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From Galápagos albatrosses to Arctic mammals, primates to great apes, certain species engage in mouth-to-mouth contact. Currently, researchers propose that Neanderthals did it too – and possibly locked lips with modern humans.

Common Oral Evidence

It is not the first time scientists have proposed ancient relatives and Homo sapiens were closely connected. Among previous studies, researchers have found modern people and their thick-browed cousins possessed the identical oral bacteria for hundreds of thousands of years after the evolutionary divergence, implying they swapped saliva.

"Probably they were kissing," the researcher noted, explaining that the idea chimed with studies that has revealed people of certain genetic backgrounds contain Neanderthal DNA in their genome, demonstrating interbreeding was at play.

Romantic Spin

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

Publishing in the journal Evolution and Human Behavior, Brindle and her team report how, to explore the evolutionary origins of kissing, they first had to come up with a description that was not restricted by how people kiss.

Describing Intimate Contact

"Previously there were some efforts to define a intimate act, but it's largely focused on humans, which implies that basically non-human species don't kiss. Now we understand that they probably do, it may appear different from what human kissing looks like," said the evolutionary biologist.

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

As a result the research group developed a definition of intimate contact centered around friendly interactions involving intentional oral interaction with a individual of the same species, with some movement of the oral area but no transfer of food.

Research Approach

Brindle explained they focused on reports of kissing in primates from Africa and Asian regions, including primates, chimpanzees and great apes, and used online videos to confirm the observations.

Scientists then integrated this information with information on the evolutionary relationships between living and extinct species of such animals.

Historical Timeline

The team propose the results suggest intimate contact developed somewhere between 21.5 million and 16.9m years ago in the ancestors of the great primates.

The position of Neanderthals on this family tree means it is probable they, too, engaged in a intimate act, the scientists conclude. But the activity may not have been confined to their specific group.

"The fact that modern people kiss, the fact that we currently have demonstrated that ancient relatives very likely kissed, suggests that the both groups are also likely to have kissed," Brindle noted.

Evolutionary Importance

Although the evolutionary explanation is debated, Brindle said kissing could be employed in sexual contexts to possibly increase reproductive success or assist in selecting between partners, while it could assist strengthen connections when practiced in a non-sexual manner.

A separate researcher in the behavior of great apes commented that as intimate contact was observed in a wide range of primates it made sense its origins extend far into our ancient history, and an analysis of various types of kissing among a wider variety of animals might extend its origins back further still.

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

Social Elements

An archaeology expert explained that kissing had a cultural element as it was not universal to all societies.

"However, as humans we thrive or fail on the quality of our relationships, and methods of encouraging confidence and intimacy will have been important for eons," the professor stated. "It might be an image that seems a bit contradictory to our incorrect assumptions of a rather ruthless and ancient history, but really it should be expected that Neanderthals – and including them and our human ancestors collectively – engaged intimately."