Everybody knows the picture, a man, meticulously rendered by Leonardo da Vinci, standing with arms and legs outstretched in a circle and a square. Deployed today to celebrate subjects as various as the grandeur of art, the beauty of the human form, and the universality of the human spirit, the drawing turns up just about everywhere, in books, on coffee cups, on corporate logos, even on spacecraft. It has, in short, become the world's most famous cultural...