America has been shaped by a hidden phenomenon that touches all of our lives. A rigid hierarchy of human rankings, or caste system, influences our culture, politics, and even our health. Race is the metric by which one’s position in the caste system is determined. In her book, Caste: The Origins of Our Discontents, Isabel Wilkerson describes how these inherited rankings have been passed down through generations from the country's very founding. She says this system is the underlying architecture of division in America. She speaks with Elizabeth Alexander, president of the Andrew W. Mellon Foundation.