In Frame 1 agents and cops are scattered randomly, and the bolder agents (in red) are setting upon their victims. When they commit murder near a cop, the agents go to jail. Even so, the cops are initially overwhelmed by the sheer quantity of violence, and in Frames 2 and 3 an enclave of embattled greens forms, just as before. Now, however, there is an important difference: the enclave is stable. Once it has dwindled to a certain size, the cops are able to contain the violence by making arrests along the border. As long as the cops stay in place, the enclave is safe. But what if the cops are withdrawn? The result is exactly the same as what happened when peacekeepers abandoned enclaves in Bosnia and Rwanda. In Frame 4 the cops have all departed. Again, Frames 5 and 6 speak for themselves.

I don't think I'm alone in finding this artificial genocide eerie. The outcome, of course, is chilling; but what is at least as spooky is that such complicated—to say nothing of familiar—social patterns can be produced by mindless packets of data following a few almost ridiculously simple rules. If I showed you these illustrations and told you they represented genocide, you might well assume you were seeing a schematic diagram of an actual event. Moreover, the model is designed without any element of imitation or communication, so mass hysteria or organized effort is literally impossible. No agent is knowingly copying his peers or following the crowd; none is consciously organizing a self-protective enclave. All the agents are separately and individually reacting "rationally"—according to rules, in any case—to local conditions that the agents themselves are rapidly altering. As hotheads begin to go active, the odds that any one misbehaving agent will be arrested decline, emboldening more-timid agents nearby to act up, reducing the odds of arrest still further, emboldening more agents, and so on. As in real life, the violence, once begun, can spread rapidly as cops are overwhelmed in one neighborhood after another. Although the agents are atomized and disorganized, the violence is communal and coherent. It has form and direction and even a sort of malevolent logic.



At a Brookings conference last year, where Epstein presented his artificial genocide, Alison Des Forges was in attendance. Des Forges, a senior adviser to Human Rights Watch Africa, is one of the world's leading authorities on the Rwandan genocide of 1994. After the session I asked her what she made of Epstein's demonstration. Neither she nor anyone else, Epstein included, believes that an array of little dots explains the Rwandan cataclysm or any other real-world event; the very notion is silly. What the simulation did suggest to Des Forges is that disparate social breakdowns, in widely separated parts of the world, may have common dynamics—linking Rwanda, for instance, to other horrors far away. She also told me that Epstein's demonstration reminded her of Hutu killers' attack on Tutsis who had gathered on a Rwandan hilltop: the torches, the fires, the killing working its way up the hill.

Cyber-Anasazi

In 1994 Epstein went back to the Santa Fe Institute, this time to lecture on Sugarscape. He told me, "I came to a run in the Sugarscape that we called the Protohistory, which was really this made-up toy history of civilization, where it starts with some little soup of agents and they go to peaks on the Sugarscape and coalesce into tribes and have lots of kids and this forces them down in between the peaks and they smash into the other tribe and they have all this assimilation and combat and all this other stuff. And I showed that toy history to this typically unlikely Santa Fe collection of archaeologists and biologists and physicists, and I said, 'Does this remind anyone of anything real?' And a hand shot up, and it was George Gumerman's hand. I had never met George. And he said, 'It reminds me of the Anasazi.' I said, 'What the heck is that?' And he told me the story of this tribe that flourished in the Southwest and suddenly vanished. And why did they suddenly vanish? I thought, That's a fascinating question."