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From Galápagos albatrosses to Arctic mammals, primates to orangutans, certain species engage in mouth-to-mouth contact. Now, researchers suggest that ancient hominins did it too – and might even have locked lips with early Homo sapiens.

Common Oral Clues

It is not the first time experts have proposed ancient relatives and Homo sapiens were intimately acquainted. Among earlier research, scientists have discovered modern people and their Neanderthal relatives shared the identical oral bacteria for hundreds of thousands of years after the evolutionary divergence, implying they swapped saliva.

"Likely they were kissing," she said, adding that the idea chimed with research that has revealed people of non-African ancestry contain Neanderthal DNA in their genetic makeup, demonstrating interbreeding was at play.

Romantic Spin

"This offers a different spin on human-Neanderthal relations," the lead researcher commented.

Publishing in the publication Evolution and Human Behavior, the researcher and colleagues report how, to explore the evolutionary origins of intimate contact, they first had to develop a definition that was not limited to how humans smooch.

Defining Kissing

"Previously there were some efforts to define a intimate act, but it's largely focused on humans, which means that essentially other animals do not engage in this. Currently we understand that they probably do, it might just not look from what human kissing resembles," explained the evolutionary biologist.

However, she said some behaviors that resembled intimate contact were distinct activities – such as the chewing and transfer of food, or "mouth contact", seen in aquatic species called certain marine animals.

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

Research Methods

The lead researcher explained they focused on reports of intimate behavior in non-human species from Africa and Asia, including bonobos, chimpanzees and great apes, and used digital recordings to verify the observations.

The researchers then integrated this information with details on the genetic connections between extant and extinct species of such animals.

Evolutionary Timeline

Researchers propose the findings indicate kissing developed somewhere between 21.5m and 16.9m years ago in the predecessors of the large apes.

Placement of Neanderthals on this family tree means it is probable they, too, engaged in a intimate act, the scientists conclude. But the activity might not have been confined to their own species.

"Reality that modern people kiss, the fact that we now have demonstrated that ancient relatives probably engaged, indicates that the two [species] are probably did engage," the researcher noted.

Evolutionary Importance

While the scientific reasoning is discussed, Brindle explained kissing could be used in sexual contexts to possibly enhance reproductive success or help choose between mates, while it could assist strengthen connections when practiced in a platonic way.

Another expert in the activities of primates said that as intimate contact was seen in a wide range 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 species might extend its origins back even earlier still.

"Things that we think of as characteristics of human life, like intimate contact, are not unique to us if we look closely at other animals," the expert noted.

Social Elements

An archaeology expert explained that intimate contact had a cultural element as it was not universal to all human groups.

"However, as humans we thrive or fail on the quality of our relationships, and ways of promoting confidence and closeness will have been significant for eons," the professor stated. "This could represent an concept that appears a bit contradictory to our misplaced ideas of a supposedly aggressive and ancient history, but actually it ought to be no surprise that Neanderthals – and even them and our own species together – engaged intimately."