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From seabirds to Arctic mammals, chimpanzees to great apes, certain species appear to kiss. Currently, scientists propose that Neanderthals also engaged in this behavior – and possibly locked lips with modern humans.

Shared Oral Clues

It is not the first time experts have suggested ancient relatives and early modern humans were intimately acquainted. In previous studies, scientists have found humans and their Neanderthal relatives possessed the identical oral bacteria for hundreds of thousands of years after the evolutionary divergence, implying they swapped saliva.

"Probably they were engaging in intimate contact," she said, adding that the concept aligned with studies that has revealed humans of certain genetic backgrounds contain Neanderthal DNA in their genome, revealing genetic mixing was at play.

Romantic Interpretation

"This offers a more romantic spin on human-Neanderthal relations," Brindle commented.

Writing in the publication a scientific periodical, the researcher and colleagues detail how, to investigate the historical roots of intimate contact, they first had to come up with a description that was not limited to how humans kiss.

Defining Kissing

"Previously there were some efforts to define a intimate act, but it's very much been focused on humans, which means that basically other animals don't kiss. Now we know that they probably do, it may appear different from what our intimate contact resembles," said Brindle.

However, she noted some behaviors that resembled kissing were something rather different – such as the processing and food sharing, or "kiss-fighting", seen in fish known as French grunts.

Consequently the team developed a description of intimate contact based on social behaviors involving intentional mouth-to-mouth contact with a member of the same species, with some movement of the mouth but absence of food.

Research Approach

The lead researcher said they concentrated on accounts of intimate behavior in non-human species from Africa and Asian regions, including primates, apes and great apes, and employed online videos to confirm the observations.

Scientists then combined this information with information on the genetic connections between extant and extinct types of such animals.

Historical Origins

The team say the findings indicate kissing developed approximately 21.5 million and 16.9 million years ago in the ancestors of the great primates.

Placement of Neanderthals on this evolutionary lineage suggests it is probable they, too, engaged in a kiss, the scientists say. But the activity may not have been limited to their own species.

"Reality that modern people kiss, the fact that we now have demonstrated that Neanderthals probably kissed, suggests that the both groups are also likely to have engage," the researcher added.

Biological Importance

While the scientific reasoning is discussed, the expert explained kissing could be employed in sexual contexts to potentially enhance reproductive success or help choose between partners, while it might help strengthen connections when used in a platonic way.

A separate researcher in the behavior of great apes said that as intimate contact was observed in a broad spectrum of primates it was logical its origins lie deep in our evolutionary past, and an analysis of various types of intimate behavior among a wider variety of animals might push its beginnings back even earlier still.

"Behaviors that we consider as characteristics of human life, like kissing, are not exclusive to us if we examine carefully at different species," he said.

Cultural Elements

Another professor explained that intimate contact had a cultural element as it was not common to all human groups.

"However, as humans we thrive or fail on the strength of our relationships, and methods of encouraging confidence and closeness will have been significant for millions of years," the professor stated. "It might be an concept that seems a bit incongruous to our misplaced ideas of a rather ruthless and ancient history, but actually it ought to be no surprise that ancient hominins – and even Neanderthals and our human ancestors collectively – kissed."