Homosexual behaviors among mammals are more frequent in social species. Sporadic relationships between individuals of the same sex, whether males or females, help establish and maintain bonds in the most socially complex groups of mammals, and could constitute an evolutionary adaptation. Among males, they also represent a way to mitigate aggression and conflicts.
Scientists around the world have recorded homosexual behavior in more than 1,500 species of animals over the years. There are documented examples among mammals, birds, fish, reptiles and amphibians, but also in insects, arachnids and echinoderms. However, and despite the richness and diversity of cases, the scientific community is not so clear about what motivates these behaviors, given that they do not contribute to the reproduction of a species and, therefore, do not seem to directly favor its survival.
“The expression of sexual behavior that does not end in reproduction has always been considered a Darwinian puzzle,” says José María Gómez, researcher at the Experimental Station for Arid Zones of Almería (EEZA-CSIC), in conversation with La Vanguardia. The scientist has led a study, published this Tuesday in Nature Communications, in which he tries to shed some light on the evolutionary meaning of these behaviors among mammals.
The team of Spanish evolutionary biologists led by Gómez has analyzed the 261 species of mammals in which homosexual behavior is documented, and has seen that it occurs with the same frequency in males and females. On the other hand, the behavior does not occur transversally among all species, but rather the cases are concentrated in some lineages, especially among non-human primates (such as lemurs and apes).
By comparing the frequency of behaviors with the level of socialization and violence of each species, researchers have found two associations. Firstly, homosexual behaviors appear, in both sexes, more frequently in social animals. Second, they are more prevalent among males who exhibit greater violence towards other males.
“Our significant associations suggest that at least social behavior and intrasexual violence, that is, between individuals of the same sex, are two drivers that have helped this sexual behavior emerge,” describes the expert. That is to say, according to the authors, homosexual behaviors in mammals may have arisen as a result of socialization, and represent a way of establishing, maintaining and reinforcing social relationships, in addition to helping to calm conflicts.
However, “we do not rule out that other causes, in combination with these that we have found, have helped shape this very complex behavior,” Gómez asserts. Their work has not evaluated non-adaptive hypotheses, in which sporadic sexual relations with individuals of the same sex are the result of an error, a limited number of individuals of the opposite sex, or simply a consequence of frustration derived from rejection, therefore which cannot confirm or reject them.
The idea that sporadic sexual relations between animals of the same sex may have arisen as a result of socialization or violence is not new. Both have been verified at the species level in macaques, bonobos, dolphins and bison and, in fact, represent the starting point of this research.
The novelty here is that Spanish biologists have evaluated both hypotheses with respect to all mammals, using as a basis the knowledge accumulated over the years by the scientific community. That is, instead of focusing on a single species or lineage, they have evaluated them at a much higher level of complexity. This has made it possible to identify the development of homosexual behaviors in mammals as one of the evolutionary strategies that allows establishing the cohesion and stability of social groups.
Experts emphasize that their results do not explain human homosexual relationships. The behaviors analyzed in animals are “a trait that the way it manifests is very different from how we are used to talking about gender issues: it is a transitory trait, it is not permanent, many times instantaneous and of course it is manifested by individuals who Then they also manifest sexual behavior with individuals of the opposite sex,” says the EEZA-CSIC researcher.
Now, the fact that human behavior cannot be explained by the hypotheses of socialization and violence does not mean that our species does not provide solidity to the study. “We are social, we have intersexual violence, and we manifest both types of sexual behavior between individuals of the same sex, both male and female,” Gómez explains. “The human being fits very well into our results, but these cannot express how the human being expresses himself,” she concludes.
