SEXUAL SELECTION. 241 



production of the young a period which must be deter- 

 mined by the seasons of the year. On the whole, there 

 can be no doubt that with almost all animals in which the 

 sexes are separate there is a constantly recurrent struggle 

 between the males for the possession of the females. 



Our difficulty in regard to sexual selection lies in under- 

 standing how it is that the males which conquer other 

 males, or those which prove the most attrative to the 

 females, leave a greater number of off spring to inherit their 

 superiority than their beaten and less attractive rivals. 

 Unless this result does follow the characters which give to 

 certain males an advantage over others could not be per- 

 fected and augmented through sexual selection. When 

 the sexes exist in exactly equal numbers the worst endowed 

 males will (except where polygamy prevails) ultimately 

 find females and leave as many offspring as well fitted for 

 their general habits of life as the best-endowed males. 

 From various facts and considerations I formerly inferred 

 that with most animals, in which secondary sexual charac- 

 ters are well developed, the males considerably exceeded 

 the females in number; but this is not by any means 

 always true. If the males were to the females as two to 

 one, or three to two, or even in a somewhat lower ratio the 

 whole affair would be simple; for the better armed or more 

 attractive males would leave the largest number of offspring. 

 But after investigating as far as possible the numerical 

 proportion of the sexes I do not believe that any great in- 

 equality 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 divide 

 the females inhabiting a district into two equal bodies, the 

 one consisting of the more vigorous and better-nourished 

 individuals, and the other of the less vigorous 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 vigorous, best-nourished and earliest 

 breeders would on an average succeed in rearing the 

 largest number of fine offspring.* The males, as we have 



* Here is excellent evidence on the character of the offspring from 

 an, experienced ornithologist. Mr. J. A. Allen, in speaking (" Main- 



