i. e., by evil.\n\nNow suppose, once more, this knowledge and conformity be complete, and\nthe ideal of humanity be attained, and from this final and highest\nposition we look back over the whole ground. Shall that be called evil\nwhich from the very nature of a moral being and the laws of evolution\nwas obviously the necessary condition of attaining the goal? Shall\nwe not from this final position call it a good in disguise? Evil,\ndoubtless, it seems to us who suffer and stumble and mayhap fall by the\nway; but shall the mishap of the individual be weighed as an equivalent\nagainst the evolution of the race and the attainment of its goal?\n\nAh! there is the rub. It is all well enough to talk of sacrificing\nthe _physical_ individual to the race, but not so the _spiritual_. If\nwe believe in the immortality of the human spirit, if we do indeed\nstand related to God in the manner explained in Chapter IV, then\nmoral evil in the individual has an entirely peculiar and an eternal\nsignificance--then the individual human spirit has an infinite worth\nand can not be sacrificed to the race; for the evolution of the race\nitself is only in order to the perfecting of individual human souls.\nWhat shall we say now? I answer: The sacrifice is not necessary. There\nis in the realm of morals _alone_ a way of escape--a saving element\nwhich redeems the individual without violating the law. Let me explain.\n\nIt will, I think, be admitted by all that _innocence_ and _virtue_ are\ntwo very different things. Innocence is a _pre-established_, virtue\na _self-established_, harmony of spiritual activities. The course of\nhuman development, whether individual or racial, is from innocence\nthrough more or less discord and conflict to virtue. And virtue\ncompleted, regarded as a condition, is holiness, as an activity, is\nspiritual freedom. Not happiness nor innocence but virtue is the goal\nof humanity. Happiness will surely come in the train of virtue, but\nif we seek primarily happiness we miss both. Two things must be borne\nsteadily in mind: virtue is the _goal of humanity_; virtue can not be\ngiven, it must be _self-acquired_.\n\nNow we have already seen that in all evil the remedy, which not\nonly cures it but transmutes it into good, is knowledge of law and\nconformity of conduct thereto--a true science and a successful art--in\na word, knowledge of the laws of God and obedience to these laws. In\nthe physical world ignorance of these laws is necessarily fatal, but\nnot so in the moral world. Ignorance here is not necessarily fatal\nthough dangerous. By the very nature of a moral being, the essential\nthing is not knowledge but _character_ or virtue--the _will_ to know\nand the _effort_ to obey. In the physical realm, knowledge is the goal;\nin the moral realm, knowledge is only in order to virtue. Therefore,\nin the case of the individual struggling with moral evil within and\nwithout, the victory is always in his power. If he fails, it is his\nown fault. His utmost effort in this field must be successful, because\nthe result is not external, but internal and in the realm of moral\nfreedom. The spirit of man is self-acting and in some sense, though\nnot absolutely, self-existing, and can not be ruined except by its own\nact. In the moral world, where the goal is not knowledge but character,\nattainment must be in proportion to honest endeavor in the right spirit.\n\nEvil, then, has its roots in the necessary law of evolution. It is a\nnecessary condition of all progress, and pre-eminently so of moral\nprogress. But some will ask, \u201cWhy could not man have been made a\nperfectly pure, innocent, happy being, unplagued by evil and incapable\nof sin?\u201d I answer: The thing is impossible even to omnipotence, because\nit is a contradiction in terms. Such a being would also be incapable of\nvirtue, would not be a moral being at all, would not in fact be man.\nWe can not even conceive of a moral being without freedom to choose.\nWe can not even conceive of virtue without successful conflict with\nsolicitations to debasement. But these solicitations are so strong and\nso often overcome us, that we are prone to regard the solicitations\nthemselves as essential evil instead of our weak surrender to them.\n\nAll evolution, all progress, is from lower to higher plane. From a\nphilosophic point of view, things are not good and evil, but only\nhigher and lower. All things are good in their true places, each under\neach, and all must work together for the good of the ideal man. Each\nlower forms the basis and underlying condition of the higher; each\nhigher must subordinate the lower to its own higher uses, or else it\nfails of its true end. The physical world forms the basis and condition\nof the organic, yet the organism rises to a higher plane only by\nceaseless conflict with and adaptation to the physical environment,\nwhich therefore seems in some sense evil. The organic world in its\nturn underlies and conditions and _nourishes_ the rational moral\nworld. As the senses are the necessary feeders of the intellect, so\nthe appetites are the necessary feeders of the moral nature. Yes, even\nthe lowest sensual appetites are the necessary basis and nourishers\nof our highest moral sentiments. And yet the struggle for mastery of\nthe higher spiritual with the lower animal is often so severe that the\nlatter seems to many as _essential evil_ to be extirpated, instead of\na useful _servant_ to be controlled. This view is asceticism. Now the\nwhole view of evil usually held is a kind of asceticism, and therefore,\nlike asceticism, must be only a transition phase of human thought. All\nthat we call evil both in the material and the spiritual world is good,\nso long as we hold it in subjection as servants to the spirit, and only\nbecomes evil when we succumb. All evil consists in the dominance of the\nlower over the higher; all good in the rational use of the lower by\nthe higher. Asceticism may, indeed, be the best philosophy for some.\nIf we can not subdue the lower nature, we must try to extirpate it,\nand thus at any cost set free the higher from humiliating bondage. If\nwe can not practice the higher virtue of _temperance_ in _all_ things,\nwe must even try the lower virtue of _total abstinence_ in _some_\nthings. If our right eye offends, we must not hesitate to pluck it\nout; but let us not imagine that one eye is better than two--let us\nclearly understand that thereby our spiritual nature is sadly maimed,\nand therefore that the highest virtue, which is spiritual beauty and\nstrength, can not thus be attained. True virtue consists, not in the\nextirpation of the lower, but in its subjection to the higher. The\nstronger the lower is, the better, _if only_ it be held in subjection.\nFor the higher is nourished and strengthened by its connection with the\nmore robust lower, and the lower is purified, refined, and glorified by\nits connection with the diviner higher, and by this mutual action the\nwhole plane of being is elevated. It is only by action and reaction of\nall parts of our complex nature that true virtue is attained.\n\n\n\n\nFOOTNOTES:\n\n\n[1] The term _Chorology_, used by Haeckel, nearly covers the ground.\n\n[2] _Ontos-gennao_ (individual-making, or genesis of the individual).\n\n[3] _Taxis, nomos_ (relating to science of arrangement).\n\n[4] This statement is general; it will be modified hereafter.\n\n[5] _Phule-gennao_ (kind-making); genesis of the race.\n\n[6] This formulation of the laws of organic succession was given by\nme in 1860, before I knew anything of either Darwin\u2019s or Spencer\u2019s\nevolution. They were my own mode of formulating Agassiz\u2019s views.\n\n[7] Genesis without previous life--spontaneous generation.\n\n[8] Fishes were first introduced in the later Silurian; but became\ndominant in the Devonian.\n\n[9] Amphibians were introduced in the Carboniferous, but true reptile\nnot until the Permian.\n\n[10] Of course I mean downward in _social function_. Individually the\nscavenger may be nobler than the statesman.\n\n[11] Cope, \u201cScience,\u201d vol. ii, p. 274, 1883.\n\n[12] Boston Society of Natural History--anniversary memoir, 1880. Also,\n\u201cAmerican Naturalist,\u201d June, 1882.\n\n[13] \u201cArchives des Sciences,\u201d vol. liv, 1875.\n\n[14] \u201cNature,\u201d vol. xxxi, p. 4, 1884.\n\n[15] See abstract of Dr. Romanes\u2019s views, \u201cNature,\u201d vol. xxxiv, pp.\n314, 336, 362. Also, discussions of the same by Meldola, Galton,\nWallace, etc., in immediately subsequent numbers.\n\n[16] This subject is more fully treated in chapter IX, p. 240 _et seq._\n\n[17] See an article entitled \u201cGenesis of Sex,\u201d \u201cPopular Science\nMonthly,\u201d 1879, vol. xvi, p. 167.\n\n[18] Mr. Wallace has recently, in his work on \u201cDarwinism,\u201d taken\nstrong ground against this Darwinian factor. He thinks, for example,\nthat sexual vigor is the cause of both the splendor of color and the\npertinacity which secures the female. We see little difference in this\nway of putting it. Our object, however, is not to argue the question of\nwhat are true factors, but simply to give the most accepted, and, as it\nseems to us, also the most probable view.\n\n[19] By _reason_ I mean the faculty of dealing with the phenomena of\nthe _inner world of consciousness and ideas_. Animals live in one\nworld--the outer world of _sense_; man in two--the outer world of\nsense, like animals, but also in an inner and higher world of _ideas_.\nAll that is characteristic of man comes of this capacity of dealing\nwith the inner world. In default of a better word I call it reason. If\nany one can suggest a better word, I will gladly adopt it.\n\n[20] While all comparative anatomists agree that the lung is a\ndiverticulum from the \u0153sophagus, like the air-bladder of the gar-fish,\nsome think that it is a _different_ diverticulum, which is seen first\nin the dipnoi.\n\n[21] Undoubtedly the true principle on which primary groups ought to be\nmade is, _identity of general plan of structure_, or _traceableness of\nhomology throughout_. For these groups are the great primary branches\nof the tree of life, and classification ought to represent degrees of\ngenetic relationship. This was Agassiz\u2019s principle, although he did not\nadmit the genetic relation. This principle has been, it seems to us,\ntoo much neglected by later systematists.\n\n[22] The Amphioxus, the lowest of all vertebrates--if vertebrate it may\nbe called--is an exception to 2 and 3. In this animal the vertebrate\ntype is not yet fully declared.\n\n[23] This is only one example under a general law which it may be\nwell to stop a moment to illustrate. A repetition of similar parts\nperforming the same function is always an evidence of low organization,\nand as we rise in the scale of organization such parts usually become\nfewer and more efficient. Thus, to give one example, myriapods, as\ntheir name indicates, have hundreds of locomotive organs--lower\ncrustaceans perhaps thirty or forty. As we go up, they are reduced to\nfourteen (tetradecapods), then to ten (decapods), then in spiders to\neight, in insects to six, in vertebrates to four, and in man to two.\nA similar reduction in number, but increase in efficiency, is found\nin toes, _when they are used for support and locomotion only_. In man\nwe find the normal number of five (1), because his hands are used for\ngrasping and the functions of the fingers are not the same; and (2),\nbecause man\u2019s development was almost wholly _brainward_. In other\nrespects his structure is far less specialized than most other mammals.\nHe can not compete with carnivores in strength and ferocity, nor with\nherbivores in fleetness. In the struggle for life, therefore, there\nwas nothing left for him but increase in intelligence. Probably four\nis the smallest number of locomotive organs consistent with highest\nefficiency. In retaining but two legs for locomotion, man has lost in\nlocomotive efficiency, but by the sacrifice he liberates two limbs for\nhigher functions.\n\n[24] \u201cProceedings of American Academy of Arts and Sciences,\u201d vol. xiv,\nMay, 1878.\n\n[25] Fol., \u201cArchives des Sciences,\u201d vol. xiv, p. 84, 1885; \u201cScience,\u201d\nvol. vi, p. 92, 1885.\n\n[26] Of course, this is a purely imaginary case. The conditions of\ndevelopment of the eggs of higher animals forbid continuous watching\nthe process. Yet we do observe in different individuals all these\nstages in mammals as well as other animals.\n\n[27] These baleen plates are not modifications of teeth, as might at\nfirst be supposed, but rather of the transverse gum-ridges found on the\nroof of the mouth of many mammals, and conspicuous in the horse.\n\n[28] \u201cProceedings of the California Academy of Science,\u201d vol. v, p.\n152. 1873.\n\n[29] For fuller discussion of this subject, see \u201cBulletin of the\nCalifornia Academy of Science,\u201d No. 8, 1887, and \u201cAmerican Journal of\nScience,\u201d for Dec., 1887.\n\n[30] \u201cOrigin of Races of the Dog.\u201d \u201cAnnals and Magazine of Natural\nHistory,\u201d vol. xvii, p. 295. 1886.\n\n[31] Mr. Galton (\u201cNature,\u201d August 26, 1886) has used a diagram similar\nto the above (which I first used in 1879) to illustrate the law of\nsexual attraction and repugnance.\n\n[32] This subject is more fully discussed by the author in an article\nentitled \u201cGenesis of Sex,\u201d in \u201cThe Popular Science Monthly,\u201d vol. xvi,\np. 167, 1879.\n\n[33] For examples of this the reader is referred to Cope, \u201cBulletin\nof the National Museum,\u201d No. 1; and to Coues\u2019s \u201cKey to North American\nBirds,\u201d last edition.\n\n[34] \u201cMonatsbericht d. k. Preuss. Akademie d. Wissenschaft zu Berlin,\u201d\nfor July, 1866.\n\n[35] \u201cGenesis of Tertiary Species of Planorbis at Steinheim.\u201d A. Hyatt,\nAnniversary Memoir of the Boston Society of Natural History, 1880.\n\n[36] In a letter to the author, dated February 13, 1887, Prof. Cope\nsays: \u201cSuch transitions of species are clearly indicated in the\n_Oreodontid\u00e6_, where such different forms as _O. gracilis_ and _O.\nCulbertsoni_ are connected by intergradations.\u201d\n\n[37] \u201cAmerican Naturalist,\u201d 1873; \u201cPopular Science Monthly,\u201d June, 1873.\n\n[38] For a fuller development of this subject the reader is referred to\nan article by the author, entitled \u201cCritical Periods in the History of,\nand their Relation to, Evolution\u201d (\u201cAmerican Journal of Science,\u201d vol.\nxiv, p. 99, 1877).\n\n[39] \u201cReflex Action and Theism,\u201d William James, \u201cUnitarian Review\u201d for\nNovember, 1881.\n\n[40] See an article by the author on this subject, \u201cAmerican Journal of\nScience,\u201d series ii, vol. xxviii, p. 305, 1859, and in \u201cPopular Science\nMonthly,\u201d vol. iv, p. 156, 1873.\n\n[41] All chemical compounds are dissociated by sufficient heat.\n\n[42] The origin of vital from chemical force in the green leaves of\nplants can not be doubted; but this does not, of course, explain the\nmystery of the _first origin of life on the earth_, for one condition\nof the change _now_ is the _contact of living matter_.\n\n[43] I know it is the fashion to ridicule the use of the terms\nvitality, vital force, as a remnant of an old superstition; and yet the\nsame men who do so use the terms gravity, electricity, chemical force,\netc. Vital force is indeed _correlated_ with other forces of Nature,\nbut is none the less a distinct _form_ of force, far more distinct\nthan any other unless it be the still higher form of psychical, and\ntherefore it better deserves a distinct name than any lower form. Each\nform of force gives rise to a peculiar group of phenomena, and the\nstudy of these to a special department of science. Now, the group of\nphenomena called vital is more peculiar, more different from other\ngroups than these are from each other, and the science of physiology\nis a more distinct department than either physics or chemistry, and\ntherefore the form of force, which determines these phenomena, is more\ndistinct and better entitled to a name than any physical or chemical\nforce.\n\n[44] \u201cPrinceton Review\u201d for May, 1884.\n\n[45] \u201cPopular Science Monthly,\u201d December, 1873.\n\n[46] For a fuller statement of this antithesis, see an article by the\nauthor entitled \u201cEvolution in Relation to Materialism,\u201d \u201cPrinceton\nReview,\u201d for March, 1881.\n\n[47] Johnstone Stoney, \u201cNature,\u201d vol. xxxi, p. 422.\n\n[48] \u201cNature,\u201d vol. xxxiv, p. 385. 1886.\n\n[49] So, again, see a book recently published (\u201cNature,\u201d vol. xliii, p.\n460, 1891), entitled \u201cWhence comes Man, from Nature or from God?\u201d The\nanswer is plain. From both--from God through Nature. Evolution is the\nmethod of creation.\n\n\n\n\nINDEX\n\n\n  Acceleration, law of, 178.\n\n  African fauna explained, 204.\n\n  Agassiz, his greatest result, 29, 43;\n    relation to evolution, 32, 37, 43;\n    relation to Darwin, 46;\n    compared with Kepler, 47.\n\n  Ages of geological history, 16.\n\n  Alpine species explained, 215.\n\n  Amphibians, development of, 150.\n\n  Analogy and homology, 99.\n\n  _Anima_ of animals, 313, 317.\n\n  Animal architecture, styles of, 209.\n\n  Animal kingdom, primary divisions of, 107.\n\n  Animals, relation of man to, 311;\n    spirit embryonic in, 311.\n\n  Antiquity of man, religion and, 282;\n    of the earth, religion and, 281.\n\n  Aortic arches, proofs of evolution from, 151.\n\n  Arthropods, 132.\n\n  Artificial production of varieties, 222.\n\n  Australia, fauna and flora of, explained, 200;\n    when isolated, 202.\n\n\n  Barriers limit faunal and floral regions, 188.\n\n  Beauty, origin of, 269.\n\n  Birds\u2019 tails, changes of, 174.\n\n  Brain, vertebrate, proofs of evolution from, 162;\n    vertebrate, changes of, in phylogenic series, 168;\n    relation to mind, 327, 338.\n\n  Brain-physiology as a basis for materialism, 306.\n\n  Branching tree illustrates evolution, 13-15, 18, 110, 250.\n\n  Brooks, W. K., on the cause of variations, 262.\n\n\n  Californian coast-islands, fauna and flora of, 211.\n\n  Causation, idea of, from within, 342.\n\n  Cause, first and second, 354.\n\n  Cells, somatic and germ, 93.\n\n  Centers of creation, specific, 194.\n\n  Cephalization, 171.\n\n  Chambers, his views on evolution, 34.\n\n  Changes slow at present, 266.\n\n  Christ, the, 359;\n    relation of evolution to, 359;\n    as an agent in human progress, 363.\n\n  Close-breeding, effects of, 236, 243.\n\n  Coast-islands of California, fauna and flora of, 211.\n\n  Comparison, method of, 41.\n\n  Conflict between religion and science, 280.\n\n  Continental faunas and floras, 188.\n\n  Continental island life, 208.\n\n  Continuity, law of, 53;\n    law of, applied to inorganic forms, 54;\n    to organic forms, 56.\n\n  Cope\u2019s law of acceleration, 178.\n\n  Creation, special, 30, 69;\n    specific centers of, 194;\n    changes in our notions of, 348;\n    question of mode, 358.\n\n  Cross-breeding, law of, 236.\n\n  Cross-fertility of artificial varieties, 232.\n\n  Cross-sterility, 77, 234.\n\n  Cyclical movement, law of, 16, 22.\n\n\n  Darwin, relation to Agassiz, 46;\n    compared with Newton, 48;\n    factors of evolution discovered by, 74;\n    objections to his theory of evolution, 76.\n\n  Derivation, origin of inorganic forms by, 54;\n    origin of organic forms by, 56.\n\n  Design, idea of, from within, 345;\n    argument from, not destroyed by evolution, 346;\n    changes in our ideas of, 348;\n    in Nature, question of, 357.\n\n  Differentiation, law of, 11, 19;\n    law of, in embryonic development, 19;\n    law of, illustrated, 144;\n    of the animal kingdom illustrated, 176.\n\n  Disease, necessity of, 367.\n\n  Divine energy, forms of, 318.\n\n  Divisions of the animal kingdom, 117.\n\n  Dogmatism, theological and scientific, 293.\n\n  Domestication, changes produced by, 222.\n\n\n  Egg, development of, 3, 19.\n\n  Egyptian species unchanged in three thousand years, 265.\n\n  Embryology, proofs of evolution from, 148.\n\n  Environment, physical, 73.\n\n  Evil, problem of, relation of evolution to, 365;\n    physical, necessity of, 366;\n    a condition of progress, 366, 373;\n    organic, necessity of, 367;\n    moral, necessity of, 369.\n\n  Evolution, what is, 3, 8;\n    scope of, 3;\n    type of, 3, 8;\n    examples of, 5;\n    popularly limited to the organic kingdom, 7;\n    progressive change in, 9;\n    laws of, 11;\n    illustrated by branching tree, 13-15, 18, 90, 250;\n    misconception of, 14;\n    produced by resident forces, 27;\n    germs of the idea, 32;\n    relation of Agassiz to, 32, 37, 43;\n    Lamarck\u2019s views on, 33;\n    Chambers\u2019s views on, 34;\n    obstacle to, removed, 35;\n    confliction with religion imaginary, 45;\n    how related to gravitation, 49;\n    general evidences of, 53;\n    artificial, 60;\n    observed, 62;\n    certainty of, 65;\n    special proofs of, 67;\n    factors of, 73, 81;\n    human contrasted with organic, 88;\n    monotypal and polytypal, 85;\n    proofs of, from the vertebrate skeleton, 111;\n    from the articulate skeleton, 132;\n    from embryology, 148;\n    from development of amphibians, 150;\n    from aortic arches, 151;\n    from vertebrate brain, 162;\n    from rudimentary organs, 179;\n    from geographical distribution of organisms, 183;\n    explains geographical diversity, 195;\n    objection to this view, 217;\n    answer, 219;\n    proofs of, from artificial modifications, 222;\n    factors of, operative in domestication, 228;\n    paroxysmal, 257;\n    material, nearly completed, 267;\n    thoroughly established, 275;\n    relation to religion, 276, 282;\n    relation to materialism, 284;\n    necessitates great change in religious thought, 295;\n    of forces, 315;\n    relation to revelation, 331;\n    pantheistic objection answered, 335;\n    relation to problem of evil, 365.\n\n  Experimental method largely fails on plane of life, 40.\n\n\n  Factors of evolution, 73;\n    their grades and order of introduction, 81;\n    Lamarckian, 81;\n    selection, 82-85;\n    Darwinian, 83;\n    rational, 86.\n\n  Faculties, evolution of, 23.\n\n  Faunas and floras, geographical, 183;\n    continental, 188;\n    marine, 192;\n    special cases of distinct, 192;\n    of Australia, 200;\n    of Africa, 204;\n    of Madagascar, 205;\n    of continental islands, 208;\n    of the coast-islands of California, 211;\n    of oceanic islands, 213;\n    of lofty mountains, 215.\n\n  Fish-tails, changes of, in development, 172;\n    in evolution, 174.\n\n  Fishes, age of, 17.\n\n  Floras and faunas, geographical, 183.\n\n  Force, vital, correlation of, 36;\n    planes of, 314;\n    evolution of, 315;\n    idea of, from within, 342.\n\n  Forces, resident, evolution by, 27;\n    of Nature are forms of Divine energy, 317;\n    different planes of, 314.\n\n  Fore-limbs, vertebrate, homologies of, 113.\n\n\n  Generation, spontaneous, 15.\n\n  Geographical faunas and floras, 183;\n    diversity, theory of, 193;\n    diversity explained by evolution, 195;\n    present diversity determined by Glacial epoch, 198;\n    objection to this view, 217;\n    answer, 219.\n\n  Geological record, imperfection of, 252.\n\n  Glacial epoch determined distribution of species, 195, 198, 215;\n    changes during, in America, 198;\n    in Europe, 199.\n\n  God, relation of, to Nature, 297;\n    immanence of, in Nature, 300;\n    relation of, to man, 326;\n    personality of, 332;\n    necessary belief in, 344;\n    different forms of conception, 351.\n\n  Good and the true, relation of, 277.\n\n  Grasshopper, external anatomy of, 143.\n\n  Gravitation, relation of, to evolution, 49;\n    and religion, 281.\n\n  Gyroscope, 288.\n\n\n  Heliocentric theory and religion, 280.\n\n  Hind-limbs, vertebrate, homologies of, 121.\n\n  Horse, genesis of, 126.\n\n  Homologies of vertebrate skeleton, 111;\n    of vertebrate fore-limbs, 113;\n    of vertebrate hind-limbs, 121;\n    of articulate skeleton, 132.\n\n  Homology and analogy, 99;\n    only within primary divisions, 108.\n\n  Hyatt, A., on Planorbis, 254.\n\n\n  Ideal, relative and absolute, 364.\n\n  Idealism, true and false, 301.\n\n  Immortality in accord with law, 316.\n\n  Individuality, organic, 325;\n    spiritual, 325.\n\n  Innocence and virtue compared, 372.\n\n  Inorganic forms, law of continuity applied to, 54.\n\n  Intermediate forms between artificial varieties, 232.\n\n  Islands, continental and oceanic, 207.\n\n\n  Kepler compared with Agassiz, 47.\n\n\n  Lamarck, evolutionary views of, 33, 74.\n\n  Law of differentiation, 11, 19;\n    of progress of the whole, 13, 22;\n    of cyclical movement, 16, 22;\n    of continuity, 53;\n    of continuity applied to inorganic forms, 54;\n    to organic forms, 56;\n    of differentiation illustrated, 144;\n    of acceleration, 178;\n    of cross-breeding, 218, 236.\n\n  Laws of evolution, 11, 19.\n\n  Lepidosiren, 101.\n\n  Life, nature of, 35;\n    imperfectly subject to experiment, 40;\n    relation of, to philosophy, 277.\n\n  Limbs, vertebrate, homology of, 113.\n\n  Links, connecting, 12, 57, 145;\n    connecting, elimination of, 248;\n    connecting, usually absent from geological faunas, 251.\n\n  Liquidambar, 218, 220.\n\n  Lobster, external anatomy of, 136.\n\n  Lungs, formation of, 100.\n\n\n  Madagascan fauna explained, 205.\n\n  Mammals, age of, 17.\n\n  Man, age of, 18;\n    relation of, to Nature, 304;\n    relation of, to animals, 311;\n    spirit of, in relation to the forces of Nature, 313, 316;\n    relation of God to, 331.\n\n  Marsupials, 201.\n\n  Materialism, relation of, to evolution, 284;\n    basis for, in brain-physiology, 306;\n    basis for, in evolution, 311.\n\n  Methods, scientific, 38.\n\n  Migration favors diversification, 77.\n\n  Mind, relation of, to brain, 327, 338;\n    _versus_ mechanics in Nature, 340.\n\n  Miracles, question of, 356.\n\n  Mollusks, age of, 16.\n\n  Monotremes, 201.\n\n  Mystery, changes in our sense of, 347.\n\n\n  Nature, relation of God to, 297;\n    immanence of God in, 300;\n    relation of man to, 304;\n    has no meaning without spirit, 329;\n    mind _versus_ mechanics in, 340.\n\n  Natural and supernatural, 355.\n\n  Neo-Darwinism, 93;\n    relation of, to human progress, 97.\n\n  Newton compared with Darwin, 48.\n\n  Nominalism and realism reconciled, 329.\n\n\n  Obstacle to evolution removed, 35.\n\n  Oceanic island life, 213.\n\n  Ontogenic series, 9, 40.\n\n  Organic forms, views of origin of, 29, 68, 72, 292;\n    law of continuity applied to, 56.\n\n  Organs, incipient, 270.\n\n  Origin of varieties unexplained, 270.\n\n\n  Pantheism, true and false, 302, 335.\n\n  Paroxysmal evolution, 257.\n\n  Personality behind Nature, 338.\n\n  Personality of God, 337, 341.\n\n  Philosophy and life, relations of, 277.\n\n  Phylogenic series, 10, 41.\n\n  Planorbis of Steinheim, 254.\n\n  Primal animals, 145.\n\n  Progress of the whole, law of, 13, 22.\n\n  Progressive change in evolution, 9.\n\n  Providence, question of general and special, 355.\n\n\n  Ranges of organic forms, 186.\n\n  Realism and nominalism reconciled, 329.\n\n  Record, geological, imperfection of, 252.\n\n  Religion, so-called conflict of, with evolution, 45, 280.\n\n  Religious thought to be reconstructed, 295.\n\n  Reproduction, methods of, 237.\n\n  Reptiles, age of, 17.\n\n  Revelation, relation of evolution to, 331;\n    not inconsistent with the laws of Nature, 332;\n    nature of, 333.\n\n  Reversion of artificial forms, 229.\n\n  Romanes, G. J., his idea of physiological selection, 76, 84;\n    the idea applied, 245.\n\n  Rudimentary organs, proofs of evolution from, 179;\n    organs in man, 181.\n\n\n  Selection, sexual, 74, 85;\n    natural, 74, 79, 83;\n    physiological, 75, 79, 84;\n    natural, compared with artificial, 225;\n    physiological, applied, 245.\n\n  Self-consciousness the sign of spirit-individuality, 325.\n\n  Sequoia, 219, 220.\n\n  Sexes, characters of, compared, 262.\n\n  Shrimp, external anatomy of, 134.\n\n  Sin a condition of moral evolution, 350.\n\n  Skeleton, vertebrate, homologies of, 111;\n    articulate, homologies of, 132;\n    articulate, general structure of, 134.\n\n  Society, progress of, 25.\n\n  Space and time the two fundamental conditions of material\n          existence, 48.\n\n  Species, natural, more permanent than artificial varieties, 229;\n    more distinct, 232;\n    cross-sterile, 232.\n\n  Spirit embryonic in animals, 311;\n    of man related to _anima_ of animals, 313;\n    to forces of Nature, 313, 316;\n    origin of illustrated, 320-322;\n    Plato\u2019s view, 326;\n    orthodox view, 326;\n    no meaning in Nature without, 329.\n\n  Steinheim, Planorbis of, 254.\n\n  Supernatural and the natural, 355.\n\n\n  Taxonomic series, 9, 40.\n\n  Temperature-regions, 184.\n\n  Tread, plantigrade and digitigrade, 123.\n\n  True and the good, relation of, 277.\n\n  Truth tested by effect on life, 277;\n    not compromise, 291.\n\n  Types, generalized, 13.\n\n\n  Use and disuse of organs, 73.\n\n  Useless structures, how produced, 76.\n\n\n  Variation depends on sexual reproduction, 238;\n    caused by unfavorable conditions, 264.\n\n  Varieties, artificial production of, 222, 235;\n    artificial production of, illustrated, 224;\n    natural and artificial, compared, 228;\n    origin of, unexplained, 270.\n\n  \u201cVestiges of Creation,\u201d 34.\n\n  Virtue and innocence compared, 372.\n\n  Vital principle, 328.\n\n  Voluntary social progress, 26.\n\n\n  Weismann\u2019s views, 93.\n\n  Whales, rudimentary organs of, 180.\n\n\nTHE END.\n\n\n\n\nTranscribers\u2019 Notes:\n\n\nPunctuation, hyphenation, and spelling were made consistent when a\npredominant preference was found in this book; otherwise they were not\nchanged.\n\nSimple typographical errors were corrected; occasional unbalanced\nquotation marks retained.\n\nAmbiguous hyphens at the ends of lines were retained.\n\nSubscripts in chemical formulas are represented here as simple numbers,\nsuch as H2O and NH3.\n\nIllustrations were printed mid-paragraph but have been moved between\nparagraphs, usually near to text that references them.\n\nFootnotes have been collected and repositioned just before the Index.\n\nSome in-line paragraph headings are in boldface and some are in\nitalics; this emphasis has been retained.\n\nIndex not checked for proper alphabetization or correct page references,\nbut a reference to page 274 was a typographical error and has been\nchanged to 174.\n\nPage 155: Text refers to _c c\u2032_ in Figs. 38-39, but neither figure\nappears to contain a _c\u2032_ label.","title":"Evolution: Its nature, its evidence, and its relation to religious thought","tradition":"scripture-revelation","translated_text":null,"word_count":93178}