Paul Krugman, the distinguished Princeton University economics professor and New York Times columnist, once explained the jejune motives for his choice of career. "In my early teens my secret fantasy was to become a psychohistorian," he wrote, referring to the central gimmick, "psycho­history," of Isaac Asimov's Foundation trilogy. Krugman continued, "Someday there will exist a unified social science of the kind that Asimov imagined, but for the time being economics is as close to psycho­history as you can get."

That's risible, given the gulf between Asimov's fantasy of a predictive calculus of human affairs and the actuality of mainstream economics--indeed, of any of the social sciences--as practiced during most of the last century. Recent decades, though, have seen new approaches. One of the most promising was described by Joshua Epstein, a senior fellow at the Brookings Institution, in Growing Artificial Societies: Social Science from the Bottom Up, a book he published in 1996 in collaboration with Robert Axtell. "Perhaps one day people will interpret the question, 'Can you explain it?' as asking 'Can you grow it?'" Epstein suggested. "Artificial society modeling allows us to 'grow' social structures in silico demonstrating that certain sets of microspecifications are sufficient to generate the macro­phenomena of interest."