Could cancer be our cells’ way of running in ‘safe mode’, like a damaged computer operating system trying to preserve itself, when faced with an external threat? That’s the conclusion reached by cosmologist Paul Davies at Arizona State University in Tempe and his colleagues, who have devised a controversial new theory for cancer’s origins, based on its evolutionary roots. If correct, their model suggests that a number of alternative therapies, including treatment with oxygen and infection with viral or bacterial agents, could be particularly effective.