SEXUAL SELECTION 285 



several years in the proportion of between 90 and 99 to 

 100 female children. 



For our present purpose we are concerned with the pro- 

 portion of the sexes not only at birth, but also at maturity, 

 and this adds another element of doubt; for it is a well- 

 ascertained fact that with man the number of males dying 

 before or during birth, and during the first few years of 

 infancy, is considerably larger than that of females. So 

 it almost certainly is with male. lambs, and probably with 

 some other animals. The males of some species kill one 

 another by fighting, or they drive one another about until 

 they become greatly emaciated. They must also be often 

 exposed to various dangers, while wandering about in eager 

 search for the females. In many kinds of fisli the males are 

 much smaller than the females, and they are believed often 

 to be devoured by the latter, or by other fishes. The fe- 

 males of some birds appear to die earlier than the males; 

 they are also liable to be destroyed on their nests, or while 

 in charge of their young. With insects the female larvae 

 are often larger than those of the males, and would conse- 

 quently be more likely to be devoured. In some cases the 

 mature females are less active and less rapid in their move- 

 ments than the males, and could not escape so well from 

 danger. Hence, with animals in a state of nature, we must 

 rely on mere estimation, in order to judge of the proportions 

 of the sexes at maturity; and this is but little trustworthy, 

 except when the inequality is strongly marked. Neverthe- 

 less, as far as a judgment can be formed, we may conclude, 

 from the facts given in the supplement, that the males of 

 some few mammals, of many birds, of some fish and insects, 

 are considerably more numerous than the females. 



The proportion between the sexes fluctuates slightly 

 during successive years: thus with race- horses, for every 

 100 mares born the stallions varied from 107.1 in one year 

 4o 92.6 in another year, and with greyhounds from 116.3 to 

 05.8. But had larger numbers been tabulated throughout 

 an area more extensive than England, these fluctuations 



