Page:The British Warblers A History with Problems of Their Lives - 5 of 9.djvu/41

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state the position with regard to the theory of sexual selection, for, as I shall presently show, a struggle for territory is not compatible with one part of that theory.

The theory of sexual selection really contains two distinct propositions; in the one the male is represented as attaining to reproduction by conquering other males, while in the other by directly exciting the pairing impulse of the female. The first of these is the law of battle, to which is attributed the greater strength of the male, the development of the antlers of the stag, or the mane of the lion, since it is only the better equipped males that will conquer, and thus be enabled to reproduce and leave descendants similarly endowed, and differs altogether from the second proposition, which refers to a peaceable process, whereby it is claimed that vocal and instrumental music, plumes, and colours in birds have been developed owing to the fact that the males, which possess a greater development of those characters excite the females in a higher degree, and are thus more likely to attain to reproduction. This second proposition leaves no scope for the law of battle. Inasmuch, therefore, as they ignore or regard as of secondary importance the desperate and frequent struggles in bird life, while at the same time pleading the immense importance of similar struggles amongst the mammals, the advocates of sexual selection are not consistent, for I cannot believe that such battles have, in the one case, decided the question of reproduction, but in the other in no way influenced it. Moreover, they admit that the conflicts at the period of sexual activity are not confined to mammals, but that they occur amongst the lower vertebrates, amongst beetles and crustaceans, amongst some insects, and even amongst some birds. And I therefore submit that, on their own showing, it is highly improbable that this scheme by which the male has attained to reproduction, the standard of efficiency of the species has been maintained, and the position of the species improved in its relation to the struggle for existence—a scheme elsewhere so uniform