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Among Galápagos albatrosses to Arctic mammals, chimpanzees to orangutans, certain species appear to kiss. Currently, scientists propose that Neanderthals did it too – and possibly exchanged kisses with modern humans.

Shared Oral Clues

This isn't the initial instance scientists have proposed Neanderthals and early modern humans were closely connected. In previous studies, researchers have discovered humans and their Neanderthal relatives shared the same mouth microbe for hundreds of thousands of years after the two species split, implying they exchanged oral fluids.

"Likely they were kissing," the researcher noted, adding that the idea chimed with research that has found humans of non-African ancestry contain ancient genetic material in their genome, revealing genetic mixing was at play.

Romantic Interpretation

"It certainly puts a different spin on ancient interactions," the lead researcher said.

Writing in the publication a scientific periodical, the researcher and colleagues detail how, to investigate the historical roots of kissing, they first had to develop a definition that was not limited to how people smooch.

Describing Intimate Contact

"Previously there were some previous attempts to define a kiss, but it's largely focused on humans, which means that essentially other animals do not engage in this. Now we know that they likely engage, it might just not look from what our intimate contact resembles," explained the evolutionary biologist.

However, she said some actions that resembled intimate contact were distinct activities – such as the processing and food sharing, or "mouth contact", observed in fish known as certain marine animals.

Consequently the team came up with a definition of intimate contact centered around social behaviors involving directed oral interaction with a member of the identical group, with some motion of the oral area but absence of nutrition.

Study Methods

The lead researcher explained they concentrated on accounts of intimate behavior in non-human species from Africa and Asian regions, including bonobos, apes and great apes, and used online videos to confirm the reports.

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

Evolutionary Origins

The team say the results suggest kissing evolved somewhere between 21.5 million and 16.9 million years ago in the predecessors of the great primates.

Placement of Neanderthals on this evolutionary lineage suggests it is likely they, too, indulged in a intimate act, the scientists conclude. But the behavior may not have been limited to their specific group.

"The fact that modern people kiss, the reality that we now have demonstrated that Neanderthals probably engaged, indicates that the two [species] are also likely to have kissed," Brindle noted.

Evolutionary Importance

While the scientific reasoning is discussed, Brindle said intimate contact could be employed in sexual contexts to potentially increase reproductive success or assist in selecting between partners, while it could assist reinforce bonding when used in a non-sexual manner.

Another expert in the behavior of primates commented that as kissing behavior was observed in a wide range of primates it was logical its roots lie deep in our evolutionary past, and an analysis of different forms of intimate behavior among a broader range of species might push its beginnings back further still.

"Behaviors that we think of as signatures of human life, like intimate contact, are not unique to us if we examine carefully at different species," he said.

Cultural Aspects

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

"Nonetheless, as humans we thrive or fail on the quality of our emotional bonds, and ways of promoting trust and closeness will have been significant for millions of years," she said. "This could represent an concept that appears a bit incongruous to our incorrect assumptions of a supposedly aggressive and aggressive past, but really it ought to be expected that Neanderthals – and even them and our human ancestors together – kissed."