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From seabirds to Arctic mammals, primates to great apes, certain species engage in mouth-to-mouth contact. Currently, scientists suggest that Neanderthals did it too – and might even have locked lips with early Homo sapiens.

Common Microbial Evidence

It is not the first time experts have proposed Neanderthals and Homo sapiens were closely connected. Among previous studies, researchers have discovered humans and their Neanderthal relatives possessed the identical oral bacteria for hundreds of thousands of years after the two species split, implying they exchanged oral fluids.

"Probably they were kissing," the researcher noted, explaining that the idea chimed with research that has found humans of certain genetic backgrounds contain Neanderthal DNA in their genome, demonstrating genetic mixing was at play.

Intimate Spin

"It certainly puts a different perspective on ancient interactions," Brindle said.

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

Defining Kissing

"There have been some previous attempts to describe a kiss, but it's very much been focused on humans, which means that essentially non-human species don't kiss. Now we know that they probably do, it may appear different from what human kissing looks like," said Brindle.

Nonetheless, she said some behaviors that looked like kissing were something rather different – such as the chewing and transfer of food, or "kiss-fighting", seen in fish known as French grunts.

As a result the research group came up with a description of kissing centered around social behaviors involving intentional oral interaction with a individual of the same species, with some movement of the oral area but no transfer of food.

Study Methods

The lead researcher said they focused on reports of intimate behavior in primates from Africa and Asian regions, including bonobos, chimpanzees and orangutans, and used digital recordings to verify the reports.

Scientists then integrated this information with details on the genetic connections between extant and ancient species of such primates.

Historical Timeline

Researchers propose the results indicate kissing developed approximately 21.5m and 16.9m years ago in the predecessors of the large apes.

Placement of ancient hominins on this evolutionary lineage means it is likely they, too, engaged in a kiss, the researchers conclude. But the behavior might not have been limited to their own species.

"The fact that modern people engage intimately, the reality that we now have demonstrated that ancient relatives probably kissed, suggests that the both groups are probably did kissed," Brindle added.

Evolutionary Significance

Although the scientific reasoning is discussed, Brindle said intimate contact could be used in sexual contexts to potentially increase reproductive success or assist in selecting between partners, while it might help reinforce bonding when practiced in a non-sexual manner.

Another expert in the activities of great apes said that as intimate contact was seen in a broad spectrum of primates it was logical its origins lie deep in our ancient history, and an examination of various types of intimate behavior among a wider variety of animals might extend its origins back even earlier still.

"Behaviors that we think of as signatures of our species, like kissing, are not exclusive to us if we look closely at different species," the expert noted.

Social Elements

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

"However, as people we thrive or fail on the quality of our emotional bonds, and methods of promoting confidence and closeness will have been important for eons," the professor stated. "This could represent an image that appears a bit incongruous to our misplaced ideas of a rather ruthless and ancient history, but actually it ought to be no surprise that ancient hominins – and even them and our human ancestors together – engaged intimately."