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Among seabirds to polar bears, chimpanzees to great apes, various animals appear to kiss. Now, researchers propose that Neanderthals also engaged in this behavior – and might even have exchanged kisses 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 discovered modern people and their Neanderthal relatives possessed the identical oral bacteria for millions of years after the two species split, suggesting they exchanged oral fluids.

"Likely they were kissing," she said, adding that the idea chimed with studies that has found people of non-African ancestry have bits of ancient genetic material in their genetic makeup, demonstrating genetic mixing was occurring.

Intimate Spin

"It certainly puts a different spin on human-Neanderthal relations," the lead researcher commented.

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

Defining Intimate Contact

"Previously there were some efforts to describe a intimate act, but it's largely focused on humans, which implies that basically non-human species don't kiss. Currently we understand that they probably do, it may appear different from what human kissing looks like," explained Brindle.

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

Consequently the research group developed a definition of kissing centered around social behaviors involving intentional oral interaction with a member of the identical group, with some movement of the mouth but no transfer of food.

Study Approach

Brindle said they concentrated on reports of kissing in primates from Africa and Asia, including primates, chimpanzees and orangutans, and employed digital recordings to confirm the reports.

The researchers then integrated this information with details on the genetic connections between living and ancient species of such primates.

Evolutionary Origins

Researchers say the findings suggest intimate contact developed somewhere between 21.5m and 16.9 million years ago in the predecessors of the great primates.

Placement of ancient hominins on this evolutionary lineage means it is probable they, too, engaged in a intimate act, the researchers conclude. But the behavior may not have been confined to their specific group.

"The fact that modern people engage intimately, the fact that we now have shown that Neanderthals probably kissed, indicates that the two [species] are probably did kissed," Brindle added.

Evolutionary Significance

Although the scientific reasoning is debated, Brindle said intimate contact could be used in sexual contexts to potentially enhance reproductive success or assist in selecting between mates, while it might help strengthen connections when practiced in a non-sexual manner.

A separate researcher in the activities of primates commented that as intimate contact was seen in a wide range of primates it was logical its roots lie deep in our ancient history, and an examination of various types of kissing among a broader range of animals might extend its origins back even earlier still.

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

Social Elements

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

"Nonetheless, as people we succeed or struggle on the strength of our emotional bonds, and methods of encouraging confidence and closeness will have been significant for eons," she said. "It might be an concept that seems a bit contradictory to our misplaced ideas of a rather ruthless and ancient history, but really it ought to be no surprise that ancient hominins – and including Neanderthals and our own species collectively – kissed."