326 THE DESCENT OP MAN. 



able that all these characters have been gained through the same 

 means, namely, sexual selection. With butterflies we have the 

 best evidence, as the males sometimes 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 in- 

 sects. 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 provided 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. What- 

 ever explanation applies to the one class probably applies to the 

 other; and this explanation, as we shall hereafter attempt to 

 show in further detail, is sexual selection. 



