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From seabirds to Arctic mammals, chimpanzees to orangutans, certain species engage in mouth-to-mouth contact. Currently, researchers suggest that ancient hominins did it too – and might even have exchanged kisses with modern humans.

Common Oral Clues

It is not the first time scientists have suggested ancient relatives and Homo sapiens were intimately acquainted. Among previous studies, scientists have found humans and their thick-browed cousins shared the same mouth microbe for hundreds of thousands of years after the evolutionary divergence, suggesting they swapped saliva.

"Probably they were kissing," she said, explaining that the concept aligned with studies that has found humans of non-African ancestry have bits of Neanderthal DNA in their genome, demonstrating interbreeding was at play.

Romantic Spin

"This offers a more romantic spin on human-Neanderthal relations," the lead researcher commented.

Publishing in the journal a scientific periodical, Brindle and colleagues report how, to investigate the evolutionary origins of kissing, they first had to develop a definition that was not limited to how people kiss.

Describing Kissing

"There have been some efforts to define a kiss, but it's very much been human-centric, which implies that basically other animals don't kiss. Now we know that they probably do, it may appear different from what our intimate contact looks like," said the evolutionary biologist.

However, she noted some behaviors that resembled intimate contact were distinct activities – such as the processing and food sharing, or "mouth contact", observed in aquatic species known as French grunts.

As a result the team came up with a description of kissing centered around social behaviors involving intentional mouth-to-mouth contact with a individual of the identical group, with some movement of the oral area but absence of nutrition.

Research Methods

Brindle said they concentrated on reports of kissing in primates from Africa and Asian regions, including bonobos, apes and great apes, and used online videos to verify the observations.

Scientists then combined this data with details on the genetic connections between extant and ancient species of such animals.

Historical Origins

Researchers say the findings indicate intimate contact evolved approximately 21.5m and 16.9m years ago in the ancestors of the great primates.

Placement of ancient hominins on this family tree suggests it is likely 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 shown that Neanderthals very likely engaged, suggests that the both groups are probably did engage," Brindle noted.

Biological Importance

Although the scientific reasoning is discussed, Brindle said intimate contact could be employed in sexual contexts to potentially increase mating outcomes or assist in selecting between partners, while it might help reinforce bonding when practiced in a platonic way.

Another expert in the activities of primates commented that as intimate contact was observed in a broad spectrum of apes it was logical its roots extend far into our evolutionary past, and an examination of different forms of kissing among a wider variety of animals might extend its beginnings back even earlier still.

"Things that we think of as characteristics of our species, like kissing, are not unique to us if we examine carefully 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.

"Nonetheless, as people we thrive or fail on the quality of our emotional bonds, and methods of encouraging trust and closeness will have been important for millions of years," the professor stated. "It might be an concept that appears a bit incongruous to our incorrect assumptions of a supposedly aggressive and aggressive past, but actually it should be no surprise that ancient hominins – and even them and our own species together – engaged intimately."