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Among Galápagos albatrosses to Arctic mammals, primates to orangutans, various animals appear to kiss. Now, scientists propose that ancient hominins did it too – and might even have exchanged kisses with modern humans.

Common Microbial Evidence

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

"Likely they were kissing," the researcher noted, adding that the concept aligned with studies that has found humans of certain genetic backgrounds contain Neanderthal DNA in their genetic makeup, revealing interbreeding was at play.

Intimate Interpretation

"This offers a more romantic perspective on ancient interactions," the lead researcher commented.

Writing in the journal Evolution and Human Behavior, Brindle and colleagues detail how, to explore the evolutionary origins of kissing, they first had to come up with a definition that was not limited to how people smooch.

Describing Kissing

"Previously there were some efforts to define a intimate act, but it's very much been focused on humans, which implies that basically non-human species don't kiss. Now we understand that they likely engage, it might just not look from what our intimate contact resembles," explained Brindle.

However, she said some behaviors that looked like intimate contact were distinct activities – such as the chewing and food sharing, or "mouth contact", seen in aquatic species called French grunts.

As a result the team developed a description of intimate contact based on social behaviors involving directed mouth-to-mouth contact with a individual of the same species, with some movement of the mouth but absence of food.

Research Approach

Brindle said they focused on reports of intimate behavior in primates from the African continent and Asia, including bonobos, apes and great apes, and employed online videos to verify the observations.

Scientists then integrated this data with details on the evolutionary relationships between extant and ancient species of such primates.

Evolutionary Timeline

The team propose the findings suggest kissing evolved somewhere between 21.5 million and 16.9m years ago in the predecessors of the great primates.

The position of Neanderthals on this evolutionary lineage suggests it is probable they, too, engaged in a kiss, the scientists say. But the behavior may not have been confined to their own species.

"The fact that modern people kiss, the fact that we currently have shown that Neanderthals very likely kissed, suggests that the both groups are probably did engage," the researcher noted.

Biological Importance

Although the evolutionary explanation is discussed, Brindle explained intimate contact could be employed in reproductive situations to potentially increase mating outcomes or assist in selecting between mates, while it could assist reinforce bonding when used in a non-sexual manner.

A separate researcher in the behavior of great apes commented that as kissing behavior was observed in a wide range of apes it was logical its roots lie deep in our evolutionary past, and an analysis of various types of intimate behavior among a wider variety of species might extend its beginnings back further still.

"Things that we consider as characteristics of our species, like kissing, are not exclusive to us if we examine carefully at different species," the expert noted.

Cultural Elements

An archaeology expert explained that intimate contact had a cultural element as it was not universal to all human groups.

"However, as humans we thrive or fail on the strength of our emotional bonds, and methods of promoting confidence and intimacy will have been important for eons," the professor stated. "This could represent an image that appears a bit incongruous to our incorrect assumptions of a rather ruthless and aggressive past, but actually it ought to be expected that ancient hominins – and including them and our own species together – kissed."