n action for the exclusive good of another of a
distinct species, yet each species tries to take advantage of the instincts
of others, as each takes advantage of the weaker bodily structure of
others. So again, in some few cases, certain instincts cannot be considered
as absolutely perfect; but as details on this and other such points are not
indispensable, they may be here passed over.

As some degree of variation in instincts under a state of nature, and the
inheritance of such variations, are indispensable for the action of natural
selection, as many instances as possible ought to be here given; but want
of space prevents me. I can only assert, that instincts certainly do
vary--for instance, the migratory instinct, both in extent and direction,
and in its total loss. So it is with the nests of birds, which vary partly
{212} in dependence on the situations chosen, and on the nature and
temperature of the country inhabited, but often from causes wholly unknown
to us: Audubon has given several remarkable cases of differences in the
nests of the same species in the northern and southern United States. Fear
of any particular enemy is certainly an instinctive quality, as may be seen
in nestling birds, though it is strengthened by experience, and by the
sight of fear of the same enemy in other animals. But fear of man is slowly
acquired, as I have elsewhere shown, by various animals inhabiting desert
islands; and we may see an instance of this, even in England, in the
greater wildness of all our large birds than of our small birds; for the
large birds have been most persecuted by man. We may safely attribute the
greater wildness of our large birds to this cause; for in uninhabited
islands large birds are not more fearful than small; and the magpie, so
wary in England, is tame in Norway, as is the hooded crow in Egypt.

That the general disposition of individuals of the same species, born in a
state of nature, is extremely diversified, can be shown by a multitude of
facts. Several cases also, could be given, of occasional and strange habits
in certain species, which might, if advantageous to the species, give rise,
through natural selection, to quite new instincts. But I am well aware that
these general statements, without facts given in detail, can produce but a
feeble effect on the reader's mind. I can only repeat my assurance, that I
do not speak without good evidence.

The possibility, or even probability, of inherited v