It is surprising that sexual behavior between individuals of the same sex has been observed in more than 1,500 animal species, covering a wide range of taxonomic groups. These species range from invertebrates – such as insects, spiders, echinoderms and nematodes – to vertebrates – such as fish, amphibians, reptiles, birds and mammals. It is a phenomenon that challenges conventional explanations of reproduction and raises important questions about its function and evolution in the natural world.
Perhaps that is why it has attracted the attention of various academic disciplines, including zoology and evolutionary biology. Same-sex sexual behavior is defined as any momentary behavior, normally performed with a member of the opposite sex, but instead directed toward individuals of the same sex. Despite not directly contributing to reproduction, this type of sexual behavior represents a mystery from an evolutionary perspective.
Our research group has explored the evolution of sexual behavior between individuals of the same sex in mammals in a study that has just been published in the magazine Nature Communications.
Sexual behavior between individuals of the same sex appears to be a common tendency in mammals. So far it has been recorded in approximately 5% of species and 50% of families, and is practiced with similar prevalence by males and females.
According to available data, this behavior is not randomly distributed among mammalian lineages, but rather tends to be more prevalent in some groups, especially primates, where it has been observed in at least 51 species, from lemurs to apes.
In some species, this behavior is occasional and manifests itself only under very specific circumstances. However, in 40% of species homosexual behavior is a moderate or even frequent activity during the mating season.
These findings raise fascinating questions about the biology and evolution of sexuality in the animal kingdom.
A way to strengthen social relationships
Our study has made an intriguing discovery by revealing significant links between same-sex sexual behavior in mammals and their patterns of social behavior.
Our analysis confirmed that species that exhibit more developed social behavior, both in males and females, have a greater probability of manifesting these sexual interactions between individuals of the same sex. These results support the hypothesis that this sexual behavior has been evolutionarily favored as a way to establish, maintain and reinforce social relationships that can increase ties and alliances between members of the same group.
This comparative phylogenetic analysis also found a relationship between this sexual behavior and intrasexual violence – between individuals of the same sex – but only in the case of males. Species whose males are more violent are more likely to exhibit this sexual behavior at some point in their lives.
The study therefore suggests that same-sex sexual behavior exhibited by non-human mammals is an adaptation that plays an important role in maintaining social relationships in both sexes and mitigating conflicts primarily between males.
Be careful with extrapolating to human beings
In any case, we emphasize the need for caution, since these associations could be due to other factors. Furthermore, the results do not exclude other hypotheses about the evolution of sexual behavior between individuals of the same sex, which require further investigation.
It is also important to note that the results should not be used to explain the evolution of sexual orientation in humans. This is because the study focused on sexual behavior between individuals of the same sex defined as short-term courtship or mating interactions, rather than as a more permanent sexual preference.
Finally, we must keep in mind that sexual behavior has only been carefully studied in a minority of mammalian species. This implies that our understanding of the evolution of same-sex sexual behavior in mammals could change as more species are investigated in the future.
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