one sex this being in the great majority of cases the male first
acquired through variation and sexual selection bright colours or other
ornaments, and transmitted them in various ways, in accordance with the
recognised laws of inheritance. Why variations have occurred at
different periods of life, even sometimes with species of the same
group, we do not know, but with respect to the form of transmission,
one important determining cause seems to be the age at which the
variations first appear.
From the principle of inheritance at corresponding ages, and from any
variations in colour which occurred in the males at an early age not
being then selected on the contrary being often eliminated as
dangerous whilst similar variations occurring at or near the period of
reproduction have been preserved, it follows that the plumage of the
young will often have been left unmodified, or but little modified. We
thus get some insight into the colouring of the progenitors of our
existing species. In a vast number of species in five out of our six
classes of cases, the adults of one sex or of both are bright coloured,
at least during the breeding-season, whilst the young are invariably
less brightly coloured than the adults, or are quite dull coloured; for
no instance is known, as far as I can discover, of the young of
dull-coloured species displaying bright colours, or of the young of
bright-coloured species being more brilliant than their parents. In the
fourth class, however, in which the young and the old resemble each
other, there are many species (though by no means all), of which the
young are bright-coloured, and as these form old groups, we may infer
that their early progenitors were likewise bright. With this exception,
if we look to the birds of the world, it appears that their beauty has
been much increased since that period, of which their immature plumage
gives us a partial record.
ON THE COLOUR OF THE PLUMAGE IN RELATION TO PROTECTION.
It will have been seen that I cannot follow Mr. Wallace in the belief
that dull colours, when confined to the females, have been in most
cases specially gained for the sake of protection. There can, however,
be no doubt, as formerly remarked, that both sexes of many birds have
had their colours modified, so as to escape the notice of their
enemies; or in some instances, so as to approach their prey unobserved,
just as owls have had their plumage rendered soft, that their flight
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