The higher reaches of the inclined plane of behaviour show intelligence
in the strict sense. They include those kinds of behaviour which cannot
be described without the suggestion that the animal makes some sort of
perceptual inference, not only profiting by experience but learning by
ideas. Such intelligent actions show great individual variability; they
are plastic and adjustable in a manner rarely hinted at in connection
with instincts where routine cannot be departed from without the
creature being nonplussed; they are not bound up with particular
circumstances as instinctive actions are, but imply an appreciative
awareness of relations.
When there is an experimenting with general ideas, when there is
_conceptual_ as contrasted with _perceptual_ inference, we speak of
Reason, but there is no evidence of this below the level of man. It is
not, indeed, always that we can credit man with rational conduct, but he
has the possibility of it ever within his reach.
Animal instinct and intelligence will be illustrated in another part of
this work. We are here concerned simply with the general question of the
evolution of behaviour. There is a main line of tentative experimental
behaviour both below and above the level of intelligence, and it has
been part of the tactics of evolution to bring about the hereditary
enregistration of capacities of effective response, the advantages being
that the answers come more rapidly and that the creature is left free,
if it chooses, for higher adventures.
There is no doubt as to the big fact that in the course of evolution
animals have shown an increasing complexity and masterfulness of
behaviour, that they have become at once more controlled and more
definitely free agents, and that the inner aspect of the
behaviour--experimenting, learning, thinking, feeling, and willing--has
come to count for more and more.
§ 3