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Among seabirds to Arctic mammals, chimpanzees to great apes, various animals appear to kiss. Currently, researchers propose that Neanderthals did it too – and possibly exchanged kisses with modern humans.

Shared Oral Evidence

It is not the first time scientists have proposed ancient relatives and Homo sapiens were intimately acquainted. In previous studies, scientists have discovered modern people and their thick-browed cousins possessed the identical oral bacteria for hundreds of thousands of years after the two species split, implying they exchanged oral fluids.

"Probably they were engaging in intimate contact," the researcher noted, adding that the concept chimed with research that has found people of certain genetic backgrounds contain Neanderthal DNA in their genome, revealing genetic mixing was occurring.

Romantic Spin

"It certainly puts a different spin on human-Neanderthal relations," Brindle said.

Publishing in the publication a scientific periodical, Brindle and her team detail how, to investigate the evolutionary origins of kissing, they first had to come up with a definition that was not limited to how humans kiss.

Describing Kissing

"Previously there were some previous attempts to define a intimate act, but it's very much been 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," said Brindle.

Nonetheless, she said some actions that resembled intimate contact were something rather different – such as the processing and food sharing, or "kiss-fighting", observed in fish known as certain marine animals.

Consequently the research group developed a definition of kissing centered around friendly interactions involving intentional oral interaction with a member of the same species, with some motion of the oral area but absence of food.

Research Methods

The lead researcher said they focused on reports of kissing in primates from the African continent and Asian regions, including primates, apes and orangutans, and used digital recordings to verify the reports.

Scientists then combined this data with information on the genetic connections between extant and ancient species of such primates.

Evolutionary Origins

The team propose the findings indicate intimate contact developed somewhere between 21.5 million and 16.9m years ago in the predecessors of the large apes.

The position of Neanderthals on this family tree suggests it is likely they, too, engaged in a intimate act, the scientists say. But the activity may not have been limited to their own species.

"Reality that humans engage intimately, the fact that we currently have shown that Neanderthals probably kissed, suggests that the both groups are probably did kissed," the researcher noted.

Evolutionary Significance

While the scientific reasoning is discussed, Brindle explained intimate contact could be employed in sexual contexts to potentially enhance mating outcomes or assist in selecting between mates, while it could assist strengthen connections when used in a platonic way.

Another expert in the behavior of great apes commented that as intimate contact was observed in a broad spectrum of primates it was logical its roots extend far into our ancient history, and an analysis of different forms of intimate behavior among a wider variety of animals might push its beginnings back even earlier still.

"Things that we consider as signatures of our species, like intimate contact, are not unique to us if we look closely at different species," he said.

Cultural Aspects

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

"However, as people we succeed or struggle on the quality of our relationships, and ways of encouraging confidence and closeness will have been important for millions of years," she said. "This could represent an image that seems a bit contradictory to our incorrect assumptions of a supposedly aggressive and aggressive past, but actually it ought to be no surprise that Neanderthals – and even them and our human ancestors collectively – kissed."