Sex between two males is extremely common in wild macaque monkeys

Gay behaviour seems to be widespread amongst male macaque monkeys within the wild and the trait could also be at the very least 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 School London.

“They kind bonds, and so they assist one another in a struggle,” says Savolainen. “After which the concept is that in the event that they do that, then they may even have entry to extra females and, in impact, have extra infants.”

Occasional same-sex touching has been noticed in quite a few animal species, however it’s usually 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 on the market must be eradicated by pure choice.

To research homosexuality in different primates, Savolainen and his colleagues determined to review a colony of 1700 wild rhesus macaques (Macaca mulatta) on the Puerto Rican island of Cayo Santiago. The colony has been adopted by scientists day-after-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. As a result of they didn’t wish to intervene with the animals, the scientists solely visually noticed the animals from a distance and couldn’t at all times 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 in opposition to different monkeys earlier than participating in intercourse.

Identical-sex mounting turned much less widespread with age, nonetheless, offering help for a standard speculation that it might function “follow” 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 elements, says Savolainen. The behaviour appeared to don’t have any detrimental penalties on reproductive success, he provides. Quite the opposite, males participating 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, for the reason that monkeys have been mounting higher-ranking males practically half the time. “They’ve erections typically; they’ve penetration typically, and so they even have ejaculation typically,” he says. “So I believe it’s sufficient to name it intercourse, and never dominance.”

Whereas 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 in some way unnatural, says Jon Richardson on the College of Minnesota, who wasn’t concerned within the examine. “I’m hopeful that we actually are beginning to transfer away from the antiquated concept that [homosexuality] in animals is an evolutionary paradox or aberration.”