Homosexual behavior is widespread in the animal kingdom. It has been observed in penguins, bottlenose dolphins and bonobos, among others. In addition to mammals and birds, cases have also been observed in reptiles, amphibians, fish and invertebrates. Scientists from Imperial College London have studied sexual practices between males in a group of 236 rhesus monkeys on the island of Cayo Santiago, Puerto Rico, and the findings were published this Monday in the journal Nature Ecology & Evolution. It’s the first time this behavior has been studied long-term, and the experts found it may be a common trait among primates and doesn’t affect the subjects’ reproduction.
According to these observations, sexual practices were more common between men (72% of respondents) than between people of the opposite sex (46%). The team discovered that this behavior in rhesus monkeys is related to what they call “coalition borrowing.” Subjects that ride each other are more likely to support each other in a conflict, giving a group advantage. “We think the gender they have helps them bond with each other,” says Vincent Savaloinen, one of the authors of the study. They also believe that this very advantage for the coalitions favors access to the females and their reproductive success.
The researchers were able to show that homosexual and heterosexual relationships are independent of each other in these animals. The authors explain in the text that sometimes it is assumed that there is a balance between one and the other and that they lose reproductive possibilities, but this is not the case. “The fact that they have homosexual relationships doesn’t mean they have fewer heterosexual relationships,” Savaloinen says. The scientists saw no connection between the role of males in their sexual relationship and their social position within the group, leading them to suggest that it is not important for rhesus monkeys to assert their hierarchical position in these practices.
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Another aspect they looked at as part of the research was whether homosexual behavior might have a genetic factor. Since 1956, all individuals living on the island of Cayo Santiago are captured for identification and a blood sample is taken from them. This has allowed scientists to create a family tree and determine that it has a hereditary component: “6.4% of the variability in sexual behavior is due to their genes,” the author states. This is the first evidence of a genetic basis for this behavior in primates other than humans, the study said.
Sexual intercourse between males decreased with age, leading researchers to believe that rhesus monkeys engage in homosexual practices before mating with females, among other things, Savaloinen says. Carmen Hernández, a postdoctoral researcher at the Institute for Research on Hunting Resources (IREC), part of the University of Castile-La Mancha and the CSIC, points out that this practice has also been observed in other primates, such as baboons. However, he adds, it could also be because it serves to “establish a dominance in young people that carries less risk of injury than aggressive conflict.”
Using the results of his research, Savaloinen theorizes that the reproductive costs currently incurred by homosexual relationships in humans may be due to social factors specific to human societies rather than biological reasons. The researcher says that with his work, they want to provide a new vision of the relationship between those who study the biology of homosexuality and those who do social and psychological research on humans, to show that they can learn from each other.
The research findings challenge beliefs in certain sectors of society that view homosexual relationships as unnatural and uniquely human, the authors say. Savaloinen affirms that this type of work helps to refute this reasoning and hopes that it can help further advance the fight against homophobia. “We hope that this can open up a new dialogue about human beings,” he concludes.
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