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Among seabirds to Arctic mammals, primates to orangutans, certain species appear to kiss. Now, scientists suggest that Neanderthals did it too – and possibly locked lips with early Homo sapiens.

Common Microbial Clues

It is not the first time experts have suggested ancient relatives and early modern humans were closely connected. In previous studies, researchers have found modern people and their Neanderthal relatives shared the same mouth microbe for hundreds of thousands of years after the two species split, implying they exchanged oral fluids.

"Likely they were engaging in intimate contact," she said, explaining that the idea chimed with studies that has found people of certain genetic backgrounds have bits of ancient genetic material in their genome, demonstrating interbreeding was occurring.

Intimate Spin

"This offers a more romantic spin on ancient interactions," the lead researcher said.

Publishing in the journal a scientific periodical, Brindle and her team report how, to explore the evolutionary origins of kissing, they first had to come up with a description that was not limited to how people kiss.

Describing Intimate Contact

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

However, she said some actions that resembled intimate contact were something rather different – such as the processing and transfer of food, or "mouth contact", seen in fish known as French grunts.

As a result the team came up with a description of kissing based on friendly interactions involving directed mouth-to-mouth contact with a member of the identical group, with some movement of the mouth but no transfer of food.

Research Methods

The lead researcher explained they concentrated on accounts of intimate behavior in non-human species from the African continent and Asian regions, including primates, chimpanzees and orangutans, and employed digital recordings to confirm the observations.

Scientists then integrated this data with information on the genetic connections between extant and ancient types of such animals.

Evolutionary Origins

Researchers say the findings indicate intimate contact developed somewhere between 21.5 million and 16.9 million years ago in the predecessors of the great primates.

The position of Neanderthals on this evolutionary lineage suggests it is probable they, too, indulged in a intimate act, the researchers say. But the behavior might not have been confined to their specific group.

"Reality that humans engage intimately, the fact that we now have demonstrated that ancient relatives very likely kissed, indicates that the both groups are also likely to have kissed," the researcher noted.

Biological Importance

Although the evolutionary explanation is debated, Brindle said kissing could be used in reproductive situations to possibly increase reproductive success or help choose between partners, while it could assist strengthen connections when practiced in a non-sexual manner.

A separate researcher in the behavior of primates said that as kissing behavior was seen in a wide range of apes it made sense its origins lie deep in our ancient history, and an analysis of various types of intimate behavior among a wider variety of species might extend its origins back even earlier still.

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

Cultural Elements

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

"Nonetheless, as humans we succeed or struggle on the quality of our relationships, and methods of encouraging confidence and closeness will have been important for eons," the professor stated. "This could represent an concept that seems a bit incongruous to our misplaced ideas of a supposedly aggressive and aggressive past, but actually it ought to be expected that ancient hominins – and including them and our own species collectively – kissed."