I don't know how many economists, teaching business fluctuations or the corn-hog cycle, have devoted an hour to the household thermostat; I know several. Cybernetics, I am told, drew attention to similarities between vacuum tubes and animal nerve cells, and made predictions about the human nervous system that were verified by surgery. An article on feedback related artillery fire-control and automatic oil-pipeline systems to the ecological complementarity of the lynx and the rabbit. Economists compare the closeness of election campaigns to the market forces that make two brands of cider taste much alike. Analysts of rumor, best sellers, and epidemic diseases have been led independently to the equation for the logistic curve; and the collapse of Batista has been compared to the collapse of a stock market. Individuals with conflicting internal values have been likened to a two-person committee with a complicated voting system; and recently the paradigm of the “prisoners' dilemma” has been used to characterize preemptive attack, cheating on a test ban, and Rousseau's illustration (five men cooperating in a stag hunt when one spies a hare) of the value of enforceable contract.