Bisexuality a ‘common’ trait among species of monkeys, finds study

In the animal kingdom, same-sex behaviour is not uncommon. In fact, it has been observed in over 1,500 species, including dolphins, penguins, and even lions.

A new study published in the journal Current Biology has found that 72% of male macaque monkeys engage in same-sex behaviour.

The study, which was conducted by researchers from Imperial College London, tracked the behaviour of male macaque monkeys in Puerto Rico.

‘We found most males were behaviourally bisexual, and that variation in same-sex activity was heritable,’ said the first author Jackson Clive from Imperial College London.

‘Our research therefore shows that same-sex sexual behaviours can be common amongst animals and can evolve. I hope our results encourage further discoveries in this area.’

This study observed 236 male rhesus macaques within a colony of 1,700 on the Puerto Rican island, Cayo Santiago. The observations were taken from 2017 to 2020, and was accompanied by  genetic analysis, and a review of the macaques’ pedigree (or family tree) records back to the mid-1950s.

They found that 72% of the males in the study undertook same-sex mounting, while only 46% did different-sex mounting.

The researchers also found that the same-sex behaviour in male macaque monkeys was inheritable in around 6.4% of the group. This means that it is likely that some of the genes that make a male macaque more likely to engage in same-sex behaviour are passed down from parents to offspring.

This is the first evidence of a genetic link to primate same-sex behaviour outside of humans. They also found a genetic correlation between which role – the mounter or the mountee – the males undertook.

Demographic factors such as age and social status didn’t affect the likelihood of the macaque undertaking same-sex behaviour or which role they took.

The researchers say that this challenges the belief that same-sex behaviour is rare, or only a product of particular environmental conditions.

‘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,’ says senior author Professor Vincent Savolainen also from Imperial College London.

‘Our research shows that same-sex behaviour is in fact widespread amongst non-human animals.’

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