Sex between two males is extremely common in wild macaque monkeys

Homosexual behaviour seems to be widespread amongst male macaque monkeys within the wild and the trait could also be not less than partially handed down in genes from father to son. Such behaviour might present evolutionary benefits stemming from robust male alliances, says Vincent Savolainen at Imperial College London.

“They form bonds, and they help each other in a fight,” says Savolainen. “And then the idea is that if they do this, then they might also have access to more females and, in effect, have more babies.”

Occasional same-sex touching has been noticed in quite a few animal species, however it’s typically regarded as uncommon. Savolainen has typically questioned a well-liked perception generally known as the “Darwinian paradox of homosexuality”, which means that as a result of gay behaviour doesn’t result in copy, it has no profit and any genes that put it up for sale ought to be eradicated by pure choice.

To examine homosexuality in different primates, Savolainen and his colleagues determined to check a colony of 1700 wild rhesus macaques (Macaca mulatta) on the Puerto Rican island of Cayo Santiago. The colony has been adopted by scientists every single day for the previous 67 years and DNA-tested for paternity since 1992. In 2017, 2019 and 2020, the workforce noticed 236 of the colony’s males, which belonged to 2 social teams, for 7 hours a day over 72 days.

The researchers discovered that 72 per cent of the males mounted different males, whereas solely 46 per cent have been noticed mounting females. Because they didn’t need to intervene with the animals, the scientists solely visually noticed the animals from a distance and couldn’t all the time see precise penetration, though they generally noticed sperm plugs – which kind after ejaculation – within the anuses of some males.

In 16.5 per cent of instances of same-sex mounting, the 2 males fought collectively towards different monkeys earlier than partaking in intercourse.

Same-sex mounting turned much less widespread with age, nonetheless, offering assist for a typical speculation that it could function “practice” for future reproductive exercise, says Savolainen.

The household historical past of the monkeys revealed that same-sex mounting was 6.4 per cent heritable – which means genetics might play a small function along with different components, says Savolainen. The behaviour appeared to haven’t any unfavorable penalties on reproductive success, he provides. On the opposite, males partaking in same-sex mounting tended to have barely extra offspring.

The males’ mounting exercise is unlikely to be merely a present of dominance, says Savolainen, because the monkeys have been mounting higher-ranking males almost half the time. “They have erections sometimes; they have penetration sometimes, and they even have ejaculation sometimes,” he says. “So I think it’s enough to call it sex, and not dominance.”

While researchers can’t decide what animals are considering as they choose sexual companions, the examine helps to dispel the notion that same-sex behaviour is one way or the other unnatural, says Jon Richardson on the University of Minnesota, who wasn’t concerned within the examine. “I am hopeful that we really are starting to move away from the antiquated idea that [homosexuality] in animals is an evolutionary paradox or aberration.”