How is the human body able to produce antibodies to mount a defence against any attacking microorganism – even those it’s never encountered before? After all, our mere 20,000 genes seem woefully inadequate to produce the billions of different antibodies necessary to fight every possible disease. The problem stumped researchers for decades until the Japanese scientist Susumu Tonegawa discovered the key to our incredible adaptive capacity for fighting contagions – an accomplishment that earned him the Nobel Prize in Physiology or Medicine in 1987. The answer, explored in this brief animation from Nature, lies in recombination-activating genes (RAGs) – DNA-‘shuffling’ enzymes that can create proteins capable of fighting any foreign invader.