Researchers from the University of Oxford conclude that kissing likely originated 17–21 million years ago in the ancestors of large apes. Treating kissing as a trait, they mapped mouth-to-mouth contact across primates using observations of chimpanzees, bonobos and orangutans and evolutionary simulations. The trait appears to have persisted into modern large apes and may have served social functions — a possibility supported by evidence of shared oral microbes between humans and Neanderthals.
Ancient Kisses: Study Suggests Kissing Dates Back 17–21 Million Years — Neanderthals and Apes Likely Kissed
Researchers from the University of Oxford conclude that kissing likely originated 17–21 million years ago in the ancestors of large apes. Treating kissing as a trait, they mapped mouth-to-mouth contact across primates using observations of chimpanzees, bonobos and orangutans and evolutionary simulations. The trait appears to have persisted into modern large apes and may have served social functions — a possibility supported by evidence of shared oral microbes between humans and Neanderthals.
01:17 AM, 11/20/2025Science
New research suggests that kissing is far older than previously thought — possibly originating 17–21 million years ago in the ancestors of today’s large apes. The study, led by researchers at the University of Oxford and published in the journal Evolution and Human Behaviour, treats kissing as a measurable behavioural trait and traces its presence across the primate family tree.
For this analysis the team defined kissing as “non-aggressive, mouth-to-mouth contact that did not involve food transfer.” They compiled observational records of mouth-to-mouth contact in living primates, notably chimpanzees, bonobos and orangutans, then mapped the behaviour onto primate phylogeny and ran evolutionary simulations to estimate its likelihood in ancestral species.
The models indicate that mouth-to-mouth contact likely emerged in the common ancestors of the large apes roughly 17–21 million years ago and was retained in most large-ape lineages. The authors argue this long persistence makes kissing an ancient social behaviour in our broader ape family.
Researchers note the behaviour’s function is not necessarily reproductive; possible roles include social bonding, stress relief and even thermoregulatory benefits — a suggestion used to explain why Neanderthals, living in Ice Age conditions, may have exchanged pecks to share warmth. The study also points to earlier genetic and microbial evidence showing shared oral microbes between modern humans and Neanderthals, which is consistent with direct saliva exchange.
"This is the first time anyone has taken a broad evolutionary lens to examine kissing," said co-author Matilda Brindle, an evolutionary biologist at the University of Oxford. She added that the findings expand our understanding of the diversity of social and sexual behaviours among primates.
While kissing may carry risks such as disease transmission, its apparent deep evolutionary roots suggest the behaviour offers benefits that outweighed those costs in many primate societies. The authors call for further observational and microbiological studies to clarify how kissing functions across different species and social contexts.
Key takeaway: Kissing appears to be an ancient trait among large apes, potentially shared by ancestral species and even Neanderthals, with implications for social bonding and the evolutionary history of human behaviour.