I have Darwin on my mind these days, perhaps because tomorrow is Darwin Day. To celebrate Darwin Day, I sat down to read the February 2009 edition of National Geographic, which, according to the front cover, features an article entitled "What Darwin Didn't Know." Once you get inside the magazine, however, you'll see that the main article is actually entitled "Darwin's First Clues." It is an extraordinary article setting straight some of the misconceptions about the manner in which Darwin developed his theory of evolution by natural selection. You can read that article online here. you can also watch a short introductory video by writer David Quammen, who explains that Darwin "is a man who just will not go away," and whose ideas are not only still relevant, but "central" to the field of biology. If you read this article, you'll see that Darwin's first clue toward evolution occurred not in the Galapagos, but three years earlier on the northern coast of Argentina, where Darwin found fossils of giant sloths. You read about his numerous fossil finds of giant mammals, "extinct Pleistocene giants." Quammen's article points out that, for all of his gifts, Dawn was not a comparative anatomist. For this reason, he entrusted much of that work to others, including John Stevens Henslow, a botanist at Cambridge and Richard Owens, "an up-and-coming authority on extinct mammals." Darwin was certainly aware of the implications of the diversity and distributions of the flora and fauna he studied. The fact that fossils of giant extinct mammals could be found in the same places as still-living relatives suggested the idea of "relatedness and succession among closely allied species" rather than a God who had specially created species, placing them on the planet in arbitrary locations. Darwin's explanation was certainly "more economical, more inductive and more persuasive than the creationist scenario."