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Among Galápagos albatrosses to polar bears, primates to great apes, certain species appear to kiss. Now, scientists suggest that Neanderthals also engaged in this behavior – and might even have locked lips with modern humans.

Common Microbial Evidence

This isn't the initial instance scientists have suggested ancient relatives and early modern humans were intimately acquainted. Among earlier research, researchers have discovered modern people and their thick-browed cousins shared the identical oral bacteria for hundreds of thousands of years after the evolutionary divergence, suggesting they swapped saliva.

"Probably they were engaging in intimate contact," she said, explaining that the concept aligned with studies that has revealed humans of non-African ancestry contain Neanderthal DNA in their genetic makeup, demonstrating interbreeding was at play.

Intimate Spin

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

Writing in the journal Evolution and Human Behavior, Brindle and colleagues report how, to investigate the evolutionary origins of intimate contact, they first had to come up with a definition that was not limited to how people smooch.

Defining Kissing

"Previously there were some efforts to define a kiss, but it's very much been human-centric, which implies that essentially other animals don't kiss. Now we understand that they likely engage, it may appear different from what human kissing looks like," said the evolutionary biologist.

However, she noted some behaviors that looked like kissing were distinct activities – such as the chewing and transfer of food, or "mouth contact", observed in fish known as certain marine animals.

Consequently the team came up with a description of intimate contact centered around friendly interactions involving intentional oral interaction with a individual of the identical group, with some motion of the mouth but absence of nutrition.

Study Methods

Brindle explained they concentrated on reports of kissing in non-human species from Africa and Asia, including bonobos, chimpanzees and great apes, and employed online videos to confirm the reports.

The researchers then combined this data with details on the genetic connections between extant and extinct types of such animals.

Evolutionary Origins

Researchers propose the findings indicate intimate contact evolved somewhere between 21.5 million and 16.9m years ago in the predecessors of the great primates.

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

"The fact that modern people engage intimately, the reality that we currently have shown that Neanderthals probably kissed, indicates that the both groups are also likely to have engage," Brindle added.

Biological Importance

Although the evolutionary explanation is discussed, Brindle explained kissing could be used in sexual contexts to potentially enhance reproductive success or help choose between mates, while it might help strengthen connections when used in a non-sexual manner.

A separate researcher in the behavior of great apes said that as kissing behavior was seen in a wide range of apes it was logical its roots extend far into our evolutionary past, and an examination of various types of kissing among a broader range of animals might push its origins back even earlier still.

"Things that we think of as signatures of human life, like intimate contact, are not exclusive to us if we look closely at other animals," he said.

Social Aspects

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

"However, as humans we thrive or fail on the strength of our relationships, and methods of encouraging confidence and closeness will have been important for eons," the professor stated. "It might be an concept that seems a bit contradictory to our incorrect assumptions of a supposedly aggressive and ancient history, but really it ought to be no surprise that ancient hominins – and including Neanderthals and our own species together – kissed."