The American philosopher Samuel Scheffler reveals a hidden force which motivates our actions: our belief in the continuation of humanity after our deaths. In an interview with Edward Stourton, plus a Q&A from an audience at the London School of Economics and Political Science, Scheffler proposes thought experiments which expose the importance of this conception of the afterlife. It is, he argues, this continued existence of the human race in general - and not just of our own descendants - which gives meaning and purpose to much of our lives. With references to Woody Allen, National Porn Shops and Martin Luther. Scheffler is professor of philosophy and law at New York University. Producer: David Edmonds.