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Among Galápagos albatrosses to polar bears, chimpanzees to great apes, certain species appear to kiss. Now, researchers propose that Neanderthals did it too – and might even have exchanged kisses with modern humans.

Shared Oral Clues

This isn't the initial instance experts have suggested Neanderthals and Homo sapiens were intimately acquainted. In earlier research, scientists have found humans and their Neanderthal relatives possessed the same mouth microbe for millions of years after the two species split, implying they exchanged oral fluids.

"Likely they were engaging in intimate contact," the researcher noted, explaining that the concept chimed with research that has revealed people of non-African ancestry contain Neanderthal DNA in their genetic makeup, demonstrating genetic mixing was at play.

Romantic Interpretation

"It certainly puts a more romantic perspective on ancient interactions," the lead researcher commented.

Publishing in the journal Evolution and Human Behavior, Brindle and her team report how, to explore the historical roots of kissing, they first had to develop a description that was not limited to how people smooch.

Describing Intimate Contact

"Previously there were some previous attempts to define a kiss, but it's largely focused on humans, which means that essentially other animals do not engage in this. Now we know that they likely engage, it may appear different from what our intimate contact resembles," said Brindle.

Nonetheless, she noted some behaviors that resembled kissing were distinct activities – such as the chewing and transfer of food, or "mouth contact", observed in aquatic species called French grunts.

As a result the team came up with a definition of kissing based on friendly interactions involving directed mouth-to-mouth contact with a member of the identical group, with some motion of the mouth but no transfer of food.

Research Methods

Brindle said they concentrated on reports of intimate behavior in primates from the African continent and Asia, including primates, apes and great apes, and used digital recordings to confirm the reports.

Scientists then combined this information with information on the evolutionary relationships between extant and ancient species of such primates.

Historical Timeline

Researchers say the results suggest intimate contact evolved somewhere between 21.5m and 16.9m years ago in the ancestors of the large apes.

Placement of ancient hominins on this family tree suggests it is likely they, too, indulged in a intimate act, the researchers conclude. But the behavior may not have been limited to their own species.

"The fact that modern people kiss, the reality that we now have demonstrated that Neanderthals very likely engaged, suggests that the both groups are also likely to have kissed," Brindle added.

Biological Importance

Although the scientific reasoning is discussed, the expert explained intimate contact could be employed in sexual contexts to potentially increase mating outcomes or assist in selecting between partners, while it might help strengthen connections when practiced in a platonic way.

Another expert in the behavior of great apes commented that as kissing behavior was observed in a broad spectrum of primates it was logical its roots lie deep in our ancient history, and an analysis of various types of kissing among a broader range of animals might push its origins back even earlier still.

"Things that we consider as signatures of our species, like kissing, are not exclusive to us if we examine carefully at other animals," the expert noted.

Cultural Elements

An archaeology expert explained that kissing had a social component as it was not universal to all societies.

"Nonetheless, as people we thrive or fail on the strength of our emotional bonds, and methods of promoting trust and intimacy will have been important for millions of years," she said. "It might be an image that seems a bit incongruous to our misplaced ideas of a supposedly aggressive and aggressive past, but really it ought to be expected that ancient hominins – and even Neanderthals and our own species together – kissed."