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Among seabirds to polar bears, chimpanzees to great apes, certain species appear to kiss. Now, scientists propose that Neanderthals did it too – and possibly locked lips with modern humans.

Common Microbial Evidence

It is not the first time scientists have proposed Neanderthals and Homo sapiens were closely connected. Among earlier research, researchers have discovered modern people and their Neanderthal relatives possessed the identical oral bacteria for millions of years after the evolutionary divergence, implying they exchanged oral fluids.

"Likely they were engaging in intimate contact," the researcher noted, adding that the idea aligned with studies that has revealed people of non-African ancestry contain Neanderthal DNA in their genetic makeup, demonstrating genetic mixing was occurring.

Intimate Interpretation

"It certainly puts a more romantic spin on ancient interactions," the lead researcher said.

Writing in the journal Evolution and Human Behavior, the researcher and her team detail how, to explore the evolutionary origins of intimate contact, they first had to develop a definition that was not limited to how people smooch.

Describing Intimate Contact

"Previously there were some efforts to describe a kiss, but it's largely focused on humans, which means that basically other animals do not engage in this. Currently we know that they likely engage, it may appear different from what our intimate contact looks like," explained Brindle.

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

As a result the research group developed a description of intimate contact centered around friendly interactions involving intentional 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 explained they focused on accounts of intimate behavior in non-human species from Africa and Asia, including bonobos, chimpanzees and great apes, and employed digital recordings to verify the reports.

The researchers then combined this information with details on the evolutionary relationships between living and ancient species of such animals.

Historical Timeline

Researchers propose the results suggest intimate contact evolved approximately 21.5 million and 16.9 million years ago in the ancestors of the great primates.

Placement of ancient hominins on this evolutionary lineage means it is likely they, too, engaged in a intimate act, the scientists conclude. But the behavior might not have been confined to their specific group.

"Reality that modern people engage intimately, the fact that we currently have shown that ancient relatives very likely engaged, suggests that the both groups are also likely to have engage," Brindle added.

Evolutionary Significance

While the scientific reasoning is debated, Brindle explained kissing could be employed in reproductive situations to possibly enhance reproductive success or assist in selecting between partners, while it might help strengthen connections when used in a platonic way.

Another expert in the behavior of primates commented that as intimate contact was seen in a broad spectrum of apes it was logical its roots lie deep in our evolutionary past, and an examination of various types of intimate behavior among a broader range of species might push its beginnings back even earlier still.

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

Social Aspects

Another professor said that intimate contact had a cultural element as it was not common to all human groups.

"However, as people we thrive or fail on the quality of our emotional bonds, and ways of promoting confidence and intimacy will have been important for eons," the professor stated. "It might be an concept that seems a bit contradictory to our incorrect assumptions of a supposedly aggressive and ancient history, but actually it ought to be expected that Neanderthals – and including Neanderthals and our human ancestors collectively – engaged intimately."