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From seabirds to polar bears, chimpanzees to great apes, certain species appear to kiss. Now, researchers suggest that Neanderthals also engaged in this behavior – and possibly exchanged kisses with modern humans.

Shared Oral Evidence

It is not the first time experts have suggested ancient relatives and Homo sapiens were intimately acquainted. Among previous studies, scientists have discovered modern people and their Neanderthal relatives shared the identical oral bacteria for hundreds of thousands of years after the evolutionary divergence, suggesting they exchanged oral fluids.

"Likely they were engaging in intimate contact," the researcher noted, adding that the concept aligned with studies that has found people of certain genetic backgrounds contain ancient genetic material in their genetic makeup, revealing interbreeding was at play.

Romantic Spin

"This offers a more romantic perspective on ancient interactions," Brindle said.

Writing in the publication a scientific periodical, the researcher and her team report how, to explore the evolutionary origins of intimate contact, they first had to develop a description that was not limited to how humans smooch.

Defining Intimate Contact

"There have been some previous attempts to define a intimate act, but it's very much been focused on humans, which means that basically non-human species don't kiss. Currently we know that they likely engage, it may appear different from what human kissing looks like," said Brindle.

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

Consequently the research group developed a description of kissing centered around social behaviors involving intentional 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 said they focused on accounts of intimate behavior in primates from the African continent and Asia, including primates, chimpanzees and orangutans, and employed digital recordings to confirm the reports.

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

Evolutionary Timeline

The team propose the results indicate kissing evolved somewhere between 21.5 million and 16.9 million years ago in the ancestors of the great primates.

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

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

Evolutionary Significance

While the evolutionary explanation is discussed, the expert said kissing could be employed in reproductive situations to potentially increase mating outcomes or help choose between partners, while it could assist strengthen connections when used in a non-sexual manner.

Another expert in the behavior of primates commented that as kissing behavior was observed in a broad spectrum of primates it was logical its roots extend far into our evolutionary past, and an examination of various types of intimate behavior among a broader range of animals might extend its origins back further still.

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

Cultural Aspects

An archaeology expert explained that intimate contact had a social component as it was not universal to all human groups.

"However, as humans we succeed or struggle on the strength of our relationships, and ways of promoting trust and closeness will have been significant for eons," the professor stated. "It might be an image that seems a bit contradictory to our incorrect assumptions of a rather ruthless and ancient history, but actually it ought to be expected that ancient hominins – and including Neanderthals and our own species collectively – kissed."