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Among Galápagos albatrosses to polar bears, primates to great apes, various animals engage in mouth-to-mouth contact. Now, researchers suggest that ancient hominins did it too – and possibly exchanged kisses with modern humans.

Shared Oral Clues

This isn't the initial instance experts have proposed Neanderthals and early modern humans were closely connected. Among previous studies, scientists have discovered modern people and their Neanderthal relatives possessed the same mouth microbe for millions of years after the two species split, suggesting they exchanged oral fluids.

"Likely they were kissing," the researcher noted, adding that the idea aligned with studies that has revealed people of certain genetic backgrounds contain Neanderthal DNA in their genome, revealing genetic mixing was occurring.

Intimate Spin

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

Publishing in the publication a scientific periodical, the researcher and her team report how, to investigate the historical roots of intimate contact, they first had to come up with a description that was not limited to how humans kiss.

Describing Intimate Contact

"There have been some previous attempts to describe a intimate act, but it's very much been human-centric, which implies that basically other animals don't kiss. Currently we know that they likely engage, it may appear different from what our intimate contact looks like," explained Brindle.

However, she said some actions that looked like intimate contact were distinct activities – such as the chewing and transfer of food, or "mouth contact", observed in aquatic species known as French grunts.

As a result the research group came up with a definition of kissing based on friendly interactions involving intentional mouth-to-mouth contact with a member of the same species, with some motion of the mouth but no transfer of food.

Research Methods

Brindle said they focused on accounts of intimate behavior in primates from the African continent and Asian regions, including bonobos, chimpanzees and great apes, and employed online videos to confirm the observations.

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

Evolutionary Origins

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

The position of Neanderthals on this family tree suggests it is likely they, too, indulged in a kiss, the scientists conclude. But the behavior might not have been limited to their specific group.

"The fact that humans kiss, the reality that we now have demonstrated that ancient relatives probably kissed, suggests that the two [species] are also likely to have kissed," Brindle noted.

Biological Importance

Although the evolutionary explanation is discussed, the expert said intimate contact could be used in sexual contexts to potentially increase reproductive success or assist in selecting between partners, while it could assist reinforce bonding when practiced in a non-sexual manner.

A separate researcher in the behavior of great apes commented that as kissing behavior was seen in a broad spectrum of primates it made sense its origins lie deep in our ancient history, and an examination of different forms of intimate behavior among a wider variety of species might extend its beginnings back further still.

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

Social Elements

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

"However, as humans we thrive or fail on the strength of our emotional bonds, and methods of encouraging confidence and closeness will have been significant for millions of years," she said. "This could represent an image that appears a bit contradictory to our incorrect assumptions of a supposedly aggressive and ancient history, but really it ought to be no surprise that ancient hominins – and including them and our own species together – engaged intimately."