Ancient Origins of Kissing Uncovered: Study Dates It to 21 Million Years Ago

A groundbreaking study published on March 15, 2024, suggests that the practice of kissing can be traced back approximately 21 million years, well before the emergence of modern humans. Researchers from the Journal of the Human Behavior and Evolution Society have explored the evolutionary history of kissing, revealing that this intimate act likely predates the first appearance of Homo sapiens by millions of years.

Lead researcher Matilda Brindle, an evolutionary biologist at Oxford University, stated, “These are deep-rooted evolutionary behaviors.” The study challenges conventional understandings of kissing by examining its origins from a biological perspective, an area previously neglected in academic discussions.

The researchers defined kissing as a “non-agonistic interaction involving directed, intraspecific, oral-oral contact with some movement of the lips or mouthparts and no food transfer.” This definition was crucial in avoiding anthropomorphism, allowing them to analyze kissing across different species without imposing human traits on animal behavior.

To uncover the evolutionary lineage of kissing, the team gathered data on kissing behavior among various primates. By employing phylogenetic methods to reconstruct this history, they found that the behavior likely evolved among most extant large apes and possibly Neanderthals. Brindle explained, “We paired our data on observations of kissing in living primates with genetic relationships, and we basically then tracked back through evolution.”

The findings support the hypothesis that early humans and Neanderthals engaged in kissing, aligning with previous research indicating that both species shared commensal oral microbes through saliva. Brindle noted, “Given that humans and Neanderthals were interbreeding and sharing saliva, we suggest that it tips the scale toward the idea that humans and Neanderthals might have been kissing each other.” This revelation offers a more romantic interpretation of the relationship between the two species.

The study also revealed that kissing has a “strong phylogenetic signal” within the Afro-Eurasian monkeys and apes, indicating it was a common trait among their ancestors. Brindle highlighted the close evolutionary ties between humans, bonobos, and chimpanzees, stating, “These are incredibly closely related to one another, so it makes sense that the ancestor those species share also kissed.”

While the specific evolutionary function of kissing remains unclear, Brindle and her colleagues aim to illustrate that this behavior extends beyond humans. “Humans aren’t the only animals to kiss. It happens across the animal kingdom. We found polar bears kiss each other,” she remarked. This insight positions humans within the broader context of animal behavior rather than above it.

Brindle concluded with a quote attributed to actress Ingrid Bergman, emphasizing that a kiss is more than a mere biological function: “It is a lovely trick designed by nature to stop speech when words become superfluous.” This study not only uncovers the ancient origins of kissing but also highlights the intricate connections between human and animal behaviors.