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Among seabirds to Arctic mammals, primates to great apes, various animals engage in mouth-to-mouth contact. Currently, scientists suggest that Neanderthals also engaged in this behavior – and might even have locked lips with early Homo sapiens.

Shared Oral Evidence

It is not the first time scientists have suggested Neanderthals and early modern humans were intimately acquainted. In earlier research, scientists have discovered modern people and their thick-browed cousins possessed the identical oral bacteria for hundreds of thousands of years after the two species split, suggesting they exchanged oral fluids.

"Probably they were kissing," she said, explaining that the concept aligned with studies that has revealed people of certain genetic backgrounds contain Neanderthal DNA in their genome, revealing interbreeding was at play.

Intimate Spin

"This offers a different spin on ancient interactions," the lead researcher said.

Publishing in the publication a scientific periodical, Brindle and colleagues report how, to explore the evolutionary origins of intimate contact, 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 don't kiss. Now we understand that they likely engage, it may appear different from what human kissing resembles," said Brindle.

However, she noted some actions that looked like intimate contact were something rather different – such as the processing and food sharing, or "kiss-fighting", observed in fish known as French grunts.

As a result the team developed a description of intimate contact centered around friendly interactions involving directed mouth-to-mouth contact with a member of the same species, with some motion of the mouth but absence of nutrition.

Research Approach

The lead researcher explained they concentrated on reports of intimate behavior in primates from the African continent and Asian regions, including bonobos, chimpanzees and orangutans, and employed digital recordings to confirm the observations.

Scientists then integrated this data with information on the evolutionary relationships between living and ancient types of such primates.

Historical Timeline

The team say the results suggest intimate contact developed approximately 21.5m and 16.9m years ago in the predecessors of the great primates.

The position of ancient hominins on this family tree suggests it is likely they, too, engaged in a intimate act, the researchers conclude. But the behavior may not have been limited to their specific group.

"Reality that modern people engage intimately, the fact that we now have shown that ancient relatives very likely engaged, suggests that the both groups are also likely to have kissed," the researcher added.

Evolutionary Significance

Although the evolutionary explanation is discussed, Brindle explained kissing could be used in sexual contexts to potentially increase reproductive success or help choose between partners, while it might help reinforce bonding when practiced in a platonic way.

Another expert in the activities of great apes said that as kissing behavior was seen in a wide range of primates it made sense its origins lie deep in our ancient history, and an examination of various types of intimate behavior among a broader range of species might extend its beginnings back even earlier still.

"Behaviors that we think of as signatures of our species, like kissing, are not exclusive to us if we examine carefully at different species," the expert noted.

Cultural Aspects

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

"Nonetheless, as humans we succeed or struggle on the quality of our relationships, and methods of encouraging confidence and intimacy will have been important for eons," the professor stated. "This could represent an concept that appears a bit contradictory 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."