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From Galápagos albatrosses to polar bears, chimpanzees to orangutans, various animals appear to kiss. Currently, scientists propose that Neanderthals did it too – and possibly exchanged kisses with modern humans.

Common Microbial Clues

It is not the first time experts have suggested ancient relatives and early modern humans were intimately acquainted. Among previous studies, researchers have discovered humans and their Neanderthal relatives shared the identical oral bacteria for millions of years after the two species split, suggesting they swapped saliva.

"Likely they were engaging in intimate contact," she said, explaining that the idea aligned with studies that has revealed people of certain genetic backgrounds contain Neanderthal DNA in their genetic makeup, revealing genetic mixing was occurring.

Intimate Interpretation

"It certainly puts a different spin on human-Neanderthal relations," Brindle said.

Publishing in the journal Evolution and Human Behavior, the researcher and her team report how, to explore the evolutionary origins of intimate contact, they first had to come up with a description that was not restricted by how people kiss.

Describing Intimate Contact

"There have been some efforts to define a kiss, but it's largely human-centric, which means that essentially non-human species don't kiss. Currently we understand that they probably do, it may appear different from what our intimate contact resembles," said the evolutionary biologist.

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

Consequently the research group developed a definition of intimate contact centered around friendly interactions involving directed mouth-to-mouth contact with a individual of the identical group, with some movement of the oral area but absence of food.

Research Methods

Brindle explained they concentrated on reports of kissing in non-human species from the African continent and Asia, including primates, apes and orangutans, and used online videos to confirm the reports.

Scientists then integrated this data with details on the evolutionary relationships between extant and extinct species of such animals.

Evolutionary Timeline

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

Placement of Neanderthals on this family tree suggests it is probable they, too, engaged in a intimate act, the researchers conclude. But the activity may not have been limited to their own species.

"The fact that modern people kiss, the reality that we currently have demonstrated that Neanderthals very likely kissed, suggests that the both groups are probably did engage," Brindle added.

Evolutionary Significance

While the evolutionary explanation is discussed, Brindle explained intimate contact could be employed in reproductive situations to possibly enhance reproductive success or help choose between partners, while it could assist reinforce bonding when practiced in a platonic way.

A separate researcher in the activities of great apes commented that as kissing behavior was seen in a wide range of primates it made sense its origins extend far into our ancient history, and an analysis of different forms of intimate behavior among a broader range of species might push its beginnings back further still.

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

Social Aspects

Another professor said that kissing had a cultural element as it was not universal to all societies.

"However, as people we succeed or struggle on the quality of our relationships, and ways of encouraging trust and closeness will have been significant for eons," she said. "It might be an image that seems a bit contradictory to our incorrect assumptions of a supposedly aggressive and ancient history, but actually it ought to be no surprise that Neanderthals – and including them and our own species collectively – kissed."