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From Galápagos albatrosses to Arctic mammals, chimpanzees to great apes, various animals engage in mouth-to-mouth contact. Now, scientists propose that ancient hominins did it too – and might even have exchanged kisses with early Homo sapiens.

Shared Oral Clues

It is not the first time scientists have proposed ancient relatives and Homo sapiens were closely connected. Among previous studies, scientists have found modern people and their thick-browed cousins possessed the same mouth microbe for hundreds of thousands of years after the evolutionary divergence, implying they exchanged oral fluids.

"Likely they were kissing," she said, explaining that the concept chimed with studies that has found people of non-African ancestry have bits of ancient genetic material in their genome, revealing interbreeding was at play.

Romantic Spin

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

Writing in the publication Evolution and Human Behavior, Brindle and her team report how, to investigate the evolutionary origins of intimate contact, they first had to develop a definition that was not restricted by how people kiss.

Describing Kissing

"There have been some previous attempts to define a intimate act, but it's very much been focused on humans, which means that essentially non-human species do not engage in this. Currently we know that they probably do, it might just not look from what our intimate contact resembles," explained the evolutionary biologist.

However, she said some actions that resembled intimate contact were distinct activities – such as the chewing and food sharing, or "mouth contact", seen in aquatic species known as certain marine animals.

As a result the research group came up with a description of kissing centered around friendly interactions involving intentional oral interaction with a member of the same species, with some motion of the oral area but no transfer of food.

Study Methods

Brindle explained they concentrated on accounts of intimate behavior in primates from the African continent and Asian regions, including bonobos, apes and orangutans, and employed online videos to confirm the observations.

The researchers then combined this data with details on the evolutionary relationships between extant and extinct types 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.

The position of Neanderthals on this evolutionary lineage means it is likely they, too, engaged in a kiss, the scientists say. But the activity might not have been limited to their own species.

"Reality that modern people kiss, the reality that we now have demonstrated that Neanderthals very likely kissed, indicates that the two [species] are probably did kissed," the researcher added.

Evolutionary Importance

Although the evolutionary explanation is debated, Brindle said kissing could be employed in reproductive situations to possibly enhance reproductive success or assist in selecting between mates, while it might help strengthen connections when used in a platonic way.

Another expert in the behavior of primates said that as kissing behavior was observed in a broad spectrum of apes it made sense its origins lie deep in our evolutionary past, and an examination of various types of kissing among a broader range of animals might push its origins back even earlier still.

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

Cultural Elements

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

"Nonetheless, as humans we succeed or struggle on the quality of our relationships, and ways of encouraging trust and closeness will have been important for eons," she said. "It might be an concept that appears a bit contradictory to our misplaced ideas of a rather ruthless and ancient history, but actually it ought to be expected that ancient hominins – and including them and our human ancestors collectively – engaged intimately."