“Humans, chimps, and bonobos all kiss,” explained lead researcher Dr Matilda Brindle, an evolutionary biologist from the University of Oxford.
From that, she concluded, “it’s likely that their most recent common ancestor kissed.”
The research also found that early humans, such as Neanderthals, would likely have kissed before they died out around 40,000 years ago.
One previous piece of research on Neanderthal DNA showed that modern humans and Neanderthals shared an oral microbe – a type of bacteria found in our saliva.
This means Neanderthals and humans “must have been swapping saliva for hundreds of thousands of years after the two species split,” Dr Brindle added.