Today, the voices of Roebuck "Pops" Staples and his four children — Cleotha, Mavis, Pervis and Yvonne — are woven into America's DNA. As the Staple Singers, the family created a sound that was part blues, part gospel and part folk, breaking down musical walls and inspiring civil rights leaders. Biographer Greg Kot wrote about the Staples family in his new book, I'll Take You There: Mavis Staples, the Staple Singers, and the March Up Freedom's Highway. He says that unique sound began with Pops Staples and the musical apprenticeship he dreamed up for his offspring. "He had a cheap...