In the mid-1980s, The New York Times ran a profile of the American writer and activist Alice Walker. Her novel, The Color Purple, had won the Pulitzer prize and was being turned into a film by Steven Spielberg. The article was illustrated by a photograph of Walker sitting on her teenaged daughter’s knee. It was meant to be a “fun” picture; but, in retrospect, according to Rebecca Walker, the photographer unwittingly portrayed the true nature of her relationship with her mother. Alice Walker was, and remains, an icon of the American civil rights movement. “People adore her. I can’t tell...