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Among seabirds to polar bears, chimpanzees to orangutans, certain species appear to kiss. Now, researchers suggest that Neanderthals did it too – and might even have exchanged kisses with early Homo sapiens.

Common Microbial Evidence

This isn't the initial instance experts have suggested Neanderthals and Homo sapiens were intimately acquainted. In previous studies, scientists have discovered modern people and their Neanderthal relatives shared the same mouth microbe for hundreds of thousands of years after the evolutionary divergence, implying they exchanged oral fluids.

"Likely they were kissing," she said, explaining that the idea aligned with studies that has found people of certain genetic backgrounds contain ancient genetic material in their genetic makeup, demonstrating genetic mixing was at play.

Intimate Interpretation

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

Writing in the publication a scientific periodical, Brindle and her team report how, to investigate the evolutionary origins of kissing, they first had to come up with a definition that was not limited to how people kiss.

Describing Intimate Contact

"Previously there were some efforts to describe a intimate act, but it's largely human-centric, which means that basically other animals do not engage in this. Currently we know that they probably do, it might just not look from what our intimate contact resembles," said Brindle.

However, she said some behaviors that resembled kissing were distinct activities – such as the processing and food sharing, or "mouth contact", seen in fish called certain marine animals.

Consequently the research group came up with a description of intimate contact centered around friendly interactions involving directed oral interaction with a member of the same species, with some movement of the mouth but absence of food.

Research Approach

Brindle said they concentrated on accounts of intimate behavior in non-human species from Africa and Asia, including bonobos, chimpanzees and great apes, and employed digital recordings to confirm the observations.

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

Historical Timeline

Researchers say the results indicate kissing developed somewhere between 21.5m and 16.9m years ago in the ancestors of the great primates.

The position of ancient hominins on this family tree means it is likely they, too, engaged in a kiss, the researchers conclude. But the behavior may not have been limited to their own species.

"Reality that modern people kiss, the fact that we now have demonstrated that Neanderthals very likely kissed, indicates that the both groups are also likely to have engage," the researcher noted.

Evolutionary Significance

Although the scientific reasoning is debated, the expert explained intimate contact could be used in sexual contexts to potentially increase mating outcomes or help choose between partners, while it might help strengthen connections when used in a non-sexual manner.

Another expert in the activities of primates said that as kissing behavior was seen in a wide range of primates it was logical its origins extend far into our ancient history, and an analysis of different forms of intimate behavior among a broader range of species might push its beginnings back even earlier still.

"Things that we consider as signatures of our species, like kissing, are not exclusive to us if we look closely at other animals," the expert noted.

Cultural Elements

Another professor said that kissing had a cultural element as it was not common to all human groups.

"However, as humans we succeed or struggle on the strength of our emotional bonds, and ways of encouraging trust and intimacy will have been important for eons," she said. "It might be an image that seems a bit incongruous to our misplaced ideas of a supposedly aggressive and aggressive past, but actually it ought to be no surprise that Neanderthals – and including them and our own species together – engaged intimately."