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From Galápagos albatrosses to Arctic mammals, primates to orangutans, various animals appear to kiss. Now, researchers suggest that ancient hominins did it too – and might even have exchanged kisses with modern humans.

Common Microbial Clues

It is not the first time experts have proposed ancient relatives and Homo sapiens were intimately acquainted. Among previous studies, scientists have discovered humans and their thick-browed cousins shared the identical oral bacteria for hundreds of thousands of years after the two species split, implying they swapped saliva.

"Likely they were kissing," she said, explaining that the concept aligned with research that has revealed humans of non-African ancestry have bits of Neanderthal DNA in their genetic makeup, revealing genetic mixing was occurring.

Romantic Spin

"This offers a more romantic spin on ancient interactions," the lead researcher said.

Writing in the journal a scientific periodical, the researcher and colleagues report how, to investigate the evolutionary origins of intimate contact, they first had to come up with a definition that was not limited to how humans smooch.

Describing Intimate Contact

"There have been some efforts to define a kiss, but it's very much been focused on humans, which implies that basically non-human species do not engage in this. Currently we know that they likely engage, it might just not look from what human kissing resembles," said the evolutionary biologist.

Nonetheless, she said some behaviors that looked like intimate contact were distinct activities – such as the chewing and food sharing, or "mouth contact", observed in aquatic species called French grunts.

As a result the research group came up with a description of kissing based on social behaviors involving intentional oral interaction with a individual of the identical group, with some motion of the oral area but no transfer of nutrition.

Research Methods

Brindle said they focused on reports of kissing in primates from Africa and Asia, including bonobos, apes and orangutans, and used online videos to verify the reports.

The researchers then integrated this data with information on the genetic connections between extant and ancient types of such animals.

Evolutionary Timeline

The team propose the findings suggest kissing developed somewhere between 21.5m and 16.9m years ago in the ancestors of the large apes.

The position of ancient hominins on this family tree means it is likely they, too, indulged in a kiss, the scientists say. But the activity might not have been confined to their own species.

"Reality that modern people engage intimately, the fact that we currently have shown that Neanderthals probably engaged, suggests that the two [species] are also likely to have kissed," the researcher noted.

Evolutionary Importance

While the evolutionary explanation is discussed, Brindle said intimate contact could be used in reproductive situations to potentially increase reproductive success or help choose between mates, while it might help strengthen connections when used in a non-sexual manner.

A separate researcher in the behavior of great apes said that as kissing behavior was seen in a wide range of apes it was logical its roots extend far into our ancient history, and an analysis of various types of kissing among a broader range of animals might push its beginnings back further still.

"Things that we think of as characteristics of human life, like kissing, are not unique to us if we look closely at other animals," the expert noted.

Social Elements

Another professor explained that kissing had a cultural element as it was not universal to all societies.

"However, as humans we thrive or fail on the quality of our emotional bonds, and methods of encouraging confidence and closeness will have been significant for eons," the professor stated. "It might be an image that appears a bit contradictory to our incorrect assumptions of a supposedly aggressive and ancient history, but actually it ought to be expected that Neanderthals – and including Neanderthals and our own species collectively – kissed."