Chap. VIIL] SEXUAL SELECTION. 251 



plies powers of discrimination and taste on the part of the 

 female which will at first appear extremely improbable ; 

 but I hope hereafter to show that this is not the case. 



From our ignorance on several points, the precise man- 

 ner in which sexual selection acts is to a certain extent 

 uncertain. Nevertheless if those naturalists who already 

 believe in the mutability of species, will read the following 

 chapters, they will, I think, agree with me that sexual se- 

 lection has played an important part in the history of the 

 organic world. It is certain that with almost all animals 

 there is a struggle between the males for the possession of 

 the female. This fact is so notorious that it would be su- 

 perfluous to give instances. Hence the females, supposing 

 that their mental capacity sufficed for the exertion of a 

 choice, could select one out of several males. But in nu- 

 merous cases it appears as if it had been specially arranged 

 that there should be a struggle between many males. 

 Thus with migratory birds, the males generally arrive be- 

 fore the females at their place of breeding, so that many 

 males are ready to contend for each female. The bird- 

 catchers assert that this is invariably the case with the 

 nightingale and blackcap, as I am informed by Mr. Jenner 

 Weir, who confirms the statement with respect to the lat- 

 ter species. 



Mr. Swaysland, of Brighton, who has been in the habit, 

 during the last forty years, of catching our migratory 

 birds on their first arrival, writes to me that he has never 

 known the females of any species to arrive before their 

 males. During one spring he shot thirty-nine males of 

 Kay's wagtail {JBudytes JRaii) before he saw a single fe- 

 male. Mr. Gould has ascertained by dissection, as he in- 

 forms me, that male snipes arrive in this country before 

 the females. In the case of fish, at the period when the 

 salmon ascend our rivers, the males in large numbers are 

 ready to breed before the females. So it apparently is 



