Chap. VIII.] SEXUAL SELECTION. 255 



supposing that they selected not only the more attractive, 

 but likewise the more vigorous individuals. 



Numerical Proportion of the Two Sexes.— I have re- 

 marked that sexual selection would be a simple affair if 

 the males considerably exceeded in number the females. 

 Hence I was led to investigate, as far as I could, the pro- 

 portions 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 opportunity of ascertaining the proportional 

 numbers at birth ; but no records have been specially kept 

 for this purpose. By indirect means, however, I have col- 

 lected a considerable body of statistical data, from which 

 it appears that with most of our domestic animals the 

 sexes are nearly equal at birth. Thus with race-horses, 

 25,560 births have been recorded during twenty-one years, 

 and the male births have been to the female births as 99.7 

 to 100. With greyhounds the inequality is greater than 

 with any other animal, for during twelve years, out of 

 6,878 births, the male births have been as 110.1 to 100 

 female births. It is, however, in some degree doubtful 

 whether it is safe to infer that the same proportional num- 

 bers would hold good under natural conditions as under 

 domestication ; for slight and unknown differences in the 

 conditions affect to a certain extent 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 females. The proportion is also 

 mysteriously affected by the circumstance of the births 

 being legitimate or illegitimate. 



For our present purpose we are concerned with the 

 proportion of the sexes, not at birth, but at maturity, and 



