A large scientific study published Monday in Nature indicates that genes associated with same-sex sexual behavior could confer certain evolutionary advantages to heterosexual individuals.
That is one of the conclusions of research led by experts from the University of Queensland (Australia), with which they try to answer a “Darwinian paradox” about sexuality.
In human societies, between two and 10% of individuals engage in “same-sex sexual behavior” (SSB), either “exclusively or predominantly,” explains Brendan Zietsch, the study’s lead author, in a statement.
However, he recalls that evolution “tends to favor genes and traits” that facilitate the reproduction of species.
“So, given that individual differences in sexual behavior towards one sex or the other are associated with genetic differences, why might the genes associated with non-reproductive sexual behavior have survived evolution?
One hypothesis, he explains, is that the genes associated with SSB, when present in individuals who engage in opposite-sex sexual behavior” (OSB), may “be advantageous” and, consequently, “counteract their evolutionary cost.
To explore that premise, the team led by Zietsch analyzed the genetic effects of OSB with a genome-wide association study (GWAS) of 477,522 individuals registered in U.S. and U.K. databases.
They also estimated the genetic effects of OBS with a GWAS of 358,426 individuals (from those same two countries) who claimed to have had only opposite-sex partners and who specified how many they have had so far.
“We have shown that, among individuals who have never had a same-sex partner, the genetic effects associated with SSB are related to having more opposite-sex partners throughout life,” says Zietsch, who speaks, in that sense, of “mating advantage” and, ultimately, for the reproduction of the species.
“Computer simulations,” he continues, suggest that “this advantage for genes associated with SSB” would lead populations to “maintain their predisposition” toward “same-sex sexual behavior.”
Zietsch acknowledges that “many questions remain to be resolved” and warns that this study has “important caveats.”
For example, he says, this analysis only includes current individuals from the United States and the United Kingdom, “where social conventions regulating sexual behavior” make it difficult to “draw robust conclusions” on this issue over “thousands of years of evolutionary history.”
“We also recognize that mating success is difficult to measure and that the number of opposite-sex mates over a lifetime has substantial limitations. In addition, the DNA variants analyzed capture only a small proportion of all genetic variation in sexual behaviors,” Zietsch concludes.