The Doctrine of Evolution: Its Basis and Its Scope

by Henry Edward Crampton

We must not underestimate the many difficulties to be encountered, for the field before us is a vast territory of complex human life and of manifold human relations. Without prolonged exercise in scientific methods, it is impossible to view our own kind impersonally, as we do the creatures of lower nature. Furthermore it seems to many that an analysis of human life and biological history, even if it is possible, must alter or degrade mankind in some degree; this is no more true than that a knowledge of the principles of engineering according to which the Brooklyn Bridge has been constructed renders that structure any different or unsafe for travel. Man remains man, whether we are in utter ignorance of his mode of origin, or whether we know all about his ancestry and about the factors that have made him human. It is because our species appears to occupy a superior and isolated position above the rest of nature that the mind seems reluctant to follow the guidance of science when it conducts its investigations into the history of seemingly privileged human nature. And it is feared also, that if evolution is proven for man as well as for all other kinds of animals, our cherished ideas and our outlook upon many departments of human life must be profoundly affected. This may be so, but science endeavors only to find out the truth; it cannot alter truth, nor does it seek to do so. We might well wish that the world were different in many respects and that we were free from the control of many natural laws besides that of evolution, but if the real is what it is, then our duty is plain before us; as we think more widely and deeply on the basis of ripened experience, it becomes ever clearer that a knowledge of human history gives the only sure guidance for human life.

To the zoölogist it seems strange that so many are opposed to a scientific inquiry into the facts of human evolution, and to the conclusions established by such an inquiry,—though, to be sure, this opposition is directly proportional to ignorance or misunderstanding of the nature and purpose of scientific investigation and of human evolution. The naturalist comes to view our species as a kind of animal, and as a single one of the hundreds of thousands of known forms of life; thus the question of human origin is but a small part of organic evolution, which is itself only an episode in the great sweep of cosmic evolution, endless in past time and in the future. Were we some other order of beings, and not men, human evolution would appear to us in its proper scientific proportions, namely, as a minute fraction of the whole progress of the world.

While the foregoing statements are true, it is nevertheless right that a close study should be made of the particular case of mankind. No doubt much of the naturalist's interest in nature at large is due to his conviction that the laws revealed by the organisms of a lower sphere must hold true for man, and may explain many things that cannot be so clearly discerned when only the highest type is the subject of investigation. It is only too evident that little more than a general outline can be given of the wide subject or group of subjects included under the head of human evolution. We must divide the subject logically into parts, so that each one may be taken up without being complicated by questions relating to topics of another category, although the findings in any one department must surely be of importance for comparison with the results established in another section; for if evolution is universally true, the main conclusion in any case must assist the investigation of another, just as comparative anatomy and embryology supplement and corroborate each other in the larger survey of organic evolution. As before, the illustrations of each department of the subject must be selected from the stock of everyday observation and information that we already possess, for we gain much when we realize that evolution includes all the happenings of everyday life and thought, as well as the occurrences of the remote past.

For the present, then, the questions relating to the higher aspects of human life must be put aside, only that they may be taken up at the last. Social evolution likewise finds its place in a later section, after the phenomena of mind and mental evolution receive due attention and description. At the present juncture, the human species presents itself as a subject for organic analysis and classification, merely as a physical organism. Just as the study of locomotives must begin with the detailed structure of machines in the workshop before they can be profitably understood as working mechanisms, so the physical evolution of mankind must first be made intelligible before it is possible to prosecute successfully the studies dealing with the psychology, social relations, and higher conceptions that seem at first to be the exclusive properties of our species.

The problems of physical evolution of man and of men fall into two groups. Those of the first deal with the origin of the human species as a unit, and its comparative relation to lower organisms, while those of the second part are concerned with the further evolution of human races that have come to be different in certain details of structure since the human type as such arose. In the first part, all men will be assumed to be alike and the members of a homogeneous species whose fundamental attributes are to be compared with those of other animals; only afterwards will attention be directed to the differences, previously ignored, that divide human beings into well-marked varieties. It must be evident even at this point that the mode of evolution demonstrated by the first investigation will be likely to bear some close relation to the methods by which human races have evolved to their present diverse anatomical situations.

* * * * *

The foregoing classification of the problems concerned with the nature and origin of the human species renders it possible to restrict the immediate inquiry to a definite and precise question. It is this: does the evidence relating to the physical characteristics of our species prove that man is the product of a supernatural act of creation, or does it show that man's place in nature has been reached by a gradual process of natural evolution? In order to obtain an equally precise and definite answer to this question, referring to the particular case of most concern to us, it is obvious that the method to be employed is the one which has given us an understanding of organic evolution as an all-inclusive natural process. The data must be verified, related, and classified, so that their meaning may be concisely stated in the form of scientific principles. What are the facts of human structure, comparatively treated? How does the human body develop? Does palæontology throw any light on the antiquity of man? Do the rules of nature's order control the lives of men? Our course is now clear; we shall take up serially the anatomy, embryology, and fossil history of the human species, in order to see that there is ample proof of the actual occurrence of evolution, and then, as before, we may look about for the causes which have produced this result by natural methods.

While it is necessary to treat the subject directly, namely, by examining the actual evidences relating to the particular case in question, it is worthwhile before doing so to point out that, as the whole includes a part, human evolution has already been proved beyond question. This conclusion must be accepted, unless reasons can be given for excluding mankind from the rest of the living world as an absolutely unique type, supreme and isolated because of some peculiar endowments not shared with the rest of animate nature. If these reasons are lacking, and the unity of organic nature be recognized, human evolution cannot be denied unless some interpretation more reasonable and logical than evolution can be given for the whole mass of facts exemplified and discussed in the foregoing chapters. We may accordingly approach the main questions by asking if there are any reasons for regarding the human species as a unique and isolated type of organism.

At the outset, we must recognize that in so far as the human body is material, its movements and mass relations are controlled by physical principles, like all other masses of matter. It is well, indeed, that this is so, for if gravitation and the laws of inertia were not consistent and reliable principles holding true at all times and not intermittently, it would be difficult to order our lives with confidence. In the next place, the general principles of biology hold true for the structure and physiology of the human species as they do for all other living things. A human body is composed of eight systems of organs, whose functions are identical with the eight vital tasks of every other animal. All these organs are made up of cells as ultimate vital units, and the materials of which human cells are composed belong to the class of substances called protoplasm. Human protoplasm, like all other living materials, must replenish itself, and respire and oxidize in obedience to biological laws that have been found to be uniform everywhere. Thus the human organism is no more unique in fundamental organic respects than it is apart from the world of physical processes and laws.

How does the matter stand when the general structural plan of a human being is examined? Is it entirely different from everything else? It is a fact of common knowledge that the human body is supported by a bony axis, the vertebral column, to which the skull is articulated and to which also the skeletal framework of the limbs is attached. These characteristics place man inevitably among the so-called vertebrata; he is certainly not an invertebrate, nor is the basic structure of his body such that a third group, outside the invertebrata and vertebrata, can be made to include only the single type—man.