{"collection":"scripture-revelation","full_text_available":true,"graph_url":"https://unchartedknowledge.5gfusion.net/v2/api/page/gutenberg_2629/graph","html_url":"https://unchartedknowledge.5gfusion.net/v2/page/gutenberg_2629","id":"gutenberg_2629","license":"Public Domain (US)","rights_basis":"gutenberg_metadata_copyright_false","source":"gutenberg","source_url":"https://www.gutenberg.org/ebooks/2629","summary":null,"tags":["Bible and science","Biology","Category: Science - Biology","Evolution","Paleontology","Science"],"text":"Produced by D. R. Thompson\n\n\n\n\n\nLECTURES ON EVOLUTION\n\nESSAY #3 FROM \"SCIENCE AND HEBREW TRADITION\"\n\n\nBy Thomas Henry Huxley\n\n\n\n\nI. THE THREE HYPOTHESES RESPECTING THE HISTORY OF NATURE\n\nWe live in and form part of a system of things of immense diversity\nand perplexity, which we call Nature; and it is a matter of the deepest\ninterest to all of us that we should form just conceptions of the\nconstitution of that system and of its past history. With relation to\nthis universe, man is, in extent, little more than a mathematical point;\nin duration but a fleeting shadow; he is a mere reed shaken in the winds\nof force. But as Pascal long ago remarked, although a mere reed, he is\na thinking reed; and in virtue of that wonderful capacity of thought,\nhe has the power of framing for himself a symbolic conception of the\nuniverse, which, although doubtless highly imperfect and inadequate as\na picture of the great whole, is yet sufficient to serve him as a chart\nfor the guidance of his practical affairs. It has taken long ages of\ntoilsome and often fruitless labour to enable man to look steadily at\nthe shifting scenes of the phantasmagoria of Nature, to notice what is\nfixed among her fluctuations, and what is regular among her apparent\nirregularities; and it is only comparatively lately, within the last few\ncenturies, that the conception of a universal order and of a definite\ncourse of things, which we term the course of Nature, has emerged.\n\nBut, once originated, the conception of the constancy of the order of\nNature has become the dominant idea of modern thought. To any person who\nis familiar with the facts upon which that conception is based, and\nis competent to estimate their significance, it has ceased to be\nconceivable that chance should have any place in the universe, or that\nevents should depend upon any but the natural sequence of cause and\neffect. We have come to look upon the present as the child of the past\nand as the parent of the future; and, as we have excluded chance from a\nplace in the universe, so we ignore, even as a possibility, the notion\nof any interference with the order of Nature. Whatever may be men's\nspeculative doctrines, it is quite certain that every intelligent person\nguides his life and risks his fortune upon the belief that the order of\nNature is constant, and that the chain of natural causation is never\nbroken.\n\nIn fact, no belief which we entertain has so complete a logical basis as\nthat to which I have just referred. It tacitly underlies every process\nof reasoning; it is the foundation of every act of the will. It is based\nupon the broadest induction, and it is verified by the most constant,\nregular, and universal of deductive processes. But we must recollect\nthat any human belief, however broad its basis, however defensible it\nmay seem, is, after all, only a probable belief, and that our widest and\nsafest generalisations are simply statements of the highest degree of\nprobability. Though we are quite clear about the constancy of the order\nof Nature, at the present time, and in the present state of things, it\nby no means necessarily follows that we are justified in expanding this\ngeneralisation into the infinite past, and in denying, absolutely, that\nthere may have been a time when Nature did not follow a fixed order,\nwhen the relations of cause and effect were not definite, and when\nextra-natural agencies interfered with the general course of Nature.\nCautious men will allow that a universe so different from that which we\nknow may have existed; just as a very candid thinker may admit that a\nworld in which two and two do not make four, and in which two straight\nlines do inclose a space, may exist. But the same caution which forces\nthe admission of such possibilities demands a great deal of evidence\nbefore it recognises them to be anything more substantial. And when\nit is asserted that, so many thousand years ago, events occurred in a\nmanner utterly foreign to and inconsistent with the existing laws of\nNature, men, who without being particularly cautious, are simply honest\nthinkers, unwilling to deceive themselves or delude others, ask for\ntrustworthy evidence of the fact.\n\nDid things so happen or did they not? This is a historical question, and\none the answer to which must be sought in the same way as the solution\nof any other historical problem.\n\nSo far as I know, there are only three hypotheses which ever have been\nentertained, or which well can be entertained, respecting the past\nhistory of Nature. I will, in the first place, state the hypotheses,\nand then I will consider what evidence bearing upon them is in our\npossession, and by what light of criticism that evidence is to be\ninterpreted.\n\nUpon the first hypothesis, the assumption is, that phenomena of Nature\nsimilar to those exhibited by the present world have always existed; in\nother words, that the universe has existed, from all eternity, in what\nmay be broadly termed its present condition.\n\nThe second hypothesis is that the present state of things has had only\na limited duration; and that, at some period in the past, a condition\nof the world, essentially similar to that which we now know, came into\nexistence, without any precedent condition from which it could have\nnaturally proceeded. The assumption that successive states of Nature\nhave arisen, each without any relation of natural causation to an\nantecedent state, is a mere modification of this second hypothesis.\n\nThe third hypothesis also assumes that the present state of things has\nhad but a limited duration; but it supposes that this state has been\nevolved by a natural process from an antecedent state, and that from\nanother, and so on; and, on this hypothesis, the attempt to assign any\nlimit to the series of past changes is, usually, given up.\n\nIt is so needful to form clear and distinct notions of what is really\nmeant by each of these hypotheses that I will ask you to imagine what,\naccording to each, would have been visible to a spectator of the events\nwhich constitute the history of the earth. On the first hypothesis,\nhowever far back in time that spectator might be placed, he would see\na world essentially, though perhaps not in all its details, similar to\nthat which now exists. The animals which existed would be the ancestors\nof those which now live, and similar to them; the plants, in like\nmanner, would be such as we know; and the mountains, plains, and waters\nwould foreshadow the salient features of our present land and water.\nThis view was held more or less distinctly, sometimes combined with\nthe notion of recurrent cycles of change, in ancient times; and its\ninfluence has been felt down to the present day. It is worthy of remark\nthat it is a hypothesis which is not inconsistent with the doctrine of\nUniformitarianism, with which geologists are familiar. That doctrine was\nheld by Hutton, and in his earlier days by Lyell. Hutton was struck by\nthe demonstration of astronomers that the perturbations of the planetary\nbodies, however great they may be, yet sooner or later right themselves;\nand that the solar system possesses a self-adjusting power by which\nthese aberrations are all brought back to a mean condition. Hutton\nimagined that the like might be true of terrestrial changes; although no\none recognised more clearly than he the fact that the dry land is being\nconstantly washed down by rain and rivers and deposited in the sea; and\nthat thus, in a longer or shorter time, the inequalities of the earth's\nsurface must be levelled, and its high lands brought down to the ocean.\nBut, taking into account the internal forces of the earth, which,\nupheaving the sea-bottom give rise to new land, he thought that these\noperations of degradation and elevation might compensate each other; and\nthat thus, for any assignable time, the general features of our planet\nmight remain what they are. And inasmuch as, under these circumstances,\nthere need be no limit to the propagation of animals and plants, it is\nclear that the consistent working out of the uniformitarian idea might\nlead to the conception of the eternity of the world. Not that I mean\nto say that either Hutton or Lyell held this conception--assuredly\nnot; they would have been the first to repudiate it. Nevertheless, the\nlogical development of some of their arguments tends directly towards\nthis hypothesis.\n\nThe second hypothesis supposes that the present order of things, at some\nno very remote time, had a sudden origin, and that the world, such as\nit now is, had chaos for its phenomenal antecedent. That is the doctrine\nwhich you will find stated most fully and clearly in the immortal poem\nof John Milton--the English _Divina Commedia--_ \"Paradise Lost.\" I\nbelieve it is largely to the influence of that remarkable work, combined\nwith the daily teachings to which we have all listened in our childhood,\nthat this hypothesis owes its general wide diffusion as one of the\ncurrent beliefs of English-speaking people. If you turn to the seventh\nbook of \"Paradise Lost,\" you will find there stated the hypothesis to\nwhich I refer, which is briefly this: That this visible universe of ours\ncame into existence at no great distance of time from the present;\nand that the parts of which it is composed made their appearance, in\na certain definite order, in the space of six natural days, in such a\nmanner that, on the first of these days, light appeared; that, on the\nsecond, the firmament, or sky, separated the waters above, from the\nwaters beneath the firmament; that, on the third day, the waters drew\naway from the dry land, and upon it a varied vegetable life, similar\nto that which now exists, made its appearance; that the fourth day was\nsignalised by the apparition of the sun, the stars, the moon, and the\nplanets; that, on the fifth day, aquatic animals originated within the\nwaters; that, on the sixth day, the earth gave rise to our four-footed\nterrestrial creatures, and to all varieties of terrestrial animals\nexcept birds, which had appeared on the preceding day; and, finally,\nthat man appeared upon the earth, and the emergence of the universe from\nchaos was finished. Milton tells us, without the least ambiguity, what a\nspectator of these marvellous occurrences would have witnessed. I doubt\nnot that his poem is familiar to all of you, but I should like to recall\none passage to your minds, in order that I may be justified in what I\nhave said regarding the perfectly concrete, definite, picture of the\norigin of the animal world which Milton draws. He says:--\n\n     \"The sixth, and of creation last, arose\n     With evening harp and matin, when God said,\n     'Let the earth bring forth soul living in her kind,\n     Cattle and creeping things, and beast of the earth.\n     Each in their kind!' The earth obeyed, and, straight\n     Opening her fertile womb, teemed at a birth\n     Innumerous living creatures, perfect forms,\n     Limbed and full-grown. Out of the ground uprose,\n     As from his lair, the wild beast, where he wons\n     In forest wild, in thicket, brake, or den;\n     Among the trees in pairs they rose, they walked;\n     The cattle in the fields and meadows green;\n     Those rare and solitary; these in flocks\n     Pasturing at once, and in broad herds upsprung.\n     The grassy clods now calved; now half appears\n     The tawny lion, pawing to get free\n     His hinder parts--then springs, as broke from bonds,\n     And rampant shakes his brinded mane; the ounce,\n     The libbard, and the tiger, as the mole\n     Rising, the crumbled earth above them threw\n     In hillocks; the swift stag from underground\n     Bore up his branching head; scarce from his mould\n     Behemoth, biggest born of earth, upheaved\n     His vastness; fleeced the flocks and bleating rose\n     As plants; ambiguous between sea and land,\n     The river-horse and scaly crocodile.\n     At once came forth whatever creeps the ground,\n     Insect or worm.\"\n\nThere is no doubt as to the meaning of this statement, nor as to what a\nman of Milton's genius expected would have been actually visible to an\neye-witness of this mode of origination of living things.\n\nThe third hypothesis, or the hypothesis of evolution, supposes that,\nat any comparatively late period of past time, our imaginary spectator\nwould meet with a state of things very similar to that which now\nobtains; but that the likeness of the past to the present would\ngradually become less and less, in proportion to the remoteness of\nhis period of observation from the present day; that the existing\ndistribution of mountains and plains, of rivers and seas, would show\nitself to be the product of a slow process of natural change operating\nupon more and more widely different antecedent conditions of the mineral\nframe-work of the earth; until, at length, in place of that frame-work,\nhe would behold only a vast nebulous mass, representing the constituents\nof the sun and of the planetary bodies. Preceding the forms of life\nwhich now exist, our observer would see animals and plants, not\nidentical with them, but like them, increasing their differences with\ntheir antiquity and, at the same time, becoming simpler and simpler;\nuntil, finally, the world of life would present nothing but that\nundifferentiated protoplasmic matter which, so far as our present\nknowledge goes, is the common foundation of all vital activity.\n\nThe hypothesis of evolution supposes that in all this vast progression\nthere would be no breach of continuity, no point at which we could say\n\"This is a natural process,\" and \"This is not a natural process;\"\nbut that the whole might be compared to that wonderful operation of\ndevelopment which may be seen going on every day under our eyes, in\nvirtue of which there arises, out of the semi-fluid comparatively\nhomogeneous substance which we call an egg, the complicated organisation\nof one of the higher animals. That, in a few words, is what is meant by\nthe hypothesis of evolution.\n\nI have already suggested that, in dealing with these three hypotheses,\nin endeavouring to form a judgment as to which of them is the more\nworthy of belief, or whether none is worthy of belief--in which case\nour condition of mind should be that suspension of judgment which is so\ndifficult to all but trained intellects--we should be indifferent to\nall _a priori_ considerations. The question is a question of historical\nfact. The universe has come into existence somehow or other, and the\nproblem is, whether it came into existence in one fashion, or whether\nit came into existence in another; and, as an essential preliminary to\nfurther discussion, permit me to say two or three words as to the nature\nand the kinds of historical evidence.\n\nThe evidence as to the occurrence of any event in past time may be\nranged under two heads which, for convenience' sake, I will speak of\nas testimonial evidence and as circumstantial evidence. By testimonial\nevidence I mean human testimony; and by circumstantial evidence I mean\nevidence which is not human testimony. Let me illustrate by a familiar\nexample what I understand by these two kinds of evidence, and what is to\nbe said respecting their value.\n\nSuppose that a man tells you that he saw a person strike another and\nkill him; that is testimonial evidence of the fact of murder. But it is\npossible to have circumstantial evidence of the fact of murder; that\nis to say, you may find a man dying with a wound upon his head having\nexactly the form and character of the wound which is made by an axe,\nand, with due care in taking surrounding circumstances into account, you\nmay conclude with the utmost certainty that the man has been murdered;\nthat his death is the consequence of a blow inflicted by another man\nwith that implement. We are very much in the habit of considering\ncircumstantial evidence as of less value than testimonial evidence,\nand it may be that, where the circumstances are not perfectly clear and\nintelligible, it is a dangerous and unsafe kind of evidence; but it\nmust not be forgotten that, in many cases, circumstantial is quite as\nconclusive as testimonial evidence, and that, not unfrequently, it is\na great deal weightier than testimonial evidence. For example, take the\ncase to which I referred just now. The circumstantial evidence may be\nbetter and more convincing than the testimonial evidence; for it may be\nimpossible, under the conditions that I have defined, to suppose that\nthe man met his death from any cause but the violent blow of an axe\nwielded by another man. The circumstantial evidence in favour of a\nmurder having been committed, in that case, is as complete and as\nconvincing as evidence can be. It is evidence which is open to no doubt\nand to no falsification. But the testimony of a witness is open to\nmultitudinous doubts. He may have been mistaken. He may have been\nactuated by malice. It has constantly happened that even an accurate man\nhas declared that a thing has happened in this, that, or the other way,\nwhen a careful analysis of the circumstantial evidence has shown that it\ndid not happen in that way, but in some other way.\n\nWe may now consider the evidence in favour of or against the three\nhypotheses. Let me first direct your attention to what is to be said\nabout the hypothesis of the eternity of the state of things in which we\nnow live. What will first strike you is, that it is a hypothesis which,\nwhether true or false, is not capable of verification by any evidence.\nFor, in order to obtain either circumstantial or testimonial evidence\nsufficient to prove the eternity of duration of the present state\nof nature, you must have an eternity of witnesses or an infinity\nof circumstances, and neither of these is attainable. It is utterly\nimpossible that such evidence should be carried beyond a certain point\nof time; and all that could be said, at most, would be, that so far\nas the evidence could be traced, there was nothing to contradict the\nhypothesis. But when you look, not to the testimonial evidence--which,\nconsidering the relative insignificance of the antiquity of human\nrecords, might not be good for much in this case--but to the\ncircumstantial evidence, then you find that this hypothesis is\nabsolutely incompatible with such evidence as we have; which is of so\nplain and so simple a character that it is impossible in any way to\nescape from the conclusions which it forces upon us.\n\nYou are, doubtless, all aware that the outer substance of the earth,\nwhich alone is accessible to direct observation, is not of a homogeneous\ncharacter, but that it is made up of a number of layers or strata, the\ntitles of the principal groups of which are placed upon the accompanying\ndiagram. Each of these groups represents a number of beds of sand, of\nstone, of clay, of slate, and of various other materials.\n\nOn careful examination, it is found that the materials of which each of\nthese layers of more or less hard rock are composed are, for the most\npart, of the same nature as those which are at present being formed\nunder known conditions on the surface of the earth. For example, the\nchalk, which constitutes a great part of the Cretaceous formation in\nsome parts of the world, is practically identical in its physical and\nchemical characters with a substance which is now being formed at the\nbottom of the Atlantic Ocean, and covers an enormous area; other beds\nof rock are comparable with the sands which are being formed upon\nsea-shores, packed together, and so on. Thus, omitting rocks of igneous\norigin, it is demonstrable that all these beds of stone, of which a\ntotal of not less than seventy thousand feet is known, have been formed\nby natural agencies, either out of the waste and washing of the dry\nland, or else by the accumulation of the exuviae of plants and animals.\nMany of these strata are full of such exuviae--the so-called \"fossils.\"\nRemains of thousands of species of animals and plants, as perfectly\nrecognisable as those of existing forms of life which you meet with in\nmuseums, or as the shells which you pick up upon the sea-beach, have\nbeen imbedded in the ancient sands, or muds, or limestones, just as they\nare being imbedded now, in sandy, or clayey, or calcareous subaqueous\ndeposits. They furnish us with a record, the general nature of which\ncannot be misinterpreted, of the kinds of things that have lived upon\nthe surface of the earth during the time that is registered by this\ngreat thickness of stratified rocks. But even a superficial study of\nthese fossils shows us that the animals and plants which live at the\npresent time have had only a temporary duration; for the remains of\nsuch modern forms of life are met with, for the most part, only in the\nuppermost or latest tertiaries, and their number rapidly diminishes in\nthe lower deposits of that epoch. In the older tertiaries, the places\nof existing animals and plants are taken by other forms, as numerous and\ndiversified as those which live now in the same localities, but more or\nless different from them; in the mesozoic rocks, these are replaced\nby others yet more divergent from modern types; and, in the paleozoic\nformations, the contrast is still more marked. Thus the circumstantial\nevidence absolutely negatives the conception of the eternity of the\npresent condition of things. We can say, with certainty, that the\npresent condition of things has existed for a comparatively short\nperiod; and that, so far as animal and vegetable nature are concerned,\nit has been preceded by a different condition. We can pursue this\nevidence until we reach the lowest of the stratified rocks, in which we\nlose the indications of life altogether. The hypothesis of the eternity\nof the present state of nature may therefore be put out of court.\n\n     Fig. 1.--Ideal Section of the Crust of the Earth.\n\nWe now come to what I will term Milton's hypothesis--the hypothesis that\nthe present condition of things has endured for a comparatively short\ntime; and, at the commencement of that time, came into existence within\nthe course of six days. I doubt not that it may have excited some\nsurprise in your minds that I should have spoken of this as Milton's\nhypothesis, rather than that I should have chosen the terms which are\nmore customary, such as \"the doctrine of creation,\" or \"the Biblical\ndoctrine,\" or \"the doctrine of Moses,\" all of which denominations, as\napplied to the hypothesis to which I have just referred, are certainly\nmuch more familiar to you than the title of the Miltonic hypothesis. But\nI have had what I cannot but think are very weighty reasons for taking\nthe course which I have pursued. In the first place, I have discarded\nthe title of the \"doctrine of creation,\" because my present business is\nnot with the question why the objects which constitute Nature came into\nexistence, but when they came into existence, and in what order. This\nis as strictly a historical question as the question when the Angles\nand the Jutes invaded England, and whether they preceded or followed the\nRomans. But the question about creation is a philosophical problem,\nand one which cannot be solved, or even approached, by the historical\nmethod. What we want to learn is, whether the facts, so far as they are\nknown, afford evidence that things arose in the way described by Milton,\nor whether they do not; and, when that question is settled it will be\ntime enough to inquire into the causes of their origination.\n\nIn the second place, I have not spoken of this doctrine as the Biblical\ndoctrine. It is quite true that persons as diverse in their general\nviews as Milton the Protestant and the celebrated Jesuit Father Suarez,\neach put upon the first chapter of Genesis the interpretation embodied\nin Milton's poem. It is quite true that this interpretation is that\nwhich has been instilled into every one of us in our childhood; but I\ndo not for one moment venture to say that it can properly be called the\nBiblical doctrine. It is not my business, and does not lie within my\ncompetency, to say what the Hebrew text does, and what it does not\nsignify; moreover, were I to affirm that this is the Biblical doctrine,\nI should be met by the authority of many eminent scholars, to say\nnothing of men of science, who, at various times, have absolutely denied\nthat any such doctrine is to be found in Genesis. If we are to listen to\nmany expositors of no mean authority, we must believe that what seems so\nclearly defined in Genesis--as if very great pains had been taken that\nthere should be no possibility of mistake--is not the meaning of the\ntext at all. The account is divided into periods that we may make just\nas long or as short as convenience requires. We are also to understand\nthat it is consistent with the original text to believe that the most\ncomplex plants and animals may have been evolved by natural processes,\nlasting for millions of years, out of structureless rudiments. A\nperson who is not a Hebrew scholar can only stand aside and admire\nthe marvellous flexibility of a language which admits of such diverse\ninterpretations. But assuredly, in the face of such contradictions of\nauthority upon matters respecting which he is incompetent to form any\njudgment, he will abstain, as I do, from giving any opinion.\n\nIn the third place, I have carefully abstained from speaking of this as\nthe Mosaic doctrine, because we are now assured upon the authority of\nthe highest critics and even of dignitaries of the Church, that there is\nno evidence that Moses wrote the Book of Genesis, or knew anything\nabout it. You will understand that I give no judgment--it would be an\nimpertinence upon my part to volunteer even a suggestion--upon such a\nsubject. But, that being the state of opinion among the scholars and the\nclergy, it is well for the unlearned in Hebrew lore, and for the laity,\nto avoid entangling themselves in such a vexed question. Happily, Milton\nleaves us no excuse for doubting what he means, and I shall therefore be\nsafe in speaking of the opinion in question as the Miltonic hypothesis.\n\nNow we have to test that hypothesis. For my part, I have no prejudice\none way or the other. If there is evidence in favour of this view, I am\nburdened by no theoretical difficulties in the way of accepting it; but\nthere must be evidence. Scientific men get an awkward habit--no, I won't\ncall it that, for it is a valuable habit--of believing nothing unless\nthere is evidence for it; and they have a way of looking upon belief\nwhich is not based upon evidence, not only as illogical, but as immoral.\nWe will, if you please, test this view by the circumstantial evidence\nalone; for, from what I have said, you will understand that I do not\npropose to discuss the question of what testimonial evidence is to be\nadduced in favour of it. If those whose business it is to judge are not\nat one as to the authenticity of the only evidence of that kind which is\noffered, nor as to the facts to which it bears witness, the discussion\nof such evidence is superfluous.\n\nBut I may be permitted to regret this necessity of rejecting the\ntestimonial evidence the less, because the examination of the\ncircumstantial evidence leads to the conclusion, not only that it is\nincompetent to justify the hypothesis, but that, so far as it goes, it\nis contrary to the hypothesis.\n\nThe considerations upon which I base this conclusion are of the simplest\npossible character. The Miltonic hypothesis contains assertions of a\nvery definite character relating to the succession of living forms. It\nis stated that plants, for example, made their appearance upon the third\nday, and not before. And you will understand that what the poet means by\nplants are such plants as now live, the ancestors, in the ordinary way\nof propagation of like by like, of the trees and shrubs which flourish\nin the present world. It must needs be so; for, if they were different,\neither the existing plants have been the result of a separate\norigination since that described by Milton, of which we have no record,\nnor any ground for supposition that such an occurrence has taken place;\nor else they have arisen by a process of evolution from the original\nstocks.\n\nIn the second place, it is clear that there was no animal life before\nthe fifth day, and that, on the fifth day, aquatic animals and birds\nappeared. And it is further clear that terrestrial living things, other\nthan birds, made their appearance upon the sixth day and not before.\nHence, it follows that, if, in the large mass of circumstantial evidence\nas to what really has happened in the past history of the globe we find\nindications of the existence of terrestrial animals, other than birds,\nat a certain period, it is perfectly certain that all that has taken\nplace, since that time, must be referred to the sixth day.\n\nIn the great Carboniferous formation, whence America derives so vast a\nproportion of her actual and potential wealth, in the beds of coal which\nhave been formed from the vegetation of that period, we find abundant\nevidence of the existence of terrestrial animals. They have been\ndescribed, not only by European but by your own naturalists. There are\nto be found numerous insects allied to our cockroaches. There are to\nbe found spiders and scorpions of large size, the latter so similar to\nexisting scorpions that it requires the practised eye of the naturalist\nto distinguish them. Inasmuch as these animals can be proved to have\nbeen alive in the Carboniferous epoch, it is perfectly clear that, if\nthe Miltonic account is to be accepted, the huge mass of rocks extending\nfrom the middle of the Palaeozoic formations to the uppermost members of\nthe series, must belong to the day which is termed by Milton the sixth.\nBut, further, it is expressly stated that aquatic animals took their\norigin on the fifth day, and not before; hence, all formations in which\nremains of aquatic animals can be proved to exist, and which therefore\ntestify that such animals lived at the time when these formations were\nin course of deposition, must have been deposited during or since the\nperiod which Milton speaks of as the fifth day. But there is absolutely\nno fossiliferous formation in which the remains of aquatic animals are\nabsent. The oldest fossils in the Silurian rocks are exuviae of marine\nanimals; and if the view which is entertained by Principal Dawson and\nDr. Carpenter respecting the nature of the _Eozoon_ be well-founded,\naquatic animals existed at a period as far antecedent to the deposition\nof the coal as the coal is from us; inasmuch as the _Eozoon_ is met\nwith in those Laurentian strata which lie at the bottom of the series\nof stratified rocks. Hence it follows, plainly enough, that the whole\nseries of stratified rocks, if they are to be brought into harmony with\nMilton, must be referred to the fifth and sixth days, and that we cannot\nhope to find the slightest trace of the products of the earlier days in\nthe geological record. When we consider these simple facts, we see\nhow absolutely futile are the attempts that have been made to draw a\nparallel between the story told by so much of the crust of the earth\nas is known to us and the story which Milton tells. The whole series of\nfossiliferous stratified rocks must be referred to the last two days;\nand neither the Carboniferous, nor any other, formation can afford\nevidence of the work of the third day.\n\nNot only is there this objection to any attempt to establish a harmony\nbetween the Miltonic account and the facts recorded in the fossiliferous\nrocks, but there is a further difficulty. According to the Miltonic\naccount, the order in which animals should have made their appearance in\nthe stratified rocks would be thus: Fishes, including the great whales,\nand birds; after them, all varieties of terrestrial animals except\nbirds. Nothing could be further from the facts as we find them; we\nknow of not the slightest evidence of the existence of birds before the\nJurassic, or perhaps the Triassic, formation; while terrestrial animals,\nas we have just seen, occur in the Carboniferous rocks.\n\nIf there were any harmony between the Miltonic account and the\ncircumstantial evidence, we ought to have abundant evidence of the\nexistence of birds in the Carboniferous, the Devonian, and the Silurian\nrocks. I need hardly say that this is not the case, and that not a trace\nof birds makes its appearance until the far later period which I have\nmentioned.\n\nAnd again, if it be true that all varieties of fishes and the great\nwhales, and the like, made their appearance on the fifth day, we ought\nto find the remains of these animals in the older rocks--in those which\nwere deposited before the Carboniferous epoch. Fishes we do find, in\nconsiderable number and variety; but the great whales are absent, and\nthe fishes are not such as now live. Not one solitary species of fish\nnow in existence is to be found in the Devonian or Silurian formations.\nHence we are introduced afresh to the dilemma which I have already\nplaced before you: either the animals which came into existence on the\nfifth day were not such as those which are found at present, are not the\ndirect and immediate ancestors of those which now exist; in which\ncase, either fresh creations of which nothing is said, or a process of\nevolution, must have occurred; or else the whole story must be given up,\nas not only devoid of any circumstantial evidence, but contrary to such\nevidence as exists.\n\nI placed before you in a few words, some little time ago, a statement of\nthe sum and substance of Milton's hypothesis. Let me now try to state as\nbriefly, the effect of the circumstantial evidence bearing upon the\npast history of the earth which is furnished, without the possibility\nof mistake, with no chance of error as to its chief features, by the\nstratified rocks. What we find is, that the great series of formations\nrepresents a period of time of which our human chronologies hardly\nafford us a unit of measure. I will not pretend to say how we ought to\nestimate this time, in millions or in billions of years. For my purpose,\nthe determination of its absolute duration is wholly unessential. But\nthat the time was enormous there can be no question.\n\nIt results from the simplest methods of interpretation, that leaving\nout of view certain patches of metamorphosed rocks, and certain volcanic\nproducts, all that is now dry land has once been at the bottom of the\nwaters. It is perfectly certain that, at a comparatively recent period\nof the world's history--the Cretaceous epoch--none of the great physical\nfeatures which at present mark the surface of the globe existed. It\nis certain that the Rocky Mountains were not. It is certain that\nthe Himalaya Mountains were not. It is certain that the Alps and the\nPyrenees had no existence. The evidence is of the plainest possible\ncharacter and is simply this:--We find raised up on the flanks of these\nmountains, elevated by the forces of upheaval which have given rise\nto them, masses of Cretaceous rock which formed the bottom of the sea\nbefore those mountains existed. It is therefore clear that the elevatory\nforces which gave rise to the mountains operated subsequently to the\nCretaceous epoch; and that the mountains themselves are largely made up\nof the materials deposited in the sea which once occupied their place.\nAs we go back in time, we meet with constant alternations of sea and\nland, of estuary and open ocean; and, in correspondence with these\nalternations, we observe the changes in the fauna and flora to which I\nhave referred.\n\nBut the inspection of these changes gives us no right to believe that\nthere has been any discontinuity in natural processes. There is no trace\nof general cataclysms, of universal deluges, or sudden destructions of a\nwhole fauna or flora. The appearances which were formerly interpreted\nin that way have all been shown to be delusive, as our knowledge has\nincreased and as the blanks which formerly appeared to exist between\nthe different formations have been filled up. That there is no absolute\nbreak between formation and formation, that there has been no sudden\ndisappearance of all the forms of life and replacement of them by\nothers, but that changes have gone on slowly and gradually, that one\ntype has died out and another has taken its place, and that thus,\nby insensible degrees, one fauna has been replaced by another, are\nconclusions strengthened by constantly increasing evidence. So that\nwithin the whole of the immense period indicated by the fossiliferous\nstratified rocks, there is assuredly not the slightest proof of any\nbreak in the uniformity of Nature's operations, no indication that\nevents have followed other than a clear and orderly sequence.\n\nThat, I say, is the natural and obvious teaching of the circumstantial\nevidence contained in the stratified rocks. I leave you to consider\nhow far, by any ingenuity of interpretation, by any stretching of the\nmeaning of language, it can be brought into harmony with the Miltonic\nhypothesis.\n\nThere remains the third hypothesis, that of which I have spoken as the\nhypothesis of evolution; and I purpose that, in lectures to come, we\nshould discuss it as carefully as we have considered the other two\nhypotheses. I need not say that it is quite hopeless to look for\ntestimonial evidence of evolution. The very nature of the case precludes\nthe possibility of such evidence, for the human race can no more be\nexpected to testify to its own origin, than a child can be tendered as\na witness of its own birth. Our sole inquiry is, what foundation\ncircumstantial evidence lends to the hypothesis, or whether it lends\nnone, or whether it controverts the hypothesis. I shall deal with the\nmatter entirely as a question of history. I shall not indulge in the\ndiscussion of any speculative probabilities. I shall not attempt to show\nthat Nature is unintelligible unless we adopt some such hypothesis.\nFor anything I know about the matter, it may be the way of Nature to be\nunintelligible; she is often puzzling, and I have no reason to suppose\nthat she is bound to fit herself to our notions.\n\nI shall place before you three kinds of evidence entirely based upon\nwhat is known of the forms of animal life which are contained in the\nseries of stratified rocks. I shall endeavour to show you that there is\none kind of evidence which is neutral, which neither helps evolution\nnor is inconsistent with it. I shall then bring forward a second kind\nof evidence which indicates a strong probability in favour of evolution,\nbut does not prove it; and, lastly, I shall adduce a third kind of\nevidence which, being as complete as any evidence which we can hope to\nobtain upon such a subject, and being wholly and strikingly in favour\nof evolution, may fairly be called demonstrative evidence of its\noccurrence.\n\n\n\n\n\nII. THE HYPOTHESIS OF EVOLUTION. THE NEUTRAL AND THE FAVOURABLE\nEVIDENCE.\n\n\nIn the preceding lecture I pointed out that there are three hypotheses\nwhich may be entertained, and which have been entertained, respecting\nthe past history of life upon the globe. According to the first of these\nhypotheses, living beings, such as now exist, have existed from\nall eternity upon this earth. We tested that hypothesis by the\ncircumstantial evidence, as I called it, which is furnished by the\nfossil remains contained in the earth's crust, and we found that it was\nobviously untenable. I then proceeded to consider the second hypothesis,\nwhich I termed the Miltonic hypothesis, not because it is of any\nparticular consequence whether John Milton seriously entertained it or\nnot, but because it is stated in a clear and unmistakable manner in his\ngreat poem. I pointed out to you that the evidence at our command as\ncompletely and fully negatives that hypothesis as it did the preceding\none. And I confess that I had too much respect for your intelligence\nto think it necessary to add that the negation was equally clear and\nequally valid, whatever the source from which that hypothesis might be\nderived, or whatever the authority by which it might be supported.\nI further stated that, according to the third hypothesis, or that of\nevolution, the existing state of things is the last term of a long\nseries of states, which, when traced back, would be found to show no\ninterruption and no breach in the continuity of natural causation.\nI propose, in the present and the following lecture, to test this\nhypothesis rigorously by the evidence at command, and to inquire how\nfar that evidence can be said to be indifferent to it, how far it can be\nsaid to be favourable to it, and, finally, how far it can be said to be\ndemonstrative.\n\nFrom almost the origin of the discussions about the existing condition\nof the animal and vegetable worlds and the causes which have determined\nthat condition, an argument has been put forward as an objection to\nevolution, which we shall have to consider very seriously. It is an\nargument which was first clearly stated by Cuvier in his criticism of\nthe doctrines propounded by his great contemporary, Lamarck. The French\nexpedition to Egypt had called the attention of learned men to the\nwonderful store of antiquities in that country, and there had been\nbrought back to France numerous mummified corpses of the animals which\nthe ancient Egyptians revered and preserved, and which, at a reasonable\ncomputation, must have lived not less than three or four thousand\nyears before the time at which they were thus brought to light. Cuvier\nendeavoured to test the hypothesis that animals have undergone gradual\nand progressive modifications of structure, by comparing the skeletons\nand such other parts of the mummies as were in a fitting state of\npreservation, with the corresponding parts of the representatives of the\nsame species now living in Egypt. He arrived at the conviction that no\nappreciable change had taken place in these animals in the course of\nthis considerable lapse of time, and the justice of his conclusion is\nnot disputed.\n\nIt is obvious that, if it can be proved that animals have endured,\nwithout undergoing any demonstrable change of structure, for so long a\nperiod as four thousand years, no form of the hypothesis of evolution\nwhich assumes that animals undergo a constant and necessary progressive\nchange can be tenable; unless, indeed, it be further assumed that\nfour thousand years is too short a time for the production of a change\nsufficiently great to be detected.\n\nBut it is no less plain that if the process of evolution of animals is\nnot independent of surrounding conditions; if it may be indefinitely\nhastened or retarded by variations in these conditions; or if evolution\nis simply a process of accommodation to varying conditions; the argument\nagainst the hypothesis of evolution based on the unchanged character of\nthe Egyptian fauna is worthless. For the monuments which are coeval with\nthe mummies testify as strongly to the absence of change in the physical\ngeography and the general conditions of the land of Egypt, for the time\nin question, as the mummies do to the unvarying characters of its living\npopulation.\n\nThe progress of research since Cuvier's time has supplied far more\nstriking examples of the long duration of specific forms of life than\nthose which are furnished by the mummified Ibises and Crocodiles of\nEgypt. A remarkable case is to be found in your own country, in the\nneighbourhood of the falls of Niagara. In the immediate vicinity of the\nwhirlpool, and again upon Goat Island, in the superficial deposits which\ncover the surface of the rocky subsoil in those regions, there are\nfound remains of animals in perfect preservation, and among them, shells\nbelonging to exactly the same species as those which at present inhabit\nthe still waters of Lake Erie. It is evident, from the structure of the\ncountry, that these animal remains were deposited in the beds in which\nthey occur at a time when the lake extended over the region in which\nthey are found. This involves the conclusion that they lived and died\nbefore the falls had cut their way back through the gorge of Niagara;\nand, indeed, it has been determined that, when these animals lived,\nthe falls of Niagara must have been at least six miles further down the\nriver than they are at present. Many computations have been made of\nthe rate at which the falls are thus cutting their way back. Those\ncomputations have varied greatly, but I believe I am speaking within\nthe bounds of prudence, if I assume that the falls of Niagara have\nnot retreated at a greater pace than about a foot a year. Six miles,\nspeaking roughly, are 30,000 feet; 30,000 feet, at a foot a year, gives\n30,000 years; and thus we are fairly justified in concluding that no\nless a period than this has passed since the shell-fish, whose remains\nare left in the beds to which I have referred, were living creatures.\n\nBut there is still stronger evidence of the long duration of certain\ntypes. I have already stated that, as we work our way through the great\nseries of the Tertiary formations, we find many species of animals\nidentical with those which live at the present day, diminishing in\nnumbers, it is true, but still existing, in a certain proportion, in the\noldest of the Tertiary rocks. Furthermore, when we examine the rocks\nof the Cretaceous epoch, we find the remains of some animals which the\nclosest scrutiny cannot show to be, in any important respect, different\nfrom those which live at the present time. That is the case with one of\nthe cretaceous lamp-shells (_Terebratula_), which has continued to exist\nunchanged, or with insignificant variations, down to the present\nday. Such is the case with the _Globigerin\u00e6,_ the skeletons of which,\naggregated together, form a large proportion of our English chalk. Those\n_Globigerinae_ can be traced down to the _Globigerinae_ which live\nat the surface of the present great oceans, and the remains of which,\nfalling to the bottom of the sea, give rise to a chalky mud. Hence\nit must be admitted that certain existing species of animals show no\ndistinct sign of modification, or transformation, in the course of a\nlapse of time as great as that which carries us back to the Cretaceous\nperiod; and which, whatever its absolute measure, is certainly vastly\ngreater than thirty thousand years.\n\nThere are groups of species so closely allied together, that it needs\nthe eye of a naturalist to distinguish them one from another. If we\ndisregard the small differences which separate these forms, and consider\nall the species of such groups as modifications of one type, we\nshall find that, even among the higher animals, some types have had a\nmarvellous duration. In the chalk, for example, there is found a fish\nbelonging to the highest and the most differentiated group of osseous\nfishes, which goes by the name of _Beryx._ The remains of that fish are\namong the most beautiful and well-preserved of the fossils found in our\nEnglish chalk. It can be studied anatomically, so far as the hard parts\nare concerned, almost as well as if it were a recent fish. But the\ngenus _Beryx_ is represented, at the present day, by very closely allied\nspecies which are living in the Pacific and Atlantic Oceans. We may\ngo still farther back. I have already referred to the fact that the\nCarboniferous formations, in Europe and in America, contain the remains\nof scorpions in an admirable state of preservation, and that those\nscorpions are hardly distinguishable from such as now live. I do not\nmean to say that they are not different, but close scrutiny is needed in\norder to distinguish them from modern scorpions.\n\nMore than this. At the very bottom of the Silurian series, in beds which\nare by some authorities referred to the Cambrian formation, where the\nsigns of life begin to fail us--even there, among the few and scanty\nanimal remains which are discoverable, we find species of molluscous\nanimals which are so closely allied to existing forms that, at one time,\nthey were grouped under the same generic name. I refer to the well-known\n_Lingula_ of the _Lingula_ flags, lately, in consequence of some slight\ndifferences, placed in the new genus _Lingulella._ Practically, it\nbelongs to the same great generic group as the _Lingula,_ which is to\nbe found at the present day upon your own shores and those of many other\nparts of the world.\n\nThe same truth is exemplified if we turn to certain great periods of the\nearth's history--as, for example, the Mesozoic epoch. There are groups\nof reptiles, such as the _Ichthyosauria_ and the _Plesiosauria,_ which\nappear shortly after the commencement of this epoch, and they occur in\nvast numbers. They disappear with the chalk and, throughout the whole of\nthe great series of Mesozoic rocks, they present no such modifications\nas can safely be considered evidence of progressive modification.\n\nFacts of this kind are undoubtedly fatal to any form of the doctrine of\nevolution which postulates the supposition that there is an intrinsic\nnecessity, on the part of animal forms which have once come into\nexistence, to undergo continual modification; and they are as distinctly\nopposed to any view which involves the belief, that such modification\nmay occur, must take place, at the same rate, in all the different types\nof animal or vegetable life. The facts, as I have placed them before\nyou, obviously directly contradict any form of the hypothesis of\nevolution which stands in need of these two postulates.\n\nBut, one great service that has been rendered by Mr. Darwin to the\ndoctrine of evolution in general is this: he has shown that there\nare two chief factors in the process of evolution: one of them is the\ntendency to vary, the existence of which in all living forms may\nbe proved by observation; the other is the influence of surrounding\nconditions upon what I may call the parent form and the variations which\nare thus evolved from it. The cause of the production of variations is\na matter not at all properly understood at present. Whether variation\ndepends upon some intricate machinery--if I may use the phrase--of the\nliving organism itself, or whether it arises through the influence of\nconditions upon that form, is not certain, and the question may, for\nthe present, be left open. But the important point is that, granting the\nexistence of the tendency to the production of variations; then, whether\nthe variations which are produced shall survive and supplant the parent,\nor whether the parent form shall survive and supplant the variations, is\na matter which depends entirely on those conditions which give rise to\nthe struggle for existence. If the surrounding conditions are such that\nthe parent form is more competent to deal with them, and flourish in\nthem than the derived forms, then, in the struggle for existence,\nthe parent form will maintain itself and the derived forms will be\nexterminated. But if, on the contrary, the conditions are such as to be\nmore favourable to a derived than to the parent form, the parent form\nwill be extirpated and the derived form will take its place. In the\nfirst case, there will be no progression, no change of structure,\nthrough any imaginable series of ages; in the second place there will be\nmodification of change and form.\n\nThus the existence of these persistent types, as I have termed them, is\nno real obstacle in the way of the theory of evolution. Take the case\nof the scorpions to which I have just referred. No doubt, since the\nCarboniferous epoch, conditions have always obtained, such as existed\nwhen the scorpions of that epoch flourished; conditions in which\nscorpions find themselves better off, more competent to deal with the\ndifficulties in their way, than any variation from the scorpion type\nwhich they may have produced; and, for that reason, the scorpion type\nhas persisted, and has not been supplanted by any other form. And\nthere is no reason, in the nature of things, why, as long as this world\nexists, if there be conditions more favourable to scorpions than to\nany variation which may arise from them, these forms of life should not\npersist.\n\nTherefore, the stock objection to the hypothesis of evolution, based on\nthe long duration of certain animal and vegetable types, is no objection\nat all. The facts of this character--and they are numerous--belong to\nthat class of evidence which I have called indifferent. That is to say,\nthey may afford no direct support to the doctrine of evolution, but they\nare capable of being interpreted in perfect consistency with it.\n\nThere is another order of facts belonging to the class of negative or\nindifferent evidence. The great group of Lizards, which abound in the\npresent world, extends through the whole series of formations as far\nback as the Permian, or latest Palaeozoic, epoch. These Permian lizards\ndiffer astonishingly little from the lizards which exist at the present\nday. Comparing the amount of the differences between them and modern\nlizards, with the prodigious lapse of time between the Permian epoch\nand the present day, it may be said that the amount of change is\ninsignificant. But, when we carry our researches farther back in time,\nwe find no trace of lizards, nor of any true reptile whatever, in the\nwhole mass of formations beneath the Permian.\n\nNow, it is perfectly clear that if our palaeontological collections are\nto be taken, even approximately, as an adequate representation of all\nthe forms of animals and plants that have ever lived; and if the record\nfurnished by the known series of beds of stratified rock covers the\nwhole series of events which constitute the history of life on the\nglobe, such a fact as this directly contravenes the hypothesis of\nevolution; because this hypothesis postulates that the existence of\nevery form must have been preceded by that of some form little different\nfrom it. Here, however, we have to take into consideration that\nimportant truth so well insisted upon by Lyell and by Darwin--the\nimperfection of the geological record. It can be demonstrated that the\ngeological record must be incomplete, that it can only preserve remains\nfound in certain favourable localities and under particular conditions;\nthat it must be destroyed by processes of denudation, and obliterated by\nprocesses of metamorphosis. Beds of rock of any thickness crammed full\nof organic remains, may yet, either by the percolation of water through\nthem, or by the influence of subterranean heat, lose all trace of\nthese remains, and present the appearance of beds of rock formed under\nconditions in which living forms were absent. Such metamorphic rocks\noccur in formations of all ages; and, in various cases, there are very\ngood grounds for the belief that they have contained organic remains,\nand that those remains have been absolutely obliterated.\n\nI insist upon the defects of the geological record the more because\nthose who have not attended to these matters are apt to say, \"It is\nall very well, but, when you get into a difficulty with your theory of\nevolution, you appeal to the incompleteness and the imperfection of the\ngeological record;\" and I want to make it perfectly clear to you that\nthis imperfection is a great fact, which must be taken into account in\nall our speculations, or we shall constantly be going wrong.\n\nYou see the singular series of footmarks, drawn of its natural size in\nthe large diagram hanging up here (Fig. 2), which I owe to the kindness\nof my friend Professor Marsh, with whom I had the opportunity recently\nof visiting the precise locality in Massachusetts in which these tracks\noccur. I am, therefore, able to give you my own testimony, if needed,\nthat the diagram accurately represents what we saw. The valley of the\nConnecticut is classical ground for the geologist. It contains great\nbeds of sandstone, covering many square miles, which have evidently\nformed a part of an ancient sea-shore, or, it may be, lake-shore. For a\ncertain period of time after their deposition, these beds have remained\nsufficiently soft to receive the impressions of the feet of whatever\nanimals walked over them, and to preserve them afterwards, in exactly\nthe same way as such impressions are at this hour preserved on the\nshores of the Bay of Fundy and elsewhere. The diagram represents the\ntrack of some gigantic animal, which walked on its hind legs. You see\nthe series of marks made alternately by the right and by the left foot;\nso that, from one impression to the other of the three-toed foot on the\nsame side, is one stride, and that stride, as we measured it, is six\nfeet nine inches. I leave you, therefore, to form an impression of the\nmagnitude of the creature which, as it walked along the ancient shore,\nmade these impressions.\n\n     Fig. 2.--Tracks of Brontozoum.\n\nOf such impressions there are untold thousands upon these sandstones.\nFifty or sixty different kinds have been discovered, and they cover vast\nareas. But, up to this present time, not a bone, not a fragment, of any\none of the animals which left these great footmarks has been found;\nin fact, the only animal remains which have been met with in all these\ndeposits, from the time of their discovery to the present day--though\nthey have been carefully hunted over--is a fragmentary skeleton of one\nof the smaller forms. What has become of the bones of all these animals?\nYou see we are not dealing with little creatures, but with animals that\nmake a step of six feet nine inches; and their remains must have been\nleft somewhere. The probability is, that they have been dissolved away,\nand completely lost.\n\nI have had occasion to work out the nature of fossil remains, of which\nthere was nothing left except casts of the bones, the solid material of\nthe skeleton having been dissolved out by percolating water. It was\na chance, in this case, that the sandstone happened to be of such a\nconstitution as to set, and to allow the bones to be afterward dissolved\nout, leaving cavities of the exact shape of the bones. Had that\nconstitution been other than what it was, the bones would have been\ndissolved, the layers of sandstone would have fallen together into one\nmass, and not the slightest indication that the animal had existed would\nhave been discoverable.\n\nI know of no more striking evidence than these facts afford, of the\ncaution which should be used in drawing the conclusion, from the absence\nof organic remains in a deposit, that animals or plants did not exist\nat the time it was formed. I believe that, with a right understanding of\nthe doctrine of evolution on the one hand, and a just estimation of the\nimportance of the imperfection of the geological record on the other,\nall difficulty is removed from the kind of evidence to which I have\nadverted; and that we are justified in believing that all such cases\nare examples of what I have designated negative or indifferent\nevidence--that is to say, they in no way directly advance the hypothesis\nof evolution, but they are not to be regarded as obstacles in the way of\nour belief in that doctrine.\n\nI now pass on to the consideration of those cases which, for reasons\nwhich I will point out to you by and by, are not to be regarded as\ndemonstrative of the truth of evolution, but which are such as must\nexist if evolution be true, and which therefore are, upon the whole,\nevidence in favour of the doctrine. If the doctrine of evolution be\ntrue, it follows, that, however diverse the different groups of animals\nand of plants may be, they must all, at one time or other, have been\nconnected by gradational forms; so that, from the highest animals,\nwhatever they may be, down to the lowest speck of protoplasmic matter in\nwhich life can be manifested, a series of gradations, leading from\none end of the series to the other, either exists or has existed.\nUndoubtedly that is a necessary postulate of the doctrine of evolution.\nBut when we look upon living Nature as it is, we find a totally\ndifferent state of things. We find that animals and plants fall into\ngroups, the different members of which are pretty closely allied\ntogether, but which are separated by definite, larger or smaller,\nbreaks, from other groups. In other words, no intermediate forms which\nbridge over these gaps or intervals are, at present, to be met with.\n\nTo illustrate what I mean: Let me call your attention to those\nvertebrate animals which are most familiar to you, such as mammals,\nbirds, and reptiles. At the present day, these groups of animals are\nperfectly well-defined from one another. We know of no animal now living\nwhich, in any sense, is intermediate between the mammal and the bird, or\nbetween the bird and the reptile; but, on the contrary, there are many\nvery distinct anatomical peculiarities, well-defined marks, by which the\nmammal is separated from the bird, and the bird from the reptile. The\ndistinctions are obvious and striking if you compare the definitions of\nthese great groups as they now exist.\n\nThe same may be said of many of the subordinate groups, or orders, into\nwhich these great classes are divided. At the present time, for example,\nthere are numerous forms of non-ruminant pachyderms, or what we may call\nbroadly, the pig tribe, and many varieties of ruminants. These\nlatter have their definite characteristics, and the former have their\ndistinguishing peculiarities. But there is nothing that fills up the gap\nbetween the ruminants and the pig tribe. The two are distinct. Such also\nis the case in respect of the minor groups of the class of reptiles. The\nexisting fauna shows us crocodiles, lizards, snakes, and tortoises; but\nno connecting link between the crocodile and lizard, nor between the\nlizard and snake, nor between the snake and the crocodile, nor between\nany two of these groups. They are separated by absolute breaks. If,\nthen, it could be shown that this state of things had always\nexisted, the fact would be fatal to the doctrine of evolution. If the\nintermediate gradations, which the doctrine of evolution requires to\nhave existed between these groups, are not to be found anywhere in the\nrecords of the past history of the globe, their absence is a strong and\nweighty negative argument against evolution; while, on the other hand,\nif such intermediate forms are to be found, that is so much to the good\nof evolution; although, for reasons which I will lay before you by and\nby, we must be cautious in our estimate of the evidential cogency of\nfacts of this kind.\n\nIt is a very remarkable circumstance that, from the commencement of\nthe serious study of fossil remains, in fact, from the time when Cuvier\nbegan his brilliant researches upon those found in the quarries of\nMontmartre, palaeontology has shown what she was going to do in this\nmatter, and what kind of evidence it lay in her power to produce.\n\nI said just now that, in the existing Fauna, the group of pig-like\nanimals and the group of ruminants are entirely distinct; but one of\nthe first of Cuvier's discoveries was an animal which he called the\n_Anoplotherium,_ and which proved to be, in a great many important\nrespects, intermediate in character between the pigs, on the one hand,\nand the ruminants on the other. Thus, research into the history of the\npast did, to a certain extent, tend to fill up the breach between the\ngroup of ruminants and the group of pigs. Another remarkable animal\nrestored by the great French palaeontologist, the _Palaeotherium,_\nsimilarly tended to connect together animals to all appearance so\ndifferent as the rhinoceros, the horse, and the tapir. Subsequent\nresearch has brought to light multitudes of facts of the same order; and\nat the present day, the investigations of such anatomists as Rutimeyer\nand Gaudry have tended to fill up, more and more, the gaps in our\nexisting series of mammals, and to connect groups formerly thought to be\ndistinct.\n\nBut I think it may have an especial interest if, instead of dealing with\nthese examples, which would require a great deal of tedious osteological\ndetail, I take the case of birds and reptiles; groups which, at the\npresent day, are so clearly distinguished from one another that there\nare perhaps no classes of animals which, in popular apprehension, are\nmore completely separated. Existing birds, as you are aware, are covered\nwith feathers; their anterior extremities, specially and peculiarly\nmodified, are converted into wings by the aid of which most of them are\nable to fly; they walk upright upon two legs; and these limbs, when\nthey are considered anatomically, present a great number of exceedingly\nremarkable peculiarities, to which I may have occasion to advert\nincidentally as I go on, and which are not met with, even approximately,\nin any existing forms of reptiles. On the other hand, existing reptiles\nhave no feathers. They may have naked skins, or be covered with horny\nscales, or bony plates, or with both. They possess no wings; they\nneither fly by means of their fore-limbs, nor habitually walk upright\nupon their hind-limbs; and the bones of their legs present no such\nmodifications as we find in birds. It is impossible to imagine any two\ngroups more definitely and distinctly separated, notwithstanding certain\ncharacters which they possess in common.\n\nAs we trace the history of birds back in time, we find their remains,\nsometimes in great abundance, throughout the whole extent of the\ntertiary rocks; but, so far as our present knowledge goes, the birds of\nthe tertiary rocks retain the same essential characters as the birds\nof the present day. In other words, the tertiary birds come within the\ndefinition of the class constituted by existing birds, and are as much\nseparated from reptiles as existing birds are. Not very long ago no\nremains of birds had been found below the tertiary rocks, and I am not\nsure but that some persons were prepared to demonstrate that they could\nnot have existed at an earlier period. But, in the course of the\nlast few years, such remains have been discovered in England; though,\nunfortunately, in so imperfect and fragmentary a condition, that it\nis impossible to say whether they differed from existing birds in any\nessential character or not. In your country the development of the\ncretaceous series of rocks is enormous; the conditions under which the\nlater cretaceous strata have been deposited are highly favourable to the\npreservation of organic remains; and the researches, full of labour and\nrisk, which have been carried on by Professor Marsh in these cretaceous\nrocks of Western America, have rewarded him with the discovery of forms\nof birds of which we had hitherto no conception. By his kindness, I am\nenabled to place before you a restoration of one of these extraordinary\nbirds, every part of which can be thoroughly justified by the more or\nless complete skeletons, in a very perfect state of preservation, which\nhe has discovered. This _Hesperornis_ (Fig. 3), which measured between\nfive and six feet in length, is astonishingly like our existing divers\nor grebes in a great many respects; so like them indeed that, had the\nskeleton of _Hesperornis_ been found in a museum without its skull, it\nprobably would have been placed in the same group of birds as the divers\nand grebes of the present day. [1] But _Hesperornis_ differs from\nall existing birds, and so far resembles reptiles, in one important\nparticular--it is provided with teeth. The long jaws are armed with\nteeth which have curved crowns and thick roots (Fig. 4), and are not\nset in distinct sockets, but are lodged in a groove. In possessing true\nteeth, the _Hesperornis_ differs from every existing bird, and from\nevery bird yet discovered in the tertiary formations, the tooth-like\nserrations of the jaws in the _Odontopteryx_ of the London clay being\nmere processes of the bony substance of the jaws, and not teeth in the\nproper sense of the word. In view of the characteristics of this bird we\nare therefore obliged to modify the definitions of the classes of birds\nand reptiles. Before the discovery of _Hesperornis,_ the definition of\nthe class Aves based upon our knowledge of existing birds might have\nbeen extended to all birds; it might have been said that the absence of\nteeth was characteristic of the class of birds; but the discovery of\nan animal which, in every part of its skeleton, closely agrees with\nexisting birds, and yet possesses teeth, shows that there were ancient\nbirds which, in respect of possessing teeth, approached reptiles more\nnearly than any existing bird does, and, to that extent, diminishes the\n_hiatus_ between the two classes.\n\n     Fig. 3--Hesperornis regalis (Marsh)\n\n     Fig. 4--Hesperornis regalis (Marsh)\n     (Side and upper views of half the lower jaw; side and end views\n     of a vertebra and a separate tooth.)\n\nThe same formation has yielded another bird, _Ichthyornis_ (Fig. 5),\nwhich also possesses teeth; but the teeth are situated in distinct\nsockets, while those of _Hesperornis_ are not so lodged. The latter also\nhas such very small, almost rudimentary wings, that it must have been\nchiefly a swimmer and a diver like a Penguin; while _Ichthyornis_ has\nstrong wings and no doubt possessed corresponding powers of flight.\n_Ichthyornis_ also differed in the fact that its vertebrae have not\nthe peculiar characters of the vertebrae of existing and of all known\ntertiary birds, but were concave at each end. This discovery leads us to\nmake a further modification in the definition of the group of birds,\nand to part with another of the characters by which almost all existing\nbirds are distinguished from reptiles.\n\n     Figure. 5--Ichthyornis Dispar (Marsh). Side and upper views\n     of half the lower jaw; and side and end views of a\n     vertebra.\n\nApart from the few fragmentary remains from the English greensand, to\nwhich I have referred, the Mesozoic rocks, older than those in which\n_Hesperornis_ and _Ichthyornis_ have been discovered, have afforded\nno certain evidence of birds, with the remarkable exception of the\nSolenhofen slates. These so-called slates are composed of a fine grained\ncalcareous mud which has hardened into lithographic stone, and in which\norganic remains are almost as well preserved as they would be if they\nhad been imbedded in so much plaster of Paris. They have yielded the\n_Archaeopteryx,_ the existence of which was first made known by the\nfinding of a fossil feather, or rather of the impression of one. It is\nwonderful enough that such a perishable thing as a feather, and nothing\nmore, should be discovered; yet, for a long time, nothing was known\nof this bird except its feather. But by and by a solitary skeleton\nwas discovered which is now in the British Museum. The skull of\nthis solitary specimen is unfortunately wanting, and it is therefore\nuncertain whether the _Archaeopteryx_ possessed teeth or not. [2] But\nthe remainder of the skeleton is so well preserved as to leave no doubt\nrespecting the main features of the animal, which are very singular. The\nfeet are not only altogether bird-like, but have the special characters\nof the feet of perching birds, while the body had a clothing of true\nfeathers. Nevertheless, in some other respects, _Archaeopteryx_ is\nunlike a bird and like a reptile. There is a long tail composed of many\nvertebrae. The structure of the wing differs in some very remarkable\nrespects from that which it presents in a true bird. In the latter, the\nend of the wing answers to the thumb and two fingers of my hand; but\nthe metacarpal bones, or those which answer to the bones of the fingers\nwhich lie in the palm of the hand, are fused together into one mass; and\nthe whole apparatus, except the last joints of the thumb, is bound up in\na sheath of integument, while the edge of the hand carries the principal\nquill-feathers. In the _Archaeopteryx,_ the upper-arm bone is like that\nof a bird; and the two bones of the forearm are more or less like those\nof a bird, but the fingers are not bound together--they are free. What\ntheir number may have been is uncertain; but several, if not all,\nof them were terminated by strong curved claws, not like such as are\nsometimes found in birds, but such as reptiles possess; so that, in the\n_Archaeopteryx,_ we have an animal which, to a certain extent, occupies\na midway place between a bird and a reptile. It is a bird so far as\nits foot and sundry other parts of its skeleton are concerned; it is\nessentially and thoroughly a bird by its feathers; but it is much more\nproperly a reptile in the fact that the region which represents the\nhand has separate bones, with claws resembling those which terminate the\nforelimb of a reptile. Moreover, it has a long reptile-like tail with\na fringe of feathers on each side; while, in all true birds hitherto\nknown, the tail is relatively short, and the vertebrae which constitute\nits skeleton are generally peculiarly modified.\n\nLike the _Anoplotherium_ and the _Palaeotherium,_ therefore,\n_Archaeopteryx_ tends to fill up the interval between groups which, in\nthe existing world, are widely separated, and to destroy the value\nof the definitions of zoological groups based upon our knowledge of\nexisting forms. And such cases as these constitute evidence in favour\nof evolution, in so far as they prove that, in former periods of the\nworld's history, there were animals which overstepped the bounds of\nexisting groups, and tended to merge them into larger assemblages. They\nshow that animal organisation is more flexible than our knowledge of\nrecent forms might have led us to believe; and that many structural\npermutations and combinations, of which the present world gives us no\nindication, may nevertheless have existed.\n\nBut it by no means follows, because the _Palaeotherium_ has much in\ncommon with the horse, on the one hand, and with the rhinoceros on the\nother, that it is the intermediate form through which rhinoceroses have\npassed to become horses, or _vice versa;_ on the contrary, any such\nsupposition would certainly be erroneous. Nor do I think it likely that\nthe transition from the reptile to the bird has been effected by such\na form as _Archaeopteryx._ And it is convenient to distinguish these\nintermediate forms between two groups, which do not represent the actual\npassage from the one group to the other, as _intercalary_ types, from\nthose _linear_ types which, more or less approximately, indicate the\nnature of the steps by which the transition from one group to the other\nwas effected.\n\nI conceive that such linear forms, constituting a series of natural\ngradations between the reptile and the bird, and enabling us to\nunderstand the manner in which the reptilian has been metamorphosed\ninto the bird type, are really to be found among a group of ancient and\nextinct terrestrial reptiles known as the _Ornithoscelida._ The remains\nof these animals occur throughout the series of mesozoic formations,\nfrom the Trias to the Chalk, and there are indications of their\nexistence even in the later Palaeozoic strata.\n\nMost of these reptiles, at present known, are of great size, some having\nattained a length of forty feet or perhaps more. The majority resembled\nlizards and crocodiles in their general form, and many of them were,\nlike crocodiles, protected by an armour of heavy bony plates. But, in\nothers, the hind limbs elongate and the fore limbs shorten, until\ntheir relative proportions approach those which are observed in the\nshort-winged, flightless, ostrich tribe among birds.\n\nThe skull is relatively light, and in some cases the jaws, though\nbearing teeth, are beak-like at their extremities and appear to have\nbeen enveloped in a horny sheath. In the part of the vertebral column\nwhich lies between the haunch bones and is called the sacrum, a number\nof vertebrae may unite together into one whole, and in this respect,\nas in some details of its structure, the sacrum of these reptiles\napproaches that of birds.\n\nBut it is in the structure of the pelvis and of the hind limb that some\nof these ancient reptiles present the most remarkable approximation to\nbirds, and clearly indicate the way by which the most specialised and\ncharacteristic features of the bird may have been evolved from the\ncorresponding parts of the reptile.\n\nIn Fig. 6, the pelvis and hind limbs of a crocodile, a three-toed bird,\nand an ornithoscelidan are represented side by side; and, for facility\nof comparison, in corresponding positions; but it must be recollected\nthat, while the position of the bird's limb is natural, that of the\ncrocodile is not so. In the bird, the thigh bone lies close to the\nbody, and the metatarsal bones of the foot (ii., iii., iv., Fig. 6)\nare, ordinarily, raised into a more or less vertical position; in the\ncrocodile, the thigh bone stands out at an angle from the body, and the\nmetatarsal bones (i., ii., iii., iv., Fig. 6) lie flat on the ground.\nHence, in the crocodile, the body usually lies squat between the legs,\nwhile, in the bird, it is raised upon the hind legs, as upon pillars.\n\nIn the crocodile, the pelvis is obviously composed of three bones\non each side: the ilium (_Il._), the pubis (_Pb._), and the ischium\n(_Is._). In the adult bird there appears to be but one bone on each\nside. The examination of the pelvis of a chick, however, shows that\neach half is made up of three bones, which answer to those which remain\ndistinct throughout life in the crocodile. There is, therefore, a\nfundamental identity of plan in the construction of the pelvis of both\nbird and reptile; though the difference in form, relative size, and\ndirection of the corresponding bones in the two cases are very great.\n\nBut the most striking contrast between the two lies in the bones of the\nleg and of that part of the foot termed the tarsus, which follows upon\nthe leg. In the crocodile, the fibula (_F_) is relatively large and its\nlower end is complete. The tibia (_T_) has no marked crest at its upper\nend, and its lower end is narrow and not pulley-shaped. There are\ntwo rows of separate tarsal bones (_As., Ca., &c._) and four distinct\nmetatarsal bones, with a rudiment of a fifth.\n\nIn the bird, the fibula is small and its lower end diminishes to a\npoint. The tibia has a strong crest at its upper end and its lower\nextremity passes into a broad pulley. There seem at first to be no\ntarsal bones; and only one bone, divided at the end into three heads\nfor the three toes which are attached to it, appears in the place of the\nmetatarsus.\n\nIn the young bird, however, the pulley-shaped apparent end of the tibia\nis a distinct bone, which represents the bones marked _As., Ca.,_ in the\ncrocodile; while the apparently single metatarsal bone consists of three\nbones, which early unite with one another and with an additional bone,\nwhich represents the lower row of bones in the tarsus of the crocodile.\n\nIn other words, it can be shown by the study of development that the\nbird's pelvis and hind limb are simply extreme modifications of the\nsame fundamental plan as that upon which these parts are modelled in\nreptiles.\n\nOn comparing the pelvis and hind limb of the ornithoscelidan with that\nof the crocodile, on the one side, and that of the bird, on the other\n(Fig. 6), it is obvious that it represents a middle term between the\ntwo. The pelvic bones approach the form of those of the birds, and\nthe direction of the pubis and ischium is nearly that which is\ncharacteristic of birds; the thigh bone, from the direction of its head,\nmust have lain close to the body; the tibia has a great crest; and,\nimmovably fitted on to its lower end, there is a pulley-shaped bone,\nlike that of the bird, but remaining distinct. The lower end of the\nfibula is much more slender, proportionally, than in the crocodile.\nThe metatarsal bones have such a form that they fit together immovably,\nthough they do not enter into bony union; the third toe is, as in\nthe bird, longest and strongest. In fact, the ornithoscelidan limb is\ncomparable to that of an unhatched chick.\n\n     Fig. 6.--Bird. Ornithoscelidan. Crocodile. The letters have\n     the same signification in all the figures. _Il.,_ Ilium;\n     _a._ anterior end; _b._ posterior end; _Ia._ ischium; _Pb.,_\n     pubis; _T,_ tibia; _F,_ fibula; _As.,_ astragalus; _Ca.,_\n     calcaneum; I, distal portion of the tarsus; i., ii., iii.,\n     iv., metatarsal bones.\n\nTaking all these facts together, it is obvious that the view, which was\nentertained by Mantell and the probability of which was demonstrated by\nyour own distinguished anatomist, Leidy, while much additional evidence\nin the same direction has been furnished by Professor Cope, that some of\nthese animals may have walked upon their hind legs as birds do, acquires\ngreat weight. In fact, there can be no reasonable doubt that one of the\nsmaller forms of the _Ornithoscelida, Compsognathus,_ the almost entire\nskeleton of which has been discovered in the Solenhofen slates, was a\nbipedal animal. The parts of this skeleton are somewhat twisted out of\ntheir natural relations, but the accompanying figure gives a just view\nof the general form of _Compsognathus_ and of the proportions of its\nlimbs; which, in some respects, are more completely bird-like than those\nof other _Ornithoscelida._\n\n     Fig. 7.--Restoration of Compsognathus Longipes\n\nWe have had to stretch the definition of the class of birds so as to\ninclude birds with teeth and birds with paw-like fore limbs and long\ntails. There is no evidence that _Compsognathus_ possessed feathers;\nbut, if it did, it would be hard indeed to say whether it should be\ncalled a reptilian bird or an avian reptile.\n\nAs _Compsognathus_ walked upon its hind legs, it must have made tracks\nlike those of birds. And as the structure of the limbs of several of the\ngigantic _Ornithoscelida,_ such as _Iguanodon,_ leads to the conclusion\nthat they also may have constantly, or occasionally, assumed the same\nattitude, a peculiar interest attaches to the fact that, in the Wealden\nstrata of England, there are to be found gigantic footsteps, arranged\nin order like those of the _Brontozoum,_ and which there can be no\nreasonable doubt were made by some of the _Ornithoscelida,_ the remains\nof which are found in the same rocks. And, knowing that reptiles that\nwalked upon their hind legs and shared many of the anatomical characters\nof birds did once exist, it becomes a very important question whether\nthe tracks in the Trias of Massachusetts, to which I referred some time\nago, and which formerly used to be unhesitatingly ascribed to birds, may\nnot all have been made by ornithoscelidan reptiles; and whether, if we\ncould obtain the skeletons of the animals which made these tracks, we\nshould not find in them the actual steps of the evolutional process by\nwhich reptiles gave rise to birds.\n\nThe evidential value of the facts I have brought forward in this Lecture\nmust be neither over nor under estimated. It is not historical proof of\nthe occurrence of the evolution of birds from reptiles, for we have no\nsafe ground for assuming that true birds had not made their appearance\nat the commencement of the Mesozoic epoch. It is, in fact, quite\npossible that all these more or less avi-form reptiles of the Mesozoic\nepochs are not terms in the series of progression from birds to reptiles\nat all, but simply the more or less modified descendants of Palaeozoic\nforms through which that transition was actually effected.\n\nWe are not in a position to say that the known _Ornithoscelida_ are\nintermediate in the order of their appearance on the earth between\nreptiles and birds. All that can be said is that, if independent\nevidence of the actual occurrence of evolution is producible, then these\nintercalary forms remove every difficulty in the way of understanding\nwhat the actual steps of the process, in the case of birds, may have\nbeen.\n\nThat intercalary forms should have existed in ancient times is a\nnecessary consequence of the truth of the hypothesis of evolution; and,\nhence, the evidence I have laid before you in proof of the existence of\nsuch forms, is, so far as it goes, in favour of that hypothesis.\n\nThere is another series of extinct reptiles which may be said to be\nintercalary between reptiles and birds, in so far as they combine some\nof the characters of both these groups; and which, as they possessed the\npower of flight, may seem, at first sight, to be nearer representatives\nof the forms by which the transition from the reptile to the bird was\neffected, than the _Ornithoscelida._\n\nThese are the _Pterosauria,_ or Pterodactyles, the remains of which are\nmet with throughout the series of Mesozoic rocks, from the lias to the\nchalk, and some of which attained a great size, their wings having\na span of eighteen or twenty feet. These animals, in the form and\nproportions of the head and neck relatively to the body, and in the\nfact that the ends of the jaws were often, if not always, more or less\nextensively ensheathed in horny beaks, remind us of birds. Moreover,\ntheir bones contained air cavities, rendering them specifically lighter,\nas is the case in most birds. The breast bone was large and keeled, as\nin most birds and in bats, and the shoulder girdle is strikingly\nsimilar to that of ordinary birds. But, it seems to me, that the special\nresemblance of pterodactyles to birds ends here, unless I may add the\nentire absence of teeth which characterises the great pterodactyles\n_(Pteranodon)_ discovered by Professor Marsh. All other known\npterodactyles have teeth lodged in sockets. In the vertebral column and\nthe hind limbs there are no special resemblances to birds, and when\nwe turn to the wings they are found to be constructed on a totally\ndifferent principle from those of birds.\n\n     Fig. 8.--Pterodactylus Spectabilis (Von Meyer).\n\nThere are four fingers. These four fingers are large, and three of\nthem, those which answer to the thumb and two following fingers in my\nhand--are terminated by claws, while the fourth is enormously prolonged\nand converted into a great jointed style. You see at once, from what I\nhave stated about a bird's wing, that there could be nothing less like\na bird's wing than this is. It was concluded by general reasoning that\nthis finger had the office of supporting a web which extended between it\nand the body. An existing specimen proves that such was really the case,\nand that the pterodactyles were devoid of feathers, but that the fingers\nsupported a vast web like that of a bat's wing; in fact, there can be no\ndoubt that this ancient reptile flew after the fashion of a bat.\n\nThus, though the pterodactyle is a reptile which has become modified\nin such a manner as to enable it to fly, and therefore, as might be\nexpected, presents some points of resemblance to other animals which\nfly; it has, so to speak, gone off the line which leads directly from\nreptiles to birds, and has become disqualified for the changes which\nlead to the characteristic organisation of the latter class.\nTherefore, viewed in relation to the classes of reptiles and birds, the\npterodactyles appear to me to be, in a limited sense, intercalary forms;\nbut they are not even approximately linear, in the sense of exemplifying\nthose modifications of structure through which the passage from the\nreptile to the bird took place.\n\n\n\n\nIII. THE DEMONSTRATIVE EVIDENCE OF EVOLUTION\n\n\nThe occurrence of historical facts is said to be demonstrated, when\nthe evidence that they happened is of such a character as to render the\nassumption that they did not happen in the highest degree improbable;\nand the question I now have to deal with is, whether evidence in favour\nof the evolution of animals of this degree of cogency is, or is not,\nobtainable from the record of the succession of living forms which is\npresented to us by fossil remains.\n\nThose who have attended to the progress of palaeontology are aware that\nevidence of the character which I have defined has been produced in\nconsiderable and continually-increasing quantity during the last few\nyears. Indeed, the amount and the satisfactory nature of that evidence\nare somewhat surprising, when we consider the conditions under which\nalone we can hope to obtain it.\n\nIt is obviously useless to seek for such evidence except in localities\nin which the physical conditions have been such as to permit of the\ndeposit of an unbroken, or but rarely interrupted, series of strata\nthrough a long period of time; in which the group of animals to be\ninvestigated has existed in such abundance as to furnish the requisite\nsupply of remains; and in which, finally, the materials composing the\nstrata are such as to ensure the preservation of these remains in a\ntolerably perfect and undisturbed state.\n\nIt so happens that the case which, at present, most nearly fulfils\nall these conditions is that of the series of extinct animals which\nculminates in the horses; by which term I mean to denote not merely the\ndomestic animals with which we are all so well acquainted, but their\nallies, the ass, zebra, quagga, and the like. In short, I use \"horses\"\nas the equivalent of the technical name _Equidae,_ which is applied to\nthe whole group of existing equine animals.\n\nThe horse is in many ways a remarkable animal; not least so in the fact\nthat it presents us with an example of one of the most perfect pieces\nof machinery in the living world. In truth, among the works of human\ningenuity it cannot be said that there is any locomotive so perfectly\nadapted to its purposes, doing so much work with so small a quantity\nof fuel, as this machine of nature's manufacture--the horse. And, as\na necessary consequence of any sort of perfection, of mechanical\nperfection as of others, you find that the horse is a beautiful\ncreature, one of the most beautiful of all land-animals. Look at the\nperfect balance of its form, and the rhythm and force of its action. The\nlocomotive machinery is, as you are aware, resident in its slender fore\nand hind limbs; they are flexible and elastic levers, capable of being\nmoved by very powerful muscles; and, in order to supply the engines\nwhich work these levers with the force which they expend, the horse\nis provided with a very perfect apparatus for grinding its food and\nextracting therefrom the requisite fuel.\n\nWithout attempting to take you very far into the region of osteological\ndetail, I must nevertheless trouble you with some statements respecting\nthe anatomical structure of the horse; and, more especially, will it be\nneedful to obtain a general conception of the structure of its fore and\nhind limbs, and of its teeth. But I shall only touch upon those points\nwhich are absolutely essential to our inquiry.\n\nLet us turn in the first place to the fore-limb. In most quadrupeds, as\nin ourselves, the fore-arm contains distinct bones called the radius\nand the ulna. The corresponding region in the horse seems at first\nto possess but one bone. Careful observation, however, enables us to\ndistinguish in this bone a part which clearly answers to the upper end\nof the ulna. This is closely united with the chief mass of the bone\nwhich represents the radius, and runs out into a slender shaft which may\nbe traced for some distance downwards upon the back of the radius, and\nthen in most cases thins out and vanishes. It takes still more trouble\nto make sure of what is nevertheless the fact, that a small part of the\nlower end of the bone of the horse's fore arm, which is only distinct in\na very young foal, is really the lower extremity of the ulna.\n\nWhat is commonly called the knee of a horse is its wrist. The \"cannon\nbone\" answers to the middle bone of the five metacarpal bones, which\nsupport the palm of the hand in ourselves. The \"pastern,\" \"coronary,\"\nand \"coffin\" bones of veterinarians answer to the joints of our middle\nfingers, while the hoof is simply a greatly enlarged and thickened nail.\nBut if what lies below the horse's \"knee\" thus corresponds to the\nmiddle finger in ourselves, what has become of the four other fingers or\ndigits? We find in the places of the second and fourth digits only two\nslender splint-like bones, about two-thirds as long as the cannon bone,\nwhich gradually taper to their lower ends and bear no finger joints, or,\nas they are termed, phalanges. Sometimes, small bony or gristly nodules\nare to be found at the bases of these two metacarpal splints, and it\nis probable that these represent rudiments of the first and fifth toes.\nThus, the part of the horse's skeleton, which corresponds with that of\nthe human hand, contains one overgrown middle digit, and at least two\nimperfect lateral digits; and these answer, respectively, to the third,\nthe second, and the fourth fingers in man.\n\nCorresponding modifications are found in the hind limb. In ourselves,\nand in most quadrupeds, the leg contains two distinct bones, a large\nbone, the tibia, and a smaller and more slender bone, the fibula. But,\nin the horse, the fibula seems, at first, to be reduced to its upper\nend; a short slender bone united with the tibia, and ending in a point\nbelow, occupying its place. Examination of the lower end of a young\nfoal's shin bone, however, shows a distinct portion of osseous matter,\nwhich is the lower end of the fibula; so that the apparently single,\nlower end of the shin bone is really made up of the coalesced ends of\nthe tibia and fibula, just as the apparently single, lower end of the\nfore-arm bone is composed of the coalesced radius and ulna.\n\nThe heel of the horse is the part commonly known as the hock. The hinder\ncannon bone answers to the middle metatarsal bone of the human foot, the\npastern, coronary, and coffin bones, to the middle toe bones; the hind\nhoof to the nail; as in the fore-foot. And, as in the fore-foot, there\nare merely two splints to represent the second and the fourth toes.\nSometimes a rudiment of a fifth toe appears to be traceable.\n\nThe teeth of a horse are not less peculiar than its limbs. The living\nengine, like all others, must be well stoked if it is to do its work;\nand the horse, if it is to make good its wear and tear, and to exert the\nenormous amount of force required for its propulsion, must be well and\nrapidly fed. To this end, good cutting instruments and powerful and\nlasting crushers are needful. Accordingly, the twelve cutting teeth of a\nhorse are close-set and concentrated in the fore-part of its mouth, like\nso many adzes or chisels. The grinders or molars are large, and have an\nextremely complicated structure, being composed of a number of different\nsubstances of unequal hardness. The consequence of this is that they\nwear away at different rates; and, hence, the surface of each grinder is\nalways as uneven as that of a good millstone.\n\nI have said that the structure of the grinding teeth is very\ncomplicated, the harder and the softer parts being, as it were,\ninterlaced with one another. The result of this is that, as the tooth\nwears, the crown presents a peculiar pattern, the nature of which is\nnot very easily deciphered at first; but which it is important we should\nunderstand clearly. Each grinding tooth of the upper jaw has an _outer\nwall_ so shaped that, on the worn crown, it exhibits the form of two\ncrescents, one in front and one behind, with their concave sides turned\noutwards. From the inner side of the front crescent, a crescentic _front\nridge_ passes inwards and backwards, and its inner face enlarges into a\nstrong longitudinal fold or _pillar._ From the front part of the hinder\ncrescent, a _back ridge_ takes a like direction, and also has its\n_pillar._\n\nThe deep interspaces or _valleys_ between these ridges and the outer\nwall are filled by bony substance, which is called _cement,_ and coats\nthe whole tooth.\n\nThe pattern of the worn face of each grinding tooth of the lower jaw is\nquite different. It appears to be formed of two crescent-shaped ridges,\nthe convexities of which are turned outwards. The free extremity of each\ncrescent has a _pillar,_ and there is a large double _pillar_ where\nthe two crescents meet. The whole structure is, as it were, imbedded in\ncement, which fills up the valleys, as in the upper grinders.\n\nIf the grinding faces of an upper and of a lower molar of the same\nside are applied together, it will be seen that the opposed ridges are\nnowhere parallel, but that they frequently cross; and that thus, in the\nact of mastication, a hard surface in the one is constantly applied to\na soft surface in the other, and _vice versa._ They thus constitute a\ngrinding apparatus of great efficiency, and one which is repaired as\nfast as it wears, owing to the long-continued growth of the teeth.\n\nSome other peculiarities of the dentition of the horse must be noticed,\nas they bear upon what I shall have to say by and by. Thus the crowns\nof the cutting teeth have a peculiar deep pit, which gives rise to the\nwell-known \"mark\" of the horse. There is a large space between the\nouter incisors and the front grinder. In this space the adult male horse\npresents, near the incisors on each side, above and below, a canine or\n\"tush,\" which is commonly absent in mares. In a young horse, moreover,\nthere is not unfrequently to be seen in front of the first grinder, a\nvery small tooth, which soon falls out. If this small tooth be counted\nas one, it will be found that there are seven teeth behind the canine\non each side; namely, the small tooth in question, and the six great\ngrinders, among which, by an unusual peculiarity, the foremost tooth is\nrather larger than those which follow it.\n\nI have now enumerated those characteristic structures of the horse which\nare of most importance for the purpose we have in view.\n\nTo any one who is acquainted with the morphology of vertebrated animals,\nthey show that the horse deviates widely from the general structure\nof mammals; and that the horse type is, in many respects, an extreme\nmodification of the general mammalian plan. The least modified mammals,\nin fact, have the radius and ulna, the tibia and fibula, distinct and\nseparate. They have five distinct and complete digits on each foot, and\nno one of these digits is very much larger than the rest. Moreover,\nin the least modified mammals, the total number of the teeth is very\ngenerally forty-four, while in horses, the usual number is forty, and in\nthe absence of the canines, it may be reduced to thirty-six; the incisor\nteeth are devoid of the fold seen in those of the horse: the grinders\nregularly diminish in size from the middle of the series to its front\nend; while their crowns are short, early attain their full length, and\nexhibit simple ridges or tubercles, in place of the complex foldings of\nthe horse's grinders.\n\nHence the general principles of the hypothesis of evolution lead to the\nconclusion that the horse must have been derived from some quadruped\nwhich possessed five complete digits on each foot; which had the\nbones of the fore-arm and of the leg complete and separate; and which\npossessed forty-four teeth, among which the crowns of the incisors and\ngrinders had a simple structure; while the latter gradually increased\nin size from before backwards, at any rate in the anterior part of the\nseries, and had short crowns.\n\nAnd if the horse has been thus evolved, and the remains of the different\nstages of its evolution have been preserved, they ought to present\nus with a series of forms in which the number of the digits becomes\nreduced; the bones of the fore-arm and leg gradually take on the equine\ncondition; and the form and arrangement of the teeth successively\napproximate to those which obtain in existing horses.\n\nLet us turn to the facts, and see how far they fulfil these requirements\nof the doctrine of evolution.\n\nIn Europe abundant remains of horses are found in the Quaternary and\nlater Tertiary strata as far as the Pliocene formation. But these\nhorses, which are so common in the cave-deposits and in the gravels of\nEurope, are in all essential respects like existing horses. And that is\ntrue of all the horses of the latter part of the Pliocene epoch. But, in\ndeposits which belong to the earlier Pliocene and later Miocene epochs,\nand which occur in Britain, in France, in Germany, in Greece, in India,\nwe find animals which are extremely like horses--which, in fact, are so\nsimilar to horses, that you may follow descriptions given in works upon\nthe anatomy of the horse upon the skeletons of these animals--but which\ndiffer in some important particulars. For example, the structure of\ntheir fore and hind limbs is somewhat different. The bones which, in the\nhorse, are represented by two splints, imperfect below, are as long\nas the middle metacarpal and metatarsal bones; and, attached to the\nextremity of each, is a digit with three joints of the same general\ncharacter as those of the middle digit, only very much smaller. These\nsmall digits are so disposed that they could have had but very little\nfunctional importance, and they must have been rather of the nature of\nthe dew-claws, such as are to be found in many ruminant animals. The\n_Hipparion,_ as the extinct European three-toed horse is called, in\nfact, presents a foot similar to that of the American _Protohippus_\n(Fig. 9), except that, in the _Hipparion,_ the smaller digits are\nsituated farther back, and are of smaller proportional size, than in the\n_Protohippus._\n\nThe ulna is slightly more distinct than in the horse; and the whole\nlength of it, as a very slender shaft, intimately united with the\nradius, is completely traceable. The fibula appears to be in the same\ncondition as in the horse. The teeth of the _Hipparion_ are essentially\nsimilar to those of the horse, but the pattern of the grinders is in\nsome respects a little more complex, and there is a depression on the\nface of the skull in front of the orbit, which is not seen in existing\nhorses.\n\nIn the earlier Miocene, and perhaps the later Eocene deposits of some\nparts of Europe, another extinct animal has been discovered, which\nCuvier, who first described some fragments of it, considered to be a\n_Palaeotherim._ But as further discoveries threw new light upon its\nstructure, it was recognised as a distinct genus, under the name of\n_Anchitherium._\n\nIn its general characters, the skeleton of _Anchitherium_ is very\nsimilar to that of the horse. In fact, Lartet and De Blainville called\nit _Pal\u00e6otherium equinum_ or _hippoides;_ and De Christol, in 1847, said\nthat it differed from _Hipparion_ in little more than the characters of\nits teeth, and gave it the name of _Hipparitherium._ Each foot\npossesses three complete toes; while the lateral toes are much larger in\nproportion to the middle toe than in _Hipparion,_ and doubtless rested\non the ground in ordinary locomotion.\n\nThe ulna is complete and quite distinct from the radius, though firmly\nunited with the latter. The fibula seems also to have been complete. Its\nlower end, though intimately united with that of the tibia, is clearly\nmarked off from the latter bone.\n\nThere are forty-four teeth. The incisors have no strong pit. The canines\nseem to have been well developed in both sexes. The first of the seven\ngrinders, which, as I have said, is frequently absent, and, when it does\nexist, is small in the horse, is a good-sized and permanent tooth, while\nthe grinder which follows it is but little larger than the hinder ones.\nThe crowns of the grinders are short, and though the fundamental pattern\nof the horse-tooth is discernible, the front and back ridges are\nless curved, the accessory pillars are wanting, and the valleys, much\nshallower, are not filled up with cement.\n\nSeven years ago, when I happened to be looking critically into the\nbearing of palaentological facts upon the doctrine of evolution, it\nappeared to me that the _Anchitherium,_ the _Hipparion,_ and the modern\nhorses, constitute a series in which the modifications of structure\ncoincide with the order of chronological occurrence, in the manner in\nwhich they must coincide, if the modern horses really are the result\nof the gradual metamorphosis, in the course of the Tertiary epoch, of a\nless specialised ancestral form. And I found by correspondence with the\nlate eminent French anatomist and palaeontologist, M. Lartet, that he\nhad arrived at the same conclusion from the same data.\n\nThat the _Anchitherium_ type had become metamorphosed into the\n_Hipparion_ type, and the latter into the _Equine_ type, in the course\nof that period of time which is represented by the latter half of the\nTertiary deposits, seemed to me to be the only explanation of the facts\nfor which there was even a shadow of probability. [3]\n\nAnd, hence, I have ever since held that these facts afford evidence of\nthe occurrence of evolution, which, in the sense already defined, may be\ntermed demonstrative.\n\nAll who have occupied themselves with the structure of _Anchitherium,_\nfrom Cuvier onwards, have acknowledged its many points of likeness to a\nwell-known genus of extinct Eocene mammals, _Palaeotherium._ Indeed, as\nwe have seen, Cuvier regarded his remains of _Anchitherium_ as those of\na species of _Palaeotherium._ Hence, in attempting to trace the pedigree\nof the horse beyond the Miocene epoch and the Anchitheroid form, I\nnaturally sought among the various species of Palaeotheroid animals\nfor its nearest ally, and I was led to conclude that the _Palaeotherium\nminus (Plagiolophus)_ represented the next step more nearly than any\nform then known.\n\nI think that this opinion was fully justifiable; but the progress of\ninvestigation has thrown an unexpected light on the question, and has\nbrought us much nearer than could have been anticipated to a knowledge\nof the true series of the progenitors of the horse.\n\nYou are all aware that, when your country was first discovered by\nEuropeans, there were no traces of the existence of the horse in any\npart of the American Continent. The accounts of the conquest of Mexico\ndwell upon the astonishment of the natives of that country when they\nfirst became acquainted with that astounding phenomenon--a man seated\nupon a horse. Nevertheless, the investigations of American geologists\nhave proved that the remains of horses occur in the most superficial\ndeposits of both North and South America, just as they do in Europe.\nTherefore, for some reason or other--no feasible suggestion on that\nsubject, so far as I know, has been made--the horse must have died out\non this continent at some period preceding the discovery of America. Of\nlate years there has been discovered in your Western Territories\nthat marvellous accumulation of deposits, admirably adapted for the\npreservation of organic remains, to which I referred the other evening,\nand which furnishes us with a consecutive series of records of the fauna\nof the older half of the Tertiary epoch, for which we have no\nparallel in Europe. They have yielded fossils in an excellent state of\nconservation and in unexampled number and variety. The researches of\nLeidy and others have shown that forms allied to the _Hipparion_ and\nthe _Anchitherium_ are to be found among these remains. But it is only\nrecently that the admirably conceived and most thoroughly and patiently\nworked-out investigations of Professor Marsh have given us a just idea\nof the vast fossil wealth, and of the scientific importance, of these\ndeposits. I have had the advantage of glancing over the collections in\nYale Museum; and I can truly say that, so far as my knowledge extends,\nthere is no collection from any one region and series of strata\ncomparable, for extent, or for the care with which the remains have\nbeen got together, or for their scientific importance, to the series of\nfossils which he has deposited there. This vast collection has yielded\nevidence bearing upon the question of the pedigree of the horse of the\nmost striking character. It tends to show that we must look to America,\nrather than to Europe, for the original seat of the equine series;\nand that the archaic forms and successive modifications of the horse's\nancestry are far better preserved here than in Europe.\n\nProfessor Marsh's kindness has enabled me to put before you a diagram,\nevery figure in which is an actual representation of some specimen which\nis to be seen at Yale at this present time (Fig. 9).\n\n     Fig. 9.\n\nThe succession of forms which he has brought together carries us from\nthe top to the bottom of the Tertiaries. Firstly, there is the\ntrue horse. Next we have the American Pliocene form of the horse\n(_Pliohippus_); in the conformation of its limbs it presents some\nvery slight deviations from the ordinary horse, and the crowns of\nthe grinding teeth are shorter. Then comes the _Protohippus,_ which\nrepresents the European _Hipparion,_ having one large digit and two\nsmall ones on each foot, and the general characters of the fore-arm and\nleg to which I have referred. But it is more valuable than the\nEuropean _Hipparion_ for the reason that it is devoid of some of the\npeculiarities of that form--peculiarities which tend to show that the\nEuropean _Hipparion_ is rather a member of a collateral branch, than a\nform in the direct line of succession. Next, in the backward order\nin time, is the _Miohippus,_ which corresponds pretty nearly with the\n_Anchitherium_ of Europe. It presents three complete toes--one large\nmedian and two smaller lateral ones; and there is a rudiment of that\ndigit, which answers to the little finger of the human hand.\n\nThe European record of the pedigree of the horse stops here; in the\nAmerican Tertiaries, on the contrary, the series of ancestral equine\nforms is continued into the Eocene formations. An older Miocene form,\ntermed _Mesohippus,_ has three toes in front, with a large splint-like\nrudiment representing the little finger; and three toes behind. The\nradius and ulna, the tibia and the fibula, are distinct, and the short\ncrowned molar teeth are anchitherioid in pattern.\n\nBut the most important discovery of all is the _Orohippus,_ which\ncomes from the Eocene formation, and is the oldest member of the equine\nseries, as yet known. Here we find four complete toes on the front limb,\nthree toes on the hind limb, a well-developed ulna, a well-developed\nfibula, and short-crowned grinders of simple pattern.\n\nThus, thanks to these important researches, it has become evident that,\nso far as our present knowledge extends, the history of the horse-type\nis exactly and precisely that which could have been predicted from\na knowledge of the principles of evolution. And the knowledge we now\npossess justifies us completely in the anticipation, that when the still\nlower Eocene deposits, and those which belong to the Cretaceous epoch,\nhave yielded up their remains of ancestral equine animals, we shall\nfind, first, a form with four complete toes and a rudiment of the\ninnermost or first digit in front, with, probably, a rudiment of the\nfifth digit in the hind foot; [4] while, in still older forms, the series\nof the digits will be more and more complete, until we come to the\nfive-toed animals, in which, if the doctrine of evolution is well\nfounded, the whole series must have taken its origin.\n\nThat is what I mean by demonstrative evidence of evolution. An inductive\nhypothesis is said to be demonstrated when the facts are shown to be in\nentire accordance with it. If that is not scientific proof, there are\nno merely inductive conclusions which can be said to be proved. And the\ndoctrine of evolution, at the present time, rests upon exactly as secure\na foundation as the Copernican theory of the motions of the heavenly\nbodies did at the time of its promulgation. Its logical basis is\nprecisely of the same character--the coincidence of the observed facts\nwith theoretical requirements.\n\nThe only way of escape, if it be a way of escape, from the conclusions\nwhich I have just indicated, is the supposition that all these different\nequine forms have been created separately at separate epochs of time;\nand, I repeat, that of such an hypothesis as this there neither is, nor\ncan be, any scientific evidence; and, assuredly, so far as I know, there\nis none which is supported, or pretends to be supported, by evidence\nor authority of any other kind. I can but think that the time will come\nwhen such suggestions as these, such obvious attempts to escape the\nforce of demonstration, will be put upon the same footing as the\nsupposition made by some writers, who are I believe not completely\nextinct at present, that fossils are mere simulacra, are no indications\nof the former existence of the animals to which they seem to belong;\nbut that they are either sports of nature, or special creations,\nintended--as I heard suggested the other day--to test our faith.\n\nIn fact, the whole evidence is in favour of evolution, and there is none\nagainst it. And I say this, although perfectly well aware of the\nseeming difficulties which have been built up upon what appears to the\nuninformed to be a solid foundation. I meet constantly with the argument\nthat the doctrine of evolution cannot be well founded, because it\nrequires the lapse of a very vast period of time; while the duration of\nlife upon the earth thus implied is inconsistent with the conclusions\narrived at by the astronomer and the physicist. I may venture to say\nthat I am familiar with those conclusions, inasmuch as some years ago,\nwhen President of the Geological Society of London, I took the liberty\nof criticising them, and of showing in what respects, as it appeared to\nme, they lacked complete and thorough demonstration. But, putting that\npoint aside, suppose that, as the astronomers, or some of them, and some\nphysical philosophers, tell us, it is impossible that life could have\nendured upon the earth for as long a period as is required by the\ndoctrine of evolution--supposing that to be proved--I desire to be\ninformed, what is the foundation for the statement that evolution does\nrequire so great a time? The biologist knows nothing whatever of the\namount of time which may be required for the process of evolution. It\nis a matter of fact that the equine forms which I have described to you\noccur, in the order stated, in the Tertiary formations. But I have not\nthe slightest means of guessing whether it took a million of years, or\nten millions, or a hundred millions, or a thousand millions of years,\nto give rise to that series of changes. A biologist has no means of\narriving at any conclusion as to the amount of time which may be needed\nfor a certain quantity of organic change. He takes his time from the\ngeologist. The geologist, considering the rate at which deposits are\nformed and the rate at which denudation goes on upon the surface of the\nearth, arrives at more or less justifiable conclusions as to the time\nwhich is required for the deposit of a certain thickness of rocks; and\nif he tells me that the Tertiary formations required 500,000,000 years\nfor their deposit, I suppose he has good ground for what he says, and\nI take that as a measure of the duration of the evolution of the horse\nfrom the _Orohippus_ up to its present condition. And, if he is right,\nundoubtedly evolution is a very slow process, and requires a great\ndeal of time. But suppose, now, that an astronomer or a physicist--for\ninstance, my friend Sir William Thomson--tells me that my geological\nauthority is quite wrong; and that he has weighty evidence to show\nthat life could not possibly have existed upon the surface of the earth\n500,000,000 years ago, because the earth would have then been too hot to\nallow of life, my reply is: \"That is not my affair; settle that with\nthe geologist, and when you have come to an agreement among yourselves\nI will adopt your conclusion.\" We take our time from the geologists and\nphysicists; and it is monstrous that, having taken our time from the\nphysical philosopher's clock, the physical philosopher should turn round\nupon us, and say we are too fast or too slow. What we desire to know is,\nis it a fact that evolution took place? As to the amount of time which\nevolution may have occupied, we are in the hands of the physicist and\nthe astronomer, whose business it is to deal with those questions.\n\nI have now, ladies and gentlemen, arrived at the conclusion of the task\nwhich I set before myself when I undertook to deliver these lectures.\nMy purpose has been, not to enable those among you who have paid no\nattention to these subjects before, to leave this room in a condition\nto decide upon the validity or the invalidity of the hypothesis of\nevolution; but I have desired to put before you the principles upon\nwhich all hypotheses respecting the history of Nature must be judged;\nand furthermore, to make apparent the nature of the evidence and the\namount of cogency which is to be expected and may be obtained from it.\nTo this end, I have not hesitated to regard you as genuine students and\npersons desirous of knowing the truth. I have not shrunk from taking\nyou through long discussions, that I fear may have sometimes tried\nyour patience; and I have inflicted upon you details which were\nindispensable, but which may well have been wearisome. But I shall\nrejoice--I shall consider that I have done you the greatest service\nwhich it was in my power to do--if I have thus convinced you that the\ngreat question which we have been discussing is not one to be dealt with\nby rhetorical flourishes, or by loose and superficial talk; but that it\nrequires the keen attention of the trained intellect and the patience of\nthe accurate observer.\n\nWhen I commenced this series of lectures, I did not think it necessary\nto preface them with a prologue, such as might be expected from a\nstranger and a foreigner; for during my brief stay in your country, I\nhave found it very hard to believe that a stranger could be possessed\nof so many friends, and almost harder that a foreigner could express\nhimself in your language in such a way as to be, to all appearance, so\nreadily intelligible. So far as I can judge, that most intelligent, and\nperhaps, I may add, most singularly active and enterprising body, your\npress reporters, do not seem to have been deterred by my accent from\ngiving the fullest account of everything that I happen to have said.\n\nBut the vessel in which I take my departure to-morrow morning is even\nnow ready to slip her moorings; I awake from my delusion that I am other\nthan a stranger and a foreigner. I am ready to go back to my place and\ncountry; but, before doing so, let me, by way of epilogue, tender to you\nmy most hearty thanks for the kind and cordial reception which you have\naccorded to me; and let me thank you still more for that which is\nthe greatest compliment which can be afforded to any person in my\nposition--the continuous and undisturbed attention which you have\nbestowed upon the long argument which I have had the honour to lay\nbefore you.\n\n\n\n\nFOOTNOTES:\n\n[Footnote 1: The absence of any keel on the breast-bone and some other\nosteological peculiarities, observed by Professor Marsh, however,\nsuggest that _Hesperornis_ may be a modification of a less specialised\ngroup of birds than that to which these existing aquatic birds belong.]\n\n[Footnote 2: A second specimen, discovered in 1877, and at present in\nthe Berlin museum, shows an excellently preserved skull with teeth; and\nthree digits, all terminated by claws, in the fore limb. 1893.]\n\n[Footnote 3: I use the word \"type\" because it is highly probable that\nmany forms of _Anchitherium-_like and _Hipparion-_like animals existed\nin the Miocene and Pliocene epochs, just as many species of the horse\ntribe exist now, and it is highly improbable that the particular species\nof _Anchitherium_ or _Hipparion,_ which happen to have been discovered,\nshould be precisely those which have formed part of the direct line of\nthe horse's pedigree.]\n\n[Footnote 4: Since this lecture was delivered, Professor Marsh has\ndiscovered a new genus of equine mammals (_Eohippus_) from the lowest\nEocene deposits of the West, which corresponds very nearly to this\ndescription.--_American Journal of Science,_ November, 1876.]","title":"Lectures on Evolution: Essay #3 from \"Science and Hebrew Tradition\"","tradition":"scripture-revelation","translated_text":null,"word_count":20564}