Same-sex sexual behaviour among non-human primates may help reinforce social bonds and maintain group cohesion during times of environmental or social stress, according to new research. Writing in Nature Ecology & Evolution, scientists analysed documented cases across 59 primate species, including chimpanzees, Barbary macaques and mountain gorillas. The study, led by researchers including Prof Vincent Savolainen of Imperial College London, found the behaviour to be widespread, suggesting either deep evolutionary roots or repeated independent evolution.
The analysis showed same-sex sexual behaviour was more common in species living in harsher, drier environments with scarce resources and higher predation risk. It was also associated with longer lifespans, pronounced size differences between sexes, and complex social hierarchies, all factors linked to intense social competition. Lead author Chloe Coxshall said environmental influences had been underestimated alongside known heritable factors.
Researchers propose the behaviour may reduce tension, limit aggression and strengthen affiliative bonds, helping groups navigate challenges. While cautioning against direct comparisons with humans, the authors suggested early human species likely faced similar pressures. External experts welcomed the study’s contribution, though some warned against drawing conclusions about human sexuality, stressing the complexity and diversity of behaviours across both humans and the animal kingdom.
