Same-sex sexual behaviour among non-human primates may help reinforce social bonds and maintain group cohesion during environmental or social stress, researchers suggest. Writing in Nature Ecology & Evolution, a team led by scientists from Imperial College London analysed documented cases across primate species and found the behaviour to be widespread. Reports were identified in 59 species, including chimpanzees, Barbary macaques and mountain gorillas.
The researchers found such behaviour was more common in species living in harsher, drier environments with scarce resources and higher predation risk. It was also linked to longer lifespans, pronounced size differences between males and females, and complex social hierarchies, all factors associated with intense social competition. Lead author Chloe Coxshall said environmental influences on the behaviour had often been overlooked.
Co-author Prof Vincent Savolainen said same-sex sexual behaviour appeared to function as an affiliative tool, reducing tension and aggression while strengthening bonds. The team suggested similar pressures may have existed for early human species, though they cautioned against directly applying the findings to modern humans.
External experts welcomed the study’s contribution while urging caution. Prof Zanna Clay of Durham University said it showed same-sex behaviour was a common and adaptive feature of primate societies. Josh Davis of the Natural History Museum added that queer behaviours occur widely across nature and warned against drawing simplistic parallels with human sexuality.
