🔗 Share this article

From seabirds to Arctic mammals, primates to great apes, various animals engage in mouth-to-mouth contact. Now, scientists propose that ancient hominins also engaged in this behavior – and possibly exchanged kisses with modern humans.

Common Microbial Clues

It is not the first time experts have suggested ancient relatives and Homo sapiens were intimately acquainted. In earlier research, researchers have found modern people and their Neanderthal relatives shared the identical oral bacteria for hundreds of thousands of years after the evolutionary divergence, implying they swapped saliva.

"Likely they were kissing," the researcher noted, adding that the idea chimed with studies that has revealed humans of certain genetic backgrounds contain ancient genetic material in their genetic makeup, demonstrating interbreeding was occurring.

Romantic Interpretation

"This offers a different perspective on ancient interactions," the lead researcher commented.

Publishing in the publication a scientific periodical, Brindle and colleagues report how, to investigate the historical roots of intimate contact, they first had to develop a description that was not limited to how humans smooch.

Defining Intimate Contact

"Previously there were some efforts to define a kiss, but it's very much been human-centric, which implies that basically other animals do not engage in this. Now we understand that they likely engage, it may appear different from what human kissing resembles," said Brindle.

Nonetheless, she said some behaviors that looked like intimate contact were distinct activities – such as the chewing and transfer of food, or "kiss-fighting", observed in aquatic species called French grunts.

Consequently the research group came up with a definition of kissing centered around friendly interactions involving directed oral interaction with a individual of the identical group, with some motion of the oral area but absence of food.

Study Approach

Brindle explained they focused on reports of intimate behavior in non-human species from the African continent and Asia, including primates, apes and great apes, and used digital recordings to verify the reports.

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

Historical Origins

The team say the findings suggest intimate contact developed somewhere between 21.5 million and 16.9m years ago in the predecessors of the large apes.

Placement of ancient hominins on this evolutionary lineage suggests it is probable they, too, engaged in a intimate act, the scientists say. But the activity might not have been confined to their own species.

"Reality that modern people engage intimately, the fact that we currently have shown that ancient relatives probably engaged, indicates that the two [species] are probably did engage," Brindle noted.

Biological Significance

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

A separate researcher in the behavior of primates commented that as intimate contact was seen in a broad spectrum of primates it was logical its roots extend far into our ancient history, and an examination of different forms of intimate behavior among a wider variety of species might extend its origins back even earlier still.

"Behaviors that we consider as signatures of human life, like kissing, are not unique to us if we examine carefully at other animals," he said.

Cultural Aspects

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

"However, as people we thrive or fail on the strength of our relationships, and ways of encouraging confidence and closeness will have been important for eons," the professor stated. "It might be an image that appears a bit contradictory to our misplaced ideas of a rather ruthless and ancient history, but really it ought to be no surprise that ancient hominins – and including them and our own species together – kissed."