558 THE DESCENT OF MAN. 



ive manner; and this coloring is all the more striking, as 

 with most of these birds it differs from that of their con- 

 geners. Both sexes of thirteen out of the twenty-six 

 species are colored in the same manner; but these belong 

 to genera in which this rule commonly prevails, so that 

 they tell us nothing about the protective colors being the 

 same in both sexes of desert-birds. Of the other thirteen 

 species three belong to genera in which the sexes usually 

 differ from each other, yet here they have the sexes alike. 

 In the remaining ten species the male differs from the 

 female; but the difference is confined chiefly to the under 

 surface of the plumage, which is concealed when the bird 

 crouches on the ground; the head and back being of the 

 same sand-colored hue in the two sexes. So that in these 

 ten species the upper surfaces of both sexes have been acted 

 on and rendered alike through natural selection for the 

 sake of protection; while the lower surfaces of the males 

 alone have been diversified through sexual selection for the 

 sake of ornament. Here, as both sexes are equally well 

 protected, we clearly see that the females have not been 

 prevented by natural selection from inheriting the colors of 

 their male parents ; so that we must look to the law of 

 sexually limited transmission. 



In all parts of the world both sexes of many soft-billed 

 birds, especially those which frequent reeds or hedges, are 

 obscurely colored. No doubt if their colors had been 

 brilliant, they would have been much more conspicuous to 

 their enemies; but whether their dull tints have been 

 specially gained for the sake of protection seems, as far as 

 I can judge, rather doubtful. It is still more doubtful 

 whether such dull tints can have been gained for the sake 

 of ornament. We must, however, bear in mind that male 

 birds, though dull-colored, often differ much from their 

 females (as with the common sparrow), and this leads to 

 the belief that such colors have been gained through sexual 

 selection from being attractive. Many of the soft-billed 

 birds are songsters; and a discussion in a former chapter 

 should not be forgotten, in which it was shown that the 

 best songsters are rarely ornamented with bright tints. It 

 would appear that female birds, as a general rule, have 

 selected their mates either for their sweet voices or gay 

 colors, but not for both charms combined. Some species 

 which are manifestly colored for the sake of protection, 



