In this chapter of Darwin or Design, I talk with Dr Elliot Sober. Dr Sober has taught at University of Wisconsin Madison since 1974. He is currently Hans Reichenbach Professor of Philosophy and a William Vilas Research Professor. His research is in philosophy of science, especially in the philosophy of evolutionary biology. Sober's books include The Nature of Selection -- Evolutionary Theory in Philosophical Focus (MIT Press, 1984; 2nd edition, University of Chicago Press, 1993), Reconstructing the Past -- Parsimony, Evolution, and Inference (MIT Press, 1988), Philosophy of Biology (Westview Press, 1993), >From a Biological Point of View -- Essays in Evolutionary Philosophy (Cambridge University Press, 1994), and, most recently (with David Sloan Wilson) Unto Others -- The Evolution and Psychology of Unselfish Behavior (Harvard University Press, 1998).