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Among seabirds to polar bears, primates to orangutans, various animals appear to kiss. Currently, scientists propose that Neanderthals did it too – and might even have locked lips with early Homo sapiens.

Common Microbial Clues

This isn't the initial instance scientists have suggested Neanderthals and early modern humans were closely connected. In earlier research, researchers have found humans and their thick-browed cousins shared the same mouth microbe for millions of years after the evolutionary divergence, suggesting they exchanged oral fluids.

"Likely they were kissing," the researcher noted, explaining that the concept aligned with research that has revealed humans of non-African ancestry have bits of ancient genetic material in their genetic makeup, revealing genetic mixing was at play.

Intimate Spin

"This offers a different perspective on human-Neanderthal relations," the lead researcher said.

Publishing in the journal Evolution and Human Behavior, the researcher and her team detail how, to explore the evolutionary origins of intimate contact, they first had to come up with a definition that was not restricted by how people smooch.

Describing Intimate Contact

"There have been some previous attempts to describe a intimate act, but it's very much been human-centric, which implies that basically non-human species do not engage in this. Currently we understand that they likely engage, it might just not look from what our intimate contact looks like," said the evolutionary biologist.

Nonetheless, she noted some actions that resembled kissing were distinct activities – such as the processing and food sharing, or "mouth contact", seen in aquatic species known as French grunts.

As a result the team came up with a definition of intimate contact centered around social behaviors involving intentional mouth-to-mouth contact with a individual of the same species, with some motion of the oral area but no transfer of food.

Research Methods

Brindle explained they concentrated on reports of kissing in primates from Africa and Asian regions, including primates, chimpanzees and great apes, and employed online videos to verify the observations.

The researchers then integrated this data with details on the genetic connections between extant and ancient species of such animals.

Historical Timeline

Researchers propose the results suggest intimate contact evolved approximately 21.5m and 16.9m years ago in the predecessors of the large apes.

The position of Neanderthals on this family tree suggests it is probable they, too, engaged in a kiss, the researchers conclude. But the behavior might not have been limited to their own species.

"The fact that modern people kiss, the reality that we currently have shown that Neanderthals probably kissed, indicates that the both groups are probably did kissed," the researcher noted.

Evolutionary Importance

Although the evolutionary explanation is discussed, the expert said kissing could be employed in sexual contexts to potentially enhance mating outcomes or assist in selecting between mates, while it could assist reinforce bonding when used in a non-sexual manner.

A separate researcher in the activities of primates commented that as intimate contact was seen in a wide range of apes it made sense its roots extend far into our evolutionary past, and an analysis of different forms of kissing among a broader range of animals might push its beginnings back further still.

"Things that we think of as signatures of our species, like intimate contact, are not exclusive to us if we look closely at other animals," the expert noted.

Cultural Elements

An archaeology expert explained that intimate contact had a social component as it was not common to all human groups.

"Nonetheless, as people we succeed or struggle on the strength of our emotional bonds, and methods of promoting trust and intimacy will have been significant for millions of years," she said. "This could represent an concept that seems a bit incongruous to our misplaced ideas of a supposedly aggressive and aggressive past, but really it ought to be expected that Neanderthals – and including them and our own species collectively – engaged intimately."