In Biblical language, the question of the hour in biology is, Who (or what) made thee to differ? "It is the question," in the words of C. H. Eigenmann, "of how the straight line of exact hereditary repetition may be caused to swerve in a definite direction to reach an adaptive point. This is the question of the present generation, perhaps of the entire twentieth century."[56]
The Newton of biology, who will discover the laws of variation and heredity, has not, it is safe to say, yet appeared. Variation in a definite direction in virtue of an internal tendency in the organism (Nägeli); variation in response to the specific stimulus of the environment (Eimer); variation due, at least in animals, to the conscious effort of the individual (Lamarck); variation inciting a corresponding strengthening of parts of the individual organism, until time should be given for hereditary strengthening of these parts (organic selection as taught by Baldwin, Osborn and Lloyd Morgan); variation due to the preservation and accumulation of minute fluctuations by natural selection (Darwinism in its usual form); variation from unknown causes suddenly and discontinuously (the mutationism of de Vries); variation due to a mystical vital impulse in organic life as a whole (the creative evolution of Bergson):—no one of these views, if we take scientific opinion as a whole, can be said to have torn aside the veil behind which nature carries on her creative works.
The most notable attempt to supplement and strengthen the theory of natural selection has been made by Weismann in his theory of Germinal Selection. In Weismann's hypothesis, which has furnished in a sense the philosophical basis for the popular Eugenics movement, the struggle for existence is transferred to a struggle among the constituents of the germ-plasm. The minute invisible "determinants" of the germ-plasm, which give rise to the variations in the organ, or cell, which they determine, are unequally nourished by the nutritive stream. A determinant at first favoured by chance may at length gain strength actively to nourish itself to the detriment of its fellow-determinants, and thus attain a permanent upward movement. With Weismann the fluctuations within the germ-plasm "are the real root of all hereditary variations, and the preliminary condition for the occurrence of the Darwin-Wallace factor of selection." The struggle for existence, or the struggle for possession of the mate in sexual selection, practically goes back to "the struggle between the determinants within the germ-plasm"[57] for food and space.
Let us see how this theory of determinants will apply to the famous case of the antlers of the elk or stag. The antlers would increase in size, in this case, only because the determinants, corresponding in the germ-plasm to the antlers in the adult organism, attracted nourishment to themselves, and withdrew it to a certain extent from their fellows. Instead, therefore, of a corresponding strengthening in the whole anterior half of the animal, which Weismann admits would be necessary,[58] we should have, with the increased weight of the antlers, a decrease in weight and strength of other parts of the body. The problem, instead of being solved, seems to be involved in deeper mystery, and there will be hesitation in accepting the statement that "thus in our time the great riddle has been solved—the riddle of the origin of what is suited to its purpose without the coöperation of purposive forces."[59] T. H. Morgan thinks it unfortunate that Weismann should seek to supply the deficiencies of Darwin's theory by new speculative matter skilfully removed from the field of verification.[60]
Biologists are generally agreed in holding the doctrine of "descent with modifications," but there is no agreement as to the method by which variations in species are brought about. Bateson even declares that "evolutionary orthodoxy developed too fast," and that "the time is not ripe for the discussion of the origin of species."[61] S. Herbert concludes: "In short, while natural selection can be looked upon as the efficient cause of the progress of evolutionary lines, their first beginnings must still be attributed to a still 'unknown factor in evolution.'"[62]
The neo-Darwinian who sees in the accumulation of minute chance variations a sufficient explanation of the origin of species, cannot be said to hold the field in such a way as to call for the unquestioning acceptance of his views by the lay public; far less need the more remote philosophical inferences sometimes drawn from his premises be accepted without challenge as the teaching of science. While the central mystery, in the opinion of leading biologists, remains unsolved in the biological field, evolution or natural selection should be used with caution as the solvent of all the problems of the universe. The masterkey should first unlock the doors nearer home.
II. The Meaning of Evolution
The more philosophical discussion of the Meaning of Evolution includes in its scope the questions of mechanism and design and of preformation and epigenesis.
1. Is the doctrine of evolution a foe to design, or does evolution make more teleology than it destroys? Let us assume for the present the neo-Darwinian position, and ask whether design can be excluded, first from the organic world without man, and then from the organic world including man. The whole system of things so ordered that through the operation of the laws of variability, struggle for existence, inheritance, elimination and selection, there should be worked out the myriad forms of life in ever increasing complexity, calls more loudly for the postulate of intelligence than do the special contrivances and adaptations in nature when viewed from the standpoint of their separate origin. If Paley's watch calls for a watchmaker, a system or arrangement of nature which has been likened, not to a simple watch, but rather to a watch (or a sundial) which makes all other watches, and these watches of a constantly improved quality and increased complexity, cannot permanently be regarded in any other than a teleological light. If the whole process should prove to be mechanical, the evidence for design is seen even more strikingly in the complex machinery itself than in the product.
Huxley says that "there is a wider teleology which is not touched by the doctrine of evolution, but is actually based upon the fundamental proposition of evolution."[63] When A. R. Wallace at first argued that many of the characteristic human qualities were not due to natural selection, because of no value in the struggle for existence,[64] his view incurred the ridicule of his critics, who interpreted it to mean that "our brains are made by God and our lungs by natural selection." After forty years of reflection, Wallace now takes a broader view of the place of purpose in evolution, and says: "I now uphold the doctrine that not man alone, but the whole World of Life, in almost all its varied manifestations, leads us to the same conclusion—that to afford any rational explanation of its phenomena, we require to postulate the continuous action and guidance of higher intelligences; and further, that these have probably been working towards a single end, the development of intellectual, moral, and spiritual beings."[65] A distinguished biologist has said that "to believe that all the countless myriads of centres of coöperation and coördination which have been required for this cosmos could have been originated and maintained by unintelligent force acting fortuitously makes an immensely greater strain upon faith than the alternative hypothesis."[66]