Scientists have found unusual origins of kissing—and it wasn't romantic at all

Kissing is now a universal gesture of affection, but you might be surprised to learn it wasn’t always meant to express love. According to a study published in the journal Evolutionary Anthropology, researchers have traced the origins of this modern symbol of intimacy. So, get ready to kiss old beliefs goodbye—the original reasons behind a smooch might seem bizarre by today’s standards.

Over the centuries, kissing has evolved into an expression of social bonding. But before becoming a romantic gesture, research found that our hairy ape ancestors used it for grooming. Yes, you read that right! Additionally, experts drew parallels between humans kissing each other and certain animal behaviors. In fact, it has been well established that kisses were planted during the ancient Mesopotamian civilization, some 4,500 years ago.

Kissing was considered a “common practice,” according to thousands of clay tablets recovered between the Euphrates and Tigris rivers in modern-day Iraq and Syria. Early humans incorporated it as part of everyday intimacy so much that it was well documented. However, there has been an ongoing debate about this now-romantic gesture, with theories suggesting it initially served feeding purposes.

Among the dominant theories, human behavior experts saw kissing as a way of nurturing and showing care through premastication. Notably, it is a “kiss feeding” act, in which caregivers feed infants with pre-chewed food. Later in life, it transitioned into a “compatibility test” for potential mates to taste and sample each other orally to determine health. This new study, published in October, explored these traditional views about kissing to propose a fresh hypothesis.

England’s University of Warwick’s associate professor Adriano R. Lameira, who authored the research, revealed kissing to be an evolutionary instinct used for grooming other beings. “Evidence supports that kissing isn’t a derived signal of affection in humans. Instead, it represents a surviving, devolved, vestigial form of primate grooming that conserved its ancestral form, context, and function,” the psychologist told Daily Mail. In other words, the research pointed out that apes often ended grooming with pursed lips and a light suction motion to remove dirt or parasites. "This made grooming important for hygienic purposes given the high parasitic load on the ground. Only once kissing was used as a general convention for showing affection, could kissing become a mutual mouth-to-mouth act," he added.

This "grooming kiss" persisted even though it was no longer necessary for hygiene as humans evolved and shed most of their body hair. “What was once a time- and labor-intensive ritual to cement and strengthen close social ties gradually compressed until a groomer’s final kiss turned into a crystallized symbol of trust and affiliation,” an excerpt from the research read. The findings, emphasized by scientists, also led many to believe that kissing became the norm among human ape ancestors after they started spending considerable time on the ground, away from trees. Researchers suggest this shift might have happened “only after” ancient climatic changes led to the transition from forested habitats to drier and more open landscapes.