It's difficult to find a garment as widely embraced, worn and loved as jeans. The denim trousers are a staple of wardrobes around the world. But why?

Anthropologist Danny Miller has just written a book on the subject. He says that in every country he's visited, almost half the population wore jeans.

They were designed as work-wear for labourers in America's Western states in the late 19th Century. When a Nevada tailor called Jacob Davis was asked to make a pair of sturdy trousers for a local woodcutter, he had the idea of reinforcing them with rivets. They proved extremely durable and were soon in high demand.

Jeans represented the American West and when they started to be worn as casual wear, they were a symbol of rebellion. They were banned in schools, which only added to the fervour with which young people embraced them.

Outside America the trend was beginning to catch on too. Many of the GIs stationed abroad during the war were working-class boys from the Western states. While off duty they wore their jeans proudly as a symbol of home. The trousers represented an easier, happier American way of life, which Europeans wanted to buy into.

Miller argues they have become so mainstream that they are now a symbol of the ordinary - a garment people put on to feel comfortable and to fit in. But according to Paul Trynka, author of Denim: From Cowboys to Catwalks, there is still something in their symbol of youth and casualness, that puts jeans beyond the reach of certain people.

Famously, George W Bush and Tony Blair went out on the street in denim during their first summit meeting. They wanted to show they were 'regular guys' but of course, says Trynka, "they both looked like dorks."