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From Galápagos albatrosses to Arctic mammals, chimpanzees to great apes, various animals engage in mouth-to-mouth contact. Now, researchers propose that Neanderthals also engaged in this behavior – and might even have locked lips with modern humans.

Shared Microbial Clues

This isn't the initial instance scientists have suggested Neanderthals and early modern humans were intimately acquainted. Among previous studies, researchers have discovered modern people and their Neanderthal relatives possessed the identical oral bacteria for hundreds of thousands of years after the two species split, implying they swapped saliva.

"Probably they were engaging in intimate contact," the researcher noted, explaining that the concept aligned with studies that has revealed people of certain genetic backgrounds contain ancient genetic material in their genetic makeup, revealing interbreeding was occurring.

Romantic Interpretation

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

Writing in the publication Evolution and Human Behavior, Brindle and her team detail how, to explore the historical roots of intimate contact, they first had to come up with a description that was not limited to how humans smooch.

Describing Kissing

"There have been some efforts to describe 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 our intimate contact resembles," explained the evolutionary biologist.

However, she said some actions that looked like kissing were distinct activities – such as the processing and food sharing, or "mouth contact", seen in aquatic species known as French grunts.

Consequently the research group came up with a description of intimate contact centered around social behaviors involving directed mouth-to-mouth contact with a individual of the same species, with some motion of the oral area but no transfer of nutrition.

Study Approach

The lead researcher explained they concentrated on accounts of kissing in non-human species from the African continent and Asia, including bonobos, chimpanzees and orangutans, and used digital recordings to confirm the reports.

Scientists then combined this information with information on the evolutionary relationships between living and ancient species of such animals.

Evolutionary Timeline

The team propose the results indicate intimate contact evolved approximately 21.5 million and 16.9m years ago in the ancestors of the great primates.

The position of ancient hominins on this evolutionary lineage means it is likely they, too, indulged in a intimate act, the researchers say. But the behavior may not have been limited to their specific group.

"Reality that modern people engage intimately, the reality that we currently have shown that Neanderthals probably kissed, suggests that the both groups are also likely to have engage," the researcher added.

Evolutionary Significance

While the evolutionary explanation is discussed, Brindle explained intimate contact could be used in sexual contexts to potentially increase mating outcomes or help choose between mates, while it could assist strengthen connections when practiced in a platonic way.

Another expert in the behavior of primates commented that as intimate contact was observed in a wide range of apes it made sense its origins lie deep in our evolutionary past, and an examination of different forms of kissing among a wider variety of animals might push its origins back further still.

"Things that we think of as characteristics of our species, like intimate contact, are not exclusive to us if we look closely at other animals," he said.

Social Elements

An archaeology expert explained that kissing had a social component as it was not universal to all human groups.

"Nonetheless, as humans we succeed or struggle on the quality of our emotional bonds, and methods of encouraging confidence and closeness will have been significant for eons," she said. "It might be an image that seems a bit incongruous to our incorrect assumptions of a rather ruthless and ancient history, but really it should be expected that ancient hominins – and even them and our human ancestors together – engaged intimately."