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From seabirds to Arctic mammals, chimpanzees to great apes, certain species engage in mouth-to-mouth contact. Currently, scientists suggest that Neanderthals did it too – and possibly exchanged kisses with modern humans.

Shared Microbial Evidence

This isn't the initial instance experts have suggested ancient relatives and early modern humans were closely connected. In previous studies, scientists have found humans and their thick-browed cousins shared the same mouth microbe for hundreds of thousands of years after the two species split, implying they swapped saliva.

"Likely they were engaging in intimate contact," she said, adding that the idea aligned with research that has found people of certain genetic backgrounds contain Neanderthal DNA in their genetic makeup, demonstrating interbreeding was occurring.

Romantic Spin

"It certainly puts a different perspective on human-Neanderthal relations," Brindle commented.

Publishing in the publication a scientific periodical, the researcher and her team report how, to explore the evolutionary origins of kissing, they first had to come up with a definition that was not limited to how people smooch.

Describing Intimate Contact

"Previously there were some efforts to describe a kiss, but it's largely human-centric, which means that essentially non-human species don't kiss. Now we know that they probably do, it might just not look from what our intimate contact resembles," said the evolutionary biologist.

However, she said some behaviors that resembled kissing were distinct activities – such as the chewing and food sharing, or "mouth contact", seen in aquatic species known as certain marine animals.

Consequently the team came up with a definition of kissing centered around social behaviors involving intentional mouth-to-mouth contact with a member of the same species, with some motion of the mouth but absence of food.

Study Methods

The lead researcher said they concentrated on reports of intimate behavior in non-human species from Africa and Asian regions, including primates, chimpanzees and orangutans, and used digital recordings to verify the reports.

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

Historical Origins

The team propose the results indicate kissing evolved somewhere between 21.5 million and 16.9 million years ago in the ancestors of the large apes.

The position of Neanderthals on this evolutionary lineage means it is likely they, too, indulged in a intimate act, the researchers conclude. But the activity might not have been confined to their specific group.

"Reality that modern people engage intimately, the reality that we currently have shown that Neanderthals very likely kissed, indicates that the both groups are probably did kissed," the researcher added.

Biological Importance

While the evolutionary explanation is discussed, the expert said intimate contact could be employed in reproductive situations to potentially increase reproductive success or help choose between partners, while it might help reinforce bonding when used in a non-sexual manner.

A separate researcher in the activities of primates said that as intimate contact was observed in a broad spectrum of apes it was logical its origins lie deep in our evolutionary past, and an examination of different forms of intimate behavior among a broader range of animals might push its beginnings back even earlier still.

"Things that we consider as characteristics of human life, like intimate contact, are not exclusive to us if we examine carefully at other animals," he said.

Social Elements

Another professor said that kissing had a social component as it was not common to all societies.

"Nonetheless, as humans we succeed or struggle on the quality of our emotional bonds, and methods of encouraging confidence and closeness will have been important for eons," the professor stated. "It might be an image that seems a bit contradictory to our misplaced ideas of a supposedly aggressive and aggressive past, but actually it should be expected that Neanderthals – and even them and our human ancestors collectively – engaged intimately."