g reached a certain state of development.

The maturing of an instinct depends upon both age and use, that is to
say, upon the age of the animal and the amount of use or exercise that
the instinctive activity has had. The most important factor, however,
seems to be age. While our knowledge of the dependence of an instinct
upon the age of the animal is not quite so definite in the case of human
instincts, the matter has been worked out in the case of chickens.

The experiment was as follows: Chickens were taken at the time of
hatching, and some allowed to peck from the first, while others were
kept in a dark room and not allowed to peck. When the chickens were
taken out of the dark room at the end of one, two, three, and four days,
it was found that in a few hours they were pecking as well as those
that had been pecking from birth. It seems probable, if we may judge
from our limited knowledge, that in the human child, activities are for
the most part dependent upon the age of the child, and upon the state of
development of the nervous system and of the organs of the body.

=Significance of Inherited Tendencies.= Although human nature is very
complex, although human action nearly always has some element of habit
in it, nevertheless, inborn tendencies are throughout life powerful
factors in determining action. This will at once be apparent if we
consider how greatly we are influenced by anger, jealousy, love, fear,
and competition. Now we do not have to learn to be jealous, to hate, to
love, to be envious, to fight, or to fear. These are emotions common to
all members of the human race, and their expression is an inborn
tendency. Throughout life no other influences are so powerful in
determining our action as are these. So, although most of our detailed
actions in life are habits which we learn or acquire, the fundamental
influences which decide the course of our action are inherited
tendencies.

=Classification of Instincts.= For convenience in treatment the instincts
are grouped in classes. Those instincts most closely related to
individual survival are called _individualistic_ instincts. Those more
closely related to the survival of the group are called _socialistic_.
Those individualistic tendencies growing out of periodic changes of the
environment may be called _environmental_ instincts. Those closely
related to human infancy, adapting and adjusting the child to the world
in which he lives, may be called _adaptive