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From Galápagos albatrosses to polar bears, chimpanzees to great apes, various animals engage in mouth-to-mouth contact. Now, researchers propose that Neanderthals also engaged in this behavior – and might even have locked lips with modern humans.

Shared Oral Clues

This isn't the initial instance experts have suggested ancient relatives and early modern humans were intimately acquainted. Among earlier research, researchers have discovered humans and their Neanderthal relatives possessed the same mouth microbe for hundreds of thousands of years after the evolutionary divergence, suggesting they swapped saliva.

"Probably they were engaging in intimate contact," she said, adding that the idea chimed with research that has found humans of certain genetic backgrounds have bits of ancient genetic material in their genetic makeup, revealing genetic mixing was at play.

Intimate Interpretation

"It certainly puts a more romantic spin on ancient interactions," Brindle commented.

Writing in the publication a scientific periodical, the researcher and colleagues report how, to investigate 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

"Previously there were some previous attempts to describe a intimate act, but it's largely focused on humans, which implies that essentially non-human species do not engage in this. Now we understand that they likely engage, it might just not look from what our intimate contact resembles," said Brindle.

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

As a result the team developed a definition of intimate contact centered around social behaviors involving directed oral interaction with a member of the identical group, with some motion of the mouth but no transfer of nutrition.

Study Approach

The lead researcher explained they concentrated on accounts of intimate behavior in non-human species from the African continent and Asian regions, including primates, apes and orangutans, and employed digital recordings to verify the observations.

The researchers then combined this information with details on the evolutionary relationships between extant and ancient types of such animals.

Historical Origins

Researchers propose the findings suggest kissing developed somewhere between 21.5m and 16.9 million years ago in the predecessors 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 may not have been confined to their specific group.

"The fact that modern people engage intimately, the reality that we now have demonstrated that ancient relatives very likely kissed, suggests that the both groups are probably did kissed," Brindle noted.

Evolutionary Importance

Although the evolutionary explanation is discussed, the expert said intimate contact could be used in reproductive situations to potentially enhance reproductive success or help choose between partners, while it might help strengthen connections when practiced in a non-sexual manner.

Another expert in the activities of primates said that as intimate contact was seen in a broad spectrum of apes it was logical its origins extend far into our ancient history, and an examination of different forms of intimate behavior among a wider variety of species might extend its origins back even earlier still.

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

Cultural Aspects

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

"However, as people we succeed or struggle on the quality of our emotional bonds, and methods of encouraging trust and closeness will have been significant for eons," she said. "It might be an concept that seems a bit contradictory to our incorrect assumptions of a rather ruthless and aggressive past, but really it should be no surprise that Neanderthals – and including them and our own species collectively – engaged intimately."