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Among Galápagos albatrosses to Arctic mammals, chimpanzees to great apes, certain species appear to kiss. Currently, scientists suggest that ancient hominins did it too – and possibly locked lips with early Homo sapiens.

Shared Oral Clues

This isn't the initial instance scientists have proposed Neanderthals and Homo sapiens were intimately acquainted. In earlier research, scientists have found modern people and their Neanderthal relatives shared the identical oral bacteria for millions of years after the evolutionary divergence, implying they exchanged oral fluids.

"Probably they were engaging in intimate contact," the researcher noted, explaining that the idea aligned with research that has revealed humans of certain genetic backgrounds have bits of Neanderthal DNA in their genetic makeup, demonstrating interbreeding was at play.

Romantic Interpretation

"This offers a different perspective on ancient interactions," the lead researcher commented.

Publishing in the journal a scientific periodical, Brindle and her team detail how, to investigate the historical roots of intimate contact, they first had to develop a description that was not restricted by how humans smooch.

Describing Kissing

"Previously there were some efforts to define a intimate act, but it's very much been human-centric, which means that basically non-human species don't kiss. Now we understand that they likely engage, it might just not look from what human kissing resembles," explained the evolutionary biologist.

Nonetheless, she noted some actions that resembled kissing were something rather different – such as the chewing and food sharing, or "kiss-fighting", observed in aquatic species called certain marine animals.

As a result the team developed a definition of kissing based on social behaviors involving intentional mouth-to-mouth contact with a individual of the identical group, with some movement of the mouth but no transfer of food.

Research Approach

Brindle explained they concentrated on accounts of kissing in non-human species from Africa and Asia, including primates, chimpanzees and orangutans, and used online videos to verify the observations.

Scientists then combined this information with information on the genetic connections between living and ancient types of such animals.

Evolutionary Timeline

Researchers propose the findings indicate kissing evolved approximately 21.5 million and 16.9 million years ago in the ancestors of the large apes.

Placement of ancient hominins on this evolutionary lineage suggests it is likely they, too, engaged in a kiss, the researchers say. But the behavior might not have been limited to their own species.

"Reality that modern people engage intimately, the reality that we currently have shown that Neanderthals very likely kissed, suggests that the both groups are also likely to have kissed," Brindle added.

Biological Significance

Although the scientific reasoning is discussed, the expert said intimate contact could be used in sexual contexts to possibly enhance reproductive success or help choose between mates, while it could assist strengthen connections when practiced in a platonic way.

A separate researcher in the behavior of great apes commented that as intimate contact was seen in a wide range of apes it was logical its origins extend far into our ancient history, and an analysis of various types of kissing among a wider variety of species might extend its origins back even earlier still.

"Behaviors that we consider as characteristics of our species, like kissing, are not exclusive to us if we examine carefully at different species," the expert noted.

Cultural Aspects

An archaeology expert said that kissing had a cultural element as it was not universal to all human groups.

"However, as humans we thrive or fail on the strength of our emotional bonds, and ways of encouraging trust and intimacy will have been important for millions of years," the professor stated. "It might be an concept that appears a bit contradictory to our misplaced ideas of a rather ruthless and ancient history, but really it ought to be no surprise that ancient hominins – and even Neanderthals and our own species collectively – kissed."