While human enhancement has little mainstream scientific support, gene-editing to eliminate diseases from human populations is a vision many share. Now, following breakthrough technologies and the shocking case of He Jiankui editing the germ-line of two human girls, the editing of heritable human cells has appeared on the horizon whether we like it or not. What will the dream of human gene editing deliver? Sahotra Sarka, author of 'Cut-and-Paste Genetics', weighs up the credibility and safety of the new science of the CRISPR revolution.