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From Galápagos albatrosses to polar bears, chimpanzees to great apes, various animals engage in mouth-to-mouth contact. Currently, researchers suggest that Neanderthals did it too – and might even have exchanged kisses with early Homo sapiens.

Shared Oral Evidence

It is not the first time scientists have proposed ancient relatives and early modern humans were closely connected. Among earlier research, researchers have found modern people and their Neanderthal relatives possessed the identical oral bacteria for hundreds of thousands of years after the two species split, implying they swapped saliva.

"Probably they were engaging in intimate contact," the researcher noted, adding that the concept aligned with studies that has found people of non-African ancestry contain ancient genetic material in their genetic makeup, revealing interbreeding was occurring.

Intimate Spin

"It certainly puts a different perspective on human-Neanderthal relations," the lead researcher commented.

Writing in the publication Evolution and Human Behavior, Brindle and her team detail how, to investigate the historical roots of intimate contact, they first had to come up with a definition that was not restricted by how people smooch.

Describing Kissing

"There have been some efforts to describe a kiss, but it's largely focused on humans, which implies that essentially other animals do not engage in this. Now we understand that they likely engage, it might just not look from what human kissing resembles," said Brindle.

However, she noted some behaviors that looked like kissing were something rather different – such as the chewing and transfer of food, or "kiss-fighting", seen in fish called French grunts.

Consequently the research group developed a description of kissing based on social behaviors involving intentional mouth-to-mouth contact with a member of the same species, with some motion of the oral area but absence of nutrition.

Research Approach

The lead researcher said they focused on reports of kissing in non-human species from Africa and Asian regions, including primates, chimpanzees and orangutans, and used online videos to verify the observations.

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

Evolutionary Timeline

Researchers say the findings suggest kissing developed approximately 21.5m and 16.9m years ago in the predecessors of the great primates.

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

"The fact that humans engage intimately, the reality that we currently have shown that Neanderthals probably engaged, suggests that the both groups are probably did kissed," Brindle added.

Evolutionary Significance

Although the evolutionary explanation is discussed, the expert said intimate contact could be employed in sexual contexts to potentially enhance mating outcomes or assist in selecting between mates, while it could assist reinforce bonding when practiced in a non-sexual manner.

A separate researcher in the activities of primates commented that as kissing behavior was seen in a wide range of primates it made sense its roots lie deep in our ancient history, and an examination of different forms of kissing among a wider variety of animals might push its beginnings back even earlier still.

"Behaviors that we consider as characteristics of our species, like intimate contact, are not unique to us if we examine carefully at different species," he said.

Cultural Aspects

An archaeology expert explained that kissing had a cultural element as it was not common to all societies.

"However, as people we thrive or fail on the strength of our emotional bonds, and ways of encouraging confidence and closeness will have been significant for millions of years," the professor stated. "It might be an concept that appears a bit incongruous to our incorrect assumptions of a supposedly aggressive and ancient history, but actually it should be expected that Neanderthals – and even Neanderthals and our human ancestors collectively – engaged intimately."