Among seabirds to Arctic mammals, primates to great apes, various animals appear to kiss. Now, scientists suggest that Neanderthals did it too – and might even have exchanged kisses with early Homo sapiens.
Common Oral Clues
This isn't the initial instance experts have proposed ancient relatives and Homo sapiens were intimately acquainted. In earlier research, scientists have discovered humans 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," she said, explaining that the concept aligned with research that has found people of non-African ancestry contain ancient genetic material in their genome, demonstrating genetic mixing was at play.
Romantic Spin
"This offers a different perspective on ancient interactions," Brindle commented.
Writing in the journal a scientific periodical, the researcher and colleagues report how, to explore the evolutionary origins of intimate contact, they first had to come up with a definition that was not restricted by how people smooch.
Defining Kissing
"Previously there were some previous attempts to describe a kiss, but it's largely human-centric, which implies that basically other animals do not engage in this. Now we understand that they probably do, it might just not look from what our intimate contact looks like," said Brindle.
Nonetheless, she noted some behaviors that resembled intimate contact were distinct activities – such as the processing and food sharing, or "kiss-fighting", observed in aquatic species known as French grunts.
Consequently the research group came up with a definition of intimate contact based on social behaviors involving directed mouth-to-mouth contact with a individual of the same species, with some motion of the oral area but absence of food.
Research Methods
Brindle said they focused on accounts of intimate behavior in non-human species from the African continent and Asia, including bonobos, apes and great apes, and used digital recordings to confirm the observations.
The researchers then integrated this information with details on the genetic connections between living and extinct species of such primates.
Historical Timeline
The team propose the results suggest intimate contact evolved approximately 21.5 million and 16.9 million years ago in the ancestors of the great primates.
Placement of ancient hominins on this evolutionary lineage suggests it is probable they, too, indulged in a intimate act, the scientists say. But the behavior might not have been limited to their own species.
"The fact that modern people kiss, the fact that we currently have demonstrated that ancient relatives probably engaged, suggests that the two [species] are also likely to have engage," Brindle added.
Biological Importance
While the evolutionary explanation is discussed, Brindle said kissing could be employed in sexual contexts to possibly increase reproductive success or assist in selecting between mates, while it could assist reinforce bonding when practiced in a platonic way.
Another expert in the activities of great apes said that as intimate contact was seen in a wide range of primates it made sense its roots lie deep in our evolutionary past, and an examination of different forms of kissing among a broader range of species might push its origins back even earlier still.
"Behaviors that we consider as signatures of human life, like intimate contact, are not exclusive to us if we look closely at other animals," the expert noted.
Cultural Elements
An archaeology expert explained that intimate contact had a social component as it was not universal to all human groups.
"However, as people we thrive or fail on the quality of our emotional bonds, and methods of promoting confidence and intimacy will have been significant for eons," she said. "It might be an concept that appears a bit incongruous to our incorrect assumptions of a rather ruthless and ancient history, but actually it should be no surprise that Neanderthals – and even Neanderthals and our own species together – kissed."
