A week in books: Is there a universal potion that propels globe-trotting tales?

Before J K Rowling's publisher, Bloomsbury, screened the Harry Potter film to an intimate gathering of 2,000 or so friends on Monday, its chairman, Nigel Newton, announced that the series has now sold over 123 million copies. That mind-stretching figure looks rather more fantastical than anything in the books. Yet explanations of this worldwide wizardry have a rudimentary air. Carpet marketing by Coca-Cola and Warner Bros now plays its part, but Harry took off internationally well before the giant corporations climbed aboard his Nimbus 2000.

So commentators are reduced to wondering why the British boarding-school arcana of house points, chilly dorms, rough contact sports and eccentric beaks communicate so well in Taiwan or Tierra del Fuego. That is to grasp the wrong end of the broomstick. The movie's lavish visual spectacle underlines one great cross-cultural strength of all the titles: within the Gothic corridors and cellars of Hogwarts, Rowling cooks up a gleeful synthesis, or fusion-food platter, of legend and lore from around the storytelling world.

Harry and his pals segue from a baby dragon (medieval European) and a mountain troll (Scandinavian) to the triple-headed guard-dog Fluffy (aka the Greek hell-hound Cerberus) and a decisive, deadly game of (Persian-Indian) chess. Unicorns and werewolves lurk in the woods; the wise messenger owls fly straight out of classical myth, while Harry's first magical encounter – with the speaking snake – slides us straight back into Eden.

Children have always had fewer problems with such multicultural narratives than their adult artistic gate-keepers. Through the centuries when Europe either fought or forgot Islam, the venerable Arabic tales of The Thousand and One Nights – or, at least, some of the less bawdy ones – circulated freely in the West. This Christmas we will witness the usual (paradoxical) crop of panto Aladdins, Ali Babas and Sindbads.

The knack that traditional tales and figures have of seeping across frontiers of time and place has led scholars to suggest that they must all emerge from some universal "grammar" of stories. The Russian critic Vladimir Propp identified 31 consistent plot-moves in the folk tale but only a handful of fundamental characters: hero, villain, donor, helper, princess (and her dad) and dispatcher. Will Harry Potter be ready for a princess soon? We'll have to wait for the fifth episode. Lest anyone think that this abstract knowledge has no real-world pay-off, there are script gurus in Hollywood who will relieve you of several thousand dollars for a masterclass in what amounts to structuralist narratology. Except that they'll call it "Secrets of how to earn $2m for your foolproof screenplay" instead.

A much less cynical, and more endearing, use of the family ties that link the world's yarns appears in a new book by Brian Patten, former Liverpool poet and now a much-loved children's author. In The Story Giant (HarperCollins, £12.99), four children from around the globe – Riyadh, Patna, Devon and Los Angeles – dream their way into the crumbling castle of a moribund giant who guards the planet's treasury of tales. The stories that they remember or discover allow Patten to create a delightful chain of narratives, some familiar (such as that migrant African, Brer Rabbit, or Chaucer's Pardoner's Tale, which seems to crop up in some guise everywhere on earth) and some fresher for a Western reader – such as the favourite Arabic scamp Djuha, who features in one fable that can also be found in the Brothers Grimm.

Patten shows how his much-travelled plots – "those little tadpoles that lay at the root of all imagination" – mutate into fully grown folk tales that reflect a local landscape and culture, yet have cousins all around the world. Older children, or curious adults, can trace his tales back to their sources via the useful bibliography. He even allows himself to make up one or two of his own.

I'm not sure that any of this really explains why Dumbledore or Voldemort should fill the dreams of Potter fans in Beijing and Barking alike. But Patten's storytellers will show you how to see off a threatening vampire (you have to be very rude to them) and where to find Hell or Heaven. Inside yourself, on both counts, of course – but then you knew that, and Harry (through the Mirror of Erised) soon finds out.