Neil MacGregor's history of the world as told through things. Throughout this week he is examining the global economy of the 19th century - of mass production and mass consumption. Today he is with an instrument that first helped Europeans to navigate with precision around the world - a marine chronometer. The one Neil has chosen actually accompanied Darwin on his great voyage to South America and the Galapagos Islands - a journey that was to help lead him to his revolutionary theories on evolution. The geographer Nigel Thrift and the geneticist Steve Jones celebrate the chronometer and the profound changes it prompted.Producer: Anthony Denselow