The red grapefruit eaten today is a product of a 1950s program in the United States called Atoms for Peace, whose goal was to promote practical uses for nuclear power outside of a wartime context. One of the things Atoms for Peace came up with is the gamma garden which is exactly as amazing as it sounds. Radioactive material was planted in the middle of a garden, around which concentric rings of plants farthest away were largely unaffected, but the plants in the middle mutated. Some of those mutations were useful, and among them was the modern red grapefruit: a sweeter, atomically-induced mutation of the existing red grapefruit, whose flesh often faded to a less-desirable pink. Most red grapefruit today comes from the descendants of those atomically mutated plants.