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From Galápagos albatrosses to Arctic mammals, chimpanzees to orangutans, various animals appear to kiss. Currently, researchers suggest that Neanderthals also engaged in this behavior – and might even have exchanged kisses with modern humans.

Shared Microbial Clues

This isn't the initial instance scientists have proposed ancient relatives and early modern humans were intimately acquainted. Among earlier research, researchers have discovered humans and their Neanderthal relatives possessed the identical oral bacteria for hundreds of thousands of years after the two species split, suggesting they exchanged oral fluids.

"Likely they were kissing," the researcher noted, adding that the concept aligned with studies that has revealed humans of certain genetic backgrounds contain ancient genetic material in their genome, revealing interbreeding was at play.

Romantic Spin

"It certainly puts a different perspective on human-Neanderthal relations," the lead researcher said.

Publishing in the publication Evolution and Human Behavior, Brindle and her team detail how, to investigate the evolutionary origins of kissing, they first had to develop a description that was not limited to how humans kiss.

Defining Kissing

"Previously there were some efforts to describe a intimate act, but it's largely human-centric, which means that essentially other animals don't kiss. Currently we know that they probably do, it might just not look from what human kissing resembles," explained Brindle.

Nonetheless, she said some actions that resembled kissing were something rather different – such as the processing and food sharing, or "mouth contact", seen in aquatic species known as certain marine animals.

As a result the research group developed a definition of intimate contact based on friendly interactions involving intentional oral interaction with a member of the same species, with some motion of the oral area but no transfer of food.

Study Approach

Brindle said they concentrated on reports of intimate behavior in non-human species from Africa and Asia, including primates, apes and orangutans, and employed online videos to confirm the reports.

The researchers then integrated this information with details on the evolutionary relationships between living and ancient species of such primates.

Historical Timeline

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

Placement of Neanderthals on this family tree means it is likely they, too, indulged in a intimate act, the scientists conclude. But the activity might not have been confined to their own species.

"Reality that humans kiss, the fact that we now have shown that Neanderthals very likely engaged, indicates that the both groups are probably did engage," Brindle added.

Biological Importance

While the evolutionary explanation is debated, Brindle explained kissing could be used in reproductive situations to potentially enhance mating outcomes or help choose between mates, while it could assist reinforce bonding when practiced in a non-sexual manner.

Another expert in the activities of primates commented that as kissing behavior was seen in a broad spectrum of apes it made sense its roots lie deep in our ancient history, and an analysis of various types of kissing among a wider variety of species might extend its beginnings back even earlier still.

"Behaviors that we consider as characteristics of our species, like kissing, are not exclusive to us if we look closely at other animals," the expert noted.

Social Aspects

Another professor explained that intimate contact had a social component as it was not common to all societies.

"However, as humans we succeed or struggle on the strength of our emotional bonds, and ways of encouraging trust and intimacy will have been significant for eons," she said. "This could represent an image that appears a bit incongruous to our misplaced ideas of a supposedly aggressive and aggressive past, but really it ought to be no surprise that Neanderthals – and including them and our human ancestors collectively – kissed."