282 THE DESCENT OF MAN 



and leave aa 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 characters 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 as 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 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 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 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 



' Here is excellent evidence on the character of the offspring from an ex- 

 perienced ornithologist. Mr. J. A. Allen, in speaking ("Mammals and Winter 

 Birds of E. Florida," p. 229) of the later broods, after the accidental destruction 

 of the first, says that these "are found to be smaller and paler-colored than 

 those hatched earlier in the season. In cases where several broods are reared 

 each year, as a general rule the birds of the earlier broods seem in all respects 

 the most perfect and vigorous." 



8 Hermann Miiller has come to this same conclusion with respect to those 

 female bees which are the first to emerge from the pupa each year. See hia 



