Describe a kiss to someone who has never seen one and it sounds like a dare. Two people press their mouths together, swap breath and a little spit, and then call it the best part of the night.
Whole cultures have looked at that and said no thanks. Others have been doing it for as long as anyone has kept records. And our ape relatives were at it long before there were records, or humans, at all.
This is the origin story: when kissing started, who does it, and what it's for. If you came for what happens in your brain mid-kiss, that lives in the science of kissing.
When Did Humans Start Kissing?
Before we were humans.
In 2025, a team led by Matilda Brindle at the University of Oxford traced kissing through the primate family tree. They used a strict definition: friendly mouth-to-mouth contact between two members of the same species, with some movement of the lips and no food changing hands. Then they checked which monkeys and apes do it and worked backward.
Their best estimate is that kissing first appeared in the common ancestor of the great apes, somewhere between 21.5 and 16.9 million years ago, and stuck around in most of its descendants. That includes us. Their model also gave about an 84 percent chance that Neanderthals kissed, which fits earlier evidence that humans and Neanderthals shared mouth microbes. If they did swap saliva, that took a certain closeness.
The written record is far younger. For a long time the oldest known reference to kissing was in the Vedas, Sanskrit texts from South Asia about 3,500 years old. In 2023, Troels Pank Arbøll and Sophie Lund Rasmussen, researchers at the Universities of Copenhagen and Oxford, pushed that back about a thousand years. Mesopotamian clay tablets from around 2500 BCE already describe kissing, between lovers and also between family and friends.
Their bigger point: kissing didn't start in one place and spread outward. It turns up in several ancient cultures over thousands of years. Mesopotamian medical texts even describe a mouth disease, bu'shanu, with some symptoms that resemble cold sores.
Do Other Animals Kiss?
Yes, and a few of them are surprisingly good at it.
Brindle's team found kissing in most great apes and at least eight species of Old World monkeys. Each ape does it a little differently:
- Bonobos are the enthusiasts. Primatologist Frans de Waal described their kisses as long and full of tongue. Bonobos beat the French to it.
- Chimpanzees kiss mostly to make up. Their kisses tend to be brief and a little tense, and they show up most after a fight.
- Orangutans kiss rarely, sometimes as affection between family members.
- Eastern gorillas are the blank spot: the review found no record of them kissing, which may only mean nobody has seen it.
Outside the primates, the paper's examples of kiss-like behavior include wolves, prairie dogs, polar bears and albatrosses. Your dog licking your face doesn't count, by the way. The definition only covers kisses within a species. Sorry.
One caveat matters. Most ape kissing reports come from zoos and sanctuaries, and bonobos, for all their enthusiasm in captivity, haven't been seen kissing in the wild yet. Kissing might be partly learned even in apes.
Where Did Kissing Come From? Three Theories
Nobody knows for certain, and the experts disagree in entertaining ways.
Kiss-feeding. Long before baby food came in jars, caregivers chewed food and passed it mouth to mouth to their infants. It's called premastication, and it still happens in some cultures, especially among hunter-gatherers. Brindle's team found it in every ape species known to kiss, and called it, along with nursing, a more promising candidate than grooming for how kissing began, with an honest caveat: they had no data on the species that don't kiss.
The groomer's final kiss. Adriano Lameira of the University of Warwick argues that kissing is what's left of grooming. Grooming is how primates keep friendships and family ties strong. In his account, ancestral grooming sessions ended with the groomer pushing out its lips and sucking at the skin to lift off a last bit of debris or a parasite. As our ancestors lost their fur, grooming sessions shrank, but that final step survived until it was all that was left: a small ritual that means you're one of mine. He also spots a flaw in the feeding theory. Passing chewed food pushes outward. A kiss pulls in.
The Oxford team fires back with a fair challenge: nobody has yet checked whether today's apes really finish a grooming session with a kiss.
The close-range sniff. The third idea is that kissing grew out of smelling each other up close. Darwin noted in 1872 that in some parts of the world, rubbing noses took the place of kissing. And in many societies without mouth kissing, lovers often keep some face-to-face ritual of sniffing, licking or rubbing. A kiss puts your nose right against someone's skin, which may be part of the point.
My bet is that the answer isn't either-or. Evolution reuses old parts all the time, and a kiss could easily carry a little of all three.
What Is Kissing For?
An origin story explains how a habit started. It doesn't explain why we kept it. The best test I know comes from Oxford researchers Rafael Wlodarski and Robin Dunbar, who in 2013 surveyed 902 adults about when and why kissing matters to them. Three possible jobs, three verdicts:
- Sizing someone up: supported. Women, and people more open to casual sex, put more weight on kissing and were more likely to say a first kiss had changed how attracted they felt.
- Keeping a bond strong: supported. Kissing mattered more in long-term relationships, and how often couples kissed went along with how satisfied they were. How often they had sex did not.
- Getting things started: barely. The researchers found very little evidence that kissing's main job is to raise arousal and lead to sex.
That second finding is the one I'd frame and hang on the wall. A kiss is maintenance. It's probably also why a kiss outside a relationship can feel like far more than a kiss, and why couples argue over whether kissing counts as cheating.
What your body does during all this (the hormones, the racing heart, the drop in stress) is its own story, and I've laid it out in what kissing does to your body.
Does Every Culture Kiss?
No.
In 2015, anthropologists William Jankowiak, Shelly Volsche and Justin Garcia checked 168 cultures for romantic lip-to-lip kissing. They found it in 46 percent. Less than half.
The map is lopsided. All 10 Middle Eastern cultures in the sample kissed romantically, along with 73 percent in Asia, 70 percent in Europe and 55 percent in North America. In Central America they found none. Ethnographers working with foragers and small-scale farming groups in sub-Saharan Africa, New Guinea and the Amazon reported none either.
The pattern underneath: the more socially complex and stratified the society, the more likely it is to kiss. Most egalitarian hunter-gatherer groups don't kiss romantically. The big exception is the Arctic, where 9 of the 11 foraging communities in the sample did. The researchers' guess: when everyone is bundled head to toe in fur, the face is the main part left to explore.
Why would complexity matter? The authors float a few guesses: more leisure (they call kissing delayed eroticism, a tease), class etiquette that separates polite kisses from intimate ones, and maybe better oral hygiene.
People who didn't grow up with it are often unimpressed, the researchers wrote in a 2016 essay. When the Thonga of southern Africa first saw Europeans kissing in 1890, they were disgusted. The Mehinaku of Brazil reacted the same way a century later, and the Trobriand Islanders of Melanesia reportedly considered kissing "a rather insipid and silly form of amusement." Not that any of them were prudes: the Mehinaku are known to nibble each other's eyebrows during sex.
Two more things worth knowing. Kissing of some kind is close to universal: the same researchers note that at least 90 percent of cultures have it, mostly parents kissing children. And greeting kisses are a separate tradition with their own rules, from the kiss on the cheek to the kiss on the hand.
Is Kissing Instinct or Learned?
Both, and Darwin had the shape of the answer in 1872. Since so many peoples didn't kiss, he wrote, it couldn't be innate in the strict sense. But it was natural in a looser one, because it grows out of the pleasure of close contact with someone you love.
That still holds up. The pull toward close mouth contact is ancient: it's in our ape relatives and probably was in Neanderthals. The specific form, a romantic kiss on the lips, gets taught by the culture around you, which is why less than half of the cultures in that survey had it.
If your first kiss felt like a skill you were somehow supposed to have already, you weren't imagining it. It's an old urge that arrives without instructions.
What This Means the Next Time You Kiss Someone
Line up the theories and a pattern shows. Every serious explanation for kissing is about closeness and attention: feeding a baby, grooming a friend, getting near enough to smell someone, sizing up a new partner, keeping an old bond alive.
That's the oldest layer of every kiss you'll ever give. Craft sits on top of it. The kisses that stay with people, in my experience, are the ones where that attention comes through, which may also be why so many of our kissing habits are about shutting out everything else. Even closing your eyes turns out to be about where your attention goes.
We were kissing long before we were human. The least we can do is pay attention while we're at it.
Frequently Asked Questions
Do all humans kiss?
No. In a 2015 survey of 168 cultures, romantic lip-to-lip kissing showed up in only 46 percent, and it was rare among egalitarian hunter-gatherer groups. Some kind of kissing, mostly between parents and children, is far more widespread.
Did Neanderthals kiss?
Probably. A 2025 Oxford analysis of the primate family tree put the probability at about 84 percent, and earlier research found that humans and Neanderthals shared mouth microbes, which is what you'd expect if they were swapping saliva.
When was the first kiss in history?
Nobody can date it, because kissing is probably older than our species: it likely began in the common ancestor of the great apes, 21.5 to 16.9 million years ago. The oldest known written evidence of kissing comes from Mesopotamian clay tablets from around 2500 BCE.
Is kissing unique to humans?
No. Bonobos, chimpanzees and orangutans all kiss, and so do at least eight species of Old World monkeys, though most records come from zoos and sanctuaries. Researchers have also described kiss-like behavior in animals as different as wolves, prairie dogs, polar bears and albatrosses.
Why do some cultures think kissing is gross?
To people who didn't grow up with it, kissing can look unpleasant, unclean or just plain weird. The Thonga of southern Africa and later the Mehinaku of Brazil both reacted with disgust when they first saw it. Some cultures have their own close-contact rituals instead, such as rubbing noses.
