From fi tness to utility

This essay develops two themes. One is methodological, focusing on the role of model-based science in the human sciences, and, in particular, on model pluralism. I shall discuss three formally similar but causally distinct models of human agency, and shall argue that all three are important in understanding the interaction of individuals and their social context. Two are variants of the rational actor model derived from economics. The simplest of these is the classic rational economic agent model that treats agents as if they act to maximize their material wealth. I contrast it with another version, developed by Herb Gintis and others (Gintis 2006, 2007, 2009), that combines the formal machinery of game theory with the hypothesis that humans are strong reciprocators, and that the psychology of default co-operation plus revenge explains the uniquely co-operative nature of human social life. The third model is formally similar but different in both parentage and underlying causal assumptions, which derive from evolutionary biology. Human behavioural ecology sees humans as fitness rather than utility maximizers. This makes a difference, as we shall see when I take up the second and substantive theme of this essay: I aim to reveal the changing nature of individual agency in the transition from intimate to complex, stratified societies. I shall suggest that we need multiple models as a consequence of diachronic changes in the nature of agency, not just because of the complexity of individuals’ relations with their social world. I begin by contrasting the Gintis model of rational agency with its ancestor, and then contrast both to a formally similar approach with roots in a different discipline, evolutionary biology. I then exploit these contrasts in exploring the changing demands on human decision making in the transition from simpler Pleistocene social worlds to the much more complex ones that followed in the Holocene. Gintis (often in collaboration with Sam Bowles) has argued that humans can be modelled as utility-maximizing agents, thus keeping the formal and conceptual machinery of rational actor models of agency. But Gintis proposes reshaping the standard economists’ version of that idea: the version that models humans as self-interested agents making optimal decisions about individual resource acquisition. Rational economic agents will co-operate when that is in their economic interest – you can do business with them – but they are never altruistic (or spiteful).