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Among seabirds to polar bears, primates to orangutans, various animals appear to kiss. Now, researchers suggest that ancient hominins did it too – and possibly locked lips with early Homo sapiens.

Shared Oral Evidence

This isn't the initial instance experts have suggested Neanderthals and early modern humans were closely connected. Among previous studies, scientists have found humans 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," the researcher noted, explaining that the idea chimed with studies that has revealed humans of certain genetic backgrounds have bits of Neanderthal DNA in their genome, revealing interbreeding was occurring.

Romantic Interpretation

"It certainly puts a different spin on human-Neanderthal relations," Brindle commented.

Publishing in the publication Evolution and Human Behavior, the researcher and her team detail how, to explore the historical roots of kissing, they first had to develop a definition that was not restricted by how humans smooch.

Describing Intimate Contact

"There have been some efforts to define a kiss, but it's very much been human-centric, which means that basically other animals do not engage in this. Currently we understand that they likely engage, it might just not look from what our intimate contact looks like," explained the evolutionary biologist.

However, she noted some actions that resembled intimate contact were distinct activities – such as the chewing and food sharing, or "mouth contact", observed in aquatic species called certain marine animals.

Consequently the research group came up with a definition of intimate contact based on friendly interactions involving intentional oral interaction with a member of the same species, with some movement of the mouth but absence of food.

Study Methods

The lead researcher said they concentrated on accounts of intimate behavior in primates from Africa and Asian regions, including primates, chimpanzees and orangutans, and used online videos to verify the reports.

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

Historical Timeline

Researchers propose the results indicate intimate contact developed approximately 21.5m and 16.9 million years ago in the predecessors of the great primates.

The position of ancient hominins on this evolutionary lineage suggests it is likely they, too, engaged in a kiss, the researchers conclude. But the behavior may not have been limited to their specific group.

"The fact that humans engage intimately, the fact that we now have shown that Neanderthals probably engaged, indicates that the both groups are probably did kissed," Brindle added.

Biological Importance

While the scientific reasoning is discussed, Brindle said intimate contact could be employed in reproductive situations to potentially increase reproductive success or assist in selecting between mates, while it might help reinforce bonding when practiced in a platonic way.

A separate researcher in the activities of great apes commented that as intimate contact was seen in a wide range of primates it made sense its roots lie deep in our evolutionary past, and an examination of different forms of kissing among a broader range of species might push its beginnings back further still.

"Behaviors that we consider as signatures of our species, like intimate contact, are not unique to us if we examine carefully at different species," he said.

Social Aspects

An archaeology expert said that intimate contact had a social component as it was not universal to all human groups.

"However, as humans we succeed or struggle on the quality of our emotional bonds, and methods of encouraging confidence and intimacy will have been significant for millions of years," she said. "This could represent an image that seems a bit incongruous to our incorrect assumptions of a rather ruthless and aggressive past, but actually it ought to be no surprise that Neanderthals – and even Neanderthals and our own species together – engaged intimately."