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Among Galápagos albatrosses to polar bears, chimpanzees to orangutans, certain species engage in mouth-to-mouth contact. Currently, researchers propose that Neanderthals also engaged in this behavior – and possibly exchanged kisses with modern humans.

Common Oral Clues

This isn't the initial instance experts have proposed Neanderthals and Homo sapiens were closely connected. Among earlier research, researchers have discovered humans and their Neanderthal relatives possessed the same mouth microbe for hundreds of thousands of years after the two species split, implying they swapped saliva.

"Probably they were kissing," she said, explaining that the idea chimed with studies that has revealed people of certain genetic backgrounds have bits of ancient genetic material in their genome, demonstrating interbreeding was occurring.

Romantic Spin

"It certainly puts a more romantic spin on ancient interactions," the lead researcher commented.

Publishing in the journal Evolution and Human Behavior, the researcher and her team report how, to investigate the evolutionary origins of kissing, they first had to develop a description that was not limited to how people kiss.

Describing Intimate Contact

"Previously there were some efforts to define a kiss, but it's largely human-centric, which implies that essentially non-human species do not engage in this. Currently we understand that they probably do, it might just not look from what human kissing resembles," explained Brindle.

However, she noted some behaviors that looked like kissing were something rather different – such as the chewing and food sharing, or "mouth contact", observed in aquatic species known as French grunts.

As a result the research group came up with a description of intimate contact centered around friendly interactions involving intentional oral interaction with a member of the identical group, with some motion of the mouth but no transfer of food.

Research Methods

Brindle explained they focused on accounts of kissing in primates from the African continent and Asian regions, including primates, chimpanzees and great apes, and employed digital recordings to verify the reports.

Scientists then integrated this information with details on the evolutionary relationships between extant and extinct types of such primates.

Evolutionary Timeline

The team propose the findings indicate intimate contact evolved somewhere between 21.5m and 16.9m years ago in the predecessors of the great primates.

Placement of ancient hominins on this evolutionary lineage means it is probable they, too, engaged in a intimate act, the scientists say. But the behavior might not have been confined to their own species.

"Reality that humans kiss, the fact that we currently have demonstrated that Neanderthals very likely kissed, suggests that the both groups are probably did kissed," the researcher added.

Biological Significance

Although the scientific reasoning is debated, the expert explained intimate contact could be employed in reproductive situations to possibly enhance mating outcomes or assist in selecting between partners, while it might help strengthen connections when used in a non-sexual manner.

Another expert in the behavior of primates commented that as intimate contact was seen in a wide range of primates it made sense its origins lie deep in our ancient history, and an analysis of different forms of intimate behavior among a wider variety of species might extend its beginnings back even earlier still.

"Things that we think of as signatures of human life, like intimate contact, are not exclusive to us if we examine carefully at other animals," he said.

Social Elements

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

"Nonetheless, as people we succeed or struggle on the strength of our relationships, and ways of encouraging confidence and closeness will have been significant for eons," she said. "This could represent an concept that seems a bit incongruous to our incorrect assumptions of a supposedly aggressive and aggressive past, but really it ought to be expected that Neanderthals – and even Neanderthals and our own species collectively – engaged intimately."