256 THE PRINCIPLES OF [Part II. 



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

 tained fact that with man a considerably larger proportion 

 of males than of females die before or during birth, and 

 during the first few years of infancy. So it almost cer- 

 tainly is with male lambs, and so it may be with the males 

 of other animals. The males of some animals kill each 

 other by fighting ; or they drive each other about until 

 they become greatly emaciated. They must, also, while 

 wandering about in eager search for the females, be often 

 exposed to various dangers. With many kinds of fish the 

 males are much smaller than the females, and they are be- 

 lieved often to be devoured by the latter or by other fishes. 

 With some birds the females appear to die in larger pro- 

 portion- than the males: they are also liable to be de- 

 stroyed on their nests, or while in charge of their young. 

 With insects the female larvss are often larger than those 

 of the males, and would consequently be more likely to 

 be devoured : in some cases the mature females are less 

 active and less rapid in their movements than the males, 

 and would not be so well able to escape from danger. 

 Hence, with animals in a state of nature, in order to judge 

 of the proportions of the sexes at maturity, we must rely 

 on mere estimation ; and this, except perhaps when the 

 inequality is strongly marked, is but little trustworthy. 

 Nevertheless, 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, considerably exceed in number the females. 



The proportion between the sexes fluctuates slightly 

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

 100 females born, the males varied from 107.1 in one year 

 to 92.6 in another year, and with greyhounds from 116.3 

 to 95.3. But had larger numbers been tabulated through- 

 out a more extensive area than England, these fluctuations 

 would probably have disappeared ; and such as they are, 



