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From 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 exchanged kisses with modern humans.

Common Microbial Evidence

This isn't the initial instance scientists have suggested ancient relatives and Homo sapiens were intimately acquainted. Among previous studies, researchers have found humans and their Neanderthal relatives shared the same mouth microbe for hundreds of thousands of years after the evolutionary divergence, implying they swapped saliva.

"Probably they were engaging in intimate contact," the researcher noted, adding that the concept chimed with studies that has revealed people of certain genetic backgrounds contain ancient genetic material in their genetic makeup, revealing genetic mixing was at play.

Intimate Spin

"This offers a different perspective on ancient interactions," the lead researcher commented.

Publishing in the journal a scientific periodical, Brindle and colleagues report how, to investigate the evolutionary origins of kissing, they first had to come up with a description that was not limited to how people kiss.

Describing Intimate Contact

"There have been some previous attempts to define a intimate act, but it's very much been focused on humans, which implies that basically non-human species don't kiss. Currently we know that they likely engage, it may appear different from what human kissing resembles," explained Brindle.

Nonetheless, she said some behaviors that looked like intimate contact were something rather different – such as the chewing and food sharing, or "kiss-fighting", observed in fish called French grunts.

Consequently the research group developed 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 explained they focused on accounts of intimate behavior in non-human species from Africa and Asia, including bonobos, apes and great apes, and used digital recordings to verify the reports.

The researchers then integrated this information with details on the genetic connections between living and ancient types of such primates.

Historical Timeline

Researchers propose the findings indicate kissing evolved approximately 21.5 million and 16.9 million years ago in the ancestors of the large apes.

Placement of ancient hominins on this evolutionary lineage suggests it is likely they, too, engaged in a kiss, the scientists conclude. But the behavior might not have been confined to their own species.

"Reality that humans kiss, the reality that we currently have demonstrated that Neanderthals probably kissed, indicates that the both groups are probably did engage," Brindle added.

Biological Significance

Although the evolutionary explanation is debated, Brindle said kissing could be used in sexual contexts to possibly enhance mating outcomes or help choose between mates, while it could assist reinforce bonding when used in a platonic way.

Another expert in the behavior of great apes commented that as intimate contact was seen in a wide range of primates it made sense its origins extend far into our evolutionary past, and an analysis of various types of kissing among a wider variety of animals might push its beginnings back further still.

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

Social Elements

Another professor 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 quality of our relationships, and ways of encouraging confidence and intimacy will have been important for eons," she said. "It might be an image that seems a bit contradictory to our incorrect assumptions of a rather ruthless and ancient history, but really it ought to be expected that ancient hominins – and including them and our human ancestors together – kissed."