458 THE DESCENT OF MAN. 



CHAPTER XVI. 



BIRDS— concluded. 



The immature plumage in relation to the character of the plumage in 

 both sexes when adult— Six classes of cases— Sexual differences 

 between the males of closely-allied or representative species— The 

 female assuming the characters of the male — Plumage of the young 

 in relation to the summer and winter plumage of the adults— On 

 the increase of beauty in the birds of the world — Protective color- 

 ing— Conspicuously-colored birds- Novelty appreciated— Summary 

 of the four chapters on Birds. 



We must now consider the transmission of characters, as limited 

 by age, in reference to sexual selection. The truth and impor- 

 tance of the principle of inheritance at corresponding ages need 

 not here be discussed, as enough has already been said on the sub- 

 ject. Before giving the several rather complex rules or classes of 

 cases, under which the differences in plumage between the young 

 and the old, as far as known to me, may be included, it will be 

 well to make a few preliminary remarks. 



With animals of all kinds when the adults differ in color from 

 the young, and the colors of the latter are not, as far as we can 

 see, of any special service, they may generally be attributed, like 

 various embryological structures, to the retention of a former char- 

 acter. But this view can be maintained with confidence, only when 

 the young of several species resemble each other closely, and like- 

 wise resemble other adult species belonging to the same group; 

 for the latter are the living proofs that such a state of things 

 was formerly possible. Young lions and pumas are marked with 

 feeble stripes or rows of spots, and as many allied species both 

 young and old are similarly marked, no believer in evolution will 

 doubt that the progenitor of the lion and puma was a striped ani- 

 mal, and that the young have retained vestiges of the stripes, like 

 the kittens of black cats, which are not in the least striped when 

 grown up. Many species of deer, which when mature are not 

 spotted, are whilst young covered with white spots, as are like- 

 wise some few species in the adult state. So again the young in 

 the whole family of pigs (Suidse), and in certain rather distantly 



