“In physics, optimization is an organizing principle for natural phenomena. Entropy tends toward its maximum and marbles roll toward minimum potential energy, all without intent or purpose. Injection of this principle into economics initially followed the physicists' organizing perspective, and helped develop the powerful insights of the abstract partial and general equilibrium theory. However, humans and their institutions being their unit of analysis, it was not long before optimization in economics acquired a behavioral spin. Photons may travel along paths that minimize their travel time without intent or purpose; but economists were too human to think in a similar vein of the people buying ice cream or cars. Once optimization was posited as a behavioral principle of individual human beings, it was easy for cognitive sciences to show that it lacked descriptive validity; however, individual behavior is more complex and less predictable. The aggregate characterizations of Walrasian abstraction could not be derived starting from such complex micro-level behavior. If psychology and equilibrium theory were to be reduced into a single science, something had to give. Given the cognitive limitations humans share with all organisms, validity and relevance of the conclusions of equilibrium theory became suspect.”