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From seabirds to polar bears, primates to orangutans, various animals engage in mouth-to-mouth contact. Now, scientists suggest that Neanderthals did it too – and possibly locked lips with early Homo sapiens.

Common Microbial Evidence

It is not the first time scientists have suggested Neanderthals and Homo sapiens were intimately acquainted. In earlier research, researchers have discovered humans and their Neanderthal relatives shared the identical oral bacteria for hundreds of thousands of years after the two species split, implying they exchanged oral fluids.

"Likely they were engaging in intimate contact," the researcher noted, adding that the idea chimed with research that has revealed humans of non-African ancestry have bits of Neanderthal DNA in their genome, demonstrating genetic mixing was occurring.

Romantic Spin

"This offers a different spin on human-Neanderthal relations," Brindle commented.

Writing in the journal Evolution and Human Behavior, the researcher and her team report how, to investigate the evolutionary origins of intimate contact, they first had to come up with a description that was not restricted by how people smooch.

Describing Kissing

"Previously there were some previous attempts to define a intimate act, but it's largely human-centric, which implies that essentially non-human species don't kiss. Currently we understand that they probably do, it may appear different from what our intimate contact resembles," said the evolutionary biologist.

However, she noted some actions that looked like intimate contact were something rather different – such as the processing and food sharing, or "mouth contact", observed in fish known as certain marine animals.

As a result the research group developed a definition of intimate contact based on social behaviors involving directed oral interaction with a member of the identical group, with some movement of the oral area but absence of food.

Study Methods

The lead researcher said they focused on accounts of intimate behavior in non-human species from the African continent and Asian regions, including bonobos, chimpanzees and great apes, and employed digital recordings to verify the reports.

The researchers then combined this information with details on the evolutionary relationships between living and extinct types of such animals.

Evolutionary Origins

The team propose the findings suggest kissing evolved somewhere between 21.5 million and 16.9 million years ago in the ancestors of the large apes.

The position of ancient hominins on this family tree means it is probable they, too, engaged in a intimate act, the researchers conclude. But the behavior might not have been limited to their specific group.

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

Evolutionary Significance

While the scientific reasoning is discussed, Brindle explained kissing could be used in reproductive situations to possibly enhance reproductive success or assist in selecting between mates, while it could assist strengthen connections when practiced in a platonic way.

Another expert in the behavior of great apes commented that as intimate contact was observed in a wide range of primates it made sense its origins lie deep in our ancient history, and an examination of various types of intimate behavior among a wider variety of species might extend its beginnings back even earlier still.

"Things that we consider as signatures of human life, like kissing, are not unique to us if we examine carefully at other animals," the expert noted.

Social Elements

Another professor explained that kissing had a cultural element as it was not common to all human groups.

"However, as people we thrive or fail on the strength of our relationships, and methods of encouraging confidence and intimacy will have been important for millions of years," the professor stated. "This could represent an image that appears a bit contradictory to our misplaced ideas of a supposedly aggressive and aggressive past, but really it ought to be no surprise that ancient hominins – and even them and our own species together – kissed."