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From Galápagos albatrosses to polar bears, primates to orangutans, certain species appear to kiss. Now, scientists suggest that Neanderthals did it too – and might even have exchanged kisses with modern humans.

Common Oral Clues

This isn't the initial instance experts have proposed ancient relatives and early modern humans were closely connected. In previous studies, researchers have discovered modern people and their thick-browed cousins possessed the identical oral bacteria for hundreds of thousands of years after the two species split, implying they swapped saliva.

"Likely they were engaging in intimate contact," the researcher noted, explaining that the concept aligned with research that has found people of non-African ancestry contain Neanderthal DNA in their genetic makeup, revealing genetic mixing was occurring.

Romantic Spin

"It certainly puts a more romantic spin on human-Neanderthal relations," the lead researcher said.

Writing in the publication Evolution and Human Behavior, the researcher and her team report how, to investigate the evolutionary origins of kissing, they first had to develop a description that was not restricted by how people kiss.

Describing Kissing

"There have been some previous attempts to define a kiss, but it's very much been focused on humans, which means that essentially other animals don't kiss. Now we understand that they probably do, it might just not look from what human kissing looks like," said the evolutionary biologist.

However, she noted some behaviors that resembled kissing were something rather different – such as the chewing and transfer of food, or "kiss-fighting", seen in aquatic species called French grunts.

As a result the team came up with a definition of intimate contact based on social behaviors involving directed oral interaction with a individual of the identical group, with some movement of the mouth but no transfer of food.

Study Approach

Brindle said they focused on accounts of kissing in non-human species from Africa and Asian regions, including primates, apes and orangutans, and employed online videos to verify the reports.

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

Evolutionary Origins

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

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

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

Evolutionary Significance

Although the scientific reasoning is discussed, Brindle said intimate contact could be employed in sexual contexts to potentially increase reproductive success or assist in selecting between mates, while it could assist reinforce bonding when practiced in a non-sexual manner.

A separate researcher in the activities of great apes commented that as kissing behavior was observed in a broad spectrum of apes it was logical its roots extend far into our ancient history, and an analysis of various types of intimate behavior among a wider variety of animals might push its beginnings back even earlier still.

"Things that we think of as signatures of human life, like intimate contact, are not unique to us if we look closely at different species," the expert noted.

Social Elements

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

"However, as people we succeed or struggle on the strength of our relationships, and methods of promoting confidence and intimacy will have been significant for millions of years," she said. "This could represent an concept that seems a bit contradictory to our misplaced ideas of a rather ruthless and aggressive past, but really it should be no surprise that ancient hominins – and even them and our human ancestors collectively – kissed."