Homosexuality may not be completely genetically programmed, and environment — or how one is reared — can play a very important role in shaping, or even changing one’s sexuality, suggests new research.While the findings are based on a study conducted on fruit flies, the researchers believe that some aspects of sexual orientation in humans could have a similar mechanistic basis to that of flies.“Our study offers a conceptual basis to explain how nature and nurture interact in shaping human sexual orientation,” said one of the researchers Daisuke Yamamoto, professor at Tohoku University in Sendai, Japan.The scientists discovered that homosexual behavior in certain groups of male fruit flies can be altered by their environment. Specifically, they showed that the sexual preferences of male fruit flies with a mutant version of a gene known to affect male sexual behavior can vary depending on whether the flies are reared in groups or alone.The neurons that express the fruitless (fru) gene “basically govern the whole aspect of male sexual behavior,” Yamamoto explained.Normal male fruit flies tap the abdomen of a female to get a whiff of her sex pheromones before pursuing her to mate. In contrast, males with a mutant version of the fru gene show no interest in females. Instead, they set off in vigorous pursuit of other males.Yamamoto wanted to analyze the role of vision in the courtship behavior of normal and mutant fruit flies. The researchers found that visually induced courtship behavior in the fru mutant males can be blocked by isolating them right after their emergence from the pupa.The finding that courtship behavior in mutant flies can change according to how they are reared suggests that experience can shape behavior. Yamamoto said he was “terribly surprised” by the results, because he had previously never doubted that male-to-male courtship in fru mutant males was “solely genetically programmed”.The findings appeared in the journal Nature Communications.