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Among Galápagos albatrosses to Arctic mammals, chimpanzees to great apes, certain species appear to kiss. Now, researchers propose that Neanderthals also engaged in this behavior – and might even have locked lips with modern humans.

Common Microbial Evidence

It is not the first time experts have suggested ancient relatives and Homo sapiens were intimately acquainted. Among previous studies, researchers have found humans and their Neanderthal relatives 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 chimed with research that has revealed humans of non-African ancestry have bits of ancient genetic material in their genetic makeup, demonstrating genetic mixing was at play.

Romantic Spin

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

Writing in the journal a scientific periodical, Brindle and colleagues detail how, to explore the historical roots of intimate contact, they first had to come up with a definition that was not restricted by how people smooch.

Defining Kissing

"There have been some efforts to define a intimate act, but it's very much been focused on humans, which means that basically non-human species don't kiss. Now we understand that they probably do, it may appear different from what human kissing resembles," explained the evolutionary biologist.

Nonetheless, she noted some actions that looked like kissing were distinct activities – such as the chewing and food sharing, or "kiss-fighting", observed in fish called certain marine animals.

As a result the research group developed a definition of kissing centered around social behaviors involving intentional oral interaction with a individual of the identical group, with some motion of the oral area but absence of nutrition.

Research Methods

Brindle said they concentrated on accounts of intimate behavior in non-human species from Africa and Asian regions, including bonobos, apes and orangutans, and employed digital recordings to confirm the reports.

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

Evolutionary Timeline

Researchers say the findings indicate intimate contact evolved somewhere between 21.5 million and 16.9m years ago in the predecessors of the large apes.

Placement of ancient hominins on this family tree means it is probable they, too, engaged in a intimate act, the scientists say. But the activity may not have been limited to their own species.

"The fact that humans kiss, the fact that we now have demonstrated that Neanderthals very likely kissed, indicates that the both groups are also likely to have engage," the researcher noted.

Biological Significance

While the evolutionary explanation is discussed, Brindle said kissing could be used in sexual contexts to possibly enhance mating outcomes or help choose between partners, while it might help strengthen connections when used in a non-sexual manner.

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 origins extend far into our evolutionary past, and an analysis of various types of kissing among a broader range of animals might push its beginnings back even earlier still.

"Behaviors that we think of as signatures of our species, like kissing, are not exclusive to us if we examine carefully at different species," he said.

Cultural Aspects

An archaeology expert explained that intimate contact had a social component as it was not universal to all societies.

"Nonetheless, as people we thrive or fail on the quality of our relationships, and methods of promoting trust and intimacy will have been significant for millions of years," the professor stated. "This could represent an concept that appears a bit incongruous to our misplaced ideas of a rather ruthless and ancient history, but really it should be expected that ancient hominins – and even them and our human ancestors collectively – engaged intimately."