430 THE DESCENT OF MAN 



species possessing weapons for sexual strife, others furnished 

 with, wonderful horns, many with stridulating organs, and 

 others ornamented with splendid metallic tints. Hence it 

 seems probable that all these characters have been gained 

 through the same means, namely, sexual selection. With 

 butterflies we have the best evidence, as the males some- 

 times take pains to display their beautiful colors; and we 

 cannot believe that they would act thus, unless the display 

 was of use to them in their courtship. 



When we treat of Birds, we shall see that they present 

 in their secondary sexual characters the closest analogy with 

 insects. Thus many male birds are highly pugnacious, and 

 some are furnished with special weapons for fighting with 

 their rivals. They possess organs which are used during 

 the breeding- season for producing vocal and instrumental 

 music. They are frequently ornamented with combs, horns, 

 wattles, and plumes of the most diversified kinds, and are 

 decorated with beautiful colors, all evidently for the sake 

 of display. We shall find that, as with insects, both sexes 

 in certain groups are equally beautiful, and are equally pro- 

 vided with ornaments which are usually confined to the male 

 sex. In other groups both sexes are equally plain- colored 

 and unornamented. Lastly, in some few anomalous cases 

 the females are more beautiful than the males. We shall 

 often find, in the same group of birds, every gradation from 

 no difference between the sexes to an extreme difference. 

 We shall see that female birds, like female insects, often 

 possess more or less plain traces or rudiments of characters 

 which properly belong to the males and are of use only to 

 them. The analogy, indeed, in all these respects between 

 birds and insects is curiously close. Whatever explanation 

 applies to the one class probably applies to the other; and 

 this explanation, as we shall hereafter attempt to show ia 

 further detail, is sexual selection. 



END OF TOLUME OKB 



