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Among seabirds to Arctic mammals, primates to great apes, various animals appear to kiss. Currently, researchers suggest that Neanderthals did it too – and possibly locked lips with early Homo sapiens.

Shared Oral Clues

It is not the first time scientists have suggested Neanderthals and Homo sapiens were closely connected. Among earlier research, researchers have discovered modern people and their Neanderthal relatives shared the same mouth microbe for millions of years after the evolutionary divergence, implying they swapped saliva.

"Likely they were kissing," she said, explaining that the concept chimed with research that has revealed humans of non-African ancestry contain Neanderthal DNA in their genetic makeup, revealing genetic mixing was at play.

Intimate Spin

"It certainly puts a different perspective on ancient interactions," the lead researcher said.

Publishing in the publication a scientific periodical, the researcher and colleagues detail how, to explore the evolutionary origins of intimate contact, they first had to develop a definition that was not restricted by how people kiss.

Describing Intimate Contact

"There have been some efforts to define a kiss, but it's very much been human-centric, which means 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," said the evolutionary biologist.

However, she said some behaviors that looked like kissing were something rather different – such as the processing and transfer of food, or "mouth contact", observed in aquatic species called French grunts.

Consequently the team came up with a definition of kissing centered around social behaviors involving intentional mouth-to-mouth contact with a individual of the identical group, with some movement of the mouth but absence of nutrition.

Study Approach

The lead researcher said they concentrated on reports of kissing in non-human species from Africa and Asia, including primates, chimpanzees and great apes, and used online videos to verify the observations.

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

Evolutionary Timeline

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

The position of ancient hominins on this evolutionary lineage suggests it is probable they, too, indulged in a kiss, the researchers say. But the behavior might not have been confined to their specific group.

"Reality that humans engage intimately, the reality that we currently have demonstrated that Neanderthals probably engaged, suggests that the two [species] are probably did engage," the researcher noted.

Biological Significance

Although the evolutionary explanation is debated, the expert explained intimate contact could be employed in reproductive situations to potentially increase mating outcomes or assist in selecting between partners, while it might help reinforce bonding when used in a platonic way.

A separate researcher in the activities of great apes said that as kissing behavior was seen in a wide range of apes it was logical its origins lie deep in our evolutionary past, and an examination of various types of intimate behavior among a wider variety of species might extend its origins back even earlier still.

"Things that we consider as signatures of human life, like kissing, are not exclusive to us if we look closely at different species," he said.

Social Elements

Another professor said that intimate contact had a social component as it was not universal to all human groups.

"However, as humans we thrive or fail on the strength of our emotional bonds, and methods of promoting trust and intimacy will have been significant for millions of years," the professor stated. "It might be an image that appears a bit contradictory to our incorrect assumptions of a supposedly aggressive and ancient history, but really it ought to be expected that ancient hominins – and even them and our human ancestors together – engaged intimately."