Neanderthal Kissing: New Research Suggests Our Ancestors Smooched—and Maybe with Them
A new study suggests that kissing isn’t uniquely human, and may have been practiced by our Neanderthal ancestors, potentially even with early humans. Researchers at the University of Oxford have reconstructed the evolutionary history of kissing, finding evidence it dates back at least 21.5 million years and was likely a common behavior among ancient apes – including Neanderthals.
The question of whether kissing is innate or learned has long fascinated scientists. To tackle this, a team led by postdoctoral researcher Matilda Brindle needed a working definition applicable across species. “Lots of behavior looks like kissing at first glance,” Brindle explains, noting the challenges of differentiating genuine affection from other mouth-to-mouth interactions.
The team carefully excluded behaviors like the “kiss-fighting” of tropical French grunt fish – a dominance display involving lip-locking – and the food-sharing practice of primates known as premastication. Even trophallaxis, the mouth-to-mouth exchange of fluids and food observed in ants, was deemed distinct. “We define kissing as non-aggressive, directed, mouth-to-mouth contact between members of the same species, that doesn’t involve food transfer,” Brindle clarifies.
Using this definition, researchers found that kissing, or behaviors closely resembling it, are surprisingly widespread in the animal kingdom. From “tonsil-tennis” among polar bears to the gentle “canoodling” of prairie dogs, mouth-to-mouth contact serves various purposes. A review of scientific literature revealed that kissing is observed in a handful of monkey species and most apes, with notable exceptions like Eastern gorillas and gibbons.
The nature of these kisses varies. Bonobos, for example, engage in “prolonged tongue-tongue interaction” that is explicitly sensual, while other apes may kiss during foreplay or sexual activity. However, kissing also occurs in non-sexual contexts, such as mothers comforting their infants or as a gesture of reconciliation.
By applying a technique called phylogenetic comparative analysis, the researchers modeled the evolutionary history of kissing. Their findings indicate that the ancestors of large apes were already engaging in this behavior as far back as 21.5 to 16.9 million years ago.
But what about Neanderthals? The study’s most provocative implication arises from previous research demonstrating that modern humans and Neanderthals shared oral microbes long after their species diverged. This suggests a transfer of saliva – and, potentially, something more. “In other words, they were swapping saliva,” Brindle states. While sharing food around a campfire could explain the microbial exchange, the researchers point out that the prevalence of Neanderthal ancestry in many non-African populations, combined with their finding of kissing in Neanderthals, paints a more intriguing picture.
Did humans and Neanderthals actually kiss? The fossil record, unfortunately, doesn’t preserve such intimate details. “Unfortunately, kissing doesn’t preserve in the fossil record, so we’ll never be able to say for sure, but the evidence certainly points in that direction,” Brindle concedes. However, the possibility is now firmly on the table, prompting a reassessment of our understanding of interactions between these ancient hominins.
One thing is certain: this research has irrevocably changed how Brindle views our extinct relatives. “I’ll never look at a Neanderthal the same way again.”
