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From Galápagos albatrosses to polar bears, chimpanzees to great apes, various animals engage in mouth-to-mouth contact. Currently, researchers propose that Neanderthals also engaged in this behavior – and possibly exchanged kisses with modern humans.

Shared Microbial Evidence

It is not the first time experts have proposed Neanderthals and early modern humans were intimately acquainted. In previous studies, researchers have discovered modern people and their Neanderthal relatives shared the same mouth microbe for hundreds of thousands of years after the evolutionary divergence, suggesting they swapped saliva.

"Likely they were kissing," the researcher noted, adding that the idea chimed with research that has found humans of certain genetic backgrounds have bits of Neanderthal DNA in their genome, revealing genetic mixing was at play.

Romantic Spin

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

Publishing in the journal Evolution and Human Behavior, Brindle and colleagues detail how, to investigate the historical roots of kissing, they first had to come up with a description that was not limited to how humans kiss.

Describing Kissing

"Previously there were some previous attempts to describe a intimate act, but it's largely human-centric, 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," said the evolutionary biologist.

Nonetheless, she noted some actions that looked like intimate contact were distinct activities – such as the chewing and food sharing, or "kiss-fighting", seen in aquatic species called certain marine animals.

Consequently the team developed a description of kissing based on social behaviors involving directed mouth-to-mouth contact with a individual of the identical group, with some motion of the mouth but no transfer of nutrition.

Research Approach

The lead researcher explained they focused on accounts of kissing in primates from the African continent and Asia, including primates, chimpanzees and great apes, and employed online videos to confirm the reports.

The researchers then integrated this data with information on the evolutionary relationships between living and ancient species of such animals.

Historical Timeline

Researchers say the findings indicate intimate contact developed somewhere between 21.5m and 16.9m years ago in the ancestors of the great primates.

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

"The fact that modern people kiss, the reality that we currently have shown that ancient relatives probably kissed, suggests that the both groups are probably did engage," Brindle noted.

Evolutionary Importance

Although the evolutionary explanation is debated, Brindle explained intimate contact could be employed in reproductive situations to possibly enhance mating outcomes or assist in selecting between mates, while it could assist reinforce bonding when practiced in a platonic way.

Another expert in the behavior of primates said that as kissing behavior was seen in a wide range of primates it was logical its origins lie deep in our ancient history, and an analysis of various types of kissing among a broader range of species might push its origins back even earlier still.

"Behaviors that we think of as characteristics of our species, like intimate contact, are not unique to us if we look closely at different species," the expert noted.

Social Aspects

Another professor explained that kissing had a social component as it was not universal to all societies.

"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 millions of years," the professor stated. "This could represent an concept that seems a bit contradictory to our incorrect assumptions of a rather ruthless and aggressive past, but actually it ought to be no surprise that Neanderthals – and even them and our human ancestors together – engaged intimately."