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From seabirds to Arctic mammals, primates to orangutans, various animals appear to kiss. Currently, scientists suggest that Neanderthals did it too – and possibly locked lips with early Homo sapiens.

Common Microbial Evidence

It is not the first time experts have proposed Neanderthals and early modern humans were closely connected. In earlier research, scientists have discovered modern people and their thick-browed cousins possessed the same mouth microbe for hundreds of thousands of years after the evolutionary divergence, implying they swapped saliva.

"Likely they were engaging in intimate contact," the researcher noted, adding that the idea aligned with studies that has revealed humans of non-African ancestry contain Neanderthal DNA in their genome, demonstrating genetic mixing was occurring.

Romantic Interpretation

"It certainly puts a more romantic spin on human-Neanderthal relations," Brindle commented.

Writing in the publication a scientific periodical, Brindle and her team detail how, to investigate the evolutionary origins of intimate contact, they first had to develop a description that was not restricted by 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 resembles," explained Brindle.

Nonetheless, she noted some actions that resembled intimate contact were something rather different – such as the processing and transfer of food, or "kiss-fighting", observed in aquatic species known as French grunts.

As a result the research group developed a definition of kissing based on friendly interactions involving intentional mouth-to-mouth contact with a individual of the same species, with some motion of the oral area but absence of food.

Study Methods

The lead researcher explained they focused on accounts of kissing in primates from the African continent and Asian regions, including primates, apes and orangutans, and used online videos to verify the reports.

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

Evolutionary Timeline

Researchers say the results suggest intimate contact evolved 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 likely they, too, indulged in a kiss, the researchers say. But the activity might not have been limited to their own species.

"Reality that modern people kiss, the fact that we now have demonstrated that ancient relatives very likely kissed, indicates that the both groups are also likely to have kissed," the researcher added.

Biological Importance

While the scientific reasoning is discussed, Brindle said intimate contact could be used in reproductive situations to potentially enhance reproductive success or assist in selecting between partners, while it could assist reinforce bonding when used in a non-sexual manner.

A separate researcher in the activities of great apes commented that as intimate contact was observed in a wide range of primates it made sense its roots lie deep in our evolutionary past, and an examination of different forms of intimate behavior among a wider variety of species might extend its beginnings back even earlier still.

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

Social Aspects

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

"Nonetheless, as humans we succeed or struggle on the quality of our relationships, and ways of encouraging confidence and intimacy will have been important for eons," she said. "It might be an image that appears a bit contradictory to our incorrect assumptions of a rather ruthless and ancient history, but actually it should be no surprise that ancient hominins – and even them and our human ancestors collectively – kissed."