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Among seabirds to Arctic mammals, primates to great apes, various animals appear to kiss. Now, scientists suggest that ancient hominins did it too – and might even have locked lips with modern humans.

Common Oral Clues

This isn't the initial instance experts have suggested ancient relatives and Homo sapiens were intimately acquainted. Among earlier research, researchers have found modern people and their thick-browed cousins shared the same mouth microbe for millions of years after the two species split, suggesting they swapped saliva.

"Likely they were kissing," she said, explaining that the idea aligned with studies that has revealed humans of certain genetic backgrounds contain Neanderthal DNA in their genome, demonstrating interbreeding was at play.

Intimate Spin

"This offers a more romantic spin on ancient interactions," the lead researcher commented.

Publishing in the publication a scientific periodical, Brindle and colleagues detail how, to explore the historical roots of intimate contact, they first had to develop a description that was not limited to how people smooch.

Defining Intimate Contact

"Previously there were some efforts to define a intimate act, but it's largely focused on humans, which implies that basically other animals do not engage in this. Currently we know that they probably do, it might just not look from what human kissing looks like," said Brindle.

However, she noted some behaviors that resembled intimate contact were distinct activities – such as the processing and food sharing, or "mouth contact", observed in fish called certain marine animals.

Consequently the team came up with a description of kissing based on friendly interactions involving intentional oral interaction with a member of the identical group, with some motion of the oral area but absence of nutrition.

Study Approach

Brindle explained they concentrated on reports of intimate behavior in primates from Africa and Asia, including bonobos, apes and orangutans, and used online videos to verify the reports.

Scientists then combined this data with information on the genetic connections between living and ancient types of such animals.

Evolutionary Timeline

The team say the findings indicate intimate contact developed somewhere between 21.5 million and 16.9 million years ago in the predecessors of the great primates.

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

"Reality that modern people engage intimately, the fact that we now have shown that Neanderthals very likely kissed, suggests that the two [species] are probably did kissed," Brindle noted.

Evolutionary Importance

Although the evolutionary explanation is discussed, the expert said intimate contact could be employed in sexual contexts to possibly increase reproductive success or help choose between partners, while it could assist reinforce bonding when practiced in a non-sexual manner.

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

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

Social Aspects

An archaeology expert said that kissing had a social component as it was not universal to all societies.

"However, as people we thrive or fail on the strength of our emotional bonds, and methods of promoting confidence and intimacy will have been important for millions of years," the professor stated. "This could represent an image that appears a bit incongruous to our misplaced ideas of a rather ruthless and aggressive past, but really it should be expected that Neanderthals – and even them and our own species together – engaged intimately."