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Among Galápagos albatrosses to Arctic mammals, chimpanzees to great apes, certain species engage in mouth-to-mouth contact. Now, scientists suggest that ancient hominins did it too – and possibly locked lips with modern humans.

Common Microbial Clues

This isn't the initial instance experts have suggested ancient relatives and Homo sapiens were closely connected. In previous studies, researchers have found modern people and their Neanderthal relatives possessed the identical oral bacteria for millions of years after the two species split, suggesting they swapped saliva.

"Probably they were engaging in intimate contact," the researcher noted, explaining that the idea aligned with research that has revealed people of non-African ancestry have bits of Neanderthal DNA in their genome, demonstrating genetic mixing was occurring.

Intimate Spin

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

Writing in the publication a scientific periodical, Brindle and her team report how, to explore the evolutionary origins of intimate contact, they first had to come up with a description that was not limited to how people kiss.

Describing Kissing

"Previously there were some previous attempts to define a intimate act, but it's largely focused on humans, which implies that basically other animals don't kiss. Now we understand that they probably do, it may appear different from what our intimate contact looks like," explained Brindle.

However, she noted some actions that looked like intimate contact were distinct activities – such as the processing and food sharing, or "kiss-fighting", seen in fish called French grunts.

As a result the team came up with a description of kissing centered around friendly interactions involving directed oral interaction with a member of the same species, with some motion of the mouth but no transfer of nutrition.

Research Methods

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

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

Historical Origins

The team say the findings suggest intimate contact evolved 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 kiss, the researchers say. But the activity may not have been limited to their own species.

"Reality that modern people kiss, the fact that we now have shown that ancient relatives very likely engaged, indicates that the both groups are also likely to have engage," Brindle added.

Evolutionary Importance

Although the scientific reasoning is discussed, Brindle said intimate contact could be employed in sexual contexts to possibly increase mating outcomes or help choose between partners, while it might help reinforce bonding when used in a platonic way.

Another expert in the activities of primates said that as intimate contact was observed in a wide range of apes it was logical its origins extend far into our ancient history, and an examination of various types of kissing among a broader range of species might push its beginnings back even earlier still.

"Things that we consider as signatures of human life, like kissing, are not exclusive to us if we examine carefully at different species," the expert noted.

Cultural Aspects

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

"Nonetheless, as people we succeed or struggle on the strength of our relationships, and methods of encouraging confidence and closeness will have been important for eons," the professor stated. "This could represent an concept that appears a bit incongruous to our incorrect assumptions of a rather ruthless and aggressive past, but really it should be no surprise that Neanderthals – and even Neanderthals and our human ancestors collectively – engaged intimately."