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Among seabirds to Arctic mammals, chimpanzees to orangutans, certain species appear to kiss. Currently, scientists suggest that Neanderthals also engaged in this behavior – and might even have exchanged kisses with early Homo sapiens.

Shared Microbial Clues

This isn't the initial instance scientists have suggested ancient relatives and early modern humans were intimately acquainted. Among earlier research, scientists have discovered modern people and their Neanderthal relatives shared the identical oral bacteria for millions of years after the evolutionary divergence, suggesting they exchanged oral fluids.

"Likely they were engaging in intimate contact," the researcher noted, adding that the idea aligned with studies that has revealed humans of certain genetic backgrounds have bits of Neanderthal DNA in their genome, revealing interbreeding was at play.

Intimate Spin

"It certainly puts a different spin on ancient interactions," the lead researcher said.

Writing in the publication a scientific periodical, the researcher and her team detail how, to investigate the historical roots of intimate contact, they first had to come up with a definition that was not limited to how humans kiss.

Defining Kissing

"Previously there were some previous attempts to define a kiss, but it's very much been focused on humans, which means that basically non-human species do not engage in this. Currently we understand that they probably do, it may appear different from what our intimate contact resembles," explained the evolutionary biologist.

Nonetheless, she said some behaviors that resembled kissing were distinct activities – such as the processing and food sharing, or "kiss-fighting", seen in fish known as French grunts.

As a result the research group came up with a definition of kissing centered around friendly interactions involving intentional oral interaction with a member of the identical group, with some motion of the mouth but no transfer of food.

Research Approach

Brindle explained they focused on accounts of intimate behavior in non-human species from the African continent and Asian regions, including primates, apes and great apes, and used online videos to verify the observations.

The researchers then integrated this information with details on the evolutionary relationships between living and ancient types of such animals.

Evolutionary Origins

Researchers say the results suggest intimate contact evolved somewhere between 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 probable they, too, engaged in a kiss, the scientists say. But the behavior may not have been confined to their specific group.

"Reality that modern people kiss, the fact that we currently have shown that Neanderthals very likely kissed, suggests that the both groups are probably did engage," the researcher noted.

Biological Significance

While the scientific reasoning is discussed, the expert said intimate contact could be used in reproductive situations to potentially enhance reproductive success or assist in selecting between partners, while it could assist reinforce bonding when practiced in a platonic way.

A separate researcher in the behavior of great apes commented that as intimate contact was seen in a broad spectrum of primates it made sense its origins lie deep in our ancient history, and an analysis of various types of kissing among a broader range of species might extend its origins back further still.

"Behaviors that we consider as signatures of our species, like intimate contact, are not unique to us if we examine carefully at different species," he said.

Cultural Elements

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

"However, as people we succeed or struggle on the quality of our emotional bonds, and methods of promoting trust and intimacy will have been significant for eons," the professor stated. "It might be an image that seems a bit incongruous to our misplaced ideas of a supposedly aggressive and ancient history, but really it should be no surprise that ancient hominins – and including Neanderthals and our human ancestors collectively – engaged intimately."