F. James Davis is a retired professor of sociology at Illinois State University. He is the author of numerous books, including Who is Black? One Nation's Definition (1991), from which this excerpt was taken. Reprinted with permission of Penn State University Press To be considered black in the United States not even half of one's ancestry must be African black. But will one-fourth do, or one-eighth, or less? The nation's answer to the question 'Who is black?" has long been that a black is any person with any known African black ancestry. This definition reflects the long experience with slavery and later with Jim Crow segregation. In the South it became known as the "one-drop rule,'' meaning that a single drop of "black blood" makes a person a black. It is also known as the "one black ancestor rule," some courts have called it the "traceable amount rule," and anthropologists call it the "hypo-descent r