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From Galápagos albatrosses to polar bears, chimpanzees to great apes, various animals appear to kiss. Now, scientists suggest that Neanderthals did it too – and might even have locked lips with early Homo sapiens.

Shared Oral Clues

This isn't the initial instance scientists have suggested ancient relatives and early modern humans were closely connected. In previous studies, scientists have discovered modern people and their Neanderthal relatives shared the same mouth microbe for hundreds of thousands of years after the evolutionary divergence, suggesting they swapped saliva.

"Likely they were kissing," she said, explaining that the concept aligned with research that has found people of certain genetic backgrounds have bits of Neanderthal DNA in their genetic makeup, demonstrating interbreeding was at play.

Intimate Interpretation

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

Writing in the publication a scientific periodical, Brindle and her team detail how, to investigate the evolutionary origins of kissing, they first had to come up with a description that was not limited to how humans kiss.

Defining Intimate Contact

"Previously there were some efforts to define a intimate act, but it's largely human-centric, which implies that basically non-human species don't kiss. Currently we know that they probably do, it might just not look from what our intimate contact resembles," said the evolutionary biologist.

However, she noted some behaviors that resembled intimate contact were distinct activities – such as the processing and transfer of food, or "mouth contact", seen in fish called certain marine animals.

As a result the research group developed a definition of intimate contact based on friendly interactions involving intentional mouth-to-mouth contact with a member of the identical group, with some movement of the oral area but absence of food.

Research Methods

The lead researcher said they focused on reports of intimate behavior in non-human species from the African continent and Asia, including bonobos, chimpanzees and great apes, and employed digital recordings to verify the reports.

The researchers then integrated this information with information on the evolutionary relationships between living and extinct types of such animals.

Historical Origins

The team propose the results indicate kissing evolved approximately 21.5m and 16.9 million years ago in the ancestors of the large apes.

The position of ancient hominins on this family tree means it is likely they, too, indulged in a intimate act, the scientists conclude. But the behavior might not have been limited to their specific group.

"The fact that humans kiss, the fact that we currently have shown that ancient relatives probably engaged, indicates that the both groups are probably did kissed," the researcher added.

Evolutionary Significance

Although the evolutionary explanation is debated, Brindle explained kissing could be used in sexual contexts to potentially increase reproductive success or help choose between mates, while it could assist reinforce bonding when used in a platonic way.

Another expert in the behavior of primates commented that as kissing behavior was seen in a broad spectrum of primates it was logical its origins extend far into our ancient history, and an examination of various types of intimate behavior among a broader range of animals might extend its beginnings back even earlier still.

"Behaviors that we think of as signatures of our species, like intimate contact, are not unique to us if we look closely at other animals," he said.

Cultural Elements

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

"However, as people we succeed or struggle on the strength of our emotional bonds, and ways of promoting trust and intimacy will have been important for millions of years," the professor stated. "It might be an image that appears a bit incongruous to our misplaced ideas of a rather ruthless and ancient history, but actually it should be no surprise that ancient hominins – and even them and our own species together – kissed."