x COLOURS AND ORNAMENTS CHARACTERISTIC OF SEX 283 



the pupa, and among migrating birds the males arrive first 

 both in this country and in North America. The struggle 

 is thus intensified, and the most vigorous males are the 

 first to have offspring. This in all probability is a great 

 advantage, as the early breeders have the start in securing 

 food, and the young are strong enough to protect themselves 

 while the later broods are being produced. 



It is to this form of male rivalry that Mr. Darwin first 

 applied the term " sexual selection." It is evidently a real 

 power in nature ; and to it we must impute the development of 

 the exceptional strength, size, and activity of the male, together 

 with the possession of special offensive and defensive weapons, 

 and of all other characters which arise from the development 

 of these or are correlated with them. But he has extended 

 the principle into a totally different field of action, which 

 has none of that character of constancy and of inevitable 

 result that attaches to natural selection, including male 

 rivalry; for by far the larger portion of the phenomena, 

 which he endeavours to explain by the direct action of 

 sexual selection, can only be so explained on the hypothesis 

 that the immediate agency is female choice or preference. 

 It is to this that he imputes the origin of all secondary 

 sexual characters other than weapons of offence and defence, 

 of all the ornamental crests and accessory plumes of birds, 

 the stridulating sounds of insects, the crests and beards 

 of monkeys and other mammals, and the brilliant colours and 

 patterns of male birds and butterflies. He even goes further, 

 and imputes to it a large portion of the brilliant colour that 

 occurs in both sexes, on the principle that variations occurring 

 in one sex are sometimes transmitted to the same sex only, 

 sometimes to both, owing to peculiarities in the laws of inherit- 

 ance. In this extension of sexual selection to include the 

 action of female choice or preference, and in the attempt to 

 give to that choice such wide-reaching effects, I am unable 

 to follow him more than a very little way ; and I will now 

 state some of the reasons why I think his views are unsound. 



Sexual Characters due to Natural Selection. 



Besides the acquisition of weapons by the male for the 

 purpose of fighting with other males, there are some other 



