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From seabirds to polar bears, chimpanzees to great apes, certain species engage in mouth-to-mouth contact. Now, researchers suggest that ancient hominins did it too – and possibly exchanged kisses with early Homo sapiens.

Shared Oral Clues

It is not the first time experts have suggested Neanderthals and early modern humans were closely connected. Among earlier research, researchers have discovered modern people 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 engaging in intimate contact," she said, explaining that the concept chimed with studies that has found people of non-African ancestry contain Neanderthal DNA in their genetic makeup, demonstrating genetic mixing was occurring.

Romantic Spin

"This offers a more romantic perspective on ancient interactions," the lead researcher commented.

Publishing in the publication a scientific periodical, the researcher and colleagues detail how, to explore the evolutionary origins of intimate contact, they first had to develop a definition that was not restricted by how people kiss.

Defining Kissing

"There have been some efforts to describe a intimate act, but it's very much been focused on humans, which implies that basically non-human species don't kiss. Currently we know that they likely engage, it might just not look from what human kissing resembles," explained the evolutionary biologist.

However, she noted some actions that resembled kissing were something rather different – such as the chewing and food sharing, or "mouth contact", observed in fish known as French grunts.

Consequently the research group developed a definition of intimate contact based on friendly interactions involving intentional mouth-to-mouth contact with a member of the identical group, with some movement of the mouth but no transfer of nutrition.

Research Approach

Brindle explained they focused on reports of intimate behavior in primates from the African continent and Asia, including primates, chimpanzees and great apes, and employed digital recordings to verify the observations.

The researchers then integrated this information with details on the genetic connections between extant and extinct species of such animals.

Evolutionary Timeline

The team propose the results 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 probable they, too, indulged in a intimate act, the researchers say. But the activity might not have been confined to their specific group.

"The fact that modern people kiss, the fact that we currently have demonstrated that Neanderthals probably engaged, indicates that the both groups are also likely to have engage," Brindle noted.

Evolutionary Significance

While the scientific reasoning is discussed, the expert explained intimate contact could be used in sexual contexts to potentially enhance mating outcomes or help choose between mates, while it could assist strengthen connections when used in a non-sexual manner.

Another expert in the activities of primates commented that as intimate contact was seen in a wide range of primates it was logical its origins lie deep in our evolutionary past, and an examination of various types of intimate behavior 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 examine carefully at other animals," he said.

Social Elements

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

"Nonetheless, as humans we succeed or struggle on the strength of our emotional bonds, and methods of promoting confidence and intimacy will have been significant for millions of years," the professor stated. "It might be an image that seems a bit incongruous to our misplaced ideas of a supposedly aggressive and ancient history, but actually it should be expected that ancient hominins – and including them and our own species collectively – kissed."