From seabirds to Arctic mammals, primates to orangutans, certain species engage in mouth-to-mouth contact. Currently, researchers suggest that ancient hominins did it too – and possibly exchanged kisses with early Homo sapiens.
Common Oral Clues
This isn't the initial instance experts have proposed ancient relatives and early modern humans were intimately acquainted. In previous studies, researchers have found modern people and their thick-browed cousins shared the identical oral bacteria for millions of years after the evolutionary divergence, implying they exchanged oral fluids.
"Probably they were engaging in intimate contact," the researcher noted, explaining that the concept chimed with studies that has found humans of certain genetic backgrounds have bits of Neanderthal DNA in their genome, demonstrating interbreeding was occurring.
Intimate Spin
"It certainly puts a different perspective on human-Neanderthal relations," Brindle commented.
Publishing in the journal a scientific periodical, Brindle and her team report how, to investigate the evolutionary origins of intimate contact, they first had to develop a definition that was not limited to how people kiss.
Defining Kissing
"There have been some previous attempts to describe a kiss, but it's very much been human-centric, which implies that basically other animals don't kiss. Currently we understand that they likely engage, it may appear different from what human kissing looks like," explained the evolutionary biologist.
Nonetheless, she noted some actions that resembled intimate contact were something rather different – such as the chewing and transfer of food, or "kiss-fighting", seen in fish called certain marine animals.
As a result the team developed a description of kissing based on social behaviors involving directed oral interaction with a individual of the same species, with some motion of the oral area but absence of nutrition.
Research Approach
The lead researcher said they concentrated on accounts of intimate behavior in non-human species from the African continent and Asian regions, including bonobos, apes and orangutans, and used digital recordings to verify the reports.
The researchers then combined this information with information on the genetic connections between extant and extinct species of such animals.
Historical Timeline
Researchers propose the results suggest intimate contact evolved approximately 21.5 million and 16.9 million years ago in the ancestors of the large apes.
Placement of ancient hominins on this evolutionary lineage suggests it is likely they, too, indulged in a intimate act, the researchers say. But the activity might not have been limited to their specific group.
"Reality that modern people kiss, the reality that we now have demonstrated that ancient relatives very likely engaged, suggests that the both groups are probably did engage," Brindle noted.
Biological Significance
Although the evolutionary explanation is discussed, the expert explained kissing could be employed in sexual contexts to possibly enhance mating outcomes or help choose between mates, while it might help reinforce bonding when used in a non-sexual manner.
Another expert in the behavior of primates said that as intimate contact was observed in a wide range of primates it made sense its origins extend far into our evolutionary past, and an analysis of various types of kissing among a wider variety of animals might extend its origins back further still.
"Behaviors that we consider as characteristics of our species, like kissing, are not exclusive to us if we examine carefully at other animals," the expert noted.
Social Aspects
An archaeology expert said that kissing had a social component as it was not universal to all societies.
"Nonetheless, as humans we thrive or fail on the quality of our relationships, and methods of promoting confidence and closeness will have been significant for millions of years," she said. "This could represent an concept that appears a bit contradictory to our incorrect assumptions of a supposedly aggressive and ancient history, but really it ought to be expected that Neanderthals – and even Neanderthals and our human ancestors collectively – kissed."
