Sexual selection. 245 



wild animals, as shown in the supplement, the proportions 

 seem to fluctuate either during different seasons or in dif- 

 ferent localities in a sufficient degree to lead to such selec- 

 tion. For it should be observed that any advantage gained 

 during certain 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 succeeding seasons, when from the equality of 

 the sexes every male was 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 weaker or less attractive. 



Polygamy. The practice of polygariiy 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 f 

 mammals and some few birds are polygamous, but with 

 animals belonging to the lower classes I have found no evi- 

 dence of this habit. The intellectual powers of such ani- j 

 mals are, perhaps, not sufficient to lead them to collect and ! 

 guard a harem of females. Cjhat some relation exists be- 

 tween polygamy and the development of secondary sexual 

 characters 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; while 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 .goriUaseems to be polygamous, 

 and the male differs consmeraBly from the female ; so 

 it is with some baboons, which live in herds containing 

 twice as many adult females as males. In South America 

 the Mycetes caraya presents well-marked sexual differences, 

 in color, beard, and vocal organs ; and the male generally 

 lives with two or three wives; the male of the Cebti.^ capnci- 

 nus differs somewhat from the female, and appears to be 



