What is the place of rivalry in human behaviour? What drives it? And where is the dividing line between competition as a positive force and one that wreaks havoc? Samira Ahmed discusses rivalry in sport, in cities and in our minds with psychologist Stephen Garcia, sport morality expert Maria Kavussanu and historian Philip Mansel. (Photo: The finish line at the men's 100 meters final at the Seoul Olympic Games in 1988. Credit: Getty Images)