gy_, 2nd edition, 1920.

Another full treatment is that of Titchener, in his _Textbook of
Psychology_, 1909, pp. 265-302.

On the topic of distraction, see John J. B. Morgan's _Overcoming of
Distraction and Other Resistances_, 1916.

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CHAPTER XII

INTELLIGENCE

HOW INTELLIGENCE IS MEASURED, WHAT IT CONSISTS IN AND EVIDENCE OF ITS
BEING LARGELY A MATTER OF HEREDITY

Before leaving the general topic of native traits and passing to the
process of learning or acquiring traits, we need to complete our
picture of the native mental constitution by adding intelligence to
reflex action, instinct, emotion, feeling, sensation and attention.
Man is an intelligent animal by nature. The fact that he is the most
intelligent of animals is due to his native constitution, as the fact
that, among the lower animals, some species are more intelligent than
others is due to the native constitution of each species. A rat has
more intelligence than a frog, a dog than a rat, a monkey than a dog,
and a man than a monkey, because of their native constitutions as
members of their respective species.

But the different individuals belonging to the same species are not
all equal in intelligence, any more than in size or strength or
vitality. Some dogs are more intelligent than others, and the same is
notably true of men. Now, are these differences between members of the
same species due to heredity or environment? This question we can
better approach after considering the methods by which psychologists
undertake to measure intelligence; and an analysis of these methods
may also serve to indicate what is included under the term
"intelligence".

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Intelligence Tests

Not far from the year 1900 the school authorities of the city of
Paris, desiring to know whether the backwardness of many children in
school resulted from inattention, mischievousness and similar
difficulties of a moral nature, or from genuine inability to learn,
put the problem into the hands of Alfred Binet, a leading psychologist
of the day; and within a few years thereafter he and a collaborator
brought out the now famous Binet-Simon tests for intelligence. In
devising these tests, Binet's plan was to leave school knowledge to
one side, and look for information and skill picked up by the child
from his elders and playmates in the ordinary experience of life.
Further, Binet wisely decided not to seek for any _single_ test for so
broad a matter as intelligen