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Among Galápagos albatrosses to polar bears, primates to great apes, various animals appear to kiss. Now, researchers propose that ancient hominins also engaged in this behavior – and might even have locked lips with modern humans.

Shared Oral Clues

This isn't the initial instance scientists have suggested Neanderthals and early modern humans were closely connected. Among earlier research, scientists have discovered modern people and their Neanderthal relatives shared the same mouth microbe for hundreds of thousands of years after the two species split, suggesting 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 have bits of ancient genetic material in their genome, revealing genetic mixing was occurring.

Intimate Spin

"It certainly puts a different perspective on ancient interactions," Brindle commented.

Writing in the journal a scientific periodical, the researcher and her team report how, to explore the evolutionary origins of kissing, they first had to develop a description that was not limited to how humans smooch.

Describing Intimate Contact

"There have been some efforts to define a intimate act, but it's very much been human-centric, which means that essentially non-human species do not engage in this. Now we understand that they likely engage, it might just not look from what human kissing resembles," said Brindle.

Nonetheless, she noted some behaviors that looked like intimate contact were distinct activities – such as the processing and food sharing, or "kiss-fighting", seen in fish called French grunts.

Consequently the research group developed a definition of intimate contact based on friendly interactions involving intentional oral interaction with a member of the identical group, with some motion of the oral area but no transfer of nutrition.

Research Methods

The lead researcher explained they focused on accounts of kissing in primates from the African continent and Asian regions, including primates, chimpanzees and great apes, and used online videos to verify the observations.

Scientists then integrated this data with details on the evolutionary relationships between living and ancient types of such animals.

Historical Timeline

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

The position of Neanderthals on this evolutionary lineage suggests it is probable they, too, indulged in a kiss, the researchers conclude. But the behavior may not have been limited to their specific group.

"The fact that modern people engage intimately, the reality that we now have shown that Neanderthals probably engaged, indicates that the both groups are also likely to have engage," the researcher noted.

Evolutionary Importance

Although the scientific reasoning is debated, Brindle explained intimate contact could be employed in reproductive situations to potentially increase mating outcomes or assist in selecting between partners, while it might help strengthen connections when practiced in a non-sexual manner.

A separate researcher in the behavior of primates commented that as kissing behavior was observed in a wide range of apes it made sense its origins lie deep in our evolutionary past, and an analysis of different forms of kissing among a broader range of species might extend its beginnings back further still.

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

Social Elements

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

"Nonetheless, as people we thrive or fail on the quality of our relationships, and methods of promoting confidence and intimacy will have been significant for eons," the professor stated. "It might be an concept that seems a bit contradictory to our misplaced ideas of a rather ruthless and aggressive past, but actually it ought to be no surprise that ancient hominins – and even Neanderthals and our own species collectively – kissed."