on the fringe of
the region which seems to be concerned in mental operations. For reasons
which will appear presently, we may add that the centres for controlling
the muscles of the face and head are in the same region. Any finer
training or the use of the hands will develop the centre for the fore
limbs, and, on the principles, may react on the more important region of
the cortex. Hence in turning the fore foot into a hand, for climbing
and grasping purposes, the primitive Primate entered upon the path
of brain-development. Even the earliest Primates show large brains in
comparison with the small brains of their contemporaries.

It is a familiar fact in the animal world that when a certain group
enters upon a particular path of evolution, some members of the group
advance only a little way along it, some go farther, and some outstrip
all the others. The development of social life among the bees will
illustrate this. Hence we need not be puzzled by the fact that the
lemurs have remained at one mental level, the monkeys at another, and
the apes at a third. It is the common experience of life; and it is
especially clear among the various races of men. A group becomes fitted
to its environment, and, as long as its surroundings do not change, it
does not advance. A related group, in a different environment, receives
a particular stimulation, and advances. If, moreover, a group remains
unstimulated for ages, it may become so rigid in its type that it loses
the capacity to advance. It is generally believed that the lowest
races of men, and even some of the higher races like the Australian
aboriginals, are in this condition. We may expect this "unteachability"
in a far more stubborn degree in the anthropoid apes, which have been
adapted to an unchanging environment for a million years.

All that we need further suppose is--and it is one of the commonest
episodes in terrestrial life--that one branch of the Miocene
anthropoids, which were spread over a large part of the earth, received
some stimulus to change which its cousins did not experience. It is
sometimes suggested that social life was the great advantage which led
to the superior development of mind in man. But such evidence as there
is would lead us to suppose that primitive man was solitary, not social.
The anthropoid apes are not social, but live in families, and are very
unprogressive. On the other hand, the earliest remains of prehistoric
man give no indication of