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Among Galápagos albatrosses to polar bears, chimpanzees to great apes, various animals engage in mouth-to-mouth contact. Now, researchers suggest that Neanderthals also engaged in this behavior – and possibly locked lips with modern humans.

Shared Microbial Evidence

This isn't the initial instance scientists have proposed Neanderthals and early modern humans were intimately acquainted. In previous studies, scientists have found modern people and their Neanderthal relatives shared the same mouth microbe for millions of years after the two species split, implying they swapped saliva.

"Likely they were engaging in intimate contact," she said, adding that the concept chimed with studies that has found humans of certain genetic backgrounds contain Neanderthal DNA in their genome, revealing genetic mixing was occurring.

Intimate Interpretation

"This offers a more romantic spin on ancient interactions," Brindle commented.

Publishing in the publication a scientific periodical, Brindle and colleagues report how, to investigate the evolutionary origins of intimate contact, they first had to develop a description that was not limited to how people smooch.

Defining Intimate Contact

"Previously there were some efforts to define a intimate act, but it's largely focused on humans, which implies that essentially other animals do not engage in this. Currently we know that they likely engage, it may appear different from what human kissing resembles," explained Brindle.

However, she said some behaviors that resembled intimate contact were distinct activities – such as the chewing and food sharing, or "mouth contact", observed in fish known as certain marine animals.

Consequently the research group developed a description of kissing based on friendly interactions involving directed mouth-to-mouth contact with a member of the identical group, with some motion of the oral area but no transfer of nutrition.

Study Approach

The lead researcher said they concentrated on reports of kissing in non-human species from Africa and Asia, including primates, chimpanzees and orangutans, and employed online videos to confirm the observations.

The researchers then integrated this data with details on the genetic connections between living and extinct species of such animals.

Evolutionary Origins

The team say the results indicate kissing developed somewhere between 21.5m and 16.9m years ago in the ancestors of the large apes.

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

"Reality that humans kiss, the fact that we currently have shown that ancient relatives very likely kissed, suggests that the both groups are probably did engage," the researcher added.

Biological Importance

Although the scientific reasoning is debated, Brindle said intimate contact could be used in sexual contexts to possibly increase mating outcomes or assist in selecting between partners, while it could assist strengthen connections when practiced in a platonic way.

Another expert in the activities of great apes said that as intimate contact was observed in a broad spectrum of primates it was logical its origins lie deep in our evolutionary past, and an analysis of various types of intimate behavior among a wider variety of animals might extend its origins back even earlier still.

"Things that we think of as characteristics of human life, like intimate contact, are not unique to us if we examine carefully at other animals," he said.

Social Elements

An archaeology expert explained that intimate contact had a cultural element as it was not universal to all societies.

"However, as humans we succeed or struggle on the strength of our emotional bonds, and methods of encouraging confidence and closeness will have been important for millions of years," she said. "This could represent an image that seems a bit contradictory to our incorrect assumptions of a supposedly aggressive and aggressive past, but really it ought to be expected that Neanderthals – and including Neanderthals and our own species collectively – engaged intimately."