the preservation of the young?

The violence of this natural love is exemplified by a very barbarous
experiment; which I shall quote at length, as I find it in an excellent
author, and hope my readers will pardon the mentioning such an instance
of cruelty, because there is nothing can so effectually show the
strength of that principle in animals of which I am here speaking. 'A
person who was well skilled in dissections opened a bitch, and as she
lay in the most exquisite tortures, offered her one of her young
puppies, which she immediately fell a licking; and for the time seemed
insensible of her own pain: On the removal, she kept her eye fixt on it,
and began a wailing sort of cry, which seemed rather to proceed from the
loss of her young one, than the sense of her own torments.'

But, notwithstanding this natural love in brutes is much more violent
and intense than in rational creatures, providence has taken care that
it should be no longer troublesome to the parent than it is useful to
the young; for so soon as the wants of the latter cease, the mother
withdraws her fondness, and leaves them to provide for themselves: And,
what is a very remarkable circumstance in this part of instinct, we find
that the love of the parent may be lengthened out beyond its usual time,
if the preservation of the species requires it; as we may see in birds
that drive away their young as soon as they are able to get their
livelihood, but continue to feed them if they are tied to the nest, or
confined within a cage, or by any other means appear to be out of a
condition of supplying their own necessities.

This natural love is not observed in animals to ascend from the young to
the parent, which is not at all necessary for the continuance of the
species; nor indeed in reasonable creatures does it rise in any