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Among seabirds to polar bears, chimpanzees to orangutans, certain species appear to kiss. Now, researchers propose that Neanderthals also engaged in this behavior – and might even have locked lips with modern humans.

Common Oral Evidence

This isn't the initial instance experts have suggested ancient relatives and early modern humans were closely connected. In earlier research, researchers have found modern people and their thick-browed cousins possessed the same mouth microbe for millions of years after the two species split, implying they swapped saliva.

"Probably they were engaging in intimate contact," she said, adding that the idea aligned with research that has found humans of certain genetic backgrounds contain Neanderthal DNA in their genetic makeup, demonstrating interbreeding was at play.

Romantic Interpretation

"It certainly puts a more romantic perspective on human-Neanderthal relations," the lead researcher said.

Publishing in the publication a scientific periodical, the researcher and her team detail how, to investigate the historical roots of intimate contact, they first had to come up with a definition that was not limited to how humans smooch.

Describing Kissing

"There have been some efforts to define a kiss, but it's largely human-centric, which implies that essentially non-human species don't kiss. Now we understand that they probably do, it might just not look from what human kissing looks like," said the evolutionary biologist.

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

Consequently the team developed a definition of kissing centered around friendly interactions involving intentional mouth-to-mouth contact with a member of the identical group, with some motion of the oral area but absence of nutrition.

Study Methods

The lead researcher said they focused on reports of kissing in non-human species from Africa and Asian regions, including bonobos, chimpanzees and great apes, and employed digital recordings to verify the observations.

Scientists then integrated this data with information on the evolutionary relationships between living and ancient types of such animals.

Evolutionary Timeline

Researchers propose the findings indicate intimate contact developed approximately 21.5m and 16.9m years ago in the ancestors of the large apes.

Placement of ancient hominins on this evolutionary lineage suggests it is likely they, too, indulged in a kiss, the scientists conclude. But the behavior might not have been limited to their own species.

"The fact that humans kiss, the fact that we now have shown that Neanderthals very likely kissed, suggests that the both groups are probably did engage," Brindle noted.

Evolutionary Significance

Although the scientific reasoning is discussed, Brindle said intimate contact could be used in sexual contexts to potentially increase mating outcomes or assist in selecting between mates, while it could assist strengthen connections when practiced in a platonic way.

Another expert in the activities of primates commented that as kissing behavior was observed in a wide range of primates it made sense its roots extend far into our evolutionary past, and an analysis of different forms of intimate behavior among a broader range of species might extend its beginnings back further still.

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

Social Elements

Another professor explained that intimate contact had a social component as it was not universal to all human groups.

"However, as people we thrive or fail on the quality of our emotional bonds, and ways of promoting confidence and closeness will have been significant for eons," she said. "This could represent an image that seems a bit incongruous to our incorrect assumptions of a rather ruthless and aggressive past, but actually it should be no surprise that ancient hominins – and even Neanderthals and our human ancestors collectively – kissed."