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From Galápagos albatrosses to Arctic mammals, primates to orangutans, certain species appear to kiss. Now, researchers suggest that Neanderthals also engaged in this behavior – and might even have exchanged kisses with modern humans.

Shared Microbial Evidence

This isn't the initial instance experts have suggested Neanderthals and Homo sapiens were closely connected. Among earlier research, researchers have found modern people and their thick-browed cousins possessed the same mouth microbe for hundreds of thousands of years after the evolutionary divergence, implying they swapped saliva.

"Likely they were engaging in intimate contact," she said, adding that the idea aligned with studies that has revealed humans of certain genetic backgrounds contain ancient genetic material in their genome, demonstrating interbreeding was occurring.

Romantic Interpretation

"This offers a more romantic perspective on human-Neanderthal relations," the lead researcher said.

Publishing in the journal a scientific periodical, Brindle and colleagues detail how, to investigate the evolutionary origins of kissing, they first had to come up with a description that was not restricted by how humans smooch.

Defining Intimate Contact

"Previously there were some previous attempts to define a kiss, but it's very much been focused on humans, which implies that essentially non-human species don't kiss. Now we know that they likely engage, it might just not look from what our intimate contact resembles," said the evolutionary biologist.

Nonetheless, she noted some actions that looked like kissing were distinct activities – such as the chewing and transfer of food, or "kiss-fighting", observed in aquatic species known as French grunts.

Consequently the research group developed a description of kissing based on social behaviors involving directed oral interaction with a member of the same species, with some motion of the oral area but no transfer of food.

Study Approach

The lead researcher said they concentrated on reports of intimate behavior in non-human species from the African continent and Asia, including bonobos, apes and orangutans, and employed digital recordings to verify the reports.

Scientists then integrated this data with information on the evolutionary relationships between extant and extinct species of such animals.

Historical Origins

Researchers say the findings suggest kissing evolved somewhere between 21.5 million and 16.9 million years ago in the predecessors of the large apes.

Placement of Neanderthals on this evolutionary lineage means it is probable they, too, indulged in a kiss, the scientists say. But the behavior may not have been limited to their specific group.

"The fact that modern people engage intimately, the reality that we now have shown that Neanderthals very likely kissed, suggests that the both groups are probably did kissed," Brindle added.

Biological Importance

Although the scientific reasoning is discussed, the expert explained kissing could be used 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 activities of great apes commented that as intimate contact was seen in a broad spectrum of apes it was logical its roots extend far into our evolutionary past, and an analysis of various types of intimate behavior among a wider variety of animals might push its origins back further still.

"Things that we consider as signatures of our species, like intimate contact, are not exclusive to us if we look closely at different species," he said.

Cultural Aspects

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

"Nonetheless, as people we succeed or struggle on the quality of our emotional bonds, and methods of encouraging trust and closeness will have been important for eons," she said. "This could represent an concept that appears a bit contradictory to our incorrect assumptions of a supposedly aggressive and aggressive past, but really it ought to be no surprise that Neanderthals – and even Neanderthals and our human ancestors collectively – kissed."