Recent research reveals that the act of kissing may have begun more than 20 million years ago, predating the existence of modern humans. A team of scientists from Oxford University in England conducted a comprehensive review of existing studies on primates to explore the evolutionary roots of this intimate behavior. Their findings were published in the journal Evolution and Human Behavior.
The researchers employed statistical modeling to analyze the kissing behaviors of various primate species, including chimpanzees, bonobos, orangutans, and gorillas. By examining these living relatives, they estimated that an ancient ancestor of today’s apes likely engaged in mouth-to-mouth contact between 16.9 million and 21.5 million years ago. According to study lead author Matilda Brindle, who is an evolutionary biologist at Oxford, the results present an “evolutionary conundrum.”
Brindle explained that kissing is surprising due to the inherent risks it carries, such as the potential for spreading germs. Despite these risks, kissing may serve a variety of functions across different primate species. The research indicates that behaviors like kissing are not fossilized, so scientists must turn to living species for insights into historical practices.
The oldest known written records of human kissing date back approximately 4,500 years to ancient civilizations in Mesopotamia and Egypt. Interestingly, kissing is not a universal practice among humans; a study from 2015 found that only 46% of the global population engages in the act. Brindle noted, “We did find a strong evolutionary signal in kissing but it doesn’t mean it has to be retained.”
She emphasized that primates, known for their intelligence and adaptability, may find kissing beneficial in certain contexts, while in others it could pose significant health risks. The research team conducted over 10 million simulations to assess the likelihood of early ape ancestors kissing. Their results suggest that even extinct relatives, such as Neanderthals, who coexisted with early humans, likely engaged in similar behaviors.
While the study provides intriguing insights, it does not clarify the original purpose of kissing or how its significance has evolved over time. Additionally, much of the data on primate behavior comes from animals in captivity, highlighting the need for further research in natural environments.
Experts view this study as a foundation for future research. Justin Garcia, an evolutionary biologist and director of The Kinsey Institute at Indiana University in Bloomington, remarked, “This is a wonderful example of the interplay of nature and nurture, including for a behavior many of us humans consider so deeply intimate.” He pointed out that kissing is both biological and cultural, engaging the senses while also varying significantly across individuals and populations.
As researchers continue to unravel the complexities surrounding kissing, this study opens the door to understanding more about the origins of this seemingly simple yet profound human behavior.
