Chimps apparently live in troops of between 20 and 50 animals. Within these troops, they form small groups of varying composition; the most basic group consists of females spending much time together, who often turn out to be mother and daughter or sisters. Mother and offspring live together consistently, at least for the first four or five years of life, longer than with any other primate except man. During this time the young learn from their mother and from other chimps, all the complicated acquired behaviors of chimpanzee adult life. Life for the young chimpanzee is relaxed and tolerant, and an infant will spend much of its time playing with other infants, with its mother and with its brothers and sisters. After this five-year initial period, contacts with the mother are still maintained, particularly by daughters. Even sons return from time to time from their wanderings to greet their mothers affectionately.

  (From David Pilbeam, The Evolution of Man, quoted in M.  Swam, Understanding Ideas. Cambridge:  CUP,  1976,  pp. 13-14).