🔗 Share this article

From seabirds to polar bears, primates to orangutans, certain species engage in mouth-to-mouth contact. Currently, scientists propose that ancient hominins did it too – and might even have locked lips with early Homo sapiens.

Common Oral Clues

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

"Probably they were engaging in intimate contact," the researcher noted, adding that the idea aligned with studies that has found people of certain genetic backgrounds contain Neanderthal DNA in their genome, demonstrating genetic mixing was occurring.

Romantic Interpretation

"It certainly puts a more romantic spin on ancient interactions," Brindle commented.

Publishing in the journal Evolution and Human Behavior, Brindle and colleagues detail how, to investigate the evolutionary origins of intimate contact, they first had to develop a definition that was not limited to how people smooch.

Describing Kissing

"There have been some efforts to describe a kiss, but it's very much been human-centric, which means that basically other animals don't kiss. Now we know that they probably do, it may appear different from what human kissing resembles," said Brindle.

However, she noted some actions that looked like intimate contact were distinct activities – such as the processing and transfer of food, or "mouth contact", seen in aquatic species called French grunts.

Consequently the team developed 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 mouth but absence of food.

Research Methods

The lead researcher explained they concentrated on reports of kissing in non-human species from the African continent and Asia, including bonobos, chimpanzees and great apes, and employed digital recordings to verify the observations.

Scientists then integrated this data with information on the genetic connections between extant and extinct types of such animals.

Evolutionary Origins

Researchers say the findings suggest kissing evolved approximately 21.5m and 16.9m years ago in the ancestors of the great primates.

Placement of Neanderthals on this family tree suggests it is likely they, too, indulged in a intimate act, the scientists say. But the behavior might not have been confined to their specific group.

"The fact that modern people engage intimately, the reality that we currently have demonstrated that Neanderthals probably kissed, suggests that the both groups are probably did engage," the researcher noted.

Biological Significance

Although the scientific reasoning is discussed, Brindle said intimate contact could be used in reproductive situations to potentially enhance mating outcomes or help choose between mates, while it could assist reinforce bonding when practiced in a non-sexual manner.

Another expert in the behavior of great apes said that as intimate contact was observed in a broad spectrum of apes it made sense its origins extend far into our evolutionary past, and an examination of various types of intimate behavior among a wider variety of animals might extend its origins back even earlier still.

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

Social Elements

An archaeology expert said that kissing had a social component as it was not universal to all human groups.

"However, as humans we succeed or struggle on the quality of our emotional bonds, and methods of promoting confidence and closeness will have been important for eons," she said. "This could represent an concept that appears a bit incongruous to our misplaced ideas of a supposedly aggressive and ancient history, but really it should be expected that Neanderthals – and including them and our own species collectively – engaged intimately."