The Descent of Man

quired the habit of taking refuge from danger
in holes or crevices in the rocks.
With respect to the above groups in which the
females are conspicuously coloured and build
concealed nests, it is not necessary to suppose
that each separate species had its nidifying instinct
specially modified; but only that the early
progenitors of each group were gradually led
to build domed or concealed nests, and afterwards
transmitted this instinct, together with
their bright colours, to their modified descendants.
As far as it can be trusted, the conclusion
is interesting, that sexual selection together
with equal or nearly equal inheritance by both
sexes, have indirectly determined the manner
of nidification of whole groups of birds.
According to Mr. Wallace, even in the groups
in which the females, from being protected in
domed nests during incubation, have not had
their bright colours eliminated through natural
selection, the males often differ in a slight, and