Same-sex sexual behaviour among non-human primates may help reinforce social bonds and maintain group stability during periods of environmental or social stress, according to new research. Writing in Nature Ecology & Evolution, scientists analysed documented cases across primate species and found the behaviour widespread, appearing in 59 species including chimpanzees, Barbary macaques and mountain gorillas. The study was co-authored by Prof Vincent Savolainen of Imperial College London, who suggested the findings may also shed light on early human societies facing similar pressures.
The researchers found same-sex behaviour was more common in species living in harsh, dry 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 the results highlight the often-overlooked role of environmental conditions alongside genetics. The behaviour appears to reduce tension, limit aggression and strengthen affiliative bonds, helping groups navigate challenging conditions.
While the authors cautioned against directly mapping these findings onto humans, they noted the research raises questions about how social pressures shape behaviour. Prof Zanna Clay of Durham University welcomed the study as evidence that same-sex behaviour is a common and adaptive feature of primate societies. However, Josh Davis of the Natural History Museum stressed that human sexuality is shaped by far more complex and distinct factors, warning against simplistic comparisons.
