soon as it was seen that instinct, like other animal functions,
rested upon conditions many of which can be assigned, that
it does not spring into existence all at once in full per-
fection, but is subject, like other features of organic life,
to growth and change and possibly to decay, that it is not
always perfect or unerring, that no impassable gulf severs
it from intelligence, but rather that intelligence first arises
within the sphere of instinct--when instinct was thus
brought into relation with more commonplace facts, the
awe and mystery surrounding it were dissolved, and the
central feature of animal psychology became susceptible of
scientific treatment. No one supposes that all instincts
are explained, or are easy to understand in the present
state of our knowledge. The central conception of instinct
itself is not as clearly defined as might be desired. But
instinct is no longer a mysterious faculty which may at
once be set down as a sufficient explanation of anything in
the behaviour of animals that we do not understand.
Instinct cannot do anything and everything. It has limits
even if we have difficulties in drawing them with precision.
And secondly, its territory is not apart, but strictly con-
tinuous with other powers of organised beings. Instinct
in short is a product of evolution. It presides at a certain
phase, and has, all in due order, its beginning, its rise, its
culmination, and its decline.

To give the full proof of what I have said would be
merely to repeat or summarise the works of authors far
more competent to deal with the matter than myself. I
may merely advert briefly to the abundant evidence showing
that instinct is not always perfect in its working; that it
does not proceed on an unchangeable model; that it is on
occasion applied mistakenly, uselessly and injuriously; that
it is often incomplete at birth, and requires development;
and that, at any rate among the higher animals, it is so
interwoven with intelligence that the two factors become
exceedingly difficult to disentangle.

Nothing seems more instinctive than the impulse of the
young mammal to suck its mother's breast. Undoubtedly
there is an innate tendency to suck, and an impulse to suck
the breast. But there is no unerring inward guide leading

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