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Among Galápagos albatrosses to Arctic mammals, chimpanzees to great apes, various animals appear to kiss. Now, scientists propose that ancient hominins did it too – and might even have locked lips with early Homo sapiens.

Shared Oral Evidence

It is not the first time experts have proposed ancient relatives and early modern humans were closely connected. Among earlier research, researchers have found modern people and their Neanderthal relatives possessed the same mouth microbe for hundreds of thousands of years after the two species split, suggesting they swapped saliva.

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

Romantic Spin

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

Writing in the publication a scientific periodical, the researcher and colleagues report how, to investigate the historical roots of intimate contact, they first had to develop a definition that was not limited to how people kiss.

Defining Intimate Contact

"Previously there were some efforts to describe a kiss, but it's largely human-centric, which means that basically non-human species do not engage in this. Now we understand that they probably do, it may appear different from what our intimate contact resembles," said the evolutionary biologist.

However, she said some behaviors that resembled kissing were distinct activities – such as the processing and food sharing, or "kiss-fighting", seen in aquatic species known as French grunts.

As a result the research group developed a description of intimate contact based on social behaviors involving directed oral interaction with a member of the identical group, with some movement of the oral area but absence of nutrition.

Research Approach

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

The researchers then combined this data with information on the evolutionary relationships between extant and extinct species of such animals.

Historical Timeline

Researchers propose the results suggest intimate contact developed somewhere between 21.5 million and 16.9 million years ago in the ancestors of the great primates.

The position of Neanderthals on this family tree means it is likely they, too, engaged in a kiss, the scientists say. But the behavior might not have been limited to their specific group.

"Reality that modern people engage intimately, the reality that we currently have demonstrated that Neanderthals probably kissed, indicates that the two [species] are also likely to have kissed," Brindle added.

Biological Significance

While the scientific reasoning is discussed, the expert said intimate contact could be employed in reproductive situations to possibly enhance reproductive success or assist in selecting between mates, while it might help strengthen connections when practiced in a platonic way.

Another expert in the activities of great apes commented that as intimate contact was observed in a broad spectrum of primates it made sense its roots lie deep in our ancient history, and an analysis of various types of kissing among a broader range of species might push its beginnings back further still.

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

Cultural Aspects

An archaeology expert said that intimate contact had a cultural element as it was not common to all human groups.

"Nonetheless, as people we thrive or fail on the quality of our emotional bonds, and methods of encouraging confidence and closeness will have been important for millions of years," the professor stated. "This could represent an concept that appears a bit incongruous to our misplaced ideas of a rather ruthless and aggressive past, but really it ought to be no surprise that ancient hominins – and even Neanderthals and our human ancestors collectively – kissed."