Andre Holland (left) and Clive Owen get serious in Episode 3 of the second season of The Knick. Mary Cybulski/HBO hide caption

Lacey Schwartz grew up believing she was the daughter of white, Jewish parents. It wasn't until a university labeled her as black that she decided to explore the doubts she's always had about her race. Courtesy of Independent Lens hide caption

Actors John Kerr and France Nuyen in a scene from the 1958 film South Pacific. The interracial romance between the onstage pair unsettled some audiences. 20th Century Fox/Getty Images hide caption

Clarence B. Jones, legal adviser to Martin Luther King Jr., takes notes behind King at a press conference regarding in Birmingham, Ala., in February 1963. Ernst Haas/Getty Images hide caption

Clarence B. Jones this month in Palo Alto, Calif. As Martin Luther King Jr.'s attorney and adviser, Jones contributed to many of King's speeches, including his famous speech at the March on Washington in 1963. Norbert von der Groeben/Reuters/Landov hide caption

Joseph Burden (third row, third from right) with his graduating class at Washington, D.C.'s Metropolitan Police Department training academy in 1960. Every officer on the force was required to work the day of the March on Washington. Courtesy of Joseph Burden hide caption

Robert Avery has been a councilman in his hometown of Gadsden, Ala., for almost three decades. As a teen, he and two friends hitchhiked to the nation's capital, where they made signs for the March on Washington. Erica Yoon/NPR hide caption

A newspaper clipping from The Cincinnati Herald on Sept. 14, 1963, included a picture of Jack Hansan and other members of the Cincinnati delegation. Courtesy of Jack Hansan hide caption

The Freedom Singers make several appearances in our mix of songs inspired by the civil rights movement — a collection that ranges from 1963 to the present day. Joe Alper hide caption

Alabama Gov. George Wallace (right) blocks the door of the the Foster Auditorium at the University of Alabama in Tuscaloosa, Ala., on June 11, 1963. Wallace, who had vowed to prevent integration of the campus, gave way to federal troops. AP hide caption

Elysha O'Brien and her husband, Michael, with their sons. Elysha never learned Spanish but is determined that her children will. Courtesy of the O'Brien family hide caption