A new evolutionary study is pushing the timeline of the “first kiss” far deeper into the past than expected. Researchers now say that the behaviour likely emerged more than 21 million years ago, long before modern humans appeared, and was almost certainly practised by the common ancestor of great apes.
Evidence from primates and beyond
According to Science.org, the team worked on a basic question: if kissing offers no clear survival advantage, why is it so common? They began by mapping where the behaviour appears in animals. That meant setting a narrow definition - non-aggressive, mouth-to-mouth contact, some movement, no food exchanged - as laid out in Evolution and Human Behaviour.
Once defined, examples started stacking up. Wolves. Prairie dogs. Polar bears, often with exaggerated “tongue-heavy” contact. Even albatrosses. But the focus stayed on primates.
“Humans, chimps, and bonobos all kiss,” said lead researcher Matilda Brindle of the University of Oxford. In her view, that pattern points to a shared origin. “It’s likely that their most recent common ancestor kissed. We think kissing probably evolved around 21.5 million years ago in the large apes,” she told BBC.
Links between modern humans, Neanderthals and shared microbes
The study also looked at ancient relatives, as per the BBC. Researchers noted earlier DNA work showing that Neanderthals and modern humans shared an oral microbe - a bacterium typically passed through saliva. A previous study on Neanderthal DNA signals saliva exchange long after the evolutionary split, suggesting that Neanderthals engaged in the same behaviour.
Researchers did not attempt to explain why kissing emerged. Their findings only address when the behaviour likely appeared, leaving existing theories unchanged. Some of them link it to grooming in early apes, while others suggest it acted as a health or compatibility check between partners. The new timeline doesn’t rule out any explanation.
A behaviour shared across species
For researchers, the study’s broader takeaway is that kissing is not uniquely human and not simply romantic. It appears repeatedly in nature, across species that otherwise share little.
“It’s important for us to understand that this is something we share with our non-human relatives,” Brindle said.
She added that the behaviour should be studied with the same seriousness as other social interactions, rather than dismissed because of its association with human relationships.
With primates, ancient human relatives and even distant animal groups showing similar mouth-to-mouth contact, researchers argue that kissing may be less of a cultural invention and more of a long-standing social tool.
FAQs
How old is the earliest evidence of kissing?
Scientists estimate the behaviour emerged more than 21 million years ago.
Did Neanderthals kiss as well?
The study suggests they likely did, supported by shared oral microbes with modern humans.
Which animals show kiss-like behaviour today?
Examples include chimps, bonobos, wolves, prairie dogs, polar bears and some birds.
