598 THE DESCENT OF MAN 



CHAPTEE 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 as- 

 suming the characters of the male — Plumage of the young in relation 

 to the summer and winter plumage of the adult,s — On the increase 

 of beauty in the birds of the world — Protecliye coloring — Oonspicu- 

 ously colored birds — Novelty appreciated — Summary of the four chap- 

 ters on birds 



WE MUST now consider the transmission of char- 

 acters, as limited by age, in reference to sexual 

 selection. The truth and importance of the prin- 

 ciple of inheritance at corresponding ages need not here be 

 discussed, as enough has already been said on the subject. 

 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 in- 

 cluded, 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 character. But this view can be 

 maintained with confidence only when the young of several 

 species resemble each other closely, and likewise 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 be- 



