The Descent of Man

some degree of beauty. From the many cases of
gradation in the amount of difference between
the sexes, and from the prevalence of the same
general type of coloration throughout the whole
of the same group, we may conclude that the
causes have generally been the same which
have determined the brilliant colouring of the
males alone of some species, and of both sexes
of other species.
As so many gorgeous butterflies inhabit the
tropics, it has often been supposed that they
owe their colours to the great heat and moisture
of these zones; but Mr. Bates (6. 'The Naturalist
on the Amazons,' vol. i. 1863, p. 19.) has
shown by the comparison of various closelyallied
groups of insects from the temperate and
tropical regions, that this view cannot be maintained;
and the evidence becomes conclusive
when brilliantly- coloured males and plaincoloured
females of the same species inhabit
the same district, feed on the same food, and