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From seabirds to polar bears, primates to orangutans, various animals appear to kiss. Now, scientists suggest that Neanderthals did it too – and possibly exchanged kisses with modern humans.

Common Oral Clues

It is not the first time scientists have proposed ancient relatives and Homo sapiens were intimately acquainted. Among previous studies, researchers have discovered modern people and their Neanderthal relatives shared the same mouth microbe for hundreds of thousands of years after the evolutionary divergence, suggesting they swapped saliva.

"Likely they were engaging in intimate contact," she said, explaining that the idea chimed with studies that has revealed people of certain genetic backgrounds contain ancient genetic material in their genome, revealing genetic mixing was at play.

Romantic Spin

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

Publishing in the journal Evolution and Human Behavior, Brindle and her team report how, to explore the historical roots of kissing, they first had to come up with a description that was not restricted by how people kiss.

Defining Intimate Contact

"There have been some previous attempts to define a intimate act, but it's largely human-centric, which implies that basically non-human species don't kiss. Now we understand that they likely engage, it might just not look from what our intimate contact resembles," explained Brindle.

Nonetheless, she noted some behaviors that resembled intimate contact were distinct activities – such as the processing and food sharing, or "mouth contact", observed in aquatic species known as French grunts.

As a result the research group came up with a definition of kissing centered around social behaviors involving intentional oral interaction with a member of the same species, with some movement of the mouth but no transfer of food.

Research Methods

Brindle said they focused on reports of kissing in primates from Africa and Asia, including bonobos, apes and great apes, and used digital recordings to verify the reports.

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

Evolutionary Origins

Researchers say the findings suggest kissing evolved approximately 21.5 million and 16.9 million years ago in the predecessors of the great primates.

Placement of ancient hominins on this family tree suggests it is likely they, too, indulged in a intimate act, the researchers conclude. But the activity might not have been confined to their own species.

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

Biological Importance

While the scientific reasoning is debated, the expert said kissing could be used in sexual contexts to possibly enhance reproductive success or assist in selecting between partners, while it could assist reinforce bonding when practiced in a non-sexual manner.

A separate researcher in the behavior of primates said that as kissing behavior was observed in a wide range of apes it made sense its roots lie deep in our evolutionary past, and an examination of various types of intimate behavior among a broader range of animals might push its beginnings back further still.

"Behaviors that we consider as signatures of our species, like kissing, are not unique to us if we examine carefully at other animals," the expert noted.

Social Aspects

An archaeology expert explained that intimate contact had a social component as it was not common to all societies.

"Nonetheless, as people we thrive or fail on the strength of our emotional bonds, and methods of encouraging trust and closeness will have been significant for eons," the professor stated. "This could represent an image that appears a bit incongruous to our incorrect assumptions of a supposedly aggressive and aggressive past, but really it should be expected that Neanderthals – and including them and our own species together – engaged intimately."