Economic theories of rational addiction aim to describe consumer behavior in the presence of habit-forming goods. We provide a biological foundation for this body of work by formally specifying conditions under which it is optimal to form a habit. We demonstrate the empirical validity of our thesis with an in-depth review and synthesis of the biomedical literature concerning the action of opiates in the mammalian brain and their effects on behavior. Our results lend credence to many of the unconventional behavioral assumptions employed by theories of rational addiction, including adjacent complementarity and the importance of cues, attention, and self-control in determining the behavior of addicts. Our approach suggests, however, that addiction is “harmful” only when the addict fails to implement the optimal solution. We offer evidence for the special case of the opiates that harmful addiction is the manifestation of a mismatch between behavioral algorithms encoded in the human genome and the expanded menu of choices--generated for example, by advances in drug delivery technology--faced by consumers in the modern world.

A comparison of accepted nutritional advice with actual American dietary practice suggests that many people fail to eat well in spite of well-documented health consequences. Popular culture often labels the worst offenders as lacking in “self-control,” and many blame the aggressive advertising campaigns of the fast-food and snack-food industries for manipulating consumers into poor diets, but these conclusions are not easily reconciled with a neoclassical approach to economic decision theory. This essay considers the consumer’s “diet problem” in light of emerging evidence from a number of behavioral sciences. In particular, it is argued that human evolution in the distant past resulted in an elegant solution to this problem (of search for a suitable diet in an uncertain environment), which any neoclassical economist would recognize. In modern environments, however, the signals that formerly provided information in the consumer’s search problem are subject to manipulation by food-producing firms. Confirmation by molecular biologists that many human responses to these signals are firmly encoded in our genes suggests a need to re-evaluate the welfare economics of the food industry.

The modern prevalence and negative consequences of obesity suggest that many people have a tendency to eat more than is optimal. This paper examines the biological underpinnings of mammalian feeding behavior in an attempt to reconcile the “self-control problem” with the normative tradition of neoclassical economics. Medical, genetic, and molecular evidence suggest that overeating is a manifestation of the fundamental mismatch between ancient environments—in which preferences for eating evolved—and modern environments. The phenomenon can be described with a simple optimal foraging model in which both the utility function and the Bayesian prior are generated endogenously in the distant past. The implied disparity between subjective probabilities and actual probabilities has potentially broad implications for welfare economics.