SEXUAL SELECTION 621 



CliASS IV. When the adult male resembles the adult fe- 

 male, the young of both sexes in their jvrst plumage resemble 

 ike adults. — In this class the young and the adults of both 

 sexes, whether brilliantly or obscurely colored, resemble 

 each other. Such cases are. I think, more common than 

 those in the last class. We have in England instances in 

 the kingfisher, some woodpeckers, the jay, magpie, crow, 

 and many small dull-colored birds, such as the hedge-war- 

 bler or kitty-wren. But the similarity in plumage between 

 the young and the old is never complete, and graduates away 

 into dissimilarity. Thus the young of some members of the 

 kingfisher family are not only less vividly colored than 

 the adults, but many of the feathers on the lower surface 

 are edged with brown " — a vestige probably of a former 

 state of the plumage. Frequently in the same group of 

 birds, even within the same genus, for instance, in an Aus- 

 tralian genus of paroquets (Platycercus), the young af some 

 species closely resemble, while the young of other species 

 differ considerably, from their parents of both sexes, which 

 are alike." Both sexes and the young of the common jay 

 are closely similar; but in the Canada jay {Perisorcus cana- 

 densis) the young differ so much from their parents that they 

 were formerly described as distinct species. °° 



I may remark before proceeding that, under the present 

 and next two classes of cases, the facts are so complex and 

 the conclusions so doubtful, that any one who feels no es- 

 pecial interest in the subject had better pass them over. 



The brilliant or conspicuous colors which characterize 

 many birds in the present class can rarely or never be of ser- 

 vice to them as a protection; so that they have probably 

 been gained by the males through sexual selection, and 

 then transferrea to the females and the young. It is, how- 



s' Jerdon, "Birds of India," vol. i. pp. 222, 228. Gould's "Handbook to 

 the Birds of Australia," vol. i. pp. 12i, 130. 

 »8 Gould, ibid., vol. ii. pp. 37, 46, 56. 

 >• Audubon, "Omith. Biography," vol. ii. p. 65. 

 Descent — Vol. IL — 9 



