mammals, however, there is one group more teachable than the rest.
Monkeys, with their greater power of handling things, have also
more inquisitiveness and more capacity for sustained attention than
any other mammals; and the higher apes are fertile in varied
resources. The orang-outang and gorilla are for this reason
dreaded by other animals, and roam the undisputed lords of their
native forests. They have probably approached the critical point
where variations in intelligence, always important, have come to be
supremely important, so as to be seized by natural selection in
preference to variations in physical constitution. At some remote
epoch of the past--we cannot say just when or how--our half-human
forefathers reached and passed this critical point, and forthwith
their varied struggles began age after age to result in the
preservation of bigger and better brains, while the rest of their
bodies changed but little. This particular work of natural
selection must have gone on for an enormous length of time, and as
its result we see that while man remains anatomically much like an
ape, be has acquired a vastly greater brain with all that this
implies. Zoologically the distance is small between man and the
chimpanzee; psychologically it has become so great as to be
immeasurable.

But this steady increase of intelligence, as our forefathers began
to become human, carried with it a steady prolongation of infancy.
As mental life became more complex and various, as the things to be
learned kept ever multiplying, less and less could be done before
birth, more and more must be left to be done in the earlier years
of life. So instead of being born with a few simple capacities
thoroughly organized, man came at last to be born with the germs of
many complex capacities which were reserved to be unfolded and