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From seabirds to polar bears, chimpanzees to orangutans, 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 Microbial Evidence

It is not the first time experts have proposed Neanderthals and Homo sapiens were closely connected. In earlier research, researchers have discovered humans and their thick-browed cousins possessed the same mouth microbe for millions of years after the two species split, implying they exchanged oral fluids.

"Likely they were kissing," the researcher noted, adding that the concept chimed with studies that has revealed people of certain genetic backgrounds contain Neanderthal DNA in their genome, demonstrating genetic mixing was occurring.

Romantic Interpretation

"This offers a different perspective on human-Neanderthal relations," Brindle said.

Publishing in the journal a scientific periodical, the researcher and her team report how, to explore the historical roots of kissing, they first had to come up with a description that was not limited to how people smooch.

Describing Kissing

"Previously there were some efforts to describe a intimate act, but it's largely human-centric, which means that essentially other animals do not engage in this. Currently we know that they probably do, it might just not look from what human kissing resembles," explained Brindle.

Nonetheless, she noted some behaviors that resembled kissing were distinct activities – such as the chewing and transfer of food, or "kiss-fighting", observed in aquatic species known as French grunts.

Consequently the team developed a description of kissing based on friendly interactions involving directed mouth-to-mouth contact with a member of the same species, with some movement of the oral area but no transfer of nutrition.

Research Methods

Brindle explained they focused on reports of kissing in non-human species from Africa and Asia, including bonobos, apes and great apes, and used digital recordings to confirm the observations.

The researchers then integrated this data with information on the evolutionary relationships between living and ancient types of such primates.

Historical Timeline

The team propose the results suggest intimate contact evolved somewhere between 21.5m and 16.9m years ago in the predecessors of the large apes.

Placement of Neanderthals on this family tree suggests it is probable they, too, engaged in a kiss, the scientists conclude. But the behavior may not have been confined to their own species.

"The fact that modern people engage intimately, the fact that we now have demonstrated that ancient relatives probably engaged, indicates that the two [species] are probably did kissed," Brindle added.

Evolutionary Significance

Although the evolutionary explanation is debated, Brindle said kissing could be used in reproductive situations to possibly enhance reproductive success or help choose between mates, while it might help reinforce bonding when used in a platonic way.

A separate researcher in the activities of great apes commented that as intimate contact was seen in a wide range of apes it made sense its roots extend far into our ancient history, and an examination of various types of kissing among a wider variety of species might extend its origins back further still.

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

Cultural Aspects

An archaeology expert said that intimate contact had a cultural element as it was not universal to all societies.

"Nonetheless, as people we succeed or struggle on the strength of our emotional bonds, and methods of promoting confidence and closeness 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 supposedly aggressive and aggressive past, but really it ought to be no surprise that ancient hominins – and including them and our human ancestors collectively – kissed."