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From seabirds to polar bears, primates to great apes, various animals appear to kiss. Currently, scientists propose that Neanderthals also engaged in this behavior – and possibly exchanged kisses with modern humans.

Shared Oral Evidence

It is not the first time scientists have proposed Neanderthals and Homo sapiens were closely connected. Among earlier research, researchers have found humans and their Neanderthal relatives shared the identical oral bacteria for millions of years after the two species split, suggesting they exchanged oral fluids.

"Probably they were engaging in intimate contact," she said, adding that the concept aligned with research that has found people of non-African ancestry contain ancient genetic material in their genome, demonstrating interbreeding was occurring.

Romantic Spin

"It certainly puts a more romantic spin on human-Neanderthal relations," the lead researcher commented.

Writing in the journal Evolution and Human Behavior, the researcher 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 limited to how people kiss.

Defining Kissing

"There have been some previous attempts to define a intimate act, but it's largely focused on humans, which implies that basically non-human species don't kiss. Now we know that they probably do, it may appear different from what our intimate contact resembles," said the evolutionary biologist.

However, she noted some actions that looked like kissing were something rather different – such as the processing and food sharing, or "kiss-fighting", seen in aquatic species called French grunts.

Consequently the research group came up with a definition of kissing based on social behaviors involving intentional mouth-to-mouth contact with a individual of the identical group, with some movement of the oral area but no transfer of food.

Study Methods

The lead researcher said they concentrated on accounts of kissing in primates from the African continent and Asia, including primates, apes and great apes, and used digital recordings to verify the reports.

The researchers then combined this data with details on the genetic connections between living and ancient species of such primates.

Evolutionary Timeline

The team propose the results suggest kissing developed somewhere between 21.5m and 16.9m years ago in the predecessors of the great primates.

Placement of ancient hominins on this evolutionary lineage means it is probable they, too, engaged in a intimate act, the scientists conclude. But the activity might not have been limited to their specific group.

"Reality that humans engage intimately, the fact that we now have demonstrated that Neanderthals very likely kissed, suggests that the two [species] are also likely to have kissed," the researcher added.

Evolutionary Significance

Although 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 reinforce bonding when used in a non-sexual manner.

Another expert in the behavior of great apes said that as kissing behavior was observed in a wide range of primates it made sense its roots extend far into our evolutionary past, and an analysis of different forms of kissing among a broader range of animals might extend its beginnings back even earlier still.

"Behaviors that we consider as signatures of our species, like intimate contact, are not unique to us if we look closely at other animals," he said.

Cultural Elements

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

"Nonetheless, as people we succeed or struggle on the strength of our emotional bonds, and methods of promoting trust and intimacy will have been significant for eons," the professor stated. "This could represent an concept that appears a bit incongruous to our misplaced ideas of a supposedly aggressive and ancient history, but actually it should be no surprise that Neanderthals – and even Neanderthals and our human ancestors collectively – kissed."