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Among Galápagos albatrosses to Arctic mammals, chimpanzees to orangutans, certain species engage in mouth-to-mouth contact. Currently, scientists suggest that Neanderthals did it too – and might even have exchanged kisses with early Homo sapiens.

Common Oral Evidence

It is not the first time scientists have suggested ancient relatives and early modern humans were closely connected. In previous studies, researchers have discovered modern people and their thick-browed cousins shared the same mouth microbe for millions of years after the two species split, suggesting they swapped saliva.

"Likely they were engaging in intimate contact," she said, explaining that the concept chimed with studies that has found humans of non-African ancestry have bits of Neanderthal DNA in their genetic makeup, demonstrating interbreeding was at play.

Intimate Spin

"This offers a different perspective on ancient interactions," the lead researcher said.

Writing in the journal a scientific periodical, Brindle and colleagues detail how, to investigate the evolutionary origins of kissing, they first had to come up with a definition that was not limited to how people smooch.

Defining Kissing

"Previously there were some previous attempts to define a intimate act, but it's very much been human-centric, which implies that basically other animals don't kiss. Currently we know that they probably do, it might just not look from what human kissing looks like," said the evolutionary biologist.

Nonetheless, she said some behaviors that looked like kissing were distinct activities – such as the processing and transfer of food, or "kiss-fighting", seen in aquatic species known as French grunts.

As a result the research group came up with a description of kissing based on friendly interactions involving directed mouth-to-mouth contact with a individual of the identical group, with some movement of the mouth but absence of food.

Study Methods

The lead researcher said they focused on accounts of kissing in non-human species from Africa and Asian regions, including primates, apes and great apes, and used online videos to verify the reports.

The researchers then combined this information with information on the evolutionary relationships between living and extinct species of such primates.

Historical Timeline

Researchers propose the findings suggest intimate contact evolved somewhere between 21.5 million and 16.9 million years ago in the ancestors of the large apes.

The position of ancient hominins on this family tree means it is likely they, too, engaged in a kiss, the researchers conclude. But the behavior might not have been confined to their specific group.

"The fact that modern people engage intimately, the fact that we currently have demonstrated that ancient relatives probably engaged, indicates that the both groups are also likely to have engage," the researcher noted.

Biological Significance

While the scientific reasoning is discussed, the expert explained kissing could be used in sexual contexts to potentially increase reproductive success 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 said that as intimate contact was seen in a broad spectrum of apes it made sense its origins extend far into our evolutionary past, and an examination of different forms of kissing among a wider variety of species 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 look closely at other animals," the expert noted.

Social Elements

Another professor explained that intimate contact had a cultural element as it was not universal to all societies.

"Nonetheless, as people we thrive or fail on the strength of our emotional bonds, and ways of encouraging trust and intimacy will have been significant for millions of years," the professor stated. "It might be an concept that appears a bit contradictory to our incorrect assumptions of a supposedly aggressive and ancient history, but actually it should be no surprise that Neanderthals – and including them and our own species collectively – engaged intimately."