species, the male differs from the female; but the difference is
confined chiefly to the under surface of the plumage, which is
concealed when the bird crouches on the ground; the head and back being
of the same sand-coloured hue in the two sexes. So that in these ten
species the upper surfaces of both sexes have been acted on and
rendered alike, through natural selection, for the sake of protection;
whilst the lower surfaces of the males alone have been diversified,
through sexual selection, for the sake of ornament. Here, as both sexes
are equally well protected, we clearly see that the females have not
been prevented by natural selection from inheriting the colours of
their male parents; so that we must look to the law of sexually-limited
transmission.
In all parts of the world both sexes of many soft-billed birds,
especially those which frequent reeds or sedges, are obscurely
coloured. No doubt if their colours had been brilliant, they would have
been much more conspicuous to their enemies; but whether their dull
tints have been specially gained for the sake of protection seems, as
far as I can judge, rather doubtful. It is still more doubtful whether
such dull tints can have been gained for the sake of ornament. We must,
however, bear in mind that male birds, though dull-coloured, often
differ much from their females (as with the common sparrow), and this
leads to the belief that such colours have been gained through sexual
selection, from being attractive. Many of the soft-billed birds are
songsters; and a discussion in a former chapter should not be
forgotten, in which it was shewn that the best songsters are rarely
ornamented with bright tints. It would appear that female birds, as a
general rule, have selected their mates either for their sweet voices
or gay colours, but not for both charms combined. Some species, which
are manifestly coloured for the sake of protection, such as the
jack-snipe, woodcock, and night-jar, are likewise marked and shaded,
according to our standard of taste, with extreme elegance. In such
cases we may conclude that both natural and sexual selection have acted
conjointly for protection and ornament. Whether any bird exists which
does not possess some special attraction, by which to charm the
opposite sex, may be doubted. When both sexes are so obscurely coloured
that it would be rash to assume the agency of sexual selection, and
when no direct evidence can be advanced shewing that such colours serve
as a protection, it is best to own complete ignorance of the cause, or,
which comes to nearly the same thing, to attribute the result to the
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