You slowly start to take off your partner’s clothes, and make your way down with prowess to their nether regions until your mouth is on their groin. After a few “oohs” and “ahs,” your partner gratefully returns the favor, and before you know it, you’re both on the bed, couch, or floor (if you’re feeling frisky) having penetrative sex. Although the foreplay feels good, is there any evolutionary purpose to oral sex aside from being a precursor to intercourse?

“Going Down” In The 21st Century

Oral sex hasn’t always been acceptable to discuss in public. In 1997, the Bill Clinton-Monica Lewinsky sex scandal shed light on the discrepancies that exist between oral sex and intercourse. The then 22-year-old White House intern kept in her possession a dress that still bore the semen stain that came from her giving oral sex to former President Clinton. Examination of both the semen sample and a sample of Clinton’s blood confirmed the semen came from the president.

However, Clinton denied allegations and recited the popular phrase: “I did not have sexual relations with that woman, Miss Lewinsky.” Meanwhile, in an interview with Barbara Walters, Lewinsky described her actions with Clinton as merely “fooling around.” Or, in other words, oral sex was just child’s play.

This scandal added to the misconception that oral sex is not real sex. Relationship expert and author April Masini notes that often young women are psychologically pressured into giving oral sex because they’re sold this story that it isn’t really sex.

“It’s a way of their giving and engaging in sex with their clothes on. That helps them believe that it’s not really sex,” she told Medical Daily.

Oral sex has evolved to be just as or even more common than vaginal sex among sexually active adults and teenagers, because it doesn’t lead to pregnancy. According to a national survey conducted from 2011 to 2013 by the National Center for Health Statistics, more than 80 percent of youth and adults ages 15 to 44 years reported having had oral sex at least once with a partner of the opposite sex. The same survey found that of teens ages 15 to 19, 47 percent of girls and 51 percent of boys are engaging in fellatio — oral sex performed on a male — and cunnilingus — oral sex performed on a female.

Drawing of mouth with tongue sticking out. Pixabay, Public Domain

Masini believes the high percentages of oral sex among teens derives from the idea oral sex is “safer” because it can’t get girls pregnant.

“Teen pregnancy used to be the dark cloud that hung over teen sex. Oral sex made it impossible to have sex and get pregnant so sex became “safer” for many teens who wouldn’t otherwise be having this type of sex," she said.

Previously, oral sex, specifically fellatio, was seen as a social stigma, and was even considered a felony in 48 states in 1950. However, it slowly evolved to become acceptable in marriages and known as an act more intimate than intercourse. It was not until the 1970s that oral sex was deemed socially permissible for unmarried couples to engage in, and eventually anilingus, stimulation of the anus with one’s tongue, gained some acceptance. States like Michigan, however, still keep an “anti-sodomy” law which criminalizes oral and anal sex, while most states dropped theirs when the Supreme Court ruled that law unconstitutional.

So, how did humans come to adopt this sexual behavior?

The Uprising Of Oral Sex: The Animal Kingdom

Researchers have speculated oral sex has several evolutionary roots in heterosexual relationships.

After all, when it comes to sex, we are all animals, according to Dr. Fran Walfish, Beverly Hills relationship and sex psychologist.

“When you look at people having intercourse, it’s all about movement, noise, grunting, pleasure, speed, and losing oneself to orgasm as animals do,” she told Medical Daily.

There is evidence that a type of chimpanzee called bonobos engages in fellatio, but this is infrequent and usually among the young. Because fellatio among bonobos is considered part of play, primatologists believe fellatio emerged as part of play rather than as part of sex since humans share up to 98 percent of their DNA with bonobos.

The Evolution Of Fellatio

However, a 2009 study observing fruit bats and their sexual behavior suggests they exhibit similar human-like mannerisms when it comes to oral sex. The short-nosed fruit bat penis is morphologically and physiologically similar to the primate and human penis because they both contain erectile tissue. The female fruit bat performs fellatio on the male to increase the duration of intercourse. This boosts the penis’ rigidity to make the erection last longer. At the same time, the female’s saliva may increase lubrication, according to the researchers, which prolongs sex.

Researchers theorize this effect has been transcended onto humans. Evolutionarily speaking, they believe fellatio will help a man’s erection last longer and improve thrusting during intercourse.

Carol Queen, a Staff Sexologist at Good Vibrations and author of The Sex & Pleasure Book: Good Vibrations Guide to Great Sex for Everyone, agrees oral sex can help prepare men for penetrative sex.

Many men will find “the extra arousal that fellatio can provide to be helpful in readying them for insertive sex — making the penis that much firmer, for instance,” she told Medical Daily.

Ice cream in waffle cone. Pexels, Public Domain

It’s likely to bring about ejaculation more quickly and help men “ride a wave” of arousal, but this will depend on the person’s sexual specificity.

Fellatio has also been linked to reducing the risk of sexually transmitted infections in male fruit bats. Saliva functions as an antibacterial and has antifungal, anti-chlamydial, and antiviral properties. After intercourse, fruit bats regularly lick their penises, which is believed to increase reproductive success and could provide an evolutionary explanation for fellatio in humans.

So, can oral sex also protect your offspring? Perhaps.

Evolutionarily speaking, fellatio could have come about to ensure survival of the fittest via the birth of a healthy offspring.  

The idea that “going down” on a man can help women prevent miscarriages sounds like fiction, but researchers suggest the science is real. A 2000 study found that with prolonged exposure to proteins in a mate’s semen a female’s immune system will acclimate to his sperm, as will a developing fetus. Women who regularly expose themselves to their partner’s semen, especially by mouth, help their immune system get used to the sperm.

In other words, because many of the “foreign” proteins in a woman’s immune system will come from the father’s genes in her body, her baby will be more likely to accept them with regular exposure. Typically, disorders during pregnancy stem from a woman’s immune system viewing a fetus as a “foreign body.” Although unconventional, swallowing semen could help carry pregnancies to full term, according to this study.

The Evolution Of Cunnilingus

Some hypothesize that, similar to fellatio, cunnilingus helps keep partners faithful. A 2013 study questioned 240 men in committed, sexual, heterosexual relationships to observe whether they perform oral sex to boost their female partners’ satisfaction with their relationship, thereby decreasing the probability she will cheat and potentially get pregnant by another man. The research showed that men who were most likely to report getting their partner to orgasm during oral sex were more likely to think their woman was sought after by other men. Therefore, the more eager men are to please partners believed to have better options the more likely they may be to perform cunnilingus to keep their mates from cheating.

Queen believes there are some advantages of cunnilingus before intercourse.

“It’s likely to greatly improve the experience of intercourse for women, because it tends to increase the degree of arousal she feels, which in turn will often make the difference between boring or even unpleasant intercourse and satisfying intercourse,” she said.

However, oral sex or intercourse will not stop infidelity in a relationship. Infidelity isn’t about sex, but rather, it’s about someone not feeling the way they want to feel in a relationship.

“It’s rarely about sex or someone who’s hotter. It’s usually just about feeling valued,” she said.

Whether fellatio or cunnilingus, oral sex is all about “pure pleasure.”

Oral Sex: What’s Your Pleasure?

The evolutionary roots of cunnilingus and fellatio are left to interpretation, but do leave the act of intercourse to be more closely associated with an objective to procreate. Oral sex however is often a precursor to sex that behaves like a lubricant.

“It lubricates women as a preparatory step toward intercourse, and it feels good too,” said Walfish.  

Moreover, engaging in oral sex is a way to stay connected to your partner. It’s often considered very intimate, even more so than penetration.  The act is purely selfless because you give while receiving nothing in return. Here, this shows you care about your partner and their needs, not just your own.

“You find pleasure in giving pleasure,” said Walfish.

Perhaps oral sex doesn’t have an evolutionary purpose, or perhaps it does, but one thing that’s clear — once you relax and let go, you only have more pleasure to gain, and less to lose.