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From seabirds to polar bears, chimpanzees to great apes, various animals appear to kiss. Now, scientists propose that Neanderthals did it too – and might even have exchanged kisses with early Homo sapiens.

Shared Oral Evidence

It is not the first time scientists have suggested ancient relatives and early modern humans 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, suggesting they exchanged oral fluids.

"Likely they were engaging in intimate contact," she said, adding that the idea chimed with research that has found people of certain genetic backgrounds contain Neanderthal DNA in their genome, demonstrating genetic mixing was occurring.

Romantic Interpretation

"This offers a different spin on human-Neanderthal relations," Brindle commented.

Writing in the journal a scientific periodical, Brindle and her team detail how, to explore the evolutionary origins of intimate contact, they first had to come up with a description that was not limited to how people kiss.

Defining Intimate Contact

"Previously there were some previous attempts to define a kiss, but it's very much been human-centric, which implies that basically other animals do not engage in this. Currently we know that they likely engage, it may appear different from what human kissing looks like," explained Brindle.

However, she noted some actions that looked like intimate contact were distinct activities – such as the processing and transfer of food, or "kiss-fighting", seen in aquatic species called French grunts.

Consequently the team came up with a definition of kissing based on friendly interactions involving intentional mouth-to-mouth contact with a member of the identical group, with some motion of the oral area but no transfer of nutrition.

Research Approach

The lead researcher said they concentrated on reports of intimate behavior in primates from Africa and Asia, including bonobos, chimpanzees and great apes, and used online videos to verify the reports.

The researchers then combined this information with details on the genetic connections between extant and extinct species of such animals.

Historical Origins

Researchers say the findings indicate intimate contact developed approximately 21.5 million and 16.9 million years ago in the ancestors of the large apes.

Placement of Neanderthals on this evolutionary lineage means it is probable they, too, engaged in a kiss, the researchers conclude. But the activity might not have been confined to their specific group.

"The fact that modern people kiss, the reality that we currently have demonstrated that ancient relatives very likely kissed, indicates that the two [species] are also likely to have engage," Brindle noted.

Evolutionary Significance

Although the evolutionary explanation is discussed, Brindle explained intimate contact could be used in reproductive situations to possibly enhance reproductive success or help choose between mates, while it could assist strengthen connections when used in a platonic way.

A separate researcher in the behavior of great apes commented that as kissing behavior was observed 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 wider variety of animals might extend its beginnings back further still.

"Things that we think of as characteristics of our species, like kissing, are not unique to us if we look closely at other animals," he said.

Cultural Elements

Another professor explained that kissing had a social component as it was not universal to all human groups.

"Nonetheless, as humans we succeed or struggle on the strength of our emotional bonds, and methods of encouraging confidence and closeness will have been significant for eons," the professor stated. "It might be an concept that seems a bit incongruous to our misplaced ideas of a supposedly aggressive and aggressive past, but actually it ought to be expected that Neanderthals – and including them and our own species together – kissed."