ds, and this goes on in the human race. The
cranial capacity of the European exceeds that of the Australian by forty
cubic inches, or nearly four times as much as that by which the
Australian exceeds the gorilla; and the expansion is almost entirely in
the upper and anterior portions. But the increase of the cerebral
surface is shown not only in the general size of the organ, but to a
still greater extent in the irregular creasing and furrowing of the
surface. This creasing and furrowing begins to occur in the higher
mammals, and in civilized man it is carried to an astonishing extent.
The amount of intelligence is correlated with the number, the depth, and
the irregularity of the furrows. A cat's brain has a few symmetrical
creases. In an ape the creases are deepened into slight furrows, and
they run irregularly, somewhat like the lines in the palm of your hand.
With age and experience the furrows grow deeper and more sinuous, and
new ones appear; and in man these phenomena come to have great
significance. The cerebral surface of a human infant is like that of an
ape. In an adult savage, or in a European peasant, the furrowing is
somewhat marked and complicated. In the brain of a great scholar, the
furrows are very deep and crooked, and hundreds of creases appear which
are not found at all in the brains of ordinary men. In other words, the
cerebral surface of such a man, the seat of conscious mental life, has
become enormously enlarged in area; and we must further observe that it
goes on enlarging in some cases into extreme old age.[6]

Putting all these facts together, it becomes plain that in the lowest
animals, whose lives consist of sundry reflex actions monotonously
repeated from generation to generation, there can be nothing, or next to
nothing, of what we know as consciousness. It is only when the life
becomes more complicated and various, so that reflex action can no
longer determine all its movements and the higher nerve-centres begin to
be evolved, that the dawning of consciousness is reached. But with the
growth of the higher centres the capacities of action become so various
and indeterminate that definite direction is not given to them until
after birth. The creature begins life as an infant, with its partially
developed cerebrum representing capabilities which it is left for its
individual experience to bring forth and modify.

VI.

Lengthening of Infancy, and Concomitant Increase of Brain-Surface