The Descent of Man

progenitors of these two species, we should
probably see the adults dark-coloured. I infer
that this would be the case, from the analogy of
many other birds, which are dark whilst young,
and when adult are white; and more especially
from the case of the Ardea gularis, the colours
of which are the reverse of those of A. asha, for
the young are dark-coloured and the adults
white, the young having retained a former state
of plumage. It appears therefore that, during a
long line of descent, the adult progenitors of
the Ardea asha, the Buphus, and of some allies,
have undergone the following changes of colour:
first, a dark shade; secondly, pure white;
and thirdly, owing to another change of fashion
(if I may so express myself), their present slaty,
reddish, or golden-buff tints. These successive
changes are intelligible only on the principle of
novelty having been admired by birds for its
own sake.