WHAT IS IT? ----------- This model is an example of localized random selection. 
It shows that patches which randomly exchange colors converge on a single color.

The model starts with a random distribution of colors.  Each patch randomly picks
a patch within its local five-patch domain (to the immedieate top, bottom, right,
left, or itself) to copy the color from, and changes itself to that patch's
color.   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 many series of 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: -------------- 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: ---------------- Notice the Graphs of the colors.  Often colors
that start with a higher initial number fail to win the grid.

EXTENDING THE MODEL: -------------------- Try writing the model with turtle
agents who move, and exchange colors on contact.

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

GD-Global Patches GD-Random-walking Turtles GD-Reproducing turtles