SEXUAL SELECTION. 243 



only to the strength and fighting powers of the males, 

 but likewise to their various ornaments or other attractions. 

 In the converse and much rarer case of the males select- 

 ing particular females it is plain that those which were the 

 most vigorous and had conquered others would have the 

 freest choice; and it is almost certain that they would select 

 vigorous as well as attractive females. Such pairs would 

 have an advantage 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 preferred and selected certain 

 individuals of the opposite sex; supposing that they selected 

 not only the more attractive, but likewise the more vigor- 

 ous individuals. 



Numerical Proportion of the Two^ Sexes. I have remarked 

 that sexual selection would be a simple affair if the males 

 were considerably 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 supple- 

 mentary discussion so as not to interfere with the course of 

 my argument. Domesticated animals alone afford the 

 means of ascertaining the proportional 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 inequality is 

 greater than with any other animal, for out of 6,878 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 

 ghall recur to this curious point of the excess of male births 



