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From Galápagos albatrosses to polar bears, primates to orangutans, certain species appear to kiss. Currently, researchers suggest that Neanderthals did it too – and might even have locked lips with early Homo sapiens.

Shared Microbial Evidence

It is not the first time experts have suggested ancient relatives and Homo sapiens were closely connected. In earlier research, scientists have found humans and their Neanderthal relatives shared the identical oral bacteria for hundreds of thousands of years after the two species split, suggesting they swapped saliva.

"Probably they were kissing," the researcher noted, explaining that the idea chimed with research that has revealed humans of non-African ancestry contain Neanderthal DNA in their genetic makeup, revealing interbreeding was occurring.

Intimate Spin

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

Writing in the journal Evolution and Human Behavior, the researcher and her team report how, to explore the historical roots of intimate contact, they first had to come up with a definition that was not limited to how people smooch.

Defining Kissing

"There have been some efforts to describe a kiss, but it's very much been focused on humans, which means that essentially non-human species do not engage in this. Currently we understand that they likely engage, it may appear different from what our intimate contact resembles," said Brindle.

However, she noted some actions that looked like kissing were distinct activities – such as the chewing and transfer of food, or "kiss-fighting", seen in aquatic species called French grunts.

Consequently the research group developed a definition of intimate contact based on social behaviors involving directed oral interaction with a individual of the same species, with some movement of the oral area but no transfer of food.

Study Methods

The lead researcher explained they focused on accounts of intimate behavior in non-human species from Africa and Asian regions, including primates, apes and orangutans, and used online videos to verify the reports.

Scientists then combined this information with details on the evolutionary relationships between living and extinct types of such primates.

Evolutionary Timeline

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

The position of Neanderthals on this family tree suggests it is likely they, too, engaged in a kiss, the researchers conclude. But the activity might not have been limited to their specific group.

"Reality that modern people kiss, the fact that we currently have shown that ancient relatives very likely engaged, suggests that the two [species] are also likely to have kissed," the researcher added.

Biological Significance

Although the scientific reasoning is debated, the expert explained intimate contact could be used in reproductive situations to possibly increase mating outcomes or assist in selecting between mates, while it might help strengthen connections when used in a non-sexual manner.

A separate researcher in the behavior of primates commented that as intimate contact was observed in a broad spectrum of apes it made sense its origins extend far into our evolutionary past, and an examination of various types of kissing among a wider variety of species might extend its origins back further still.

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

Social Elements

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

"Nonetheless, as humans we thrive or fail on the quality of our relationships, and methods of promoting confidence and intimacy will have been important for eons," the professor stated. "This could represent an image that appears a bit incongruous to our incorrect assumptions of a supposedly aggressive and ancient history, but actually it should be expected that Neanderthals – and including them and our own species collectively – kissed."