The Descent of Man

give more pleasure in their performance, and
more distress in their prevention, than others;
or, which is probably quite as important, they
are, through inheritance, more persistently followed,
without exciting any special feeling of
pleasure or pain. We are ourselves conscious
that some habits are much more difficult to
cure or change than others. Hence a struggle
may often be observed in animals between different
instincts, or between an instinct and some
habitual disposition; as when a dog rushes
after a hare, is rebuked, pauses, hesitates, pursues
again, or returns ashamed to his master; or
as between the love of a female dog for her
young puppies and for her master,—for she
may be seen to slink away to them, as if half
ashamed of not accompanying her master. But
the most curious instance known to me of one
instinct getting the better of another, is the migratory
instinct conquering the maternal instinct.
The former is wonderfully strong; a confined
bird will at the proper season beat her