Chap. VIII. 
SEXUAL SELECTION. 
263 
the males, but likewise to their various ornaments or 
other attractions. 
In the converse and much rarer case of the males 
selecting 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 in providing for the 
young. The same principles would apply if both sexes 
mutually preferred 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 considerably exceeded in number 
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 dis- 
cussion, 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 
collected 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 
