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From Galápagos albatrosses to Arctic mammals, primates to great apes, various animals engage in mouth-to-mouth contact. Currently, researchers suggest that ancient hominins also engaged in this behavior – and possibly 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. Among previous studies, scientists have discovered humans and their thick-browed cousins possessed the same mouth microbe for millions of years after the two species split, suggesting they exchanged oral fluids.

"Probably they were engaging in intimate contact," she said, explaining that the concept chimed with research that has found humans of certain genetic backgrounds contain Neanderthal DNA in their genome, demonstrating interbreeding was occurring.

Romantic Spin

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

Writing in the journal a scientific periodical, the researcher and her team report how, to explore the evolutionary origins of intimate contact, they first had to come up with a description that was not limited to how humans kiss.

Describing Intimate Contact

"There have been some previous attempts to describe a kiss, but it's very much been human-centric, which means that essentially other animals do not engage in this. Now we understand that they probably do, it may appear different from what human kissing looks like," said Brindle.

Nonetheless, she said some behaviors that looked like intimate contact were distinct activities – such as the chewing and transfer of food, or "mouth contact", observed in aquatic species known as French grunts.

As a result the research group came up with a definition of intimate contact based on social behaviors involving directed mouth-to-mouth contact with a individual of the same species, with some movement of the oral area but no transfer of nutrition.

Study Methods

Brindle said they concentrated on accounts of kissing in non-human species from the African continent and Asia, including primates, apes and great apes, and used online videos to confirm the reports.

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

Historical Origins

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

Placement of ancient hominins on this family tree means it is likely they, too, indulged in a kiss, the scientists say. But the behavior might not have been limited to their specific group.

"Reality that humans kiss, the fact that we currently have demonstrated that Neanderthals probably kissed, suggests that the both groups are also likely to have kissed," Brindle noted.

Evolutionary Significance

While the scientific reasoning is discussed, the expert said intimate contact could be employed in sexual contexts to possibly increase mating outcomes or help choose between mates, while it might help strengthen connections when practiced in a platonic way.

Another expert in the activities 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 analysis of different forms of kissing among a wider variety of animals might extend its origins back further still.

"Behaviors that we think of as signatures of human life, like intimate contact, are not exclusive to us if we examine carefully at other animals," he said.

Cultural Elements

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

"Nonetheless, as people we succeed or struggle on the quality of our emotional bonds, and ways of encouraging confidence and closeness will have been significant for millions of years," the professor stated. "This could represent an concept that appears a bit contradictory to our incorrect assumptions of a supposedly aggressive and ancient history, but really it ought to be expected that ancient hominins – and including Neanderthals and our own species collectively – engaged intimately."