Author of the best-selling book "Caste: The Origins of Our Discontent," Isabel Wilkerson, discusses how the book examines the "infrastructure of division that is built into society" with CBS News national correspondent Errol Barnett. Wilkerson, a Pulitzer Prize winning journalist, explains what prompted her to look into the "structure that's place to hold people in a fixed ranking." Plus, she reacts to news that Ava DuVernay is set to turn the book into a new Netflix film.