A tendency to aggression and antisocial behaviour is encoded in certain people’s DNA, argues Kathryn Paige Harden — and it could have profound implications for crime and punishment. In the autumn of 2021, behavioural geneticist Kathryn Paige Harden received a letter at her office at the University of Texas in Austin, where she is a professor of psychology. It was from a man held in one of the oldest prisons in Texas, where he had been imprisoned since he was 16 years old. The letter described his crime. It read: ‘‘Why would a young boy of 16 attack a total stranger, a female, at knife point in broad daylight at a busy intersection and make the female drive against her will to sexually assault her? What would drive a boy to do such a thing?’’ The prisoner had come to Harden hoping for an explanation because of her research into how people’s genes, as well as their environment, combine to influence their behaviour.…