On a foggy Saturday morning in 1953, a tall, skinny 24-year-old man fiddled with shapes he had cut out of cardboard. They represented fragments of a DNA molecule, and young James Watson was trying to figure how they fit together in a way that let DNA do its job as the stuff of genes.
Suddenly, he realized that they joined together to form the “rungs” of a long, twisted ladder, a shape better known nowadays as a double helix.
