Chap. VIII.] SEXUAL SELECTION. 257 



they would hardly suffice to lead under a state of nature 

 to the effective action of sexual selection. Nevertheless 

 with some few wild animals, the proportions seem, as 

 shown in the supplement, to fluctuate either during differ- 

 ent seasons or in different localities in a sufficient degree 

 to lead to such action. For it should be observed that 

 any advantage gained during certain years or in certain 

 localities by those males which were able to conquer other 

 males, or were the most attractive to the females, would 

 probably be transmitted to the offspring and would not 

 subsequently be eliminated. During the succeeding sea- 

 sons, when from the equality of the sexes every male was 

 everywhere able to procure a female, the stronger or more 

 attractive males previously produced would still have at 

 least as good a chance of leaving offspring as the less 

 strong 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 will not be able to 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 intel- 

 lectual powers of such animals are, perhaps, not sufficient 

 to lead them to collect and guard a harem of females. 

 That some relation exists between polygamy and the de- 

 velopment of secondary sexual characters, appears nearly 

 certain ; and this supports the view that a numerical pre- 

 ponderance of males would be eminently favorable to the 

 action of sexual selection. Nevertheless many animals, 

 especially birds, which are strictly monogamous, display 

 strongly-marked secondary sexual characters ; while some 

 few animals, which are polygamous, are not thus charac- 

 terized. 



