Study Reveals Origin of Kissing Dates Back 21 Million Years

A groundbreaking study published on March 15, 2024, suggests that the act of kissing dates back approximately 21 million years, long before the emergence of modern humans. This research, featured in the Journal of the Human Behavior and Evolution Society, indicates that the first instances of lips meeting likely occurred between 21.5 and 16.9 million years ago, significantly predating the appearance of Homo sapiens roughly 300,000 years ago.

Lead researcher Matilda Brindle, an evolutionary biologist at Oxford University, highlighted that this study marks the first comprehensive exploration of the evolutionary history of kissing. “Kissing is a socio-cultural phenomenon that has seen extensive discussion in various academic fields, yet it has rarely been addressed from an evolutionary biology standpoint,” she noted.

The research team began their work by establishing a precise definition of kissing: a “non-agonistic interaction involving directed, intraspecific, oral-oral contact with some movement of the lips or mouthparts, and no food transfer.” This definition allowed the researchers to analyze kissing behaviors across various species without anthropomorphizing non-human entities.

Using data collected from observations of kissing among primates, the researchers employed phylogenetic methods to trace the evolutionary lineage of this behavior. The study found that kissing likely first evolved among most extant large apes and may have also been present in Neanderthals.

“We paired our data on observations of kissing in living primates with genetic relationships among these species, allowing us to track kissing through evolutionary history,” Brindle explained. This approach revealed that both humans and Neanderthals engaged in kissing, supporting earlier findings that suggested the two species exchanged “commensal oral microbes,” or saliva.

Brindle remarked, “Given that humans and Neanderthals interbred and shared saliva, along with evidence that both were known to kiss, we propose that this points toward the likelihood that humans and Neanderthals engaged in kissing.” She referred to this insight as a “much more romantic spin on human-Neanderthal relationships.”

The study also illustrated that kissing has a “strong phylogenetic signal” among Afro-Eurasian monkeys and apes, indicating it was a common trait among their ancestors. “Humans, bonobos, and chimpanzees all kiss. These species are incredibly closely related, so it follows that their shared ancestor also engaged in kissing,” Brindle stated.

Although the exact evolutionary function of kissing remains uncertain, Brindle and her colleagues hope their findings encourage readers to appreciate the deeper significance of a kiss. Citing actress Ingrid Bergman, she remarked that a kiss is “a lovely trick designed by nature to stop speech when words become superfluous.”

The research emphasizes that humans are not the only species that kiss; similar behaviors have been documented across the animal kingdom, including among polar bears. “This finding positions humans within the broader context of the animal world, rather than suggesting we are above or different from other species,” Brindle concluded.

This study not only sheds light on the ancient origins of kissing but also opens up new avenues for understanding the social and evolutionary significance of this universal behavior.