Tim Harford presents the last in the series, 'Pop-up Ideas'.

Tim explores the concept of 'The Tragedy of the Commons' - a term coined by the American ecologist Garrett Hardin in a hugely influential 1968 essay.

He compares Hardin's work to that of the American political economist Elinor Ostrom, to reflect on the impact of mankind on the world around us.

Producer: Adele Armstrong.