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Among seabirds to polar bears, primates to great apes, various animals appear to kiss. Now, researchers suggest that Neanderthals did it too – and possibly exchanged kisses with early Homo sapiens.

Shared Microbial Clues

This isn't the initial instance scientists have proposed Neanderthals and early modern humans were intimately acquainted. Among earlier research, researchers have discovered modern people and their Neanderthal relatives shared the same mouth microbe for hundreds of thousands of years after the evolutionary divergence, suggesting they swapped saliva.

"Likely they were engaging in intimate contact," the researcher noted, explaining that the idea chimed with studies that has found humans of certain genetic backgrounds contain ancient genetic material in their genetic makeup, demonstrating interbreeding was at play.

Intimate Spin

"It certainly puts a more romantic perspective on human-Neanderthal relations," Brindle commented.

Writing in the journal a scientific periodical, the researcher and colleagues detail how, to explore the historical roots of kissing, they first had to develop a definition that was not limited to how people kiss.

Describing Kissing

"There have been some previous attempts to describe a intimate act, but it's largely human-centric, which means that essentially other animals do not engage in this. Currently we know that they probably do, it may appear different from what our intimate contact resembles," said Brindle.

Nonetheless, she said some behaviors that resembled kissing were distinct activities – such as the processing and transfer of food, or "mouth contact", seen in aquatic species called certain marine animals.

As a result the team came up with a definition of intimate contact centered around social behaviors involving directed oral interaction with a individual of the identical group, with some motion of the oral area but absence of food.

Study Methods

The lead researcher explained they focused on accounts of kissing in primates from Africa and Asian regions, including primates, chimpanzees and great apes, and used digital recordings to confirm the reports.

Scientists then integrated this information with information on the genetic connections between living and extinct types of such animals.

Historical Timeline

Researchers say the findings indicate intimate contact developed approximately 21.5 million and 16.9 million years ago in the ancestors of the great primates.

The position of Neanderthals on this family tree suggests it is probable they, too, indulged in a intimate act, the scientists say. But the behavior may not have been limited to their specific group.

"The fact that humans kiss, the fact that we now have shown that ancient relatives probably engaged, suggests that the both groups are also likely to have engage," the researcher noted.

Evolutionary Importance

While the evolutionary explanation is debated, the expert said kissing could be used in reproductive situations to potentially increase mating outcomes or help choose between mates, while it could assist reinforce bonding 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 roots extend far into our evolutionary past, and an examination of various types of kissing among a wider variety of animals might push its beginnings back further still.

"Behaviors that we consider as characteristics of human life, like intimate contact, are not exclusive to us if we examine carefully at other animals," he said.

Social Aspects

Another professor said that intimate contact had a social component as it was not common to all human groups.

"Nonetheless, as people we thrive or fail on the strength 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 image that seems a bit contradictory to our incorrect assumptions of a rather ruthless and aggressive past, but really it ought to be expected that Neanderthals – and even them and our own species collectively – engaged intimately."