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Kissing dates back over 21 million years, shared by apes and possibly Neanderthals
A new study published in Evolution and Human Behaviour reveals that mouth-to-mouth kissing likely emerged more than 21 million years ago, practiced by the last common ancestor of humans and great apes. Researchers also suggest Neanderthals engaged in the behavior-and may have even exchanged kisses with early humans.
The evolutionary puzzle of kissing
Kissing presents a biological mystery: it confers no clear survival or reproductive advantage, yet it appears across species, from primates to polar bears. To trace its origins, scientists defined kissing strictly as non-aggressive, directed oral contact involving lip or mouth movement, without food transfer.
By analyzing this behavior in animals-including wolves, prairie dogs, and albatrosses-the team constructed an evolutionary timeline. Their findings indicate kissing likely arose 21.5 million years ago in large apes, shared by humans, chimpanzees, and bonobos today.
Neanderthals in the kiss: Evidence from ancient DNA
The study also proposes that Neanderthals, who coexisted with modern humans until ~40,000 years ago, kissed. Supporting this, prior research identified a shared oral microbe in Neanderthal and human saliva, implying centuries of saliva exchange post-species divergence.
"They must have been swapping saliva for hundreds of thousands of years after the two species split," said lead researcher Dr. Matilda Brindle, an evolutionary biologist at the University of Oxford.
Unanswered questions: Why do we kiss?
While the when of kissing's evolution is clearer, the why remains speculative. Theories include:
- An extension of grooming behaviors in ape ancestors,
- A method to assess partner health or genetic compatibility via chemical cues.
Dr. Brindle emphasized the need for further study: "We should be studying this behavior, not dismissing it as trivial because of its romantic associations in humans."
Beyond humans: Kissing in the animal kingdom
The research documented kissing-like behaviors in diverse species:
- Polar bears: "Sloppy" tongue-heavy contact,
- Wolves and prairie dogs: Lip-based interactions,
- Albatrosses: Beak-to-beak touching, akin to a "bird kiss."
This cross-species evidence underscores kissing's deep evolutionary roots-far older than human romance.
