Primates' same-sex behaviour may reinforce bonds under environmental stress

A study found same-sex sexual behaviour is widespread across many primate species and may help reinforce social bonds in species facing environmental stress and social competition.

Researchers report that same-sex sexual behaviour is common across many non-human primate species and may function to reinforce bonds when groups face environmental or social challenges. The analysis, published in Nature Ecology & Evolution and co-authored by Prof Vincent Savolainen of Imperial College London, reviewed published accounts across primate groups. The authors recorded reports in 59 species, including chimpanzees, Barbary macaques and mountain gorillas. They examined links between the behaviour and environmental conditions, life-history traits and social systems. Key findings: - Same-sex sexual behaviour was reported in 59 primate species, spanning most major primate groups. - The behaviour was more likely to occur in species living in drier environments, where resources are scarce, and where predator risk is higher. - It was also associated with longer-lived species, greater male–female size differences, and more complex social hierarchies. - The authors report these factors appear interlinked, with environmental pressures shaping life-history traits that influence social systems. - The research team cautioned against direct extrapolation to humans and noted that sexual orientation, preferences and identities in people are complex. Summary: The study suggests same-sex sexual behaviour in primates often appears in contexts of environmental stress and intense social competition and may serve affiliative roles such as reducing tension and strengthening bonds. Researchers and external commentators say the work adds an evolutionary perspective and points to comparative studies across other animal groups; implications for human behaviour are reported as uncertain and undetermined at this time.