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Among seabirds to Arctic mammals, primates to great apes, various animals appear to kiss. Now, researchers suggest that ancient hominins did it too – and might even have locked lips with modern humans.

Shared Microbial Evidence

This isn't the initial instance scientists have suggested Neanderthals and Homo sapiens were intimately acquainted. In previous studies, scientists have found humans and their Neanderthal relatives shared the identical oral bacteria for millions of years after the evolutionary divergence, suggesting they swapped saliva.

"Probably they were engaging in intimate contact," the researcher noted, explaining that the idea chimed with research that has revealed humans of non-African ancestry have bits of ancient genetic material in their genome, demonstrating interbreeding was occurring.

Intimate Spin

"This offers a more romantic perspective on ancient interactions," Brindle said.

Publishing in the journal a scientific periodical, the researcher and colleagues detail how, to explore the historical roots of intimate contact, they first had to come up with a description that was not restricted by how humans kiss.

Defining Kissing

"Previously there were some efforts to describe a intimate act, but it's largely 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 our intimate contact resembles," explained the evolutionary biologist.

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

Consequently the research group came up with a description of kissing centered around social behaviors involving directed mouth-to-mouth contact with a member of the identical group, with some motion of the oral area but no transfer of nutrition.

Study Approach

The lead researcher explained they concentrated on reports of kissing in primates from the African continent and Asian regions, including bonobos, chimpanzees and great apes, and used digital recordings to confirm the reports.

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

Evolutionary Origins

The team say the findings suggest kissing developed somewhere between 21.5m and 16.9 million years ago in the predecessors of the great primates.

Placement of Neanderthals on this family tree suggests it is probable they, too, engaged in a intimate act, the researchers conclude. But the activity might not have been limited to their own species.

"Reality that humans kiss, the fact that we now have demonstrated that ancient relatives probably engaged, suggests that the both groups are probably did engage," the researcher noted.

Evolutionary Significance

Although the evolutionary explanation is debated, the expert explained intimate contact could be employed in reproductive situations to potentially increase mating outcomes or help choose between partners, while it could assist reinforce bonding when used in a non-sexual manner.

A separate researcher in the activities of primates said that as kissing behavior was seen in a broad spectrum of apes it made sense its origins lie deep in our evolutionary past, and an analysis of different forms of kissing among a wider variety of animals might push its origins back even earlier still.

"Behaviors that we think of as signatures of our species, like intimate contact, are not unique to us if we examine carefully at different species," he said.

Social Aspects

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

"However, as people we thrive or fail on the quality of our relationships, and methods of promoting confidence and intimacy will have been important for millions of years," the professor stated. "It might be an image that appears a bit contradictory to our incorrect assumptions of a rather ruthless and ancient history, but really it ought to be expected that Neanderthals – and including them and our human ancestors collectively – engaged intimately."