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From Galápagos albatrosses to Arctic mammals, chimpanzees to orangutans, various animals engage in mouth-to-mouth contact. Currently, researchers suggest that Neanderthals did it too – and might even have exchanged kisses with modern humans.

Common Oral Clues

It is not the first time scientists have proposed ancient relatives and early modern humans were closely connected. Among earlier research, scientists have discovered humans 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," the researcher noted, explaining that the idea chimed with research that has found humans of non-African ancestry have bits of Neanderthal DNA in their genome, demonstrating interbreeding was at play.

Intimate Spin

"It certainly puts a more romantic spin on human-Neanderthal relations," the lead researcher commented.

Writing in the journal Evolution and Human Behavior, the researcher and colleagues report how, to investigate the evolutionary origins of kissing, they first had to develop a description that was not limited to how humans kiss.

Describing Kissing

"Previously there were some previous attempts to define a kiss, but it's largely human-centric, which means that essentially non-human species don't kiss. Currently we understand that they probably do, it may appear different from what human kissing looks like," said Brindle.

Nonetheless, she said some actions that looked like kissing were something rather different – such as the chewing and transfer of food, or "mouth contact", observed in fish known as French grunts.

Consequently the research group came up with a definition of intimate contact centered around social behaviors involving directed mouth-to-mouth contact with a member of the identical group, with some movement of the mouth but absence of food.

Study Approach

Brindle said they concentrated on reports of kissing in non-human species from the African continent and Asia, including primates, apes and great apes, and employed digital recordings to verify the observations.

Scientists then integrated this data with information on the evolutionary relationships between extant and extinct species of such primates.

Evolutionary Origins

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

Placement of Neanderthals on this family tree means it is probable they, too, indulged in a intimate act, the researchers say. But the behavior might not have been limited to their specific group.

"Reality that humans kiss, the reality that we currently have demonstrated that ancient relatives probably engaged, suggests that the two [species] are probably did kissed," the researcher noted.

Evolutionary Importance

Although the evolutionary explanation is discussed, Brindle explained kissing could be employed in reproductive situations to possibly enhance mating outcomes or help choose between mates, while it could assist strengthen connections when practiced in a non-sexual manner.

Another expert in the activities of great apes said that as kissing behavior was observed in a wide range of apes it was logical its roots lie deep in our evolutionary past, and an analysis of different forms of kissing among a broader range of species might extend its beginnings back even earlier still.

"Behaviors that we think of as characteristics of our species, like intimate contact, are not exclusive to us if we examine carefully at different species," the expert noted.

Cultural Elements

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

"However, as people we succeed or struggle on the strength of our relationships, and methods of encouraging confidence and closeness will have been important for eons," she said. "This could represent an image that appears a bit incongruous to our incorrect assumptions of a supposedly aggressive and ancient history, but actually it ought to be expected that Neanderthals – and including Neanderthals and our human ancestors collectively – kissed."