The secrets of our genetic heritage are finally being unlocked. The massive scientific effort to sequence the human genome is in fact just the beginning of a long journey as the extraordinary genetic diversity that exists between individuals becomes clear. Work in this field is yielding profound insights into the wider implications for understanding biology, human health and history. It promises much: to understand our evolutionary origins, to define us as individuals, to predict our risk of disease and to more effectively understand, treat and prevent illness. Genetics can help us understand...