In a single lifetime, Christianity has witnessed one of the most extraordinary about-turns in attitudes to sex and gender in human history, bringing liberation for some and fury and fear for others. Oxford University professor Diarmaid MacCulloch places recent changes into the 2,000-year-long tale of Christians trying to make sense of sexual desire. MacCulloch is author of the award-winning A History of Christianity, adapted into a six-part BBC television series. He talks to broadcaster Francine Stock.