SEXUAL SELECTION 231 



that the gorgeousness of colour, the eye-spots on the train of the 

 peacock and the Argus pheasant, and the hundreds of different kinds 

 of beautiful feathers, do not also exercise a fascinating influence ; on 

 the contrarji', we cannot avoid assuming this, since otherwise we could 

 find no sufficient reason for their origin. But the primary effect in 

 wooing is not due to the mere pleasure in the sight, or in the odour, 

 or in the song, but to the contagious excitement which these express. 

 The females do not behave as dispassionate judges, but as excitable 

 persons which fall to the lot of the male who is able to excite them 

 most strongly. It may be, however, that a sense of aesthetic satis- 

 faction in perceiving such symptoms of excitement may also have 

 been evolved as an accessory effect, at least in the higher and more 

 intelligent animals. 



In the lower animals, which are lacking not only in intelligence 

 but also in the higher and more complex differentiation of the sensory 

 system, the development of such secondary sex characters is rare or 

 altogether absent. Animals which have no sense of hearing can 

 develop no song, and animals which do not see cannot acquire 

 gorgeous colours as a means of exciting one sex through the other. 

 But distinctive sex coloration may arise even in lowly animals, 

 though there can be no question of aesthetic pleasure associated there- 

 with ; if the animals are able to see the colours at all, sexual 

 excitement may be associated with these. 



We need not wonder, therefore, that in the somewhat stupid 

 fishes, in the butterflies, and in the lower crustaceans, like the 

 Daphnids, we still find brilliant colours, which we can hardly 

 interpret otherwise than as the results of sexual selection. On the 

 other hand, the absence of such characters in animals of a still lower 

 order, with still simpler sense-organs, like the Polyps, Medusae, 

 Echinoderms, most Worms, and the Sponges, affoi'ds an indirect con- 

 firmation of the correctness of our view as to the reality of a sexual 

 selection in the more highly organized animals. 



We see, then, that numerous peculiarities which distinguish the 

 males of a species from the females depend on the process of sexual 

 selection. This may be said of ornamental outgrowths, colours, 

 remarkable feathers and feather-groups, peculiar odoriferous organs, 

 vocal organs, artistic instincts, and also weapons, like antlers, tusks, 

 and spurs, notable size and strength of body, and protective devices 

 like manes ; and again, the various organs for catching and holding 

 the females, or for finding them out by sight or smell, must also be 

 referred, at least in part, to sexual selection. The diversity of the 

 male sexual characters is so great that I cannot give more than 



