From Galápagos albatrosses to Arctic mammals, primates to orangutans, certain species appear to kiss. Now, scientists suggest that ancient hominins also engaged in this behavior – and possibly exchanged kisses with modern humans.
Shared Oral Evidence
This isn't the initial instance experts have proposed ancient relatives and Homo sapiens were intimately acquainted. In earlier research, scientists have found modern people and their thick-browed cousins possessed the same mouth microbe for hundreds of thousands of years after the evolutionary divergence, implying they swapped saliva.
"Probably they were kissing," she said, explaining that the concept chimed with research that has revealed people of non-African ancestry contain Neanderthal DNA in their genome, demonstrating interbreeding was occurring.
Romantic Interpretation
"This offers a different spin on human-Neanderthal relations," the lead researcher said.
Writing in the journal Evolution and Human Behavior, Brindle and her team report how, to explore the evolutionary origins of kissing, they first had to develop a definition that was not restricted by how humans kiss.
Defining Intimate Contact
"There have been some previous attempts to define a kiss, but it's largely focused on humans, which means that essentially other animals do not engage in this. Now we know that they likely engage, it may appear different from what our intimate contact resembles," said the evolutionary biologist.
Nonetheless, she noted some actions that resembled kissing were distinct activities – such as the chewing and transfer of food, or "mouth contact", observed in fish called French grunts.
As a result the team came up with a definition of intimate contact centered around friendly interactions involving intentional oral interaction with a individual of the same species, with some movement of the mouth but absence of nutrition.
Research Methods
Brindle said they focused on accounts of intimate behavior in non-human species from Africa and Asia, including primates, chimpanzees and orangutans, and used digital recordings to verify the observations.
Scientists then combined this information with details on the evolutionary relationships between living and ancient types of such animals.
Historical Timeline
The team propose the results indicate kissing evolved approximately 21.5 million and 16.9 million years ago in the predecessors of the large apes.
Placement of ancient hominins on this evolutionary lineage means it is probable they, too, engaged in a kiss, the researchers say. But the activity may not have been confined to their specific group.
"The fact that humans engage intimately, the reality that we currently have demonstrated that ancient relatives probably engaged, indicates that the both groups are also likely to have kissed," the researcher added.
Evolutionary Importance
While the scientific reasoning is debated, the expert said intimate contact could be employed in reproductive situations to possibly increase mating outcomes or help choose between mates, while it might help reinforce bonding when practiced in a non-sexual manner.
Another expert in the activities of primates commented that as intimate contact was seen in a wide range of primates it made sense its origins lie deep in our ancient history, and an analysis of different forms of kissing among a wider variety of animals might push its origins back further still.
"Behaviors that we consider as characteristics of human life, like kissing, are not unique to us if we look closely at other animals," he said.
Cultural Elements
An archaeology expert explained that intimate contact had a cultural element as it was not common to all human groups.
"However, as humans we succeed or struggle on the quality of our relationships, and methods of promoting confidence and intimacy will have been important for eons," the professor stated. "This could represent an concept that seems a bit contradictory to our misplaced ideas of a supposedly aggressive and aggressive past, but actually it ought to be expected that Neanderthals – and even Neanderthals and our own species together – kissed."
