The discovery that cellular development is not a one-way street has earned this year's Nobel Prize in physiology or medicine. John B. Gurdon, a developmental biologist at the Wellcome Trust/Cancer Research UK Gurdon Institute at the University of Cambridge in the United Kingdom, and Shinya Yamanaka, a stem cell researcher at Kyoto University in Japan and the Gladstone Institute at the University of California, San Francisco, have won the prize for their discovery that mature cells can be reprogrammed to resemble the versatile cells of a very early embryo. These so-called pluripotent cells have the ability to become any of...