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From seabirds to polar bears, primates to great apes, certain species engage in mouth-to-mouth contact. Now, scientists suggest that Neanderthals did it too – and might even have locked lips with early Homo sapiens.

Shared Oral Evidence

This isn't the initial instance scientists have suggested ancient relatives and early modern humans were intimately acquainted. Among previous studies, researchers have discovered modern people and their Neanderthal relatives shared the same mouth microbe for hundreds of thousands of years after the evolutionary divergence, suggesting they exchanged oral fluids.

"Probably they were kissing," the researcher noted, adding that the idea aligned with studies that has revealed people of certain genetic backgrounds have bits of Neanderthal DNA in their genome, revealing interbreeding was occurring.

Intimate Interpretation

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

Publishing in the publication a scientific periodical, Brindle and colleagues report how, to explore the historical roots of intimate contact, they first had to develop a definition that was not restricted by how people smooch.

Defining Kissing

"Previously there were some previous attempts to describe a intimate act, but it's largely human-centric, which means that essentially other animals do not engage in this. Now we understand that they likely engage, it might just not look from what human kissing resembles," explained Brindle.

Nonetheless, she said some behaviors that looked like intimate contact were something rather different – such as the chewing and transfer of food, or "mouth contact", seen in fish known as French grunts.

Consequently the research group developed a definition of kissing based on social behaviors involving directed mouth-to-mouth contact with a member of the same species, with some movement of the mouth but no transfer of nutrition.

Study Approach

Brindle said they concentrated on accounts of kissing in non-human species from Africa and Asia, including bonobos, apes and great apes, and used digital recordings to verify the reports.

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

Historical Timeline

Researchers propose the results suggest intimate contact evolved somewhere between 21.5m and 16.9m years ago in the predecessors of the large apes.

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

"Reality that modern people engage intimately, the fact that we now have shown that ancient relatives very likely kissed, suggests that the both groups are also likely to have kissed," Brindle added.

Biological Importance

While the evolutionary explanation is debated, the expert said intimate contact could be employed in reproductive situations to potentially increase mating outcomes or help choose between mates, while it might help reinforce bonding when practiced 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 apes it made sense its roots lie deep in our evolutionary past, and an analysis of various types of intimate behavior among a wider variety of animals might extend its beginnings back further still.

"Things that we think of as characteristics of human life, like intimate contact, are not exclusive to us if we examine carefully at other animals," the expert noted.

Social Aspects

An archaeology expert said that intimate contact had a cultural element as it was not universal to all human groups.

"Nonetheless, as humans we thrive or fail on the quality of our emotional bonds, and ways of encouraging confidence and closeness will have been significant for millions of years," she said. "This could represent an image 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 including them and our own species collectively – engaged intimately."