11.2. Schelling’s Model¶
In 1969 Thomas Schelling published “Models of Segregation”, which proposed a simple model of racial segregation.
The Schelling model of the world is a grid where each cell represents a house. The houses are occupied by two kinds of agents, labeled red and blue, in roughly equal numbers. About 10% of the houses are empty.
At any point in time, an agent might be happy or unhappy, depending on the other agents in the neighborhood, where the “neighborhood” of each house is the set of eight adjacent cells. In one version of the model, agents are happy if they have at least two neighbors like themselves, and unhappy if they have one or zero.
The simulation proceeds by choosing an agent at random and checking to see whether they are happy. If so, nothing happens; if not, the agent chooses one of the unoccupied cells at random and moves.
You will not be surprised to hear that this model leads to some segregation, but you might be surprised by the degree. From a random starting point, clusters of similar agents form almost immediately. The clusters grow and coalesce over time until there are a small number of large clusters and most agents live in homogeneous neighborhoods.
If you did not know the process and only saw the result, you might assume that the agents were racist, but in fact all of them would be perfectly happy in a mixed neighborhood. Since they prefer not to be greatly outnumbered, they might be considered mildly xenophobic. Of course, these agents are a wild simplification of real people, so it may not be appropriate to apply these descriptions at all.
Racism is a complex human problem; it is hard to imagine that such a simple model could shed light on it. But in fact it provides a strong argument about the relationship between a system and its parts: if you observe segregation in a real city, you cannot conclude that individual racism is the immediate cause, or even that the people in the city are racists.
Of course, we have to keep in mind the limitations of this argument: Schelling’s model demonstrates a possible cause of segregation, but says nothing about actual causes.