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Among Galápagos albatrosses to polar bears, primates to orangutans, certain species appear to kiss. Now, researchers suggest that ancient hominins did it too – and might even have locked lips with early Homo sapiens.

Common Microbial Clues

It is not the first time experts have proposed Neanderthals and early modern humans were intimately acquainted. In previous studies, researchers have found modern people and their thick-browed cousins shared the identical oral bacteria for hundreds of thousands of years after the two species split, suggesting they exchanged oral fluids.

"Probably they were kissing," the researcher noted, adding that the idea chimed with research that has found people of non-African ancestry have bits of ancient genetic material in their genome, demonstrating interbreeding was occurring.

Romantic Interpretation

"It certainly puts a different spin on human-Neanderthal relations," the lead researcher said.

Publishing in the publication Evolution and Human Behavior, the researcher 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 humans smooch.

Describing Kissing

"Previously there were some previous attempts to describe a kiss, but it's largely human-centric, which means that basically other animals don't kiss. Now we know that they probably do, it might just not look from what our intimate contact looks like," explained the evolutionary biologist.

However, she noted some behaviors that resembled intimate contact were something rather different – such as the chewing and transfer of food, or "mouth contact", seen in fish called French grunts.

Consequently the research group developed a definition of kissing based on social behaviors involving intentional oral interaction with a individual of the identical group, with some movement of the oral area but absence of food.

Study Methods

Brindle explained they concentrated on accounts of kissing in primates from Africa and Asian regions, including primates, apes and orangutans, and used online videos to verify the observations.

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

Evolutionary Origins

The team say the findings indicate intimate contact evolved approximately 21.5 million and 16.9m years ago in the ancestors of the large apes.

Placement of ancient hominins on this family tree suggests it is likely they, too, engaged in a kiss, the scientists conclude. But the activity may not have been limited to their own species.

"The fact that humans kiss, the fact that we currently have demonstrated that ancient relatives very likely engaged, suggests that the both groups are probably did engage," Brindle added.

Evolutionary Importance

Although the evolutionary explanation is discussed, Brindle explained kissing could be employed in reproductive situations to possibly increase mating outcomes or assist in selecting between mates, while it might help strengthen connections when practiced in a platonic way.

Another expert in the behavior of great apes commented that as kissing behavior was seen in a broad spectrum of apes it made sense its roots lie deep in our ancient history, and an examination of various types of intimate behavior among a wider variety of animals might push its origins back further still.

"Behaviors that we consider as characteristics of human life, like intimate contact, are not exclusive to us if we examine carefully at different species," he said.

Cultural Elements

An archaeology expert said that kissing 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 closeness will have been important for millions of years," she said. "It might be an concept that seems a bit contradictory to our incorrect assumptions of a supposedly aggressive and aggressive past, but really it ought to be no surprise that ancient hominins – and even Neanderthals and our own species together – engaged intimately."