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From seabirds to Arctic mammals, primates to orangutans, certain species appear to kiss. Now, scientists suggest that ancient hominins did it too – and might even have locked lips with modern humans.

Common Microbial Clues

It is not the first time experts have proposed Neanderthals and Homo sapiens were closely connected. Among previous studies, scientists have found modern people and their Neanderthal relatives shared the identical oral bacteria for millions of years after the evolutionary divergence, implying they swapped saliva.

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

Romantic Spin

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

Publishing in the journal a scientific periodical, the researcher and her team report how, to explore the evolutionary origins of intimate contact, they first had to develop a description that was not limited to how humans kiss.

Defining Kissing

"There have been some efforts to define a kiss, but it's very much been human-centric, which implies that basically non-human species don't kiss. Now we know that they probably do, it may appear different from what our intimate contact resembles," said the evolutionary biologist.

However, she said some behaviors that looked like intimate contact were something rather different – such as the processing and transfer of food, or "kiss-fighting", observed in aquatic species known as French grunts.

As a result the team developed a description of kissing centered around friendly interactions involving directed oral interaction with a member of the same species, with some movement of the mouth but no transfer of nutrition.

Study Approach

Brindle said they focused on reports of kissing in primates from the African continent and Asian regions, including primates, apes and great apes, and used digital recordings to verify the observations.

The researchers then combined this data with information on the genetic connections between living and ancient species of such primates.

Evolutionary Origins

The team propose the findings indicate intimate contact evolved approximately 21.5 million and 16.9m years ago in the ancestors of the large apes.

The position of ancient hominins on this evolutionary lineage suggests it is probable they, too, engaged in a intimate act, the scientists say. But the behavior might not have been confined to their specific group.

"Reality that humans kiss, the fact that we now have shown that ancient relatives very likely engaged, suggests that the both groups are probably did kissed," the researcher noted.

Biological Significance

While the evolutionary explanation is discussed, the expert explained kissing could be used in sexual contexts to potentially increase mating outcomes or assist in selecting between mates, while it could assist strengthen connections when practiced in a non-sexual manner.

A separate researcher in the activities of great apes said that as kissing behavior was seen in a wide range of primates it was logical its roots lie deep in our ancient history, and an examination of different forms of intimate behavior among a wider variety of animals might push its origins back further still.

"Behaviors that we think of as signatures of human life, like intimate contact, are not unique to us if we look closely at different species," the expert noted.

Social Elements

An archaeology expert said that intimate contact had a social component as it was not universal to all societies.

"Nonetheless, as humans we succeed or struggle on the quality of our emotional bonds, and ways of encouraging trust and closeness will have been significant for millions of years," the professor stated. "It might be an concept that seems a bit contradictory to our incorrect assumptions of a rather ruthless and aggressive past, but really it ought to be no surprise that Neanderthals – and even Neanderthals and our human ancestors together – engaged intimately."