In Capital (volume 3), Karl Marx observed: “In London . . . they can do nothing better with the excrement produced by 4 1/2 million people than pollute the Thames with it, at monstrous expense”. That would not have happened if Matt Damon had been around. Marx was railing against the loss of nutrients from the soil caused by contemporary (and modern) sewage systems. In Ridley Scott’s new 3D blockbuster, The Martian, Damon is inadvertently left behind on Mars by his NASA crew mates and is obliged to survive until help comes. As is so often the way, inspiration strikes...