Ancient Hominins and Modern Humans Were Likely Engaging in Intimate Contact, Researchers Propose

From Galápagos albatrosses to Arctic mammals, primates to orangutans, certain species appear to kiss. Now, scientists propose that Neanderthals did it too – and might even have locked lips with early Homo sapiens.

Shared Oral Clues

It is not the first time scientists have proposed ancient relatives and early modern humans were intimately acquainted. Among previous studies, researchers have discovered modern people and their thick-browed cousins possessed the same mouth microbe for hundreds of thousands of years after the evolutionary divergence, implying they swapped saliva.

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

Romantic Interpretation

"This offers a different spin on human-Neanderthal relations," the lead researcher said.

Publishing in the publication Evolution and Human Behavior, the researcher and her team detail how, to investigate the evolutionary origins of intimate contact, they first had to come up with a definition that was not restricted by how humans kiss.

Describing Kissing

"There have been some previous attempts to define a intimate act, but it's largely focused on humans, which implies that essentially non-human species don't kiss. Now we understand that they probably do, it may appear different from what our intimate contact looks like," explained Brindle.

However, she noted some behaviors that resembled intimate contact were something rather different – such as the processing and food sharing, or "kiss-fighting", seen in fish known as French grunts.

As a result the research group came up with a definition of kissing centered around friendly interactions involving directed mouth-to-mouth contact with a individual of the identical group, with some motion of the oral area but no transfer of nutrition.

Study Approach

The lead researcher said they focused on reports of intimate behavior in non-human species from Africa and Asia, including primates, apes and orangutans, and used online videos to verify the observations.

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

Evolutionary Timeline

Researchers say the results indicate intimate contact developed approximately 21.5 million and 16.9 million years ago in the ancestors of the large apes.

Placement of ancient hominins on this family tree means it is probable they, too, indulged in a kiss, the scientists say. But the behavior might not have been limited to their own species.

"Reality that modern people engage intimately, the fact that we currently have shown that ancient relatives very likely engaged, indicates that the both groups are also likely to have kissed," Brindle added.

Biological Importance

While the scientific reasoning is discussed, Brindle explained kissing could be used in sexual contexts to potentially enhance mating outcomes or help choose between partners, while it might help strengthen connections when practiced in a non-sexual manner.

A separate researcher in the activities of great apes said that as intimate contact was seen in a wide range of apes it made sense its roots extend far into our evolutionary past, and an examination of various types of intimate behavior among a broader range of animals might extend its beginnings back even earlier still.

"Behaviors that we consider as signatures of our species, like intimate contact, are not exclusive to us if we examine carefully at different species," the expert noted.

Social Elements

Another professor explained that kissing had a cultural element 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 promoting confidence and intimacy will have been significant for eons," she said. "It might be an concept that appears a bit contradictory to our misplaced ideas of a rather ruthless and ancient history, but actually it should be expected that ancient hominins – and even Neanderthals and our own species together – engaged intimately."