A mathematical model of unintended consequences: Fisher’s geometric model and social evolution

Biological change and social change are similar. Both involve attempts to alter complex arrangements that have been pieced together through long periods of time. And both run the risk of unintended consequences. In biology, an apparently helpful mutation that confers, say, insecticide resistance in an insect might inadvertently also cause, say, sterility. And in societies, an apparently helpful change to correct a conspicuous problem might inadvertently also cause other, perhaps more serious, problems. Biological and social change also differ in some ways. Biological evolution depends on a random process of mutation whereas social change involves agents who sometimes rationally conceive of ideas directed at fixing a problem. Evolutionary biologists have modeled biological change using Fisher’s so-called geometric model of adaptation. Here we slightly modify Fisher’s model to study social change. We find that, even when agents (e.g., central planners) are skilled enough to perfectly correct the problem that they set out to fix, unintended consequences are so common and severe that half the time society is left worse off than before. Put differently, the median society is no better or worse off after a “perfect” intervention than before.