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From seabirds to Arctic mammals, chimpanzees to great apes, certain species appear to kiss. Currently, scientists propose that Neanderthals also engaged in this behavior – and possibly locked lips with early Homo sapiens.

Shared Microbial Clues

It is not the first time experts have suggested Neanderthals and early modern humans were intimately acquainted. In earlier research, researchers have found humans and their thick-browed cousins shared the same mouth microbe for hundreds of thousands of years after the two species split, suggesting they swapped saliva.

"Probably they were engaging in intimate contact," she said, explaining that the idea chimed with studies that has found people of certain genetic backgrounds have bits of ancient genetic material in their genome, demonstrating interbreeding was at play.

Intimate Spin

"It certainly puts a more romantic perspective on ancient interactions," Brindle said.

Writing in the journal a scientific periodical, Brindle and colleagues report how, to explore the evolutionary origins of intimate contact, they first had to develop a definition that was not limited to how humans smooch.

Defining Intimate Contact

"Previously there were some efforts to describe a intimate act, but it's largely human-centric, which means that essentially non-human species don't kiss. Currently we know that they likely engage, it may appear different from what our intimate contact resembles," said the evolutionary biologist.

However, she noted some actions that resembled kissing were something rather different – such as the processing and food sharing, or "kiss-fighting", observed in aquatic species known as certain marine animals.

Consequently the research group came up with a description of intimate contact based on friendly interactions involving intentional mouth-to-mouth contact with a individual of the identical group, with some movement of the mouth but no transfer of food.

Study Approach

Brindle said they concentrated on accounts of kissing in primates from Africa and Asia, including bonobos, apes and great apes, and employed online videos to verify the reports.

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

Evolutionary Origins

Researchers propose the findings indicate intimate contact evolved approximately 21.5m and 16.9m years ago in the ancestors of the large apes.

Placement of ancient hominins on this evolutionary lineage suggests it is likely they, too, indulged in a intimate act, the researchers say. But the activity might not have been confined to their own species.

"The fact that modern people engage intimately, the fact that we currently have demonstrated that Neanderthals probably engaged, indicates that the both groups are probably did engage," the researcher added.

Biological Significance

Although the scientific reasoning is discussed, the expert said kissing could be used in sexual contexts to possibly increase reproductive success or assist in selecting between partners, while it could assist strengthen connections when practiced in a non-sexual manner.

Another expert in the behavior of great apes commented that as kissing behavior was observed in a wide range of apes it was logical its origins lie deep in our ancient history, and an analysis of different forms of intimate behavior among a broader range of animals might push its origins back even earlier still.

"Things that we consider as characteristics of our species, like intimate contact, are not unique 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 societies.

"Nonetheless, as humans we succeed or struggle on the quality of our emotional bonds, and methods of promoting trust and intimacy will have been significant for eons," the professor stated. "This could represent an image that appears a bit incongruous to our incorrect assumptions of a supposedly aggressive and aggressive past, but really it should be no surprise that ancient hominins – and even Neanderthals and our human ancestors collectively – kissed."