BRITISH WARBLERS
the antics take in closely-related species, and the fact that they may be scarcely perceptible in one variety, whereas in another closely akin their very frequency and intensity compels our attention, we find little enough support for the first proposition in the lives of these particular species. This view, however, has in a great measure been discarded, opinion generally favouring the second proposition as being a more reasonable interpretation, since conscious display is discarded and replaced by a more mechanical process, which readily comes under the sway of natural selection. Thus Professor Groos in his "Play of Animals" develops a theory which is accepted by many as a provisional hypothesis. I quote it as summarised in his preface to the above work. "The disciple of Weismann who cannot accept Spencer's explanation of such phenomena must either cleave to Darwin's sexual selection, as Weismann himself does, or seek a new principle. Such a principle I believe I have found. It depends on two closely related facts. As sexual impulse must have tremendous power, it is for the interest of the preservation of the species that its discharge should be rendered difficult. This result is partly accomplished in the animal world by the necessity for great and often long continued excitement as a prelude to the act of pairing. This thought at once throws light on the peculiar hereditary arts of courtship, especially on the indulgence in flying, dancing, or singing by a whole flock at once. But the hindrance to the sexual function that is most efficacious, though hitherto unappreciated, is the instinctive coyness of the female. This it is that necessitates all the arts of courtship, and the probability is that seldom or never does the female exert any choice. She is not awarder of the prize, but rather a hunted creature. So, just as the beast of prey has special instincts for finding his prey, the ardent male must have special instincts for subduing feminine reluctance; and just as in the beast of prey the instinct of ravenous pursuit is refined into the various arts of the chase, so from such crude efforts at wooing that courtship has finally developed
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