Very few of the instincts are present at birth; most of them develop later in the child's life. Pillsbury says, "One may recognize the food-taking instincts, the vocal protests at discomfort, but relatively few others." This delay in the appearance of instincts and capacities is dependent upon the development of the nervous system. No one of them can appear until the connections between nerve centers are ready, making the path of discharge perfect. Just when these various nervous connections mature, and therefore just when the respective tendencies should appear, is largely unknown. In only a few of the most prominent and comparatively simple responses is it even approximately known. Holding the head up is accomplished about the fourth month, walking and talking somewhere near the twelfth, but the more complex the tendency and the more they involve intellectual factors, the greater is the uncertainty as to the time of development. We are told that fear is most prominent at about "three or four" years of age, spontaneous imitation "becomes very prominent the latter part of the first year," the gang instinct is characteristic of the preadolescent period, desire for adventure shows itself in early adolescence, altruism "appears in the early teens," and the sex instinct "after about a dozen years of life." The child of from four to six is largely sensory, from seven to nine he is motor, from then to twelve the retentive powers are prominent. In the adolescent period he is capable of thinking logically and reasoning, while maturity finds him a man of responsibilities and affairs. Although there is some truth in the belief that certain tendencies are more prominent at certain periods in the development of the child than at others, still it must be borne in mind that just when these optimum periods occur is not known. Three of the most important reasons for this lack of knowledge are: first, the fact that all inborn tendencies mature gradually and do not burst into being; second, we do not know how transitory they are; and, third, the fact of the great influence of environment in stimulating or repressing such capacities. Although the tendency to make collections is most prominent at nine, the beginnings of it may be found before the child is five. Moll finds that the sex instinct begins its development at about six years of age, despite the fact that it is always quoted as the adolescent instinct. Children in the kindergarten can think out their little problems purposively, even though reasoning is supposed to mark the high school pupil. The elements of most tendencies show themselves early in crude, almost unrecognizable, beginnings, and from these they grow gradually to maturity.