In about A.D. 1300 the Anasazi people abandoned Long House Valley. To this day the valley, though beautiful in its way, seems touched by desolation. It runs eight miles more or less north to south, on the Navajo reservation in northern Arizona, just west of the broad Black Mesa and half an hour's drive south of Monument Valley. To the west Long House Valley is bounded by gently sloping domes of pink sandstone; to the east are low cliffs of yellow-white sedimentary rock crowned with a mist of windblown juniper. The valley floor is riverless and almost perfectly flat, a sea of blue-gray sagebrush and greasewood in sandy reddish soil carried in by wind and water. Today the valley is home to a modest Navajo farm, a few head of cattle, several electrical transmission towers, and not much else.
Artificial Society Animations
Watch QuickTime animations of the artificial societies discussed in this article.
Interviews: "The World on a Screen" (March 29, 2002)
Jonathan Rauch talks about what the study of artificial societies has to tell us about the real world.
Yet it is not hard to imagine the vibrant farming district that this once was. The Anasazi used to cultivate the valley floor and build their settlements on low hills around the valley's perimeter. Remains of their settlements are easy to see, even today. Because the soil is sandy and the wind blows hard, not much stays buried, so if you leave the highway and walk along the edge of the valley (which, by the way, you can't do without a Navajo permit), you frequently happen upon shards of Anasazi pottery, which was eggshell-perfect and luminously painted. On the site of the valley's eponymous Long House—the largest of the ancient settlements—several ancient stone walls remain standing.
Last year I visited the valley with two University of Arizona archaeologists, George Gumerman and Jeffrey Dean, who between them have studied the area for fifty or more years. Every time I picked up a pottery shard, they dated it at a glance. By now they and other archaeologists know a great deal about the Anasazi of Long House Valley: approximately how many lived here, where their dwellings were, how much water was available to them for farming, and even (though here more guesswork is involved) approximately how much corn each acre of farmland produced. They have built up a whole prehistoric account of the people and their land. But they still do not know what everyone would most like to know, which is what happened to the Anasazi around A.D. 1300.
"Really, we've been sort of spinning our wheels in the last eight to ten years," Gumerman told me during the drive up to the valley. "Even though we were getting more data, we haven't been able to answer that question." Recently, however, they tried something new. Unable to interrogate or observe the real Long House Valley Anasazi, they set about growing artificial ones.
Growing artificial societies on computers—in silico, so to speak—requires quite a lot of computing power and, still more important, some sophisticated modern programming languages, so the ability to do it is of recent vintage. Moreover, artificial societies do not belong to any one academic discipline, and their roots are, accordingly, difficult to trace. Clearly, however, one pioneer is Thomas C. Schelling, an economist who created a simple artificial neighborhood a generation ago.
Today Schelling is eighty years old. He looks younger than his age and is still active as an academic economist, currently at the University of Maryland. He and his wife, Alice, live in a light-filled house in Bethesda, Maryland, where I went to see him one day not long ago. Schelling is of medium height and slender, with a full head of iron-gray hair, big clear-framed eyeglasses, and a mild, soft-spoken manner. Unlike most other economists I've dealt with, Schelling customarily thinks about everyday questions of collective organization and disorganization, such as lunchroom seating and traffic jams. He tends to notice the ways in which complicated social patterns can emerge even when individual people are following very simple rules, and how those patterns can suddenly shift or even reverse as though of their own accord. Years ago, when he taught in a second-floor classroom at Harvard, he noticed that both of the building's two narrow stairwells—one at the front of the building, the other at the rear—were jammed during breaks with students laboriously jostling past one another in both directions. As an experiment, one day he asked his 10:00 A.M. class to begin taking the front stairway up and the back one down. "It took about three days," Schelling told me, "before the nine o'clock class learned you should always come up the front stairs and the eleven o'clock class always came down the back stairs"—without, so far as Schelling knew, any explicit instruction from the ten o'clock class. "I think they just forced the accommodation by changing the traffic pattern," Schelling said.
In the 1960s he grew interested in segregated neighborhoods. It was easy in America, he noticed, to find neighborhoods that were mostly or entirely black or white, and correspondingly difficult to find neighborhoods where neither race made up more than, say, three fourths of the total. "The distribution," he wrote in 1971, "is so U-shaped that it is virtually a choice of two extremes." That might, of course, have been a result of widespread racism, but Schelling suspected otherwise. "I had an intuition," he told me, "that you could get a lot more segregation than would be expected if you put people together and just let them interact."
One day in the late 1960s, on a flight from Chicago to Boston, he found himself with nothing to read and began doodling with pencil and paper. He drew a straight line and then "populated" it with Xs and Os. Then he decreed that each X and O wanted at least two of its six nearest neighbors to be of its own kind, and he began moving them around in ways that would make more of them content with their neighborhood. "It was slow going," he told me, "but by the time I got off the plane in Boston, I knew the results were interesting." When he got home, he and his eldest son, a coin collector, set out copper and zinc pennies (the latter were wartime relics) on a grid that resembled a checkerboard. "We'd look around and find a penny that wanted to move and figure out where it wanted to move to," he said. "I kept getting results that I found quite striking."
To see what happens in this sort of artificial neighborhood, look at Figure 1, which contains a series of stills captured from a Schelling-style computer simulation created for the purposes of this article. (All the illustrations in the article are taken from animated artificial-society simulations that you can view online, at www.theatlantic.com/rauch.) You are looking down on an artificial neighborhood containing two kinds of people, blue and red, with—for simplicity's sake—no blank spaces (that is, every "house" is occupied). The board wraps around, so if a dot exits to the right, it reappears on the left, and if it exits at the top, it re-enters at the bottom.