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Among Galápagos albatrosses to Arctic mammals, chimpanzees to great apes, certain species appear to kiss. Currently, scientists suggest that Neanderthals did it too – and possibly locked lips with modern humans.

Shared Oral Clues

This isn't the initial instance scientists have suggested ancient relatives and Homo sapiens were closely connected. Among previous studies, scientists have discovered modern people and their thick-browed cousins shared the identical oral bacteria for millions of years after the two species split, suggesting they swapped saliva.

"Likely they were kissing," she said, explaining that the idea chimed with studies that has found humans of non-African ancestry contain Neanderthal DNA in their genetic makeup, demonstrating genetic mixing was at play.

Intimate Interpretation

"This offers a more romantic perspective on ancient interactions," Brindle commented.

Publishing in the publication a scientific periodical, the researcher and her team report how, to explore the historical roots of kissing, they first had to develop a definition that was not limited to how humans smooch.

Describing Intimate Contact

"Previously there were some efforts to describe a kiss, but it's very much been focused on humans, which implies that basically non-human species do not engage in this. Now we know that they likely engage, it might just not look from what our intimate contact looks like," said Brindle.

However, she said some actions that resembled kissing were distinct activities – such as the processing and transfer of food, or "mouth contact", observed in fish known as French grunts.

As a result the research group came up with a definition of intimate contact based on friendly interactions involving intentional oral interaction with a member of the same species, with some movement of the mouth but absence of nutrition.

Study Approach

The lead researcher explained they focused on reports of intimate behavior in non-human species from Africa and Asian regions, including bonobos, apes and great apes, and used digital recordings to verify the reports.

Scientists then integrated this information with information on the genetic connections between living and extinct types of such primates.

Historical Origins

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

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

"Reality that modern people kiss, the fact that we now have demonstrated that ancient relatives probably kissed, suggests that the two [species] are also likely to have kissed," the researcher noted.

Evolutionary Significance

Although the evolutionary explanation is discussed, Brindle explained intimate contact could be employed in reproductive situations to possibly increase reproductive success or help choose between partners, while it could assist strengthen connections when used in a platonic way.

A separate researcher in the behavior of primates commented that as kissing behavior was seen in a broad spectrum of primates it was logical its origins extend far into our evolutionary past, and an analysis of various types of intimate behavior among a broader range of species might push its origins back further still.

"Behaviors that we consider as signatures of our species, like kissing, are not exclusive to us if we look closely at different species," the expert noted.

Cultural Elements

An archaeology expert said that intimate contact had a social component as it was not universal to all human groups.

"Nonetheless, as humans we succeed or struggle on the strength of our emotional bonds, and ways of promoting trust and intimacy will have been important for millions of years," she said. "It might be an image that seems a bit incongruous to our incorrect assumptions of a supposedly aggressive and ancient history, but actually it ought to be expected that Neanderthals – and even Neanderthals and our human ancestors collectively – engaged intimately."