Like its predecessor, The Science of Discworld II contains a short Discworld fantasy by Terry Pratchett whose chapters alternate with popular science commentary from Ian Stewart and Jack Cohen. In the Discworld strand, the bickering Unseen University wizards revisit their accidental creation Roundworld--that astonishing place where there"s no magic. Our world, in fact. But it"s being influenced by elves (bad news in the Pratchett cosmos), who bring superstition and irrational terrors to evolving humanity. They feed on fear. This is the cue for Stewart and Cohen to develop their ideas of stories as a shaping power in the evolution of human intelligence. Whether they"re called spells, memes, creeds, theorems, artworks or lies, satisfying stories are Roundworld"s equivalent of Discworld magic. It"s just that it all happens in our heads: "headology" as top witch Granny Weatherwax puts it. Struggling to make Roundworld history come out right despite elvish interference, the wizards entangle themselves in complications of time travel and must eventually beg advice from Granny. To encourage a rational attitude to facts, it seems, Roundworld needs transcendent fictions--represented, in narrative shorthand, by the works of one William Shakespeare. The trick is to make sure he gets born... The racy exposition of the non-fiction chapters covers plenty of ground, including astrology, cargo cults, phase spaces, information theory, and the evolution of species, art, science and religion, all reflecting the human tendency not to let facts spoil a good story. Meanwhile the Discworld chapters--though sometimes disappointingly short--are fast and funny, climaxing with much unscripted action at the first night of a famous play. The Science of Discworld II is ultimately entertaining and genuinely thought-provoking, as expected from this team. Laugh and learn! --David Langford