id="pgepubid00078"/>science of embryology affords perhaps the strongest of all the strong arguments in favour of evolution. From the nature of the case, however, the evidence under this head requires special training to appreciate; so I will merely observe, in general terms, that the higher animals almost invariably pass through the same embryological stages as the lower ones, up to the time when the higher animal begins to assume its higher characters. Thus, for instance, to take the case of the highest animal, man, his development begins from a speck of living matter similar to that from which the development of a plant begins. And, when his animality becomes established, he exhibits the fundamental anatomical qualities which characterise such lowly animals as the jelly-fish. Next he is marked off as a vertebrate, but it cannot be said whether he is to be a fish, a snake, a bird or a beast. Later on it is evident that he is to be a mammal; but not till still later can it be said to which order of mammals he belongs.

Now this progressive inheritance by higher types of embryological characters common to lower types is a fact which tells greatly in favour of the theory of descent, whilst it seems almost fatal to the theory of design. For instance, to take a specific case, Mr. Lewes remarks of a species of salamander—which differs from most salamanders in being exclusively terrestrial—that although its young ones can never require gills, yet on cutting open a pregnant female we find the young ones to possess gills like aquatic salamanders; and when placed in the water the young ones swim about like the tadpoles of the water newt. Now, to suppose that these utterly useless gills were specially designed is to suppose design without any assignable purpose; for even the far-fetched assumption that a unity of ideal is the cause of organic affinities, becomes positively ridiculous when applied to the case of embryonic structures, which are destined to disappear before the animal is born. Who, for instance, would have the courage to affirm that the Deity had any such motive in providing, not only the unborn young of specially created salamanders, but also the unborn young of specially created man, with the essential anatomical features of gills?

But this remark leads us to consider a little more attentively the anatomical features presented by the human embryo. The gill-slits just mentioned occur on each side of the neck, and to them the arteries run in branching arches, as in a fish. This, in fact, is the stage through which the branchiæ of a fish are developed, and therefore in fish the slits remain open during life, while the so called “visceral arches” throw out filaments which receive the arterial branches coming from the aortic arches, and so become the organs of respiration, or branchiæ. But in all the other vertebrata (i.e. except fish and amphibia) the gill-slits do not develop branchiæ, become closed (with the frequent exception of the first), and so never subserve the function of respiration. Or, as Mr. Darwin states it, “At this period the arteries run in arch-like branches, as if to carry the blood to branchiæ which are not present in the higher vertebrata, though the slits on the sides of the neck still remain, marking their former position.”

The heart is at first a simple pulsating vessel, like the heart of the lowest fishes, and the excreta are voided through a common cloacal passage—an anatomical feature so characteristic of the lower vertebrata, that it occurs in no fully formed member of the mammalian group, with the exception of the bird-like order of monotremata, which takes its name from presenting so striking a peculiarity.

At a later period the human embryo is provided with a very conspicuous tail, which is considerably longer than the rudimentary legs occurring at that period of development, and which Professor Turner has found to be provided with muscles—the extensor, which is so largely developed in many animals, being especially well marked.

Again, as Mr. Darwin says, “In the embryos of all air-breathing vertebrates, certain glands, called the corpora Wolffiana, correspond with and act like the kidneys of mature fishes;” and during the sixth month the whole body is covered very thickly with wool-like hair—even the forehead and ears being closely coated; but it is, as Mr. Darwin observes, “a significant fact that the palms of the hands and the soles of the feet are quite naked, like the inferior surfaces of all four extremities in most of the lower animals,” including monkeys.

Lastly, Professor Wyman has found that in a human embryo about an inch in length, “the great toe was shorter than the others; and, instead of being parallel to them, projected at an angle from the side of the foot, thus corresponding with the permanent condition of this part in the quadrumana.”[1]

Therefore, on the whole, we may conclude these brief remarks on embryology with the words of Professor Huxley:—“Without question, the mode of origin, and the early stages of the development of man, are identical with those of the animals immediately below him in the scale; without a doubt, in these respects he is far nearer to apes than the apes are to the dog.”[2]

VI.

ARGUMENTS DRAWN FROM CERTAIN GENERAL CONSIDERATIONS.

There are two or three arguments of a somewhat weighty character, which do not fall under any of the previous headings, but which we must not on this account neglect.

1. It is justly deemed a substantiation of a scientific theory if it is found to furnish an explanation of other classes of phenomena than those for the explanation of which it was first devised. And this is the case with the theory of natural selection in the region of psychology. The theory was first devised to explain the facts of biology, and proving so successful in that region, Mr. Darwin proceeded to test it in the region of psychology. The result has been to show that large classes of phenomena in this region which were previously unaccountable become fully intelligible. This is especially the case with the phenomena of instinct, and in a lesser degree with those of reason and conscience. For the theory shows that if structures admit of being moulded to their special uses by natural selection, the same must be true of instincts; and it is found an easy matter to understand how, by seizing upon and fixing, through hereditary beneficial variations of habit (whether instinctive or intelligent), natural selection is as competent to fashion the mental structure of an animal as it is to shape its bodily structure into agreement with the external conditions of life. Thus the whole philosophy of animal intelligence is greatly elucidated, and this fact may justly be regarded as lending much additional credence to the theory.

Again, by observing that sympathy and the social instincts generally are developed to a large extent in many of the lower animals, and particularly so in the quadrumana, the theory of natural selection is provided with a reasonable basis for furnishing a scientific explanation of the moral sense in man; and by observing that many of the lower animals are capable of drawing simple inferences, the theory is likewise able to explain the development of reason. So that in the province of human psychology no less than in that of animal, the theory of natural selection, in showing itself competent to explain much which is otherwise inexplicable, is seen to derive a large additional measure of argumentative support.

2. Although the majority of structures and instincts met with in the animal kingdom are in a marvellous degree suited to the performance of their functions and uses, it is nevertheless far from being an invariable rule that the suitability is perfect. Thus, for instance, even in the case of the eye—which is perhaps the most wonderful and most highly elaborated structure in organic nature—it is demonstrable that the organ, considered as an optical instrument, is not ideally perfect; so that, if it were an artificial production, opticians would know how to improve it. And as for instinct, numberless cases might be adduced of imperfection, ranging in all degrees from a slight deficiency to fatal blundering.

Now if all organic structures are supposed to be mechanisms designed by the Deity, and all instincts are supposed to be mental attributes implanted by Him, it becomes unintelligible that in the result the human mind should thus be able to perceive, either an ignorance of natural principles in the Author of nature, or a singular absence of thought in applying His knowledge. But, on the other hand, if all the structures and instincts are supposed to be due to natural selection (whether alone or in conjunction with other natural causes), we have no need to feel staggered at flagrant cases of imperfection; we have only to wonder at the number of cases in which perfection, more or less complete, has been attained.

3. Lastly, there is still another general consideration, and one which appeals to my mind as of immense weight. The question, it will be remembered, lies between beneficent design and natural selection, and I think that the consideration about to be adduced is in itself alone sufficient to decide the question.

This consideration is that amid all the millions of mechanisms and instincts in the animal kingdom, there is no one instance of a mechanism or instinct occurring in one species for the exclusive benefit of another species, although there are a few cases in which a mechanism or instinct that is of benefit to its possessor has come also to be utilised by other species. Now, on the beneficent design theory it is impossible to explain why, when all the mechanisms in the same species are invariably correlated for the benefit of that species, there should never be any such correlation between mechanisms in different species, or why the same remark should apply to instincts. For how magnificent a display of divine beneficence would organic nature have afforded, if all, or even some, species had been so inter-related as to minister to each other's necessities. Organic species might then have been likened to a countless multitude of voices all singing in one harmonious psalm of praise. But, as it is, we see no vestige of such co-ordination; every species is for itself, and for itself alone—an outcome of the always and everywhere fiercely raging struggle for life.

Such, then, is a sketch of the evidence in favour of organic evolution. Of course in such a meagre outline it has not been possible to do justice to that evidence, which should be studied in detail rather than looked at in such a bird's-eye view as I have presented. Nevertheless, enough, I hope, has been said to convince all reasonable persons, that any longer to withhold assent from so vast a body of evidence is a token, not of intellectual prudence, but of intellectual incapacity. With Professor Huxley, therefore, I exclaim,—“Choose your hypothesis; I have chosen mine,” and “I refuse to run the risk of insulting any sane man by supposing that he seriously holds such a notion” as that of special creation. These words, I submit, are not in the least too strong; for if any man can study the many and important lines of evidence all converging on the central truth that evolution has been the law of organic nature, and still fail to perceive the certainty of that truth, then I say that that man—either on account of his prejudices, or from his inability to estimate the value of evidence—must properly be regarded as a weak-minded man. Or, to state the case in another way, if such a man were to say to me,—Notwithstanding all your lines of evidence, I still believe in special design manifested in creation; I should reply,—And in this I fully agree with you; for if, notwithstanding these numerous and important lines of evidence, the theory which they substantiate is false, then to my mind we have the best conceivable evidence of very special design having been manifested in creation—the special design, namely, to deceive mankind by an elaborate, detailed, and systematic fraud. For, if the theory of special creation is true, I hold that as no one fact can be adduced in its favour, whilst so vast a body of facts can be adduced against it, the only possible explanation of so extraordinary a circumstance is that of a mendacious intelligence of superhuman power carefully disposing all the observable facts of his creation in such a way as to compel his rational creatures, by the best and most impartial use of their rational faculties, to conclude that the theory of evolution is as certainly true as the theory of special creation is conspicuously false.

But having now concluded this brief review of the leading arguments in favour of organic evolution, and having expressed as forcibly as I am able my own opinion upon them, I do not wish it to be supposed, either that I am intolerant of opinions which are held by others, or that I have been trying to, “make out a case” by suppressing adverse facts. I am not intolerant, because I believe that dissent from the general doctrine of evolution can only arise either from ignorance of some special departments of science, or from a bias of feeling against the doctrine—to both of which weaknesses evolutionists can afford to be indulgent. And in order to show that I have not been trying unfairly to make out a case, I shall conclude by briefly reviewing the arguments which have been adduced against the doctrine in question.

The only argument of this kind that I know from the side of reason (if we neglect those special objections which have been fully shown by Mr. Darwin himself to be based on inadequate information or erroneous