🔗 Share this article

Among Galápagos albatrosses to polar bears, chimpanzees to orangutans, various animals appear to kiss. Currently, scientists suggest that ancient hominins also engaged in this behavior – and possibly exchanged kisses with early Homo sapiens.

Common Microbial Clues

It is not the first time scientists have proposed ancient relatives and Homo sapiens were closely connected. In earlier research, scientists have discovered modern people and their thick-browed cousins shared the same mouth microbe for hundreds of thousands of years after the evolutionary divergence, implying they swapped saliva.

"Probably they were kissing," she said, explaining that the idea aligned with studies that has found humans of certain genetic backgrounds have bits of Neanderthal DNA in their genetic makeup, revealing genetic mixing was at play.

Romantic Spin

"This offers a more romantic perspective on human-Neanderthal relations," the lead researcher said.

Publishing in the publication Evolution and Human Behavior, Brindle and her team detail how, to investigate the historical roots of kissing, they first had to come up with a definition that was not limited to how people kiss.

Describing Intimate Contact

"Previously there were some previous attempts to describe a kiss, but it's largely focused on humans, which implies that basically other animals don't kiss. Now we understand that they probably do, it may appear different from what human kissing resembles," said Brindle.

However, she said some behaviors that looked like kissing were distinct activities – such as the chewing and food sharing, or "kiss-fighting", seen in fish called certain marine animals.

As a result the team came up with a definition of kissing based on friendly interactions involving intentional oral interaction with a member of the same species, with some motion of the oral area but no transfer of food.

Research Methods

The lead researcher explained they concentrated on reports of kissing in primates from the African continent and Asia, including primates, chimpanzees and great apes, and employed digital recordings to verify the observations.

The researchers then combined this data with details on the evolutionary relationships between living and extinct species of such animals.

Historical Origins

Researchers propose the results indicate intimate contact developed somewhere between 21.5 million and 16.9m years ago in the predecessors of the large apes.

Placement of Neanderthals on this family tree means it is probable they, too, indulged in a kiss, the scientists conclude. But the activity might not have been limited to their specific group.

"The fact that modern people engage intimately, the fact that we now have demonstrated that ancient relatives probably kissed, suggests that the two [species] are also likely to have kissed," Brindle added.

Biological Importance

Although the scientific reasoning is debated, the expert said intimate contact could be used in reproductive situations to possibly enhance reproductive success or help choose between mates, while it could assist reinforce bonding when used in a platonic way.

A separate researcher in the activities of primates commented that as intimate contact was observed in a wide range of apes it made sense its origins lie deep in our evolutionary past, and an examination of different forms of kissing among a broader range of species might extend its origins back further still.

"Behaviors that we consider as signatures of human life, like kissing, are not exclusive to us if we examine carefully at other animals," the expert noted.

Social Elements

An archaeology expert said that intimate contact had a cultural element as it was not common to all human groups.

"However, as humans we succeed or struggle on the strength of our emotional bonds, and methods of encouraging confidence and closeness will have been important for millions of years," she said. "This could represent an image that appears a bit incongruous to our incorrect assumptions of a supposedly aggressive and ancient history, but actually it should be no surprise that Neanderthals – and even them and our own species collectively – kissed."