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Among Galápagos albatrosses to Arctic mammals, primates to great apes, certain species engage in mouth-to-mouth contact. Currently, researchers suggest that Neanderthals did it too – and possibly exchanged kisses with modern humans.

Common Microbial Clues

This isn't the initial instance experts have proposed ancient relatives and Homo sapiens were intimately acquainted. Among previous studies, researchers have found humans and their Neanderthal relatives possessed the identical oral bacteria for hundreds of thousands of years after the evolutionary divergence, suggesting they exchanged oral fluids.

"Probably they were kissing," the researcher noted, explaining that the concept aligned with studies that has revealed humans of non-African ancestry contain Neanderthal DNA in their genome, demonstrating genetic mixing was occurring.

Romantic Interpretation

"It certainly puts a more romantic perspective on ancient interactions," Brindle said.

Writing in the publication Evolution and Human Behavior, the researcher and her team detail how, to explore the evolutionary origins of kissing, they first had to come up with a description that was not limited to how people kiss.

Describing Kissing

"There have been some previous attempts to define a kiss, but it's largely human-centric, which means that essentially 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 Brindle.

Nonetheless, she noted some behaviors that looked like kissing were distinct activities – such as the chewing and food sharing, or "mouth contact", seen in fish called French grunts.

As a result the team developed a description of kissing centered around friendly interactions involving directed mouth-to-mouth contact with a individual of the identical group, with some movement of the oral area but no transfer of nutrition.

Research Methods

Brindle explained they focused on accounts of kissing in primates from the African continent and Asian regions, including bonobos, chimpanzees and orangutans, and employed online videos to confirm the observations.

Scientists then combined this information with information on the genetic connections between living and extinct species of such primates.

Historical Timeline

Researchers say the findings suggest intimate contact evolved somewhere between 21.5m and 16.9m years ago in the predecessors of the large apes.

Placement of Neanderthals on this family tree suggests it is probable they, too, engaged in a intimate act, the scientists conclude. But the behavior may not have been confined to their own species.

"The fact that modern people engage intimately, the fact that we now have shown that Neanderthals very likely kissed, indicates that the two [species] are probably did kissed," Brindle added.

Biological Significance

While the scientific reasoning is debated, Brindle said intimate contact could be used in sexual contexts to possibly enhance reproductive success or assist in selecting between partners, while it might help strengthen connections when used in a non-sexual manner.

Another expert in the behavior of great apes said that as intimate contact was observed in a broad spectrum of primates it was logical its origins lie deep in our evolutionary past, and an analysis of different forms of intimate behavior among a wider variety of species might push its beginnings back further still.

"Things that we think of as characteristics of our species, like intimate contact, are not unique to us if we look closely at different species," the expert noted.

Social Aspects

An archaeology expert explained that kissing had a cultural element as it was not universal to all human groups.

"However, as humans we succeed or struggle on the quality of our relationships, and ways of promoting confidence and closeness will have been significant for eons," the professor stated. "It might be an image that seems a bit contradictory to our incorrect assumptions of a supposedly aggressive and ancient history, but really it ought to be expected that Neanderthals – and including them and our human ancestors collectively – engaged intimately."