198 THE BIOLOGY OF BIRDS 



them together. Forel thinks that there was no question 

 of any direct sexual excitement (of course " sex " is not an 

 insulable activity) ; the peahen was simply filled with 

 aesthetic pleasure at the novel sight of such a gorgeous 

 kinsman ! 



§ 10. Reconsideration of Darwin's Theory of Sexual 



Selection 



Darwin's theory of Sexual Selection is no longer wholly 

 acceptable in the form in which he stated it, but modern 

 criticism has erred in over-destructiveness. In regard to 

 some of the questions involved, the wisest course is probably 

 to suspend judgment until fresh facts, especially of an 

 experimental kind, accumulate. In regard to some other 

 implications, however, it seems possible to meet some of the 

 chief objections by a re-statement in the light of new data. 



(A) It was primarily in reference to secondary sex- 

 characters that Darwin suggested his theory of sexual 

 selection. Certain variations, e.g. in the improvement of 

 weapons and food-catching apparatus, are favoured by 

 natural selection in the course of the every- day struggle for 

 existence ; in the same way, variations which are advan- 

 tageous in securing mates and consummating sexual repro- 

 duction will be favoured by sexual selection. 



Darwin began 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-nourished females, because they are 

 the first to breed. Such vigorous 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. i. p. 329). 



