Playful activity.
The kicking and throwing the arms about that we see in a well-rested baby is evidently satisfying on its own account. It leads to no result of consequence, except indeed that the exercise is good for the child's muscles and nerves. The movements, taken singly, are not uncoordinated by any means, but they accomplish no definite result, produce no definite change in external objects, and so seem random and aimless to adult eyes. It is impossible to specify the stimulus for any given movement, though probably stimuli from the interior of the body first arouse these responses. They are most apt to occur during the organic state of "euphoria", and tend to disappear during fatigue.
There is a counter-tendency to this tendency towards general activity, and that is inertia, the tendency towards inactivity or economy of effort. Most pronounced in fatigue, this also appears in lassitude and inert states that cannot be called fatigue because not brought on by excessive activity. After sleep, many people are inert, and require a certain amount of activity to "warm up" to the active condition. As the child grows older, the [{152}] "economy of effort" motive becomes stronger, and the random activity motive weaker, so that the adult is less playful and less responsive to slight stimuli. He has to have some definite goal to get up his energy, whereas the child is active by preference and just for the sake of activity.
During the first year or so of the child's life, his playful activity takes shape in several ways. First, out of the great variety of the random movements certain ones are picked out and fixed. This is the way with putting the hand into the mouth or drumming on the floor with the heels, and these instances illustrate the important fact that many learned acts develop out of the child's random activity. Without play activity there would be little work or accomplishment of the distinctively human type. Second, certain specific movements, those of locomotion and vocalization, appear with the ripening of the child's native equipment, and take an important place in his play. Third, his play comes to consist more and more of responses to external objects, instead of to internal stimuli as at first. The playful responses to external objects fall into two classes, according as they manipulate objects or simply examine them.
We have, then, a small group of instincts that is very closely related to the fundamental instinct of random activity.
Locomotion.
Evidence has already been presented [Footnote: [See p. 95.]] indicating that walking is instinctive and not learned, so that the human species is no exception to the rule that every species has its instinctive mode of locomotion. Simpler performances which enter into the very complex movement of walking make their appearance separately in the infant before being combined into walking proper. Holding up the head, sitting up, kicking with an alternate motion of the [{153}] two legs, and creeping, ordinarily precede walking and lead up to it.
What is the natural stimulus to locomotion? It is as difficult to say as it is to specify the stimulus in other forms of playful activity. From the fact that blind children are usually delayed in beginning to walk, we judge that the sense of sight furnishes some of the most effective stimuli to this response. Often the impulse attending locomotion is the impulse to approach some seen object, but probably some satisfaction is derived simply from the free movement itself. There certainly is no special emotion going with locomotion. Locomotion has, of course, plenty of "survival value", and might have been included among the organic instincts.
Some of the other varieties of human locomotion, such as running and jumping, are probably native. Others, like hopping and skipping, are probably learned. As to climbing, there is some evolutionary reason for suspecting that an instinctive tendency in this direction might persist in the human species, and certainly children show a great propensity for it; while the acrobatic ability displayed by those adults whose business leads them to continue climbing is so great as to raise the question whether the ordinary citizen is right when he thinks of man as essentially a land-living or surface-living animal. As to swimming, the theory is sometimes advanced that this too is a natural form of locomotion for man, and that, consequently, any one thrown into deep water will swim by instinct. Experiments of this sort result badly, the victim clutching frantically at any support, and sometimes dragging down with him the theorist who is administering this drastic sort of education. In short, the instinctive response of a man to being in deep water is the same as in other cases of sudden withdrawal of solid support; it consists in clinging and is attended by the emotion of fear.