l and psychological evolution.
The first step towards this is to interpret the phenomena of
instinctive behaviour in terms of stimulation and response. It may be
well to take a particular case. Swimming on the part of a duckling is,
from the biological point of view, a typical example of instinctive
behaviour. Gently lower a recently hatched bird into water:
coordinated movements of the limbs follow in rhythmical sequence. The
behaviour is new to the individual though it is no doubt closely
related to that of walking, which is no less instinctive. There is a
group of stimuli afforded by the "presentation" which results from
partial immersion: upon this there follows as a complex response an
application of the functional activities in swimming; the sequence of
adaptive application on the appropriate presentation is determined by
racial preparation. We know, it is true, but little of the
physiological details of what takes place in the central nervous
system; but in broad outline the nature of the organic mechanism and
the manner of its functioning may at least be provisionally
conjectured in the present state of physiological knowledge. Similarly
in the case of the pecking of newly-hatched chicks; there is a visual
presentation, there is probably a cooeperating group of stimuli from
the alimentary tract in need of food, there is an adaptive application
of the activities in a definite mode of behaviour. Like data are
afforded in a great number of cases of instinctive procedure,
sometimes occurring very early in life, not infrequently deferred
until the organism is more fully developed, but all of them dependent
upon racial preparation. No doubt there is some range of variation in
the behaviour, just such variation as the theory of natural selection
demands. But there can be no question that the higher animals inherit
a bodily organisation and a nervous system, the functional working of
which gives rise to those inherited modes of behaviour which are
termed instinctive.

It is to be noted that the term "instinctive" is here employed in the
adjectival form as a descriptive heading under which may be grouped
many and various modes of behaviour due to racial preparation. We
speak of these as inherited; but in strictness what is transmitted
through heredity is the complex of anatomical and physiological
conditions under which, in appropriate circumstances, the organism so
behaves. So far the term "instinctive" has a restricte