212 THE DESCENT OP MAN. 



proportions of the sexes at maturity; and this is but little trust- 

 worthy, except when the inequality is strongly marked. Never- 

 theless, aa far as a judgment can he 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, are con- 

 siderably more numerous than the females. 



The proportion between the sexes fluctuates slightly during 

 successive years: thus with race-horses, for every 110 mares born 

 the stallions varied from 107.1 in one ysar to 92.6 in another year, 

 and with greyhounds from 116.3 to 95.3. But had larger num- 

 bers been tabulated throughout an area more extensive than Eng- 

 land, these fluctuations would probably have disappeared; and 

 such as they are, would hardly suffice to lead to effective sexual 

 selection in a state of nature. Nevertheless, in the cases of 

 some few wild animals, as shown in the supplement, the propor- 

 tions seem to fluctuate either during different seasons or in dif- 

 ferent localities in a sulTicient degree to lead to such selection. 

 For it should be observed that any advantage, gained during cer- 

 tain years or in certain localities by those males which were able 

 to conquer their rivals, or were the most attractive to the females, 

 would probably be transmitted to the offspring, and would not 

 subsequently be eliminated. During the Eucceeding seasons, 

 when, from the equality of the sexes, every male was able to pro- 

 cure a female, the stronger or more attractive males previously 

 produced would still have at least as good a chance of leaving off- 

 spring as the weaker or less attractive. 



Polygamy.— The practice of polygamy leads to the same results 

 as would follow from an actual inequality in the number of the 

 sexes; for if each male secures two or more females, many males 

 cannot pair; and the latter assuredly will be the weaker or less 

 attractive individuals. Many mammals and some few birds are 

 polygamous, but with animals belonging to the lower classes I 

 have found no evidence of this habit. The intellectual powers 

 of such animals are, perhaps, not sufflcient to lead them to collect 

 and guard a harem of females. That some relation exists be- 

 tween polygamy and the development of secondary sexual char- 

 acters, appears nearly certain; and this supports the view that a 

 numerical preponderance of males would be eminently favorable 

 to the action of sexual selection. Nevertheless many animals, 

 which are strictly monogamous, especially birds, display strongly- 

 marked secondary sexual characters; whilst some few animals, 

 which are polygamous, do not have such characters. 



We will first briefly run through the mammals, and then turn 

 to birds. The gorilla seems to be polygamous, and the male dif- 

 fers considerably from the female; so it is with soiiig baboons, 

 which live in herds containing twice as many adult females as 



