Chap. VIII.] SEXUAL SELECTION. 253 



sexual characters were well developed, the males considera- 

 bly exceeded the females in number ; and this does hold 

 good in some few cases. If the males were to the females 

 as two to one, or as three to two, or even in a somewhat 

 lower ratio, the whole affair would be simple : for the bet- 

 ter-armed or more attractive males would leave the lar- 

 gest number of offspring. But after investigating, as far 

 as possible, the numerical proportions 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 

 bodies : the one consisting of the more vigorous and bet- 

 ter-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 dur- 

 ing many years carefully attended to the habits of birds. 

 There can also be no doubt that the most vigorous, 

 healthy, and best-nourished females would on an average 

 succeed in rearing the largest number of offspring. The 

 males, as we have seen, are generally ready to breed be- 

 fore the females ; of the males the strongest, and with 

 some species the best armed, drive away the weaker 

 males ; and the former would then unite with the more 

 vigorous and best-nourished females, as these are the first 

 to breed. Such vigorous pairs would surely rear a larger 

 number of offspring than the retarded females, which 

 would be compelled, supposing the sexes to be numeri- 

 cally equal, to unite with the conquered and less powerful 

 males ; and this is all that is wanted to add, in the course 

 of successive generations, to the size, strength, and cour- 

 age of the males, or to improve their weapons. 



But in a multitude of cases the males which conquer ' 



