The lemur, a primitive primate, can move about on its own shortly after birth and is soon able to eat adult food and fend for itself. The newborn monkey is dependent for several months; the infant baboon remains with its mother for several years.
The human baby is dependent for many years. He is subjected to a long period of learning and interaction with others before all the mammals, man is the most immature at birth and requires the longest period of development before he is capable of all the activities and skills characteristic of his species. In general, the higher on the phylogenetic scale the organism, the more complex its nervous system, and the longer the time required to reach maturity.
Adult behaviour and personality characteristics are shaped by events occurring during the early years of life. The saying “the child is father of the man” reflects this continuity between childhood and adulthood.
Thus, we can see that to understand the psychological processes of the human adult-his perceptions, patterns of thinking, motives, emotions, conflicts, and ways of coping with conflicts-we need to know how these processes originate and how they change over time.