Mollusks are fabulous architects. They build houses that protect their soft bodies from predators and the elements—shells of uncommon strength, durability and beauty. Many of these shells have spectacularly complex shapes—logarithmic spirals bedecked with fractal spines or other ornaments, all executed with near-perfect mathematical regularity. Yet mollusks, of course, know nothing of math. How, researchers have wondered, do these humble creatures produce such intricate patterns so precisely?