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Among seabirds to polar bears, primates to great apes, 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 Microbial Evidence

It is not the first time experts have suggested ancient relatives and Homo sapiens were intimately acquainted. Among earlier research, researchers have found modern people and their thick-browed cousins possessed the same mouth microbe for hundreds of thousands of years after the two species split, implying they exchanged oral fluids.

"Likely they were engaging in intimate contact," the researcher noted, explaining that the concept chimed with research that has revealed humans of non-African ancestry contain Neanderthal DNA in their genome, demonstrating genetic mixing was occurring.

Intimate Spin

"This offers a more romantic spin on ancient interactions," the lead researcher commented.

Publishing in the publication a scientific periodical, the researcher and colleagues detail how, to explore the historical roots of kissing, they first had to come up with a description that was not restricted by how humans kiss.

Defining Kissing

"There have been some efforts to describe a kiss, but it's very much been human-centric, which means that basically other animals do not engage in this. Currently we understand that they probably do, it might just not look from what our intimate contact looks like," explained the evolutionary biologist.

Nonetheless, she said some behaviors that looked like kissing were something rather different – such as the chewing and transfer of food, or "kiss-fighting", seen in aquatic species known as certain marine animals.

Consequently the research group developed a definition of intimate contact centered around friendly interactions involving intentional oral interaction with a member of the identical group, with some movement of the mouth but absence of food.

Research Approach

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

The researchers then combined this data with details on the evolutionary relationships between living and ancient species of such animals.

Historical Timeline

The team say the findings indicate intimate contact evolved somewhere between 21.5 million and 16.9 million years ago in the ancestors of the large apes.

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

"The fact that humans engage intimately, the fact that we now have shown that ancient relatives probably engaged, suggests that the both groups are probably did engage," the researcher added.

Biological Importance

Although the evolutionary explanation is discussed, the expert said kissing could be employed in reproductive situations to possibly increase reproductive success or assist in selecting between mates, while it could assist reinforce bonding when used in a platonic way.

A separate researcher in the behavior of primates said that as kissing behavior was seen in a broad spectrum of primates it was logical its origins extend far into our ancient history, and an examination of various types of kissing among a wider variety of animals might extend its origins back even earlier still.

"Things that we consider as characteristics of human life, like intimate contact, are not unique to us if we examine carefully at different species," he said.

Social Aspects

An archaeology expert explained that intimate contact had a cultural element as it was not universal to all societies.

"However, as people we succeed or struggle on the quality of our emotional bonds, and methods of promoting trust and closeness will have been important for millions of years," the professor stated. "This could represent an concept that appears a bit incongruous to our incorrect assumptions of a rather ruthless and ancient history, but really it ought to be expected that Neanderthals – and even them and our human ancestors together – engaged intimately."