If, on the other hand, we assume the change of conditions not to have been temporary but permanent, and also assume that this permanent change of conditions was accidentally synchronous with the change of structure, we have a coincidence of very remote probability indeed.

But if, again, we accept the presence of some harmonizing law simultaneously determining the two changes, or connecting the second with the first by causation, then, of course, we remove the accidental character of the coincidence.
Again, how explain the external position of the male sexual glands in certain mammals?
The utility of the modification, when accomplished, is problematical enough, and no less so the incipient stages of the descent.
As was said in the first chapter, Mr.Darwin explains the brilliant plumage of the peacock or the humming-bird by the action of sexual selection: the more and more brilliant males being selected by the females (which are thus attracted) to become the fathers of the next generation, to which generation they tend to communicate their own bright nuptial vesture.

But there are peculiarities of colour and of form which it is exceedingly difficult to account for by any such action.

Thus, amongst apes, the female is notoriously weaker, and is armed with much less powerful canine tusks than the male.

When we consider what is known of the emotional nature of these animals, and the periodicity of its intensification, it is hardly credible that a female would often risk life or limb through her admiration of a trifling shade of colour, or an infinitesimally greater though irresistibly fascinating degree of wartiness.[38] {49} [Illustration: RATTLESNAKE.] Yet the males of some kinds of ape are adorned with quite exceptionally brilliant local decoration, and the male orang is provided with remarkable, projecting, warty lumps of skin upon the cheeks.