Japanese monkey
New research has found that homosexual relationships are more common in primate species with more complex social dynamics, which indicates that the behavior will have the advantage of strengthening bonds.
Same-sex sexual behavior is not randomly distributed among nonhuman primates and may perform important social functionsaccording to a new study that analyzed data from hundreds of species.
Research suggests that this behavior is more common in primates that face complex social dynamics or challenging environmental conditions, where strengthening social bonds can provide an evolutionary advantage.
The study, in Nature Ecology & Evolution, examined reports of 491 non-human primate species and found documented cases of same-sex sexual behavior in 59 of them. Although researchers acknowledge that the behavior is likely underreported, the uneven distribution points to specific factors that increase its probability, says .
Sexual activity between individuals of the same sex has been observed throughout the animal kingdom, from mammals and birds to insects. In primates, however, the new analysis indicates that it is more frequent in species with a long life expectancycomplex social hierarchies and higher levels of social stress. Examples include chimpanzees, bonobos, baboons and several species of monkeys.
Primates living in conditions of food scarcity or high predation risk were also more likely to report same-sex sexual behaviors. The researchers argue that, in such contexts, strengthening social ties can improve cooperationvigilance and survival of the group.
An unexpected discovery was that the species with sexual dimorphismin which males and females differ greatly in size, also showed higher levels of same-sex sexual behavior. Species such as gorillas fall into this category. The authors suggest that this may be linked to dominance-related conflicts, where non-aggressive behaviors help to reduce tension and maintain social stability.
Not all proposed explanations were corroborated by the data. Smaller primate species were not more likely to engage in same-sex behaviors, and some environmental factors appeared to affect only one sex. For example, colder climates have been associated with higher rates of same-sex behavior in males but not in females.
The researchers also addressed the potential observer bias. Some species have been studied much more extensively than others, increasing the likelihood that behaviors between individuals of the same sex will be documented. When taking observation time into account, the team found marked differences, with some species rarely exhibiting this behavior and others demonstrating it frequently.
