can soon through habit be performed with the quickness and certainty of
a reflex action, yet it is not improbable that there is a certain amount
of interference between the development of free intelligence and of
instinct, since the latter implies some inherited modification of the
brain. Little is known about the functions of the brain, but we can
perceive that as the intellectual powers become highly developed the
various parts of the brain must be connected by very intricate channels
of the freest intercommunication; and as a consequence each separate
part would perhaps tend to be less well fitted to answer to particular
sensations or associations in a definite and inherited--that is,
instinctive--manner. There seems even to exist some relation between a
low degree of intelligence and a strong tendency to the formation of
fixed, though not inherited, habits; for as a sagacious physician
remarked to me, persons who are slightly imbecile tend to act in
everything by routine or habit; and they are rendered much happier if
this is encouraged.

I have thought this digression worth giving, because we may easily
underrate the mental powers of the higher animals, and especially of
man, when we compare their actions founded on the memory of past events,
on foresight, reason and imagination, with exactly similar actions
instinctively performed by the lower animals; in this latter case the
capacity of performing such actions has been gained, step by step,
through the variability of the mental organs and natural selection,
without any conscious intelligence on the part of the animal during each
successive generation. No doubt, as Mr. Wallace has argued, much of the
intelligent work done by man is due to imitation and not to reason; but
there is this great difference between his actions and many of those
performed by the lower animals, namely, that man cannot, on his first
trial, make, for instance, a stone hatchet or a canoe, through his power