In “Darwin’s First Clues” By David Quammen (published February 2009) on NationalGeographic.com, Mr. Quammen says:
He hinted at the subject in 1845, in the second edition of his Beagle narrative, revised by him to include coy hints about the theory he was still unprepared to publish. The relationships between fossil and living forms among the rodents, the sloths, the camels, and the armadillos were “most interesting facts,” he noted. Further work by other investigators had meantime revealed the same kind of pattern in Brazil—fossil and living forms of anteater, of tapir, of monkey and peccary and possum. “This wonderful relationship in the same continent between the dead and the living,” Darwin wrote, would “throw more light on the appearance of organic beings on our earth, and their disappearance from it, than any other class of facts.” But what sort of light? What would that light reveal? Throwing light was one of his favorite metaphors, and it would return, but not for a decade and a half—not until he was ready to shine the blinding beam of his theory in public. There’s another intriguing question about the South American fossils and rheas: When did this evidence register on Darwin, tipping him toward the idea of evolution? The widely accepted view is that he returned from the Beagle voyage not yet an evolutionist, merely puzzled by what he had seen, and that he made the big leap to evolutionary thinking after his consultations in London, with John Gould and Richard Owen, about the bird and fossil specimens he had consigned to them. (Soon after that he began using a new term for the process: “transmutation.”) But not everyone agrees.Interesting article. Read the rest. National Geographic has an upcoming show called Morphed. Be sure to watch! They also have some video segments you can watch — including a short segment on how whales evolved from land mammals (clues from the plains of Pakistan!).