Flowers, flagella, feathers. Life is rife with complex features–structures and systems made up of many interacting parts. National Geographic magazine asked me to take a tour of complexity in life and report on the latest research on how it evolved. What struck me over and over again was how scientists studying everything from bacteria to humans are drawn back to the same concepts–making new copies of old parts, for example, or borrowing parts of one complex trait to evolve a new one. And in each case, complexity opens up the way to diversity, because something many parts can be rearranged in many ways. There’s not yet a general theory for the evolution of complexity, but scientists are certainly converging on