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Among Galápagos albatrosses to Arctic mammals, primates to orangutans, certain species 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 Evidence

This isn't the initial instance experts have proposed ancient relatives and Homo sapiens were intimately acquainted. Among earlier research, researchers have discovered modern people and their thick-browed cousins shared the identical oral bacteria for millions of years after the evolutionary divergence, implying they exchanged oral fluids.

"Probably they were kissing," she said, explaining that the idea aligned with studies that has found humans of non-African ancestry have bits of Neanderthal DNA in their genome, revealing genetic mixing was occurring.

Romantic Spin

"This offers a more romantic spin on ancient interactions," 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 come up with a definition that was not restricted by how humans kiss.

Describing Intimate Contact

"There have been some efforts to define a intimate act, but it's largely human-centric, which means that essentially other animals don't kiss. Now we understand that they likely engage, it might just not look from what our intimate contact looks like," explained Brindle.

However, she noted some behaviors that resembled kissing were distinct activities – such as the chewing and food sharing, or "kiss-fighting", seen in aquatic species called French grunts.

As a result the research group developed a definition of kissing based on friendly interactions involving intentional oral interaction with a member of the identical group, with some movement of the oral area but no transfer of nutrition.

Study Approach

The lead researcher said they concentrated on accounts of kissing in primates from the African continent and Asia, including bonobos, apes and orangutans, and used online videos to verify the observations.

The researchers then integrated this information with details on the genetic connections between living and extinct types of such primates.

Evolutionary Timeline

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

The position of ancient hominins on this evolutionary lineage means it is probable they, too, engaged in a kiss, the researchers conclude. But the activity might not have been confined to their specific group.

"The fact that humans kiss, the fact that we currently have demonstrated that ancient relatives probably engaged, indicates that the two [species] are also likely to have engage," Brindle added.

Evolutionary Significance

Although the evolutionary explanation is discussed, the expert said kissing could be used in reproductive situations to potentially increase mating outcomes or assist in selecting between partners, while it might help reinforce bonding when practiced in a non-sexual manner.

Another expert in the activities of primates said that as kissing behavior was observed in a broad spectrum of primates it was logical its roots extend far into our evolutionary past, and an analysis of different forms of intimate behavior among a broader range of species might extend its beginnings back further still.

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

Cultural Aspects

Another professor explained that kissing had a cultural element as it was not universal to all human groups.

"Nonetheless, as people we succeed or struggle on the strength of our relationships, and methods of encouraging confidence and intimacy will have been important for eons," the professor stated. "It might be an concept that appears a bit contradictory to our misplaced ideas of a rather ruthless and ancient history, but really it ought to be no surprise that Neanderthals – and including them and our own species collectively – engaged intimately."