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view/download model file: Ethnocentrism-Wilensky.nlogo

WHAT IS IT?

This model suggests that pre-programmed "ethnocentric" behavior can proliferate under some conditions. Agents compete for limited space via Prisoner Dilemma's type interactions. "Ethnocentric" agents treat agents within their group differently from those outside their group. The model includes a mechanism for inheritance (genetic or cultural) of strategies.

HOW IT WORKS

Each agent has three traits: a) color, b) whether they cooperate with same colored agents, and c) whether they cooperate with different colored agents. An "ethnocentric" agent is one which cooperates with same colored agents, but does not cooperate with different colored agents. Ethnocentric agents are represented as triangles. An "altruist" cooperates with all agents, while an "egoist" cooperates with no one.

At each time step, the following events occur:

1. Up to IMMIGRATION-RATE, empty patches sprout turtles with random traits.

2. Agents start with an INITIAL-BIRTH-RATE chance of reproducing. Each pair of adjacent agents interact in a one-move Prisoner's Dilemma in which each chooses whether or not to help the other. They either gain, or lose some of their potential to reproduce. See documentation of CCSCORE and related sliders for details.

3. In random order, each agent is given a chance to reproduce. Offspring have the same traits as their parents, with a MUTATION_RATE chance of each trait mutating. Each agent's birth-rate is reset to the INITIAL-BIRTH-RATE.

4. Each agent rolls a hundred sided die, and if the result is below DEATH-RATE, it dies, making room for future offspring and immigrants.

HOW TO USE IT

To prepare the simulation for a new run, press SETUP. Press GO to start the simulation running, press GO again to stop it.

The USER-VIEW chooser allows you to watch the world from two different perspectives. In the "breed" view, each agent is colored according to its color attribute. If it is an ethnocentric agent, then it is drawn as an X, otherwise it is drawn as a circle. In the "behavior" view, all agents are drawn as circles and they are orange if their behavior is ethnocentric, and gray if not.

CCSCORE, CDSCORE, DCSCORE and DDSCORE determine the benefit or cost interacting agents receive when they cooperate or defect. If both cooperate, they both get CCSCORE added to their birth-rate. If one cooperates and the other doesn't, the cooperating turtle loses CDSCORE from their birth-rate and the defecting turtle gets DCSCORE added to their birth-rate. If both defect, they get DDSCORE added to their birth-rates.

DISTINGUISHABILITY determines how accurately turtles can tell the color of the turtle they are interacting with. It is the chance they will incorrectly perceive the turtle as being the same color.

LOCAL-BIRTHS? controls whether turtles give birth to their offspring only in adjacent empty patches, or in any empty patch.

LOCAL-INTERACTIONS? controls whether turtles interact only with adjacent turtles, or with any turtle on the screen.

The REMOVE-ETHNO button will mutate all ethnocentric agents in the world until they are no longer ethnocentric.

THINGS TO NOTICE

Observe the interaction along the edge of a group of ethnocentric agents, and non-ethnocentric agents. What behaviors do you see? Is one more stable? Does one expand into the other group?

Observe the ETHNICITY-COUNTS plot. Does one color grow faster than others? If so, does it remain the largest ethnicity over a long run?

Observer the INTERACTIONS plot. Does one strategy occur more than others? What happens when we change the model? Is there a relation between the ethnocentricity of the population, as plotted in the BEHAVIOR-COUNTS plot, and INTERACTIONS plot?

Observer the ETHNOCENTRICITY plot. Is there a relation between the ethnocentricity of a given color, and it's population in the model? Are all colors uniformly ethnocentric?

THINGS TO TRY

Turn off LOCAL-BIRTH? and observe the BEHAVIOR-COUNTS and INTERACTIONS plots.

Turn off LOCAL-INTERACTION? and observe the BEHAVIOR-COUNTS and INTERACTIONS plots.

Press the REMOVE-ETHNO button to remove ethnocentric agents. Do they re-appear? Why?

Vary the DISTINGUISHABILITY? slider and observe the BEHAVIOR-COUNTS and INTERACTIONS plots. How does distinguishability effect them?

Change the values of CCSCORE, DDSCORE, DCSCORE, and CDSCORE and observe the effects on the model and the level of ethnocentricity.

EXTENDING THE MODEL

Add more colors to the model. Will the behavior change?

Make some patches richer than others, so that agents on them have a higher chance of reproducing. Distribute this advantage across the world in different ways, in blobs, randomly, in discrete quarters.

Tag patches with a color. distribute the colors across the world in different ways: blobs, randomly, in discrete quarters. Agents use the patch color under other agents to determine whether to cooperate with them or not.

NETLOGO FEATURES

This model comes with three BehaviorSpace experiments defined:

The "Distinguishability Dynamics" experiment runs the model while varying the distinguishability variable.

The "Mutation Dynamics" experiment runs the model while varying the mutation rate.

The "Localization Dynamics" runs the model while varying the local-birth? and local-interaction? switches.

RELATED MODELS

See the Segregation model.

CREDITS AND REFERENCES

This model is a NetLogo version of the ethnocentrism model presented by Robert Axelrod at Northwestern University at the NICO (Northwestern Institute on Complex Systems) conference on October 25th, 2003.

See also: Robert Axelrod and Ross A. Hammond, The Evolution of Ethnocentric Behavior, http://www-personal.umich.edu/~axe/research/AxHamm_Ethno.pdf

To refer to this model in academic publications, please use:
Wilensky, U. (2005). NetLogo Ethnocentrism model. http://ccl.northwestern.edu/netlogo/models/Ethnocentrism. Center for Connected Learning and Computer-Based Modeling, Northwestern University, Evanston, IL.

In other publications, please use:
Copyright 2005 Uri Wilensky. All rights reserved. See http://ccl.northwestern.edu/netlogo/models/Ethnocentrism for terms of use.