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From Galápagos albatrosses to polar bears, chimpanzees to orangutans, certain species appear to kiss. Currently, scientists propose that Neanderthals did it too – and possibly locked lips with modern humans.

Common Oral Clues

It is not the first time experts have proposed Neanderthals and early modern humans were intimately acquainted. In earlier research, scientists have found humans and their Neanderthal relatives possessed the same mouth microbe 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, explaining that the idea aligned with studies that has revealed people of non-African ancestry have bits of ancient genetic material in their genetic makeup, demonstrating interbreeding was occurring.

Romantic Spin

"It certainly puts a more romantic perspective on human-Neanderthal relations," Brindle commented.

Publishing in the journal a scientific periodical, the researcher and her team detail how, to explore the historical roots of kissing, they first had to come up with a definition that was not limited to how people kiss.

Defining Intimate Contact

"There have been some efforts to describe a kiss, but it's largely 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 looks like," said the evolutionary biologist.

However, she noted some behaviors that looked like intimate contact were something rather different – such as the chewing and transfer of food, or "kiss-fighting", observed in fish called French grunts.

As a result the research group came up with a description of intimate contact centered around friendly interactions involving directed mouth-to-mouth contact with a individual of the identical group, with some movement of the oral area but absence of nutrition.

Research Methods

Brindle said they focused on reports of kissing in primates from the African continent and Asia, including primates, chimpanzees and orangutans, and employed digital recordings to verify the observations.

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

Historical Timeline

Researchers propose the findings indicate kissing developed somewhere between 21.5 million and 16.9m years ago in the ancestors of the large apes.

The position of Neanderthals on this family tree suggests it is probable they, too, engaged in a kiss, the scientists conclude. But the behavior might not have been confined to their own species.

"Reality that humans kiss, the fact that we currently have shown that Neanderthals very likely engaged, suggests that the two [species] are also likely to have engage," Brindle noted.

Evolutionary Importance

Although the scientific reasoning is debated, the expert explained kissing could be employed in sexual contexts to possibly increase reproductive success or assist in selecting between mates, while it might help reinforce bonding when practiced in a platonic way.

Another expert in the behavior of great apes commented that as intimate contact was seen in a broad spectrum of primates it was logical its roots extend far into our evolutionary past, and an examination of various types of intimate behavior among a wider variety of species might extend its beginnings back further still.

"Behaviors that we think of as characteristics of our species, like intimate contact, are not unique to us if we look closely at different species," the expert noted.

Cultural Elements

Another professor explained that kissing had a social component as it was not common to all societies.

"However, as humans we thrive or fail on the strength of our emotional bonds, and ways of encouraging trust and intimacy will have been important for millions of years," the professor stated. "This could represent an concept that seems 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 Neanderthals and our human ancestors collectively – engaged intimately."