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

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GenDrift P local

[screen shot]

If you download the NetLogo application, this model is included. (You can also run this model in your browser, but we don't recommend it; details here.)

## 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'.

## HOW IT WORKS

The model starts with a random distribution of colors. After this, at each time step, each patch in the grid changes its color to be the same as the color of one of the neighboring eight patches (chosen at random).

After enough time passes, a color will gain a slight dominance. By statistical advantage, a dominate 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 running.

## THINGS TO NOTICE

Notice that often colors can become quite dominant but still fail to win the grid.

## 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 global)
* GenDrift (T interact)
* GenDrift (T reproduce)

## HOW TO CITE

If you mention this model in a publication, we ask that you include these citations for the model itself and for the NetLogo software:

* Wilensky, U. (1997). NetLogo GenDrift P local model. http://ccl.northwestern.edu/netlogo/models/GenDriftPlocal. Center for Connected Learning and Computer-Based Modeling, Northwestern University, Evanston, IL.
* Wilensky, U. (1999). NetLogo. http://ccl.northwestern.edu/netlogo/. Center for Connected Learning and Computer-Based Modeling, Northwestern University, Evanston, IL.

## COPYRIGHT AND LICENSE

Copyright 1997 Uri Wilensky.

![CC BY-NC-SA 3.0](http://i.creativecommons.org/l/by-nc-sa/3.0/88x31.png)

This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-sa/3.0/ or send a letter to Creative Commons, 559 Nathan Abbott Way, Stanford, California 94305, USA.

Commercial licenses are also available. To inquire about commercial licenses, please contact Uri Wilensky at uri@northwestern.edu.

This model was created as part of the project: CONNECTED MATHEMATICS: MAKING SENSE OF COMPLEX PHENOMENA THROUGH BUILDING OBJECT-BASED PARALLEL MODELS (OBPML). The project gratefully acknowledges the support of the National Science Foundation (Applications of Advanced Technologies Program) -- grant numbers RED #9552950 and REC #9632612.

This model was converted to NetLogo as part of the projects: PARTICIPATORY SIMULATIONS: NETWORK-BASED DESIGN FOR SYSTEMS LEARNING IN CLASSROOMS and/or INTEGRATED SIMULATION AND MODELING ENVIRONMENT. The project gratefully acknowledges the support of the National Science Foundation (REPP & ROLE programs) -- grant numbers REC #9814682 and REC-0126227. Converted from StarLogoT to NetLogo, 2001.

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