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Among Galápagos albatrosses to Arctic mammals, primates to great apes, certain species engage in mouth-to-mouth contact. Now, scientists propose that Neanderthals also engaged in this behavior – and possibly locked lips with modern humans.

Shared Microbial Evidence

It is not the first time experts have suggested ancient relatives and early modern humans were intimately acquainted. Among earlier research, scientists have discovered humans and their thick-browed cousins possessed the identical oral bacteria for hundreds of thousands of years after the evolutionary divergence, implying they exchanged oral fluids.

"Likely they were kissing," the researcher noted, explaining that the idea chimed with studies that has revealed people of non-African ancestry contain Neanderthal DNA in their genetic makeup, revealing interbreeding was at play.

Intimate Spin

"It certainly puts a more romantic perspective on ancient interactions," the lead researcher said.

Writing in the publication a scientific periodical, Brindle and her team report how, to explore the historical roots of intimate contact, they first had to come up with a definition that was not limited to how people smooch.

Defining Kissing

"There have been some previous attempts to describe a kiss, but it's very much been human-centric, which means that essentially other animals don't kiss. Now we understand that they likely engage, it may appear different from what our intimate contact looks like," explained Brindle.

However, she said some actions that looked like kissing were something rather different – such as the chewing and food sharing, or "mouth contact", observed in aquatic species known as certain marine animals.

Consequently the research group came up with a definition of intimate contact centered around social behaviors involving directed mouth-to-mouth contact with a individual of the same species, with some movement of the oral area but absence of nutrition.

Research Approach

The lead researcher explained they concentrated on accounts of intimate behavior in primates from the African continent and Asian regions, including primates, chimpanzees and great apes, and used online videos to verify the reports.

The researchers then combined this information with details on the genetic connections between extant and ancient types of such primates.

Evolutionary Timeline

Researchers propose the findings suggest intimate contact evolved approximately 21.5 million and 16.9m years ago in the predecessors of the great primates.

The position of Neanderthals on this evolutionary lineage means it is probable they, too, engaged in a intimate act, the scientists say. But the behavior might not have been limited to their own species.

"The fact that humans kiss, the fact that we now have shown that ancient relatives probably kissed, suggests that the two [species] are also likely to have kissed," Brindle noted.

Biological Importance

While the evolutionary explanation is debated, Brindle said intimate contact could be employed in sexual contexts to potentially enhance reproductive success or assist in selecting between mates, while it could assist strengthen connections when practiced in a non-sexual manner.

Another expert in the activities of primates said that as intimate contact was observed in a broad spectrum of primates it was logical its roots extend far into our evolutionary past, and an analysis of various types of intimate behavior among a broader range of animals might extend its origins back even earlier still.

"Things that we consider as characteristics of our species, like intimate contact, are not unique to us if we look closely at other animals," the expert noted.

Cultural Elements

Another professor said that kissing had a social component as it was not universal to all societies.

"However, as humans we succeed or struggle on the quality of our relationships, and methods of promoting trust and intimacy will have been important for millions of years," she said. "This could represent an image that appears a bit contradictory to our misplaced ideas of a rather ruthless and ancient history, but actually it ought to be expected that ancient hominins – and including Neanderthals and our own species collectively – kissed."