🔗 Share this article

Among Galápagos albatrosses to Arctic mammals, chimpanzees to orangutans, various animals engage in mouth-to-mouth contact. Now, scientists propose that ancient hominins did it too – and possibly locked lips with early Homo sapiens.

Common Oral Clues

It is not the first time scientists have proposed ancient relatives and Homo sapiens were intimately acquainted. In previous studies, scientists have discovered 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 kissing," she said, adding that the concept aligned with research that has revealed humans of non-African ancestry have bits of ancient genetic material in their genome, revealing interbreeding was occurring.

Romantic Interpretation

"This offers a different perspective on ancient interactions," Brindle said.

Writing in the publication Evolution and Human Behavior, the researcher and colleagues detail how, to investigate the historical roots of kissing, they first had to come up with a definition that was not limited to how humans kiss.

Describing Intimate Contact

"Previously there were some efforts to describe a intimate act, but it's largely focused on humans, which implies that basically other animals don't kiss. Currently we understand that they probably do, it may appear different from what our intimate contact resembles," said Brindle.

Nonetheless, she noted some behaviors that looked like intimate contact were distinct activities – such as the processing and transfer of food, or "mouth contact", observed in fish called French grunts.

Consequently the research group developed a definition of intimate contact centered around social behaviors involving directed oral interaction with a individual of the identical group, with some motion of the mouth but no transfer of nutrition.

Study Methods

Brindle said they focused on accounts of kissing in non-human species from Africa and Asian regions, including bonobos, apes and great apes, and used online videos to confirm the observations.

The researchers then integrated this information with information on the genetic connections between living and ancient species of such animals.

Evolutionary Timeline

The team say the findings indicate 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 family tree suggests it is probable they, too, indulged in a kiss, the scientists say. But the behavior may not have been confined to their own species.

"Reality that humans engage intimately, the fact that we currently have shown that ancient relatives probably engaged, suggests that the two [species] are also likely to have kissed," Brindle noted.

Evolutionary Significance

Although the evolutionary explanation is debated, the expert said kissing could be used in reproductive situations to possibly enhance reproductive success or assist in selecting between mates, while it might help strengthen connections when practiced in a non-sexual manner.

Another expert in the behavior of great apes commented that as kissing behavior was seen in a wide range of primates it made sense its origins lie deep in our evolutionary past, and an examination of different forms of kissing among a wider variety of animals might push its origins back even earlier still.

"Things that we consider as characteristics of our species, like intimate contact, are not exclusive to us if we examine carefully at other animals," he said.

Cultural Elements

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

"However, as people we thrive or fail on the strength of our emotional bonds, and methods of promoting trust and closeness will have been significant for eons," she said. "This could represent an concept that appears a bit incongruous to our misplaced ideas of a supposedly aggressive and aggressive past, but really it should be no surprise that Neanderthals – and even them and our own species together – engaged intimately."