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Among Galápagos albatrosses to polar bears, chimpanzees to great apes, certain species appear to kiss. Now, researchers suggest that Neanderthals did it too – and possibly locked lips with modern humans.

Common Oral Clues

This isn't the initial instance experts have suggested ancient relatives and Homo sapiens were closely connected. In previous studies, researchers have found modern people and their thick-browed cousins shared the same mouth microbe for millions of years after the two species split, implying they exchanged oral fluids.

"Probably they were kissing," the researcher noted, explaining that the idea aligned with research that has revealed people of non-African ancestry contain ancient genetic material in their genetic makeup, demonstrating genetic mixing was at play.

Romantic Interpretation

"It certainly puts a different perspective on ancient interactions," the lead researcher commented.

Writing in the journal Evolution and Human Behavior, the researcher and colleagues detail how, to investigate the evolutionary origins of kissing, they first had to come up with a definition that was not limited to how humans kiss.

Describing Intimate Contact

"Previously there were some efforts to define a kiss, but it's largely human-centric, which means that essentially other animals don't kiss. Currently we know that they likely engage, it may appear different from what our intimate contact looks like," said Brindle.

However, she noted some actions that resembled kissing were distinct activities – such as the chewing and transfer of food, or "mouth contact", observed in fish called certain marine animals.

As a result the research group came up with a definition of kissing based on friendly interactions involving intentional mouth-to-mouth contact with a member of the same species, with some movement of the mouth but no transfer of nutrition.

Research Approach

Brindle said they concentrated on accounts of intimate behavior in primates from Africa and Asian regions, including primates, apes and great apes, and used online videos to verify the observations.

Scientists then combined this data with details on the genetic connections between extant and ancient types of such primates.

Evolutionary Timeline

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

Placement of ancient hominins on this family tree suggests it is probable they, too, engaged in a kiss, the researchers conclude. But the activity may not have been confined to their own species.

"The fact that humans engage intimately, the reality that we now have shown that Neanderthals probably kissed, indicates that the two [species] are also likely to have kissed," the researcher noted.

Biological Importance

While the evolutionary explanation is discussed, Brindle said intimate contact could be employed in sexual contexts to possibly increase reproductive success or help choose between mates, while it could assist strengthen connections when practiced in a non-sexual manner.

A separate researcher in the behavior of primates commented that as intimate contact was seen in a wide range of apes it was logical its origins lie deep in our evolutionary past, and an examination of various types of kissing among a broader range of animals might push its origins back even earlier still.

"Things that we think of as characteristics of human life, like intimate contact, are not unique to us if we look closely at other animals," the expert noted.

Social Aspects

An archaeology expert explained that kissing had a social component as it was not common to all societies.

"However, as humans we thrive or fail on the strength of our emotional bonds, and methods of promoting confidence and intimacy will have been important for eons," the professor stated. "It might be an image that seems a bit contradictory to our misplaced ideas of a rather ruthless and aggressive past, but actually it ought to be no surprise that ancient hominins – and including them and our own species collectively – engaged intimately."