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Among Galápagos albatrosses to polar bears, primates to orangutans, certain species engage in mouth-to-mouth contact. Currently, scientists suggest that Neanderthals also engaged in this behavior – and might even have locked lips with modern humans.

Shared Oral Evidence

This isn't the initial instance scientists have proposed Neanderthals and Homo sapiens were closely connected. In previous studies, researchers have discovered modern people and their thick-browed cousins possessed the identical oral bacteria for hundreds of thousands of years after the evolutionary divergence, suggesting they exchanged oral fluids.

"Probably they were engaging in intimate contact," the researcher noted, explaining that the idea aligned with studies that has revealed humans of non-African ancestry have bits of Neanderthal DNA in their genome, demonstrating genetic mixing was at play.

Intimate Interpretation

"It certainly puts a different perspective on ancient interactions," Brindle commented.

Publishing in the publication a scientific periodical, the researcher and her team detail how, to explore the historical roots of intimate contact, they first had to come up with a description that was not restricted by how humans smooch.

Defining Intimate Contact

"Previously there were some efforts to define a kiss, but it's very much been focused on humans, which means that basically other animals don't kiss. Currently we understand that they likely engage, it may appear different from what human kissing resembles," said the evolutionary biologist.

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

Consequently the research group developed a definition of intimate contact centered around friendly interactions involving intentional mouth-to-mouth contact with a individual of the same species, with some motion of the oral area but no transfer of nutrition.

Research Approach

Brindle said they focused on accounts of kissing in non-human species from Africa and Asian regions, including primates, apes and orangutans, and employed online videos to verify the observations.

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

Historical Origins

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

The position of ancient hominins on this evolutionary lineage means it is likely they, too, indulged in a kiss, the researchers conclude. But the activity may not have been limited to their specific group.

"Reality that humans kiss, the reality that we currently have demonstrated that Neanderthals probably engaged, suggests that the two [species] are probably did engage," Brindle noted.

Biological Importance

While the evolutionary explanation is discussed, Brindle explained kissing could be employed in sexual contexts to potentially enhance reproductive success or assist in selecting between partners, while it might help strengthen connections when practiced in a platonic way.

Another expert in the activities of primates commented that as kissing behavior was observed in a broad spectrum of primates it was logical its origins lie deep in our evolutionary past, and an analysis of various types of kissing among a wider variety of animals might push its origins back further still.

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

Cultural Elements

An archaeology expert said that intimate contact had a cultural element as it was not common to all societies.

"However, as humans we thrive or fail on the strength of our relationships, and ways of promoting confidence and closeness will have been significant for millions of years," the professor stated. "This could represent an concept that appears a bit incongruous to our misplaced ideas of a supposedly aggressive and aggressive past, but actually it ought to be no surprise that ancient hominins – and including Neanderthals and our human ancestors collectively – kissed."