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Among Galápagos albatrosses to Arctic mammals, primates to orangutans, certain species engage in mouth-to-mouth contact. Currently, researchers suggest that Neanderthals did it too – and might even have locked lips with early Homo sapiens.

Shared Microbial Clues

It is not the first time scientists have proposed ancient relatives and Homo sapiens were closely connected. In earlier research, scientists have found humans and their Neanderthal relatives shared the same mouth microbe for millions of years after the evolutionary divergence, implying they swapped saliva.

"Likely they were kissing," she said, adding that the idea aligned with studies that has found people of certain genetic backgrounds have bits of Neanderthal DNA in their genetic makeup, demonstrating genetic mixing was at play.

Intimate Spin

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

Publishing in the journal a scientific periodical, the researcher and her team detail how, to explore the historical roots of kissing, they first had to develop a description that was not restricted by how humans kiss.

Describing Kissing

"Previously there were some previous attempts to describe a intimate act, but it's largely focused on humans, which implies that basically non-human species do not engage in this. Now we understand that they likely engage, it might just not look from what our intimate contact resembles," explained the evolutionary biologist.

Nonetheless, she said some behaviors that looked like intimate contact were something rather different – such as the processing and food sharing, or "kiss-fighting", observed in aquatic species called French grunts.

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

Study Methods

The lead researcher explained they focused on accounts of intimate behavior in non-human species from Africa and Asia, including bonobos, chimpanzees and orangutans, and employed digital recordings to verify the observations.

The researchers then combined this data with details on the evolutionary relationships between living and ancient types of such animals.

Historical Origins

The team propose the findings suggest kissing evolved somewhere between 21.5m and 16.9m years ago in the predecessors of the great primates.

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

"Reality that modern people engage intimately, the reality that we now have shown that ancient relatives probably engaged, suggests that the both groups are also likely to have kissed," the researcher noted.

Biological Significance

Although the evolutionary explanation is discussed, the expert explained intimate contact could be employed in reproductive situations to potentially enhance reproductive success or help choose between partners, while it could assist strengthen connections when practiced in a platonic way.

Another expert in the activities of primates commented that as intimate contact was observed in a wide range of apes it was logical its roots lie deep in our evolutionary past, and an examination of various types of kissing among a broader range of species might extend its origins back even earlier still.

"Behaviors that we consider as characteristics of our species, like kissing, are not unique to us if we look closely at other animals," he said.

Cultural Aspects

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

"However, as people we succeed or struggle on the strength of our relationships, and ways of encouraging confidence and intimacy will have been important for millions of years," the professor stated. "This could represent an concept that seems a bit incongruous to our misplaced ideas of a supposedly aggressive and ancient history, but really it ought to be no surprise that ancient hominins – and including Neanderthals and our human ancestors collectively – kissed."