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Among Galápagos albatrosses to Arctic mammals, chimpanzees to great apes, certain species engage in mouth-to-mouth contact. Currently, researchers suggest that Neanderthals did it too – and might even have locked lips with early Homo sapiens.

Shared Oral Clues

It is not the first time experts have proposed ancient relatives and early modern humans were closely connected. Among earlier research, scientists have found modern people and their thick-browed cousins shared the identical oral bacteria for millions of years after the evolutionary divergence, implying they swapped saliva.

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

Intimate Spin

"This offers a different spin on ancient interactions," the lead researcher commented.

Writing in the journal a scientific periodical, Brindle and colleagues report how, to investigate the historical roots of intimate contact, they first had to come up with a description that was not restricted by how humans smooch.

Describing Intimate Contact

"Previously there were some efforts to define a kiss, but it's largely human-centric, which implies that basically non-human species don't kiss. Currently we know that they likely engage, it might just not look from what our intimate contact looks like," explained Brindle.

Nonetheless, she noted some actions that looked like intimate contact were something rather different – such as the chewing and food sharing, or "mouth contact", observed in fish known as certain marine animals.

As a result the team came up with a definition of intimate contact centered around social behaviors involving directed mouth-to-mouth contact with a individual of the identical group, with some movement of the oral area but absence of food.

Study Methods

Brindle said they concentrated on accounts of kissing in primates from the African continent and Asian regions, including primates, chimpanzees and orangutans, and used digital recordings to verify the reports.

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

Historical Timeline

Researchers propose the findings suggest intimate contact developed somewhere between 21.5m and 16.9m years ago in the ancestors of the great primates.

The position of Neanderthals on this evolutionary lineage means it is probable they, too, indulged in a kiss, the scientists say. But the behavior may not have been confined to their own species.

"Reality that modern people engage intimately, the reality that we currently have demonstrated that Neanderthals probably engaged, suggests that the both groups are also likely to have engage," Brindle noted.

Evolutionary Importance

While the scientific reasoning is discussed, the expert explained intimate contact could be used in sexual contexts to potentially enhance reproductive success or help choose between mates, while it might help reinforce bonding when used in a non-sexual manner.

Another expert in the activities of great apes said that as intimate contact was observed in a broad spectrum of apes it made sense its roots lie deep in our ancient history, and an analysis of different forms of intimate behavior among a broader range of animals might push its beginnings back further still.

"Things that we consider as signatures of human life, like intimate contact, are not exclusive to us if we look closely at other animals," he said.

Cultural Elements

An archaeology expert explained that intimate contact 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 ways of promoting confidence and intimacy will have been important for eons," the professor stated. "This could represent an concept that appears a bit contradictory to our misplaced ideas of a supposedly aggressive and aggressive past, but really it ought to be expected that Neanderthals – and even them and our own species collectively – kissed."