210 
SEXUAL SELECTION : BIKDS. 
Part II. 
Before proceeding, I may remark that under the 
present and two next classes of cases the facts are so 
complex, and the conclusions so doubtful, that any one 
who feels no especial interest in the subject had better 
pass them over. 
The brilliant or conspicuous colours which charac- 
terise many birds in the present class, can rarely 
or never be of service to them as a protection ; 
so that they have probably been gained by the males 
through sexual selection, and then transferred to the 
females and the young. It is, however, possible that 
the males may have selected the more attractive fe- 
males ; and if these transmitted their characters to 
their offspring of both sexes, the same results would 
follow as from the selection of the more attractive 
males by the females. But there is some evidence that 
this contingency has rarely, if ever, occurred in any of 
those groups of birds, in which the sexes are generally 
alike ; for if even a few of the successive variations had 
failed to be transmitted to both sexes, the females 
would have exceeded to a slight degree the males 
in beauty. Exactly the reverse occurs under nature ; 
for in almost every large group, in which the sexes 
generally resemble each other, the males of some few 
species are in a slight degree more brightly coloured 
than the females. It is again possible that the females 
may have selected the more beautiful males, these males 
having reciprocally selected the more beautiful females ; 
but it is doubtful whether this double process of selec- 
tion would be likely to occur, owing to the greater 
eagerness of one sex than the other, and whether it 
would be more efficient than selection on one side 
alone. It is, therefore, the most probable view that 
sexual selection has acted, in the present class, as far 
as ornamental characters are concerned, in accordance 
