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From Galápagos albatrosses to Arctic mammals, chimpanzees to great apes, various animals engage in mouth-to-mouth contact. Now, scientists propose that Neanderthals did it too – and possibly locked lips with early Homo sapiens.

Shared Oral Clues

It is not the first time scientists have suggested Neanderthals and Homo sapiens were closely connected. Among earlier research, scientists have discovered humans and their Neanderthal relatives possessed the identical oral bacteria for hundreds of thousands of years after the evolutionary divergence, implying they exchanged oral fluids.

"Probably they were engaging in intimate contact," the researcher noted, adding that the idea chimed with research that has found humans of non-African ancestry contain Neanderthal DNA in their genetic makeup, revealing genetic mixing was occurring.

Intimate Interpretation

"It certainly puts a more romantic perspective on ancient interactions," Brindle said.

Writing in the publication Evolution and Human Behavior, the researcher and colleagues detail how, to explore the evolutionary origins of intimate contact, they first had to develop a definition that was not limited to how humans kiss.

Describing Kissing

"Previously there were some efforts to describe a intimate act, but it's very much been human-centric, which implies that basically non-human species don't kiss. Now we understand that they probably do, it might just not look from what our intimate contact looks like," explained the evolutionary biologist.

Nonetheless, she said some actions that looked like kissing were something rather different – such as the processing and transfer of food, or "kiss-fighting", seen in aquatic species called certain marine animals.

As a result the team developed a definition of intimate contact based on social behaviors involving intentional mouth-to-mouth contact with a member of the identical group, with some motion of the mouth but absence of nutrition.

Research Methods

The lead researcher said they focused on reports of kissing in primates from the African continent and Asia, including bonobos, chimpanzees and orangutans, and employed digital recordings to verify the observations.

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

Historical Origins

Researchers propose the results indicate intimate contact developed approximately 21.5m and 16.9 million years ago in the ancestors of the great primates.

The position of Neanderthals on this evolutionary lineage suggests it is likely they, too, engaged in a intimate act, the researchers conclude. But the activity may not have been confined to their specific group.

"The fact that humans engage intimately, the fact that we now have demonstrated that ancient relatives very likely kissed, indicates that the both groups are probably did kissed," Brindle noted.

Biological Importance

While the scientific reasoning is debated, the expert explained intimate contact could be used in reproductive situations to possibly increase reproductive success or assist in selecting between partners, while it might help strengthen connections when practiced in a non-sexual manner.

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

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

Social Elements

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

"Nonetheless, as humans we thrive or fail on the strength of our relationships, and ways of encouraging confidence and intimacy will have been significant for millions of years," she said. "This could represent an image that appears a bit incongruous to our incorrect assumptions of a rather ruthless and ancient history, but really it should be no surprise that Neanderthals – and including them and our own species collectively – kissed."