If you asked me why I practice oral sex (receiving and giving) I would say “because it is so damned good and intimate!” And for most people this will be sufficient reason to put the head between the legs of another person every now and then, or to welcome that of another person in their own crotch. But there’s more. According to various scientific studies, there are other explanations why we humans occasionally spoil our partners orally.
According to a study published in the Journal of Reproductive Immunology in 2000, swallowing sperm causes a woman’s body to get used to the man’s DNA. And that could prevent the woman’s immune system from attacking the sperm when you try to get pregnant.
In other words: if you try to conceive, it may – according to this research – help to first present the DNA of the father of your future child to your immune system. This would reduce the chance of a miscarriage. The body may reject the fetus, which partly consists of ‘foreign’ DNA. Twenty years ago, the Dutch immunologist Carin Koelman came up with the idea that fellatio would be a good way to reduce that chance.
“It is known that there are antigens in seminal fluid. And the mucous in the mouth and stomach takes up antigens faster than the mucous of the vagina, and inhibits the immune system more efficiently,” says Tess Meuleman, one of the study’s authors.
There also seems to be a connection between swallowing sperm and less pregnancy poisoning. One study looked at 66 women who had had two miscarriages: although they practiced the same amount of oral sex as a control group, only a quarter swallowed the sperm, while half of those without pregnancy problems swallowed.
Meuleman warns that it is “absolutely not the intention” that after a miscarriage, women start to think “it is up to this.” About one in five pregnancies leads to a miscarriage with various causes. “We think that this is just one of many mechanisms.” Nor is it the intention that men are already ‘high-fiving’ and forcing their wives to blow them before they start making babies.
What about cunnilingus?
But going down on women also seems to have an evolutionary reason, according to scientists. A study published in Evolutionary Psychology in 2013 shows that men who think more men are interested in their partner (or in other words: that there may be men who would like to make their wives pregnant) are more likely to perform oral sex to make their partners orgasm.
The researchers think that men expect their wives to cheat less quickly if they regularly eat her. And that in itself has an evolutionary advantage, because that way the man increases his chance of his own offspring.
However, none of these studies explain why people in a non-hetero normative relationship also have oral sex. Or – in plain English- why gays and lesbians go down on each other. Perhaps there is an evolutionary component, but it is very likely that we just love giving our partners a great orgasm this way.