The team believes that, thousands of years ago, interbreeding caused the development of key traits that were then passed down to modern humans. Researchers in Europe say they’ve linked the genetics of ancient Neanderthal interbreeding to low thresholds for specific types of pain in modern humans. In the recent study on pain, researchers investigated three variations in the SCN9A gene, and reported greater pain sensitivity among humans carrying all three variants. Carrying all three variants increased pain sensitivity as compared to carrying only one. They suggested back then that Neanderthals experienced heightened pain sensitivity compared to modern humans, thanks to the SCN9A gene.