d his followers
the continuity is organic through physical heredity. Apart from
speculative hypothesis, legitimate enough in its proper place but here
out of court, we know nothing of continuity of mental evolution as such:
consciousness appears afresh in each succeeding generation. Hence it is
that for those who follow Darwin's lead, mental evolution is and must
ever be, within his universe of discourse, subservient to organic
evolution. Only in so far as conscious experience, or its neural
correlate, effects some changes in organic structure can it influence
the course of heredity; and conversely only in so far as changes in
organic structure are transmitted through heredity, is mental evolution
rendered possible. Such is the logical outcome of Darwin's teaching.

Those who abide by the cardinal results of this teaching are bound to
regard all behaviour as the expression of the functional activities
of the living tissues of the organism, and all conscious experience
as correlated with such activities. For the purposes of scientific
treatment, mental processes are one mode of expression of the same
changes of which the physiological processes accompanying behaviour
are another mode of expression. This is simply accepted as a fact
which others may seek to explain. The behaviour itself is the adaptive
application of the energies of the organism; it is called forth by some
form of presentation or stimulation brought to bear on the organism by
the environment. This presentation is always an individual or personal
matter. But in order that the organism may be fitted to respond to the
presentation of the environment it must have undergone in some way
a suitable preparation. According to the theory of evolution this
preparation is primarily racial and is transmitted through heredity.
Darwin's main thesis was that the method of preparation is predominantly
by natural selection. Subordinate to racial preparation, and always
dependent thereon, is individual or personal preparation through
some kind of acquisition; of which the guidance of behaviour through
individually won experience is a typical example. We here introduce
the mental factor because the facts seem to justify the inference. Thus
there are some modes of behaviour which are wholly and solely dependent
upon inherited racial preparation; there are other modes of behaviour
which are also dependent, in part at least, on individual preparation.
In the former case the beh