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From Galápagos albatrosses to Arctic mammals, primates to orangutans, various animals appear to kiss. Now, scientists suggest that ancient hominins did it too – and might even have exchanged kisses with modern humans.

Shared Oral Evidence

This isn't the initial instance experts have proposed Neanderthals and early modern humans were closely connected. Among previous studies, researchers have discovered humans and their thick-browed cousins possessed the same mouth microbe for hundreds of thousands of years after the two species split, implying they swapped saliva.

"Probably they were kissing," the researcher noted, adding that the concept aligned with studies that has revealed humans of certain genetic backgrounds have bits of ancient genetic material in their genome, demonstrating interbreeding was at play.

Romantic Spin

"This offers a different spin on ancient interactions," the lead researcher said.

Writing in the journal Evolution and Human Behavior, the researcher and colleagues report how, to investigate the evolutionary origins of intimate contact, they first had to come up with a definition that was not limited to how humans kiss.

Describing Kissing

"There have been some efforts to define a intimate act, but it's largely human-centric, which means that essentially non-human species do not engage in this. Currently we understand that they likely engage, it may appear different from what human kissing looks like," said Brindle.

Nonetheless, she said some actions that resembled intimate contact were something rather different – such as the chewing and transfer of food, or "mouth contact", observed in fish called certain marine animals.

As a result the research group came up with a description of intimate contact centered around friendly interactions involving intentional oral interaction with a individual of the same species, with some motion of the oral area but absence of food.

Research Methods

Brindle explained they focused on reports of intimate behavior in primates from Africa and Asian regions, including bonobos, chimpanzees and great apes, and used digital recordings to verify the reports.

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

Historical Origins

The team propose the findings indicate kissing developed somewhere between 21.5m and 16.9m years ago in the predecessors of the large apes.

The position of ancient hominins on this evolutionary lineage suggests it is likely they, too, indulged in a kiss, the researchers conclude. But the behavior may not have been confined to their specific group.

"The fact 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 added.

Biological Significance

While the scientific reasoning is discussed, the expert explained intimate contact could be used in sexual contexts to possibly enhance reproductive success or assist in selecting between mates, while it might help strengthen connections 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 different forms of intimate behavior among a wider variety of animals might extend its beginnings back even earlier still.

"Things that we consider as signatures of our species, like kissing, are not exclusive to us if we examine carefully at different species," he said.

Cultural Aspects

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

"However, as people we succeed or struggle on the quality of our emotional bonds, and ways of encouraging confidence and closeness will have been significant for millions of years," she said. "It might be an concept that seems a bit incongruous to our incorrect assumptions of a supposedly aggressive and aggressive past, but actually it ought to be expected that ancient hominins – and even Neanderthals and our own species collectively – engaged intimately."