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Among seabirds to Arctic mammals, chimpanzees to great apes, various animals appear to kiss. Now, researchers suggest that Neanderthals did it too – and might even have locked lips with modern humans.

Common Microbial Evidence

This isn't the initial instance experts have proposed Neanderthals and Homo sapiens were closely connected. In previous studies, researchers have found modern people and their Neanderthal relatives shared the identical oral bacteria for hundreds of thousands of years after the evolutionary divergence, implying they exchanged oral fluids.

"Probably they were kissing," the researcher noted, adding that the idea chimed with studies that has revealed humans of certain genetic backgrounds have bits of ancient genetic material in their genetic makeup, revealing genetic mixing was occurring.

Romantic Spin

"This offers a more romantic spin on ancient interactions," the lead researcher said.

Publishing in the journal a scientific periodical, the researcher and colleagues detail how, to explore the historical roots of kissing, they first had to develop a description that was not limited to how humans smooch.

Defining Kissing

"Previously there were some previous attempts to define a intimate act, but it's very much been human-centric, which implies that essentially other animals do not engage in this. Now we understand that they probably do, it may appear different from what our intimate contact resembles," explained the evolutionary biologist.

Nonetheless, she said some behaviors that looked like kissing were something rather different – such as the processing and transfer of food, or "kiss-fighting", observed in aquatic species known as certain marine animals.

Consequently the team developed a description of intimate contact based on social behaviors involving directed mouth-to-mouth contact with a individual of the same species, with some motion of the oral area but absence of food.

Research Approach

Brindle said they concentrated on accounts of intimate behavior in primates from Africa and Asia, including bonobos, chimpanzees and great apes, and used digital recordings to confirm the observations.

The researchers then combined this information with information on the genetic connections between extant and extinct species of such primates.

Evolutionary Timeline

Researchers propose the findings indicate kissing developed approximately 21.5m and 16.9m years ago in the ancestors of the large apes.

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

"Reality that modern people kiss, the fact that we currently have demonstrated that Neanderthals very likely kissed, suggests that the two [species] are probably did engage," the researcher noted.

Biological Significance

While the scientific reasoning is discussed, Brindle said kissing could be employed in reproductive situations to possibly enhance mating outcomes or assist in selecting between partners, 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 observed in a wide range of apes it made sense its origins lie deep in our evolutionary past, and an analysis of various types of kissing among a wider variety of animals might push its beginnings back even earlier still.

"Things that we think of as characteristics of our species, like intimate contact, are not exclusive to us if we examine carefully at different species," the expert noted.

Social Elements

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

"Nonetheless, as people we succeed or struggle on the strength of our emotional bonds, and ways of encouraging trust and intimacy will have been significant for eons," the professor stated. "This could represent an image that seems a bit incongruous to our incorrect assumptions of a supposedly aggressive and aggressive past, but actually it should be no surprise that ancient hominins – and even Neanderthals and our human ancestors collectively – engaged intimately."