SEXUAL SELECTION. 237 



investigating, as far as possible, the numerical proportion 

 of the sexes, I do not believe that any great inequality in 

 number commonly exists. In most cases sexual selection 

 appears to have been effective in the following manner : 



Let us take any species, a bird for instance, and di- 

 vide the females inhabiting a district into two equal bod- 

 ies, the one consisting of the more vigorous and better- 

 nourished individuals, and the other of the less vigor- 

 ous and healthy. The former, there can be little doubt, 

 would be ready to breed in the spring before the others ; 

 and this is the opinion of Mr. Jenner Weir, who has 

 carefully attended to the habits of birds during many 

 years. There can also be no doubt that the most vigor- 

 ous, best-nourished, and earliest breeders would on an 

 average succeed in rearing the largest number of fine off- 

 spring. The males, as we have seen, are generally ready 

 to breed before 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 fe- 

 males, which would be compelled to unite with the con- 

 quered 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. 



COUBTSHIP AMONG THE LOWER ANIMALS. 



p But in very many cases the males which 



conquer their rivals do not obtain possession 

 of the females, independently of the choice of the latter. 

 The courtship of animals is by no means so simple and 



