The reader is presented with three interpenetrating biographies: the idea of the gene, human society during its development, and the author’s family, into which this idea penetrated with the baggage of a hereditary mental illness. On the pages of this epoch-making book, the concept of the gene originates in Aristotle’s vague guesses about the informational nature of heredity and in Paracelsus’ ideas about homunculi, is woven into the images of people who created genetics in the 19th-20th centuries, is involved in eugenic projects and evolves into genome editing technologies. Observing the influence of genes on cellular and human destinies as a scientist and physician whose own family is plagued by an inherited disease, Mukherjee imbues scientific history with the dramas of people with genetic diseases and outlines the ethical challenges we face as we learn to “read” and “write” the language of DNA .