The Descent of Man

can thus be accounted for. It was further shewn
that if a male bird varied by becoming brighter
whilst young, such variations would be of no
service until the age for reproduction had arrived,
and there was competition between rival
males. But in the case of birds living on the
ground and commonly in need of the protection
of dull colours, bright tints would be far
more dangerous to the young and inexperienced
than to the adult males. Consequently the
males which varied in brightness whilst young
would suffer much destruction and be eliminated
through natural selection; on the other
hand, the males which varied in this manner
when nearly mature, notwithstanding that they
were exposed to some additional danger, might
survive, and from being favoured through
sexual selection, would procreate their kind. As
a relation often exists between the period of
variation and the form of transmission, if the
bright-coloured young males were destroyed
and the mature ones were successful in their