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Among Galápagos albatrosses to polar bears, primates to orangutans, various animals engage in mouth-to-mouth contact. Currently, researchers propose that Neanderthals did it too – and possibly exchanged kisses with early Homo sapiens.

Common Microbial Evidence

This isn't the initial instance scientists have suggested ancient relatives and Homo sapiens were closely connected. In earlier research, scientists have discovered modern people and their Neanderthal relatives possessed the identical oral bacteria for hundreds of thousands of years after the two species split, implying they swapped saliva.

"Likely they were kissing," she said, explaining that the idea chimed with studies that has revealed people of non-African ancestry contain Neanderthal DNA in their genetic makeup, revealing interbreeding was at play.

Romantic Spin

"It certainly puts a different perspective on human-Neanderthal relations," the lead researcher said.

Publishing in the publication a scientific periodical, Brindle and her team detail how, to explore the evolutionary origins of kissing, they first had to come up with a definition that was not restricted by how people kiss.

Defining Kissing

"Previously there were some efforts to define a intimate act, but it's largely human-centric, which means that basically non-human species do not engage in this. Now we understand that they likely engage, it may appear different from what human kissing resembles," explained Brindle.

However, she noted some actions that resembled kissing were something rather different – such as the processing and food sharing, or "kiss-fighting", seen in fish known as French grunts.

Consequently the research group came up with a description of kissing centered around friendly interactions involving directed oral interaction with a member of the identical group, with some movement of the mouth but absence of food.

Study Approach

Brindle explained they concentrated on reports of kissing in non-human species from the African continent and Asian regions, including primates, apes and orangutans, and employed online videos to confirm the observations.

Scientists then combined this information with information on the evolutionary relationships between extant and ancient types of such primates.

Evolutionary Origins

Researchers say the results indicate intimate contact developed somewhere between 21.5m and 16.9 million years ago in the ancestors of the large apes.

Placement of Neanderthals on this family tree means it is likely they, too, engaged in a intimate act, the researchers say. But the behavior may not have been confined to their own species.

"Reality that modern people engage intimately, the reality that we currently have demonstrated that ancient relatives very likely kissed, indicates that the two [species] are also likely to have engage," the researcher added.

Evolutionary Importance

Although the evolutionary explanation is discussed, Brindle explained kissing 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.

A separate researcher in the behavior of great apes said that as kissing behavior was observed in a wide range of primates it made sense its origins lie deep in our ancient history, and an analysis of various types of kissing among a wider variety of animals might push its origins back further still.

"Things that we think of as signatures of our species, like kissing, 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 societies.

"However, as humans we succeed or struggle on the strength of our emotional bonds, and methods of encouraging confidence and closeness will have been significant for millions of years," the professor stated. "This could represent an image that appears a bit incongruous to our misplaced ideas of a rather ruthless and ancient history, but actually it ought to be expected that ancient hominins – and including them and our own species collectively – kissed."