The Passing of the Phantoms

CHAPTER I. The Reality of Evolution

THE REALITY OF EVOLUTION

The widening of the horizon of biological knowledge within recent years has been remarkable and has cast a flood of light on the question of ‘Man’s Place in Nature.’ At the present day well-informed persons have abandoned the idea of a ‘miraculous’ or special creation of man, yet it is curious to note with what tenacity tradition adheres, and how speculative theories and poetical imaginations to a large extent still prejudice the mind to shut out pure reasoning and rational philosophical thinking. While it has become very general now-a-days to accept the idea of evolution as that method by which man came to inhabit this planet, one still asks do most of us thoroughly grasp the principles of the doctrine which we profess to accept? While many of us do, still it would appear that there are others who vaguely accept the doctrine because it is becoming more fashionable to do so every day. That is to say man, a highly gregarious animal, is carried away to follow the strong leaders of the flock. But to get a clear conception of the wonders of organic descent one must insist that it is not enough to listen only to lectures: we must be students of Nature, endowed with a wholesome amount of scepticism, and not content ourselves with accepting en masse the evidence of others without verifying for ourselves as far as we can the revelations made in the study of the biological sciences.

I introduce these few sentences at the outset because I wish to point out what a very strong attitude of mind in favour of the

reality of human evolution is fostered by those of us who have had the opportunities of making a special study of biology, more particularly when this includes a detailed knowledge of human anatomy and embryology. But it might be asked: Why then do our medical brethren who study anatomy in detail not act more fervently as propagandists of the theme of evolution? As a matter of fact, I have seldom met with a medical student who at the end of his anatomical course has not, at least in an unprejudiced and general way, accepted evolutionary principles; but, even if such fail to occupy a foremost place in his mind, it is not surprising considering the strongly utilitarian view he takes of the study in question. The medical student, and he who teaches the subject of anatomy from this utilitarian standpoint alone, obtain but a limited view of the great principles of human structure. This is brought home to us at once by taking one or two familiar examples. The medical student seldom stops to consider the significance of the presence of the mammary gland in the male. To him its presence is probably a matter of little import. But in the

mind of the anatomist the question at once arises: Why is the organ there at all, if it be useless? And he finds by further examination in an early stage of the intra-uterine development of the individual that the gland is already present when the external sex-organs are indistinguishable, and when it would be impossible to say which sex the individual would ultimately assume. The logical conclusion arrived at, then, is that this gland is only suppressed, in one sex, so that the male has incorporated in its body structural features, more fully developed and functional in the female, a distinction merely of degree but not of kind. Vice versa, an examination of the female generative organs reveals to us the fact that the male homologues have not vanished, but are merely suppressed. This short chain of reasoning from objective biological evidence regarding the presence of structures which can be examined without even resorting to dissection has a most important bearing on the whole question of the evolution of sex from an ancestral hermaphrodite stock. And, indeed, we find on comparing our human embryo in certain very early stages with some lower forms of life which are hermaphrodite, that a marked similarity can be made out. The evolutionary history of the mammary glands is highly interesting, and deserves short notice as shedding light on the reality of evolution. Sir Arthur Keith in his delightful work Human Embryology and Morphology (4th ed., 1921) says that “it is a remarkable fact that although the milk glands do not come into use until adult life, and although they must be regarded as among the later evolved structures of vertebrate animals, yet they are the first of all the glands arising from the epidermis to appear during development of the embryo. In the human embryo of the 6th week, or in the corresponding stage of a pig or of any other mammal, the primary mammary ridge or milk line――a mere surface thickening of the ectoderm――is seen extending along the body wall on either side from axilla to groin. Breslau regards these primary ridges as representatives of the brooding organs of the ancestors of mammals, from which structures he supposed that the mammary glands were evolved. In a large number of human beings (15%) one or more supernumerary nipples are to be found between the axilla and the groin, indicating the wide distribution of ancestral glands. The mammary ridge appears in both sexes alike, but this may not mean that both sexes of ancestral mammals were concerned in brooding or gave milk. The male is the father of girls as well as of boys; it is therefore necessary to provide both father and mother with a complete sexual outfit if each sex is to provide equal shares to the making of their progeny. In females the breasts undergo a great development at puberty while in males they retain their infantile form.” Many other instances could easily be cited of the presence of structures which afford us incontestable evidence of the evolution of the human body from ancestors not necessarily of human form. Suffice it to draw attention to certain muscles which in Herbivores and other Orders are well developed and functional but are only vestigial in man, and to other muscles present in certain groups of lower animals,

which, though long-since disappeared from the later human ancestry, nevertheless occasionally, by the strong strain of heredity, make their appearance again in human beings of the present day. The study of Human Embryology is most convincing, and carries with it incontrovertible proofs of evolution. We find that it is only at the later stages of development within the uterus that the human being is recognizable as such, when it is known as a foetus. In common with other higher animals, man in utero repeats the stages of his ancestral-tree from the very lowest to the highest forms of animal life, due allowance

being made for a blurred and transient picture owing to adaptative modifications which have arisen during countless ages and are purely secondary in character. Nor can it be argued that the process by which development proceeds is simply a mechanical one, built on a uniform plan or design of Nature. For, if it were, to take a simple example out of hundreds, one might ask why, just at the termination of foetal life, the digits of the limb are so specialized in different mammals? All arise alike; but compare the hoof of the horse, the flipper of the seal, the functionless and atrophied thumb of most quadrupeds, and so on, with the hand of man. There is no moulding within the uterus to produce these patterns mechanically. We are led to consider that, while we inherit through our non-human ancestors many features (more or less portrayed in our living non-human cousins), we also have had impressed upon us, demonstrable only at the termination of our embryological career, the features of our immediate predecessors, namely our own parents, and these features hall-mark us as the individual proper to which we belong, that is to say into which we have evolved. Even these few instances which I have cited regarding the study of human structure will, I think, suffice to remind us how intimately bound up become the thoughts of the anatomist with the evolution of his own body. Material for investigation is before him daily, and he cannot――even though he wished it――get away from the fact which may be expressed in Darwin’s words: “Man still bears in his bodily frame the indelible stamp of his lowly origin.” But here no thoughtful anatomist can stop.

With the material for the study of the development of the Brain in front of him, from the extremely simple membranous tubular condition of that organ to the adult form, when the scheme of its complexity seems an almost hopeless task to unravel; with the application of his knowledge of function supplementary to his knowledge of structure, he is carried onward ever more and more to consider as far as he can push his biological data, the physical basis of mental manifestations which go to form the phenomena grouped under habits, out of which the conduct or ethical aspect of the individual, relative to his fellow-creature, springs. As the processes of mental development are very imperfectly

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