Acknowledgments

Thanks to my research assistants, Zoe Geva, Jeremy Hessing-Lewis, and Rana Ahmad, for helpful feedback on earlier versions, and the anonymous referees for excellent comments. This research is supported in part by a grant from the Social Science and Humanities Research Council of Canada on Modeling Ethical Mechanisms. The analysis in this chapter was first developed in Competition among Cooperators: Altruism and Reciprocity (Danielson, 2002b), from which some material is taken.