Same-sex relationships have upsides for rhesus macaques, study finds

A group of monkeys is challenging people’s views on sexuality by showing that same-sex behavior in men strengthens their social networks and may even help them produce more offspring.

The resultsreported this month in the journal Nature Ecology and Evolution suggest that same-sex behavior in the animal kingdom is not only natural, but can also be societally beneficial.

The study “dispels doubts that same-sex behavior occurs naturally in nature,” said the senior author Vincent Savolainena biology researcher at Imperial College London.

Scientists have observed same-sex sexual behavior among themselves more than 1,500 animal species, including penguins, giraffes And elephants. However, it was unclear whether this behavior was widespread, whether it was genetically influenced, and to what extent it might affect the reproductive success of the entire population.

“We suspected same-sex behavior in these macaques, but didn’t know how common it was or what kind of partnership it developed,” Savolainen said.

To find out, he and his colleagues visited a colony of about 1,700 free-ranging rhesus monkeys living in a wildlife sanctuary in Puerto Rico. The colony has been monitored for the past 67 years, providing researchers with a comprehensive primate pedigree.

The researchers defined same-sex behavior as the act of ascension because it was the most common — and most recognizable — form of sexual contact. Although it occurs in both male and female macaques, it is much more common in males.

A rhesus monkey mounts another at a colony in Puerto Rico.

(Chloe Coxshall)

Over a three-year period, the study team followed 236 males belonging to two different social groups within the colony. During that time, they documented 1,739 cases of congestion — 722 involved male-female couples and 1,017 involved same-sex couples.

The research team had expected to see some same-sex couples in action, and Savolainen said he wasn’t surprised their pairings outnumbered male-female pairs.

In male macaques, same-sex sexual behavior is not necessarily about sex, but rather about social interaction. According to the study, male macaques mounted each other after grooming, eating, fighting, playing and resting, and when traveling. The activity could be a way to strengthen bonds between men, making them more likely to form alliances and ultimately gain access to more women, the researchers said.

It’s important to note that the same-sex sociosexual behavior observed in the study differs from homosexual behavior because its motivation and purpose are social in nature, he said Jean Baptiste Leca, who studies primate behavior at the University of Lethbridge in Canada and was not involved in the new research. To qualify as genuine homosexual behavior, the form, motivation and function must all be sexual in nature, he said. (As far as the researchers could determine, only one of the 236 macaques studied had exclusive contact with other males.)

The younger a macaque was, the more likely it was to engage in same-sex encounters, the study authors found. This could be a sign that in some cases the couplings “could serve in part as ‘practice’ for future reproductive activity,” they wrote.

In fact, participation in same-sex mating did not negatively impact a macaque’s overall reproductive success. After examining the offspring number of all 236 males, the researchers found that the more often a monkey mated with a conspecific, the higher the number of offspring tended to be.

The trend wasn’t statistically significant, but it was enough to confirm that same-sex behavior caused no reproductive costs — something Savolainen said he was surprised about. Perhaps the stronger social bonds formed during these sexual encounters strengthened their coalitions and ultimately gave participants greater access to women, the researchers wrote.

By examining the behavior of related macaques over several generations, the study authors found that about 6% of same-sex sexual behavior could be genetic. While this may not seem like much, it is comparable to the genetic component of complex behaviors in humans and other primates, such as B. Grooming or alloparenting, which is caregiving by someone other than the parents, Savolainen said.

A rhesus monkey grooms another in Puerto Rico. Researchers found that grooming often preceded same-sex sexual encounters in the colony.

(Chloe Coxshall)

Savolainen and his colleagues warned that the behaviors they observed in the Puerto Rico macaques may be specific to this population. Regardless, they said, the results challenge assumptions that same-sex sexual behavior is rare in nonhuman animals and results in fewer offspring. Others agreed.

“This study adds to our understanding of animal behavior,” said Rachna Reddy, a primatologist at the University of Utah who was not involved with the study. “Now we see that [same-sex] Behavior is very common, occurs in many species, can have many functions, and is not always costly.”