The individual has a complete set of animal needs and accompanying drives; both primary and secondary, both the need for water, food and sex, and also for knowledge, activity and survival. As these come in one at a time they preempt all other concerns. And there are approximate dates for them. Infants are born hungry, in puberty sex begins to take a position of preeminence, activity is primary for the adolescent, knowledge for the youth, activity in its constructive phase for the mature, and survival for the old. The individual has all of these drives all of the time, but there are periods of preeminence for particular drives, and these also are periods of conflict and adjustment. He has to learn to live with the new self he has developed into, and this problem is perennial from infancy to senility. The changes are challenges which have to be met and from which there are important consequences.