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From Galápagos albatrosses to Arctic mammals, chimpanzees to orangutans, various animals appear to kiss. Currently, scientists propose that ancient hominins did it too – and might even have locked lips with early Homo sapiens.

Shared Microbial Evidence

It is not the first time experts have suggested Neanderthals and Homo sapiens were closely connected. In earlier research, researchers have discovered modern people and their Neanderthal relatives 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," the researcher noted, adding that the concept aligned with studies that has found people of non-African ancestry contain Neanderthal DNA in their genome, revealing interbreeding was occurring.

Intimate Interpretation

"This offers a more romantic perspective on human-Neanderthal relations," Brindle commented.

Writing in the publication a scientific periodical, Brindle and colleagues report how, to investigate the evolutionary origins of kissing, they first had to develop a definition that was not limited to how people smooch.

Describing Kissing

"Previously there were some efforts to define a kiss, but it's very much been human-centric, which implies that essentially other animals don't kiss. Now we understand that they likely engage, it may appear different from what human kissing resembles," explained the evolutionary biologist.

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

As a result the research group developed a description of intimate contact centered around social behaviors involving directed mouth-to-mouth contact with a individual of the same species, with some motion of the mouth but absence of food.

Study Methods

The lead researcher said they focused on accounts of kissing in non-human species from the African continent and Asia, including primates, apes and great apes, and used digital recordings to confirm the observations.

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

Historical Origins

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

The position of ancient hominins on this evolutionary lineage means it is probable they, too, engaged in a kiss, the scientists conclude. But the behavior might not have been confined to their own species.

"Reality that humans engage intimately, the reality that we currently have demonstrated that Neanderthals probably engaged, suggests that the two [species] are also likely to have kissed," Brindle added.

Biological Significance

Although the scientific reasoning is discussed, the expert said intimate contact could be employed in sexual contexts to possibly enhance mating outcomes or help choose between partners, while it could assist reinforce bonding when practiced in a platonic way.

A separate researcher in the activities of great apes commented that as kissing behavior was observed in a wide range of primates it made sense its roots lie deep in our ancient history, and an analysis of different forms of kissing among a broader range of animals might push its beginnings back even earlier still.

"Things that we think of as signatures of our species, like intimate contact, are not exclusive to us if we examine carefully at different species," he said.

Cultural Aspects

Another professor explained that kissing had a cultural element as it was not common to all human groups.

"However, as humans we succeed or struggle on the quality of our emotional bonds, and methods of encouraging trust and closeness will have been significant for millions of years," she said. "This could represent an image that seems a bit incongruous to our misplaced ideas of a rather ruthless and aggressive past, but really it ought to be expected that Neanderthals – and even Neanderthals and our own species collectively – kissed."