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. {154} Vocalization. Crying at birth proves voice-production to be a native response, but we are more interested just here in the playful cooing and babbling that appear when the child is a few weeks or months old. This cheerful vocalization is also instinctive, in all probability, since the baby makes it before he shows any signs of responding imitatively to the voices of other people. It seems to be one form of the random activity that goes with euphoria. The child derives satisfaction not so much from the muscular activity of vocalization as from the sounds that he produces, so that deaf children, who begin to babble much like other children, lag behind them as the months go by, from not deriving this auditory satisfaction from the vocal activity. Though whistling, blowing a horn, shaking a rattle and beating a drum are not native responses, it is clear that the child naturally enjoys producing sounds of various sorts. The baby's cheerful babbling is the instinctive basis on which his speech later develops through a process of learning. Manipulation. While the first random activity of the baby has nothing to do with external objects, but simply consists of free movements of the arms and legs, after a time these give place to manipulation of objects. The baby turns things about, pulls and pushes them, drops them, throws them, pounds with them. Thus he acquires skill in handling things and also learns how things behave. This form of playful activity contains the germ of constructiveness and of inventiveness, and will come into view again under the head of "imagination." Exploration or curiosity.