Oxford study suggests kissing evolved 21 million years ago
Research reveals the deep evolutionary roots of kissing among primates.
A new study has found evidence that kissing originated in humans’ common ancestor with other large apes around 21 million years ago, and suggests Neanderthals likely engaged in kissing too.
Researchers say the findings provide the first evolutionary evidence that kissing is an ancient behaviour, retained by humans and most large ape species over millions of years.
The study reconstructed the evolutionary history of kissing by analysing behaviours across species and mapping them onto the primate family tree.
Analysis indicated that mouth-to-mouth contact, defined as non-aggressive and not involving food transfer, first evolved in the shared ancestor of large apes between 21.5 and 16.9 million years ago.
Modern primates including chimpanzees, bonobos, and orangutans have been observed engaging in kissing, supporting the idea that the behaviour has deep evolutionary roots.
Researchers also concluded that Neanderthals, humans’ extinct relatives, likely engaged in kissing. Evidence from earlier studies showing humans and Neanderthals exchanged oral microbes through saliva transfer and genetic material via interbreeding supports this inference.
Lead author Dr Matilda Brindle said: “This is the first time anyone has taken a broad evolutionary lens to examine kissing.
Our findings add to a growing body of work highlighting the remarkable diversity of sexual behaviours exhibited by our primate cousins.”
The researchers used a statistical method called Bayesian modelling to simulate kissing behaviours across the branches of the primate evolutionary tree, running the model 10 million times to ensure robust estimates.
Co-author Professor Stuart West commented: “By integrating evolutionary biology with behavioural data, we’re able to make informed inferences about traits that don’t fossilise - like kissing.
Dr Catherine Talbot, co-author and Assistant Professor at the Florida Institute of Technology, says the findings lay a foundation to explore further.
“While kissing may seem like an ordinary or universal behaviour, it is only documented in 46% of human cultures,” she said.