Sociologist Sara Lawrence-Lightfoot has written a new book about the Black middle class, called "I've Known Rivers: Lives of Loss and Liberation." She follows the lives of six middle-aged, African American people on the "necessary losses" they paid for their privilege. Her book was written, in part, as a response to the 1957 book "Black Bourgeoisie," by the black sociologist Franklin Frazier. Lawrence-Lightfoot took issue with Frazier's portrait of middle class blacks as materialistic assimilationists, repressed and disconnected from the larger black community. Lightfoot is herself the product of the Black middle class.