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Among Galápagos albatrosses to polar bears, chimpanzees to great apes, various animals appear to kiss. Now, researchers propose that Neanderthals did it too – and possibly exchanged kisses with early Homo sapiens.

Common Microbial Evidence

This isn't the initial instance experts have suggested Neanderthals and Homo sapiens were intimately acquainted. In previous studies, researchers have discovered modern people and their Neanderthal relatives possessed the identical oral bacteria for hundreds of thousands of years after the evolutionary divergence, implying they swapped saliva.

"Probably they were kissing," she said, adding that the concept chimed with research that has revealed people of certain genetic backgrounds have bits of ancient genetic material in their genome, revealing interbreeding was at play.

Intimate Interpretation

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

Publishing in the publication Evolution and Human Behavior, the researcher and her team detail how, to investigate the evolutionary origins of intimate contact, they first had to come up with a definition that was not restricted by how people kiss.

Describing Kissing

"Previously there were some previous attempts to define a intimate act, but it's largely focused on humans, which implies that essentially other animals don't kiss. Currently we understand that they probably do, it may appear different from what our intimate contact resembles," said Brindle.

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

Consequently the team developed a description of intimate contact based on friendly interactions involving intentional oral interaction with a individual of the same species, with some movement of the oral area but absence of food.

Research Approach

Brindle explained they concentrated on accounts of kissing in primates from Africa and Asia, including bonobos, chimpanzees and orangutans, and employed digital recordings to verify the reports.

Scientists then combined this information with information on the evolutionary relationships between living and extinct types of such animals.

Historical Origins

The team say the results suggest intimate contact evolved approximately 21.5 million and 16.9m years ago in the ancestors of the great primates.

Placement of ancient hominins on this evolutionary lineage means it is probable they, too, indulged in a kiss, the scientists say. But the activity may not have been confined to their own species.

"Reality that modern people kiss, the fact that we now have demonstrated that Neanderthals very likely engaged, suggests that the both groups are probably did engage," the researcher noted.

Biological Importance

Although the evolutionary explanation is discussed, Brindle explained intimate contact could be employed in reproductive situations to possibly increase reproductive success or assist in selecting between mates, while it might help reinforce bonding when used in a platonic way.

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

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

Social Elements

Another professor said that intimate contact had a cultural element as it was not universal to all societies.

"However, as people we succeed or struggle on the quality of our relationships, and ways of promoting trust and closeness will have been important for eons," she said. "It might be an concept that appears a bit incongruous to our incorrect assumptions of a rather ruthless and ancient history, but actually it should be no surprise that ancient hominins – and including Neanderthals and our human ancestors collectively – kissed."