Same-sex sexual behavior in primates suggests evolutionary origin

A review published in Nature Ecology & Evolution found documented same-sex sexual behavior in 59 nonhuman primate species, with repeated occurrences in 23 species. The authors report the behavior appears linked to social roles—easing tension, reducing conflict and building bonds—and to a mix of genetic and environmental or social stressors.

Researchers published a review in Nature Ecology & Evolution reporting same-sex sexual activity across many nonhuman primates. They analyzed existing observations and studies covering 491 primate species. The analysis identified documented instances in 59 species and repeated occurrences in 23 species. The authors report the behavior appears tied to social functions and to a combination of genetic and external stressors. What the study reports: - The review used previously published observations and data from studies of 491 primate species. - Same-sex sexual behavior was documented in 59 species, with repeated occurrences in 23 species. - Reported behaviors included mounting, genital touching and fellatio, and both male-male and female-female interactions were counted. - The behavior was reported as more common in groups facing harsh environments, high predation risk, intense resource competition, or strict social hierarchies. - The authors describe a combined influence of genetics and environmental or social stress on the occurrence of these behaviors. Summary: The review expands evidence that same-sex sexual behavior is widespread among nonhuman primates and that it can serve social roles such as easing tension, reducing conflict and building bonds. The authors and other experts note that many species remain poorly documented and that gaps in observation limit current understanding. Undetermined at this time