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From seabirds to Arctic mammals, primates to great apes, various animals engage in mouth-to-mouth contact. Currently, researchers suggest that Neanderthals also engaged in this behavior – and possibly locked lips with early Homo sapiens.

Common Microbial Evidence

It is not the first time scientists have suggested Neanderthals and Homo sapiens were intimately acquainted. Among previous studies, researchers have found modern people and their Neanderthal relatives shared the identical oral bacteria for hundreds of thousands of years after the two species split, implying 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 contain Neanderthal DNA in their genetic makeup, revealing genetic mixing was occurring.

Intimate Spin

"This offers a different perspective on human-Neanderthal relations," Brindle commented.

Writing in the publication Evolution and Human Behavior, the researcher and her team detail how, to investigate the historical roots of intimate contact, they first had to come up with a description that was not restricted by how humans smooch.

Describing Kissing

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

However, she said some actions that resembled kissing were distinct activities – such as the chewing and transfer of food, or "mouth contact", observed in fish known as French grunts.

As a result the team developed a description of kissing centered around friendly interactions involving intentional oral interaction with a member of the same species, with some motion of the mouth but absence of nutrition.

Study Methods

Brindle explained they concentrated on accounts of intimate behavior in primates from the African continent and Asian regions, including primates, apes and great apes, and employed online videos to confirm the reports.

The researchers then combined this data with information on the genetic connections between living and ancient types of such primates.

Historical Origins

The team propose the results indicate intimate contact evolved somewhere between 21.5 million and 16.9m years ago in the predecessors of the great primates.

Placement of Neanderthals on this evolutionary lineage means it is likely they, too, engaged in a intimate act, the scientists conclude. But the behavior might not have been confined to their specific group.

"Reality that humans engage intimately, the reality that we now have demonstrated that Neanderthals probably engaged, indicates that the both groups are probably did engage," Brindle noted.

Evolutionary Importance

While the evolutionary explanation is discussed, the expert explained intimate contact could be employed in reproductive situations to potentially increase reproductive success or assist in selecting between mates, while it might help strengthen connections when used in a platonic way.

Another expert in the behavior of primates commented that as kissing behavior was observed in a broad spectrum of apes it was logical its origins extend far into our ancient history, and an analysis of various types of kissing among a broader range of animals might extend its beginnings back even earlier still.

"Things that we consider as characteristics of our species, like kissing, are not exclusive to us if we examine carefully at different species," he said.

Social Aspects

Another professor explained that intimate contact had a social component as it was not universal to all human groups.

"However, as people we succeed or struggle on the quality of our relationships, and ways of encouraging trust and closeness will have been significant for eons," she said. "It might be an concept that seems a bit contradictory to our misplaced ideas of a supposedly aggressive and ancient history, but really it should be expected that Neanderthals – and even them and our own species collectively – kissed."