The Descent of Man

white, whilst the female P. apoda is deep
brown beneath. So, again, as I hear from Professor
Newton, the males of two species of
Oxynotus (shrikes), which represent each other
in the islands of Mauritius and Bourbon (8.
These species are described with coloured figures,
by M. F. Pollen, in 'Ibis,' 1866, p. 275.), differ
but little in colour, whilst the females differ
much. In the Bourbon species the female appears
to have partially retained an immature
condition of plumage, for at first sight she
"might be taken for the young of the Mauritian
species." These differences may be compared
with those inexplicable ones, which occur independently
of man's selection in certain subbreeds
of the game-fowl, in which the females
are very different, whilst the males can hardly
be distinguished. (9. 'Variation of Animals,' etc.,
vol. i. p. 251.)
As I account so largely by sexual selection for
the differences between the males of allied spe-