Ancient Hominins and Modern Humans Were Likely Kissing, Scientists Suggest

Among seabirds to Arctic mammals, primates to orangutans, certain species engage in mouth-to-mouth contact. Now, researchers suggest that ancient hominins also engaged in this behavior – and possibly locked lips with modern humans.

Shared Microbial Clues

This isn't the initial instance scientists have suggested Neanderthals and early modern humans were closely connected. In earlier research, scientists have found modern people and their thick-browed cousins shared the same mouth microbe for millions of years after the evolutionary divergence, implying they swapped saliva.

"Probably they were kissing," the researcher noted, adding that the concept chimed with research that has revealed humans of certain genetic backgrounds have bits of Neanderthal DNA in their genome, demonstrating genetic mixing was occurring.

Intimate Interpretation

"It certainly puts a different spin on human-Neanderthal relations," the lead researcher commented.

Writing in the journal Evolution and Human Behavior, the researcher and her team report how, to investigate the evolutionary origins of kissing, they first had to come up with a definition that was not limited to how people kiss.

Defining Kissing

"There have been some efforts to describe a kiss, but it's very much been human-centric, which implies that basically other animals don't kiss. Now we know that they likely engage, it may appear different from what human kissing resembles," said Brindle.

However, she noted some actions that resembled intimate contact were distinct activities – such as the processing and food sharing, or "kiss-fighting", seen in fish called certain marine animals.

As a result the research group came up with a definition of intimate contact centered around friendly interactions involving intentional mouth-to-mouth contact with a member of the same species, with some movement of the oral area but no transfer of nutrition.

Research Approach

The lead researcher explained they concentrated on accounts of intimate behavior in primates from Africa and Asian regions, including bonobos, apes and great apes, and employed online videos to verify the observations.

Scientists then integrated this data with details on the evolutionary relationships between extant and extinct species of such animals.

Historical Timeline

The team propose the findings indicate kissing developed approximately 21.5 million and 16.9m years ago in the predecessors of the great primates.

Placement of ancient hominins on this family tree suggests it is probable they, too, engaged in a kiss, the researchers say. But the activity may not have been confined to their own species.

"Reality that humans engage intimately, the reality that we currently have demonstrated that ancient relatives very likely kissed, indicates that the both groups are probably did kissed," Brindle added.

Evolutionary Importance

While the evolutionary explanation is discussed, Brindle explained intimate contact could be used in sexual contexts to possibly increase reproductive success or help choose between partners, while it could assist strengthen connections when practiced in a non-sexual manner.

Another expert in the behavior of great apes said that as kissing behavior was observed in a broad spectrum of apes it was logical its origins extend far into our ancient history, and an analysis of various types of kissing among a broader range of animals might push its origins 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 other animals," the expert noted.

Cultural Elements

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 strength of our emotional bonds, and methods of promoting confidence and closeness will have been important for eons," she said. "This could represent an image that appears a bit incongruous to our incorrect assumptions of a rather ruthless and ancient history, but actually it should be no surprise that Neanderthals – and including Neanderthals and our human ancestors collectively – engaged intimately."