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From seabirds to Arctic mammals, chimpanzees to great apes, certain species appear to kiss. Now, scientists propose that ancient hominins also engaged in this behavior – and possibly exchanged kisses with modern humans.

Shared Oral Clues

It is not the first time scientists have proposed 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, suggesting they swapped saliva.

"Probably they were kissing," she said, adding that the concept chimed with research that has revealed humans of certain genetic backgrounds contain Neanderthal DNA in their genome, revealing interbreeding was occurring.

Romantic Interpretation

"It certainly puts a more romantic perspective on human-Neanderthal relations," Brindle commented.

Writing in the journal a scientific periodical, the researcher and her team detail how, to explore the evolutionary origins of intimate contact, they first had to develop a definition that was not limited to how humans smooch.

Describing Intimate Contact

"There have been some efforts to describe a intimate act, but it's largely human-centric, which implies that essentially non-human species don't kiss. Now we know that they likely engage, it might just not look from what human kissing resembles," explained Brindle.

Nonetheless, she noted some behaviors that resembled intimate contact were something rather different – such as the processing and food sharing, or "mouth contact", observed in fish known as French grunts.

Consequently the team developed a description of kissing centered around friendly interactions involving directed oral interaction with a member of the identical group, with some motion of the oral area but absence of nutrition.

Study Approach

Brindle said they concentrated on reports of kissing in non-human species from Africa and Asian regions, including bonobos, chimpanzees and orangutans, and employed online videos to confirm the reports.

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

Evolutionary Timeline

Researchers say the results suggest kissing evolved approximately 21.5m and 16.9 million years ago in the predecessors of the great primates.

The position of ancient hominins on this evolutionary lineage suggests it is likely they, too, indulged in a intimate act, the scientists conclude. But the activity might not have been confined to their specific group.

"The fact that modern people engage intimately, the reality that we now have shown that ancient relatives very likely kissed, indicates that the both groups are also likely to have kissed," Brindle added.

Evolutionary Significance

While the evolutionary explanation is discussed, Brindle said kissing could be employed in reproductive situations to potentially increase reproductive success or assist in selecting between partners, while it might help strengthen connections when used in a platonic way.

A separate researcher in the activities of primates said that as kissing behavior was seen in a wide range of primates it was logical its origins lie deep in our evolutionary past, and an analysis of different forms of intimate behavior among a wider variety of animals might extend its beginnings back even earlier still.

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

Cultural Aspects

Another professor explained that intimate contact had a cultural element as it was not common to all human groups.

"Nonetheless, as humans we thrive or fail on the quality of our emotional bonds, and methods of encouraging trust and intimacy will have been important for eons," she said. "This could represent an image that appears a bit incongruous to our incorrect assumptions of a supposedly aggressive and aggressive past, but actually it ought to be expected that ancient hominins – and even Neanderthals and our own species together – engaged intimately."