The recent case of Rachel Dolezal – the “black” activist outed as white – may have seemed novel, but she's actually part of an old tradition of racial passing in this country. How long has passing been going on and how has it changed over the years? What's it tell us about racial categories and color lines? Why are we so fascinated with passing stories? I spoke with historian Allyson Hobbs about her book A Chosen Exile: A History of Racial Passing in American Life.