When the rules of classical physics, which describe the big world, break down, quantum comes in to explain. In the case of DNA, classical physics offers one explanation for why changes can suddenly appear in a single rung of the spiraling ladder of DNA, resulting in what’s called a point mutation. But according to the new study, classical proton transfer does not account for all the instances that protons bounce around in DNA. In other words, proton tunneling likely drives more proton-jumping than heat alone does, he said. This line of research should help reveal what conditions make proton transfer more likely to occur and how often the phenomenon triggers harmful genetic mutations.