From Galápagos albatrosses to Arctic mammals, primates to orangutans, certain species appear to kiss. Currently, scientists propose that Neanderthals did it too – and might even have locked lips with modern humans.
It is not the first time scientists have proposed Neanderthals and early modern humans were closely connected. In earlier research, researchers have discovered modern people and their Neanderthal relatives shared the same mouth microbe for hundreds of thousands of years after the evolutionary divergence, suggesting they swapped saliva.
"Probably they were kissing," the researcher noted, explaining that the idea aligned with research that has revealed people of certain genetic backgrounds have bits of ancient genetic material in their genome, demonstrating genetic mixing was at play.
"It certainly puts a different spin on human-Neanderthal relations," the lead researcher said.
Publishing in the publication a scientific periodical, the researcher and colleagues report how, to explore the evolutionary origins of kissing, they first had to come up with a description that was not restricted by how people smooch.
"There have been some previous attempts to describe a intimate act, but it's largely human-centric, which means that basically non-human species don't kiss. Now we understand that they probably do, it may appear different from what human kissing resembles," said Brindle.
However, she noted some actions that resembled intimate contact were distinct activities – such as the chewing and transfer of food, or "mouth contact", seen in fish called certain marine animals.
Consequently the team came up with a description of intimate contact based on friendly interactions involving intentional oral interaction with a member of the same species, with some motion of the oral area but absence of food.
The lead researcher explained they concentrated on accounts of intimate behavior in primates from the African continent and Asian regions, including bonobos, apes and great apes, and used online videos to verify the reports.
The researchers then combined this information with information on the genetic connections between extant and extinct types of such animals.
Researchers propose the findings suggest intimate contact evolved approximately 21.5m and 16.9 million years ago in the ancestors of the great primates.
The position of ancient hominins on this family tree means it is probable they, too, indulged in a kiss, the researchers conclude. But the behavior might not have been confined to their own species.
"Reality that modern people engage intimately, the reality that we currently have demonstrated that Neanderthals probably engaged, suggests that the two [species] are probably did engage," Brindle added.
While the evolutionary explanation is debated, the expert said kissing could be used in reproductive situations to potentially enhance reproductive success or assist in selecting between partners, while it might help reinforce bonding when practiced in a non-sexual manner.
A separate researcher in the activities of great apes commented that as intimate contact was observed in a broad spectrum of apes it was logical its origins extend far into our ancient history, and an analysis of various types of intimate behavior among a wider variety of animals might extend its beginnings back further still.
"Things that we think of as signatures of human life, like intimate contact, are not exclusive to us if we examine carefully at other animals," he said.
Another professor said that kissing had a cultural element as it was not common to all human groups.
"However, as humans we thrive or fail on the strength of our emotional bonds, and methods of encouraging confidence and closeness will have been significant for eons," the professor stated. "It might be an concept that appears a bit incongruous to our misplaced ideas of a rather ruthless and ancient history, but actually it should be expected that ancient hominins – and including them and our own species together – engaged intimately."
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