The Evolutionary Origins of Kissing: A Study on Primate Behavior

A recent study published in the journal *Evolution and Human Behavior* reveals that kissing, defined as "non-aggressive, mouth-to-mouth contact that did not involve food transfer," likely originated around 21 million years ago in the common ancestor of humans and great apes. This research, led by Matilda Brindle from the University of Oxford, highlights the evolutionary significance of kissing, which has been observed in various modern primates, including chimpanzees, bonobos, gorillas, orangutans, macaques, and baboons.

Kissing predates humans, and Neanderthals probably kissed tooWhat exactly counts as a kiss? Study reveals kissing goes back 21 million years, to common ancestor of humans; researchers explain evolution of kissingEvolutionary origins of primate kissing may trace back nearly 20 million years

The research team employed Bayesian modeling to reconstruct the evolutionary history of kissing. By treating kissing as a biological trait, they tested numerous scenarios to determine how this behavior may have evolved. The model, run 10 million times for reliability, indicated that kissing likely evolved once in the common ancestor of large apes between approximately 21.5 million and 16.9 million years ago. The study suggests that this behavior may have evolved from the practice of mothers pre-chewing food for their infants, which could have been repurposed into what we now recognize as kissing.

What exactly counts as a kiss? Study reveals kissing goes back 21 million years, to common ancestor of humans; researchers explain evolution of kissingKissing predates humans, and Neanderthals probably kissed tooEvolutionary origins of primate kissing may trace back nearly 20 million years

The study also posits that Neanderthals, our closest extinct relatives, may have engaged in kissing, and there is a possibility that early humans and Neanderthals kissed each other. This assertion is supported by evidence of oral microbe exchange between the two species, indicating that saliva transfer occurred, which is a key component of kissing.

Kissing predates humans, and Neanderthals probably kissed tooEvolutionary origins of primate kissing may trace back nearly 20 million yearsWhat exactly counts as a kiss? Study reveals kissing goes back 21 million years, to common ancestor of humans; researchers explain evolution of kissing

Despite its prevalence in various species, kissing remains an evolutionary puzzle. It poses risks of disease transmission and offers few obvious survival or reproductive advantages. Kissing is not universally practiced among humans; it appears in only 46% of human cultural records, suggesting that it may be more of a cultural invention than an innate behavior. Co-author Katherine Talbot from the Florida Institute of Technology noted the need for further research to explore whether kissing is an evolved behavior or a cultural phenomenon.

Evolutionary origins of primate kissing may trace back nearly 20 million years

While the study provides a comprehensive framework for understanding kissing across species, the authors acknowledge that existing data is still limited, particularly for species outside of great apes. They emphasize the importance of gathering more data to investigate the potential benefits of kissing and to better understand its role in social behavior among both modern and extinct species.

Kissing predates humans, and Neanderthals probably kissed too

• “This is the first time anyone has taken a broad evolutionary lens to examine kissing,” — Matilda Brindle, Evolutionary Biologist, University of Oxford

What exactly counts as a kiss? Study reveals kissing goes back 21 million years, to common ancestor of humans; researchers explain evolution of kissing

• “By combining evolutionary biology and behavioural data, we can make valid inferences about traits that do not leave fossil traces - such as kissing,” — Stuart West, Professor of Evolutionary Biology, University of Oxford

Kissing predates humans, and Neanderthals probably kissed too

This study represents a significant step toward understanding the evolutionary origins of kissing, providing insights into the behavior's complexity and its implications for both human and primate social interactions.

Evolutionary origins of primate kissing may trace back nearly 20 million years