The remarkable fact here is that with all these gradations and similarities leaping to Aristotle’s eyes, he does not come to the theory of evolution. He rejects Empedocles’ doctrine that all organs and organisms are a survival of the fittest,23 and Anaxagoras’ idea that man became intelligent by using his hands for manipulation rather than for movement; Aristotle thinks, on the contrary, that man so used his hands because he had become intelligent.24 Indeed, Aristotle makes as many mistakes as possible for a man who is founding the science of biology. He thinks, for example, that the male element in reproduction merely stimulates and quickens; it does not occur to him (what we now know from experiments in parthenogenesis) that the essential function of the sperm is not so much to fertilize the ovum as to provide the embryo with the heritable qualities of the male parent, and so permit the offspring to be a vigorous variant, a new admixture of two ancestral lines. As human dissection was not practised in his time, he is particularly fertile in physiological errors: he knows nothing of muscles, not even of their existence; he does not distinguish arteries from veins; he thinks the brain is an organ for cooling the blood; he believes, forgivably, that man has more sutures in the skull than woman; he believes, less forgivably, that man has only eight ribs on each side; he believes, incredibly, and unforgivably, that woman has fewer teeth than man.25 Apparently his relations with women were of the most amicable kind.
Yet he makes a greater total advance in biology than any Greek before or after him. He perceives that birds and reptiles are near allied in structure; that the monkey is in form intermediate between quadrupeds and man; and once he boldly declares that man belongs in one group of animals with the viviparous quadrupeds (our “mammals”).26 He remarks that the soul in infancy is scarcely distinguishable from the soul of animals.27 He makes the illuminating observation that diet often determines the mode of life; “for of beasts some are gregarious, and others solitary—they live in the way which is best adapted to . . . obtain the food of their choice.”28 He anticipates Von Baer’s famous law that characters common to the genus (like eyes and ears) appear in the developing organism before characters peculiar to its species (like the “formula” of the teeth), or to its individual self (like the final color of the eyes),29 and he reaches out across two thousand years to anticipate Spencer’s generalization that individuation varies inversely as genesis—that is, that the more highly developed and specialized a species or an individual happens to be, the smaller will be the number of its offspring.30 He notices and explains reversion to type—the tendency of a prominent variation (like genius) to be diluted in mating and lost in successive generations. He makes many zoological observations which, temporarily rejected by later biologists, have been confirmed by modern research—of fishes that make nests, for example, and sharks that boast of a placenta.
And finally he establishes the science of embryology. “He who sees things grow from their beginning,” he writes, “will have the finest view of them.” Hippocrates (b. 460 B.C.), greatest of Greek physicians, had given a fine example of the experimental method, by breaking a hen’s eggs at various stages of incubation; and had applied the results of these studies in his treatise “On the Origin of the Child.” Aristotle followed this lead and performed experiments that enabled him to give a description of the development of the chick which even today arouses the admiration of embryologists.31 He must have performed some novel experiments in genetics, for he disapproves the theory that the sex of the child depends on what testis supplies the reproductive fluid, by quoting a case where the right testis of the father had been tied and yet the children had been of different sexes.32 He raises some very modern problems of heredity. A woman of Elis had married a Negro; her children were all whites, but in the next generation Negroes reappeared; where, asks Aristotle, was the blackness hidden in the middle generation?33 There was but a step from such a vital and intelligent query to the epochal experiments of Gregor Mendel (1822–1882). Prudens quæstio dimidium scientiæ—to know what to ask is already to know half. Surely, despite the errors that mar these biological works, they form the greatest monument ever raised to the science by any one man. When we consider that before Aristotle there had been, so far as we know, no biology beyond scattered observations, we perceive that this achievement alone might have sufficed for one lifetime, and would have given immortality. But Aristotle had only begun.
V. Metaphysics and the Nature of God
His metaphysics grew out of his biology. Everything in the world is moved by an inner urge to become something greater than it is. Everything is both the form or reality which has grown out of something which was its matter or raw material; and it may in its turn be the matter out of which still higher forms will grow. So the man is the form of which the child was the matter; the child is the form and its embryo the matter; the embryo the form, the ovum the matter; and so back till we reach in a vague way the conception of matter without form at all. But such a formless matter would be no-thing, for every thing has a form. Matter, in its widest sense, is the possibility of form; form is the actuality, the finished reality, of matter. Matter obstructs, form constructs. Form is not merely the shape but the shaping force, an inner necessity and impulse which moulds mere material to a specific figure and purpose; it is the realization of a potential capacity of matter; it is the sum of the powers residing in anything to do, to be, or to become. Nature is the conquest of matter by form, the constant progression and victory of life.34
Everything in the world moves naturally to a specific fulfilment. Of the varied causes which determine an event, the final cause, which determines the purpose, is the most decisive and important. The mistakes and futilities of nature are due to the inertia of matter resisting the forming force of purpose—hence the abortions and monsters that mar the panorama of life. Development is not haphazard or accidental (else how could we explain the almost universal appearance and transmission of useful organs?); everything is guided in a certain direction from within, by its nature and structure and entelechy;35 the egg of the hen is internally designed or destined to become not a duck but a chick; the acorn becomes not a willow but an oak. This does not mean for Aristotle that there is an external providence designing earthly structures and events; rather the design is internal, and arises from the type and function of the thing. “Divine Providence coincides completely for Aristotle with the operation of natural causes.”36
Yet there is a God, though not perhaps the simple and human god conceived by the forgivable anthropomorphism of the adolescent mind. Aristotle approaches the problem from the old puzzle about motion—how, he asks, does motion begin? He will not accept the possibility that motion is as beginningless as he conceives matter to be: matter may be eternal, because it is merely the everlasting possibility of future forms; but when and how did that vast process of motion and formation begin which at last filled the wide universe with an infinity of shapes? Surely motion has a source, says Aristotle; and if we are not to plunge drearily into an infinite regress, putting back our problem step by step endlessly, we must posit a prime mover unmoved (primum mobile immotum), a being incorporeal, indivisible, spaceless, sexless, passionless, changeless, perfect and eternal. God does not create, but he moves, the world; and he moves it not as a mechanical force but as the total motive of all operations in the world; “God moves the world as the beloved object moves the lover.”37 He is the final cause of nature, the drive and purpose of things, the form of the world; the principle of its life, the sum of its vital processes and powers, the inherent goal of its growth, the energizing entelechy of the whole. He is pure energy;38 the Scholastic Actus Purus—activity per se; perhaps the mystic “Force” of modern physics and philosophy. He is not so much a person as a magnetic power.39.