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Among seabirds to polar bears, primates to great apes, certain species engage in mouth-to-mouth contact. Currently, researchers propose that Neanderthals also engaged in this behavior – and possibly exchanged kisses with early Homo sapiens.

Shared Microbial Clues

This isn't the initial instance experts have suggested ancient relatives and Homo sapiens were closely connected. Among earlier research, researchers have found modern people and their thick-browed cousins shared the identical oral bacteria for hundreds of thousands of years after the evolutionary divergence, suggesting they exchanged oral fluids.

"Probably they were engaging in intimate contact," she said, adding that the idea chimed with studies that has revealed humans of non-African ancestry contain Neanderthal DNA in their genetic makeup, revealing interbreeding was occurring.

Intimate Interpretation

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

Publishing in the publication a scientific periodical, the researcher and colleagues report how, to explore the historical roots of kissing, they first had to develop a definition that was not restricted by how humans kiss.

Describing Intimate Contact

"Previously there were some efforts to describe a intimate act, but it's very much been human-centric, which implies that essentially other animals don't kiss. Currently we understand that they probably do, it may appear different from what human kissing looks like," explained Brindle.

Nonetheless, she noted some actions that resembled kissing were something rather different – such as the processing and food sharing, or "mouth contact", seen in aquatic species known as French grunts.

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

Research Methods

The lead researcher explained they focused on reports of intimate behavior in non-human species from the African continent and Asian regions, including bonobos, chimpanzees and orangutans, and employed online videos to verify the observations.

The researchers then integrated this data with information on the evolutionary relationships between living and extinct species of such primates.

Evolutionary Timeline

The team say the results suggest kissing developed approximately 21.5 million and 16.9 million years ago in the predecessors of the great primates.

The position of ancient hominins on this family tree suggests it is probable they, too, indulged in a kiss, the researchers say. But the activity may not have been confined to their specific group.

"Reality that modern people engage intimately, the fact that we currently have demonstrated that Neanderthals very likely engaged, suggests that the two [species] are probably did kissed," Brindle added.

Evolutionary Importance

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

Another expert in the activities of primates said that as kissing behavior was observed in a wide range of apes it made sense its roots lie deep in our evolutionary past, and an analysis of different forms of kissing among a wider variety of animals might push its beginnings back further still.

"Behaviors that we think of as signatures of human life, like intimate contact, are not unique to us if we examine carefully at other animals," the expert noted.

Social Aspects

Another professor said that kissing had a cultural element as it was not common to all human groups.

"However, as people we succeed or struggle on the quality of our relationships, and ways of encouraging trust and intimacy will have been important for eons," the professor stated. "It might be an concept that appears a bit incongruous to our incorrect assumptions of a supposedly aggressive and ancient history, but actually it ought to be no surprise that ancient hominins – and including Neanderthals and our human ancestors together – engaged intimately."