SELECTION 457 



with instances of the importance of masculine vigour and 

 equipment when rival males compete for the possession of 

 the females. " The strongest and, with some species, the best- 

 armed of the males drive away the weaker ; and the former 

 would then unite with the more vigorous and better-nour- 

 ished females, because they are the first to breed. Such vig- 

 orous pairs would surely rear a larger number of offspring 

 than the retarded females, which would be compelled to unite 

 with the conquered and less powerful males, supposing the 

 sexes to be numerically equal ; and this is all that is wanted 

 to add, in the course of successive generations, to the size, 

 strength, and courage of the males, or to improve their 

 weapons " (Descent of Man, 2nd Ed., 1888, Vol. L, p. 329). 

 Now it is plain that forceful competition among rival males 

 for the possession of a female or of several females, does 

 not differ in kind from the ordinary struggle for food and 

 foothold, except that it is strictly intra-specific. Darwin 

 pointed out indeed (p. 349) that sexual selection is less 

 rigorous than natural selection ; that it is less of a life-and- 

 death affair ; that it operates through the unsuccessful males 

 having fewer, less vigorous, or no offspring; and that it is 

 not limited by the general conditions of life ; but there is 

 in all this no departure from the natural selection position. 

 This part of the theory, therefore, remains valid to those who 

 regard natural selection as a vera causa. 



(b) Darwin went on to those characters that are useful in 

 the recognition and capture of the females. When a male 

 excels his neighbours in his capacities for finding, pursuing, 

 and catching the female, sexual selection, he said, again comes 

 into action. (Descent of Man, p. 324.) The male moth often 

 finds his mate by the olfactory acuteness of his large anten- 

 nae; some small crustaceans recognise the other sex almost 



