Mental Evolution 425 
exercised a profound influence on this department of evolutionary 
thought. And, for those who follow Darwin’s lead, mental evolution 
is still in a measure subservient to organic evolution. Mental pro- 
cesses are the accompaniments or concomitants of the functional 
activity of specially differentiated parts of the organism. They are 
in some way dependent on physiological and physical conditions. 
But though they are not physical in their nature, and though it is 
difficult or impossible to conceive that they are physical in their 
origin, they are, for Darwin and his followers, factors in the evolu- 
tionary 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}, “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: conscious- 
ness 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 
1 Origin of Species (6th edit.), p. 205. 
