Social behavior in 6 spp. of monkeys and apes was studied. It is suggested that the society of subhuman primates may have been evolved in response to selection imposed by the behavior of predators. The considerable disruptive forces present in heterosexual groups are counteracted by attractive forces, including the attraction of males for females in spp. where sexual receptivity is prolonged, and the attraction of males for each other arising out of their awareness of the potential threat of the more dominant individuals.