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From Galápagos albatrosses to Arctic mammals, primates to orangutans, various animals engage in mouth-to-mouth contact. Now, researchers propose that ancient hominins did it too – and possibly exchanged kisses with early Homo sapiens.

Shared Microbial Clues

It is not the first time scientists have suggested ancient relatives and early modern humans were closely connected. Among previous studies, scientists have found modern people and their Neanderthal relatives shared the same mouth microbe for millions of years after the two species split, suggesting they swapped saliva.

"Likely they were kissing," she said, adding that the idea aligned with studies that has revealed people of certain genetic backgrounds have bits of ancient genetic material in their genetic makeup, revealing genetic mixing was occurring.

Intimate Interpretation

"This offers a different spin on human-Neanderthal relations," the lead researcher commented.

Publishing in the publication a scientific periodical, the researcher and her team report how, to explore the historical roots of intimate contact, they first had to develop a description that was not restricted by how humans kiss.

Describing Intimate Contact

"There have been some efforts to describe a intimate act, but it's very much been human-centric, which means that essentially non-human species don't kiss. Now we know that they probably do, it might just not look from what human kissing looks like," explained Brindle.

However, she noted some behaviors that resembled kissing were something rather different – such as the processing and food sharing, or "mouth contact", seen in aquatic species called French grunts.

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

Study Approach

Brindle said they focused on accounts of kissing in non-human species from the African continent and Asian regions, including bonobos, chimpanzees and orangutans, and employed online videos to verify the observations.

The researchers then combined this data with details on the genetic connections between living and extinct types of such primates.

Historical Origins

The team say the findings indicate kissing evolved approximately 21.5m and 16.9 million years ago in the ancestors of the great primates.

Placement of Neanderthals on this family tree means it is likely they, too, engaged in a intimate act, the researchers conclude. But the behavior may not have been limited to their specific group.

"Reality that modern people engage intimately, the fact that we now have demonstrated that Neanderthals probably kissed, indicates that the both groups are also likely to have kissed," Brindle noted.

Biological Importance

While the scientific reasoning is debated, Brindle explained kissing could be employed in sexual contexts to potentially enhance mating outcomes or assist in selecting between partners, while it could assist strengthen connections when used in a platonic way.

Another expert in the activities of primates said that as intimate contact was observed in a broad spectrum of primates it made sense its roots lie deep in our ancient history, and an examination of various types of intimate behavior among a broader range of species might extend its beginnings back further still.

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

Social Aspects

An archaeology expert explained that kissing had a cultural element as it was not common to all human groups.

"Nonetheless, as people we thrive or fail on the strength of our emotional bonds, and ways of encouraging trust and intimacy will have been important for millions of years," she said. "It might be an concept that appears a bit incongruous to our misplaced ideas of a supposedly aggressive and ancient history, but actually it ought to be no surprise that Neanderthals – and even Neanderthals and our own species collectively – engaged intimately."