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From Galápagos albatrosses to Arctic mammals, primates to orangutans, various animals appear to kiss. Now, scientists suggest that Neanderthals did it too – and possibly locked lips with modern humans.

Common Microbial Clues

It is not the first time experts have proposed ancient relatives and Homo sapiens were intimately acquainted. Among earlier research, scientists have discovered humans and their thick-browed cousins shared the same mouth microbe for millions of years after the evolutionary divergence, suggesting they swapped saliva.

"Likely they were kissing," she said, adding that the concept chimed with studies that has revealed people of certain genetic backgrounds have bits of Neanderthal DNA in their genome, demonstrating genetic mixing was at play.

Romantic Spin

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

Writing in the journal a scientific periodical, the researcher and colleagues report how, to investigate the historical roots of kissing, they first had to develop a definition that was not restricted by how humans smooch.

Describing Intimate Contact

"Previously there were some efforts to define a intimate act, but it's largely focused on humans, which implies that essentially non-human species do not engage in this. Currently we know that they likely engage, it might just not look from what our intimate contact looks like," said the evolutionary biologist.

However, she said some behaviors that resembled kissing were distinct activities – such as the chewing and food sharing, or "kiss-fighting", observed in aquatic species known as French grunts.

Consequently the team came up with a description of kissing centered around friendly interactions involving directed mouth-to-mouth contact with a individual of the identical group, with some motion of the mouth but no transfer of nutrition.

Research Approach

Brindle said they concentrated on accounts of intimate behavior in primates from the African continent and Asian regions, including primates, chimpanzees and orangutans, and used digital recordings to verify the reports.

The researchers then integrated this data with information on the genetic connections between extant and extinct species of such primates.

Historical Timeline

The team say the findings indicate kissing developed somewhere between 21.5m and 16.9m years ago in the predecessors of the great primates.

Placement of ancient hominins on this family tree means it is probable they, too, indulged in a intimate act, the scientists say. But the activity may not have been confined to their own species.

"The fact that modern people engage intimately, the reality that we currently have shown that ancient relatives probably kissed, indicates that the two [species] are also likely to have kissed," Brindle noted.

Biological Importance

While the evolutionary explanation is debated, the expert explained intimate contact could be used in sexual contexts to possibly enhance reproductive success or help choose between mates, while it might help strengthen connections when practiced in a platonic way.

Another expert in the activities of primates said that as kissing behavior was seen in a broad spectrum of apes it made sense its origins extend far into our ancient history, and an analysis of various types of intimate behavior among a broader range of species might extend its beginnings back further still.

"Things that we consider as signatures of human life, like intimate contact, are not exclusive to us if we look closely at other animals," he said.

Cultural Aspects

Another professor explained that kissing had a cultural element as it was not universal to all societies.

"Nonetheless, as humans we succeed or struggle on the strength of our relationships, and methods of promoting trust and intimacy will have been important for millions of years," she said. "This could represent an image that appears a bit contradictory to our misplaced ideas of a supposedly aggressive and aggressive past, but really it should be expected that Neanderthals – and including Neanderthals and our own species together – kissed."