NetLogo Models Library:
Sample Models/Biology/Evolution/Genetic Drift

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GenDrift P global

Run GenDrift P global in your browser uses NetLogo 4.0.2 requires Java 1.4.1+ (system requirements) Note: If you download the NetLogo application, every model in the Models Library (besides the Community Models) is included. If you have trouble running this model in your browser, you may wish to download the application instead.

WHAT IS IT?

This model is an example of random selection. It shows that patches that randomly exchange colors converge on a single color. The idea, explained in more detail in Dennett's "Darwin's Dangerous Idea", is that trait drifts can occur without any particular purpose or 'selecting pressure'.

The model starts with a random distribution of colors. Each patch then randomly picks a patch to copy its color from. (It might randomly choose itself.)

After enough time passes, a color will gain a slight dominance. By statistical advantage, a dominant color becomes more likely to win the entire grid. However, because the process is random, there will usually be many series of dominant colors before one color finally wins. A key aspect is that once a color disappears -- becomes extinct -- it can never reappear.

HOW TO USE IT

Use the COLORS slider to select the number of competing colors.

The SETUP button initializes the model.

The GO button starts it, and runs continuously.

THINGS TO NOTICE

Notice that often a color nearly becomes dominant, yet loses in the end.

EXTENDING THE MODEL

Explore other rules by which patches might randomly influence each other. What does it take for one color to "win out"?

RELATED MODELS

GenDrift (P local)
GenDrift (T interact)
GenDrift (T reproduce)

CREDITS AND REFERENCES

To refer to this model in academic publications, please use: Wilensky, U. (1997). NetLogo GenDrift P global model. http://ccl.northwestern.edu/netlogo/models/GenDriftPglobal. Center for Connected Learning and Computer-Based Modeling, Northwestern University, Evanston, IL.

In other publications, please use: Copyright 1997 Uri Wilensky. All rights reserved. See http://ccl.northwestern.edu/netlogo/models/GenDriftPglobal for terms of use.

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