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Among Galápagos albatrosses to polar bears, chimpanzees to orangutans, certain species engage in mouth-to-mouth contact. Currently, scientists propose that Neanderthals did it too – and might even have locked lips with modern humans.

Common Oral Clues

This isn't the initial instance experts have suggested Neanderthals and early modern humans were intimately acquainted. In previous studies, scientists have found humans and their Neanderthal relatives possessed the identical oral bacteria for millions of years after the two species split, suggesting they exchanged oral fluids.

"Probably they were kissing," the researcher noted, adding that the idea aligned with studies that has revealed humans of non-African ancestry contain Neanderthal DNA in their genetic makeup, demonstrating genetic mixing was at play.

Romantic Interpretation

"It certainly puts a different spin on ancient interactions," the lead researcher commented.

Writing in the journal a scientific periodical, the researcher and her team report how, to investigate the evolutionary origins of intimate contact, they first had to develop a definition that was not restricted by how people kiss.

Defining Intimate Contact

"Previously there were some efforts to describe a intimate act, but it's very much been focused on humans, which implies that essentially other animals don't kiss. Currently we know that they likely engage, it may appear different from what human kissing resembles," said Brindle.

However, she noted some actions that looked like intimate contact were distinct activities – such as the processing and transfer of food, or "kiss-fighting", observed in aquatic species known as French grunts.

Consequently the team developed a description of intimate contact based on social behaviors involving directed oral interaction with a individual of the identical group, with some movement of the mouth but absence of food.

Study Approach

The lead researcher said they focused on accounts of intimate behavior in primates from the African continent and Asian regions, including primates, chimpanzees and orangutans, and used digital recordings to confirm the observations.

The researchers then combined this information with information on the genetic connections between living and extinct types of such animals.

Historical Timeline

The team propose the results indicate kissing evolved approximately 21.5 million and 16.9 million years ago in the predecessors of the great primates.

Placement of Neanderthals on this evolutionary lineage means it is likely they, too, indulged in a kiss, the researchers say. But the behavior might not have been limited to their specific group.

"Reality that modern people kiss, the reality that we now have shown that ancient relatives very likely engaged, indicates that the two [species] are probably did kissed," Brindle noted.

Biological Importance

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

Another expert in the activities of primates commented that as intimate contact was observed in a wide range of primates it made sense its roots lie deep in our evolutionary past, and an analysis of various types of kissing among a wider variety of species might push its origins back further still.

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

Cultural Aspects

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

"Nonetheless, as humans we succeed or struggle on the quality of our relationships, and ways of promoting confidence and closeness will have been significant for eons," the professor stated. "It might be an concept that appears a bit incongruous to our misplaced ideas of a supposedly aggressive and aggressive past, but actually it ought to be no surprise that ancient hominins – and including Neanderthals and our own species together – kissed."