"The capacity to blunder slightly is the real marvel of DNA. Without this special attribute, we would still be anaerobic bacteria and there would be no music."
-- Lewis Thomas
BETHESDA, Md. -- The pedigree of human beings, Thomas wrote, probably traces to a single cell fertilized by a lightning bolt as the Earth was cooling. Fortunately, genetic "mistakes" -- mutations -- eventually made us. But they also have made illnesses. Almost all diseases