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From Galápagos albatrosses to Arctic mammals, chimpanzees to orangutans, certain species engage in mouth-to-mouth contact. Currently, scientists propose that Neanderthals also engaged in this behavior – and possibly locked lips with modern humans.

Shared Oral Evidence

This isn't the initial instance experts have proposed ancient relatives and Homo sapiens were closely connected. In previous studies, scientists 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," she said, explaining that the concept chimed with studies that has revealed humans of non-African ancestry have bits of Neanderthal DNA in their genetic makeup, demonstrating interbreeding was at play.

Romantic Spin

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

Publishing 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 description that was not limited to how humans kiss.

Defining Kissing

"There have been some previous attempts to describe a intimate act, but it's very much been focused on humans, which implies that essentially other animals do not engage in this. Currently we understand that they probably do, it might just not look from what human kissing looks like," explained Brindle.

Nonetheless, she noted some behaviors that looked like intimate contact were distinct activities – such as the processing and food sharing, or "mouth contact", observed in fish known as French grunts.

As a result the research group came up with a definition of intimate contact based on friendly interactions involving directed mouth-to-mouth contact with a member of the identical group, with some movement of the mouth but absence of nutrition.

Research Approach

Brindle said they focused on reports of kissing in primates from Africa and Asian regions, including bonobos, chimpanzees and orangutans, and used digital recordings to verify the reports.

Scientists then integrated this data with details on the evolutionary relationships between living and ancient types of such primates.

Evolutionary Origins

Researchers say the findings indicate intimate contact evolved somewhere between 21.5 million and 16.9 million years ago in the predecessors of the large apes.

Placement of ancient hominins on this family tree means it is likely they, too, indulged in a kiss, the scientists say. But the behavior might not have been limited to their specific group.

"Reality that modern people engage intimately, the fact that we now have demonstrated that Neanderthals probably kissed, indicates that the both groups are probably did engage," the researcher added.

Evolutionary Significance

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

Another expert in the activities of primates commented that as kissing behavior was observed in a wide range of primates it was logical its roots extend far into our evolutionary past, and an analysis of different forms of kissing among a broader range of animals might push its origins back further still.

"Behaviors that we think of as signatures of human life, like kissing, are not unique to us if we look closely at different species," he said.

Social Elements

An archaeology expert said that intimate contact had a social component as it was not universal to all human groups.

"Nonetheless, as humans we thrive or fail on the strength of our relationships, and ways of encouraging confidence and closeness will have been important for eons," the professor stated. "It might be an image that appears a bit contradictory to our misplaced ideas of a supposedly aggressive and ancient history, but really it ought to be expected that ancient hominins – and including Neanderthals and our human ancestors collectively – kissed."