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From Galápagos albatrosses to Arctic mammals, chimpanzees to great apes, various animals engage in mouth-to-mouth contact. Currently, researchers propose that Neanderthals did it too – and possibly exchanged kisses with modern humans.

Common Microbial Clues

It is not the first time experts have suggested ancient relatives and early modern humans were intimately acquainted. In earlier research, scientists have found modern people and their thick-browed cousins possessed the identical oral bacteria for hundreds of thousands of years after the evolutionary divergence, suggesting they swapped saliva.

"Probably they were engaging in intimate contact," she said, explaining that the concept aligned with research that has revealed people of non-African ancestry contain ancient genetic material in their genetic makeup, demonstrating interbreeding was at play.

Romantic Interpretation

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

Writing in the journal a scientific periodical, the researcher and colleagues 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 humans smooch.

Defining Kissing

"There have been some efforts to describe a intimate act, but it's largely human-centric, which means that basically non-human species don't kiss. Currently we understand that they probably do, it may appear different from what our intimate contact looks like," explained Brindle.

Nonetheless, she said some actions that resembled kissing were distinct activities – such as the chewing and food sharing, or "mouth contact", observed in aquatic species known as French grunts.

As a result the team developed a description of kissing based on friendly interactions involving intentional oral interaction with a individual of the same species, with some motion of the oral area but no transfer of food.

Research Methods

The lead researcher 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 observations.

The researchers then combined this information with information on the evolutionary relationships between living and ancient species of such primates.

Historical Timeline

The team say the findings suggest intimate contact evolved approximately 21.5m and 16.9 million years ago in the ancestors of the great primates.

The position of Neanderthals on this family tree suggests it is probable they, too, engaged in a kiss, the researchers conclude. But the behavior might not have been confined to their specific group.

"Reality that modern people engage intimately, the reality that we now have shown that ancient relatives probably kissed, suggests that the both groups are also likely to have engage," Brindle added.

Evolutionary Significance

Although the evolutionary explanation is discussed, the expert said kissing could be employed in sexual contexts to possibly increase mating outcomes or help choose between mates, while it might help reinforce bonding when used in a platonic way.

A separate researcher in the behavior of great apes said that as kissing behavior was observed in a broad spectrum of apes it made sense its origins lie deep in our ancient history, and an examination of different forms of kissing among a wider variety of species might extend its origins back even earlier still.

"Behaviors that we consider as characteristics of our species, like kissing, are not unique to us if we examine carefully at other animals," the expert noted.

Cultural Aspects

Another professor said that intimate contact had a social component as it was not universal to all human groups.

"Nonetheless, as humans we succeed or struggle on the quality of our emotional bonds, and methods of encouraging trust and intimacy will have been significant for eons," she said. "It might be an concept that seems a bit incongruous to our incorrect assumptions of a supposedly aggressive and aggressive past, but actually it should be no surprise that ancient hominins – and even them and our own species together – engaged intimately."