In a revelation that adds a surprisingly intimate dimension to our understanding of ancient human history, a new study from the University of Oxford suggests that Neanderthals are very likely to have engaged in kissing. The research further posits that this affectionate behaviour was not confined to their own species but was probably shared with early modern humans.
The Evidence for Ancient Affection
This is not the first time scientists have proposed intimate contact between Neanderthals and our direct ancestors. Previous studies have identified that both species shared a common mouth microbe for hundreds of thousands of years after their evolutionary paths diverged. The most plausible explanation for this shared oral bacteria? The exchange of saliva, potentially through intimate acts like kissing.
Dr Matilda Brindle, an evolutionary biologist at the University of Oxford and the lead author of the study, stated that while various theories had been considered, the new evidence strongly supports a straightforward conclusion. "Probably they were kissing," she said, noting that this idea aligns with existing genetic research. Scientists have previously found that humans of non-African ancestry carry segments of Neanderthal DNA in their genome, clear evidence that interbreeding occurred.
"It certainly puts a more romantic spin on human-Neanderthal relations," Dr Brindle added.
Defining the Kiss Across Species
Published in the journal Evolution and Human Behavior, the study required the team to first establish a scientific definition of kissing that wasn't limited to human behaviour. Dr Brindle explained that past definitions were too human-centric, potentially excluding similar behaviours in other animals.
The researchers distinguished true kissing from other mouth-to-mouth contact, such as the transfer of food or the 'kiss-fighting' seen in some fish species. They ultimately defined it as friendly, directed mouth-to-mouth contact between members of the same species, involving some mouth movement but no food transfer.
Focusing on primates from Africa and Asia, including bonobos, chimpanzees, and orangutans, the team analysed reports and even used YouTube videos to confirm the behaviour. By combining this data with information on the evolutionary relationships between living and extinct primate species, they were able to trace the origins of kissing back through deep time.
A Deep Evolutionary History
The team's analysis suggests that kissing evolved in the ancestors of the great apes somewhere between 21.5 million and 16.9 million years ago. Given Neanderthals' position on this family tree, it is highly probable they also indulged in this behaviour.
Dr Brindle emphasised the cross-species implications: "The fact that humans kiss, the fact that we now have shown that Neanderthals very likely kissed, indicates that the two [species] are also likely to have kissed."
While the evolutionary purpose of kissing is still debated, Dr Brindle suggested it could serve multiple roles. In sexual contexts, it might help in mate selection and increase reproductive success. In platonic settings, it could be a powerful tool for reinforcing social bonds and trust.
Dr Jake Brooker, a great ape behaviour expert at the University of Durham who was not involved in the study, agreed with its findings. He noted that since kissing is observed in a wide range of apes, it makes sense that its origins are deep in our shared evolutionary past.
Professor Penny Spikins, an archaeology professor at the University of York, added that while kissing has a cultural element and isn't universal in all human societies, the need for emotional intimacy is fundamental. "It might be an image that seems a bit incongruous to our misplaced ideas of a rather ruthless and aggressive past," she said, "but really it should be no surprise that Neanderthals—and even Neanderthals and our own species together—kissed."
