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From Galápagos albatrosses to polar bears, chimpanzees to orangutans, certain species appear to kiss. Now, researchers propose that Neanderthals did it too – and possibly locked lips with early Homo sapiens.

Common Microbial Clues

This isn't the initial instance experts have suggested Neanderthals and early modern humans were closely connected. In earlier research, scientists have found 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 engaging in intimate contact," the researcher noted, explaining that the idea aligned with studies that has revealed humans of certain genetic backgrounds have bits of Neanderthal DNA in their genetic makeup, demonstrating interbreeding was at play.

Romantic Spin

"This offers a more romantic spin on human-Neanderthal relations," Brindle said.

Writing in the publication Evolution and Human Behavior, the researcher and her team report how, to investigate the evolutionary origins of kissing, they first had to develop a description that was not limited to how people kiss.

Defining Kissing

"There have been some efforts to describe a intimate act, but it's largely human-centric, which implies that basically other animals do not engage in this. Currently we understand that they likely engage, it may appear different from what our intimate contact looks like," explained Brindle.

Nonetheless, she said some actions that resembled intimate contact were something rather different – such as the processing and food sharing, or "kiss-fighting", seen in fish known as certain marine animals.

Consequently the research group came up with a definition of intimate contact centered around social behaviors involving directed oral interaction with a individual of the identical group, with some movement of the oral area but absence of food.

Research Methods

Brindle explained they concentrated on accounts of intimate behavior in non-human species from the African continent and Asian regions, including bonobos, apes and great apes, and employed online videos to verify the reports.

The researchers then integrated this data with information on the genetic connections between extant and extinct types of such primates.

Evolutionary Origins

Researchers propose the results indicate kissing developed somewhere between 21.5 million and 16.9m years ago in the ancestors of the great primates.

Placement of ancient hominins on this family tree means it is probable they, too, indulged in a intimate act, the scientists say. But the behavior might not have been limited to their specific group.

"The fact that modern people kiss, the reality that we now have shown that Neanderthals probably engaged, suggests that the both groups are also likely to have engage," the researcher added.

Biological Significance

While the scientific reasoning is discussed, the expert said intimate contact could be used in sexual contexts to possibly increase reproductive success or help choose between mates, while it could assist reinforce bonding when practiced in a non-sexual manner.

Another expert in the behavior of great apes commented that as kissing behavior was observed in a broad spectrum of apes it made sense its origins extend far into our evolutionary past, and an examination of different forms of intimate behavior among a broader range of animals might extend its origins 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 other animals," the expert noted.

Social Aspects

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

"However, as humans we succeed or struggle on the strength of our emotional bonds, and methods of promoting confidence and intimacy will have been significant for eons," the professor stated. "This could represent an image that appears a bit incongruous to our incorrect assumptions of a supposedly aggressive and aggressive past, but really it ought to be no surprise that Neanderthals – and even them and our own species collectively – kissed."