Thanks to Eric Verhoogen, James Heintz, Stephanie Eckman, Nicole Huber, and Melissa Osborne for research assistance, to the University of Siena for providing an unparalleled environment for research and writing, to Robert Boyd, Colin Camerer, Robert Cialdini, Lilia Costabile, Joshua Cohen, Gerald Cohen, Martin Daly, Peter Dorman, Catherine Eckel, Marcus Feldman, Ernst Fehr, Nancy Folbre, Christ...