Silent reading emerges

If we weren't so used to having books, we would think of them as a "miracle." That's how historian Irene Vallego

views what she says is humankind's greatest and most influential invention: the book. "With their help, humanity has undergone an extraordinary acceleration of history, development, and progress," she tells host Nahlah Ayed. Vallego has traced written texts back to their earliest origins and she's written a book of her own, Papyrus: The Invention of Books in the Ancient World.