Same-sex sexual activity isn’t exclusive to humans; various primates engage in it too.

A recent study identified 59 non-human primate species, including bonobos, chimpanzees, and macaques, that exhibit same-sex behavior.

This extensive research, published in Nature Ecology & Evolution, is the most thorough review to date of same-sex behavior among primates (excluding humans). The findings challenge existing assumptions about the purpose of sexual activities within the animal kingdom and indicate that sex may serve a more complex social function.

The authors propose that same-sex behavior has evolved to assist primates in navigating complex social structures, reducing conflict, and strengthening bonds. They suggest that both genetic factors and external environmental stresses influence this behavior.

Vincent Savolainen, director of the Georgina Mace Center for the Living Planet at Imperial College London and lead author of the study, stated: “Our findings illustrate that homosexuality is not an anomaly; it’s widespread, beneficial, and essential.”

In their study, Savolainen and colleagues evaluated existing data from 491 primate species, focusing on documented instances of same-sex sexual activities.

“The behaviors observed included mounting, ventral-to-ventral, or ventral-to-dorsal contact, genital touching, and fellatio, encompassing both male-to-male and female-to-female interactions,” the study highlighted. Non-sexual same-sex interactions were excluded to maintain clarity.

Findings suggest that same-sex behavior is more prevalent among animals needing social cohesion to endure harsh environmental conditions, facing predation risks, or competing for resources. It is particularly common in social structures with rigid hierarchies, where sexual behaviors help individuals manage competition and foster alliances to reduce intergroup aggression.

“People often underestimate the significance of same-sex behavior in societal dynamics; it is as crucial as eating, fighting, parenting, and nurturing,” Savolainen remarked.

He likened same-sex sexual interactions to a form of “currency” that may enhance social standing, create opportunities, and facilitate resource sharing.

“In times of social strife, utilizing same-sex behavior can be advantageous,” Savolainen explained.

He noted that while this behavior is likely to be present in more than 23 primate species, limited data in the field and a lack of focused studies hinder comprehensive understanding.

Observing and interpreting same-sex sexual behavior can be challenging for scientists. Historically, many researchers viewed these behaviors as unusual and neglected documentation. Additionally, securing funding for studies on same-sex behavior in animals has been difficult, particularly from government sources.

“We have a plethora of species about which we lack knowledge. This knowledge gap is significant,” Savolainen warned. “Unless we incorporate same-sex behavior into our understanding of social dynamics, we can’t fully grasp how societies operate. We aim to gather more data in forthcoming studies.”

While the new research doesn’t directly relate its findings to contemporary human sexual behavior, it suggests that our ancestors experienced social and environmental pressures similar to those driving same-sex behavior in other primates.

Prior studies have indicated that widespread same-sex behavior exists in macaques and that certain traits are genetically inherited. Some behaviors can be linked to specific genetic lineages. Female bonobos often engage in genital rubbing during stressful situations, and same-sex behavior has also been documented in chimpanzees.

Marlene Zook, an evolutionary biologist at the University of Minnesota who studies same-sex behavior in animals, commented on the interesting breadth of the analysis.

“The extensive range of data collected in this study is particularly impressive,” she noted.

Zook expressed no surprise at the conclusion emphasizing the influence of environmental and social factors on same-sex behavior. The study prompts a reconsideration of widespread misconceptions regarding animal sexual conduct, emphasizing its complexity beyond mere reproduction.

“Sexual behavior often transcends reproduction, a fact evident in our species. However, many tend to overlook this reality in animals,” Zook observed. “People seem to assume that animals, unlike humans, conduct sexual activities purely for procreation purposes, which is quite inaccurate.”

Zook added that the scientific community has traditionally dismissed the concept of a “gay gene” that directly influences homosexual behavior.

“No single gene dictates homosexual behavior in humans or other animals. Instead, a complex interplay of genetic and environmental factors shape nearly all behaviors and traits, whether they be physical or psychological,” she concluded.