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

Common Microbial Clues

This isn't the initial instance scientists have proposed ancient relatives and Homo sapiens were closely connected. In earlier research, scientists have found modern people and their Neanderthal relatives possessed the same mouth microbe for hundreds of thousands of years after the two species split, suggesting they swapped saliva.

"Likely they were kissing," the researcher noted, adding that the concept aligned with studies that has revealed humans of certain genetic backgrounds contain Neanderthal DNA in their genetic makeup, demonstrating genetic mixing was at play.

Romantic Interpretation

"This offers a more romantic perspective on human-Neanderthal relations," the lead researcher said.

Publishing in the publication a scientific periodical, Brindle and colleagues report how, to investigate the historical roots of kissing, they first had to come up with a description that was not limited to how humans kiss.

Describing Intimate Contact

"There have been some efforts to describe a kiss, but it's very much been focused on humans, which means that basically other animals do not engage in this. Currently we know that they likely engage, it may appear different from what our intimate contact resembles," said Brindle.

Nonetheless, she said some behaviors that resembled intimate contact were distinct activities – such as the processing and transfer of food, or "mouth contact", observed in aquatic species called certain marine animals.

Consequently the research group developed a definition of intimate contact based on friendly interactions involving intentional oral interaction with a member of the identical group, with some movement of the mouth but no transfer of nutrition.

Research Approach

Brindle said they concentrated on reports of kissing in non-human species from Africa and Asia, including primates, chimpanzees and great apes, and used online videos to verify the observations.

Scientists then combined this data with information on the genetic connections between extant and ancient types of such animals.

Historical Timeline

The team propose the findings suggest kissing evolved approximately 21.5 million and 16.9 million years ago in the predecessors of the great primates.

Placement of ancient hominins on this family tree suggests it is likely they, too, indulged in a kiss, the researchers conclude. But the behavior may not have been limited to their own species.

"The fact that modern people engage intimately, the fact that we currently have shown that Neanderthals probably kissed, suggests that the two [species] are also likely to have engage," Brindle added.

Biological Importance

Although the evolutionary explanation is debated, the expert explained kissing could be used in sexual contexts to potentially increase reproductive success or help choose between mates, while it could assist reinforce bonding when practiced in a platonic way.

Another expert in the activities of great apes commented that as intimate contact was seen in a broad spectrum of apes it was logical its origins extend far into our ancient history, and an analysis of various types of kissing among a wider variety of animals might push its beginnings back even earlier still.

"Behaviors that we think of as characteristics of our species, like kissing, are not exclusive to us if we look closely at other animals," he said.

Cultural Aspects

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

"Nonetheless, as humans we thrive or fail on the quality of our relationships, and ways of promoting confidence and closeness will have been significant for millions of years," she said. "This could represent an concept that seems a bit contradictory to our incorrect assumptions of a rather ruthless and aggressive past, but actually it should be no surprise that Neanderthals – and including Neanderthals and our own species collectively – kissed."