The Descent of Man

I have as yet only referred to the species in
which the males are brighter coloured than the
females, and I have attributed their beauty to
the females for many generations having chosen
and paired with the more attractive males.
But converse cases occur, though rarely, in
which the females are more brilliant than the
males; and here, as I believe, the males have
selected the more beautiful females, and have
thus slowly added to their beauty. We do not
know why in various classes of animals the
males of some few species have selected the
more beautiful females instead of having gladly
accepted any female, as seems to be the general
rule in the animal kingdom: but if, contrary to
what generally occurs with the Lepidoptera,
the females were much more numerous than
the males, the latter would be likely to pick out
the more beautiful females. Mr. Butler shewed
me several species of Callidryas in the British
Museum, in some of which the females equalled,
and in others greatly surpassed the males