The Destiny of Man | Page 8

are repeated without variation during the
whole lifetime of the individual, there is probably little if any
consciousness. It is an essential prerequisite of consciousness that there
should be a period of delay or tension between the receipt of an
impression and the determination of the consequent movement.
Diminish this period of delay and you diminish the vividness of
consciousness. A familiar example will make this clear. When you are
learning to play a new piece of music on the piano, especially if you do
not read music rapidly, you are intensely conscious of each group of

notes on the page, and of each group of keys that you strike, and of the
relations of the one to the other. But when you have learned the piece
by heart, you think nothing of either notes or keys, but play
automatically while your attention is concentrated upon the artistic
character of the music. If somebody thoughtlessly interrupts you with a
question about Egyptian politics, you go on playing while you answer
him politely. That is, where you had at first to make a conscious act of
volition for each movement, the whole group of movements has now
become automatic, and volition is only concerned in setting the process
going. As the delay involved in the perception and the movement
disappears, so does the consciousness of the perception and the
movement tend to disappear. Consciousness implies perpetual
discrimination, or the recognition of likenesses and differences, and
this is impossible unless impressions persist long enough to be
compared with one another. The physical organs in connection with
whose activity consciousness is manifested are the upper and outer
parts of the brain,--the cerebrum and cerebellum. These organs never
receive impressions directly from the outside world, but only from
lower nerve-centres, such as the spinal cord, the medulla, the optic
lobes, and other special centres of sensation. The impressions received
by the cerebrum and cerebellum are waves of molecular disturbance
sent up along centripetal nerves from the lower centres, and presently
drafted off along centrifugal nerves back to the lower centres, thus
causing the myriad movements which make up our active life. Now
there is no consciousness except when molecular disturbance is
generated in the cerebrum and cerebellum faster than it can be drafted
off to the lower centres.[5] It is the surplus of molecular disturbance
remaining in the cerebrum and cerebellum, and reflected back and forth
among the cells and fibres of which these highest centres are composed,
that affords the physical condition for the manifestation of
consciousness. Memory, emotion, reason, and volition begin with this
retention of a surplus of molecular motion in the highest centres. As we
survey the vertebrate sub-kingdom of animals, we find that as this
surplus increases, the surface of the highest centres increases in area. In
the lowest vertebrate animal, the amphioxus, the cerebrum and
cerebellum do not exist at all. In fishes we begin to find them, but they
are much smaller than the optic lobes. In such a highly organized fish

as the halibut, which weighs about as much as an average-sized man,
the cerebrum is smaller than a melon-seed. Continuing to grow by
adding concentric layers at the surface, the cerebrum and cerebellum
become much larger in birds and lower mammals, gradually covering
up the optic lobes. As we pass to higher mammalian forms, the growth
of the cerebrum becomes most conspicuous, until it extends backwards
so far as to cover up the cerebellum, whose functions are limited to the
conscious adjustment of muscular movements. In the higher apes the
cerebrum begins to extend itself forwards, 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,