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From Galápagos albatrosses to Arctic mammals, chimpanzees to orangutans, certain species engage in mouth-to-mouth contact. Now, scientists propose that ancient hominins also engaged in this behavior – and possibly locked lips with early Homo sapiens.

Common Oral Clues

This isn't the initial instance experts have proposed Neanderthals and Homo sapiens were intimately acquainted. In previous studies, researchers have discovered humans and their Neanderthal relatives shared the identical oral bacteria for hundreds of thousands of years after the two species split, implying they swapped saliva.

"Probably they were kissing," she said, adding that the concept 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

"It certainly puts a more romantic perspective on ancient interactions," the lead researcher said.

Writing in the publication Evolution and Human Behavior, the researcher and colleagues report how, to explore the historical roots of intimate contact, they first had to develop a description that was not restricted by how humans kiss.

Defining Intimate Contact

"There have been some previous attempts to describe a intimate act, but it's very much been focused on humans, which means that essentially other animals don't kiss. Currently we understand that they probably do, it may appear different from what our intimate contact resembles," explained Brindle.

However, she noted some behaviors that looked like kissing were distinct activities – such as the processing and transfer of food, or "mouth contact", observed in fish known as French grunts.

Consequently the team came up with a description of intimate contact centered around friendly interactions involving intentional oral interaction with a individual of the same species, with some movement of the mouth but no transfer of food.

Research Methods

The lead researcher said they focused on accounts of intimate behavior in non-human species from the African continent and Asian regions, including bonobos, chimpanzees and great apes, and employed online videos to verify the reports.

The researchers then combined this data with details on the genetic connections between extant and ancient types of such animals.

Historical Timeline

The team propose the findings indicate intimate contact developed somewhere between 21.5 million and 16.9m years ago in the predecessors of the large apes.

The position of Neanderthals on this family tree suggests it is likely they, too, indulged in a intimate act, the researchers conclude. But the activity might not have been limited to their specific group.

"The fact that humans kiss, the reality that we currently have shown that Neanderthals probably kissed, indicates that the both groups are also likely to have kissed," the researcher added.

Evolutionary Importance

While the evolutionary explanation is debated, the expert said kissing could be used in sexual contexts to possibly enhance mating outcomes or assist in selecting between mates, while it might help reinforce bonding when practiced in a non-sexual manner.

Another expert in the activities of great apes commented that as kissing behavior was observed in a broad spectrum of apes it made sense its roots extend far into our evolutionary past, and an analysis of various types of intimate behavior among a broader range of species might push its origins back further still.

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

Social Aspects

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

"Nonetheless, as humans we succeed or struggle on the strength of our emotional bonds, and ways of encouraging trust and intimacy will have been significant for eons," the professor stated. "It might be an image that appears a bit contradictory to our misplaced ideas of a rather ruthless and aggressive past, but actually it should be no surprise that ancient hominins – and including Neanderthals and our own species together – kissed."