🔗 Share this article

From seabirds to Arctic mammals, chimpanzees to great apes, certain species engage in mouth-to-mouth contact. Now, scientists suggest that ancient hominins did it too – and might even have exchanged kisses with early Homo sapiens.

Common Microbial Clues

This isn't the initial instance experts have suggested Neanderthals and early modern humans were intimately acquainted. Among earlier research, researchers have found humans and their Neanderthal relatives shared the same mouth microbe for millions of years after the evolutionary divergence, suggesting they exchanged oral fluids.

"Likely they were kissing," the researcher noted, adding that the concept aligned with studies that has found humans of certain genetic backgrounds contain ancient genetic material in their genome, demonstrating genetic mixing was occurring.

Romantic Spin

"It certainly puts a more romantic spin on human-Neanderthal relations," Brindle commented.

Writing in the publication Evolution and Human Behavior, Brindle and colleagues detail how, to explore the historical roots of kissing, they first had to come up with a definition that was not limited to how humans smooch.

Describing Intimate Contact

"Previously there were some efforts to describe a intimate act, but it's largely human-centric, which means that basically non-human species do not engage in this. Now we understand that they probably do, it may appear different from what our intimate contact resembles," explained the evolutionary biologist.

However, she said some actions that looked like kissing were distinct activities – such as the processing and food sharing, or "mouth contact", observed in fish known as certain marine animals.

Consequently the team developed a definition of kissing based on friendly interactions involving directed mouth-to-mouth contact with a member of the identical group, with some motion of the mouth but no transfer of nutrition.

Research Methods

The lead researcher explained they focused on reports of kissing in non-human species from the African continent and Asian regions, including bonobos, chimpanzees and great apes, and used online videos to confirm the observations.

The researchers then integrated this data with information on the genetic connections between extant and ancient types of such primates.

Historical Origins

Researchers propose the findings suggest kissing evolved approximately 21.5 million and 16.9m years ago in the predecessors of the large apes.

The position of Neanderthals on this evolutionary lineage suggests it is likely they, too, engaged in a kiss, the scientists conclude. But the activity might not have been limited to their own species.

"Reality that humans engage intimately, the fact that we now have shown that ancient relatives probably kissed, suggests that the two [species] are probably did engage," the researcher added.

Biological Importance

While the scientific reasoning is discussed, the expert said kissing could be used in reproductive situations to potentially enhance reproductive success or assist in selecting between mates, while it might help reinforce bonding when practiced in a non-sexual manner.

A separate researcher in the activities of great apes said that as kissing behavior was observed in a broad spectrum of apes it made sense its origins extend far into our ancient history, and an examination of various types of kissing among a broader range of species might push its origins back further still.

"Things that we think of as characteristics of our species, like kissing, are not unique to us if we examine carefully at other animals," the expert noted.

Cultural Aspects

Another professor explained that intimate contact had a cultural element as it was not common to all societies.

"Nonetheless, as humans we succeed or struggle on the quality of our relationships, and methods of promoting trust and closeness will have been significant for millions of years," she said. "This could represent an concept that seems a bit incongruous to our incorrect assumptions of a rather ruthless and aggressive past, but really it ought to be no surprise that ancient hominins – and even them and our own species collectively – kissed."