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

Shared Oral Clues

It is not the first time experts have proposed ancient relatives and Homo sapiens were closely connected. Among earlier research, researchers have discovered modern people and their thick-browed cousins shared the identical oral bacteria for hundreds of thousands of years after the evolutionary divergence, suggesting they swapped saliva.

"Likely they were engaging in intimate contact," she said, explaining that the concept aligned with research that has found humans of certain genetic backgrounds have bits of ancient genetic material in their genetic makeup, revealing genetic mixing was at play.

Intimate Interpretation

"This offers a more romantic spin on human-Neanderthal relations," the lead researcher commented.

Publishing in the journal a scientific periodical, the researcher and colleagues detail how, to investigate the evolutionary origins of intimate contact, they first had to come up with a definition that was not limited to how people smooch.

Describing Kissing

"Previously there were some previous attempts to define a kiss, but it's very much been focused on humans, which means that basically other animals don't kiss. Currently we understand that they probably do, it might just not look from what human kissing looks like," explained the evolutionary biologist.

However, she noted some actions that looked like intimate contact were something rather different – such as the chewing and food sharing, or "kiss-fighting", observed in fish known as certain marine animals.

Consequently the research group came up with a definition of intimate contact based on friendly interactions involving intentional oral interaction with a member of the identical group, with some movement of the mouth but absence of nutrition.

Research Methods

The lead researcher explained they focused on accounts of kissing in primates from Africa and Asian regions, including bonobos, chimpanzees and orangutans, and employed online videos to verify the observations.

The researchers then integrated this information with information on the genetic connections between living and ancient species of such primates.

Historical Timeline

Researchers propose the findings indicate kissing developed somewhere between 21.5m and 16.9m years ago in the predecessors of the large apes.

The position of Neanderthals on this family tree means it is probable they, too, engaged in a kiss, the researchers conclude. But the behavior might not have been confined to their specific group.

"Reality that humans kiss, the fact that we currently have shown that ancient relatives probably kissed, suggests that the both groups are also likely to have engage," the researcher noted.

Evolutionary Importance

While the evolutionary explanation is discussed, Brindle said intimate contact could be used in sexual contexts to possibly increase reproductive success or help choose between partners, while it might help reinforce bonding when practiced in a non-sexual manner.

A separate researcher in the activities of primates commented that as kissing behavior was seen in a wide range of apes it made sense its origins extend far into our ancient history, and an examination of different forms of kissing among a broader range of species might extend its beginnings back further still.

"Behaviors that we think of as characteristics of human life, like kissing, are not exclusive to us if we examine carefully at other animals," the expert noted.

Cultural Elements

Another professor explained that intimate contact had a cultural element as it was not common to all societies.

"However, as humans we succeed or struggle on the strength of our relationships, and ways of promoting confidence and closeness will have been significant for eons," the professor stated. "It might be an concept that seems a bit contradictory to our incorrect assumptions of a supposedly aggressive and aggressive past, but actually it ought to be expected that Neanderthals – and even them and our own species together – kissed."