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Among Galápagos albatrosses to polar bears, chimpanzees to orangutans, certain species appear to kiss. Currently, scientists suggest that Neanderthals did it too – and might even have exchanged kisses with early Homo sapiens.

Common Microbial Clues

This isn't the initial instance scientists have proposed Neanderthals and Homo sapiens were closely connected. In earlier research, researchers have found humans and their Neanderthal relatives possessed the identical oral bacteria for hundreds of thousands of years after the evolutionary divergence, suggesting they exchanged oral fluids.

"Likely they were kissing," the researcher noted, adding that the concept chimed with research that has revealed people of certain genetic backgrounds have bits of ancient genetic material in their genetic makeup, demonstrating interbreeding was occurring.

Romantic Interpretation

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

Writing in the publication a scientific periodical, Brindle and colleagues report how, to investigate the evolutionary origins of intimate contact, they first had to come up with a definition that was not restricted by how humans smooch.

Describing Intimate Contact

"Previously there were some previous attempts to define a kiss, but it's largely focused on humans, which implies that essentially other animals do not engage in this. Currently we understand that they probably do, it might just not look from what our intimate contact looks like," said Brindle.

However, she noted some behaviors that looked like kissing were something rather different – such as the chewing and transfer of food, or "kiss-fighting", observed in fish called French grunts.

As a result the team developed a description of kissing centered around social behaviors involving intentional mouth-to-mouth contact with a individual of the same species, with some movement of the mouth but no transfer of food.

Study Approach

The lead researcher explained they concentrated on accounts of kissing in non-human species from the African continent and Asia, including bonobos, apes and orangutans, and used online videos to confirm the reports.

Scientists then integrated this data with information on the evolutionary relationships between living and ancient types of such animals.

Evolutionary Origins

Researchers propose the results indicate intimate contact evolved somewhere between 21.5 million and 16.9 million years ago in the ancestors of the large apes.

Placement of Neanderthals on this evolutionary lineage means it is probable they, too, engaged in a kiss, the scientists conclude. But the behavior might not have been limited to their own species.

"Reality that modern people kiss, the fact that we now have demonstrated that Neanderthals probably engaged, indicates that the two [species] are also likely to have engage," the researcher noted.

Biological Significance

Although the scientific reasoning is discussed, the expert explained intimate contact could be used in sexual contexts to potentially increase reproductive success or assist in selecting between partners, while it might help reinforce bonding when practiced in a platonic way.

A separate researcher in the activities of primates commented that as kissing behavior was seen in a wide range of apes it was logical its roots extend far into 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 consider as characteristics of human life, like kissing, are not unique to us if we examine carefully at different species," he said.

Social Elements

Another professor said that kissing had a social component as it was not universal to all human groups.

"Nonetheless, as people we thrive or fail on the strength of our emotional bonds, and ways of encouraging confidence and closeness will have been significant for eons," the professor stated. "It might be an concept that appears a bit incongruous to our incorrect assumptions of a supposedly aggressive and ancient history, but actually it ought to be expected that ancient hominins – and even Neanderthals and our human ancestors collectively – engaged intimately."