Black excellence in boxing can be traced to the “battle royals” that pitted slaves against each other for the entertainment of white masters, said University of Houston professor Gerald Horne, whose new book is titled “The Bittersweet Science: Racism, Racketeering and the Political Economy of Boxing.” The book “uses boxing as a vehicle to talk about the larger story of exploitation, racism, white supremacy and organized crime,” said Horne, one of the Black liberation movement’s most prolific writers.