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Among seabirds to polar bears, primates to orangutans, 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 Microbial Clues

It is not the first time experts have proposed ancient relatives and Homo sapiens were intimately acquainted. Among previous studies, researchers have discovered humans and their thick-browed cousins shared the identical oral bacteria for millions of years after the evolutionary divergence, suggesting they exchanged oral fluids.

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

Intimate Interpretation

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

Publishing in the publication Evolution and Human Behavior, Brindle and colleagues detail how, to explore the historical roots of kissing, they first had to come up with a description that was not limited to how people kiss.

Describing Kissing

"There have been some efforts to define a intimate act, but it's very much been human-centric, which means that basically non-human species do not engage in this. Now we understand that they probably do, it may appear different from what human kissing resembles," explained Brindle.

Nonetheless, she noted some actions that resembled intimate contact were distinct activities – such as the processing and food sharing, or "mouth contact", seen in aquatic species known as certain marine animals.

Consequently the team came up with a description of intimate contact 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

Brindle explained they concentrated on accounts of intimate behavior in primates from Africa and Asian regions, including primates, chimpanzees and orangutans, and employed digital recordings to confirm the observations.

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

Evolutionary Timeline

Researchers propose the findings indicate kissing evolved somewhere between 21.5m and 16.9 million years ago in the predecessors of the great primates.

The position of Neanderthals on this evolutionary lineage means it is probable they, too, engaged in a kiss, the scientists conclude. But the activity might not have been limited to their specific group.

"The fact that modern people kiss, the fact that we now have shown that Neanderthals probably kissed, indicates that the both groups are probably did engage," Brindle added.

Biological Significance

While the evolutionary explanation is discussed, Brindle explained intimate contact could be used in reproductive situations to possibly increase mating outcomes or help choose between partners, while it might help reinforce bonding when practiced in a platonic way.

A separate researcher in the activities of great apes commented that as kissing behavior was seen in a broad spectrum of apes it made sense its roots lie deep in our evolutionary past, and an examination of different forms of intimate behavior among a broader range of species might extend its origins back further still.

"Things that we consider as characteristics of human life, like intimate contact, are not unique to us if we examine carefully at different species," he said.

Social Aspects

An archaeology expert said that kissing had a social component as it was not universal to all human groups.

"However, as humans we thrive or fail on the strength of our emotional bonds, and methods of encouraging confidence and closeness will have been important for eons," the professor stated. "It might be an concept that seems a bit contradictory to our misplaced ideas of a supposedly aggressive and ancient history, but actually it ought to be no surprise that ancient hominins – and even them and our human ancestors collectively – kissed."