New research indicates that the practice of kissing may have originated over 20 million years ago, predating the existence of modern humans. A team of researchers from Oxford University in England conducted a comprehensive review of decades of studies on primates to uncover the evolutionary roots of this seemingly human behavior. Their findings have been published in the journal Evolution and Human Behavior.
The researchers employed statistical modeling to analyze the kissing behaviors of contemporary primate species, including chimpanzees, bonobos, orangutans, and a specific gorilla species. Their analysis suggests that an ancient ancestor of today’s apes engaged in mouth-to-mouth contact approximately between 16.9 million and 21.5 million years ago.
Insights into Kissing’s Evolutionary Purpose
Lead author Matilda Brindle, an evolutionary biologist at Oxford, described kissing as an “evolutionary conundrum.” She noted that while the behavior carries certain risks, such as the potential spread of germs, it may not directly contribute to survival. Despite these risks, kissing and similar behaviors across various primate species likely serve multiple functions.
Because kissing is not a fossilized behavior, researchers must rely on the study of living species to infer insights about its past. The earliest written records of human kissing date back roughly 4,500 years to ancient Mesopotamia and Egypt. Interestingly, a 2015 study revealed that only 46% of humans engage in the act of kissing, indicating that this behavior is not universally practiced.
Brindle explained that while there is a strong evolutionary signal in kissing, it is not necessarily a behavior that must persist. “Primates are extremely flexible species, very intelligent, and so kissing might be useful in some contexts but not in others,” she elaborated. “If it’s not useful, it is quite risky with high potential for disease transfer.”
Research Methods and Future Directions
The research team conducted over 10 million simulations to estimate the likelihood that early ape ancestors participated in kissing. Their findings provide strong support for the notion that extinct relatives, such as Neanderthals, who lived alongside early humans, likely engaged in kissing as well. However, Brindle acknowledged that the model does not clarify the original purpose of kissing or its evolution over time.
Much of the behavioral data utilized in the study originated from animals in captivity, prompting a need for additional insights from primates in natural habitats. Despite these limitations, experts recognize the significance of this research as a foundation for future exploration.
Justin Garcia, an evolutionary biologist and director of The Kinsey Institute at Indiana University in Bloomington, remarked on the study’s implications. “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 stated in an email to CNN. “Kissing is both biological and cultural; it invokes the bodily senses and clearly has some evolutionary origins, but it also varies across individuals and populations.”
The study underscores the complexity of human behaviors and their origins, paving the way for further investigation into the rich tapestry of evolutionary history. As researchers continue to explore the depths of this intimate act, they may uncover even more about the connections between humanity and its primate relatives.
