the caterpillar simply
re-performed the fourth, fifth, and sixth stages of construction.
If, however, a caterpillar were taken out of a hammock made up, for
instance, to the third stage, and were put into one finished up to the
sixth stage, so that much of its work was already done for it, far from
deriving any benefit from this, it was much embarrassed, and, in order
to complete its hammock, seemed forced to start from the third stage,
where it had left off, and thus tried to complete the already finished
work.

If we suppose any habitual action to become inherited--and it can be
shown that this does sometimes happen--then the resemblance between what
originally was a habit and an instinct becomes so close as not to be
distinguished. If Mozart, instead of playing the pianoforte at three
years old with wonderfully little practice, had played a tune with no
practice at all, be might truly be said to have done so instinctively.
But it would be a serious error to suppose that the greater number
of instincts have been acquired by habit in one generation, and then
transmitted by inheritance to succeeding generations. It can be clearly
shown that the most wonderful instincts with which we are acquainted,
namely, those of the hive-bee and of many ants, could not possibly have
been acquired by habit.

It will be universally admitted that instincts are as important as
corporeal structures for the welfare of each species, under its present
conditions of life. Under changed conditions of life, it is at least
possible that slight modifications of instinct might be profitable to a
species; and if it can be shown that instincts do vary ever so little,
then I can see no difficulty in natural selection preserving and
continually accumulating variations of instinct to any extent that was
profitable. It is thus, as I believe, that all the most complex and
wonderful instincts have originated. As modifications of corporeal
structure arise from, and are increased by, use or habit, and are
diminished or lost by disuse, so I do not doubt it has been with
instincts. But I believe that the effects of habit are in many cases of
subordinate importance to the effects of the natural selection of
what may be called spontaneous variations of instincts;--that is of
variations produced by the same unknown causes which produce slight
deviations of bodily structure.

No complex instinct can possibly be produced through natural selection,
except by th