A recent study suggests that kissing, a behavior often seen as uniquely human and deeply embedded in cultural practices, may have much older evolutionary roots dating back over 20 million years. This intriguing research, led by evolutionary biologist Matilda Brindle of the University of Oxford, indicates that kissing likely evolved between 16.9 and 21.5 million years ago following the divergence of the ancestors of great apes from those of lesser apes, such as gibbons. The findings also imply that early human relatives, including Neandertals, may have engaged in kissing, challenging the common notion that it is a purely human invention.
Kissing occupies a prominent place in human culture, symbolizing romantic love, religious reverence, and even betrayal, as famously depicted in popular media like *The Godfather Part II*’s “kiss of death.” Despite its cultural significance, anthropological research shows that romantic kissing is not universal among human societies; it has been documented in only about 46 percent of cultures worldwide. For those who do practice it, however, kissing remains an everyday act with profound social and emotional importance.
Motivated by these observations, Brindle and her colleagues, Catherine Talbot from the Florida Institute of Technology and Stuart West from Oxford, sought to explore the evolutionary origins of kissing by examining its presence in non-human primates. They combed through previous studies looking for examples of what they defined as “non-agonistic interaction involving directed, intraspecific, oral-oral contact with some movement of the lips or mouthparts and no food transfer.” In simpler terms, this refers to mouth-to-mouth contact among members of the same species that is friendly rather than aggressive and does not involve sharing food.
Their review revealed that great apes, including chimpanzees, orangutans, and humans, often “kiss” for a variety of reasons ranging from sexual attraction to expressions of affection and reconciliation. For example, chimpanzees frequently use kissing as a way to resolve conflicts and restore social harmony after disagreements, essentially “making up” through this gesture. Interestingly, the only great ape species for which kissing has not been observed is the eastern gorilla. Furthermore, no evidence of kissing was found among lesser apes such as gibbons, suggesting that the behavior likely emerged after the evolutionary split between these two groups.
The researchers estimate that kissing, therefore, originated in the common ancestor of great apes sometime more than 16 million years ago. This timeline makes it plausible that Neandertals, who shared a common ancestor with modern humans, also practiced kissing. Supporting this idea, preliminary genetic analyses of ancient dental plaque indicate that Neandertals and humans shared oral bacteria until about 112,000 years ago, which could imply close oral contact such as kissing.
While the presence of kissing in great apes offers clues about its evolutionary history, the available data remain limited and fragmented, hindering a full understanding of how or why kissing evolved. The study notes that species engaging in kissing tend to have mating systems where females mate with multiple males. Additionally, all kissing species observed also practice premastication—the chewing of food before feeding it to another individual—a behavior that might have served as a precursor to kissing. However, the connection between premastication and kissing is tentative because there is insufficient information about premastication in species that do not kiss.
Another unresolved question concerns the relationship between platonic and sexual kissing. Zanna Clay, a comparative psychologist at Durham University who studies primate behavior but was not involved in the research, points out that affectionate, non-sexual kissing is more commonly observed in the wild than sexual kissing. She notes that the study’s conclusions are based on a relatively limited dataset, emphasizing the need for more comprehensive observations.
Brindle herself acknowledges that primate kissing has been understudied and describes their work as a “cry” for more research in this area. She is enthusiastic about the potential for future studies to expand our understanding, stating, “It’s really exciting that we’ve traced the evolutionary history of kissing back to 21.5 million years ago, but we could do so much more if we had additional data.”
This research not only sheds light on the ancient origins of a behavior that plays a significant role in human social and emotional life but also underscores the complexity of primate social interactions. It invites scientists to look beyond human experience and consider how behaviors like kissing might have evolved to strengthen social bonds, facilitate mating, and maintain