Three interpenetrating biographies are laid out before the reader: the idea of a gene, the idea of human society as it develops during its creation, and the author’s family into which this idea has penetrated along with a hereditary mental illness. In the pages of this epochal book, the concept of the gene takes shape from Aristotle’s vague guesses about the informational nature of heredity and Paracelsus’s ideas of homunculi; it is woven into the images of the people who created genetics in the 19th–20th centuries; it is pulled into eugenic projects and evolves into genome editing technologies. Observing the impact of genes on cellular and human destinies as both a scientist and a doctor whose own family is haunted by hereditary illness, Mukerji immerses himself in the scientific story, permeated by the dramas of people with genetic diseases, and maps the ethical challenges we’ve faced by learning to “read” and “write” in the language of DNA.