Most red grapefruit today descend from mutations born of gamma ray exposure. In a 1950s "Atoms for Peace" experiment, radioactive material was placed in a garden with plants around it. Those at the right distance mutated from pink into today's red, sweeter variety.

If more cells mean higher cancer risk, whales and elephants should constantly get cancer. Yet they rarely do—less often than smaller animals. This contradictory phenomenon is called "Peto's paradox."