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Among Galápagos albatrosses to Arctic mammals, chimpanzees to orangutans, certain species engage in mouth-to-mouth contact. Currently, researchers propose that Neanderthals did it too – and possibly exchanged kisses with modern humans.

Common Microbial Evidence

This isn't the initial instance scientists have proposed Neanderthals and Homo sapiens were intimately acquainted. In earlier research, researchers have discovered 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," the researcher noted, adding that the concept chimed with studies that has revealed people of certain genetic backgrounds contain ancient genetic material in their genome, revealing interbreeding was at play.

Intimate Spin

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

Publishing in the publication Evolution and Human Behavior, the researcher and colleagues detail how, to investigate the evolutionary origins of kissing, they first had to come up with a definition that was not restricted by how people smooch.

Defining Intimate Contact

"Previously there were some efforts to describe a kiss, but it's largely human-centric, which means that essentially non-human species do not engage in this. Now we know that they probably do, it may appear different from what our intimate contact looks like," explained Brindle.

Nonetheless, she noted some behaviors that looked like kissing were distinct activities – such as the processing and transfer of food, or "kiss-fighting", observed in aquatic species called certain marine animals.

As a result the team developed a definition of kissing centered around friendly interactions involving intentional oral interaction with a individual of the identical group, with some movement of the oral area but no transfer of nutrition.

Research Methods

Brindle said they concentrated 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 observations.

The researchers then integrated this data with details on the evolutionary relationships between living and extinct types of such primates.

Historical Origins

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

Placement of ancient hominins on this family tree suggests it is probable they, too, indulged in a intimate act, the researchers say. But the activity might not have been confined to their specific group.

"Reality that humans engage intimately, the fact that we now have demonstrated that Neanderthals very likely engaged, indicates that the both groups are also likely to have engage," Brindle noted.

Evolutionary Significance

While the scientific reasoning is debated, Brindle explained intimate contact could be used in reproductive situations to potentially enhance reproductive success 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 said that as intimate contact was observed in a broad spectrum of apes it was logical its roots lie deep in our ancient history, and an analysis of various types of intimate behavior among a broader range of species might extend its beginnings back even earlier still.

"Behaviors that we think of as characteristics of human life, like kissing, are not unique to us if we examine carefully at other animals," the expert noted.

Social Aspects

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

"Nonetheless, as humans we succeed or struggle on the quality of our emotional bonds, and methods of promoting trust and intimacy will have been significant for millions of years," she said. "This could represent an image that seems a bit contradictory to our misplaced ideas of a rather ruthless and aggressive past, but really it should be expected that Neanderthals – and including Neanderthals and our own species collectively – kissed."