Finnoff and Michele Leiby for research assistance, and to Samuel Bowles, Peter Hammerstein, Hillard Kaplan, Jane Lancaster, Jim Sidanius, and other participants at the Institute for Theoretical Biology workshop on sexual differentiation (Berlin, November 2003), and to LaShawn Jefferson, Stathis Kalyvas, Gary LaFree, Karen Musalo, Mark Peceny, James Ron, Ian Shapiro, Martha Snodgrass, and Steven Wilkinson for their suggestions. Sexual Violence during War: Explaining Variation