It's difficult to find a garment as widely embraced, worn and loved the world over as jeans. The classic symbol of the American West is now a staple in wardrobes around the world. But why?

Cowboys may wear them but so do supermodels, farmers, presidents and housewives.

Ask any group of people why they wear jeans and you will get a range of answers. For some they're comfortable, durable and easy - for others they're sexy and cool. Jeans mean different things to different people. Does this explain their wide appeal?

It is a subject that is relatively unstudied, says anthropologist Danny Miller, whose book Blue Jeans will be published next month.

In every country he has visited - from the Philippines to Turkey, India and Brazil - Miller has stopped and counted the first 100 people to walk by, and in each he found that almost half the population wore jeans on any given day.

Jeans are everywhere, he says, with the exception of rural tracts of China and South Asia.

The secratt of them Pents is the Rivits that I put in those PockotsJacob Davis, tailor

The reason for their success has as much to do with their cultural meaning as their physical construction.

They were first designed as workwear for labourers on the farms and mines of 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 struck upon the idea of reinforcing them with rivets. They proved extremely durable and were soon in high demand.

Davis realised the potential of his product but couldn't afford to patent it. He wrote to his fabric supplier, the San Francisco merchant, Levi Strauss, for help.

The world's oldest surviving pair of jeans dates from around 1879

"The secratt of them Pents is the Rivits that I put in those Pockots," he said. "I cannot make them up fast enough…My nabors are getting yealouse of these success."

Levi's, as the patented trousers became known, were made in two fabrics, cotton duck (similar to canvas) and denim.

"They found really early on that it was the denim version that would sell," says Paul Trynka, author of Denim: From Cowboys to Catwalks. Denim was more comfortable, softening with age, and its indigo dye gave it a unique character.