If we set aside the Java man, as
a possible survivor of an earlier phase, we should still have to
say that, much more than a million years after his departure from
the chimpanzee level, man had merely advanced far enough to chip
stone implements; because we find no other trace whatever of
intelligence than this until near the close of the Palaeolithic
period. If there is any mystery, it is in the slowness of man's
development.
Let us further recollect that it is a common occurrence in the
calendar of life for a particular organ to be especially
developed in one member of a particular group more than in the
others. The trunk of the elephant, the neck of the giraffe, the
limbs of the horse or deer, the canines of the satire-toothed
tiger, the wings of the bat, the colouring of the tiger, the
horns of the deer, are so many examples in the mammal world
alone. The brain is a useful organ like any other, and it is easy
to conceive that the circumstances of one group may select it
just as the environment of another group may lead to the
selection of speed, weapons, or colouring. In fact, as we saw,
there was so great and general an evolution of brain in the
Tertiary Era that our modern mammals quite commonly have many
times the brain of their Tertiary ancestors.
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