CHAPTER XXI 



SEXUAL SELECTION 



Darwin -and the theory of sexual selection. The evidence on which his 

 theory was based. Objections to the theory of Alfred Russel Wallace and of 

 H. Eliot Howard. Sexual selection in absence of secondary sexual characters. 

 Consciousness in display of the effect produced, or to be produced. The factors 

 which incite display. The part which sexual selection does play. 



MUCH that concerns this chapter has already been 

 touched upon in Chapter X, wherein the relations 

 of the sexes were briefly discussed. It was there 

 shown that during the breeding season birds display very re- 

 markable activity and excitability. This displaj' is manifested, 

 as a rule, by the males alone, and reaches its highest pitch in 

 the presence of the females. With some species it takes the 

 form of passionate outpourings of song, with others of the 

 performance of strange antics, while in yet other cases it 

 culminates in fierce conflicts. But whatever form such demon- 

 strations may take, the apparent end to be attained is always 

 the same — the capture — either by whiles or by force — of mates. 

 Darwin, bringing his great intellect to bear upon these 

 phenomena, came to the conclusion that these manifestations of 

 sexual activity were to be regarded as the main factor, if not 

 the only factor, in the evolution of the " secondary sexual 

 characters" — the elaborate ornamental plumage — which char- 

 acterises so many birds. The resplendent hues of the Hum- 

 ming-birds, the gorgeous train of the Peacock, the marvellous 

 plumes of the Birds of Paradise, for example, were, he con- 

 tended, developed by the selective activity of the females, who 

 choose as mates those performers which pleased them or 

 excited them most. Though, in certain cases, he argued, 

 these wondrous plumes were the outcome of .a process rather 

 akin to natural selection, since, where mates were won by 



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