Orangutans (Pongo pygmaeus wurmbii) are great apes belonging to the rainforests of Indonesia. * Subadult males usually associate with females,particularly with adolescents,but are not generally aggressive towards other males. Adolescent females travel together,especially when age differences are minimal. This semi-solitary social system may have evolved as a result of a ripe fruit diet,scattered food distribution,and a lack of large arboreal predators.