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From Galápagos albatrosses to Arctic mammals, primates to orangutans, various animals appear to kiss. Now, scientists propose that Neanderthals also engaged in this behavior – and possibly exchanged kisses with early Homo sapiens.

Common Microbial Evidence

It is not the first time experts have proposed Neanderthals and early modern humans were intimately acquainted. Among previous studies, researchers have discovered modern people and their thick-browed cousins shared the identical oral bacteria for hundreds of thousands of years after the two species split, suggesting they swapped saliva.

"Likely they were engaging in intimate contact," she said, adding that the idea aligned with studies that has found humans of non-African ancestry contain ancient genetic material in their genetic makeup, revealing genetic mixing was at play.

Intimate Interpretation

"This offers a more romantic perspective on ancient interactions," the lead researcher commented.

Publishing in the publication Evolution and Human Behavior, Brindle and colleagues detail how, to explore the evolutionary origins of intimate contact, they first had to come up with a definition that was not limited to how humans kiss.

Defining Intimate Contact

"There have been some efforts to define a kiss, but it's very much been focused on humans, which means that basically other animals don't kiss. Now we understand that they probably do, it might just not look from what human kissing resembles," said Brindle.

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

Consequently the research group came up with a description of kissing centered around friendly interactions involving intentional oral interaction with a member of the same species, with some movement of the oral area but absence of nutrition.

Study Approach

The lead researcher explained they concentrated on accounts of intimate behavior in non-human species from Africa and Asian regions, including primates, chimpanzees and great apes, and used digital recordings to confirm the observations.

Scientists then integrated this information with information on the evolutionary relationships between living and ancient types of such animals.

Evolutionary Origins

Researchers say the results suggest intimate contact developed approximately 21.5 million and 16.9 million years ago in the predecessors of the large apes.

Placement of Neanderthals on this family tree means it is likely they, too, engaged in a intimate act, the researchers conclude. But the behavior may not have been limited to their specific group.

"The fact that humans engage intimately, the reality that we now have demonstrated that ancient relatives probably kissed, suggests that the both groups are probably did engage," the researcher noted.

Biological Significance

While the scientific reasoning is discussed, the expert explained intimate contact could be employed in sexual contexts to potentially enhance reproductive success or help choose between partners, while it might help strengthen connections when used in a platonic way.

Another expert in the behavior of primates said that as kissing behavior was observed in a wide range of primates 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 animals might push its beginnings back further still.

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

Cultural Elements

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

"Nonetheless, as humans we succeed or struggle on the strength of our relationships, and ways of encouraging confidence and intimacy will have been important for eons," the professor stated. "It might be an image that seems a bit contradictory to our incorrect assumptions of a rather ruthless and aggressive past, but actually it should be expected that ancient hominins – and including Neanderthals and our own species collectively – kissed."