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From Galápagos albatrosses to polar bears, chimpanzees to orangutans, certain species appear to kiss. Now, researchers suggest that Neanderthals also engaged in this behavior – and might even have exchanged kisses with modern humans.

Shared Microbial Evidence

It is not the first time experts have proposed ancient relatives and Homo sapiens were closely connected. Among earlier research, researchers have discovered modern people and their thick-browed cousins possessed the same mouth microbe for millions of years after the two species split, suggesting they swapped saliva.

"Probably they were kissing," the researcher noted, explaining that the idea aligned with studies that has found people of certain genetic backgrounds have bits of Neanderthal DNA in their genome, revealing interbreeding was occurring.

Romantic Interpretation

"It certainly puts a more romantic spin on human-Neanderthal relations," the lead researcher said.

Publishing in the journal Evolution and Human Behavior, the researcher and her team detail how, to explore the historical roots of intimate contact, they first had to come up with a description that was not limited to how humans smooch.

Describing Intimate Contact

"Previously there were some efforts to describe a kiss, but it's very much been human-centric, which means that basically non-human species don't kiss. Now we understand that they likely engage, it may appear different from what our intimate contact resembles," said Brindle.

Nonetheless, she said some behaviors that looked like kissing were something rather different – such as the chewing and food sharing, or "kiss-fighting", observed in aquatic species called certain marine animals.

As a result the research group developed a definition of kissing based on friendly interactions involving intentional mouth-to-mouth contact with a member of the identical group, with some movement of the oral area but absence of nutrition.

Study Methods

Brindle explained they concentrated on accounts of kissing in primates from the African continent and Asian regions, including primates, apes and orangutans, and employed online videos to confirm the reports.

Scientists then combined this information with information on the evolutionary relationships between extant and extinct types of such animals.

Historical Origins

The team say the findings indicate intimate contact developed somewhere between 21.5m and 16.9 million years ago in the predecessors of the great primates.

Placement of ancient hominins on this family tree means it is likely they, too, engaged in a kiss, the researchers conclude. But the activity might not have been limited to their specific group.

"The fact that humans engage intimately, the fact that we currently have demonstrated that ancient relatives probably kissed, indicates that the two [species] are probably did engage," the researcher added.

Evolutionary Importance

Although the evolutionary explanation is debated, the expert explained kissing could be employed in reproductive situations to possibly enhance mating outcomes or assist in selecting between mates, while it might help strengthen connections when used in a platonic way.

Another expert in the behavior of primates said that as kissing behavior was observed in a wide range of apes it made sense its origins lie deep in our ancient history, and an examination of different forms of kissing among a wider variety of animals might extend its origins back further still.

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

Social Aspects

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

"Nonetheless, as humans we thrive or fail on the strength of our emotional bonds, and ways of encouraging confidence and closeness will have been significant for eons," she said. "It might be an concept that appears a bit incongruous to our misplaced ideas of a supposedly aggressive and ancient history, but really it should be expected that Neanderthals – and including them and our human ancestors together – engaged intimately."