It’s an image that feels timeless: two lovers leaning in, eyes half-closed, lips meeting in a soft embrace. The kiss is a gesture so universal that it seems like it must always have existed. But according to new research, that intimate press of lips might be a lot older than love stories or wedding vows.

A researcher from the University of Warwick thinks the kiss could trace back millions of years — to when our ancestors used their mouths not for romance but for grooming.

In a new study out this week, Adriano Lameira, an evolutionary psychologist at the University of Warwick, explores this surprising theory. By studying the social habits of great apes (our closest evolutionary relatives) Lameira has proposed what he calls the “groomer’s final kiss hypothesis.”

This theory suggests that our intimate human kiss may have evolved from a practical gesture: the mouth-to-mouth contact of apes grooming each other to remove dirt and parasites.

“The only behavior in the great ape repertoire that fulfills the same form, function, and context as kissing is the last step of grooming,” he told Science in an interview. This “final kiss” of grooming, he argues, could be the original seed of what we now call a kiss.

From Fur to Flesh

For our thick-furred ancient ancestors, parasites and dirt were constant nuisances. For them, grooming was more than social — it was about survival. In great ape communities, individuals spend hours plucking debris from each other’s coats, forging close bonds along the way. In the final moments of a grooming session, Lameira observed, apes often lean in with protruding lips, applying light suction to pick off the last bits of grime.

“The groomer approaches the groomee with protruded lips and does a suction movement to latch on to whatever parasite or debris it may have found,” Lameira says.

As our ancestors lost their body hair and evolved into the “naked apes” we are today, the need for grooming diminished. Yet, the final step — the close lip contact — remained. For these early humans, the “last kiss” transformed from a practical habit to something else entirely: a relic of social bonding, stripped of its hygienic function but rich with symbolic meaning.

Today, we recognize this lip-to-lip contact as a symbol of love or intimacy, a gesture that says, “You’re special to me.” But Lameira suggests it’s also a behavioral fossil, a ritualized remnant of something much older. “As our lineage evolved, we lost our fur,” he explains, “but we held on to a crystalized artifact of grooming that could be used as a symbol.”

Evolutionary roots of kissing

For Lameira, understanding the evolutionary roots of a kiss means looking closer at our closest relatives. In the animal kingdom, kissing-like behavior is rare and limited to our fellow primates. Apes, for instance, share quick touches of their mouths after conflicts, a gesture that resembles the way humans reconcile.

Even so, it’s not quite the same as human kissing. Capuchin monkeys, for example, show affection by sticking fingers in their friends’ eyes — attention-grabbing, yes, but not quite affectionate to humans. His best bet for the origin of kissing seems to be this “groomer’s final” smooch.

Lameira’s theory is not definitive, but it opens new doors for exploration. He suggests that we may observe the behavior of apes with less fur or those that live in captivity. It might reveal whether this final “kiss” persists when grooming times are shortened. If the grooming ritual still ends with that light lip suction, he believes, it could support his hypothesis that this is a hard-wired behavior.

The research suggests that even the most intimate human acts have roots in ancient survival behaviors. By keeping close bonds, grooming their mates, and sharing trust, our apelike ancestors may have set the stage for the very gestures that help define us.

The Lasting Touch

For the time being, however, this is just a hypothesis — one that further research may confirm in the future. Other plausible explanations for the origin of the kiss links the act of kissing to breastfeeding. As babies, humans have an instinctive inclination to suckle, which creates a positive association with lip contact.

Another possible origin lies in a less familiar maternal behavior: premastication, or pre-chewed food transfer. In the early years of human evolution, mothers likely pre-chewed food for their infants and delivered it directly to their mouths, similar to the way many great apes feed their young.

There is also the possibility that kissing is just a weird human quirk, one that is heavily cultural. In fact, many societies, particularly indigenous hunter-gatherer groups, consider it strange or even unpleasant. In a 2015 study published in American Anthropologist, only 46% of cultures engaged in romantic kissing, showing that kissing, as we know it, is often an acquired taste rather than an instinct.

For cultures that don’t practice kissing, intimacy is expressed in other unique ways. For example, the Trobriand Islanders of Papua New Guinea practice an “eyelash kiss,” where lovers sit face-to-face and gently nibble each other’s eyelashes. In Malaysia, an ancient form of intimacy involves sniffing, where one partner would inhale the scent of the other.

Lameira’s research was reported in the journal Evolutionary Anthropology.