I returned to the city I grew up in this past weekend (by train, as always) for a major folk music festival. The shindig encompassed a very broad array of musical styles, all of which are connected to traditions that go back decades, if not centuries. While several of the styles, such as Dixieland jazz, are often thought of as old-fashioned and of a particular time, the artists at these festivals demonstrated that these idioms are living, evolving art forms. In music, as in biology, every new th...