More than 1,500 animal species exhibit same-sex sexual behavior, a phenomenon that has long been observed but rarely analyzed systematically. New research now points to its importance as a social strategy shaped by the environment, biology and the organization of groups.
A large-scale study published this week examines homosexual behavior in primates, showing that it has ancient evolutionary roots and depends on multiple factors related to the environment and social structure.
“The diversity of sexual behaviors is very common in nature, between species and in animal societies, as important as caring for offspring, fighting a predator or looking for food”, he highlighted to the France-Presse agency () Vincent Savolainen, Autor principal do
Sexual behaviors between individuals of the same sex have been documented in more than 1,500 animal species, mFor a long time, they were observed only anecdotally by researchers who saw them as a “Darwinian paradox”, given that evolution is based on the transmission of genes through reproduction, noted the biologist.
From a “Darwinian paradox” to an evolutionary advantage
Recent studies have shown that this trait has a hereditary component and can provide an evolutionary advantage.
In rhesus monkeys from Puerto Rico, which Savolainen has been studying for eight years, males that mate with each other can form coalitions, which could allow them access to more females and, therefore, more offspring.
However, comparative analyzes that could reveal the non-genetic factors that influence the expression of this characteristic are still limited.
Savolainen and his colleagues combed the scientific literature to gather existing data on 491 non-human primate species.
They identified such behaviors in 59 of them, including lemurs, monkeys from the Americas, Africa and Asia, and great apes.
Environment, risk and social organization influence these behaviors
This suggests a “deep evolutionary root” for this trait, noted the researchers, who then analyzed the influence of environmental context, “life history” (life expectancy or morphology, among others) and social organization on its expression.
Sexual dimorphism is, therefore, more common in species that live in hostile environments with limited food resources, such as Gibraltar macaques.
It is also more common in species exposed to a high risk of predation, such as vervet monkeys (small African monkeys).
This suggests that these behaviors can help manage tensions within the group during times of stress.
Sexual dimorphism is also more common in monkeys where males and females have marked differences in size, such as mountain gorillas.
Sexual dimorphism is often associated with larger social groups, intense competition and more rigid hierarchies, while species where males and females are similar in size generally live in pairs or small family groups.
These different factors interact with each other: life cycle characteristics are shaped by environmental factors, which, in turn, influence social complexity, leading to the prevalence of social cohesion strategies.
These results suggest that these behaviors are a “flexible social strategy, used to strengthen social ties, manage conflicts or build alliances in response to ecological and social pressures”, the authors highlighted.
The researchers also hypothesized that similar factors may have played a role in ancestral hominins and even modern humans.
“Our ancestors certainly had to face the same environmental and social complexities,” Savolainen pointed out.
“But there are aspects completely unique to human beings, with a complexity of sexual orientation and preference, that we haven’t addressed at all,” explained the evolutionary biologist.
