The Nobel Prize-winning biologist and former president of the Royal Society explores the science of why and how we age and die. The knowledge of death is so terrifying that we live most of our lives in denial of it, and our fear has underpinned our religions, inspired our cultures, and driven our science. Today giant strides are being made in our understanding of death, and immortality might even be within our grasp. But what are the social and ethical costs of attempting to live forever? He talks to the Radio 4 broadcaster and president of the British Humanist Association.