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Among seabirds to Arctic mammals, chimpanzees to great apes, various animals engage in mouth-to-mouth contact. Currently, researchers suggest that Neanderthals did it too – and might even have locked lips with modern humans.

Shared Oral Clues

It is not the first time scientists have proposed ancient relatives and early modern humans were intimately acquainted. In earlier research, scientists have found modern people and their Neanderthal relatives possessed the identical oral bacteria for hundreds of thousands of years after the two species split, implying they exchanged oral fluids.

"Likely they were kissing," the researcher noted, adding that the idea aligned with research that has found people of non-African ancestry contain Neanderthal DNA in their genetic makeup, demonstrating interbreeding was at play.

Intimate Spin

"This offers a different spin on ancient interactions," Brindle commented.

Publishing in the publication a scientific periodical, the researcher and colleagues detail how, to explore the historical roots of intimate contact, they first had to develop a definition that was not limited to how humans smooch.

Describing Kissing

"There have been some previous attempts to define a intimate act, but it's very much been focused on humans, which means that basically non-human species do not engage in this. Currently we understand that they probably do, it might just not look from what human kissing resembles," explained Brindle.

Nonetheless, she said some behaviors that resembled kissing were distinct activities – such as the processing and transfer of food, or "mouth contact", observed in aquatic species called certain marine animals.

As a result the research group came up with a definition of intimate contact centered around friendly interactions involving intentional mouth-to-mouth contact with a individual of the same species, with some movement of the mouth but no transfer of nutrition.

Study Methods

The lead researcher said they concentrated on accounts of kissing in non-human species from Africa and Asia, including bonobos, apes and great apes, 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.

Evolutionary Timeline

The team propose the results suggest intimate contact evolved somewhere between 21.5 million and 16.9m years ago in the predecessors of the large apes.

Placement of Neanderthals on this evolutionary lineage means it is probable they, too, engaged in a intimate act, the scientists conclude. But the activity might not have been confined to their own species.

"The fact that humans kiss, the fact that we currently have demonstrated that ancient relatives probably engaged, indicates that the two [species] are probably did kissed," Brindle added.

Evolutionary Significance

Although the evolutionary explanation is debated, Brindle explained intimate contact could be employed in reproductive situations to possibly enhance reproductive success or help choose between partners, while it could assist strengthen connections when used in a non-sexual manner.

A separate researcher in the activities of great apes said that as kissing behavior was seen in a wide range of primates it was logical its roots lie deep in 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 exclusive to us if we look closely at other animals," he said.

Cultural Elements

An archaeology expert explained that kissing had a social component as it was not common to all human groups.

"Nonetheless, as people we succeed or struggle on the quality of our emotional bonds, and ways of promoting trust and intimacy will have been significant for millions of years," the professor stated. "It might be an concept that appears a bit contradictory to our incorrect assumptions of a rather ruthless and aggressive past, but actually it ought to be expected that Neanderthals – and even them and our human ancestors together – kissed."