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From Galápagos albatrosses to Arctic mammals, primates to great apes, various animals appear to kiss. Now, researchers propose that Neanderthals did it too – and possibly exchanged kisses with modern humans.

Common Microbial Evidence

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

"Probably they were kissing," she said, explaining that the concept chimed with studies that has revealed humans of certain genetic backgrounds contain ancient genetic material in their genome, revealing genetic mixing was at play.

Romantic Interpretation

"This offers a different spin on ancient interactions," the lead researcher commented.

Writing in the journal Evolution and Human Behavior, the researcher and her team report how, to investigate the evolutionary origins of kissing, they first had to develop a description that was not restricted by how humans smooch.

Describing Intimate Contact

"Previously there were some previous attempts to describe a kiss, but it's very much been human-centric, which implies that essentially other animals don't kiss. Now we understand that they likely engage, it may appear different from what human kissing looks like," explained the evolutionary biologist.

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

Consequently the team came up with a description of kissing based on social behaviors involving directed oral interaction with a member of the identical group, with some motion of the mouth but no transfer of food.

Study Methods

The lead researcher said they focused on reports of intimate behavior in non-human species from Africa and Asia, including primates, chimpanzees and great apes, and employed digital recordings to verify the reports.

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

Historical Timeline

Researchers propose the findings indicate intimate contact developed somewhere between 21.5 million and 16.9m years ago in the ancestors of the large apes.

Placement of ancient hominins on this evolutionary lineage suggests it is likely they, too, engaged in a kiss, the scientists conclude. But the behavior might 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 two [species] are probably did engage," Brindle noted.

Evolutionary Significance

While the scientific reasoning is discussed, Brindle explained intimate contact could be used in sexual contexts to possibly enhance reproductive success or assist in selecting between mates, while it could assist strengthen connections when practiced in a non-sexual manner.

A separate researcher in the behavior of great apes commented that as kissing behavior was observed in a broad spectrum of primates it was logical its origins extend far into our ancient history, and an analysis of different forms of intimate behavior among a wider variety of animals might extend its beginnings back even earlier still.

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

Cultural Aspects

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

"However, as humans we succeed or struggle on the quality of our emotional bonds, and ways of encouraging confidence and closeness will have been important for millions of years," she said. "It might be an concept that seems a bit contradictory to our misplaced ideas of a rather ruthless and aggressive past, but really it ought to be no surprise that ancient hominins – and even them and our human ancestors collectively – kissed."