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From Galápagos albatrosses to Arctic mammals, chimpanzees to great apes, various animals engage in mouth-to-mouth contact. Currently, scientists propose that Neanderthals did it too – and might even have exchanged kisses with modern humans.

Shared Oral Evidence

This isn't the initial instance experts have suggested Neanderthals and early modern humans were intimately acquainted. In previous studies, researchers have discovered modern people and their Neanderthal relatives shared the same mouth microbe for hundreds of thousands of years after the two species split, implying they exchanged oral fluids.

"Probably they were kissing," she said, explaining that the idea aligned with research that has found humans of non-African ancestry have bits of ancient genetic material in their genome, revealing genetic mixing was at play.

Intimate Interpretation

"This offers a different spin on ancient interactions," the lead researcher said.

Writing in the publication Evolution and Human Behavior, Brindle and colleagues report how, to investigate the evolutionary origins of intimate contact, they first had to come up with a description that was not restricted by how people smooch.

Describing Intimate Contact

"Previously there were some efforts to define a kiss, but it's very much been focused on humans, which means that essentially other animals don't kiss. Currently we understand that they likely engage, it may appear different from what human kissing resembles," explained Brindle.

However, she said some behaviors that looked like intimate contact were something rather different – such as the chewing and transfer of food, or "kiss-fighting", seen 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 identical group, with some motion of the oral area but no transfer of food.

Study Methods

The lead researcher said they focused on reports of kissing in non-human species from the African continent and Asian regions, including bonobos, apes and orangutans, and employed digital recordings to verify the reports.

Scientists then combined this information with information on the genetic connections between living and ancient species of such animals.

Historical Timeline

The team say the results suggest kissing developed somewhere between 21.5 million and 16.9m years ago in the predecessors of the large apes.

The position of ancient hominins on this family tree means it is likely they, too, indulged in a intimate act, the researchers say. But the behavior may not have been limited to their own species.

"Reality that humans engage intimately, the fact that we now have shown that Neanderthals probably kissed, suggests that the two [species] are also likely to have kissed," the researcher added.

Evolutionary Importance

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

A separate researcher in the activities of primates said that as kissing behavior was observed in a wide range of primates it made sense its origins lie deep in our evolutionary past, and an examination of various types of intimate behavior among a wider variety of species might push its beginnings back even earlier still.

"Things that we think of as characteristics of our species, like intimate contact, are not unique to us if we examine carefully at other animals," he said.

Social Aspects

An archaeology expert explained that kissing had a social component as it was not common to all societies.

"Nonetheless, as humans we thrive or fail on the quality of our relationships, and methods of encouraging trust and closeness will have been significant for eons," she said. "This could represent an image that appears a bit contradictory to our misplaced ideas of a supposedly aggressive and ancient history, but actually it ought to be expected that ancient hominins – and even Neanderthals and our own species collectively – kissed."