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From Galápagos albatrosses to Arctic mammals, primates to orangutans, various animals appear to kiss. Currently, scientists propose that Neanderthals did it too – and possibly locked lips with modern humans.

Shared Microbial Evidence

It is not the first time experts have suggested ancient relatives and Homo sapiens were closely connected. Among previous studies, researchers have discovered modern people and their thick-browed cousins shared the identical oral bacteria for millions of years after the evolutionary divergence, suggesting they exchanged oral fluids.

"Probably they were engaging in intimate contact," the researcher noted, explaining that the concept aligned with studies that has revealed humans of certain genetic backgrounds contain ancient genetic material in their genetic makeup, demonstrating interbreeding was at play.

Intimate Spin

"It certainly puts a more romantic perspective on ancient interactions," Brindle commented.

Publishing in the journal a scientific periodical, Brindle and colleagues detail how, to explore the evolutionary origins of kissing, they first had to come up with a description that was not restricted by how humans kiss.

Describing Intimate Contact

"Previously there were some previous attempts to describe a intimate act, but it's largely focused on humans, which implies that essentially non-human species do not engage in this. Currently we know that they probably do, it may appear different from what human kissing looks like," said the evolutionary biologist.

Nonetheless, she said some actions that resembled kissing were something rather different – such as the chewing and transfer of food, or "kiss-fighting", observed in fish called French grunts.

Consequently the team came up with a definition of intimate contact based on friendly interactions involving directed oral interaction with a individual of the identical group, with some motion of the mouth but no transfer of food.

Research Methods

Brindle said they focused on accounts of intimate behavior in primates from Africa and Asia, including primates, apes and orangutans, and employed online videos to verify the reports.

The researchers then integrated this information with details on the genetic connections between living and ancient species of such animals.

Historical Timeline

Researchers say the results indicate kissing developed somewhere between 21.5 million and 16.9 million years ago in the predecessors of the large apes.

The position of ancient hominins on this evolutionary lineage suggests it is probable they, too, engaged in a kiss, the scientists say. But the behavior might not have been confined to their specific group.

"The fact that modern people engage intimately, the fact that we currently have shown that Neanderthals very likely engaged, suggests that the two [species] are also likely to have engage," the researcher noted.

Evolutionary Significance

While the scientific reasoning is discussed, the expert explained intimate contact could be used in sexual contexts to potentially enhance mating outcomes or help choose between mates, while it might help reinforce bonding when used in a non-sexual manner.

Another expert in the behavior of great apes commented that as intimate contact was seen in a wide range of primates it made sense its roots extend far into our evolutionary past, and an analysis of various types of intimate behavior among a wider variety of species might push its origins back even earlier still.

"Things that we consider as signatures of human life, like intimate contact, are not unique to us if we look closely at other animals," the expert noted.

Cultural Elements

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

"Nonetheless, as people we succeed or struggle on the strength of our emotional bonds, and ways of encouraging trust and closeness will have been significant for eons," she said. "It might be an concept that seems a bit contradictory to our misplaced ideas of a rather ruthless and aggressive past, but actually it ought to be expected that ancient hominins – and including them and our human ancestors collectively – engaged intimately."