The question of why we have oral sex seems like a no-brainer: because it feels damn good. But recent research shows there could be a few other, slightly less conscious and slightly more scientific reasons why both men and women engage in oral sex.
First up, there's an evolutionary explanation. According to a study published in 2000 in the Journal of Reproductive Immunology, swallowing semen can make your body accustomed to someone's DNA so that your immune system doesn't act up during pregnancy. Since a number of pregnancy disorders stem from recognizing the father's genes as foreign, introducing them into your body beforehand can help you out when you're pregnant. It sounds strange, but scientists believe it's a possible evolutionary explanation for blow jobs.
What about when men go down on women? That practice could've also been inherited from our ancestors. One study published in 2013 in Evolutionary Psychology found that men who perceived that a lot of other guys were interested in their partner (aka men who had "greater sperm competition") were more likely to make their female partners orgasm through oral sex. The authors speculate that the act might function to prevent cheating, which in turn prevents sperm competition and helps men pass on their genes.
Neither of these explanations, however, explain why people who aren't in heterosexual relationships have oral sex—which obviously happens in same sex couples all the time. It's one example of how the reasons a behavior evolved within a species aren't always the same as the reasons we actually decide to do it. Mostly, we have oral sex because it feels good or we want to make our partner feel good—and pleasure is reason enough.
Originally Appeared on Glamour