More Than Mating: Same-Sex Sex in Primate Evolution

SemIDEEV
 13/02/2026
 12:00:00
 Vincent Savolainen, Imperial College à Londres, Royaume-Uni
 IDEEV - Salle Rosalind Franklin

Same-sex sexual behaviour (SSB) is widespread in animals, yet it seems to contradict simple ideas of natural selection because it does not directly produce offspring. Its persistence across species has long puzzled evolutionary biologists. In humans, SSB has a genetic component and appears across cultures and history, but studying its biology is difficult due to stigma, self-reporting bias, and contraception. To avoid these limits, we studied free-ranging rhesus macaques on Cayo Santiago, Puerto Rico.

We asked whether SSB has a genetic basis, whether it reduces reproductive sex, and why it is so common. Using a global analysis of non-human primates, we show that SSB can promote survival and potentially reproduction itself. Same-sex bonds help primates reduce conflict, form alliances, and succeed in harsh, predator-rich environments.

Our study goes beyond anecdotal reports and narrow species studies, using rare long-term genetic and behavioural data. As The Economist observed: “Dr Savolainen has brought rigour to a topic beset by speculation and prejudice.”