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From seabirds to Arctic mammals, chimpanzees to great apes, certain species engage in mouth-to-mouth contact. Now, researchers suggest that Neanderthals did it too – and might even have locked lips with modern humans.

Shared Oral Evidence

This isn't the initial instance scientists have suggested ancient relatives and early modern humans were intimately acquainted. In previous studies, researchers have discovered humans and their Neanderthal relatives shared the identical oral bacteria for millions of years after the evolutionary divergence, implying they swapped saliva.

"Likely they were kissing," she said, explaining that the concept chimed with studies that has revealed people of certain genetic backgrounds have bits of ancient genetic material in their genetic makeup, demonstrating genetic mixing was at play.

Intimate Interpretation

"This offers a different spin on ancient interactions," Brindle said.

Publishing in the publication a scientific periodical, Brindle and colleagues 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.

Describing Intimate Contact

"There have been some efforts to define a kiss, but it's very much been human-centric, which implies that basically other animals do not engage in this. Currently we know that they probably do, it may appear different from what human kissing looks like," said Brindle.

Nonetheless, she noted some behaviors that looked like kissing were distinct activities – such as the processing and transfer of food, or "mouth contact", seen in fish called French grunts.

As a result the research group came up with a definition of kissing centered around friendly interactions involving directed oral interaction with a member of the identical group, with some motion of the oral area but absence of food.

Study Methods

Brindle said they focused on reports of kissing in non-human species from Africa and Asia, including primates, chimpanzees and great apes, and employed digital recordings to verify the reports.

Scientists then combined this data with details on the genetic connections between living and extinct types of such animals.

Historical Timeline

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

The position of Neanderthals on this family tree suggests it is likely they, too, indulged in a intimate act, the researchers say. But the behavior may not have been limited to their own species.

"Reality that humans kiss, the reality that we currently have demonstrated that ancient relatives probably engaged, suggests that the both groups are also likely to have engage," the researcher noted.

Evolutionary Importance

Although the evolutionary explanation is discussed, Brindle said intimate contact could be used in reproductive situations to potentially increase reproductive success or help choose between mates, while it might help strengthen connections when used in a non-sexual manner.

Another expert in the behavior of great apes commented that as kissing behavior was observed in a broad spectrum of apes it made sense its roots extend far into our ancient history, and an examination of various types of kissing among a wider variety of species might push its origins back even earlier still.

"Behaviors that we think of as characteristics of human life, like intimate contact, are not unique to us if we look closely at different species," he said.

Social Aspects

An archaeology expert said that intimate contact had a social component as it was not common to all societies.

"However, as people we succeed or struggle on the strength of our emotional bonds, and methods of encouraging trust and intimacy will have been significant for eons," she said. "This could represent an image that appears a bit contradictory to our incorrect assumptions of a rather ruthless and aggressive past, but really it ought to be expected that Neanderthals – and even them and our human ancestors together – kissed."