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

Shared Microbial Clues

It is not the first time experts have proposed Neanderthals and early modern humans were closely connected. Among previous studies, researchers have discovered humans 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," the researcher noted, adding that the concept aligned with studies that has found humans of non-African ancestry contain ancient genetic material in their genome, revealing interbreeding was occurring.

Romantic Spin

"It certainly puts a different perspective on ancient interactions," Brindle said.

Publishing in the publication a scientific periodical, Brindle and colleagues report how, to investigate the historical roots of kissing, they first had to come up with a description that was not restricted by how people kiss.

Describing Intimate Contact

"Previously there were some previous attempts to define a kiss, but it's very much been focused on humans, which implies that essentially non-human species do not engage in this. Currently we know that they likely engage, it may appear different from what human kissing resembles," said Brindle.

However, she said some actions that resembled intimate contact were distinct activities – such as the processing and transfer of food, or "mouth contact", seen in fish known as certain marine animals.

Consequently the research group developed a definition of kissing centered around friendly interactions involving directed mouth-to-mouth contact with a member of the same species, with some movement of the oral area but no transfer of nutrition.

Research Methods

The lead researcher explained they focused on reports of kissing in non-human species from the African continent and Asian regions, including primates, apes and orangutans, and used digital recordings to confirm the reports.

The researchers then combined this information with details on the genetic connections between living and extinct types of such primates.

Historical Timeline

The team propose the findings indicate intimate contact evolved approximately 21.5 million and 16.9 million years ago in the predecessors of the great primates.

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

"Reality that modern people kiss, the reality that we now have demonstrated that ancient relatives probably engaged, suggests that the two [species] are also likely to have kissed," Brindle added.

Evolutionary Significance

While the scientific reasoning is debated, the expert said intimate contact could be employed in reproductive situations to potentially enhance reproductive success or help choose between mates, while it might help strengthen connections when used in a platonic way.

Another expert in the behavior of primates said that as kissing behavior was observed in a wide range of apes it was logical its roots lie deep in our ancient history, and an examination of various types of intimate behavior among a wider variety of animals might extend its beginnings back even earlier still.

"Behaviors that we consider as signatures of human life, like kissing, are not exclusive to us if we look closely at other animals," he said.

Cultural Aspects

An archaeology expert explained that kissing had a social component as it was not universal to all societies.

"Nonetheless, as people we thrive or fail on the strength of our relationships, and methods of encouraging confidence and closeness will have been significant for eons," the professor stated. "This could represent an concept that seems a bit incongruous to our incorrect assumptions of a rather ruthless and ancient history, but actually it ought to be expected that ancient hominins – and even Neanderthals and our human ancestors together – kissed."