Most monkeys swing both ways
Joe Pinkstone
Tue, 11 July 2023 at 3:38 am SGT·3-min read
Academics studied a monkey colony on the tropical island of Cayo Santiago in Puerto Rico - Jackson Clive/Imperial College London/PA
Most male monkeys swing both ways and are bisexual, a study has found.
Analysis of wild macaques in Puerto Rico found that males mount and exhibit homosexual behaviours more often than they do towards females.
Almost three-quarters of monkeys followed by researchers showed male-on-male sexual behaviours and the scientists say this helped to build strong social bonds and foster supportive relationships.
The monkeys that frolicked were more likely to back each other up in a fight, for example.
The study, from scientists at Imperial College London, challenges the assumption held by many that homosexuality in nature is rare and counter-productive.
“More of the macaques were bisexual,” Prof Vincent Savolainen, lead author of the study, told The Telegraph.
“However, we also observed more macaques doing homosexual behaviour than heterosexual behaviour.”
Homosexuality ‘6.4 per cent heritable’
The study followed 236 males within a colony of 1,700 rhesus macaques living freely on the tropical island of Cayo Santiago for three years and also accessed pedigree records dating back to 1956.Each male in the study was followed and the number of “mountings” was recorded, whether it be on a male or on a female.
A total of 72 per cent of the males engaged in same-sex mounting while less than half (46 per cent) were seen mounting a female.
Scientists have previously seen evidence of homosexual behaviour in thousands of species and there has been extensive debate as to why.
Some posit that it is males practising sex, while other theories centre on establishing dominance over others and reducing tension.
But in the latest study the scientists say the bisexual tendency led to improvements in the strength of inter-monkey relationships.
Historical records show that bisexuality was also a heritable trait that had a tendency to be passed down the generations.
The researchers found same-sex behaviour in males was 6.4 per cent heritable, the first evidence of homosexuality being genetic in primates.
‘Due to common ancestry’
The scientists also suggest that because macaques and humans both exhibit homosexual traits the behaviour likely has deep evolutionary roots.“Homosexual behaviour is widespread in mammals and other vertebrates, so it dates well back before macaques and humans diverged,” Prof Savolainen said.
“Some underlying of the behaviour must be due to common ancestry.”
The scientists say that comparing the role of homosexuality in monkeys with humans is difficult but some conclusions can be inferred.
“Finding same-sex behaviour heritability in these primates may reasonably be contrasted with human populations,” Prof Savolainen told The Telegraph.
There are “large fitness costs” associated with homosexuality and bisexuality in people, he added, but the new study shows it is beneficial to macaques.
This could mean the large costs of homosexuality in humans is caused by social factors, not biological ones, he suggested.
“[We] await further research to clarify this theory,” Prof Savolainen said.
‘Same-sex behaviour is widespread’
The scientists say the findings rebut the entrenched viewpoint that homosexual or bisexual behaviour goes against nature and defies evolution as the monkeys prone to mounting other males, or being mounted, were more likely to reproduce and have offspring.“Unfortunately there is still a belief amongst some people that same-sex behaviour is ‘unnatural,’ and some countries sadly still enforce the death penalty for homosexuality,” Prof Savolainen said.
“Our research shows that same-sex behaviour is in fact widespread amongst non-human animals.
“Our mission is to advance scientific understanding of same-sex behaviour, including exploring the benefits it brings to nature and within animal societies.”
The study is published in the journal Nature Ecology and Evolution.
