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From seabirds to Arctic mammals, primates to great apes, various animals appear to kiss. Now, researchers suggest that Neanderthals did it too – and possibly locked lips with early Homo sapiens.

Shared Microbial Clues

It is not the first time experts have suggested ancient relatives and early modern humans were intimately acquainted. Among earlier research, scientists have found humans and their Neanderthal relatives possessed the identical oral bacteria for hundreds of thousands of years after the evolutionary divergence, implying they exchanged oral fluids.

"Likely they were engaging in intimate contact," the researcher noted, explaining that the concept chimed with studies that has found humans of certain genetic backgrounds have bits of Neanderthal DNA in their genome, revealing interbreeding was occurring.

Romantic Interpretation

"It certainly puts a different perspective on human-Neanderthal relations," Brindle said.

Publishing in the journal a scientific periodical, Brindle and colleagues report how, to explore the evolutionary origins of kissing, they first had to develop a description that was not restricted by how humans kiss.

Describing Kissing

"There have been some efforts to describe a kiss, but it's largely human-centric, which implies that essentially non-human species do not engage in this. Now we know that they likely engage, it may appear different from what our intimate contact resembles," explained Brindle.

However, she noted some behaviors that resembled intimate contact were something rather different – such as the chewing and transfer of food, or "mouth contact", seen in aquatic species called certain marine animals.

Consequently the research group came up with a definition of kissing based on friendly interactions involving directed oral interaction with a individual of the same species, with some movement of the mouth but absence of food.

Study Approach

The lead researcher said they focused on reports of intimate behavior in non-human species from Africa and Asian regions, including primates, apes and orangutans, and employed digital recordings to verify the reports.

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

Historical Origins

The team propose the findings indicate intimate contact evolved somewhere between 21.5m and 16.9m years ago in the predecessors of the great primates.

Placement of Neanderthals on this family tree suggests it is probable they, too, engaged in a kiss, the scientists conclude. But the behavior may not have been limited to their specific group.

"The fact that modern people engage intimately, the fact that we currently have shown that Neanderthals probably engaged, indicates that the two [species] are also likely to have kissed," the researcher noted.

Biological Importance

While the scientific reasoning is debated, the expert explained kissing could be employed in sexual contexts to possibly enhance mating outcomes or help choose between mates, while it might help reinforce bonding when used in a non-sexual manner.

A separate researcher in the behavior of primates commented that as kissing behavior 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 kissing among a broader range of species might push its origins back even earlier still.

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

Cultural Elements

Another professor explained that kissing had a cultural element as it was not common to all human groups.

"Nonetheless, as humans we thrive or fail on the strength of our emotional bonds, and methods of encouraging confidence and intimacy will have been important for millions of years," the professor stated. "It might be an concept that appears a bit incongruous to our misplaced ideas of a rather ruthless and ancient history, but really it should be no surprise that Neanderthals – and even Neanderthals and our human ancestors together – engaged intimately."