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Among Galápagos albatrosses to Arctic mammals, chimpanzees to great apes, various animals appear to kiss. Now, scientists suggest that Neanderthals did it too – and possibly exchanged kisses with modern humans.

Shared Microbial Clues

It is not the first time experts have suggested ancient relatives and Homo sapiens were closely connected. Among earlier research, researchers have found humans and their thick-browed cousins possessed the same mouth microbe for hundreds of thousands of years after the two species split, suggesting they swapped saliva.

"Probably they were engaging in intimate contact," she said, explaining that the idea chimed with research that has revealed people of certain genetic backgrounds contain Neanderthal DNA in their genetic makeup, demonstrating genetic mixing was occurring.

Intimate Spin

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

Writing in the publication Evolution and Human Behavior, the researcher and her team report how, to investigate the historical roots of kissing, they first had to come up with a definition that was not restricted by how people smooch.

Describing Kissing

"Previously there were some efforts to define a intimate act, but it's very much been human-centric, which implies that essentially other animals don't kiss. Now we know that they probably do, it might just not look from what human kissing resembles," said Brindle.

Nonetheless, she said some actions that resembled kissing were distinct activities – such as the chewing and food sharing, or "mouth contact", seen in aquatic species known as certain marine animals.

As a result the team developed a description of intimate contact based on friendly interactions involving directed oral interaction with a member of the same species, with some movement of the oral area but no transfer of food.

Research Methods

Brindle said they concentrated on accounts of intimate behavior in non-human species from Africa and Asia, including bonobos, chimpanzees and orangutans, and used online videos to confirm the reports.

Scientists then combined this information with information on the genetic connections between living and extinct types of such primates.

Evolutionary Origins

Researchers say the findings indicate kissing evolved somewhere between 21.5m and 16.9 million years ago in the predecessors of the large apes.

The position of Neanderthals on this evolutionary lineage means it is probable they, too, indulged in a intimate act, the scientists say. But the behavior may not have been confined to their specific group.

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

Biological Significance

While the evolutionary explanation is debated, Brindle said intimate contact could be used in sexual contexts to potentially enhance mating outcomes or help choose between partners, while it might help reinforce bonding when used in a non-sexual manner.

A separate researcher in the activities of primates said that as kissing behavior was seen in a wide range of primates it made sense its roots lie deep in our ancient history, and an examination of various types of kissing among a broader range of species might push its beginnings back even earlier still.

"Things that we consider as signatures of our species, like intimate contact, are not exclusive to us if we look closely at different species," the expert noted.

Cultural Elements

An archaeology expert said that kissing had a social component as it was not common to all human groups.

"However, as humans we succeed or struggle on the quality of our relationships, and ways of promoting confidence and closeness will have been important for millions of years," the professor stated. "It might be an concept that seems a bit contradictory to our incorrect assumptions of a supposedly aggressive and aggressive past, but actually it ought to be expected that ancient hominins – and including them and our own species collectively – kissed."