There's Evolutionary Advantage to Homosexuality in Mammals

The case has been made that sexual behavior between those of the same sex is "non-adaptive," meaning there is no evolutionary advantage. That's not true, according to new research that finds the behavior, witnessed across at least 1,500 animal species from crickets to dolphins to deer, could help groups get along—clearly very important to survival. Indeed, the study published Tuesday in Nature Communications aims to expand what behaviors are considered "adaptive," per the Washington Post. Researchers at the Spanish National Research Council and the University of Granada compiled a database of information on same-sex sexual behavior among 261 mammals and found it often occurs in species who live in groups with high social interaction, per the New York Times.

They argue the behavior might have evolved to help form bonds and reduce intrasexual aggression and conflict, which threatens to tear a group apart. "Rather than a maladaptive or aberrant behavior" in nonhuman mammals, it's "a convergent adaptation facilitating the maintenance of social relationships," as University of Granada professor of ecology José María Gómez puts it to the Post. Primatologist Christine Webb, who was not involved in the research, agrees "sexual behavior between same-sex partners seems to function to mitigate [social] tension." Conservation scientist Christine Wilkinson, also unaffiliated with the study, gives the example of African lions, who "travel together and help each other to survive" while "also mounting each other and sort of bonding in more physical ways," per the Post.

Others will argue that same-sex sexual behavior, which researchers found to have arisen independently in lineages scattered across the evolutionary tree, is "part of a strategy to take advantage of as many opportunities to mate as possible," reports the Times. There could be many factors at work, though previous studies looking at same-sex sexual behavior in individual species also posited the idea that it was favored in the evolution of social groups. This study found males and females were basically equally likely to be spotted engaging in same-sex sexual behavior, though the behavior was limited to only one sex among certain species. Researchers caution same-sex sexual behavior in animals is very different than in humans, a subject the study does not explore. (More homosexuality stories.)