"Bingo." Langdon began racing through slides now—spiraled pinecone petals, leaf arrangement on plant stalks, insect segmentation—all displaying astonishing obedience to the Divine Proportion.

"This is amazing!" someone cried out.

"Yeah," someone else said, "but what does it have to do with art?"

"Aha!" Langdon said. "Glad you asked." He pulled up another slide—a pale yellow parchment displaying Leonardo da Vinci's famous male nude—The Vitruvian Man—named for Marcus Vitruvius, the brilliant Roman architect who praised the Divine Proportion in his text De Architectura.

"Nobody understood better than Da Vinci the divine structure of the human body. Da Vinci actually exhumed corpses to measure the exact proportions of human bone structure. He was the first to show that the human body is literally made of building blocks whose proportional ratios always equal PHI."

Everyone in class gave him a dubious look.

"Don't believe me?" Langdon challenged. "Next time you're in the shower, take a tape measure."