208 
SEXUAL SELECTION: BIRDS. 
1’AB 1 1 
the male ; and on this view, all the facts become cle®t’ 
for the males would probably be most charmed or 
c.ted by the females which were the most attractive t0 
them by their brighter colours, other ornaments, 
vocal powers. Sexual selection would then soon d° |,S 
work, steadily adding to the attractions of the female j 
the males and the young being left not at all, or 1)11 
little modified. 
Class III. When the adult male resembles the of 1 ^ 
female, the young of loth sexes have a peculiar first 
age of their own— In this class both sexes when a clll J. 
resemble each other, and differ from the young. I* 1 !' 
occurs with many birds of many kinds. The male r° l1 "' 
can hardly be distinguished from the female, but 
young are widely different with their mottled dus^' 
olive and brown plumage. The male and female of ^ 
splendid scarlet Ibis are alike, whilst the young f1 ' 
brown ; and the scarlet-colour, though common to ho ^ 
sexes, is apparently a sexual character, for it is not 
developed with birds under confinement, in the ^ 
manner as often occurs in the case of brilliantly c °^ 
loured male birds. With many species of herons t 
young differ greatly from the adults, and their su®^ 
plumage, though common to both sexes, clearly h 
a nuptial character. Young swans are slate-colo> ire ’ 
whilst the mature birds are pure white ; but it would v 
superfluous to give additional instances. These ^ 
ences between the young and the old apparently , t 
pend, as in tiie two last classes, on the young h®^|^ 
retained a former or ancient state of plumage, which . 
been exchanged for a new plumage by the old of h 0 ^. 
sexes. When the adults are brightly coloured, we 
conclude from the remarks just made in relation to i ^ 
scarlet ibis and to many herons, and from the analog/ ^ 
the species in the first class, that such colours have h eL 
