a or orang, is closely connected with his
higher mental powers." "With respect to the lower animals," he
says,[187] "M. E. Lartet,[188] by comparing the crania of tertiary and
recent mammals belonging to the same groups, has come to the
remarkable conclusion that the brain is generally larger and the
convolutions are more complex in the more recent form."

Sir E. Ray Lankester has sought to express in the simplest terms the
implications of the increase in size of the cerebrum. "In what," he
asks, "does the advantage of a larger cerebral mass consist?" "Man,"
he replies, "is born with fewer ready-made tricks of the
nerve-centres--these performances of an inherited nervous mechanism so
often called by the ill-defined term 'instincts'--than are the monkeys
or any other animal. Correlated with the absence of inherited
ready-made mechanism, man has a greater capacity of developing in the
course of his individual growth similar nervous mechanisms (similar
to but not identical with those of 'instinct') than any other
animal.... The power of being educated--'educability' as we may term
it--is what man possesses in excess as compared with the apes. I think
we are justified in forming the hypothesis that it is this
'educability' which is the correlative of the increased size of the
cerebrum." There has been natural selection of the more educable
animals, for "the character which we describe as 'educability' can be
transmitted, it is a congenital character. But the _results_ of
education can _not_ be transmitted. In each generation they have to be
acquired afresh, and with increased 'educability' they are more
readily acquired and a larger variety of them.... The fact is that
there is no community between the mechanisms of instinct and the
mechanisms of intelligence, and that the latter are later in the
history of the evolution of the brain than the former and can only
develop in proportion as the former become feeble and defective."[189]

In this statement we have a good example of the further development of
views which Darwin foreshadowed but did not thoroughly work out. It
states the biological case clearly and tersely. Plasticity of
behaviour in special accommodation to special circumstances is of
survival value; it depends upon acquired characters; it is correlated
with increase in size and complexity of the cerebrum; under natural
selection therefore the larger and more complex cerebrum as the organ
of plastic behaviour ha