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Among Galápagos albatrosses to Arctic mammals, chimpanzees to orangutans, various animals appear to kiss. Now, researchers propose that ancient hominins did it too – and might even have exchanged kisses with early Homo sapiens.

Common Oral Evidence

This isn't the initial instance scientists have suggested Neanderthals and Homo sapiens were intimately acquainted. Among earlier research, scientists have found humans and their thick-browed cousins shared the same mouth microbe for hundreds of thousands of years after the two species split, suggesting they exchanged oral fluids.

"Likely they were kissing," the researcher noted, explaining that the idea aligned with research that has revealed people of certain genetic backgrounds have bits of Neanderthal DNA in their genetic makeup, demonstrating interbreeding was occurring.

Intimate Interpretation

"It certainly puts a different spin on human-Neanderthal relations," the lead researcher said.

Writing in the journal Evolution and Human Behavior, the researcher and her team report how, to explore the evolutionary origins of kissing, they first had to develop a description that was not restricted by how humans smooch.

Defining Kissing

"Previously there were some previous attempts to define a kiss, but it's very much been human-centric, which implies that essentially non-human species do not engage in this. Currently we know that they probably do, it might just not look from what our intimate contact looks like," explained the evolutionary biologist.

Nonetheless, she said some behaviors that looked like intimate contact were distinct activities – such as the processing and transfer of food, or "kiss-fighting", seen in aquatic species known as certain marine animals.

As a result the team came up with a definition of kissing based on social behaviors involving intentional mouth-to-mouth contact with a individual of the same species, with some motion of the mouth but absence of nutrition.

Study Methods

Brindle explained they focused on accounts of kissing in non-human species from Africa and Asia, including primates, apes and great apes, and employed online videos to verify the observations.

Scientists then combined this data with information on the genetic connections between living and ancient species of such primates.

Evolutionary Origins

Researchers say the findings suggest intimate contact developed approximately 21.5 million and 16.9 million years ago in the predecessors of the large apes.

Placement of Neanderthals on this family tree means it is probable they, too, indulged in a intimate act, the scientists conclude. But the activity may not have been limited to their own species.

"Reality that humans kiss, the fact that we now have demonstrated that ancient relatives probably kissed, indicates that the two [species] are also likely to have engage," the researcher noted.

Biological Importance

Although the scientific reasoning is discussed, the expert explained kissing could be used in sexual contexts to possibly increase mating outcomes or help choose between mates, while it could assist strengthen connections when used in a non-sexual manner.

Another expert in the activities of great apes said that as intimate contact was observed in a broad spectrum of primates it made sense its origins extend far into our evolutionary past, and an examination of different forms of kissing among a wider variety of species might push its beginnings back even earlier still.

"Things that we consider as signatures of our species, like kissing, are not unique to us if we examine carefully at other animals," the expert noted.

Cultural Elements

Another professor explained that kissing had a social component as it was not common to all societies.

"Nonetheless, as people we succeed or struggle on the quality of our emotional bonds, and methods of encouraging confidence and intimacy will have been significant for eons," the professor stated. "This could represent an image that appears a bit incongruous to our incorrect assumptions of a rather ruthless and ancient history, but actually it ought to be expected that Neanderthals – and even Neanderthals and our own species together – kissed."