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Among seabirds to Arctic mammals, primates to great apes, various animals engage in mouth-to-mouth contact. Currently, researchers suggest that Neanderthals did it too – and might even have locked lips with modern humans.

Common Microbial Evidence

It is not the first time scientists have suggested Neanderthals and Homo sapiens were closely connected. In earlier research, scientists have discovered humans and their thick-browed cousins possessed the identical oral bacteria for hundreds of thousands of years after the evolutionary divergence, suggesting they swapped saliva.

"Probably they were kissing," she said, explaining that the concept aligned with research that has found people of non-African ancestry have bits of ancient genetic material in their genetic makeup, revealing genetic mixing was occurring.

Romantic Interpretation

"This offers a more romantic perspective on ancient interactions," the lead researcher commented.

Writing in the journal a scientific periodical, the researcher and her team report how, to explore the evolutionary origins 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 define a kiss, but it's largely focused on humans, which implies that essentially non-human species don't kiss. Now we understand that they probably do, it might just not look from what our intimate contact resembles," said the evolutionary biologist.

Nonetheless, she said some behaviors that looked like intimate contact were distinct activities – such as the chewing and food sharing, or "mouth contact", observed in fish called French grunts.

As a result the research group developed a description of kissing centered around social behaviors involving intentional mouth-to-mouth contact with a member of the identical group, with some movement of the oral area but absence of food.

Research Methods

The lead researcher said they focused on reports of intimate behavior in non-human species from Africa and Asia, including primates, chimpanzees and orangutans, and used online videos to verify the reports.

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

Evolutionary Origins

The team propose the results indicate kissing evolved approximately 21.5 million and 16.9 million years ago in the predecessors of the large apes.

The position of ancient hominins on this evolutionary lineage suggests it is probable they, too, engaged in a intimate act, the researchers say. But the activity may not have been limited to their own species.

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

Evolutionary Significance

Although the scientific reasoning is discussed, the expert explained kissing could be employed in sexual contexts to possibly increase mating outcomes or assist in selecting between mates, while it might help strengthen connections when used in a non-sexual manner.

Another expert in the behavior of primates commented that as intimate contact was seen in a wide range of primates it was logical its roots extend far into our evolutionary past, and an analysis of different forms of kissing among a wider variety of species might push its origins back further still.

"Things that we consider as characteristics of our species, like kissing, are not unique to us if we examine carefully at different species," the expert noted.

Cultural Aspects

Another professor said that intimate contact had a social component as it was not common to all human groups.

"Nonetheless, as people we succeed or struggle on the strength of our emotional bonds, and methods of encouraging confidence and closeness will have been important for eons," she said. "It might be an concept that seems a bit contradictory to our incorrect assumptions of a rather ruthless and ancient history, but actually it ought to be expected that Neanderthals – and including Neanderthals and our own species together – kissed."