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Among seabirds to Arctic mammals, chimpanzees to great apes, certain species appear to kiss. Now, scientists suggest that ancient hominins did it too – and possibly locked lips with early Homo sapiens.

Shared Oral Clues

This isn't the initial instance experts have suggested ancient relatives and early modern humans were intimately acquainted. In previous studies, scientists have discovered modern people and their Neanderthal relatives possessed the identical oral bacteria for millions of years after the evolutionary divergence, suggesting they exchanged oral fluids.

"Probably they were kissing," she said, adding that the concept chimed with studies that has found people of certain genetic backgrounds have bits of ancient genetic material in their genome, revealing interbreeding was occurring.

Romantic Spin

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

Writing in the journal Evolution and Human Behavior, Brindle and her team report how, to investigate the evolutionary origins of kissing, they first had to come up with a definition that was not restricted by how humans kiss.

Describing Kissing

"Previously there were some efforts to define a kiss, but it's very much been human-centric, which implies that basically non-human species don't kiss. Currently we understand that they probably do, it may appear different from what human kissing looks like," said Brindle.

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

Consequently the research group came up with a definition of intimate contact centered around social behaviors involving intentional oral interaction with a individual of the identical group, with some movement of the oral area but absence of nutrition.

Research Methods

Brindle explained they concentrated on accounts of intimate behavior in non-human species from the African continent and Asian regions, including bonobos, chimpanzees and orangutans, and used online videos to verify the reports.

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

Evolutionary Timeline

Researchers propose the findings indicate kissing developed somewhere between 21.5 million and 16.9m years ago in the ancestors of the large apes.

Placement of ancient hominins on this family tree suggests it is likely they, too, engaged in a kiss, the scientists conclude. But the behavior may not have been limited to their own species.

"The fact that modern people kiss, the fact that we now have shown that Neanderthals very likely kissed, indicates that the two [species] are probably did kissed," the researcher noted.

Biological Importance

While the evolutionary explanation is discussed, the expert said kissing could be employed in reproductive situations to potentially increase reproductive success or assist in selecting between partners, while it could assist strengthen connections when used in a non-sexual manner.

Another expert in the behavior of great apes commented that as kissing behavior was observed in a broad spectrum of apes it was logical its origins extend far into our evolutionary past, and an analysis of different forms of intimate behavior among a broader range of species might extend its origins back even earlier still.

"Things that we think of as signatures of human life, like kissing, are not unique to us if we examine carefully at different species," the expert noted.

Social Elements

Another professor said that intimate contact had a social component as it was not common to all societies.

"Nonetheless, as humans we succeed or struggle on the quality of our relationships, and methods of encouraging confidence and intimacy will have been significant for eons," she said. "It might be an concept that appears a bit incongruous to our misplaced ideas of a supposedly aggressive and aggressive past, but really it ought to be no surprise that ancient hominins – and including them and our human ancestors collectively – engaged intimately."