Darwin s Theory of Sexual Selection 207 



is not odoriferous." Darwin believes in these cases that the 

 odor serves to attract the females. He admits that here, 

 " active and long-continued use cannot have come into 

 play as in the case of the vocal organs." He concludes, 

 therefore, that " the odor emitted must be of considerable 

 importance to the male, inasmuch as large and complex 

 glands, furnished with muscles for everting the sac, and for 

 closing or opening the orifice, have in some cases been 

 developed. The development of these organs is intelligible 

 through sexual selection, if the most odoriferous males are 

 the most successful in winning the females, and in leaving 

 offspring to inherit their gradually perfected glands and 

 colors." 



There is sometimes a difference in the mammals in the 

 hair of the two sexes both in amount and in color. In some 

 species of goats the males have a beard, in others it is 

 present in both sexes. The bull, but not the cow, has curly 

 hair on the forehead. In some monkeys the beard is con- 

 fined to the male, as in the orang ; in other species it is only 

 larger in the males. 



"The males of various members of the ox family (Bovidae), 

 and of certain antelopes, are furnished with a dewlap, or 

 great fold of skin on the neck, which is much less developed 

 in the female. 



" Now, what must we conclude with respect to such sexual 

 differences as these ? No one will pretend that the beards 

 of certain male goats, or the dewlap of the bull, or the crests 

 of hair along the backs of certain male antelopes, are of any 

 use to them in their ordinary habits. 



" Must we attribute all these appendages of hair or skin to 

 mere purposeless variability in the male ? It cannot be 

 denied that this is possible ; for in many domesticated quad- 

 rupeds, certain characters, apparently not derived through 

 reversion from any wild parent form, are confined to the 

 males, or are more developed in them than in the females 



