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Among Galápagos albatrosses to polar bears, primates to orangutans, various animals engage in mouth-to-mouth contact. Now, scientists suggest that Neanderthals also engaged in this behavior – and might even have exchanged kisses with modern humans.

Shared Microbial Evidence

It is not the first time scientists have proposed ancient relatives and early modern humans were closely connected. In earlier research, scientists have discovered humans and their Neanderthal relatives shared the identical oral bacteria for millions of years after the evolutionary divergence, suggesting they swapped saliva.

"Probably they were engaging in intimate contact," the researcher noted, explaining that the idea aligned with research that has revealed humans of non-African ancestry contain Neanderthal DNA in their genetic makeup, revealing genetic mixing was occurring.

Romantic Spin

"This offers a more romantic spin on human-Neanderthal relations," the lead researcher said.

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

Defining Intimate Contact

"There have been some efforts to describe a kiss, but it's largely focused on humans, which means that basically non-human species do not engage in this. Now 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 actions that resembled kissing were distinct activities – such as the processing and food sharing, or "mouth contact", observed in fish known as certain marine animals.

Consequently the team came up with a definition of intimate contact centered around friendly interactions involving intentional mouth-to-mouth contact with a member of the identical group, with some movement of the oral area but no transfer of nutrition.

Study Approach

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

Scientists then combined this data with details on the genetic connections between living and extinct species of such primates.

Historical Timeline

The team propose the findings indicate intimate contact developed somewhere between 21.5 million and 16.9m years ago in the predecessors of the large apes.

Placement of Neanderthals on this family tree means it is likely they, too, indulged in a kiss, the scientists say. But the behavior may not have been confined to their specific group.

"The fact that humans kiss, the fact that we currently have shown that Neanderthals probably engaged, indicates that the two [species] are also likely to have kissed," the researcher added.

Evolutionary Importance

Although the scientific reasoning is debated, Brindle explained kissing could be employed in reproductive situations to possibly increase mating outcomes or assist in selecting between mates, while it might help reinforce bonding when practiced 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 lie deep in our evolutionary past, and an examination of various types of intimate behavior among a wider variety of animals might push its beginnings back further still.

"Behaviors that we think of as characteristics of our species, like kissing, are not unique to us if we examine carefully at different species," the expert noted.

Social Elements

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

"However, as people we thrive or fail on the quality of our relationships, and methods of promoting confidence and closeness will have been important for eons," the professor stated. "It might be an concept that appears a bit incongruous to our incorrect assumptions of a supposedly aggressive and aggressive past, but really it ought to be expected that Neanderthals – and including them and our human ancestors together – engaged intimately."