WHAT IS IT?
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This model is an example of genetic drift by random selection.  It shows that
turtles that randomly exchange colors converge on a single color.  The model
starts with a random distribution of colored agents.  Turtles move by wiggling
randomly across the screen.  When two turtles bump into each other, one turtle
loses its color and adopts the color of the other one.  After enough turns, 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 several dominant colors before one color finally
wins.  The idea, explained in more detail in Dennett's "Darwin's Dangerous Idea",
is that trait drifts can occur without any particular purpose or 'selection
pressure'.

HOW TO USE IT:
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The Setup Button intializes the model.
The Go Button starts it, and runs continuously.
Use the Colors Slider to select the number of colors competing.

THINGS TO NOTICE:
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Notice the Graphs of the colors.  Often colors that start with a higher initial
number fail to win the grid.

EXTENDING THE MODEL:
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Try writing the model with a 'randomness' slider that increases the randomness in
the turtles? movements.  How does this affect the rate at which one color
dominates the space?

RELATED MODELS:
The other models in this set have slightly different mechanisms but also show
genetic drift:

GD-Local Patches
GD-Global Patches
GD-Reproducing turtles