Born in 1920 in Clover, Virginia, Henrietta Lacks was a poor tobacco farmer who worked the same land as her slave ancestors. In 1951, she developed a strangely aggressive cancer, and doctors at Johns Hopkins Hospital took a tissue sample without her knowledge. She died without knowing that her cells would become immortal—the first to grow and survive indefinitely in culture. HeLa cells, as they are called, were essential in developing the polio vaccine. They have aided in the development of in-vitro fertilization, cloning, and gene mapping, and have helped us to better understand the workings of cancer and innumerable viruses. Even today, HeLa is the most widely used cell line in labs worldwide, bought and sold by the billions. If you could pile all HeLa cells ever grown onto a scale, they would weigh more than fifty million metric tons—more than a hundred Empire State Buildings.