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From Galápagos albatrosses to Arctic mammals, chimpanzees to great apes, various animals engage in mouth-to-mouth contact. Now, scientists propose that Neanderthals did it too – and possibly locked lips with early Homo sapiens.

Common Microbial Clues

This isn't the initial instance scientists have suggested Neanderthals and Homo sapiens were intimately acquainted. Among previous studies, researchers have discovered modern people and their thick-browed cousins shared the same mouth microbe 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 studies that has found humans of non-African ancestry contain ancient genetic material in their genetic makeup, revealing interbreeding was occurring.

Romantic Interpretation

"This offers a more romantic perspective on ancient interactions," Brindle said.

Publishing in the publication Evolution and Human Behavior, Brindle and her team detail how, to explore the historical roots of kissing, they first had to develop a description that was not limited to how humans smooch.

Defining Kissing

"There have been some efforts to define a intimate act, but it's largely focused on humans, which means that basically other animals do not engage in this. Currently we understand that they probably do, it may appear different from what our intimate contact resembles," said the evolutionary biologist.

However, she noted some actions that resembled intimate contact were distinct activities – such as the chewing and transfer of food, or "kiss-fighting", seen in fish known as certain marine animals.

As a result the team developed a description of kissing based on social behaviors involving directed mouth-to-mouth contact with a individual of the same species, with some motion of the mouth but no transfer of nutrition.

Study Approach

Brindle said they focused on accounts of intimate behavior in primates from Africa and Asia, including primates, apes and orangutans, and used online videos to confirm the observations.

The researchers then combined this information with information on the evolutionary relationships between living and extinct species of such primates.

Evolutionary Origins

The team propose the findings suggest intimate contact developed somewhere between 21.5 million and 16.9m years ago in the ancestors of the large apes.

The position of ancient hominins on this family tree suggests it is probable they, too, engaged in a kiss, the scientists conclude. But the activity might not have been confined to their own species.

"The fact that modern people engage intimately, the fact that we currently have demonstrated that Neanderthals very likely engaged, suggests that the both groups are probably did kissed," the researcher added.

Biological Significance

While the evolutionary explanation is discussed, the expert said kissing could be employed in reproductive situations to possibly increase reproductive success or assist in selecting between mates, while it might help reinforce bonding when used in a non-sexual manner.

A separate researcher in the behavior of great apes commented that as intimate contact was observed in a broad spectrum of primates it was logical its origins lie deep in our ancient history, and an analysis of various types of intimate behavior among a broader range of species might extend its beginnings back further still.

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

Social Elements

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

"Nonetheless, as humans we thrive or fail on the strength of our relationships, and methods of promoting confidence and closeness will have been important for millions of years," she said. "It might be an image that seems a bit incongruous to our incorrect assumptions of a supposedly aggressive and aggressive past, but actually it should be no surprise that Neanderthals – and even them and our own species collectively – engaged intimately."