iculties of the theory of
the Natural Selection of instincts--Neuter or sterile insects--Summary.

Many instincts are so wonderful that their development will probably
appear to the reader a difficulty sufficient to overthrow my whole
theory. I may here premise, that I have nothing to do with the origin of
the mental powers, any more than I have with that of life itself. We are
concerned only with the diversities of instinct and of the other mental
faculties in animals of the same class.

I will not attempt any definition of instinct. It would be easy to show
that several distinct mental actions are commonly embraced by this term;
but every one understands what is meant, when it is said that instinct
impels the cuckoo to migrate and to lay her eggs in other birds'
nests. An action, which we ourselves require experience to enable us to
perform, when performed by an animal, more especially by a very young
one, without experience, and when performed by many individuals in the
same way, without their knowing for what purpose it is performed, is
usually said to be instinctive. But I could show that none of these
characters are universal. A little dose of judgment or reason, as Pierre
Huber expresses it, often comes into play, even with animals low in the
scale of nature.

Frederick Cuvier and several of the older metaphysicians have compared
instinct with habit. This comparison gives, I think, an accurate notion
of the frame of mind under which an instinctive action is performed, but
not necessarily of its origin. How unconsciously many habitual actions
are performed, indeed not rarely in direct opposition to our conscious
will! yet they may be modified by the will or reason. Habits easily
become associated with other habits, with certain periods of time and
states of the body. When once acquired, they often remain constant
throughout life. Several other points of resemblance between instincts
and habits could be pointed out. As in repeating a well-known song,
so in instincts, one action follows another by a sort of rhythm; if a
person be interrupted in a song, or in repeating anything by rote, he is
generally forced to go back to recover the habitual train of thought: so
P. Huber found it was with a caterpillar, which makes a very complicated
hammock; for if he took a caterpillar which had completed its hammock
up to, say, the sixth stage of construction, and put it into a
hammock completed up only to the third stage,