Media release

From: Springer Nature

1.  Animal behaviour: Investigating the evolution of same-sex sexual behaviour in mammals

Same-sex sexual behaviour may have evolved repeatedly in mammals, according to a Nature Communications paper. The authors suggest that this behaviour may play an adaptive role in social bonding and reducing conflict.

Same-sex sexual behaviour has been reported in over 1,500 animal species, including all main groups from invertebrates (such as insects, spiders, echinoderms, and nematodes), to vertebrates (including fish, amphibians, reptiles, birds, and mammals). It is particularly prevalent in nonhuman primates, where it has been observed in at least 51 species, from lemurs to apes. Many adaptive and non-adaptive hypotheses have been proposed to explain its evolution, but these are difficult to test in studies of single species.

To investigate the evolution of same-sex sexual behaviour in mammals, José Gómez and colleagues systematically surveyed the literature to compile a database of records of this behaviour. They then traced the evolution of this behaviour across mammals and tested for evolutionary relationships with other behaviours. They found that same-sex sexual behaviour is widespread across mammal species, is similarly frequent in both females and males, and appears to have multiple independent origins. The analyses showed that this behaviour was more likely to evolve in social species leading the authors to suggest that this behaviour helps establish and maintain positive social relationships. Examples include bonobos, chimpanzees, bighorn sheep, lions, wolves, and several species of wild goat. Additionally, they found that male same-sex sexual behaviour was more likely to evolve in species with adulticide (species in which adults sometimes kill other adults) by males. This suggests that it may be an adaptation to mitigate the risks of violent conflict between males.

The authors note that these associations could be driven by other factors, and the findings do not exclude other hypotheses for the evolution of same-sex sexual behaviour, which require further investigation. The authors caution that the findings should not be used to explain the evolution of sexual orientation in humans, as the study focused on same-sex sexual behaviour defined as short-term courtship or mating interactions, rather than a more permanent sexual preference. They also note that sexual behaviour has been studied carefully in only a minority of mammal species, and thus our understanding of the evolution of same-sex sexual behaviour in mammals may continue to change as more species are studied.