The Latin explosion of Marc Anthony, Ricky Martin, and the Buena Vista Social Club may look like it came out of nowhere, but the incredible variety of Latin music has been transforming the United States since the turn of the century, when Caribbean beats turned New Orleans music into jazz. In fact, we wouldn't have any of our popular music without it: Imagine pop sans the mambos of Perez Prado and Tito Puente, the garage rock of Richie Valens, or...