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From Galápagos albatrosses to Arctic mammals, primates to great apes, various animals engage in mouth-to-mouth contact. Now, researchers suggest that Neanderthals did it too – and possibly exchanged kisses with modern humans.

Shared Oral Clues

It is not the first time scientists have suggested ancient relatives and Homo sapiens were closely connected. Among previous studies, scientists have found humans and their thick-browed cousins 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 research that has revealed people of non-African ancestry contain ancient genetic material in their genome, revealing genetic mixing was occurring.

Romantic Interpretation

"It certainly puts a more romantic perspective on ancient interactions," Brindle commented.

Writing in the publication a scientific periodical, the researcher and her team report how, to investigate the evolutionary origins of kissing, they first had to develop a description that was not restricted by how people kiss.

Describing Kissing

"Previously there were some previous attempts to describe a intimate act, but it's largely human-centric, which means that essentially non-human species do not engage in this. Currently we understand that they likely engage, it may appear different from what our intimate contact resembles," explained the evolutionary biologist.

However, she said some behaviors that resembled kissing were distinct activities – such as the processing and food sharing, or "kiss-fighting", seen in fish known as certain marine animals.

As a result the research group developed a definition of intimate contact centered around social behaviors involving intentional oral interaction with a member of the identical group, with some movement of the oral area but absence of food.

Research Approach

The lead researcher said they focused on reports of kissing in non-human species from Africa and Asia, including bonobos, apes and great apes, and used online videos to verify the observations.

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

Evolutionary Origins

The team say the results indicate intimate contact developed somewhere between 21.5 million and 16.9m years ago in the predecessors of the large apes.

Placement of ancient hominins on this family tree means it is probable they, too, engaged in a intimate act, the scientists conclude. But the behavior may not have been limited to their specific group.

"Reality that modern people kiss, the fact that we currently have shown that ancient relatives very likely kissed, indicates that the two [species] are also likely to have engage," Brindle added.

Biological Importance

Although the scientific reasoning is discussed, the expert said kissing could be employed in sexual contexts to possibly enhance reproductive success or help choose between mates, while it could assist reinforce bonding when used in a platonic way.

A separate researcher in the activities of great apes said that as kissing behavior was observed in a wide range of apes it was logical its origins lie deep in our ancient history, and an analysis of various types of kissing among a broader range of species might extend its beginnings back further still.

"Things that we think of as signatures of our species, like intimate contact, are not unique to us if we examine carefully at other animals," he said.

Cultural Elements

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 important for millions of years," the professor stated. "It might be an concept that seems a bit incongruous to our incorrect assumptions of a rather ruthless and aggressive past, but actually it should be no surprise that Neanderthals – and including them and our human ancestors together – kissed."