The Foundations of Behavior: The Beliefs, Preferences, and Constraints Model

Abstract

The rational actor model is a basic organizing principle in economic theory. As I shall explain below, biologists generally employ the same model in understanding the behavior of organisms, albeit with different connotations (Grafen 1999; Gintis 2004). By contrast, psychologists generally reject this model altogether. This theoretical discrepancy must be squarely faced if fruitful collaboration between psychologists and biologists is to emerge, especially in areas where behavior is concerned, including behavioral game theory, animal behavior, gene-culture coevolution, and neuroeconomics. I argue here that the rational actor model is justified by basic evolutionary theory and should be conserved in transdisciplinary research, though it is better expressed as the beliefs, preferences, and constraints model, as the term “rational” is laden with irrelevant and misleading connotations. To document the rejection of the rational actor model in standard psychological theory, note that cognitive psychology generally defines the brain as an “information-processing organ,” but in fact the brain is a decision-making mechanism, information processing simply being a necessary element thereof. For instance, a widely used text of graduatelevel readings in psychology (Sternberg and Wagner 1999) devotes the ninth of 11 chapters to “Reasoning, Judgment, and Decision Making,” offering two papers, the first of which shows that human subjects generally fail simple logical inference tasks, and the second shows that human subjects are irrationally swayed by the way a problem is verbally “framed” by the experimenter. A leading undergraduate text (Goldstein 2005) placed “Reasoning and Decision Making” the last of 12 chapters. This includes one paragraph describing the rational actor model, followed by many pages purporting to explain why it is wrong. Behavioral psychology generally avoids positing internal states, of which preferences and beliefs, and even constraints, are examples. Not surprisingly, when the rational actor model is mentioned, it is summarily rejected (Kahneman et al. 1982; Herrnstein et al 1997). Not surprisingly, in a leading behavioral psychology text (Mazur 2002), choice is covered in the last of 14 chapters and is limited to a review of the literature on choice between concurrent reinforcement schedules and the capacity to defer gratification. Summing up a quarter century of psychological research in 1995, Paul Slovic asserted, accurately I believe, that “it is now generally recognized among psychologists that utility maximization provides only limited insight into the processes by which decisions are made” (Slovic 1995: 365). “People are not logical,” psychologists are fond of saying, “they are psychological.” Economics and biology aside, the behavioral sciences have generally spurned the rational actor model. Sociology and anthropology, in addition to cognitive, behavioral, and social psychology, broadly reject this model. Yet, the evolutionary argument for the rational actor model is strong. The fitness of an organism depends on how effectively it makes decisions in an uncertain and varying environment. Effective decision making is a function of the organism’s state of knowledge, which consists of the information supplied by the sensory inputs that monitor the organism’s internal states and its external environment. The fact that the brain is an organ adapted for fitness-maximizing decision making follows from basic biological principles. The brain is a costly organ that evolved because it enhanced the fitness of its carriers, and hence is structured to make on balance fitness-enhancing decisions in the face of the various constellations of sensory inputs it commonly faces. For every such constellation, each decision taken by the organism generates a probability distribution over fitness outcomes, the expected value of which is the fitness value associated with that decision. Since fitness is a scalar variable, for each constellation of sensory inputs, each possible action the organism might take has a specific fitness value, and organisms whose decision mechanisms are optimized for this environment will choose the available action