Scientists Closer to Understanding Gay Behavior in Animals

Animals mating with the same sex is a common trait, having evolved so repeatedly in mammals that it is now thought to be helpful for social bonding and reducing conflict.

Over 1,500 species of animal have shown some degree of same-sex sexual behavior, ranging from insects and spiders to frogs, fish, and birds, with over 50 species of non-human primates commonly showing these behaviors.

A new study in the journal Nature Communications reveals that same-sex sexual behavior has multiple evolutionary origins across mammal species and was more likely to be seen in social species, indicating that it may have evolved to help establish and maintain positive social relationships.

They also found that it was similarly prevalent in both males and females, but male same-sex sexual behavior was more likely to evolve in species where adults of the species sometimes kill each other, suggesting that it may be an adaptation to manage violence between males.

"An across-species statistical association [was found] between same-sex sexual behavior and social behavior for males and for females, and with intrasexual aggression for males," study author and behavioral ecology researcher at Estación Experimental de Zonas Aridas (EEZA-CSIC) in Spain, José M. Gómez, told Newsweek.

The study analyzed the existing literature about same-sex sexual behavior, with the authors compiling a database of the behavior, tracing its evolution across mammals, and testing for evolutionary relationships with other behaviors.

"We started with more than 1,000 species, but we were removing species from the analyses according to some methodological criteria," Gomez said. "Same-sex sexual behavior appears to be equally frequent in both sexes in mammals, as female same-sex sexual behavior has been recorded in 163 species and male same-sex sexual behavior in 199 species."

The advantages of same-sex sexual behavior are manyfold, resulting in its evolution in over 250 mammal species.

"There are several ways in which same-sex behavior can provide advantages," Vincent Savolainen, a professor of organismic biology at Imperial College London, told Newsweek. "For instance, when same-sex interactions help in forming coalitions, these alliances can elevate the status of the participating individuals within the group, granting them greater access to potential mates and increasing their reproductive success.

"This phenomenon is likely in rhesus macaques, where individuals exhibit bisexual patterns of behavior. Surprisingly, same-sex behavior does not hinder reproductive outcomes; in fact, it can enhance them."

Contrary to assumptions, same-sex sexual behavior does not limit or prevent opposite-sex reproduction and therefore the number of offspring produced by a population.

"Same-sex sexual behavior does not limit reproduction because individuals engaging in same-sex sexual behavior can also practice different-sex sexual behavior," Gomez said. "Because of this, same-sex sexual behavior may improve their individual fitness through enhancing social relationships and mitigating conflicts by same-sex sexual behavior to later have options to reproduce."

The majority of the species that perform same-sex sexual behavior are not exclusively same-sex. Most swap between same-sex and opposite-sex.

"While most animals display bisexual patterns of behavior, strict homosexuality is well-documented primarily in humans and domestic rams," Savolainen explains.

The authors of the study note that same-sex sexual behavior is any behavior that is usually performed at some stage during reproduction with a member of the opposite sex, but "does not denote sexual orientation (i.e. an overall pattern of sexual attraction/arousal over time), sexual orientation identity (i.e. the sexual orientation that individuals perceive themselves to have), categories of sexual beings (i. e. homosexuals, heterosexuals, etc.), nor sexual preference," according to Gomez.

For these reasons, Gomez cautions against direct comparisons with humans.

"The definition of same-sex sexual behavior in nonhuman animals is different from how this sexual behavior is considered in human beings. For this reason, the conclusions obtained in our work have just a limited application to humans," he said.

Other drivers may also come into play in the evolution of same-sex sexual behavior in animals,

"Same-sex behavior is prevalent across the animal kingdom and can have various underlying causes," Savolainen said. "These causes range from instances of misidentifying the sexes of potential mates to the formation of strategic coalitions, as observed in rhesus macaques. Some of these behaviors may have their origins in ancestral primates, leading to their manifestation in monkeys, apes, and humans. Consequently, it is legitimate to study animal models to gain insights into these behaviors."

Additionally, many researchers are investigating the genetic component behind this behavior in animals.

"There is a lot of literature about gay gene variants; several have been spotted—I suspect there are hundreds," Jenny Graves, a distinguished professor of evolutionary genetics at La Trobe University in Australia, told Newsweek. "The big question is why are they so common in humans? My own very strong hunch is that gay gene variants are really 'male-loving genes,' and they have been selected because female relatives induce women to mate earlier and have more kids, making up for the low reproductive rate of gay men.

"This 'sexual antagonism' can also explain why female homosexuality is so common (propose 'female-loving gene variants') and transgender ('gender identity variant genes'). It's likely that all of these factors are present—and more that we haven't thought of yet," she said.

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