Kissing: A Shared Trait of Our Ancestors and Neanderthals

A recent study led by the University of Oxford reveals that kissing may have originated in the common ancestor of humans and other large apes approximately 21 million years ago. This groundbreaking research also suggests that Neanderthals likely participated in this intimate behavior. The findings are detailed in the journal Evolution and Human Behavior.

Kissing raises fascinating questions in evolutionary biology. While it is a common practice among many species, it poses significant risks, such as disease transmission, without providing clear survival or reproductive advantages. Until now, researchers had largely overlooked its evolutionary significance, despite its cultural and emotional importance in human societies.

Uncovering the Evolutionary Roots of Kissing

The Oxford team conducted the first comprehensive analysis of kissing’s evolutionary history by examining it through a cross-species lens. Their research indicates that kissing is an ancient behavior retained by most large apes, evolving in their common ancestor around 21.5 to 16.9 million years ago. The study also posits that Neanderthals engaged in kissing, as evidenced by previous research demonstrating shared oral microbes and genetic material between humans and Neanderthals.

Dr. Matilda Brindle, the lead author of the study and an evolutionary biologist at 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.”

Defining Kissing Across Species

To conduct their analysis, the researchers needed a clear definition of what constitutes a kiss. This was challenging, as many mouth-to-mouth behaviors resemble kissing. The team defined kissing as non-aggressive, mouth-to-mouth contact that does not involve food transfer. This definition allowed them to gather data on kissing behaviors observed in various modern primate species, including chimpanzees, bonobos, and orangutans.

Using a phylogenetic analysis, the researchers treated kissing as a trait and mapped it onto the primate family tree. They employed a statistical method known as Bayesian modeling to simulate various evolutionary scenarios, running the model 10 million times to ensure robust statistical estimates.

Co-author Professor Stuart West, an expert in evolutionary biology, emphasized the importance of this approach: “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.”

The implications of this research extend beyond academic curiosity. It lays the groundwork for future studies on kissing behaviors in nonhuman animals using a consistent definition.

Catherine Talbot, co-author and Assistant Professor in the College of Psychology at the 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 a cultural invention. This is the first step in addressing that question.”

The study not only uncovers the ancient origins of kissing but also invites further exploration into its role in human culture and social behavior. By examining this seemingly simple act, researchers hope to gain deeper insights into the complexities of human relationships and social practices.

The full study can be found in the journal Evolution and Human Behavior, offering a detailed comparative approach to the evolution of kissing.