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From Galápagos albatrosses to polar bears, chimpanzees to great apes, certain species appear to kiss. Currently, researchers suggest that Neanderthals also engaged in this behavior – and might even have exchanged kisses with early Homo sapiens.

Common Oral Clues

It is not the first time experts have suggested Neanderthals and Homo sapiens were intimately acquainted. In earlier research, researchers have found humans and their thick-browed cousins possessed the same mouth microbe for millions of years after the evolutionary divergence, suggesting they swapped saliva.

"Probably they were engaging in intimate contact," the researcher noted, adding that the concept chimed with studies that has found people of non-African ancestry have bits of Neanderthal DNA in their genome, demonstrating genetic mixing was at play.

Romantic Spin

"It certainly puts a more romantic spin on ancient interactions," the lead researcher said.

Writing in the journal a scientific periodical, Brindle and her team report how, to explore the evolutionary origins of kissing, they first had to come up with a description that was not restricted by how humans smooch.

Describing Kissing

"There have been some efforts to define a kiss, but it's very much been human-centric, which implies that essentially other animals do not engage in this. Currently we understand that they probably do, it might just not look from what our intimate contact resembles," explained the evolutionary biologist.

Nonetheless, she noted some actions that looked like intimate contact were distinct activities – such as the processing and food sharing, or "mouth contact", observed in aquatic species called certain marine animals.

Consequently the team came up with a definition of intimate contact centered around friendly interactions involving directed oral interaction with a member of the identical group, with some motion of the oral area but no transfer of nutrition.

Study Methods

Brindle said they concentrated on reports of intimate behavior in non-human species from the African continent and Asia, including bonobos, chimpanzees and great apes, and used digital recordings to confirm the observations.

The researchers then combined this data with details on the evolutionary relationships between living and ancient types of such animals.

Historical Timeline

The team propose the findings indicate kissing developed somewhere between 21.5 million and 16.9 million years ago in the ancestors of the great primates.

Placement of ancient hominins on this family tree means it is probable they, too, engaged in a kiss, the scientists conclude. But the activity might not have been confined to their own species.

"Reality that modern people engage intimately, the reality that we now have demonstrated that Neanderthals probably kissed, indicates that the two [species] are probably did kissed," the researcher noted.

Biological Significance

Although the evolutionary explanation is discussed, Brindle explained intimate contact could be used in sexual contexts to possibly increase mating outcomes or assist in selecting between mates, while it might help reinforce bonding when practiced in a platonic way.

A separate researcher in the activities of primates said that as kissing behavior was observed in a broad spectrum of apes it was logical its roots extend far into our evolutionary past, and an examination of different forms of kissing among a wider variety of animals might push its origins back further still.

"Things that we consider as characteristics of our species, like intimate contact, are not exclusive to us if we look closely at other animals," he said.

Cultural Aspects

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

"However, as people we succeed or struggle on the quality of our relationships, and methods of promoting trust and intimacy will have been important for eons," she said. "This could represent an concept that seems a bit incongruous to our incorrect assumptions of a supposedly aggressive and ancient history, but really it ought to be no surprise that ancient hominins – and even them and our own species collectively – engaged intimately."