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From Galápagos albatrosses to polar bears, primates to orangutans, various animals engage in mouth-to-mouth contact. Now, researchers propose that Neanderthals also engaged in this behavior – and possibly locked lips with modern humans.

Shared Oral Evidence

It is not the first time scientists have suggested ancient relatives and Homo sapiens were closely connected. Among previous studies, scientists have discovered humans and their Neanderthal relatives shared the identical oral bacteria for hundreds of thousands of years after the evolutionary divergence, implying they swapped saliva.

"Probably they were engaging in intimate contact," she said, explaining that the idea aligned with studies that has found humans of certain genetic backgrounds contain Neanderthal DNA in their genetic makeup, demonstrating genetic mixing was occurring.

Romantic Spin

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

Publishing in the publication a scientific periodical, Brindle and colleagues report how, to explore the historical roots of kissing, they first had to come up with a definition that was not limited to how people kiss.

Describing Kissing

"Previously there were some previous attempts to describe a intimate act, but it's very much been focused on humans, which means that basically other animals don't kiss. Now we know that they likely engage, it may appear different from what our intimate contact resembles," said the evolutionary biologist.

However, she noted some actions that looked like intimate contact were something rather different – such as the chewing and transfer of food, or "kiss-fighting", observed in aquatic species known as certain marine animals.

Consequently the research group came up with a description of intimate contact based on friendly interactions involving intentional oral interaction with a member of the identical group, with some movement of the oral area but absence of nutrition.

Study Approach

The lead researcher explained they concentrated on reports of intimate behavior in non-human species from Africa and Asia, including bonobos, apes and orangutans, and used online videos to confirm the reports.

The researchers then integrated this data with details on the evolutionary relationships between extant and extinct types of such primates.

Historical Origins

Researchers propose the findings suggest kissing evolved somewhere between 21.5m and 16.9m years ago in the ancestors of the large apes.

Placement of Neanderthals on this family tree suggests it is likely they, too, indulged in a intimate act, the scientists conclude. But the behavior may not have been confined to their specific group.

"Reality that humans kiss, the fact that we currently have demonstrated that Neanderthals very likely kissed, suggests that the both groups are also likely to have engage," the researcher noted.

Biological Significance

Although the scientific reasoning is discussed, Brindle explained intimate contact could be used in sexual contexts to potentially enhance reproductive success or help choose between mates, while it could assist reinforce bonding when used in a platonic way.

A separate researcher 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 examination of various types of intimate behavior among a broader range of animals might extend its origins back even earlier still.

"Things that we consider as signatures of human life, like kissing, are not unique to us if we look closely at different species," the expert noted.

Social Elements

Another professor explained that intimate contact 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 relationships, and methods of encouraging trust and intimacy will have been important for millions of years," the professor stated. "It might be an image that seems a bit contradictory to our misplaced ideas of a rather ruthless and ancient history, but really it should be no surprise that ancient hominins – and even Neanderthals and our own species collectively – engaged intimately."