Niles Eldredge is curator in the Department of Invertebrates at the American Museum of Natural History, New York. Among his recent books are The Miner's Canary: Unraveling the Mysteries of Extinction and Fossils: The Evolution and Extinction of Species. He has coauthored and edited many books, including Phylogenetic Analysis and Paleontology, Phylogenetic Patterns and the Evolutionary Process, The Myths and Human Evolution, The Natural History Reader on Evolution, and, most recently, Systematics, Ecology, and the Biodiversity Crisis, published by Columbia University Press. Marjorie Grene, professor emeritus of philosophy, University of California, Davis, is honorary distinguished professor at Virginia Polytechnic Institute and State University. She is a well-known philosopher of science and has published widely. Her books include A Portrait of Aristotle, The Knower and the Known, The Understanding of Nature, and Descartes. Grene is the editor of Dimensions of Darwinism, as well as of other collections in the history of philosophy.