Scientific inquiry has revealed that homosexual behaviour in non-human primates possesses a profound evolutionary lineage, with its prevalence correlated to species experiencing exigencies such as challenging environmental conditions, predation pressures, or intricate societal structures, as reported by researchers on Monday.
The observation of individuals of the same sex engaging in copulation or other forms of sexual stimulation has been documented across a vast spectrum of the animal kingdom.
A considerable number of species, exceeding 1,500, have been recorded exhibiting same-sex sexual conduct, with early attestations tracing back to the era of the ancient Greek philosopher Aristotle.
However, this phenomenon, which is relatively commonplace, was for an extended period disregarded by the scientific establishment as a “Darwinian paradox.” This perspective posited that attributing homosexual behaviour in animals contradicted Charles Darwin’s evolutionary theory, as it did not facilitate the propagation of genes through procreation.
More recent investigations have substantiated that this behavioural pattern can, to a degree, be inherited from parental lineage and may confer an evolutionary advantage.
“The panorama of sexual behaviour is remarkably ubiquitous in the natural world, permeating through various species and animal communities—its significance is comparable to the imperatives of nurturing progeny, evading predators, or securing sustenance,” articulated Vincent Savolainen, a biologist at Imperial College London, in an interview with AFP.
Professor Savolainen has dedicated eight years to the study of rhesus macaques in Puerto Rico. His research cohort identified that male macaques engaging in mutual mounting establish strategic alliances, potentially enhancing their access to receptive females and, consequently, their reproductive success.
In 2023, the team further determined that the propensity for same-sex behaviour in these macaques was inherited from their progenitors in over six percent of instances. Nevertheless, the transmission of this trait was contingent upon a multiplicity of influencing factors.
‘Profound Evolutionary Underpinning’
For his latest research endeavour, culminating in findings disseminated in the esteemed journal Nature Ecology & Evolution, Professor Savolainen and his collaborators meticulously compiled information pertaining to 491 distinct non-human primate species.
Their analysis confirmed the presence of same-sex sexual behaviour in 59 species, encompassing lemurs, great apes, and a variety of monkeys from continental America, Africa, and Asia.
The pervasive distribution of this behaviour across such a wide array of taxa provides compelling evidence for its “profound evolutionary root,” as stated in the study.
Subsequently, the investigators delved into the influence of environmental variables, societal organisation, and “life history” characteristics on the manifestation of homosexual acts within primate populations.
A key finding indicated that the behaviour was more prevalent in species inhabiting challenging ecological niches with scarce food resources, exemplified by the barbary macaque.
Furthermore, it was identified as more common in species that are frequently targeted by predators; for instance, vervet monkeys in Africa must continuously evade a range of formidable adversaries, including large felines and serpentine reptiles.
A Mechanism for Tension Mitigation?
Collectively, these observations suggest that homosexual behaviour may serve as a stratagem for alleviating intergroup tension during periods of elevated stress within primate societies, according to the research team.
The behaviour also proved more frequent among species where significant size disparities exist between males and females, such as in mountain gorillas.
These pronounced dimorphic characteristics are often associated with animals residing in larger social collectives, characterised by intense competition and rigidly enforced social hierarchies. Conversely, species with more congruously sized males and females tend to form pair bonds or smaller familial units.
Consequently, same-sex sexual behaviour “may operate as a dynamic social strategy, employed to solidify social connections, mediate conflicts, or forge alliances, contingent upon the ecological and social pressures encountered by distinct species,” as elucidated in the published study.
The researchers theorised that analogous dynamics might have been operative among the evolutionary antecedents of humans.
“Our forebears undoubtedly contended with comparable environmental and societal complexities,” Professor Savolainen remarked.
“However, specific elements are entirely unique to contemporary humans, who exhibit a complexity of sexual orientation and preference that falls outside the purview of this investigation,” he clarified.
The study also issued a caution against the “misinterpretation or improper application of our findings,” particularly concerning “a misguided assumption that societal egalitarianism might eradicate” same-sex sexual behaviour in contemporary human populations.
Isabelle Winder, an anthropologist at Bangor University in the United Kingdom who was not affiliated with this research, commended the scientific effort.
“The most exhilarating aspect of their work, in my estimation, is its demonstration that modern comparative methodologies can, for what may be the first time, realistically illuminate certain intricacies in the evolutionary development of ‘human-like’ behaviours,” she stated in a commentary for Nature.
