A landmark scientific study traces the Evolution of Kissing across primates, revealing that the intimate behaviour likely began 21.5–16.9 million years ago in ancestral apes. The research also suggests Neanderthals may have kissed, offering new insights into bonding, mate choice, and social communication.
The Ancient Story of Kissing: What Primates Teach Us About an Intimate Human Gesture
For something so familiar, so instinctive, and so deeply woven into the human experience, kissing remains one of our least understood behaviours. It has inspired poetry, shaped culture, and ignited revolutions of love and longing. Yet until recently, scientists could only guess how far back this intimate act stretched in our evolutionary past.
A new comparative study by researchers at Oxford, UCL, and the Florida Institute of Technology offers the clearest picture yet. Their conclusion is astonishing: kissing is not a cultural invention, nor a quirk of human romance. It is an ancient behaviour, likely emerging over 21 million years ago in the distant ancestors of great apes.
And the trail of evidence suggests that even Neanderthals kissed.
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A New Definition for an Old Gesture
One of the study’s most important contributions is a simple yet groundbreaking idea: to understand the evolution of kissing, we must strip away the cultural baggage surrounding it.
Instead of romanticised language, the authors define kissing as:
“A non-aggressive, directed, intraspecific mouth-to-mouth contact involving movement, with no food transfer.”
This allows the act to be studied in primates on their own terms—not as proto-humans but as species with their own social worlds.
Under this definition, researchers combed through decades of field observations, videos, behavioural records, and scientific literature. The result is a surprisingly rich portrait of kissing across primate species.
Where Kissing Lives in the Primate World
Kissing, as we know it, appears most clearly in great apes:
- Bonobos kiss frequently—sometimes tenderly, sometimes erotically, sometimes to ease tension.
- Chimpanzees use brief, tight-lipped kisses after conflicts, signalling reconciliation.
- Orangutans have been observed kissing their offspring and occasionally each other.
- Gorillas kiss rarely, and Eastern gorillas show no confirmed cases at all.
Outside the great apes, the behaviour becomes more scattered. Several macaque and baboon species engage in mouth-to-mouth contact, especially in same-sex interactions, though the context differs widely—from social bonding to sexual expression.
This patchiness puzzled researchers. Was kissing an innovation that arose in several lineages? Or a relic from a deep ancestor?
Their phylogenetic analysis produced a striking answer.
Kissing Began With the Great Apes
Bayesian models indicate that kissing likely evolved once, in the ancestor of all great apes, sometime between 21.5 and 16.9 million years ago. It wasn’t lost in humans, chimpanzees, bonobos, or orangutans—but may have faded out in gorillas.
This makes kissing far older than humanity itself.
It also means that kissing is not just a behaviour we inherited from our evolutionary cousins. It is a behaviour that shaped the social lives of primates long before Homo sapiens existed.
Did Neanderthals Kiss? The Evidence Suggests They Did
Though we cannot observe Neanderthals directly, scientists can reconstruct probabilities from evolutionary patterns and ancient DNA.
Using their models, the authors estimate with 84% confidence that Neanderthals likely kissed.
The strongest supporting clue comes from their oral microbiomes. Neanderthals and early humans shared a strain of oral bacteria (Methanobrevibacter oralis) long after their evolutionary split. Such close microbial transfer is hard to explain without intimate contact—food sharing, premastication, or kissing.
This reframes how we imagine Neanderthal emotional lives. They were not brutish or aloof—they likely touched, bonded, comforted, and loved in ways uncannily familiar to us.
Why Did Kissing Evolve at All?
The evolutionary puzzle is simple: kissing doesn’t obviously help survival. It spreads disease more than it prevents it. Yet it persists across primates.
The study highlights several theories:
1. Bonding and Reconciliation
In bonobos and chimpanzees, kissing reinforces trust and soothing after conflict—an emotional glue.
2. Mate Assessment
Humans often detect chemical cues during kissing. Apes may do the same—evaluating fertility, health, or compatibility.
3. Sexual Selection
Kissing may increase arousal, strengthen pair bonds, or enhance reproductive success.
4. Microbial Exchange
Sharing microbes can strengthen immunity and synchronise group-level health.
5. Exaptation from Maternal Care
One promising idea is that kissing may have evolved from premastication—mothers pre-chewing food for infants. This requires mouth-to-mouth contact and may have been repurposed into affection and bonding.
The truth may be a combination of these factors. What is clear is that kissing is not frivolous. It is functional, meaningful, and deeply rooted in the biology of social species.
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A Gesture Carrying 21 Million Years of History
This new study offers a remarkable lens through which to view an ordinary human act. When we kiss—our partners, our children, our loved ones—we’re participating in a behaviour that predates language, tools, fire, and even humanity itself.
It is a biological inheritance older than our species, carried across millions of years, shaped by ancestors who kissed long before we ever walked the earth.
A kiss, it seems, is not just affection.
It is ancestry.