From Cardinal to Ordinal Utility Theory Darwin and Differential Capacity for Happiness By SANDRA J. PEART and DAVID M. LEVY* ABSTRACT. This paper examines the transition from cardinal to ordinal utility. We begin with the egalitarian utilitarianism of J. S. Mill and Herbert Spencer, in which everyone was supposed to count as one. That is their phrase to explain how the happiness of existing people was to be maximized. We compare Spencer’s goal with Darwin’s goal of the “general good,” in which the number of perfect people was to be maximized. Spencer’s goal was egalitarian, while Darwin’s entailed biological perfection or hierarchy. We consider Edgeworth’s hedonic calculus, in which the notion of hierarchy enters economics. For Edge- worth, agents have differential capacities for happiness. Throughout, we consider normative aspects of Darwin’s work, in particular Darwin’s challenge to the early utilitarianism of Mill and Spencer. We suggest that the Paretian principle returns utilitarianism to its egali- tarian roots. I Lionel Robbins Remembers JUST SIX YEARS AFTER his Essay on the Nature and Significance of Economic Science created a stir in economics with its query about the scientific status of interpersonal utility comparisons (Robbins [1932] 1935: 136–140), Lionel Robbins remembered how he came to be a “provisional” utilitarian: My own attitude to problems of political action has always been one of what I might call provisional utilitarianism.... I have always felt that, as a first approximation in handling questions relating to the lives and actions of large masses of people, the approach which counts each man as one, and, on that assumption, asks which way lies the greatest happiness, is American Journal of Economics and Sociology, Vol. 64, No. 3 (July, 2005). © 2005 American Journal of Economics and Sociology, Inc. *Sandra Peart is in the Economics Department, Baldwin-Wallace College, Berea, OH 44017; e-mail: speart@bw.edu. David Levy is at the Center for Study of Public Choice, George Mason University, Fairfax, VA 22030; e-mail: DavidMLevy@aol.com.