Ancient Hominins and Early Humans Were Likely Kissing, Scientists Suggest

Among seabirds to polar bears, chimpanzees to orangutans, certain species engage in mouth-to-mouth contact. Now, scientists suggest that Neanderthals also engaged in this behavior – and possibly exchanged kisses with modern humans.

Common Microbial Evidence

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

"Probably they were kissing," she said, adding that the concept aligned with research that has revealed humans of non-African ancestry have bits of ancient genetic material in their genome, demonstrating genetic mixing was occurring.

Romantic Interpretation

"This offers a different spin on ancient interactions," the lead researcher commented.

Writing in the journal a scientific periodical, Brindle and her team detail how, to explore the evolutionary origins of intimate contact, they first had to develop a definition that was not restricted by how people kiss.

Defining Intimate Contact

"There have been some previous attempts to describe a kiss, but it's very much been human-centric, which implies that basically other animals don't kiss. Currently we understand that they likely engage, it may appear different from what human kissing resembles," explained the evolutionary biologist.

Nonetheless, she said some actions that looked like intimate contact were distinct activities – such as the chewing and transfer of food, or "mouth contact", seen in aquatic species called French grunts.

As a result the research group developed a definition of intimate contact based on social behaviors involving directed oral interaction with a individual of the identical group, with some movement of the mouth but no transfer of nutrition.

Study Methods

Brindle said they focused on reports of intimate behavior in non-human species from Africa and Asian regions, including bonobos, apes and orangutans, and employed online videos to verify the observations.

Scientists then integrated this data with details on the evolutionary relationships between living and ancient types of such animals.

Evolutionary Origins

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

The position of ancient hominins on this family tree means it is likely they, too, indulged in a intimate act, the researchers say. But the activity may not have been confined to their own species.

"Reality that humans kiss, the reality that we now have demonstrated that ancient relatives very likely engaged, indicates that the two [species] are also likely to have engage," the researcher added.

Biological Significance

While the scientific reasoning is discussed, the expert said kissing could be used in sexual contexts to possibly enhance reproductive success or assist in selecting between partners, while it could assist reinforce bonding when used in a non-sexual manner.

Another expert in the activities of great apes said that as kissing behavior was seen in a wide range of apes it made sense its roots extend far into our ancient history, and an analysis of different forms of intimate behavior among a broader range of species might extend its beginnings back further still.

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

Social Aspects

Another professor said that intimate contact had a cultural element as it was not universal to all human groups.

"However, as people we succeed or struggle on the quality of our relationships, and ways of promoting confidence and intimacy will have been important for eons," she said. "It might be an image that seems a bit contradictory to our misplaced ideas of a supposedly aggressive and ancient history, but actually it should be no surprise that ancient hominins – and including them and our human ancestors collectively – engaged intimately."