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From Galápagos albatrosses to polar bears, primates to orangutans, various animals appear to kiss. Now, researchers propose that Neanderthals did it too – and possibly exchanged kisses with modern humans.

Common Oral Evidence

This isn't the initial instance experts have suggested ancient relatives and early modern humans were intimately acquainted. Among previous studies, researchers have found humans and their Neanderthal relatives shared the same mouth microbe for millions of years after the evolutionary divergence, implying they exchanged oral fluids.

"Likely they were kissing," she said, explaining that the concept aligned with studies that has revealed people of certain genetic backgrounds contain Neanderthal DNA in their genetic makeup, revealing interbreeding was at play.

Intimate Interpretation

"It certainly puts a more romantic perspective on ancient interactions," Brindle said.

Writing in the journal Evolution and Human Behavior, Brindle and colleagues detail how, to investigate the historical roots of kissing, they first had to come up with a description that was not restricted by how humans kiss.

Defining Intimate Contact

"There have been some efforts to describe a intimate act, but it's very much been focused on humans, which means that essentially other animals do not engage in this. Currently we understand that they likely engage, it might just not look from what our intimate contact resembles," explained the evolutionary biologist.

Nonetheless, she said some actions that resembled kissing were distinct activities – such as the chewing and food sharing, or "kiss-fighting", seen in fish called French grunts.

Consequently the research group developed a description of kissing centered around social behaviors involving intentional oral interaction with a member of the same species, with some movement of the mouth but absence of nutrition.

Research Methods

Brindle explained they concentrated on reports of kissing in non-human species from the African continent and Asian regions, including primates, chimpanzees and great apes, and employed digital recordings to confirm the reports.

Scientists then combined this data with information on the genetic connections between extant and extinct species of such primates.

Evolutionary Origins

Researchers propose the findings 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 evolutionary lineage suggests it is probable they, too, indulged in a intimate act, the researchers conclude. But the activity may not have been confined to their specific group.

"The fact that modern people kiss, the fact that we now have demonstrated that Neanderthals very likely kissed, suggests that the two [species] are also likely to have kissed," the researcher added.

Biological Importance

While the evolutionary explanation is discussed, Brindle explained kissing could be employed in sexual contexts to potentially enhance reproductive success or assist in selecting between partners, while it might help strengthen connections when practiced in a non-sexual manner.

A separate researcher in the behavior of great apes said that as intimate contact was seen in a broad spectrum of primates it made sense its roots lie deep in our evolutionary past, and an analysis of various types of intimate behavior among a wider variety of species might push its beginnings back even earlier still.

"Things that we consider as characteristics of human life, like kissing, are not unique to us if we look closely at different species," he said.

Social Elements

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

"Nonetheless, as people we thrive or fail on the strength of our emotional bonds, and methods of promoting confidence and closeness will have been important for millions of years," she said. "It might be an concept that appears a bit contradictory to our misplaced ideas of a supposedly aggressive and ancient history, but actually it ought to be no surprise that ancient hominins – and even them and our human ancestors collectively – kissed."