Study Reveals Kissing’s Evolutionary Roots in Primates

A new study from the University of Oxford has unveiled intriguing insights into the evolutionary history of kissing, suggesting that this behavior originated in the common ancestor of humans and large apes approximately 21 million years ago. The research, published in the journal Evolution and Human Behavior, also indicates that Neanderthals likely participated in kissing.

Kissing is observed across various animal species but poses an evolutionary puzzle. It appears to carry risks, such as the potential for disease transmission, without offering clear reproductive or survival benefits. Despite its cultural significance in many human societies, the evolutionary history of kissing has received minimal scholarly attention until now.

Unveiling Kissing’s Ancient Origins

The research team undertook a pioneering effort to map the evolutionary lineage of kissing using a cross-species analysis based on the primate family tree. Their findings point to kissing as an ancient trait retained throughout evolution among large apes. The study highlights that kissing likely existed in Neanderthals as well, supported by previous evidence of shared oral microbes and genetic material between humans and their extinct relatives.

Lead author Dr. Matilda Brindle, an evolutionary biologist at Oxford’s Department of Biology, remarked, “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.”

The researchers defined kissing as non-aggressive, mouth-to-mouth contact that does not involve the transfer of food. This definition was necessary to encompass a range of species and enable a consistent analysis of kissing behaviors across the primate family.

Methodology and Implications for Future Research

To conduct their analysis, the team collected data from existing literature on modern primate species known to engage in kissing, including chimpanzees, bonobos, and orangutans. They then performed a phylogenetic analysis, treating kissing as a trait and mapping it onto the primate family tree. By employing a statistical method known as Bayesian modeling, the researchers simulated various evolutionary scenarios to estimate the likelihood that different ancestors also engaged in kissing. This model underwent 10 million simulations for robust statistical estimates.

Co-author Professor Stuart West, a Professor of Evolutionary Biology at Oxford, noted, “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.”

Although the researchers acknowledge limitations in existing data, particularly outside the large ape group, the study lays groundwork for future research. It encourages primatologists to consistently document kissing behaviors in nonhuman animals.

Co-author Catherine Talbot, Assistant Professor at the Florida Institute of Technology, pointed out, “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 research marks a significant step in understanding the evolution of social behaviors in primates and invites further inquiry into the cultural significance of kissing in human societies. The study is expected to stimulate discussion about how behaviors evolve and adapt across different species, providing new avenues for exploration in both evolutionary biology and anthropology.