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Among Galápagos albatrosses to Arctic mammals, chimpanzees to great apes, certain species appear to kiss. Currently, scientists suggest that ancient hominins did it too – and possibly locked lips with early Homo sapiens.

Shared Oral Evidence

It is not the first time experts have proposed Neanderthals and Homo sapiens were intimately acquainted. In earlier research, researchers have found humans and their thick-browed cousins shared the identical oral bacteria for millions of years after the evolutionary divergence, implying they swapped saliva.

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

Romantic Spin

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

Writing in the journal a scientific periodical, the researcher and her team detail how, to investigate the historical roots of intimate contact, they first had to develop a description that was not restricted by how people smooch.

Describing Intimate Contact

"Previously there were some previous attempts to define a intimate act, but it's very much been focused on humans, which implies that essentially other animals do not engage in this. Currently we know that they probably do, it may appear different from what our intimate contact looks like," explained Brindle.

However, she said some behaviors that resembled intimate contact were distinct activities – such as the processing and food sharing, or "kiss-fighting", seen in aquatic species called certain marine animals.

As a result the research group came up with a description of intimate contact based on friendly interactions involving directed oral interaction with a member of the same species, with some motion of the oral area but absence of nutrition.

Research Approach

The lead researcher said they concentrated on reports of intimate behavior in non-human species from the African continent and Asia, including primates, apes and great apes, and used online videos to verify the reports.

Scientists then combined this data with information on the genetic connections between living and ancient species of such animals.

Historical Timeline

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

Placement of Neanderthals on this evolutionary lineage suggests it is likely they, too, indulged in a kiss, the scientists conclude. But the activity might not have been limited to their own species.

"The fact that humans engage intimately, the fact that we currently have shown that ancient relatives probably kissed, suggests that the two [species] are probably did kissed," Brindle noted.

Biological Importance

Although the scientific reasoning is debated, the expert explained intimate contact could be employed in sexual contexts to possibly enhance reproductive success or help choose between mates, while it could assist reinforce bonding when used in a platonic way.

A separate researcher in the behavior of great apes said that as kissing behavior was seen in a wide range of primates it made sense its roots lie deep in our evolutionary past, and an examination of various types of intimate behavior among a broader range of species might extend its beginnings back even earlier still.

"Behaviors that we consider as characteristics of our species, like kissing, are not exclusive to us if we look closely at different species," he said.

Social Elements

An archaeology expert said that kissing had a cultural element as it was not universal to all societies.

"However, as people we succeed or struggle on the quality of our emotional bonds, and methods of promoting confidence and closeness will have been significant for eons," she said. "This could represent an image that appears a bit contradictory to our incorrect assumptions of a rather ruthless and ancient history, but really it should be expected that Neanderthals – and even Neanderthals and our own species together – kissed."