An epic, moving history of a scientific idea coming to life, by the author of 'The Emperor of All Maladies'. But woven through this title, like a red line, is also an intimate history - the story of Mukherjee's own family and its recurring pattern of mental illness, reminding us that genetics is vitally relevant to everyday lives. These concerns reverberate even more urgently today as we learn to read and write the human genome - unleashing the potential to change the fates and identities of our children.