Kissing Didn’t Start With Humans – Research Says It Began 21 Million Years Earlier

New research shows kissing existed long before our species ever appeared. A new evolutionary analysis suggests that early primates were already kissing at least 21 million years ago, rewriting the origin story of one of humanity’s most iconic social and romantic rituals.

What Scientists Discovered About the First Kiss

As it happens, a team led by evolutionary biologist Matilda Brindle of the University of Oxford analyzed a wide range of observations from modern primates and reconstructed the timeline of kissing behavior across evolution, according to a report from November 18.

Their models suggest that if humans, bonobos, and chimpanzees all kiss today, then their last common ancestor likely did as well, placing the ‘first kiss’ in the early Miocene period. Brindle said she was surprised by how little empirical data exists on kissing despite its cultural prominence.

To avoid confusion with feeding or aggression, the team defined kissing narrowly: “a non-agonistic interaction involving directed, intraspecific, oral-oral contact with some movement of the lips/mouthparts and no food transfer.”

Across primates, kissing shows up in romantic, parental, and social contexts. Chimpanzees famously kiss to ‘make up’ after conflicts, mirroring human conflict-resolution behaviors. These patterns point to deeper bonding purposes rather than purely sexual ones.

Crucially, the results imply that Neanderthals, who interbred with Homo sapiens and shared oral microbes, may also have practiced some form of kissing.

Why Kissing Evolved – And What It Means Today

Meanwhile, scientists still don’t agree on the adaptive benefits of kissing. Mouth-to-mouth contact increases the risk of disease transmission, meaning the behavior must provide compelling advantages to persist for millions of years. 

One hypothesis suggests kissing allows mate assessment, helping partners gauge compatibility through smell, breath, and biological signals. Another argues that kissing serves as a social glue, strengthening bonds within highly social species.

For primates (and humans), kissing may function similarly to grooming: a behavior that reduces tension, reinforces alliances, and improves group cohesion. This may explain why kissing exists in many cultures – but not all – and why its function can be romantic, platonic, parental, or conciliatory.

Rather than a purely romantic gesture, the kiss might be one of evolution’s oldest tools for keeping groups together.

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