A new study led by researchers from the University of Oxford has traced the evolutionary origins of kissing, finding evidence that the behavior likely emerged among large apes over 16 million years ago and was also practiced by Neanderthals.
The research, published in Evolution and Human Behavior, is the first to use a cross-species approach to reconstruct the history of kissing. The team defined kissing as non-aggressive, mouth-to-mouth contact without food transfer—a definition broad enough to apply across different primate species.
Dr Matilda Brindle from Oxford’s Department of Biology, who led the study, 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.”
To gather their data, researchers reviewed literature on observed kissing behaviors in modern primates such as chimpanzees, bonobos, and orangutans. They then used Bayesian statistical modeling to map these behaviors onto the primate family tree and estimate how likely it was that ancestral species also kissed. Their analysis suggests that kissing evolved in an ancestor common to large apes between 21.5 and 16.9 million years ago and persists in most living large ape species.
The study also indicates that Neanderthals likely engaged in kissing. Previous research has shown humans and Neanderthals shared oral microbes through saliva transfer as well as genetic material via interbreeding—supporting the idea that close mouth-to-mouth contact occurred between them.
Professor Stuart West, co-author and Professor of Evolutionary Biology at Oxford, explained: “By integrating evolutionary biology with behavioural data, we’re able to make informed inferences about traits that don’t fossilise - like kissing. This lets us study social behaviour in both modern and extinct species.”
The authors acknowledge limitations due to sparse data outside great apes but suggest their framework will help future studies record kissing behaviors more consistently among nonhuman animals.
Dr Catherine Talbot, co-author from Florida Institute of Technology’s College of Psychology, noted: “While kissing may seem like an ordinary or universal behaviour, it is only documented in 46% of human cultures. The social norms and context vary widely across societies, raising the question of whether kissing is an evolved behaviour or cultural invention. This is the first step in addressing that question.”
The study provides new insights into how complex social behaviors might have developed among humans and their relatives.