Among Galápagos albatrosses to Arctic mammals, primates to great apes, certain species appear to kiss. Now, scientists propose that ancient hominins also engaged in this behavior – and might even have exchanged kisses with modern humans.
Common Oral Clues
It is not the first time experts have suggested Neanderthals and early modern humans were intimately acquainted. Among earlier research, researchers have found modern people and their thick-browed cousins possessed the identical oral bacteria for hundreds of thousands of years after the evolutionary divergence, implying they exchanged oral fluids.
"Probably they were kissing," she said, explaining that the concept chimed with research that has found people of non-African ancestry contain ancient genetic material in their genome, revealing genetic mixing was occurring.
Romantic Spin
"This offers a different spin on ancient interactions," Brindle commented.
Writing in the journal Evolution and Human Behavior, Brindle and colleagues detail how, to investigate the evolutionary origins of kissing, they first had to develop a definition that was not limited to how humans smooch.
Describing Intimate Contact
"There have been some previous attempts to describe a intimate act, but it's largely human-centric, which means that essentially non-human species don't kiss. Currently we understand that they probably do, it might just not look from what our intimate contact resembles," 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", seen in aquatic species known as certain marine animals.
As a result the research group came up with a definition of intimate contact based on friendly interactions involving directed oral interaction with a member of the same species, with some motion of the oral area but no transfer of food.
Research Approach
Brindle said they focused on accounts of kissing in non-human species from the African continent and Asian regions, including bonobos, chimpanzees and great apes, and employed online videos to verify the observations.
The researchers then integrated this information with details on the evolutionary relationships between living and ancient types of such animals.
Evolutionary Timeline
The team propose the findings indicate intimate contact developed somewhere between 21.5m and 16.9m years ago in the predecessors of the large apes.
The position of ancient hominins on this evolutionary lineage means it is likely they, too, engaged in a intimate act, the scientists conclude. But the behavior might not have been limited to their specific group.
"Reality that modern people engage intimately, the fact that we currently have shown that ancient relatives very likely engaged, indicates that the both groups are probably did kissed," the researcher noted.
Biological Importance
Although the evolutionary explanation is discussed, the expert explained kissing could be employed in sexual contexts to potentially increase mating outcomes or help choose between mates, while it might help strengthen connections when used in a non-sexual manner.
A separate researcher in the activities of great apes said that as intimate contact was seen in a wide range of apes it was logical its roots extend far into our evolutionary past, and an analysis of various types of intimate behavior among a broader range of animals might push its origins back further still.
"Behaviors that we consider as characteristics of our species, like kissing, are not unique to us if we look closely at other animals," he said.
Social Elements
Another professor said that kissing had a cultural element as it was not universal to all human groups.
"Nonetheless, as humans we thrive or fail on the quality of our relationships, and methods of encouraging confidence and intimacy will have been significant for eons," she said. "This could represent an image that seems a bit contradictory to our misplaced ideas of a rather ruthless and aggressive past, but really it ought to be expected that Neanderthals – and including Neanderthals and our own species collectively – kissed."
