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From Galápagos albatrosses to Arctic mammals, chimpanzees to orangutans, various animals engage in mouth-to-mouth contact. Now, scientists propose that Neanderthals did it too – and might even have locked lips with modern humans.

Common Oral Evidence

It is not the first time scientists have suggested ancient relatives and Homo sapiens were intimately acquainted. Among earlier research, researchers have found modern people and their Neanderthal relatives shared the identical oral bacteria for hundreds of thousands of years after the two species split, suggesting they exchanged oral fluids.

"Probably they were engaging in intimate contact," she said, explaining that the concept aligned with research that has found humans of non-African ancestry have bits of Neanderthal DNA in their genome, revealing genetic mixing was occurring.

Intimate Spin

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

Publishing in the publication Evolution and Human Behavior, Brindle and her team detail how, to investigate the historical roots of kissing, they first had to come up with a description that was not restricted by how humans kiss.

Defining Intimate Contact

"Previously there were some previous attempts to define a kiss, but it's largely focused on humans, which implies that basically other animals do not engage in this. Currently we know that they probably do, it may appear different from what human kissing looks like," explained Brindle.

However, she noted some behaviors that resembled kissing were something rather different – such as the chewing and transfer of food, or "mouth contact", seen in fish called certain marine animals.

Consequently the research group developed a description of intimate contact centered around friendly interactions involving intentional mouth-to-mouth contact with a member of the identical group, with some motion of the mouth but no transfer of food.

Study Methods

Brindle said they focused on reports of kissing in non-human species from the African continent and Asian regions, including bonobos, apes and orangutans, and used digital recordings to confirm the reports.

Scientists then combined this data with details on the genetic connections between extant and extinct types of such primates.

Evolutionary Origins

Researchers propose 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 ancient hominins on this family tree suggests it is likely they, too, engaged in a kiss, the researchers say. But the activity may not have been limited to their own species.

"Reality that humans engage intimately, the reality that we now have shown that ancient relatives probably kissed, indicates that the two [species] are probably did engage," the researcher noted.

Evolutionary Significance

Although the evolutionary explanation is debated, the expert said intimate contact could be used in reproductive situations to possibly enhance mating outcomes or help choose between mates, while it might help reinforce bonding when used in a platonic way.

Another expert in the behavior of great apes commented that as intimate contact was observed in a broad spectrum of primates it made sense its roots lie deep in our ancient history, and an examination of different forms of kissing among a broader range of animals might push its origins back further still.

"Things 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

An archaeology expert explained that kissing had a cultural element as it was not common to all societies.

"However, as people we succeed or struggle on the strength of our emotional bonds, and methods of encouraging confidence and closeness will have been important for eons," the professor stated. "This could represent an image that appears a bit contradictory to our misplaced ideas of a supposedly aggressive and aggressive past, but really it ought to be no surprise that Neanderthals – and including Neanderthals and our own species collectively – kissed."