The first recorded kiss did not occur between two lovestruck humans, but between our genetic ancestors roughly 20 million years ago, according to a new study.
Researchers from the University of Oxford and the Florida Institute of Technology sought to uncover the origins of kissing. From an evolutionary perspective, the behavior is puzzling; it offers no clear survival advantage and can even spread disease.
Yet, we humans do it, as do chimpanzees, gorillas, and orangutans. This strong cross-species prevalence suggests kissing is a trait inherited from our common ancestor.
“Using these key factors, we employed a modeling approach to simulate different evolutionary scenarios,” said lead author Matilda Brindle from Oxford’s Department of Biology.
By running millions of simulations, the team concluded that the first kiss—or what would eventually lead to our concept of kissing—happened between 16.9 and 21.5 million years ago.
While we may view kissing through a romantic lens, the researchers adhered to a clinical definition: “non-aggressive mouth-to-mouth contact that does not involve food transfer.” This includes both intimate and platonic kisses, such as those between family members or friends.
“Some suggest that sexual kissing is a useful way to assess a partner’s qualities and compatibility. Alternatively, kissing could be a form of foreplay that increases sexual arousal and improves the chance of conception,” Brindle said.
She added that platonic kissing is thought to help navigate complex social relationships and forge stronger bonds.
The study, published in the journal Evolution and Human Behavior, also posits that our human ancestors kissed Neanderthals. Evidence includes the fact that the two species interbred and shared a common oral microbe—a sign of saliva exchange—long after their evolutionary paths diverged 450,000 to 750,000 years ago.
To pinpoint the first kiss, the scientists combined observations of primate behavior with evolutionary relationship data, effectively turning back the clock.
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However, the fundamental questions of why kissing emerged and why it persists remain subjects of ongoing debate.
