es 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, he might truly be said to have done so
instinctively. But it would be the most 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 thus acquired.

It will be universally admitted that instincts are as important as
corporeal structure 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 may
be 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 of quite
subordinate importance to the effects of the natural selection of what
may be called accidental 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 the slow and gradual accumulation of numerous, slight, yet
profitable, variations. Hence, as in the case of corporeal structures,
we ought to find in nature, not the actual transitional gradations by
which each complex instinct has been acquired--for these could be found
only in the lineal ancestors of each species--but we ought to find in
the collateral lines of descent some evidence of such gradations; or
we ought at least to be able to show that gradations of some kind are
possible; and this we certainly can do. I have been surprised to find,
making allowance for the instincts of animals having been but little
observed except in Europe and North America, and for no instinct being
known amongst extinct