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Among Galápagos albatrosses to polar bears, primates to great apes, various animals engage in mouth-to-mouth contact. Now, researchers suggest that Neanderthals also engaged in this behavior – and might even have exchanged kisses with early Homo sapiens.

Common Oral Clues

This isn't the initial instance experts have proposed ancient relatives and Homo sapiens were closely connected. Among earlier research, researchers have discovered humans and their thick-browed cousins possessed the same mouth microbe for hundreds of thousands of years after the evolutionary divergence, implying they swapped saliva.

"Probably they were kissing," the researcher noted, adding that the concept aligned with studies that has revealed humans of certain genetic backgrounds have bits of ancient genetic material in their genome, demonstrating interbreeding was occurring.

Romantic Interpretation

"This offers a different perspective on human-Neanderthal relations," the lead researcher commented.

Writing in the journal a scientific periodical, the researcher and her team detail how, to explore the evolutionary origins of intimate contact, they first had to come up with a description that was not restricted by how humans kiss.

Describing Intimate Contact

"Previously there were some previous attempts to describe a kiss, but it's largely focused on humans, which implies that basically other animals do not engage in this. Now we know that they likely engage, it may appear different from what human kissing resembles," said the evolutionary biologist.

However, she noted some actions that resembled kissing were something rather different – such as the chewing and transfer of food, or "mouth contact", observed in aquatic species known as French grunts.

As a result the research group developed a definition of kissing centered around social behaviors involving intentional oral interaction with a individual of the identical group, with some movement of the mouth but absence of nutrition.

Research Approach

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

The researchers then integrated this data with information on the evolutionary relationships between extant and extinct types of such animals.

Historical Timeline

The team propose the findings indicate intimate contact developed approximately 21.5 million and 16.9 million years ago in the ancestors of the great primates.

Placement of Neanderthals on this family tree suggests it is likely they, too, indulged in a intimate act, the researchers say. But the activity may not have been limited to their own species.

"The fact that modern people kiss, the fact that we now have shown that ancient relatives very likely engaged, suggests that the two [species] are also likely to have kissed," Brindle noted.

Biological Importance

Although the scientific reasoning is debated, the expert explained intimate contact could be employed in sexual contexts to possibly enhance reproductive success or assist in selecting between mates, while it might help strengthen connections when practiced in a non-sexual manner.

Another expert in the behavior of great apes said that as kissing behavior was observed in a broad spectrum of primates it made sense 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.

"Behaviors that we think of as signatures of our species, like kissing, are not unique to us if we look closely at other animals," the expert noted.

Cultural Aspects

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

"Nonetheless, as people we succeed or struggle on the strength of our emotional bonds, and ways of encouraging trust and closeness will have been important for eons," she said. "This could represent an concept that seems a bit incongruous to our misplaced ideas of a rather ruthless and aggressive past, but really it ought to be no surprise that Neanderthals – and even Neanderthals and our human ancestors together – engaged intimately."