Kissing Likely Evolved from Our Ape Ancestors 21 Million Years Ago

Ancient beings like Neanderthals likely engaged in kissing, and our primate ancestors might have practiced it as far back as 21 million years ago.

There is considerable discussion regarding the origins of romantic kissing among humans. While ancient texts suggest sexual kissing existed in Mesopotamia and Egypt around 4,500 years ago, such evidence has only surfaced within the past 4,000 years. Some suggest that 46 percent of human cultures argue that kissing is a relatively recent cultural phenomenon.

However, it’s noted that Neanderthals shared oral bacteria, and kissing has also been documented in chimpanzees, bonobos, and orangutans, suggesting the practice may precede existing historical records.

To explore this further, Matilda Brindle and colleagues from the University of Oxford investigated the evolutionary background of kissing. “Kissing appears to be an evolutionary paradox; it likely doesn’t contribute directly to survival and can even pose risks in terms of pathogen transmission,” she states.

The researchers defined kissing in a manner applicable across various species, describing it as non-hostile, mouth-to-mouth contact that involves lip movements but excludes the exchange of food.

This definition eliminates many forms of affection, such as kisses on the cheek. “If you kiss someone on the cheek, it feels like a kiss, but according to our definition, it’s not,” Brindle explains. “Humans have elevated kissing to a new level.”

They then examined scientific literature and consulted primate researchers for instances of kissing among modern monkeys and apes from Africa, Europe, and Asia.

To gauge the probability that various ancestral species also engaged in kissing, Brindle and her team mapped this data onto the primate family tree, employing a statistical method called Bayesian modeling to simulate diverse evolutionary scenarios.

The findings indicate that kissing likely originated in the ancestors of great apes approximately 21.5 to 16.9 million years ago, with an 84 percent probability that Neanderthals also practiced it.

“Clearly, it involves Neanderthals kissing, though we can’t ascertain whom they were kissing,” Brindle notes. “Nevertheless, the similarity in oral microbiomes between humans and Neanderthals, coupled with the fact that many non-African humans carry Neanderthal DNA, supports the idea that they probably shared kisses. This certainly adds a romantic dimension to human-Neanderthal relationships.”

Brindle acknowledges a lack of sufficient data to explain why kissing developed but proposes two hypotheses.

“In the context of sexual kissing, assessing mate quality could enhance reproductive success,” she suggests. “If a partner has poor oral hygiene, they might decide against mating with them.”

Moreover, sexual kissing could facilitate post-coital success by heightening arousal and fostering conditions that allow for faster ejaculation and a vaginal pH more accommodating to sperm.

Another prevailing theory is that non-sexual kissing evolved from grooming, which serves to strengthen social bonds and alleviate tension. “Chimpanzees literally kiss and reconcile after conflicts,” Brindle points out.

“Based on current evidence, I believe kissing undoubtedly serves an affiliative purpose,” says Zanna Clay from Durham University, UK. “We know, for instance, that in chimpanzees, it plays a vital role in mending social ties. However, I find the sexual aspect somewhat uncertain.”

Regarding whether kissing is an evolved behavior or a cultural construct, Brindle asserts, “Our findings strongly indicate that kissing has evolved.”

Trolls Punk Arbor, a professor at the University of Copenhagen, who traced the initial references to kissing in ancient Mesopotamian texts, concurs. “This provides a well-rounded foundation for asserting that kissing has been a part of human behavior for an extended period,” he states.

Nonetheless, this does not encompass the entire narrative, considering many individuals do not engage in kissing. “I believe there is a significant cultural element involved, which likely varies across different cultural contexts,” Clay observes.

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