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Among seabirds to Arctic mammals, chimpanzees to orangutans, various animals appear to kiss. Now, scientists suggest that Neanderthals did it too – and might even have locked lips with modern humans.

Shared Oral Clues

It is not the first time scientists have suggested Neanderthals and early modern humans were closely connected. In earlier research, researchers have found humans and their Neanderthal relatives possessed the same mouth microbe for hundreds of thousands of years after the evolutionary divergence, implying they exchanged oral fluids.

"Probably they were kissing," the researcher noted, explaining that the idea chimed with research that has found humans of non-African ancestry contain Neanderthal DNA in their genome, demonstrating genetic mixing was occurring.

Romantic Spin

"This offers a more romantic spin on human-Neanderthal relations," Brindle said.

Publishing in the journal a scientific periodical, the researcher and her team detail how, to explore the historical roots of kissing, they first had to come up with a description that was not restricted by how humans kiss.

Defining Kissing

"There have been some efforts to define a kiss, but it's largely human-centric, which implies that basically non-human species do not engage in this. Now we know that they likely engage, it may appear different from what our intimate contact resembles," explained the evolutionary biologist.

Nonetheless, she said some actions that looked like kissing were distinct activities – such as the processing and food sharing, or "kiss-fighting", seen in fish called certain marine animals.

As a result the research group came up with a description 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 food.

Study Approach

Brindle said they concentrated on accounts of kissing in primates from the African continent and Asian regions, including primates, chimpanzees and orangutans, and used online videos to verify the observations.

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

Historical Timeline

Researchers propose the findings indicate kissing developed approximately 21.5 million and 16.9m years ago in the ancestors of the large apes.

The position of Neanderthals on this family tree means it is likely they, too, indulged in a kiss, the scientists say. But the behavior may not have been limited to their specific group.

"The fact that humans kiss, the reality that we now have demonstrated that Neanderthals very likely engaged, suggests that the both groups are probably did kissed," the researcher noted.

Evolutionary Significance

While the scientific reasoning is debated, the expert said kissing could be used in reproductive situations 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 broad spectrum of primates it was logical its origins lie deep in our evolutionary past, and an analysis of various types of kissing among a broader range of species might extend its origins back even earlier still.

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

Social Elements

Another professor explained that intimate contact had a social component as it was not common to all societies.

"Nonetheless, as humans we succeed or struggle on the quality of our relationships, and methods of encouraging confidence and intimacy will have been significant for eons," she said. "It might be an image that seems a bit contradictory to our misplaced ideas of a supposedly aggressive and ancient history, but actually it ought to be expected that ancient hominins – and including Neanderthals and our own species collectively – engaged intimately."