Among seabirds to Arctic mammals, primates to great apes, certain species appear to kiss. Now, researchers suggest that Neanderthals also engaged in this behavior – and possibly locked lips with early Homo sapiens.
It is not the first time scientists have suggested ancient relatives and Homo sapiens were intimately acquainted. Among earlier research, researchers have found modern people and their thick-browed cousins shared the same mouth microbe for millions of years after the two species split, suggesting they exchanged oral fluids.
"Probably they were kissing," she said, explaining that the idea chimed with studies that has found humans of non-African ancestry have bits of Neanderthal DNA in their genetic makeup, demonstrating genetic mixing was occurring.
"It certainly puts a more romantic spin on human-Neanderthal relations," the lead researcher commented.
Writing in the journal Evolution and Human Behavior, Brindle and colleagues detail how, to explore the historical roots of kissing, they first had to develop a definition that was not limited to how humans smooch.
"There have been some efforts to define a intimate act, but it's largely human-centric, which means that basically other animals don't kiss. Now we know that they probably do, it might just not look from what human kissing looks like," explained Brindle.
Nonetheless, she said some actions that looked like intimate contact were something rather different – such as the processing and transfer of food, or "mouth contact", observed in fish called certain marine animals.
Consequently the team developed a description of intimate contact centered around social behaviors involving intentional oral interaction with a member of the identical group, with some motion of the oral area but no transfer of food.
The lead researcher said they concentrated on accounts of intimate behavior in primates from the African continent and Asian regions, including bonobos, chimpanzees and orangutans, and employed online videos to confirm the observations.
Scientists then combined this data with information on the evolutionary relationships between living and extinct species of such animals.
The team propose the results suggest kissing developed approximately 21.5 million and 16.9m years ago in the ancestors of the large apes.
Placement of ancient hominins on this family tree suggests it is probable they, too, indulged in a kiss, the scientists say. But the behavior may not have been confined to their specific group.
"The fact that humans kiss, the fact that we currently have shown that ancient relatives very likely kissed, indicates that the two [species] are probably did kissed," Brindle added.
Although the evolutionary explanation is discussed, the expert said kissing could be employed in sexual contexts to possibly enhance 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 primates commented that as intimate contact was observed in a broad spectrum of primates it was logical its origins lie deep in our ancient history, and an analysis of different forms of kissing among a broader range of species might extend its beginnings back further still.
"Behaviors that we consider as signatures of human life, like intimate contact, are not exclusive to us if we examine carefully at different species," the expert noted.
Another professor explained that intimate contact had a social component as it was not universal to all human groups.
"Nonetheless, as humans we succeed or struggle on the strength of our relationships, and methods of promoting confidence and intimacy will have been significant for millions of years," the professor stated. "It might be an concept that appears a bit contradictory to our misplaced ideas of a rather ruthless and aggressive past, but really it ought to be no surprise that ancient hominins – and including Neanderthals and our human ancestors together – engaged intimately."
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