Researchers at the University of Oxford have determined that kissing likely originated in the shared ancestor of humans and large apes around 21 million years ago. The study, published in Evolution and Human Behavior, suggests the behavior persisted through evolution and was probably practiced by Neanderthals. This finding highlights kissing as a deep-rooted social trait among primates.
A team led by evolutionary biologists at the University of Oxford conducted the first comprehensive cross-species analysis to uncover the origins of kissing. Published on November 19 in Evolution and Human Behavior, the research indicates that the behavior emerged in the common ancestor of humans and other large apes between 21.5 and 16.9 million years ago. This timeline places kissing's beginnings well before the evolution of modern humans.
To trace this history, the scientists reconstructed kissing on the primate family tree using phylogenetic analysis. They defined kissing as non-aggressive mouth-to-mouth contact without food transfer, drawing from scientific literature on species like chimpanzees, bonobos, and orangutans across Africa, Europe, and Asia. Employing Bayesian modeling, they simulated 10 million evolutionary scenarios to assess the likelihood of ancestral kissing, confirming its persistence in most large ape species.
The study also extends to extinct relatives, concluding that Neanderthals likely engaged in kissing. This is inferred from evidence of oral microbe exchange and interbreeding with early humans.
Dr. Matilda Brindle, the lead author from Oxford's Department of Biology, stated: "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 behaviors exhibited by our primate cousins."
Professor Stuart West, a co-author, added: "By integrating evolutionary biology with behavioral data, we're able to make informed inferences about traits that don't fossilize—like kissing. This lets us study social behavior in both modern and extinct species."
Despite its prevalence in primates, kissing appears in only 46% of human cultures, suggesting a blend of biological and cultural influences. Catherine Talbot, another co-author from Florida Institute of Technology, noted: "While kissing may seem like an ordinary or universal behavior, 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 behavior or cultural invention. This is the first step in addressing that question."
The research provides a standardized framework for future observations of kissing in nonhuman primates, though data remains limited outside large apes.