"We belong to that order of mammals, the primates, distinguished by its propensity for repeated single litters, intense parental care, long life-spans, late sexual maturity, and a complex and extensive social existence... Our protracted biological and psychological helplessness, which extends well into the third year of life, intensifies the bond between infant and parents, making possible a sense of generational continuity. In contrast to other primates these bonds are not obliterated after sexual maturity."