The anthropologist, winner of the Samuel Johnson Prize for Into the Silence, discusses his new book on Colombia's complex past, present, and future, through the story of the great Río Magdalena. The river represents the political history of Colombia, home to the greatest ecological and geographical diversity on the planet. As he travels its length, he encounters people who have overcome years of conflict, informed by indigenous wisdom and an enduring spirit of place. Only in Colombia can a traveller wash ashore in a coastal desert, ascend narrow tracks through dense tropical forests and reach verdant Andean valleys rising to ice-clad summits. This wild and impossible geography finds fuses perfectly with the Colombian spirit: restive, potent, at times placid and calm, at others tortured and twisted. He talks to journalist Rosie Boycott.