ions as well as in the "general factors" of
intelligence.

Heredity of Intelligence and of Special Aptitudes

Let us now return to the question raised at the very outset of the
chapter, whether or not intelligence is a native trait. We then said
that the differing intelligence of different species of animals must
be laid to their native constitutions, but left the question open
whether the differing intelligence of human individuals was a matter
of heredity or of environment.

Intelligence is of course quite different from instinct, in that it
does not consist in ready-made native reactions. The intelligence of
an individual at any age depends on what he has learned previously.
But the factors in intelligent behavior--retentiveness, responsiveness
to relationships, persistence, etc.--may very well be native traits.

But what _evidence_ is there that the individual's degree of
intelligence is a native characteristic, like his height or color of
hair? The evidence is pretty convincing to most psychologists.

First, we have the fact that an individual's degree of intelligence is
an inherent characteristic, in the sense that it remains with him from
childhood to old age. Bright child, bright adult; dull child, dull
adult. That is the rule, and the exceptions are not numerous enough to
shake it. Many a dull child of well-to-do parents, in spite of great
pains taken with his education, is unable to escape from his inherent
limitations. The intelligence quotient remains fairly {290} constant
for the same child as he grows up, and stands for an inherent
characteristic of the individual, namely, the rate at which he
acquires knowledge and skill. Give two children the same environment,
physical and social, and you will see one child progress faster than
the other. Thus, among children who grow up in the same community,
playing together and going to the same schools, the more rapid mental
advance of some than of others is due to differences in native
constitution, and the IQ gives a measure of the native constitution in
this respect. There are exceptions, to be sure, depending on physical
handicaps such as deafness or disease, or on very bad treatment at
home, but in general the IQ can be accepted as representing a fact of
native constitution.

Another line of evidence for the importance of native constitution in
determining degrees of intelligence comes from the study of mental
resemblance among members of the same famil