New Study Reveals Kissing May Date Back 21 Million Years

A recent study led by evolutionary biologist Matilda Brindle from Oxford University suggests that kissing on the lips may have a much older origin than previously thought, possibly dating back as far as 21 million years. The research indicates that our ape ancestors, along with early humans such as Neanderthals, may have engaged in lip-locking behavior with both friends and partners.

While the earliest recorded instances of kissing appear in ancient Mesopotamia and Egypt around 4,500 years ago, Brindle highlights that kissing presents an “evolutionary conundrum.” The behavior carries notable risks, such as the transmission of diseases, yet does not seem to provide an obvious reproductive or survival advantage. “Kissing is one of these things that we were just really interested in understanding,” Brindle said in an interview. “It’s pervasive across animals, which gives you a hint that it might be an evolved trait.”

Research Methodology and Findings

Defining kissing as non-aggressive, mouth-to-mouth contact without food, the study faced challenges in detecting this behavior in the fossil record. Instead, Brindle and her team analyzed existing scientific literature to identify modern primate species known to kiss, which included chimpanzees, bonobos, orangutans, and a species of gorilla.

The researchers conducted a phylogenetic analysis, which reconstructs the relationships among different species based on genetic data. This approach allowed them to infer the likelihood of kissing in extinct species, including the last common ancestor of chimpanzees, bonobos, and humans. By simulating different evolutionary scenarios, the model was executed 10 million times to ensure robust estimates. The findings, published in the journal Evolution and Human Behavior, indicate that kissing likely evolved in a common ancestor of large apes between 21.5 million and 16.9 million years ago.

The study implies that Neanderthals likely engaged in kissing, and given the known interbreeding between Homo sapiens and Neanderthals, it raises the possibility that humans and Neanderthals shared kisses as well.

The Complexity of Kissing

Despite these fascinating insights, Brindle noted that the model does not clarify why or how kissing evolved. The behavior may have various functions, such as assessing mates, bonding, and relieving social tension. However, the limited data on kissing in non-ape species presents challenges in understanding its full evolutionary trajectory. Much of the existing information comes from animals in controlled environments, creating a gap in knowledge regarding how kissing may have developed across different contexts.

Brindle emphasized the significance of their findings, stating, “What we’ve done, which is a really important first step, is showing it’s an evolved trait. It’s really ancient. But why? And that’s the amazing next step if people want to pick up the mantle.”

The study also highlighted that kissing is not universally practiced among humans. According to a 2015 study, kissing is documented in only 46% of cultures worldwide. Brindle pointed out that while there is a strong evolutionary signal in kissing, it may not be retained across all populations. “Primates are extremely flexible species, very intelligent, and so kissing might be useful in some contexts but not in others,” she explained.

The research also raises questions about the nature of human kissing. Adriano Reis e Lameira, an evolutionary psychologist and primatologist at the University of Warwick, who was not involved in the study, noted that the majority of human kisses do not typically involve mouth-to-mouth contact. This further complicates the understanding of why humans engage in kissing behaviors as they do.

As the study opens new avenues for exploration, it invites further research into the evolutionary significance and social contexts of kissing, a behavior that remains both complex and captivating.