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Among seabirds to polar bears, chimpanzees to orangutans, various animals appear to kiss. Now, researchers suggest that ancient hominins did it too – and might even have exchanged kisses with early Homo sapiens.

Shared Oral Evidence

This isn't the initial instance experts have proposed Neanderthals and early modern humans were intimately acquainted. In earlier research, researchers have discovered modern people and their thick-browed cousins possessed the identical oral bacteria for hundreds of thousands of years after the evolutionary divergence, implying they swapped saliva.

"Probably they were kissing," the researcher noted, adding that the idea aligned with studies that has revealed people of non-African ancestry have bits of ancient genetic material in their genome, revealing interbreeding was at play.

Romantic Interpretation

"It certainly puts a more romantic spin on ancient interactions," the lead researcher commented.

Writing in the journal a scientific periodical, the researcher and colleagues detail how, to investigate the historical roots of intimate contact, they first had to develop a definition that was not limited to how people kiss.

Defining Kissing

"There have been some efforts to describe a kiss, but it's largely focused on humans, which implies that essentially non-human species don't kiss. Now we know that they likely engage, it might just not look from what our intimate contact resembles," explained Brindle.

However, she said some actions that looked like kissing were distinct activities – such as the chewing and food sharing, or "mouth contact", seen in fish known as certain marine animals.

As a result the research group developed a definition of kissing centered around friendly interactions involving directed mouth-to-mouth contact with a individual of the same species, with some movement of the mouth but absence of food.

Study Approach

The lead researcher said they concentrated on accounts of kissing in primates from the African continent and Asian regions, including bonobos, chimpanzees and orangutans, and used digital recordings to confirm the observations.

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

Historical Origins

The team propose the results indicate intimate contact evolved somewhere between 21.5m and 16.9 million years ago in the predecessors of the great primates.

Placement of Neanderthals on this evolutionary lineage suggests it is likely they, too, engaged in a kiss, the scientists conclude. But the behavior might not have been limited to their own species.

"Reality that humans kiss, the reality that we currently have demonstrated that ancient relatives probably engaged, indicates that the two [species] are probably did kissed," Brindle noted.

Biological Significance

While the scientific reasoning is discussed, the expert explained kissing could be used in sexual contexts to possibly enhance mating outcomes or help choose between partners, while it could assist reinforce bonding when used in a non-sexual manner.

Another expert in the behavior of primates said that as intimate contact was seen in a broad spectrum of primates it was logical its origins extend far into our evolutionary past, and an examination of different forms of kissing among a broader range of animals might extend its origins back even earlier still.

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

Social Aspects

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

"Nonetheless, as people we thrive or fail on the strength of our emotional bonds, and ways of encouraging trust and intimacy will have been significant for eons," she said. "This could represent an concept that seems a bit incongruous to our misplaced ideas of a rather ruthless and aggressive past, but actually it ought to be no surprise that Neanderthals – and even them and our own species collectively – kissed."