Scientists Uncover the Surprising Origins of Kissing, and It’s More Gross Than Romantic

No one knows when humans started kissing, but it’s clear that kissing isn’t something everyone does. It seems more like a cultural thing than something we’re born knowing. So, let’s rewind and explore what might have caused kissing.

Kissing is also not just a human thing.

Other primates, like bonobos and chimpanzees, kiss each other too. Adriano Lameira, a primatologist and evolutionary psychologist at the University of Warwick, thinks this might give us a clue about where kissing came from... although it’s a pretty gross idea.

Lameira believes that early kissing could’ve been part of the grooming process. Picture it: when one primate was grooming another and found dead skin or a parasite, they’d use their lips to suck it away. Over time, we didn’t need to groom each other as much, but that lip-smacking part stuck around.

There are a few theories.

Lameira writes that “the hygienic relevance of grooming decreased over human evolution due to fur-loss,” but “shorter sessions would have predictably retained a final ‘kissing’ stage, ultimately, remaining the only vestige of a once ritualistic behavior for signaling and strengthening social and kinship ties in an ancestral ape.” Humans have records of kissing going back thousands of years, so it’s clear it’s stuck around for a reason. But why?

One idea is that kissing has to do with feeding babies pre-chewed food. But kissing involves puckering up with suction, and giving food to a baby would require pushing it into their mouth, not sucking it in. So, that doesn’t add up.

Another idea is that kissing came from sniffing others as a way to check them out socially, but why would the mouth need to be involved?

Instead, Lameira thinks kissing might have started as a way to reassure each other. Humans, like other primates, are social creatures, and we form bonds through rituals.

For other primates, grooming each other is how they build those bonds.

There are a few theories. One idea is that kissing has to do with feeding babies pre-chewed food. But kissing involves puckering up with suction, and giving food to a baby would require pushing it into their mouth, not sucking it in. So, that doesn’t add up.

Another idea is that kissing came from sniffing others as a way to check them out socially, but why would the mouth need to be involved?

Instead, Lameira thinks kissing might have started as a way to reassure each other. Humans, like other primates, are social creatures, and we form bonds through rituals.

For other primates, grooming each other is how they build those bonds.

“Grooming consists of picking through the fur/hair of others to remove parasites, dead skin, and debris,” Lameira says. “It helps to establish and maintain alliances, hierarchies, and group cohesion through social touch, with the consequent release of endorphins, which reduces stress and promotes feelings of well-being between groomer and groomed, further cementing social ties.”

Humans don’t spend nearly as much time grooming each other as other primates. We don’t need to, since we don’t have fur and can clean ourselves in other ways. But as we lost our fur, we might have kept a little piece of the grooming ritual.

One of these leftover habits, Lameira says, could be what he calls the “groomer’s final kiss.” Even though grooming each other became less necessary, every grooming session might have ended with a quick lip-to-skin kiss to clean up any leftovers.

This could have naturally led to the mouth-to-mouth kiss we know today.

It might sound a little gross, but it makes more sense than some of the other theories we’ve heard. We’ll probably never know for sure, but we can look at how other primates groom each other to learn more.

Lameira adds that “it will be important to retain in mind and ponder the influence of the broader socioecological, cognitive, and communicative context of human ancestors.” So, next time you’re kissing your partner, try not to think about bugs in their hair!