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From Galápagos albatrosses to Arctic mammals, chimpanzees to orangutans, various animals appear to kiss. Currently, researchers suggest that ancient hominins also engaged in this behavior – and possibly exchanged kisses with modern humans.

Shared Oral Clues

It is not the first time scientists have suggested Neanderthals and early modern humans were closely connected. Among earlier research, researchers have discovered humans and their Neanderthal relatives shared the identical oral bacteria for millions of years after the two species split, implying they swapped saliva.

"Likely they were kissing," the researcher noted, adding that the concept chimed with research that has revealed people of non-African ancestry have bits of ancient genetic material in their genetic makeup, demonstrating interbreeding was at play.

Intimate Spin

"This offers a different spin on human-Neanderthal relations," the lead researcher commented.

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

Describing Intimate Contact

"Previously there were some previous attempts to describe a kiss, but it's very much been human-centric, which means that essentially other animals don't kiss. Now we know that they likely engage, it may appear different from what our intimate contact looks like," said the evolutionary biologist.

Nonetheless, she noted some actions that looked like kissing were something rather different – such as the chewing and food sharing, or "mouth contact", seen in aquatic species called French grunts.

As a result the team came up with a definition of intimate contact centered around friendly interactions involving intentional mouth-to-mouth contact with a member of the identical group, with some movement of the oral area but absence of nutrition.

Research Methods

The lead researcher said they focused on reports of intimate behavior in primates from Africa and Asia, including primates, chimpanzees and great apes, and employed online videos to verify the observations.

The researchers then integrated this data with information on the evolutionary relationships between living and ancient species of such animals.

Historical Timeline

Researchers say the results indicate intimate contact developed somewhere between 21.5m and 16.9 million years ago in the ancestors of the great primates.

Placement of Neanderthals on this family tree suggests it is probable they, too, engaged in a intimate act, the scientists conclude. But the activity might not have been confined to their own species.

"The fact that modern people engage intimately, the fact that we now have demonstrated that ancient relatives probably engaged, suggests that the both groups are also likely to have engage," Brindle noted.

Evolutionary Importance

Although the scientific reasoning is discussed, the expert explained kissing could be employed in reproductive situations to potentially increase mating outcomes or assist in selecting between partners, while it might help strengthen connections when practiced in a non-sexual manner.

A separate researcher in the activities of primates commented that as kissing behavior was observed in a wide range of primates it was logical its roots lie deep in our ancient history, and an examination of different forms of intimate behavior among a broader range of animals might push its origins back even earlier still.

"Behaviors that we think of as signatures of our species, like kissing, are not unique to us if we examine carefully at different species," the expert noted.

Cultural Elements

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

"Nonetheless, as humans we succeed or struggle on the quality of our relationships, and ways of promoting trust and closeness will have been important for millions of years," the professor stated. "This could represent an concept that seems a bit contradictory to our incorrect assumptions of a rather ruthless and aggressive past, but actually it should be expected that Neanderthals – and including them and our own species collectively – engaged intimately."