With the decoding of the human genome, researchers can now read the genetic program that evolution has written for the human body. A new generation of medical treatments is at hand, and researchers hope to uncover the genetic roots of illness and develop new therapies for most major diseases. Here, "New York Times" science writer Nicholas Wade describes the race to decode the genome and how the new knowledge will transform medicine. Soon, physicians will be able to screen people's genes for all the diseases to which they may be vulnerable. With the emerging art of regenerative medicine, physicians will use stem cells and genomic techniques to replace failing tissues and organs with new ones. Many drugs will be prescribed based on DNA information that will identify which pharmaceuticals are best for each patient. Medicine will be customized for a patient's genetic makeup, providing treatments based on a precise understanding of the mechanism of disease itself. It may even be possible to extend the human life span by manipulating the genes that control it.