Do your cells replace themselves every 7 years?
You have heard this one. Every seven years, every cell in your body has been replaced, so you are a physically new person, and the coffee stain you feel guilty about was technically spilled by somebody else. It is a lovely thought and it is not true. Some of the cells reading this sentence have been with you since before you were born. We know that with unusual confidence, and the reason is grim and wonderful. Between 1955 and 1963 the world tested nuclear weapons in the atmosphere, and in doing so accidentally wrote a date stamp into every living thing on the planet. ...