Weismann continues: “But the question remains, why is this the fact?” He believes his hypothesis of the existence of determinants in the germ gives a satisfactory answer to this “why.” “According to this theory every independent and hereditarily variable part is represented in the germ by a determinant, whose size and power of assimilation corresponds to the size and vigor of the part. These determinants multiply as do all vital units by growth and division, and necessarily they increase rapidly in every individual, and the more rapidly the greater the quantity of the germinal cells the individual produces. And since there is no more reason for excluding irregularities of passive nutrition, and of the supply of nutriment in these minute, microscopically invisible parts, than there is in the larger visible parts of the cells, tissues, and organs, consequently the descendants of a determinant can never all be exactly alike in size and capacity of assimilation, but they will oscillate in this respect to and fro about the maternal determinant as about their zero point, and will be partly greater, partly smaller, and partly of the same size as that. In these oscillations, now, the material for further selection is presented, and in the inevitable fluctuations of the nutrient supply, I see the reason why every step attained immediately becomes the zero point of new fluctuations, and consequently why the size of a part can be augmented or diminished by selection without limit, solely by the displacement of the zero point of variation as the result of selection.”

The best illustration of this process of germinal selection is found, Weismann believes, in the case of the degeneration of organs. “For in most retrogressive processes active selection in Darwin’s sense plays no part, and advocates of the Lamarckian principle, as above remarked, have rightly denied that active selection, that is, the selection of individuals possessing the useless organ in its most reduced state, is sufficient to explain the process of degeneration. I, for my part, have never assumed this, and have on this very account enunciated the principle of panmixia. Now, although this, as I have still no reason for doubting, is a perfectly correct principle, which really does have an essential and indispensable share in the process of retrogression, still it is not alone sufficient for a full explanation of the phenomena. My opponents, in advancing this objection, were right, to the extent indicated, and as I expressly acknowledge, although they were unable to substitute anything positive in its stead or to render my explanation complete. The very fact of the cessation of control over the organ is sufficient to explain its degeneration, that is, its deterioration, the disharmony of its parts, but not the fact which actually and always occurs where an organ has become useless—viz., its gradual and unceasing diminution continuing for thousands and thousands of years and culminating in its final and absolute effacement.”

If then neither selection of persons nor the cessation of personal selection can explain the phenomenon, we must look elsewhere for the answer. This Weismann finds in the application of Roux’s hypothesis of the struggle of the parts to obtain nourishment.

“The production of the long tail-feathers of the Japanese cock does not repose solely on the displacement directly effected by personal selection, of the zero point of variation upward, but that it is also fostered and strengthened by germinal selection. Were that not so, the phenomena of the transmutation of species, in so far as fresh growth and the enlargement and complication of organs already present are concerned, would not be a whit more intelligible than they were before.”

Thus Weismann has piled up one hypothesis on another as though he could save the integrity of the theory of natural selection by adding new speculative matter to it. The most unfortunate feature is that the new speculation is skilfully removed from the field of verification, and invisible germs whose sole functions are those which Weismann’s imagination bestows on them, are brought forward as though they could supply the deficiencies of Darwin’s theory. This is, indeed, the old method of the philosophizers of nature. An imaginary system has been invented which attempts to explain all difficulties, and if it fails, then new inventions are to be thought of. Thus we see where the theory of the selection of fluctuating germs has led one of the most widely known disciples of the Darwinian theory.

The worst feature of the situation is not so much that Weismann has advanced new hypotheses unsupported by experimental evidence, but that the speculation is of such a kind that it is, from its very nature, unverifiable, and therefore useless. Weismann is mistaken when he assumes that many zoologists object to his methods because they are largely speculative. The real reason is that the speculation is so often of a kind that cannot be tested by observation or by experiment.

CHAPTER VI
DARWIN’S THEORY OF SEXUAL SELECTION

Sexual Selection

The theory of sexual selection was formulated by Darwin, even in the first edition of the “Origin of Species,” but was developed at much greater length in “The Descent of Man.” “This form of selection depends, not on a struggle for existence in relation to other organic beings or to external conditions, but on a struggle between the individuals of one sex, generally the males, for the possession of the other sex. The result is not death to the unsuccessful competitor, but few or no offspring. Sexual selection is, therefore, less rigorous than natural selection. Generally the most vigorous males, those which are best fitted for their place in nature, will leave most progeny. But in many cases victory depends, not so much on general vigor, as on having special weapons, confined to the male sex. A hornless stag or spurless cock would have a poor chance of leaving numerous offspring. Sexual selection, by always allowing the victor to breed, might surely give indomitable courage, length to the spur, and strength to the wing to strike in the spurred leg in nearly the same manner as the brutal cock-fighter by the careful selection of his best cocks.” It is important to notice that the theory of sexual selection is admittedly an extension of the selection principle into a new field. Having accounted for domesticated animals and plants by artificial selection, and for the adaptations of wild species by natural selection, there remained only to account for the secondary sexual differences between the sexes by the principle of sexual selection.