MALES ARRIVE BEFORE FEMALES 35 



be safely accomplished, and it, too, arrives in 

 that place in advance of the female. 



With these facts at our disposal, we will 

 endeavour to find an explanation. It is unlikely 

 that specialised behaviour would occur in genera- 

 tion after generation under such widely divergent 

 conditions, and, moreover, expose the birds to 

 risk of special dangers, if it were but an 

 hereditary peculiarity to which no meaning 

 could be attached. Hence the appearance of 

 the males in their breeding haunts ahead of the 

 females becomes a fact of some importance, and 

 suggests that the extensive journey in the one 

 case, and the short journey in the other, may 

 both have a similar biological end to serve. 



Darwin evidently attached importance to 

 this difference between the males and the 

 females in their times of arrival. In the 

 Descent of Man he referred to it as follows : 

 " Those males which annually first migrated in 

 any country, or which in spring were first ready 

 to breed, or were the most eager, would leave 

 the largest number of offspring ; and these 

 would tend to inherit similar instincts and 

 constitutions. It must be borne in mind that 

 it would have been impossible to change very 

 materially the time of sexual maturity in the 

 females without at the same time interfering 

 with the period of the production of the young 

 — a period which must be determined by the 

 season of the year." Newton suggested the 

 following explanation ^ : "It is not difficult to 



^ Diclio7iary of Birds, p. 556. 



D 



