Oral sex has accompanied humanity for quite a long time, as evidenced by paleolithic cave paintings. But was the sexual practice tailored by evolution for a greater reproductive purpose than mere pleasure?
It would seem that something so intimately linked to reproduction would have some evolutionary function, since biological evolution is driven by reproductive outcomes. But whether oral sex is an evolutionary adaptation of some kind is unclear.
Researchers at Oakland University at Rochester investigated whether cunnilingus — performing oral sex on a woman — could help men pass on their genes. The results of the study were published in Evolutionary Psychology.
“What we can say for sure is that oral sex is certainly part of human evolution, as evidenced by the fact that it (1) occurs in virtually all cultures, (2) occurs in several non-human species, and (3) is depicted in human ancestral cave paintings,” Michael N. Pham, the lead author of the study, told PsyPost. “The question is whether oral sex is somehow adaptive (i.e., if it helped people increase their survival or reproduction, in the same way hunger motivates people to eat to increase their survival), or if it’s merely a byproduct of something else (in the same way that male nipples serve no survival/reproductive benefit).”
Previous research had indicated that inducing orgasm through oral sex increased sperm retention via uterine contractions, which increased the chances of conception.
In their study of 243 men, Pham and his colleagues found those at greater risk of infidelity were more likely to perform cunnilingus on their partner until she achieved orgasm. However, the men also reported that cunnilingus-assisted female orgasm did not occur during the brief time period during which it might function to retain sperm.
“There are multiple evolutionary hypotheses regarding the function of cunnilingus,” Pham said. “What we can say from the target study is that the evidence doesn’t appear to support the hypothesis that cunnilingus functions as a sperm retention strategy. Currently, I believe that cunnilingus may function to help men detect whether their partner is at high versus low fertility. Such information is valuable to men because knowing when your partner is at peak fertility allows them to guard their partner from other men, thereby reducing cuckoldry risk. Some studies already document this.”
For instance, research published in Hormones and Behavior in 2006 found women’s ovulatory cycle had an effect on their male partners’ behavior. At their most fertile period, their male partners became more defensive of the relationship.
“Guarding one’s mate during peak fertility is an extremely common behavior in non-humans, such as primates (and primates also perform oral sex during peak fertility),” Pham told PsyPost.
The study also noted a very well-documented function of cunnilingus: pleasing your partner. From an evolutionary perspective, this could help men pass on their genes by strengthening the emotional bond between partners, making men less likely to have their partner seek out a different mate. It could also encourage future copulation by making it a more enjoyable experience.
“The important caveat is that, as evolutionary scientists, we should not be so hasty to link various behaviors to adaptations,” Pham said. “Many behaviors are simply byproducts, and therefore may not be linked to any survival or reproductive benefits.”