Recent articles have explored from different perspectives the psychological foundations of American institutionalism from its beginning to the interwar years (Hodgson 1999; Lewin 1996; Rutherford 2000a, 2000b; Asso and Fiorito 2003). Other authors had previously dwelled upon the same topic in their writings on the originsand development of the social sciences in the United States (Curti 1980; Degler 1991; Ross 1991). All have a common starting point: the emergence during the second half of the nineteenth century of instinct-based theories of human agency. Although various thinkers had already acknowledged the role of impulses and proclivities, it was not until Darwin's introduction of biological explanations into behavioral analysis that instincts entered the rhetoric of the social sciences in a systematic way (Hodgson 1999; Degler 1991). William James, William McDougall, and C. Lloyd Morgan gave instinct theory its greatest refinement, soon stimulating its adoption by those economists who were looking for a viable alternative to hedonism. At the beginning of the century, early institutionalists like Thorstein Veblen, Robert F. Hoxie, Wesley C. Mitchell, and Carleton Parker employed instinct theory in their analysis of economic behavior. Their attention wasdrawn by the multiple layers of interaction between instinctive motivation and intentional economic behavior. Debates on the role of instinctsin economicswere not confined to the different souls of American Institutionalism, and many more “orthodox” figures, like Irving Fisher or Frank Taussig, actively participated.