Popular Science Monthly/Volume 10/January 1877/Professor Huxley's Lectures III

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Popular Science Monthly Volume 10 January 1877  (1877) 
Professor Huxley's Lectures III
 

PROFESSOR HUXLEY'S LECTURES.[1]
III.
THE DEMONSTRATIVE EVIDENCE OF EVOLUTION.

IN my last lecture, I had occasion to place before you evidence derived from fossil remains, which, as I stated, was perfectly consistent with the doctrine of evolution, in fact, was favorable to it, but could not be regarded as the highest kind of evidence, or as that sort of evidence that we call demonstrative.

I pointed out, in fact, that, as we go back in time, the great intervals which at present separate some of the larger divisions of animals become more or less completely obliterated by the appearance of intermediate forms, so that if we take the particular case of reptiles and birds, upon which I dwelt at length, we find in the mesozoic rocks animals which, if ranged in series, would so completely bridge over the interval between the reptile and the bird that it would be very hard to say where the reptile ends and where the bird begins. Evidence so distinctly favorable to evolution as this is far weightier than that upon which men undertake to say that they believe many important propositions; but it is not the highest kind of evidence attainable for this reason, that, as it happens, the intermediate forms to which I have referred do not occur in the exact order in which they ought to occur, if they really had formed steps in the progression from the reptile to the bird; that is to say, we find these forms in contemporaneous deposits, whereas the requirements of the demonstrative evidence of evolution demand that we should find the series of gradations between one group of animals and another in such order as they must have followed if they had constituted a succession of stages, in time, of the development of the form at which they ultimately arrive. In other words, the complete evidence of the evolution of the bird from the reptile—what I call the demonstrative evidence, because it is the highest form of this class of evidence; that evidence should be of this character, that in some ancient formation reptiles alone should be found; in some later formations birds should first be met with; and in the intermediate strata we should discover in regular succession those forms which I pointed out to you which are intermediate between reptiles and birds.

The proof of evolution cannot be complete until we have obtained evidence of this character, and that evidence has of late years been forthcoming in considerable and continually increasing quantity. Indeed, it is somewhat surprising how large is the quantity of that evidence, and how satisfactory is its nature, if we consider that our obtaining such evidence depends upon the occurrence in a particular locality of an undisturbed series deposited through a long period of time, which requires the further condition* that each of these deposits should be such that the animal remains imbedded in them are not much disturbed, and are imbedded in a state of great preservation. Evidence of this kind, as I have said, has of late years been accumulating largely, and in respect to many divisions of the animal kingdom. But I will select for my present purpose only one particular case, which is more adapted to the object I have in view, as it relates to the origin, to what we may call the pedigree, of one of our most familiar domestic animals—the horse. But I may say that in speaking of the origin of the horse I shall use that term in a general sense as equivalent to the technical term Equus, and meaning not what you ordinarily understand as such, but also asses and their modifications, zebras, etc. The horse is in many ways a most remarkable animal, inasmuch as it presents us with an example of one of the most perfect pieces of machinery in the animal kingdom. In fact, among mammals it cannot be said that there is any locomotive so perfectly adapted to its purposes, doing so much work with so small a quantity of fuel, as this animal—the horse. And, as a necessary consequence of any sort of perfection, of mechanical perfection as of others, you find that the horse is a beautiful creature, one of the most beautiful of all land animals. Look at the perfect balance of its form, and the rhythm and perfection of its action. The locomotive apparatus is, as you are aware, resident in its slender fore and hind limbs; they are flexible and elastic levers, capable of being moved by very powerful muscles; and, in order to supply the engines which work these levers with the force which they expend, the horse is provided with a very perfect feeding apparatus, a very perfect digestive apparatus.

Without attempting to take you very far into the region of osteological detail, I must nevertheless for this question depends upon the comparison of such details—trouble you with some points respecting the anatomical structure of the horse, and more especially with those which refer to the structure of its fore and hind limbs. But I shall only touch upon those points which are absolutely essential to the inquiry that we have at present put. Here is the fore-leg of a horse: The bone which is cut across at this point is that which answers to the upper-arm bone in my arm, what you would call the humerus. This bone corresponds with my forearm. What we commonly term the knee of the horse is the wrist; it answers to the wrist in man. This part of the horse's leg answers to one of the human fingers, and the hoof which covers this extended joint answers to one of my nails.

You observe that, to all appearance, there is only one bone in the forearm. Nevertheless, at the upper end I can trace two separate portions; this part of the limb, and the one I am now touching. But as I go farther down it runs at the back part into the general bone, and I cease to be able to trace it beyond a certain point. This large bone is what is termed the radius, and answers to the bone I am touching in my arm, and this other portion of bone corresponds to what is called the ulna. To all appearance in the forearm of the horse the ulna is rudimentary, and seems to be fused into one bone with the radius.

It looks thus as if the ulna, running off below, came to an end and it very often happens in works on the anatomy of the horse that you find these facts are referred to, and a horse is said to have an imperfect ulna. But a careful examination shows you that the lower extremity of the ulna is not wanting in the horse. If you examine a very young horse's limb you will find that this portion of the bone I am now showing you is separable from the rest, and only unites as the animal becomes older, and this is, in point of fact, the lower extremity of the ulna; so that we may say that in the horse the middle part of the ulna becomes rudimentary and unites with the radius, and that the lower extremity of the ulna is so early united with the lower extremity of the radius that every distinct trace of separation has vanished in the adult.

I need not trouble you with the structure of this portion that answers to the wrist, nor with a more full description of the singular peculiarities of the part, because we can do without them for the present, but I will go on to a consideration of the remarkable series of bones which terminates the fore-limb. We have one continuous series in the middle line which terminates in the coffin-bone of the horse upon which the weight of the fore-part of the body is supported. This series answers to a finger of my hand, and there are good reasons—perfectly valid and convincing reasons, which I need not stay to trouble you with—which prove that this answers to the third finger of my hand enormously enlarged.

And it looks at first as if there were only this one finger in the horse's foot. But, if I turn the skeleton round, I find on each side a bone shaped like a splint, broad at the upper and narrow at the lower end, one on each side. And those bones are obviously and plainly and can be readily shown to be the rudiments of the bones which I am now touching in my own hand—the metacarpal bones of the second and of the fourth finger—so that we may say that in the horse's fore-limb the radius and ulna are fused together, that the middle part of the ulna is excessively narrow, and that the foot is reduced to the single middle finger, with rudiments of the two other fingers, one on each side of it. Those facts are represented in the diagram I now show you of the recent horse. Here is the fore-limb (pointing to the diagram), with the metacarpal bones and the little splint-bones, one on each side. It sometimes happens that by way of a monstrosity you may have an existing horse with one or other of these toes that is, provided with its terminal joints.

Let me now point out to you what are the characteristics of the hind-limb. This (pointing to the diagram) is the shin-bone of the horse, and it appears at first to constitute the whole of the leg. But there is a little splint at this point which is the rudiment of the small bone of the leg—what is called the fibula—and then there is connected with the lower end of the tibia a little nodule which represents the lower end of the fibula, in just the same way as that little nodule in the fore-limb represents the lower end of the ulna. So that in the leg we have a modification of the same character as that which exists in the fore-limb—the suppression of the greater part of the small bone of the leg and the union of its lower end with the tibia. So, again, we find the same thing if we turn to the remainder of the leg. This (showing) is the heel of the horse, and here is the great median toe, answering to the third toe in our own foot; and here we have upon each side two little splint-bones, just as in the fore-limb, which represent the rudiments of the second and the fourth toes—rudiments, that is to say, of the metatarsal bones, the remaining bones having altogether vanished. Let me beg your attention to these peculiarities, because I shall have to refer to them by-and-by. The result of this modification is, that the fore and hind limbs are converted into long, solid, springy, elastic levers, which are the great instruments of locomotion of the horse.

As might be expected, and as I have already said, the apparatus for providing this machine with the fuel which it requires is also of a very highly differentiated character. A horse has, or rather may have, forty-four teeth, but it rarely happens that in our existing horses you find more than forty—for a reason which I will communicate directly—and in a mare it commonly happens that you find no more than thirty-six, because the "tushes," or canine teeth, of the mare are rarely developed. Then there are some curious peculiarities about these teeth. As every one who has had to do with horses knows, the cutting teeth—the incisors—are six above and six below, and those incisors present what is called a "mark;" at least, that mark is usually present in horses up to a certain age. It is a sort of dark patch across the middle of the tooth. The presence of that dark patch arises from a great peculiarity in the structure of the horse's incisor tooth. It is in fact considerably curved, with a deep pit in the middle of the crown, and then a long fang. In the young foal this pit is very deep. As the animal feeds, this pit becomes filled up with its fodder, that fodder becomes more or less carbonized, and then you have the dark mark, and the reason the dark mark serves as an indication of age, for, as the horse feeds, this is more and more worn down, until at last, in an aged horse, the tooth is worn beyond the bottom of the pit, and the mark disappears. Then, as I said, the male horse generally has canine teeth. We need not notice their structure particularly. Following that, you may occasionally notice a very small and rudimentary tooth, but it is very often absent. It really represents the first tooth of the grinding series. Then there follow six great teeth, with exceedingly long crowns. The crowns, in fact, are so long that the teeth take a very long time to wear down, whence arises the possibility of the great age to which horses sometimes attain. This is shown in the side diagram. Then the pattern and structure of a horse's tooth are very curious. The crown of the horse's tooth presents a very complicated pattern; that is to say, supposing this to be one of the grinders of the left side (illustrating) above, there is a kind of wall like a double crescent. Then there are two other crescents, which fall in that direction, and these are complicated by folds, and all the spaces between these crescentic ridges are filled up by a kind of bony matter which is called cement. Consequently the surface of the tooth is composed of very uneven materials—of the hard mass of the tooth, which is called dentine, then a very much harder enamel, and a softer cement between, the practical effect of which is the same as the lamination of the millstone. In consequence of the lamination of the millstone the ridges wear less swiftly than the intermediate substance, and therefore the surface always keeps rough and exerts a crushing effect upon the grain. The same is true of the horse's tooth, and consequently the grinding of the teeth one against the other, instead of flattening the surface of the teeth, tends to keep them always irregular, and that has a very great influence upon the rapid mastication of the hard grain or the hay upon which the horse subsists.

I think that will suffice as a brief indication of some of the most important peculiarities and characteristics of the horse. If the hypothesis of evolution is true, what ought to happen when we investigate the history of this animal? We know that the mammalian type, as a whole—that mammalian animals—are characterized by the possession of a perfectly distinct radius and ulna, two separate and distinct movable bones. We know, further, that mammals in general possess five toes, often unequal, but still as completely developed as the five digits of my hand. We know further that the general type of mammal possesses in the leg, not only a complete tibia, but a complete fibula—a complete, distinct, separable bone. Moreover, in the hind-foot we find, in animals in general, five distinct toes, just as we do in the fore-foot. Hence it follows a differentiated animal like the horse must have proceeded by way of evolution or gradual modification from a form possessing all the characteristics we find in mammals in general. If that be true, it follows that if there be anywhere preserved in the series of rocks a complete history of the horse, that is to say of the various stages through which he has passed, those stages ought gradually to lead us back to some sort of animal which possessed a radius, and an ulna, and distinct complete tibia and fibula, and in which there were five toes upon the fore-limb, no less than upon the hind-limb. Moreover, in the average general mammalian type, the higher mammalian, we find, as a constant rule, an approximation to the number of forty-four complete teeth, of which twelve are cutting teeth, four are canine, and the others are grinders. In unmodified mammals we find the incisors have no pit, and that the grinding teeth, as a rule, increase in size from that which lies in front toward those which lie in the middle or at the hinder part of the series. Consequently, if the theory of evolution be correct, if that hypothesis of the origin of living things have a foundation, we ought to find in the series the forms which have preceded the horse, animals in which the mark upon the incisor gradually more and more disappears, animals in which the canine teeth are present in both sexes, and animals in which the teeth gradually lose the complications of their crowns and have a simpler and shorter crown, while at the same time they gradually increase in size from the anterior end of the series toward the posterior. Let us turn to the facts and see how they bear upon the requirements of this doctrine of evolution.

In what is called here the Pliocene formation, that which constitutes almost the uppermost division of the tertiary series, we find the remains of horses. We also find in Europe abundant remains of horses in the most superficial of all these formations—that is, the post-tertiary, which immediately lies above the Pliocene. But these horses, which are abundant in the cave-deposits and in the gravels of England and Europe—these horses, of which we know the anatomical structure to perfection—are in all essential respects like existing horses. And that is true of all the horses of the latter part of the Pliocene epoch. But in the earlier Pliocene and later Miocene epoch, in deposits which belong to that age, and which occur in Germany and in Greece, in India, in Britain, and in France, we find animals which are like horses in all the essential particulars which I have just described, and the general character of which is so entirely like that of the horse that you may follow descriptions given in works upon the anatomy of the horse upon the skeletons of these animals. But they differ in some important particulars. There is a difference in the structure of the fore and hind limb, and that difference consists in this, that the bones which are here represented by two splints, imperfect below, are as long as the middle metacarpal bone, and that attached to the extremity of each is a small toe with its three joints of the same general character as the middle toe, only very much smaller, and so disposed that they could have had but very little functional importance, and that they must have been rather of the nature of the dew-claws such as are to be found in many ruminant animals. This Hipparion, or European three-toed horse, in fact presents a foot similar to that which you see here represented, except that in the European. Hipparion these smaller fingers are farther back, and these lateral toes are of smaller proportional size.

But nevertheless we have here a horse in which the lateral toes, almost abortive in the existing horse, are fully developed. On careful investigation you find in these animals that also in the forelimb the ulna is very thin, yet is traceable down to the extremity. In the hind-limb you find that the fibula is pretty much as in the existing horse. That is the kind of equine animal which you meet with in these older Pliocene and later Miocene formations, in which the modern horse is no longer met with. So you see that the Hipparion is the form that immediately preceded the horse. Now let us go a step farther back to the middle and older parts of which are called the Miocene formation. There you find in some parts of Europe the equine animals which differ essentially from the modern horse, though they resemble the horse in the broad features of their organization. They differ in the characters of their fore and hind limbs, and present important features of difference in the teeth. The forms to which I now refer are what constitute the genus Anchitherium. We have three complete toes; the middle toe is smaller in proportion, the inner and outer toes are larger, and in fact large enough to rest upon the ground, and to have functional importance—not an animal with two dew-claws, but an animal with three functional toes. And in the forearm you find the ulna a very distinct bone, quite readily distinguishable in its whole length from the radius, but still pretty closely united with it. In the hind-limb you also meet with three functional toes. The structure of the hind-foot corresponds with that of the fore-foot; but in the hind-leg the fibula is better developed. In some cases I have reason to think that it is complete; at any rate this lower end of it is quite distinctly recognizable. But the most curious change is that which is to be found in the character of the teeth. The teeth of the Anchitherium have, in the first place, so far as the incisors are concerned, a rudimentary pit. The canine teeth are present in both sexes. The molars are short; there is no cement, and the pattern is somewhat like this (drawing on the blackboard). In the upper jaw, there are two crescents and two oblique ridges, while in the lower jaw you have the double crescent. It is quite obvious that this (illustrating from drawing) is a simpler form than that. By increasing the complexity of those teeth there, we have the horse's teeth. These are all the forms with which we are acquainted respecting the past history of the horse in Europe. When I happened to occupy myself with this subject some years ago, notwithstanding certain difficulties, the facts left no doubt whatever in my mind that we had here a general record of the history of the evolution of the horse. You must understand that every one of these forms has undoubtedly become modified into various species, and we cannot be absolutely certain that we have found those species which constitute the exact line of mollification, but it was perfectly obvious that we had here in succession, in time, three forms of the horse-type, of which the oldest came nearest to the general mammal. We saw that the forms which had existed afterward had undergone a reduction of the number of their toes, a reduction of the fibula, a more complete coalescence of the ulna with the radius. The pattern of the molar teeth had become more complicated and the interspaces of their ridges had become filled with cement. In this succession of forms you have exactly that which the hypothesis of evolution demands. The history corresponds exactly with that which you would construct a priori from the principles of evolution. An alternative hypothesis is hardly conceivable, but the only one that could be framed would be this, that the Anchitherium, the Hipparion, and the horse, had been created separately and at separate epochs of time. For that hypothesis there could be no scientific evidence, and it is not pretended that there is the slightest evidence of any other kind that such successive creation has ever taken place. When I was investigating this subject only the collections in Europe were accessible to me, but the materials they yielded led me to think that the horse must have descended from an Anchitherium-like ancestor, and I may say, as I happen to know by correspondence with him, that very eminent anatomist, the late Prof, Lartet, of Paris, had arrived independently at the same conclusion. Indeed, the story is so plain that no one deserves any particular credit for drawing so obvious a conclusion. And since then paleontological inquiry has not only given us greater and greater knowledge of the series of horse-like forms, but enabled us to fill up the gaps in the series, and to extend that series farther back in time.

That knowledge has recently come to us, and assuredly from a most unexpected quarter. You are all aware that when this country was first discovered by Europeans there were no traces of the existence of the horse in any part of the American Continent. And, as is well known, the accounts of the earlier discoveries dwell upon the astonishment of the natives when they first became acquainted with that astounding phenomenon—a man seated upon a horse. Nevertheless, as soon as geology began to be pursued in this country, it was found that remains of horses—horses like our European horses—like the horses which exist at the present day—are to be found in abundance in the most superficial deposits in this country, just as they are in Europe. For some reason or other—no feasible suggestion on that subject, so far as I know, has been made but for some reason or other the horse must have died out on this continent at some period preceding—how long we cannot say—the discovery of America by the Europeans. Of late years there have been discovered on this continent—in your Western Territories—that marvelous thickness of tertiary deposits to which I referred the other evening, which gives us a thickness and a consecutive order of older tertiary rocks admirably calculated for the preservation of organic remains, such as we had hitherto no conception of in Europe. They have yielded fossils in a state of preservation and in number perfectly unexampled. And with respect to the horse, the researches of Leidy and others have shown that numerous forms of that type are to be found among these remains. But it is only recently that the very admirably contrived and most thoroughly and patiently worked-out investigations of Prof. Marsh have given us a just idea of the enormous wealth and scientific importance of these deposits. I have had the advantage of glancing over his collections at New Haven, and I can truly and emphatically say that, so far as my knowledge extends, there is nothing in any way comparable, for extent, or for the care with which the remains have been got together, or for their scientific importance, to the series of fossils which he has brought together. (Applause.) This enormous collection has yielded evidence of the most striking character in regard to this question of the. pedigree of the horse. Indeed, the evidence which Prof. Marsh has collected tends to show that you have in America the true original seat of the equine type—the country in which the evidence of the primitive form and successive modifications of the horse series is far better preserved than in Europe; and Prof. Marsh's kindness has enabled me to put before you the following diagram, every figure in which is an actual representation of the specimen which is preserved in New Haven at this present time. The succession of forms which he has brought together shows, in the first place, the great care and patience to which I have referred. Secondly, there is this Pliocene form of the horse (Pliohippus); the conformation of its limbs presents some very slight deviations from the ordinary horse, and with shorter crown of the grinding teeth. Then comes the form which represents the European Hipparion, which is the Protohippus, having three toes and the forearm and leg and teeth to which I have referred, and which is more valuable than the European Hipparion for this reason: it is devoid of some of the peculiarities of that form—peculiarities which tend to show that the European Hipparion is rather a side branch than one in the direct line of succession. Next comes the Miohippus, which corresponds pretty nearly with what I spoke of as the Anchitherium of Europe, but which has some interesting peculiarities. It presents three toes—one large median and two lateral ones; of the toe which answers to the little finger of the human hand, there is only a rudiment. This is, however, as far as European deposits have been enabled to carry us with any degree of certainty in the history of the horse. In the American tertiaries, on the contrary, the series of equine forms is continued down to the bottom of the Eocene. The older Miocene form, termed Mesohippus, has three toes in front and a large splint-like rudiment representing the little finger, and three toes behind. The radius and ulna are entire, and the tibia and fibula distinct, and the teeth are anchitheroid with short crowns.

But the most important discovery of all is the Orohippus—which comes from the lower part of the Eocene formation, and is the oldest member of the equine series known. Here we have four complete toes on the front-limb, three toes on the hind-limb, a well-developed ulna, a well-developed fibula, and the teeth of simple pattern. So you are able, thanks to these great researches, to show that, so far as present knowledge extends, the history of the horse-type is exactly and precisely that which could have been predicted from a knowledge of the principles of evolution. And the knowledge we now possess justifies us completely in the anticipation that when the still lower Eocene' deposits and those which belong to the Cretaceous epoch have yielded up their remains of equine animals, we shall find first an equine creature with four complete toes and a rudiment of the innermost toe in front, and probably a rudiment of the fifth toe in the

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hind-foot.[2] In still older forms the series of the digits will be more and more complete, until we come to the five-toed animals, in which most assuredly the whole series took its origin.

That is what I mean, ladies and gentlemen, by demonstrative evidence of evolution. An inductive hypothesis is said to be demonstrated when the facts are shown to be in entire accordance with it. If that is not scientific proof, there are no inductive conclusions which can be said to be scientific. And the doctrine of evolution at the present time rests upon exactly as secure a foundation as the Copernican theory of the motions of the heavenly bodies. Its basis is precisely of the same character—the coincidence of the observed facts with theoretical requirements. As I mentioned just now, the only way of escape, if it be a way of escape, from the conclusions which I have just indicated, is the supposition that all these different forms have been created separately at separate epochs of time, and I repeat that of such an hypothesis as this there neither is nor can be any scientific evidence, and assuredly, so far as I know, there is none which is supported, or pretends to be supported, by evidence or authority of any other kind. I can but think that the time will come when such suggestions as these, such obvious attempts to escape the force of demonstration, will be put upon the same footing as the supposition made by some writers, who are, I believe, not completely extinct at present, that fossils are not real existences, are no indications of the existence of the animals to which they seem to belong; but that they are either sports of Nature or special creations, intended—as I heard suggested the other day—to test our faith. In fact, the whole evidence is in favor of evolution, and there is none against it. And I say this, although perfectly well aware of the seeming difficulties which have been adduced from what appeal's to the uninformed to be a scientific foundation. I meet constantly with the argument that this doctrine of evolution cannot be correct, because it requires the Lapse of a very vast period of time, and that the duration of life upon the earth thus implied is inconsistent with the conclusions arrived at by the astronomer and the physicist. I may venture to say that I am familiar with those conclusions, inasmuch as some years ago, when President of the Geological Society of London, I took the liberty of criticising them, and of showing in what respects, as it appeared to me, they lacked complete and thorough demonstration. But, putting that point aside altogether, suppose that, as the astronomers, or some of them, and some physical philosophers, tell us, it is impossible that life could have endured upon the earth for as long a period as is required by the doctrine of evolution—supposing that to be proved, what I want to know is, what is the foundation for the statement that evolution does require so great a time? The biologist knows nothing whatever of the amount of time which may be required for the process of evolution. It is a matter of fact that those forms which I have described to you occur in the order which I have described in the tertiary formation. But I have not the slightest means of guessing whether it took a million of years, or ten millions, or a hundred millions, or a thousand millions of years, to give rise to that series of changes. As a matter of fact, the biologist has no means of arriving at any conclusion as to the amount of time which may be needed for a certain quantity of organic change. He takes his facts as to time from the geologist. The geologist, taking into consideration the rate at which deposits are formed and the rate at which denudation goes on upon the surface of the earth, arrives at certain more or less justifiable conclusions as to the time which is required for the deposit of a certain amount of rocks, and if he tells me that the tertiary formations required 500,000,000 years for their deposit, I suppose he has good ground for what he says, and I take that as the measure of the duration of the evolution of the horse from the Orohippus up to its present condition. And, if he is right, undoubtedly evolution is a very slow process, and requires a great deal of time. But suppose, now, that an astronomer or a physicist—for instance, my friend Sir William Thomson—comes to me and tells me that my geological friend is quite wrong, and that he has capital evidence to show that life could not possibly have existed upon the surface of the earth 500,000,000 of years ago, because the earth would have been too hot to allow of life, my reply is: "That is not my affair; settle that with the geologist, and when you have come to an agreement between yourselves I will adopt your conclusion." We take our time from the geologist, and it is monstrous that, having taken our time from the physical philosopher's clock, the physical philosopher should turn round upon us, and say we are going too fast. What we desire to prove is, is it a fact that evolution took place? As to the amount of time it took, we are in the hands of the physicist and the astronomer, whose business it is to deal with those questions.

I think, ladies and gentlemen, that I have now arrived at the conclusion of the task which I set before myself when I undertook to deliver these lectures before you. My purpose has been, not to enable those of you who have not paid attention to these subjects before to leave this room in a condition to decide upon the validity or the invalidity of the hypothesis of evolution, but to put before you the principles by which all such hypotheses must be judged; and, furthermore, to make apparent to you the nature of the evidence and the sort of cogency which is to be expected and may be obtained from it. To this end I have not hesitated to regard you as genuine students and persons desirous of knowing the truth. I have not hesitated to take you through arguments, even long chains of arguments, that I fear may have sometimes tried your patience, or to have inflicted upon you details which could not possibly he escaped, but which may well have been wearisome. But I shall rejoice—I shall consider I have done you the greatest service which it was in my power in such a way to do—if I have thus convinced you that this great question which we are discussing is not one to be dealt with by rhetorical flourishes or by loose and superficial talk, but that it requires the keenest attention of the trained intellect and the patience of the most accurate observer. When I commenced this series of lectures, I did not think it necessary to preface them with a prologue, such as might be expected from a stranger and a foreigner; for, during my brief stay in your country, I have found it very hard to believe that a stranger could be possessed of so many friends, and almost harder to imagine that a foreigner could express himself in your language in such a way as, to all appearances, to be so readily intelligible; for, so far as I can judge, that most intelligent, and, perhaps, I may add most singularly active and enterprising body, your press reporters, do not seem to have been deterred by my accent from giving the fullest account of everything that I happen to have said. But the vessel in which I take my departure to-morrow morning is even now ready to slip her moorings; I awake from my delusion that I am other than a stranger and a foreigner. I am ready to go back to my place and country, but, before doing so, let me, by way of epilogue, tender to you my most hearty thanks for the kind and cordial reception which you have accorded to me; and let me thank you still more for that which is the greatest compliment which can be afforded to any person in my position—the continuous and undisturbed attention which you have bestowed upon the long argument which I have had the honor to lay before you.

 
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  1. The last of three lectures on "The Direct Evidence of Evolution," delivered at Chickering Hall, New York, September 20th. From the report of the New York Tribune, carefully revised by Prof. Huxley.
  2. Since this lecture was delivered, Prof. Marsh has discovered in the lowest Eocene deposits of the West a new genus of equine mammals (Eohippus), which corresponds very nearly to this description.—American Journal of Science, November, 1876.