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Among Galápagos albatrosses to Arctic mammals, primates to orangutans, certain species appear to kiss. Currently, scientists suggest that ancient hominins did it too – and possibly locked lips with modern humans.

Common Microbial Evidence

This isn't the initial instance scientists have proposed Neanderthals and early modern humans were intimately acquainted. Among earlier research, scientists have found modern people and their thick-browed cousins possessed the same mouth microbe for hundreds of thousands of years after the two species split, implying they swapped saliva.

"Likely they were engaging in intimate contact," the researcher noted, adding that the concept chimed with studies that has found people of non-African ancestry contain ancient genetic material in their genetic makeup, demonstrating interbreeding was at play.

Intimate Interpretation

"It certainly puts a more romantic perspective on human-Neanderthal relations," Brindle said.

Publishing in the journal Evolution and Human Behavior, the researcher and colleagues detail how, to explore the evolutionary origins of intimate contact, they first had to come up with a definition that was not limited to how humans smooch.

Defining Kissing

"Previously there were some previous attempts to define a intimate act, but it's largely focused on humans, which implies that basically other animals do not engage in this. Now we understand that they likely engage, it might just not look from what human kissing looks like," explained the evolutionary biologist.

Nonetheless, she said some actions that looked like kissing were something rather different – such as the processing and transfer of food, or "kiss-fighting", observed in fish called certain marine animals.

As a result the research group came up with a description of intimate contact based on friendly interactions involving directed mouth-to-mouth contact with a individual of the identical group, with some movement of the mouth but absence of nutrition.

Research Methods

The lead researcher said they concentrated on reports of kissing in primates from Africa and Asia, including bonobos, chimpanzees and great apes, and employed online videos to confirm the observations.

The researchers then integrated this information with information on the genetic connections between living and extinct types of such animals.

Historical Origins

Researchers propose the results suggest kissing evolved approximately 21.5m and 16.9m years ago in the ancestors of the great primates.

Placement of Neanderthals on this evolutionary lineage means it is likely they, too, indulged in a kiss, the scientists conclude. But the activity may not have been limited to their own species.

"The fact that modern people kiss, the reality that we currently have demonstrated that Neanderthals probably engaged, indicates that the two [species] are probably did engage," the researcher added.

Biological Significance

While the scientific reasoning is discussed, the expert said kissing could be employed in reproductive situations to possibly increase mating outcomes or assist in selecting between partners, while it could assist strengthen connections when used in a platonic way.

Another expert in the activities of primates commented that as intimate contact was seen in a broad spectrum of apes it made sense its origins extend far into our ancient history, and an analysis of different forms of kissing among a wider variety of animals might push its beginnings back even earlier still.

"Behaviors that we consider as characteristics of our species, like kissing, are not unique to us if we look closely at different species," he said.

Social Aspects

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

"However, as humans we succeed or struggle on the quality of our emotional bonds, and ways of encouraging confidence and intimacy will have been important for millions of years," the professor stated. "This could represent an image that seems a bit incongruous to our misplaced ideas of a supposedly aggressive and aggressive past, but actually it ought to be no surprise that Neanderthals – and including Neanderthals and our own species together – engaged intimately."