Edward Luce   At the start of each school year, Rosa Brooks asks her freshmen what they think of the Constitution of the United States. Almost everyone is proud that at 233 years old America has by far the oldest constitution in the world. Brooks, a professor at Georgetown Law School in Washington DC, then asks, “You probably think it would also be great if our surgeons were working on the oldest neurological textbooks, or if our ships were steered by the oldest navigation charts?” The question usually puzzles his students. What does she think is so special about the age of a document as opposed to its usefulness? Clear answers are rarely available. Until recently, Brooks’ line of research