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From seabirds to Arctic mammals, chimpanzees to great apes, various animals engage in mouth-to-mouth contact. Now, scientists suggest that Neanderthals also engaged in this behavior – and might even have exchanged kisses with early Homo sapiens.

Common Oral Clues

This isn't the initial instance scientists have proposed Neanderthals and early modern humans were intimately acquainted. In earlier research, researchers have found modern people and their Neanderthal relatives possessed the identical oral bacteria for millions of years after the evolutionary divergence, implying they swapped saliva.

"Probably they were engaging in intimate contact," the researcher noted, explaining that the concept aligned with studies that has revealed people of certain genetic backgrounds have bits of Neanderthal DNA in their genome, revealing genetic mixing was at play.

Romantic Spin

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

Publishing in the journal Evolution and Human Behavior, Brindle and her team detail how, to investigate the historical roots of intimate contact, they first had to come up with a definition that was not restricted by how humans kiss.

Defining Intimate Contact

"Previously there were some efforts to define a intimate act, but it's very much been focused on humans, which means that basically non-human species don't kiss. Now we know that they likely engage, it may appear different from what our intimate contact looks like," said the evolutionary biologist.

Nonetheless, she said some behaviors that resembled intimate contact were something rather different – such as the processing and transfer of food, or "mouth contact", seen in aquatic species known as French grunts.

Consequently the team developed a definition of intimate contact based on social behaviors involving directed oral interaction with a member of the same species, with some motion of the oral area but absence of food.

Study Approach

Brindle explained they focused on accounts of intimate behavior in non-human species from Africa and Asia, including primates, apes and orangutans, and employed online videos to confirm the observations.

Scientists then combined this information with details on the genetic connections between living and ancient types of such primates.

Evolutionary Timeline

The team say the findings suggest kissing evolved somewhere between 21.5 million and 16.9 million years ago in the predecessors of the great primates.

Placement of Neanderthals on this evolutionary lineage 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 humans kiss, the reality that we currently have shown that Neanderthals very likely kissed, suggests that the both groups are also likely to have engage," Brindle added.

Biological Importance

While the scientific reasoning is debated, Brindle said kissing could be employed in sexual contexts to possibly increase mating outcomes or assist in selecting between partners, while it could assist reinforce bonding when used in a non-sexual manner.

Another expert in the behavior of great apes commented that as kissing behavior was seen in a wide range of apes it made sense its origins extend far into our ancient history, and an examination of various types of kissing among a broader range of animals might extend its origins back further still.

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

Cultural Elements

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

"However, as people we succeed or struggle on the strength of our emotional bonds, and methods of encouraging trust and intimacy will have been significant for eons," the professor stated. "It might be an image that appears a bit contradictory to our incorrect assumptions of a rather ruthless and aggressive past, but actually it ought to be expected that Neanderthals – and even Neanderthals and our own species together – engaged intimately."