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From Galápagos albatrosses to Arctic mammals, primates to orangutans, various animals engage in mouth-to-mouth contact. Currently, scientists suggest that Neanderthals did it too – and possibly locked lips with modern humans.

Common Microbial Evidence

It is not the first time experts have proposed ancient relatives and early modern humans were intimately acquainted. Among previous studies, scientists have discovered humans and their thick-browed cousins shared the identical oral bacteria for millions of years after the evolutionary divergence, suggesting they exchanged oral fluids.

"Likely they were kissing," the researcher noted, explaining that the idea chimed with research that has revealed people of non-African ancestry have bits of Neanderthal DNA in their genome, revealing genetic mixing was at play.

Romantic Interpretation

"This offers a different spin on human-Neanderthal relations," Brindle said.

Publishing in the journal a scientific periodical, the researcher and colleagues report how, to investigate the evolutionary origins of intimate contact, they first had to develop a definition that was not limited to how people smooch.

Describing Intimate Contact

"Previously there were some previous attempts to define a intimate act, but it's largely human-centric, which means that essentially other animals do not engage in this. Now we know that they likely engage, it might just not look from what our intimate contact looks like," explained the evolutionary biologist.

However, she said some actions that looked like intimate contact were distinct activities – such as the processing and transfer of food, or "kiss-fighting", seen in fish known as French grunts.

As a result the team developed a definition of intimate contact centered around friendly interactions involving intentional mouth-to-mouth contact with a individual of the identical group, with some motion of the mouth but no transfer of food.

Research Methods

The lead researcher said they focused on accounts of intimate behavior in non-human species from the African continent and Asian regions, including bonobos, chimpanzees and orangutans, and employed digital recordings to verify the reports.

The researchers then combined this data with information on the genetic connections between extant and ancient types of such primates.

Historical Origins

The team propose the results suggest kissing developed somewhere between 21.5m and 16.9m years ago in the predecessors of the large apes.

Placement of ancient hominins on this evolutionary lineage means it is probable they, too, indulged in a kiss, the scientists conclude. But the activity might not have been confined to their own species.

"Reality that humans engage intimately, the reality that we now have shown that Neanderthals very likely kissed, indicates that the both groups are also likely to have kissed," Brindle noted.

Biological Significance

While the evolutionary explanation is discussed, the expert explained kissing could be used in sexual contexts to potentially enhance reproductive success or help choose between partners, while it might help reinforce bonding when practiced in a non-sexual manner.

Another expert in the behavior of primates commented that as kissing behavior was seen in a wide range of primates it was logical its origins lie deep in our ancient history, and an analysis of different forms of kissing among a broader range of species might extend its beginnings back even earlier still.

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

Cultural Aspects

Another professor explained that intimate contact had a social component as it was not universal to all societies.

"Nonetheless, as humans we thrive or fail on the strength of our relationships, and methods of promoting confidence and closeness will have been important for eons," she said. "It might be an concept that seems a bit contradictory to our incorrect assumptions of a supposedly aggressive and ancient history, but actually it should be no surprise that ancient hominins – and including them and our human ancestors together – engaged intimately."