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Among Galápagos albatrosses to Arctic mammals, chimpanzees to orangutans, various animals appear to kiss. Currently, researchers propose that Neanderthals also engaged in this behavior – and possibly exchanged kisses with modern humans.

Common Oral Evidence

It is not the first time scientists have suggested ancient relatives and Homo sapiens were intimately acquainted. Among earlier research, researchers have found humans and their Neanderthal relatives possessed the same mouth microbe for hundreds of thousands of years after the evolutionary divergence, implying they swapped saliva.

"Probably they were engaging in intimate contact," the researcher noted, adding that the idea chimed with studies that has revealed humans of non-African ancestry contain Neanderthal DNA in their genetic makeup, demonstrating genetic mixing was at play.

Romantic Spin

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

Writing in the publication a scientific periodical, Brindle and colleagues report how, to explore the evolutionary origins of kissing, they first had to develop a definition that was not restricted by how humans smooch.

Defining Intimate Contact

"Previously there were some previous attempts to describe a kiss, but it's largely focused on humans, which means that basically other animals don't kiss. Now we know that they probably do, it may appear different from what our intimate contact resembles," explained Brindle.

However, she said some actions that looked like intimate contact were distinct activities – such as the processing and transfer of food, or "mouth contact", observed in aquatic species called certain marine animals.

As a result the research group came up with a description of kissing 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 food.

Research Approach

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

The researchers then integrated this information with information on the evolutionary relationships between extant and extinct species of such animals.

Historical Timeline

The team propose the results indicate kissing developed approximately 21.5m and 16.9 million years ago in the ancestors of the great primates.

The position of Neanderthals on this family tree means it is probable they, too, indulged in a intimate act, the scientists say. But the activity might not have been limited to their own species.

"Reality that modern people kiss, the fact that we currently have demonstrated that ancient relatives probably kissed, suggests that the two [species] are probably did engage," Brindle added.

Biological Importance

Although the scientific reasoning is debated, the expert explained kissing could be used in reproductive situations to potentially enhance mating outcomes or help choose between partners, while it could assist reinforce bonding when used in a platonic way.

Another expert in the activities of primates said that as intimate contact was observed in a wide range of apes it made sense its origins extend far into our evolutionary past, 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 characteristics of our species, like kissing, are not unique to us if we look closely at other animals," he said.

Social Elements

Another professor said 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 strength of our emotional bonds, and methods of promoting confidence and closeness will have been important for eons," 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 expected that ancient hominins – and even them and our own species together – kissed."