the female, are brilliantly coloured. This is well exemplified with the
pheasants, in which the male is generally so much more brilliant than
the female; but with the Eared and Cheer pheasants (Crossoptilon
auritum and Phasianus wallichii) the sexes closely resemble each other
and their colours are dull. We may go so far as to believe that if any
part of the plumage in the males of these two pheasants had been
brilliantly coloured, it would not have been transferred to the
females. These facts strongly support Mr. Wallace s view that with
birds which are exposed to much danger during incubation, the
transference of bright colours from the male to the female has been
checked through natural selection. We must not, however, forget that
another explanation, before given, is possible; namely, that the males
which varied and became bright, whilst they were young and
inexperienced, would have been exposed to much danger, and would
generally have been destroyed; the older and more cautious males, on
the other hand, if they varied in a like manner, would not only have
been able to survive, but would have been favoured in their rivalry
with other males. Now variations occurring late in life tend to be
transmitted exclusively to the same sex, so that in this case extremely
bright tints would not have been transmitted to the females. On the
other hand, ornaments of a less conspicuous kind, such as those
possessed by the Eared and Cheer pheasants, would not have been
dangerous, and if they appeared during early youth, would generally
have been transmitted to both sexes.
In addition to the effects of the partial transference of characters
from the males to the females, some of the differences between the
females of closely allied species may be attributed to the direct or
definite action of the conditions of life. (11. See, on this subject,
chap. xxiii. in the Variation of Animals and Plants under
Domestication. ) With the males, any such action would generally have
been masked by the brilliant colours gained through sexual selection;
but not so with the females. Each of the endless diversities in plumage
which we see in our domesticated birds is, of course, the result of
some definite cause; and under natural and more uniform conditions,
some one tint, assuming that it was in no way injurious, would almost
certainly sooner or later prevail. The free intercrossing of the many
individuals belonging to the same species would ultimately tend to make
any change of colour, thus induced, uniform in character.
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