The story of early hip hop, from 1970s 'block parties' in the South Bronx to the next decade when some musicians used rap for harsh social critique while others looked to it for big commercial success. Trevor Nelson talks to Duke University hip hop historian Mark Anthony Neal, film-maker and impresario Michael Holman, and one of the central figures in early hip hop, Grandmaster Caz. DJ and MC Grandmaster Caz is one of the most important and influential pioneers of old school rap. Mark Anthony Neal is professor of African and African American Studies and the founding director of the Center for Arts, Digital Culture and Entrepreneurship at Duke University. Michael Holman is a leading New York hip-hop activist: musician, filmmaker, artist manager, club promoter, journalist and critic, television producer, archivist, visual artist, and educator. (Photo: A breakdancer. Credit: Getty Images)