The significance of scientific research into the evolution of altruism for environmental ethics can be highlighted through an analysis of recent debates over William Hamilton’s theory of inclusive fitness. Recent debates over how to explain altruism have become particularly charged with ideological weight because they are seen to have some consequence for how we understand the human moral project, especially with regard to nonhuman life. By analyzing the place of evolutionary theory in the work of environmental ethicists some conclusions can be drawn about the extent to which these debates, and evolutionary research into behavior more generally, are and are not significant for environmental ethics. In particular, the most important issues a...