Homosexuality may have evolved as a ‘survival strategy’, study claims

A new study has shed light on homosexuality, and why it might have evolved. 

From dolphins to chimpanzees, same-sex behaviours (SSBs) are common among thousands of animals, but until now, why they might be beneficial has remained unclear. 

Now, experts at Imperial College London have revealed how primates show more SSBs when their habitats are harsh or dangerous, and when their social groups are larger and more complex. 

This suggests homosexuality might help forge strong bonds that allow groups to stay together to survive harsh conditions, according to the experts. 

For example, if predators are especially common, a tight-knit social group that can trust each other’s alarm calls is a survival advantage.

‘Our findings suggest that SSB is widespread rather than rare and that it has likely evolved multiple times across primate lineages, in part as a way to navigate complex social and environmental systems,’ co-author Professor Vincent Savolainen told the Daily Mail. 

However, he cautioned that the findings don’t make any direct claims about the evolution of homosexuality in humans.

‘It highlights several promising directions for future research by anthropologists and psychologists interested in the evolutionary and social contexts of same-sex behaviour,’ he added. 

In the study, published in the journal Nature Ecology & Evolution, the researchers analysed existing research looking at 491 species of non-human primates – 59 of which engage in same-sex behaviours. 

Previously, researchers have suggested that these behaviours in primates might be driven in part by genetic factors.

For example, in 2023, Professor Savolainen found that SSB was about 6.4 per cent heritable in rhesus macaques – meaning that a tendency towards homosexuality could be passed down genetically.

However, this leaves a lot of room for other factors to determine whether SSB actually occurs and a lot of uncertainty over what those causes might be.

The new analysis supports the idea that homosexual behaviour in primates is largely driven by environmental and social factors, rather than genes alone.

Among the animals where SSB is observed, the behaviour is more common when the species faces a drier environment, scarcer resources, or a lot of predators.

It is also more common among species with complex social systems, a greater size difference between males and females, and those with longer lifespans.

Based on these insights, Professor Savolainen suggests SSB ‘probably’ evolved as a survival strategy to help highly social species survive environmental challenges. 

Harsh ecological conditions may favour animals with tight social cohesion and strong bonds within groups, with SSB being another way to forge those connections.

However, the experts also point out that the study did not directly address survival or longevity, so more work will be needed to determine whether SSB really is a survival strategy.

Professor Savolainen says he plans to tackle this question with a new study focusing on SSB in macaques.

This study adds to a growing body of research suggesting that homosexual behaviour is significantly more common in non-human species than previously thought.

Scientists have now observed SSB in over 1,500 different species, ranging from primates like chimpanzees to dolphins and ducks.

Previously, scientists had written this behaviour off as a case of mistaken sexual identity, with some animals simply mixing up the genders of their chosen mates.

Now, research increasingly points towards the fact that homosexuality is a beneficial evolutionary strategy. 

Both chimpanzees and bonobos are known to start SSB when faced with ecological challenges.

Meanwhile, even male burying beetles will engage in same-sex behaviour when females are scarce, because same-sex mating alone reduces chances to display mating potential.

This suggests that the costs of SSB, in terms of lost mating opportunities, may be outweighed by the benefits in certain situations.