olutionary process in its physical
or organic aspect. By the physiologist within his special and
well-defined universe of discourse they may be properly regarded as
epiphenomena; but by the naturalist in his more catholic survey of
nature they cannot be so regarded, and were not so regarded by Darwin.
Intelligence has contributed to evolution of which it is in a sense a
product.

The facts of observation or of inference which Darwin accepted are
these: Conscious experience accompanies some of the modes of animal
behaviour; it is concomitant with certain physiological processes;
these processes are the outcome of development in the individual and
evolution in the race; the accompanying mental processes undergo a
like development. Into the subtle philosophical questions which arise
out of the naive acceptance of such a creed it was not Darwin's
province to enter; "I have nothing to do," he said,[159] "with the
origin of the mental powers, any more than I have with that of life
itself." He dealt with the natural history of organisms, including not
only their structure but their modes of behaviour; with the natural
history of the states of consciousness which accompany some of their
actions; and with the relation of behaviour to experience. We will
endeavour to follow Darwin in his modesty and candour in making no
pretence to give ultimate explanations. But we must note one of the
implications of this self-denying ordinance of science. Development
and evolution imply continuity. For Darwin and 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 org