New research from the University of Oxford suggests that kissing—a behavior often seen as uniquely human—actually has deep evolutionary roots, stretching back over 21 million years to a common ancestor of humans and large apes. The study, set to be published in Evolution and Human Behavior, reconstructs the evolutionary history of kissing using a cross-species approach, shedding light on a behavior that has puzzled scientists due to its apparent lack of obvious survival benefits.
The Evolutionary Puzzle of Kissing
Kissing presents a biological mystery: it involves close contact, which carries risks like disease transmission, yet doesn’t immediately contribute to reproduction or survival. Despite this, kissing is widespread among modern large apes and was likely practiced by Neanderthals as well. Researchers led by Dr. Matilda Brindle sought to trace the origins of this behavior using a rigorous evolutionary framework.
Defining and Tracking Kissing Across Species
The team first had to define kissing in a way that applied to multiple species. They settled on “non-aggressive, mouth-to-mouth contact that does not involve food transfer.” This definition allowed them to analyze data from modern primate species, including chimpanzees, bonobos, and orangutans—all of which exhibit kissing behaviors.
Using a statistical method called Bayesian modeling, they mapped kissing as a trait across the primate family tree, running the analysis 10 million times to ensure robust results. The model revealed that kissing likely emerged between 21.5 and 16.9 million years ago in the ancestor of modern large apes.
Implications for Human Evolution
The study also suggests that Neanderthals kissed, based on evidence of shared oral microbes (from saliva transfer) and genetic material (via interbreeding) with humans. This aligns with previous research indicating close social interactions between our ancestors. Professor Stuart West of Oxford emphasizes that this research integrates evolutionary biology with behavioral data to explore traits that don’t fossilize, such as kissing.
Cultural Variation and Future Research
Interestingly, the study notes that kissing is only documented in 46% of human cultures, with wide variations in social norms. This raises the question of whether kissing is primarily an evolved behavior or a cultural invention. Dr. Catherine Talbot of the Florida Institute of Technology suggests that this study is a crucial first step in addressing that debate.
In conclusion, this research demonstrates that kissing is not a recent or exclusively human behavior but rather an ancient trait inherited from our primate ancestors. By providing a framework for future studies, this work opens new avenues for understanding the evolution of social behaviors in both modern and extinct species.
