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From Galápagos albatrosses to polar bears, primates to orangutans, various animals appear to kiss. Currently, researchers propose that Neanderthals did it too – and might even have exchanged kisses with modern humans.

Shared Microbial Evidence

This isn't the initial instance scientists have proposed ancient relatives and Homo sapiens were intimately acquainted. In earlier research, researchers have discovered modern people and their Neanderthal relatives possessed the identical oral bacteria for hundreds of thousands of years after the evolutionary divergence, implying they exchanged oral fluids.

"Probably they were kissing," she said, adding that the idea aligned with research that has found people of non-African ancestry have bits of ancient genetic material in their genome, demonstrating interbreeding was at play.

Intimate Interpretation

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

Publishing in the publication a scientific periodical, Brindle and colleagues detail how, to explore the evolutionary origins of kissing, they first had to come up with a definition that was not restricted by how humans smooch.

Defining Intimate Contact

"There have been some efforts to describe a intimate act, but it's very much been human-centric, which means that basically other animals don't kiss. Currently we know that they probably do, it might just not look from what our intimate contact looks like," explained Brindle.

Nonetheless, she noted some behaviors that resembled kissing were distinct activities – such as the chewing and food sharing, or "kiss-fighting", seen in fish called certain marine animals.

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

Study Approach

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

Scientists then combined this information with details on the evolutionary relationships between extant and ancient types of such animals.

Evolutionary Timeline

Researchers say the results indicate kissing evolved somewhere between 21.5m and 16.9m years ago in the predecessors of the great primates.

The position of Neanderthals on this family tree suggests it is likely they, too, engaged in a kiss, the scientists conclude. But the activity may not have been confined to their own species.

"Reality that humans engage intimately, the reality that we now have demonstrated that ancient relatives probably engaged, suggests that the two [species] are probably did engage," the researcher noted.

Biological Importance

Although the evolutionary explanation is debated, the expert said kissing could be employed in sexual contexts to potentially increase reproductive success or help choose between mates, while it could assist reinforce bonding when used in a non-sexual manner.

A separate researcher in the behavior of primates said that as kissing behavior was seen in a broad spectrum of apes it was logical its origins extend far into our ancient history, and an examination of various types of kissing among a broader range of animals might push its origins back further still.

"Things that we consider as characteristics of our species, like kissing, are not unique to us if we look closely at other animals," he said.

Cultural Aspects

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

"Nonetheless, as people we succeed or struggle on the quality of our relationships, and methods of encouraging confidence and closeness will have been important for millions of years," she said. "This could represent an concept that appears a bit incongruous to our misplaced ideas of a supposedly aggressive and ancient history, but actually it should be expected that Neanderthals – and including them and our own species collectively – kissed."