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From Galápagos albatrosses to polar bears, primates to great apes, various animals engage in mouth-to-mouth contact. Now, researchers propose that Neanderthals did it too – and might even have locked lips with modern humans.

Common Oral Clues

It is not the first time scientists have suggested Neanderthals and early modern humans were intimately acquainted. Among previous studies, researchers have found modern people and their Neanderthal relatives possessed the identical oral bacteria for hundreds of thousands of years after the two species split, suggesting they exchanged oral fluids.

"Probably they were kissing," she said, explaining that the concept chimed with studies that has revealed people of non-African ancestry contain ancient genetic material in their genome, demonstrating genetic mixing was at play.

Romantic Spin

"It certainly puts a different spin on human-Neanderthal relations," the lead researcher commented.

Publishing in the journal a scientific periodical, the researcher and colleagues detail how, to investigate the historical roots of kissing, they first had to develop a definition that was not restricted by how people kiss.

Describing Intimate Contact

"Previously there were some efforts to describe a kiss, but it's very much been focused on humans, which implies that basically other animals don't kiss. Currently we understand that they probably do, it might just not look from what human kissing resembles," said Brindle.

Nonetheless, she said some actions that resembled intimate contact were distinct activities – such as the processing and food sharing, or "mouth contact", seen in fish known as French grunts.

Consequently the team came up with a description 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 mouth but absence of nutrition.

Research Approach

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

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

Historical Origins

The team say the results indicate kissing developed approximately 21.5 million and 16.9m years ago in the predecessors of the large apes.

Placement of ancient hominins on this evolutionary lineage means it is probable they, too, engaged in a kiss, the scientists conclude. But the activity might not have been limited to their own species.

"Reality that humans kiss, the reality that we currently have shown that ancient relatives very likely engaged, indicates that the both groups are also likely to have engage," Brindle added.

Evolutionary Significance

While the evolutionary explanation is debated, Brindle explained kissing could be employed in reproductive situations to possibly enhance reproductive success or help choose between partners, while it could assist strengthen connections when practiced in a non-sexual manner.

Another expert in the activities of great apes commented that as intimate contact was observed in a broad spectrum of primates it made sense its origins extend far into our evolutionary past, and an examination of various types of intimate behavior among a broader range of animals might push its origins back even earlier still.

"Things that we think of as signatures of human life, like kissing, are not exclusive to us if we look closely at different species," he said.

Social Aspects

An archaeology expert explained that intimate contact had a cultural element as it was not common to all human groups.

"Nonetheless, as humans we thrive or fail on the quality of our relationships, and methods of encouraging trust and closeness will have been significant for eons," she said. "This could represent an image that appears a bit incongruous to our incorrect assumptions of a supposedly aggressive and ancient history, but actually it should be expected that Neanderthals – and even Neanderthals and our own species collectively – engaged intimately."