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Among Galápagos albatrosses to Arctic mammals, primates to orangutans, various animals appear to kiss. Now, scientists propose that ancient hominins did it too – and possibly exchanged kisses with modern humans.

Common Microbial Evidence

It is not the first time scientists have proposed ancient relatives and early modern humans were closely connected. Among previous studies, researchers have found modern people and their thick-browed cousins possessed the identical oral bacteria for hundreds of thousands of years after the evolutionary divergence, suggesting they exchanged oral fluids.

"Probably they were kissing," she said, adding that the idea aligned with research that has revealed humans of non-African ancestry contain Neanderthal DNA in their genome, revealing genetic mixing was at play.

Romantic Interpretation

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

Writing in the publication a scientific periodical, Brindle and colleagues report how, to explore the historical roots of kissing, they first had to come up with a description that was not limited to how humans kiss.

Describing Intimate Contact

"Previously there were some efforts to describe a intimate act, but it's very much been focused on humans, which implies that basically non-human species do not engage in this. Currently we know that they probably do, it may appear different from what our intimate contact resembles," said Brindle.

However, she said some behaviors that resembled intimate contact were something rather different – such as the processing and transfer of food, or "kiss-fighting", seen in aquatic species known as certain marine animals.

Consequently the team came up with a definition of kissing based on social behaviors involving intentional oral interaction with a member of the identical group, with some movement of the oral area but absence of food.

Research Methods

The lead researcher said they concentrated on reports of kissing in primates from Africa and Asia, including bonobos, apes and great apes, and used online videos to verify the reports.

The researchers then integrated this data with information on the evolutionary relationships between extant and ancient types of such primates.

Evolutionary Timeline

The team propose the results indicate intimate contact developed somewhere between 21.5m and 16.9 million years ago in the predecessors of the large apes.

Placement of Neanderthals on this evolutionary lineage means it is likely they, too, indulged in a intimate act, the researchers say. But the activity may not have been limited to their own species.

"The fact that humans kiss, the reality that we currently have shown that ancient relatives probably kissed, suggests that the two [species] are probably did kissed," Brindle added.

Evolutionary Importance

Although the evolutionary explanation is discussed, Brindle said kissing could be employed in sexual contexts to possibly enhance mating outcomes or assist in selecting between partners, while it might help strengthen connections when used in a platonic way.

Another expert in the behavior of great apes said that as kissing behavior was seen in a wide range of apes it was logical its roots lie deep in our ancient history, and an analysis of different forms of kissing among a broader range of animals might push its origins back even earlier still.

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

Social Aspects

An archaeology expert said that kissing had a cultural element as it was not universal to all societies.

"Nonetheless, as humans we thrive or fail on the strength of our emotional bonds, and methods of encouraging confidence and intimacy will have been significant for millions of years," the professor stated. "It might be an image that seems a bit contradictory to our misplaced ideas of a supposedly aggressive and ancient history, but actually it should be no surprise that Neanderthals – and including them and our own species collectively – kissed."