Homosexual behavior in wild sumatran orangutans (Pongo pygmaeus abelii)

Wild male Sumatran orangutans at two study sites engaged in homosexual beha vior. These observations demonstrate that homosexual behavior is not an art ifact of captivity or contact with humans. In separate instances, homosexua l behavior was associated with affiliative and agonistic behaviors. These o bservations add orangutans to the list of primates in which homosexual beha vior forms part of the natural repertoire of sexual or sociosexual behavior . (C) 2001 Wiley-Liss, Inc.