Ancient Hominins and Modern Humans Were Likely Engaging in Intimate Contact, Scientists Propose

Among Galápagos albatrosses to polar bears, primates to orangutans, certain species appear to kiss. Currently, scientists propose that ancient hominins also engaged in this behavior – and possibly locked lips with early Homo sapiens.

Common Microbial Evidence

This isn't the initial instance scientists have suggested ancient relatives and Homo sapiens were closely connected. Among earlier research, scientists have discovered modern people and their thick-browed cousins possessed the identical oral bacteria for hundreds of thousands of years after the evolutionary divergence, suggesting they exchanged oral fluids.

"Likely they were kissing," the researcher noted, adding that the idea aligned with studies that has found humans of certain genetic backgrounds contain Neanderthal DNA in their genetic makeup, revealing genetic mixing was at play.

Intimate Spin

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

Writing in the publication Evolution and Human Behavior, Brindle and colleagues detail how, to explore the evolutionary origins of intimate contact, they first had to come up with a description 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 essentially non-human species do not engage in this. Currently we understand that they probably do, it might just not look from what our intimate contact resembles," said Brindle.

However, she noted some actions that looked like kissing were distinct activities – such as the processing and food sharing, or "kiss-fighting", observed in aquatic species known as certain marine animals.

As a result the research group developed a definition of intimate contact based on social behaviors involving intentional oral interaction with a individual of the identical group, with some movement of the mouth but absence of nutrition.

Study Methods

Brindle explained they focused on accounts of kissing in non-human species from Africa and Asia, including primates, apes and great apes, and employed digital recordings to verify the observations.

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

Evolutionary Timeline

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

Placement of ancient hominins on this evolutionary lineage means it is likely they, too, engaged in a intimate act, the researchers say. But the behavior may not have been limited to their own species.

"The fact that modern people kiss, the reality that we now have shown that ancient relatives probably engaged, indicates that the both groups are also likely to have kissed," the researcher noted.

Evolutionary Significance

Although the scientific reasoning is discussed, Brindle said kissing could be employed in reproductive situations to potentially enhance reproductive success or assist in selecting between partners, while it could assist strengthen connections when used in a platonic way.

A separate researcher in the activities of great apes commented that as kissing behavior was seen in a wide range of primates it was logical its roots lie deep in our evolutionary past, and an analysis of different forms of intimate behavior among a broader range of species might extend its origins back further still.

"Things 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.

Social Elements

Another professor explained that kissing had a social component as it was not universal to all human groups.

"However, as humans we succeed or struggle on the strength of our emotional bonds, and methods of encouraging confidence and closeness will have been significant for eons," the professor stated. "This could represent an concept that seems a bit contradictory to our misplaced ideas of a supposedly aggressive and ancient history, but really it should be expected that ancient hominins – and including them and our human ancestors collectively – engaged intimately."