Cross-species and cross-cultural contributions to understanding homosexual activity.

Some forms of homosexual activity are widespread if not ubiquitous among studied mammals, occur invariably in all reported subhuman primates, and are present in most human cultures. Homo sapiens is the only species, however, in which adult preferential or obligatory homosexuality occurs naturally. Existing cross-species and cross-cultural reports are reviewed from behavioral, physiological, and evolutionary perspectives with a view toward clarifying the role of homosexual behavior in species interactions. The data suggest that preferential or obligatory homosexuality in adulthood, in the presence of available and receptive heterosexual partners, is qualitatively rather than quantitatively distinct from all other manifestations of homosexual activity, and that quantitative incidence rating scales obscure meaningful understanding of this dimension of homosexual behavior.