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Among Galápagos albatrosses to polar bears, primates to great apes, certain species engage in mouth-to-mouth contact. Now, researchers suggest that Neanderthals did it too – and might even have exchanged kisses with modern humans.

Shared Microbial Evidence

This isn't the initial instance scientists have proposed Neanderthals and early modern humans were closely connected. In earlier research, scientists have discovered modern people and their Neanderthal relatives possessed the identical oral bacteria for millions of years after the two species split, implying they swapped saliva.

"Probably they were kissing," she said, adding that the concept aligned with research that has found humans of non-African ancestry contain ancient genetic material in their genome, revealing genetic mixing was at play.

Romantic Interpretation

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

Publishing in the journal Evolution and Human Behavior, the researcher and colleagues detail how, to investigate the historical roots of kissing, they first had to come up with a definition that was not restricted by how people kiss.

Describing Kissing

"Previously there were some efforts to define a kiss, but it's very much been focused on humans, which implies that basically non-human species don't kiss. Now we know that they likely engage, it might just not look from what our intimate contact looks like," explained Brindle.

However, she said some behaviors that resembled kissing were something rather different – such as the chewing and transfer of food, or "kiss-fighting", seen in fish called French grunts.

Consequently the research group came up with a definition of intimate contact based on friendly interactions involving directed oral interaction with a individual of the identical group, with some movement of the oral area but absence of food.

Study Methods

The lead researcher said they focused on accounts of kissing in primates from the African continent and Asia, including primates, chimpanzees and orangutans, and used online videos to confirm the observations.

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

Evolutionary Timeline

The team propose the findings indicate intimate contact evolved somewhere between 21.5m and 16.9 million years ago in the predecessors of the great primates.

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

"The fact that humans engage intimately, the fact that we now have demonstrated that ancient relatives very likely kissed, suggests that the both groups are probably did kissed," the researcher noted.

Evolutionary Importance

While the evolutionary explanation is discussed, Brindle said intimate contact could be employed in reproductive situations to possibly increase mating outcomes or help choose between partners, while it might help strengthen connections when practiced in a non-sexual manner.

A separate researcher in the activities of primates commented that as kissing behavior was observed in a wide range of primates it was logical its roots extend far into our evolutionary past, and an analysis of different forms of kissing among a broader range of species might push its origins back further still.

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

Social Aspects

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

"However, as humans we succeed or struggle on the quality of our relationships, and methods of promoting trust and intimacy will have been significant for eons," the professor stated. "It might be an image that seems a bit contradictory to our misplaced ideas of a supposedly aggressive and ancient history, but actually it ought to be no surprise that ancient hominins – and even Neanderthals and our human ancestors together – kissed."