In 2021, the psychologist and writer Kathryn Paige Harden co-authored a paper outlining her research into the genetic patterns linked to a higher risk of developing substance abuse problems or engaging in risk-taking behaviour, such as having unprotected sex or committing crime. The paper referred to the genetics of “traits related to self-regulation and addiction”, but Harden thought of herself as studying the genetics of sin. Harden is a professor at the University of Texas and the author of a previous book, The Genetic Lottery, on how our knowledge of genetics should shape our views on meritocracy. She once received a letter from a man who has been in prison since he was 16 for kidnapping and sexually assaulting a woman. “What would drive a boy to do such a thing?” he asked her. Her new book is a heartfelt, subtly argued response to his question, an attempt to outline how our expanding knowledge of what makes people do bad things – the interplay of our inherited tendencies and our life circumstances – should influence how …