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.
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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.