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From Galápagos albatrosses to Arctic mammals, primates to orangutans, various animals appear to kiss. Currently, researchers suggest that ancient hominins did it too – and might even have exchanged kisses with early Homo sapiens.

Shared Microbial Clues

It is not the first time experts have proposed Neanderthals and Homo sapiens were closely connected. Among previous studies, researchers have found modern people and their thick-browed cousins shared the same mouth microbe for hundreds of thousands of years after the evolutionary divergence, implying they exchanged oral fluids.

"Probably they were engaging in intimate contact," she said, explaining that the concept aligned with research that has found people of non-African ancestry contain Neanderthal DNA in their genetic makeup, revealing interbreeding was at play.

Intimate Spin

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

Writing in the journal Evolution and Human Behavior, Brindle and her team 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

"Previously there were some previous attempts to define a kiss, but it's very much been human-centric, which implies that basically other animals do not engage in this. Now we understand that they likely engage, it may appear different from what our intimate contact resembles," explained the evolutionary biologist.

Nonetheless, she noted some actions that resembled intimate contact were distinct activities – such as the chewing and transfer of food, or "kiss-fighting", seen in fish known as French grunts.

As a result the team developed a description of intimate contact centered around social behaviors involving directed mouth-to-mouth contact with a individual of the same species, with some motion of the mouth but no transfer of nutrition.

Study Approach

Brindle explained they concentrated on reports of kissing in non-human species from Africa and Asia, including primates, apes and orangutans, and used digital recordings to verify the reports.

Scientists then combined this information with details on the evolutionary relationships between living and ancient species of such primates.

Evolutionary Timeline

Researchers say the results indicate kissing developed somewhere between 21.5 million and 16.9 million years ago in the predecessors of the great primates.

The position of ancient hominins on this family tree suggests it is likely they, too, indulged in a kiss, the researchers say. But the activity might not have been confined to their specific group.

"Reality that modern people kiss, the reality that we currently have shown that Neanderthals very likely engaged, suggests that the two [species] are probably did engage," the researcher noted.

Evolutionary Significance

While the evolutionary explanation is discussed, the expert said kissing could be used in reproductive situations to potentially increase mating outcomes or assist in selecting between mates, while it could assist reinforce bonding when used in a platonic way.

Another expert in the behavior of primates commented that as intimate contact was observed in a broad spectrum of apes it made sense its roots extend far into our ancient history, and an analysis of various types of kissing among a wider variety of species might extend its beginnings back even earlier still.

"Behaviors that we consider as characteristics of our species, like intimate contact, are not unique to us if we look closely at different species," he said.

Social Aspects

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

"However, as people we thrive or fail on the strength of our emotional bonds, and ways of promoting confidence and closeness will have been significant for eons," the professor stated. "It might be an concept that seems a bit contradictory to our misplaced ideas of a rather ruthless and ancient history, but really it ought to be expected that Neanderthals – and including Neanderthals and our human ancestors collectively – kissed."