important ways--in the interest in sensory stimuli, usually discussed
under the head of curiosity, and in the delight in "being a cause" or
mental control. The interest in tastes, sounds, sights, touches, etc.,
merely for their own sake, is very evident in a baby. He spends most of
his waking time in just that enjoyment. Though more complex, it is still
strong when the child enters school, and for years any object of sense
which attracts his attention is material which arouses this instinct.
The second form in which the instinct for mental ability shows itself is
later in development and involves the secondary brain connections. It is
the satisfaction aroused by results of which the individual is the
cause. For example, the enjoyment of a child in seeing a ball swing or
hearing a whistle blown would be a manifestation of curiosity, while the
added interest which is always present when the child not only sees the
ball swing but swings it, not only hears the whistle but blows it
himself, is a result of the second tendency, that of joy in being a
cause. As the child grows older the same tendency shows itself on a
higher level when the materials dealt with, instead of being sensations
or percepts, are images or ideas. The interest in following out a train
of ideas to a logical conclusion, of building "castles in the air," of
making plans and getting results, all find their taproot in this
instinctive tendency towards mental activity.

In close connection with the general tendency towards physical activity
is the instinct of manipulation. From this crude root grows
constructiveness and destructiveness. As it shows itself at first it has
the elements of neither. The child inherits the tendency to respond by
"many different arm, hand, and finger movements to many different
objects"--poking, pulling, handling, tearing, piling, digging, and
dropping objects. Just what habits of using tools, and the like, will
grow out of this tendency will depend on the education and training it