Rhesus monkeys have a high rate of homosexual relationships – 07/10/2023 – Science

An article published this Monday (10) observed a high rate of homosexual interactions between rhesus monkeys, a species of primates. Among those who maintained this type of relationship, a greater capacity for partnership was found, something that can be seen as positive in the coexistence of the animals and in the reproduction of the species.

Published in the journal Nature Ecology & Evolution, the study was organized by scientists at Imperial College London, in the United Kingdom. They followed rhesus monkeys on the island of Cayo Santiago, in Puerto Rico, for three years to record the animals’ behavior. Of the approximately 1,700 animals that live in the region, 236 males were tracked by the scientists.

Sexual interactions, called mounts, were recorded during the research. Overall, same-sex contacts were observed 1,017 times. As for the mounts performed with animals of different sex, it was 722.

The scientists also performed estimates for the 236 males identified during the study. According to the authors, around 72% of these monitored animals had some sexual contact with other males. Meanwhile, the percentage was 46% for an interaction with females.

Irene Delval, a postdoctoral researcher at the Department of Experimental Psychology at USP in the area of ​​sexual development, says that investigations like these are increasing lately. “Same-sex sexual interactions are relatively understudied, although interest is growing,” says Delval, who was not involved in the Nature study.

The researcher herself signed an article that recorded, in an unprecedented way, a mating ritual between capuchin monkeys in Bahia. During the observations made by Delval and other scientists, mounts were also recorded among capuchin monkeys.

Already observed in several species of living beings, homosexual behavior among animals has been the object of a series of hypotheses. One of them is dominance, in which an individual would try to impose dominance over another.

This thesis, however, did not make sense for the Imperial College study. Scientists claim in the article that in 42% of relationships those who mounted on the other were from lower hierarchical categories.

Another factor, heredity, appears to be a more plausible explanation, according to the study. The authors made calculations and concluded that sexual contact between males and males was 6.4% related to genetic inheritance. According to the article, this is the first time that this type of evidence has been found to explain the behavior in non-humans.

Delval points out that “non-reproductive sex is a very strong form of communication and can have multiple functions”. These interactions, continues the researcher, may even be beneficial in some circumstances for better establishing bonds between animals.

This was also found in the study. By comparing mating records, the scientists concluded that “males who mounted each other were also more likely to support each other during conflicts with other individuals.” Other studies have already observed that the formation of alliances between primates improves the reproduction of the animals. In other words, relations between the same sex, indirectly, can collaborate with the development of the species.

This finding expresses a benefit of homosexual contact among monkeys and may be a partial explanation of why, given the evolution of primates, this behavior was maintained.

In addition, the scientists believe that the conclusion of the study puts into question the idea that relationships between individuals of the same sex would be a rarity in the most diverse species of animals.