The Descent of Man

her, so that the males alone can be distinguished,
yet the females of most species within the
same genus obviously differ from each other.
The differences, however, are rarely as great as
between the males. We see this clearly in the
whole family of the Gallinaceae: the females,
for instance, of the common and Japan pheasant,
and especially of the gold and Amherst
pheasant —of the silver pheasant and the wild
fowl—resemble one another very closely in
colour, whilst the males differ to an extraordinary
degree. So it is with the females of most of
the Cotingidae, Fringillidae, and many other
families. There can indeed be no doubt that, as
a general rule, the females have been less modified
than the males. Some few birds, however,
offer a singular and inexplicable exception;
thus the females of Paradisea apoda and P. papuana
differ from each other more than do
their respective males (7. Wallace, 'The Malay
Archipelago,' vol. ii. 1869, p. 394.); the female of
the latter species having the under surface pure