Contributions to the theory of natural selection. A series of essays ... By Alfred Russel Wallace ...

A THEORY OF BIRDS' NESTS. 231
Darwin informs me he has facts to support), I impute
the difference, in the great majority of cases, to the
greater or less need of protection in the female sex in
these groups of animals.
This need was seen to exist a century ago by
the Hon. Daines Barrington, who, in the article
already quoted (see p. 220), after alluding to the
fact that singing birds are all small, and suggesting
(but I think erroneously) that this may have arisen
from the difficulty larger birds would have in concealing themselves if they called the attention of
their enemies by loud notes, goes on thus — " I
should rather conceive it is for the same reason no
hen bird sings, because this talent would be still
more dangerous during incubation, which may possibly also account for the inferiority in point of
plumage." This is a curious anticipation of the
main idea on which this essay is founded. It has
been unnoticed for near a century, and my attention was only recently called to it by Mr. Darwin
himself.
Conclusion.
To some persons it will perhaps appear, that the
causes to which I impute so much of the external
aspect of nature are too simple, too insignificant,
and too unimportant for such a mighty work. But
I would ask them to consider, that the great object
of all the peculiarities of animal structure is to preserve the life of the individual, and to maintain the
existence of the species. Colour has hitherto been