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From Galápagos albatrosses to polar bears, chimpanzees to orangutans, various animals appear to kiss. Currently, researchers suggest that Neanderthals did it too – and possibly exchanged kisses with early Homo sapiens.

Shared Oral Evidence

This isn't the initial instance experts have suggested Neanderthals and early modern humans were closely connected. In previous studies, scientists have found modern people and their Neanderthal relatives shared the identical oral bacteria for hundreds of thousands of years after the evolutionary divergence, implying they swapped saliva.

"Probably they were kissing," the researcher noted, explaining that the concept chimed with research that has found people of non-African ancestry have bits of Neanderthal DNA in their genetic makeup, demonstrating genetic mixing was at play.

Romantic Spin

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

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

Defining Kissing

"Previously there were some efforts to define a kiss, but it's largely human-centric, which implies that essentially non-human species do not engage in this. Now we understand that they probably do, it may appear different from what human kissing looks like," said Brindle.

Nonetheless, she said some behaviors that resembled kissing were something rather different – such as the chewing and food sharing, or "kiss-fighting", seen in aquatic species called French grunts.

As a result the team developed a description of kissing centered around friendly interactions involving directed oral interaction with a individual of the same species, with some movement of the mouth but absence of food.

Study Approach

The lead researcher said they concentrated on reports of kissing in non-human species from the African continent and Asia, including primates, apes and orangutans, and employed digital recordings to confirm the reports.

The researchers then combined this information with information on the evolutionary relationships between living and extinct types of such primates.

Historical Timeline

Researchers say the findings suggest intimate contact developed somewhere between 21.5 million and 16.9m years ago in the predecessors of the great primates.

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

"Reality that modern people kiss, the fact that we now have shown that Neanderthals probably kissed, suggests that the both groups are probably did kissed," Brindle added.

Biological Importance

Although the scientific reasoning is discussed, Brindle explained kissing could be used in reproductive situations to potentially enhance mating outcomes or assist in selecting between mates, while it could assist reinforce bonding when practiced in a non-sexual manner.

A separate researcher in the behavior of primates said that as kissing behavior was observed in a broad spectrum of apes it was logical its roots lie deep in our evolutionary past, and an analysis of various types of intimate behavior among a broader range of species might push its origins back even earlier still.

"Behaviors that we consider as characteristics of human life, like intimate contact, are not unique to us if we look closely at other animals," the expert noted.

Cultural Aspects

Another professor said that intimate contact had a cultural element as it was not common to all societies.

"However, as people we thrive or fail on the quality of our emotional bonds, and ways of promoting trust and closeness will have been significant for millions of years," she said. "It might be an concept that seems a bit contradictory to our incorrect assumptions of a supposedly aggressive and aggressive past, but actually it ought to be expected that ancient hominins – and even Neanderthals and our human ancestors collectively – kissed."