Featured in the November 2006 issue of National Geographic and on the magazine's website is "A fin is a limb is a wing," by Carl Zimmer (author of Evolution: The Triumph of an Idea) and illustrated with photographs by Rosamond Purcell. "Today biologists are beginning to understand the origins of life's complexity -- the exquisite optical mechanism of the eye, the masterly engineering of the arm, the architecture of a flower or a feather, the choreography that allows trillions of cells to cooperate in a single organism," Zimmer writes. "The fundamental answer is clear: In one way or another, all these wonders evolved."
Zimmer explains on his blog, "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 [made of] 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 some of the same themes."
Among the examples of complexity Zimmer considers in his article is the bacterial flagellum, a favorite of the "intelligent design" movement. He writes, "But by comparing the flagellar proteins to those in other bacterial structures, Mark Pallen of the University of Birmingham in England and his colleagues have found clues to how this intricate mechanism was assembled from simpler parts. ... Pallen proposes that its pieces -- all of which have counterparts in today's microbes -- came together step-by-step over millions of years." On his blog, Zimmer cites a recent paper by Pallen and NCSE's Nick Matzke as a particularly good treatment.