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From Galápagos albatrosses to Arctic mammals, primates to great apes, certain species appear to kiss. Currently, researchers suggest that Neanderthals did it too – and might even have exchanged kisses with early Homo sapiens.

Common Oral Clues

This isn't the initial instance scientists have suggested Neanderthals and Homo sapiens were intimately acquainted. Among earlier research, researchers have discovered humans and their thick-browed cousins shared the same mouth microbe for hundreds of thousands of years after the evolutionary divergence, suggesting they swapped saliva.

"Likely they were kissing," the researcher noted, adding that the idea aligned with studies that has revealed humans of non-African ancestry have bits of ancient genetic material in their genetic makeup, revealing interbreeding was at play.

Intimate Spin

"It certainly puts a different perspective on ancient interactions," Brindle commented.

Writing in the journal Evolution and Human Behavior, the researcher and colleagues report how, to investigate the evolutionary origins of intimate contact, they first had to develop a description that was not limited to how people smooch.

Describing Kissing

"Previously there were some efforts to describe a intimate act, but it's very much been focused on humans, which means that basically non-human species don't kiss. Currently we know that they likely engage, it may appear different from what human kissing resembles," explained Brindle.

However, she noted some actions that resembled kissing were distinct activities – such as the chewing and transfer of food, or "kiss-fighting", seen in fish known as certain marine animals.

Consequently the team came up with a definition of kissing centered around friendly interactions involving directed oral interaction with a member of the same species, with some motion of the mouth but no transfer of food.

Research Approach

The lead researcher explained they concentrated on accounts of kissing in non-human species from Africa and Asian regions, including bonobos, apes and great apes, and used digital recordings to confirm the reports.

Scientists then integrated this data with information on the genetic connections between extant and ancient types of such animals.

Evolutionary Origins

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

The position of Neanderthals on this family tree means it is probable they, too, engaged in a kiss, the researchers say. But the activity may not have been limited to their own species.

"Reality that modern people engage intimately, the reality that we now have shown that ancient relatives very likely engaged, indicates that the both groups are probably did kissed," Brindle noted.

Biological Importance

Although the evolutionary explanation is debated, Brindle said kissing could be used in reproductive situations to possibly increase reproductive success or help choose between partners, while it might help reinforce bonding when used in a platonic way.

A separate researcher in the behavior of primates commented that as intimate contact was seen in a wide range of apes it made sense its roots extend far into our ancient history, and an analysis of various types of intimate behavior among a wider variety of animals might extend its origins back further still.

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

Social Aspects

Another professor said that kissing had a social component as it was not universal to all societies.

"Nonetheless, as people we succeed or struggle on the quality of our relationships, and methods of encouraging confidence and intimacy will have been important for millions of years," the professor stated. "It might be an concept that seems a bit incongruous to our misplaced ideas of a supposedly aggressive and ancient history, but really it should be no surprise that ancient hominins – and including Neanderthals and our human ancestors collectively – engaged intimately."