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Among seabirds to Arctic mammals, chimpanzees to great apes, various animals appear to kiss. Now, researchers suggest that Neanderthals also engaged in this behavior – and might even have locked lips with early Homo sapiens.

Common Oral Evidence

It is not the first time scientists have proposed ancient relatives and early modern humans were intimately acquainted. Among previous studies, researchers have discovered modern people and their Neanderthal relatives shared the identical oral bacteria for hundreds of thousands of years after the two species split, implying they exchanged oral fluids.

"Likely they were engaging in intimate contact," she said, adding that the concept aligned with studies that has revealed humans of certain genetic backgrounds contain ancient genetic material in their genome, revealing genetic mixing was occurring.

Romantic Spin

"This offers a more romantic perspective on human-Neanderthal relations," the lead researcher commented.

Publishing in the publication a scientific periodical, the researcher and her team detail how, to explore the historical roots of kissing, they first had to come up with a description that was not limited to how humans kiss.

Describing Intimate Contact

"There have been some previous attempts to describe a intimate act, but it's very much been human-centric, which implies that basically other animals don't kiss. Now we understand that they likely engage, it may appear different from what our intimate contact looks like," said Brindle.

Nonetheless, she noted some behaviors that looked like intimate contact were something rather different – such as the processing and transfer of food, or "kiss-fighting", observed in fish called certain marine animals.

Consequently the team developed a description of kissing based on social behaviors involving intentional mouth-to-mouth contact with a member of the same species, with some movement of the mouth but no transfer of nutrition.

Research Approach

The lead researcher 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 employed digital recordings to verify the observations.

The researchers then integrated this information with details on the evolutionary relationships between extant and extinct species of such animals.

Evolutionary Origins

Researchers say the results indicate kissing developed approximately 21.5 million and 16.9 million years ago in the predecessors of the large apes.

The position of Neanderthals on this family tree suggests it is likely they, too, indulged in a kiss, the researchers say. But the activity may not have been limited to their own species.

"Reality that humans kiss, the fact that we now have demonstrated that Neanderthals very likely engaged, suggests that the two [species] are probably did kissed," the researcher added.

Evolutionary Importance

While the evolutionary explanation is discussed, Brindle said intimate contact could be employed in reproductive situations to potentially increase reproductive success or assist in selecting between mates, while it might help strengthen connections when used in a non-sexual manner.

A separate researcher in the activities of great apes commented that as kissing behavior was seen in a wide range of primates it made sense its origins lie deep in our evolutionary past, and an analysis of various types of kissing among a wider variety of animals might extend its beginnings back further still.

"Things that we think of as characteristics of our species, like intimate contact, are not exclusive to us if we look closely at other animals," he said.

Cultural Aspects

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

"Nonetheless, as people we succeed or struggle on the strength of our emotional bonds, and methods of promoting confidence and intimacy will have been important for eons," she said. "This could represent an concept that appears a bit contradictory to our misplaced ideas of a rather ruthless and ancient history, but actually it ought to be expected that Neanderthals – and including them and our human ancestors together – engaged intimately."