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From seabirds to polar bears, primates to great apes, various animals engage in mouth-to-mouth contact. Currently, researchers propose that Neanderthals also engaged in this behavior – and might even have exchanged kisses with modern humans.

Shared Microbial Evidence

It is not the first time scientists have proposed ancient relatives and Homo sapiens were intimately acquainted. Among previous studies, researchers have found humans and their thick-browed cousins shared the identical oral bacteria for hundreds of thousands of years after the two species split, implying they exchanged oral fluids.

"Probably they were engaging in intimate contact," the researcher noted, adding that the concept chimed with research that has revealed humans of certain genetic backgrounds have bits of ancient genetic material in their genetic makeup, demonstrating genetic mixing was at play.

Romantic Interpretation

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

Writing in the publication a scientific periodical, Brindle and her team detail how, to investigate the historical roots of kissing, they first had to come up with a description that was not limited to how people smooch.

Describing Kissing

"There have been some previous attempts to describe a kiss, but it's largely focused on humans, which means that essentially other animals don't kiss. Currently we understand that they likely engage, it might just not look from what human kissing looks like," said the evolutionary biologist.

However, she said some behaviors that resembled intimate contact were something rather different – such as the chewing and transfer of food, or "kiss-fighting", seen in fish known as French grunts.

As a result the research group developed a definition of kissing based on social behaviors involving intentional oral interaction with a individual of the identical group, with some movement of the mouth but no transfer of food.

Research Approach

The lead researcher said they focused on accounts of intimate behavior in primates from Africa and Asian regions, including bonobos, chimpanzees and orangutans, and employed online videos to confirm the reports.

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

Historical Timeline

Researchers propose the findings suggest kissing evolved approximately 21.5m and 16.9m years ago in the predecessors of the large apes.

The position of Neanderthals on this family tree suggests it is probable they, too, indulged in a kiss, the scientists conclude. But the activity may not have been confined to their specific group.

"Reality that humans kiss, the reality that we now have shown that ancient relatives probably kissed, suggests that the two [species] are probably did kissed," Brindle noted.

Evolutionary Significance

Although the scientific reasoning is debated, Brindle explained intimate contact could be employed in reproductive situations to possibly enhance mating outcomes or help choose between mates, while it might help strengthen connections when practiced in a non-sexual manner.

A separate researcher in the activities of primates commented that as intimate contact was seen in a wide range of apes it made sense its origins extend far into our ancient history, and an examination of various types of kissing among a broader range of species might extend its origins back further still.

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

Social Elements

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

"Nonetheless, as humans we thrive or fail on the strength of our relationships, and ways of promoting trust and intimacy will have been significant for eons," she said. "It might be an image that appears a bit contradictory to our misplaced ideas of a supposedly aggressive and ancient history, but really it should be no surprise that Neanderthals – and even Neanderthals and our human ancestors collectively – kissed."