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From Galápagos albatrosses to Arctic mammals, chimpanzees to orangutans, certain species appear to kiss. Currently, scientists propose that Neanderthals also engaged in this behavior – and possibly exchanged kisses with modern humans.

Shared Microbial Evidence

It is not the first time experts have proposed ancient relatives and early modern humans were closely connected. Among earlier research, researchers have found humans and their thick-browed cousins possessed the identical oral bacteria for millions of years after the evolutionary divergence, implying they exchanged oral fluids.

"Probably they were engaging in intimate contact," she said, adding that the idea aligned with research that has revealed people of non-African ancestry have bits of ancient genetic material in their genetic makeup, revealing interbreeding was occurring.

Intimate Spin

"This offers a different spin on human-Neanderthal relations," Brindle commented.

Publishing in the publication a scientific periodical, Brindle and her team report how, to explore the evolutionary origins of kissing, they first had to come up with a description that was not restricted by how people kiss.

Defining Kissing

"There have been some previous attempts to describe a kiss, but it's very much been human-centric, which implies that essentially other animals do not engage in this. Now we know that they likely engage, it may appear different from what human kissing resembles," said Brindle.

However, she said some behaviors that resembled kissing 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 team came up with a definition of intimate contact centered around friendly interactions involving directed oral interaction with a member of the same species, with some movement of the mouth but no transfer of food.

Study Approach

The lead researcher explained they concentrated on reports of kissing in non-human species from the African continent and Asia, including primates, chimpanzees and orangutans, and used digital recordings to confirm the reports.

The researchers then integrated this data with details on the evolutionary relationships between living and extinct types of such primates.

Historical Timeline

Researchers propose the results suggest kissing evolved somewhere between 21.5m and 16.9 million years ago in the predecessors of the great primates.

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

"The fact that humans kiss, the fact that we now have shown that Neanderthals very likely kissed, indicates that the both groups are probably did engage," the researcher noted.

Evolutionary Significance

While the scientific reasoning is debated, Brindle explained kissing could be used in sexual contexts to potentially increase reproductive success or help choose between partners, while it might help strengthen connections when practiced in a platonic way.

A separate researcher in the activities of primates said that as kissing behavior was seen in a broad spectrum of apes it was logical its roots extend far into our ancient history, and an examination of various types of kissing among a wider variety of species might push its beginnings back further still.

"Behaviors that we think of as signatures of our species, like intimate contact, are not exclusive to us if we examine carefully at other animals," he said.

Social Elements

Another professor said that kissing had a cultural element as it was not common to all human groups.

"Nonetheless, as people we succeed or struggle on the quality of our relationships, and ways of promoting trust and closeness will have been significant for millions of years," the professor stated. "This could represent an image that appears a bit incongruous to our misplaced ideas of a supposedly aggressive and ancient history, but actually it ought to be expected that Neanderthals – and even them and our own species collectively – kissed."