instinctive actions. Such variations appear to arise from the same
unknown causes acting on the cerebral organisation, which induce slight
variations or individual differences in other parts of the body; and
these variations, owing to our ignorance, are often said to arise
spontaneously. We can, I think, come to no other conclusion with
respect to the origin of the more complex instincts, when we reflect on
the marvellous instincts of sterile worker-ants and bees, which leave
no offspring to inherit the effects of experience and of modified
habits.
Although, as we learn from the above-mentioned insects and the beaver,
a high degree of intelligence is certainly compatible with complex
instincts, and although actions, at first learnt voluntarily 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, which 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
(5. Contributions to the Theory of Natural Selection, 1870, p. 212.),
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