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Among Galápagos albatrosses to polar bears, chimpanzees to great apes, various animals appear to kiss. Now, scientists suggest that Neanderthals also engaged in this behavior – and might even have exchanged kisses with early Homo sapiens.

Shared Oral Clues

This isn't the initial instance scientists have proposed Neanderthals and early modern humans were closely connected. In earlier research, researchers have found humans and their Neanderthal relatives possessed the same mouth microbe for hundreds of thousands of years after the two species split, suggesting they swapped saliva.

"Likely they were engaging in intimate contact," the researcher noted, adding that the concept aligned with studies that has found humans of certain genetic backgrounds have bits of ancient genetic material in their genetic makeup, demonstrating genetic mixing was at play.

Intimate Interpretation

"It certainly puts a more romantic spin on ancient interactions," the lead researcher said.

Publishing in the journal a scientific periodical, the researcher and colleagues report how, to explore the evolutionary origins of intimate contact, they first had to develop a definition that was not restricted by how people smooch.

Describing Intimate Contact

"Previously there were some previous attempts to define a kiss, but it's largely human-centric, which means that basically non-human species don't kiss. Now we know that they probably do, it may appear different from what our intimate contact looks like," said Brindle.

However, she noted some actions that looked like kissing were distinct activities – such as the chewing and food sharing, or "kiss-fighting", seen in fish known as French grunts.

Consequently the team developed a definition of kissing centered around social behaviors involving intentional mouth-to-mouth contact with a individual of the identical group, with some motion of the oral area but no transfer of food.

Research Methods

Brindle explained they concentrated on accounts of intimate behavior in primates from Africa and Asian regions, including bonobos, apes and great apes, and used online videos to confirm the observations.

The researchers then combined this information with information on the genetic connections between extant and extinct species of such primates.

Historical Origins

Researchers propose the results suggest intimate contact developed approximately 21.5 million and 16.9m years ago in the predecessors of the great primates.

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

"Reality that modern people kiss, the reality that we now have demonstrated that ancient relatives probably kissed, suggests that the both groups are probably did engage," Brindle noted.

Biological Significance

While the scientific reasoning is debated, the expert explained intimate contact could be employed in sexual contexts to possibly enhance reproductive success or assist in selecting between partners, while it could assist reinforce bonding when practiced in a platonic way.

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

"Behaviors that we consider as signatures of human life, like kissing, are not exclusive to us if we look closely at different species," he said.

Cultural Aspects

Another professor explained that intimate contact had a cultural element as it was not universal to all human groups.

"Nonetheless, as humans we succeed or struggle on the strength of our emotional bonds, and ways of encouraging confidence and closeness will have been important for eons," she said. "It might be an image that appears a bit contradictory to our incorrect assumptions of a supposedly aggressive and aggressive past, but actually it should be expected that Neanderthals – and including them and our own species together – engaged intimately."