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Emergence 2009: Langton's Ant I


Biology 361 = Computer Science 361
Bryn Mawr College, Spring 2009


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This model is a variation on the classic Langton's Ant model. Whereas the original model features only a single "ant" and its behavior, this model shows the interaction, communication and cooperation between multiple "ants."
Each ant is provided with an identical set of instructions, as well as a characteristic color and heading. The instructions are simple: if the patch is black, change it to your personal color and turn right. If the patch is not black, change it to black and turn left. Each ant begins at the origin and has an initial heading of 0, 90, 180 or 270 degrees.
Begin by creating one ant. Hit the Start/Stop button to the right of the One Ant button and observe that one ant's behavior. Stop the simulation, move on to Step 2: Two Ants, and then on to Step 3: Four Ants, then on to Step 4: Four Ants (a variation). Observe the differences in behavior when multiple ants are involved.

One ant has a characteristic behavior: unordered motion that eventually switches to road-building. It appears as if the ant learns a new behavior and wants to continue that new behavior, even if it is momentarily blocked.

Two ants, both beginning at the origin and headed in opposite directions, exhibit the same combination of unordered motion and road-building. They begin by trying to act independently of one another. However, they soon interfere with one another and appear to argue before teaming up to reverse their actions and begin again in a different orientations. Between the two of them, they change their minds, repair their mistakes and try something new. They appear to communicate with one another.

Four ants take it to a whole new level. Not only do they communicate with one another, they synchronize their actions and break out of the road-building behavior they'd exhibit on their own. They can even communicate across a distance, as in the case of Step 4 when they all begin the specified number of patches from the origin headed in different directions, and still display highly symmetric repeating patterns.

What has changed in these four setups? Do the ants actually learn, communicate, argue, or synchronize of their own will? No. Other than the color and heading of each additional ant, none of the rules have changed. The ants still move forward, change a black patch to their own color and turn right, or turn a non-black patch to black and turn left. With the addition of multiple ants, behavior is observed that does not appear in only one ant. This is an example of emergent behavior: simple interactions of simple things that yeild surprisingly complex outcomes.

Thanks to Paul Grobstein and the Emergence 2009 class for their input and insight.


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