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Among Galápagos albatrosses to polar bears, chimpanzees to great apes, various animals appear to kiss. Now, researchers suggest that Neanderthals did it too – and possibly locked lips with early Homo sapiens.

Shared Oral Evidence

It is not the first time experts have suggested ancient relatives and Homo sapiens were closely connected. In earlier research, researchers have found modern people and their Neanderthal relatives shared the identical oral bacteria for hundreds of thousands of years after the evolutionary divergence, implying they exchanged oral fluids.

"Likely they were kissing," she said, explaining that the idea aligned with studies that has revealed humans of certain genetic backgrounds contain Neanderthal DNA in their genetic makeup, revealing genetic mixing was occurring.

Intimate Spin

"It certainly puts a different spin on ancient interactions," Brindle commented.

Writing in the publication Evolution and Human Behavior, the researcher 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 kiss.

Describing Kissing

"Previously there were some previous attempts to define a intimate act, but it's very much been focused on humans, which implies that basically other animals don't kiss. Currently we know that they likely engage, it might just not look from what human kissing looks like," said the evolutionary biologist.

Nonetheless, she said some actions that resembled kissing were something rather different – such as the chewing and food sharing, or "kiss-fighting", observed in aquatic species called certain marine animals.

Consequently the team developed a definition of intimate contact centered around friendly interactions involving intentional mouth-to-mouth contact with a individual of the same species, with some movement of the oral area but no transfer of nutrition.

Study Methods

Brindle explained they focused on reports of intimate behavior in primates from Africa and Asian regions, including primates, chimpanzees and great apes, and used online videos to verify the reports.

The researchers then integrated this data with information on the evolutionary relationships between extant and ancient types of such primates.

Evolutionary Origins

Researchers propose the results suggest intimate contact evolved approximately 21.5m and 16.9 million years ago in the ancestors of the great primates.

The position of ancient hominins on this evolutionary lineage suggests it is likely they, too, indulged in a kiss, the researchers conclude. But the activity might not have been limited to their own species.

"The fact that humans engage intimately, the fact that we currently have demonstrated that ancient relatives probably engaged, suggests that the two [species] are also likely to have kissed," Brindle added.

Evolutionary Significance

Although the evolutionary explanation is discussed, the expert explained kissing could be employed in sexual contexts to possibly increase reproductive success or help choose between partners, while it might help reinforce bonding when practiced in a platonic way.

Another expert in the behavior of primates said that as intimate contact was seen in a broad spectrum of primates it made sense its roots extend far into our ancient history, and an analysis of different forms of intimate behavior among a wider variety of species might push its origins back even earlier still.

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

Cultural Elements

Another professor said that intimate contact had a social component as it was not common to all societies.

"However, as people we thrive or fail on the quality of our relationships, and methods of encouraging confidence and intimacy will have been important for eons," the professor stated. "It might be an image that appears a bit contradictory to our incorrect assumptions of a rather ruthless and aggressive past, but really it ought to be expected that Neanderthals – and even Neanderthals and our own species collectively – kissed."