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From seabirds to polar bears, chimpanzees to great apes, various animals engage in mouth-to-mouth contact. Now, researchers suggest that Neanderthals did it too – and possibly locked lips with early Homo sapiens.

Shared Microbial Clues

This isn't the initial instance experts have suggested Neanderthals and Homo sapiens were intimately acquainted. Among earlier research, scientists have discovered modern people and their thick-browed cousins shared the identical oral bacteria for millions of years after the two species split, suggesting they exchanged oral fluids.

"Likely they were engaging in intimate contact," the researcher noted, explaining that the concept aligned with studies that has revealed people of non-African ancestry have bits of ancient genetic material in their genetic makeup, revealing interbreeding was at play.

Romantic Interpretation

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

Writing in the publication a scientific periodical, Brindle and colleagues detail how, to explore the evolutionary origins of intimate contact, they first had to develop a definition that was not limited to how humans smooch.

Defining Intimate Contact

"Previously there were some efforts to describe a kiss, but it's very much been human-centric, which means that basically other animals don't kiss. Now we understand that they likely engage, it might just not look from what human kissing resembles," said the evolutionary biologist.

Nonetheless, she noted some behaviors that looked like intimate contact were something rather different – such as the processing and transfer of food, or "mouth contact", observed in fish called French grunts.

As a result the team came up with a description of kissing centered around social behaviors involving directed oral interaction with a individual of the identical group, with some movement of the oral area but no transfer of food.

Research Methods

The lead researcher explained they focused 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 confirm the observations.

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

Evolutionary Timeline

The team propose the findings indicate kissing developed approximately 21.5m and 16.9m years ago in the ancestors of the great primates.

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

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

Biological Importance

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

Another expert in the behavior of primates said that as intimate contact was observed in a wide range of primates it was logical its origins extend far into our ancient history, and an analysis of various types of kissing among a wider variety of species might push its beginnings back further still.

"Behaviors 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.

Cultural Elements

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

"However, as people we thrive or fail on the quality of our emotional bonds, and ways of promoting confidence and closeness will have been significant for millions of years," she said. "It might be an concept that appears a bit contradictory to our incorrect assumptions of a supposedly aggressive and aggressive past, but really it ought to be no surprise that ancient hominins – and including them and our own species together – kissed."