Evolution isn’t against same-sex behaviour in monkeys: study Premium

Animals that engage in same-sex sexual behaviour have been considered a ‘Darwinian paradox’: if reproduction is critical to evolution, then non-reproductive behaviour should have ceased to exist. Yet a new study, published in Nature Ecology & Evolution, has found that rhesus macaque males often engage in same-sex sexual behaviour without compromising their population’s opportunities to evolve.

In 1896, controversy broke out when French entomologist Henri Gadeau de Kerville published the first sketch of two male cockchafers, a species of scarab beetles, copulating.

More than a century later, in 2012, researchers at the Tring Natural History Museum in the U.K. rediscovered a four-page pamphlet originally published in 1915 by the English naturalist George Levick. It seems Levick had observed same-sex sexual behaviour (SSB) in Adélie penguins.

Since then, scientists have reported SSB in pigeons, swans, albatrosses, lions, dolphins, bats, elephants, bonobos, gorillas, monkeys, lizards, tortoises, dragonflies, fruit flies, and bed bugs.

Animals that engage in SSB have been considered a ‘Darwinian paradox’: if reproduction is critical to evolution, then SSB – which is non-reproductive – should have ceased to exist. The supposed paradox is also fed by a longstanding belief among biologists that SSB could be evolutionarily “costly” to species because it leads to fewer offspring, thus reducing the chances of evolution mediated by natural selection.

Now, in a study published in July in Nature Ecology & Evolution, researchers at the Imperial College London have challenged the premise of this paradox. The team, led by postdoctoral fellow Jackson Clive, has reported that at least in rhesus macaques, male SSB is remarkably common and “is not [evolutionarily] costly”.

Volker Sommer, a professor of evolutionary anthropology at University College London, said the study is the first to find evidence that SSB has a “heritable component” in the case of animals. He wasn’t involved in the study.

For their study, Dr. Clive and his team observed rhesus macaques, a common monkey model, in Cayo Santiago, an island east of Puerto Rico.