Chap. VIII. Sexual Selection. 2 1 5 



tage in rearing offspring, more especially if the male had the 

 power to defend the female during the pairing-season as occurs 

 with some of the higher animals, or aided her in providing for 

 the young. The same principles would apply if each sex pre- 

 ferred and selected certain individuals of the opposite sex ; 

 supposing that they selected not only the more attractive, but 

 likewise the more vigorous individuals. 



Numerical Proportion of the Two Sexes. — I have remarked that 

 sexual selection would be a simple affair if the males were con- 

 siderably more numerous than the females. Hence I was led to 

 investigate, as far as I could, the proportions between the two 

 sexes of as many animals as possible ; but the materials are 

 scanty. I will here give only a brief abstract of the results, 

 retaining the details for a supplementary discussion, so as not 

 to interfere with the course of my argument. Domesticated 

 animals alone afford the means of ascertaining the propor- 

 tional numbers at birth; but no records have been specially 

 kept for this purpose. By indirect means, however, I have 

 collected a considerable body of statistics, from which it appears 

 that with most of our domestic animals the sexes are nearly 

 equal at birth. Thus 25,560 births of race-horses have been 

 recorded during . twenty-one years, and the male births were 

 to the female births as 99*7 to 100. In greyhounds the in- 

 equality is greater than with any other animal, for out of 6878 

 births during twelve years, the male births were to the female 

 as 110*1 to 100. It is, however, in some degree doubtful 

 whether it is safe to infer that the proportion would be the same 

 under natural conditions as under domestication ; for slight and 

 unknown differences in the conditions affect the proportion of 

 the sexes. Thus with mankind, the male births in England 

 are as 104 - 5, in Russia as 108'9, and with the Jews of Livonia as 

 120, to 100 female births. But I shall recur to this curious point 

 of the excess of male births in the supplement to this chapter. At 

 the Cape of Good Hope, however, male children of European 

 extraction have been born during several years in the proportion 

 of between 90 and 99 to 100 female children. 



For our present purpose we are concerned with the proportion 

 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 

 tbat 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 



