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From seabirds to Arctic mammals, chimpanzees to orangutans, various animals appear to kiss. Currently, researchers suggest that Neanderthals also engaged in this behavior – and possibly locked lips with modern humans.

Common Microbial Clues

It is not the first time scientists have suggested Neanderthals and early modern humans were closely connected. Among earlier research, scientists have discovered humans and their thick-browed cousins possessed the same mouth microbe for hundreds of thousands of years after the evolutionary divergence, suggesting they swapped saliva.

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

Intimate Spin

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

Publishing in the publication a scientific periodical, the researcher and colleagues report how, to investigate the historical roots of intimate contact, they first had to develop a description that was not limited to how humans smooch.

Describing Intimate Contact

"There have been some previous attempts to describe a kiss, but it's very much been human-centric, which implies that basically other animals do not engage in this. Currently we know that they probably do, it might just not look from what our intimate contact resembles," explained Brindle.

However, she said some behaviors that resembled intimate contact were distinct activities – such as the chewing and transfer of food, or "mouth contact", seen in aquatic species known as French grunts.

Consequently the research group came up with a definition of kissing based on social behaviors involving intentional oral interaction with a individual of the identical group, with some movement of the mouth but no transfer of nutrition.

Study Methods

Brindle explained they concentrated on accounts of intimate behavior in primates from the African continent and Asia, including primates, chimpanzees and orangutans, and employed digital recordings to confirm the reports.

Scientists then integrated this data with information on the genetic connections between living and ancient types 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.

Placement of ancient hominins on this family tree means it is probable they, too, engaged in a kiss, the scientists say. But the behavior might not have been limited to their own species.

"The fact that modern people engage intimately, the fact that we now have demonstrated that Neanderthals probably kissed, indicates that the both groups are probably did engage," Brindle added.

Evolutionary Significance

While the evolutionary explanation is discussed, the expert explained intimate contact could be employed in reproductive situations to potentially increase mating outcomes or assist in selecting between mates, while it might help strengthen connections when used in a platonic way.

A separate researcher in the activities of great apes said that as kissing behavior was seen in a wide range of primates it was logical its roots extend far into our evolutionary past, and an examination of different forms of kissing among a wider variety of animals might push its origins back even earlier still.

"Things that we consider as characteristics of our species, like kissing, are not exclusive to us if we look closely at other animals," he said.

Social Aspects

Another professor said that kissing had a cultural element as it was not universal to all societies.

"However, as humans we thrive or fail on the strength of our emotional bonds, and methods of promoting confidence and intimacy will have been significant for eons," the professor stated. "It might be an concept that seems a bit contradictory to our misplaced ideas of a supposedly aggressive and ancient history, but actually it should be no surprise that Neanderthals – and even Neanderthals and our own species collectively – engaged intimately."