y to be an organist
and composer of church music; while the younger, possessing
considerable ability in scholarship and literature, was never able to
learn to sing or tell one tune from another. Being a clergyman, he
desired very much to be able to lead in singing, but he simply could
not learn. Such obstinate differences, persisting in spite of the same
home environment, must depend on native constitution.

Native constitution determines mental ability in two respects. It
fixes certain limits which the individual cannot {292} pass, no matter
how good his environment, and no matter how hard he trains himself;
and, on the positive side, it makes the individual responsive to
certain stimuli, and so gives him a start towards the development of
intelligence and of special aptitudes.

Intelligence and the Brain

There is certainly some connection between the brain and intelligent
behavior. While the spinal cord and brain stem vary according to the
size of the body, and the cerebellum with the motility of the species
of animal, the size of the cerebrum varies more or less closely with
the intelligence of the species. It does vary also with bodily size,
as illustrated by the whale and elephant, which have the largest
cerebrum of all animals, including man. But the monkey, which shows
more intelligence than most animals, has also a very large cerebrum
for his size of body; and the chimpanzee and gorilla, considerably
surpassing the ordinary monkeys in intelligence, have also a much
larger cerebrum. The cerebrum of man, in proportion to the size of his
body, far surpasses that of the chimpanzee or gorilla.

The cerebrum varies considerably in size from one human individual to
another. In some adults it is twice as large as in others, and the
question arises whether greater intelligence goes with a larger brain.
Now, it appears that an extremely small cerebrum spells idiocy; not
all idiots have small brains, but all men with extremely small brains
are idiots. The brain weight of quite a number of highly gifted men
has been measured in post-mortem examination, and many of these gifted
men have had a very large cerebrum. On the whole, the gifted
individual seems to have a large brain, but there are exceptions, and
the relationship between brain size and intelligence cannot be very
close. Other factors must enter, one factor being undoubtedly the
fineness {293} of the internal structure of the cortex. Brain function
depends o