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Simulation of
Butterflies
(View Java Source Code of Mimesis)
(View Java Source Code of Stack)
In London, before the Industrial Age, peppermoths made their home on
white birch trees. Some blended into their surroundings, and the more
visible ones became lunch for local birds. As the Industrial Age began,
soot created from factories burning coal gave the city's trees a darker
haze. As a result, what were previously hidden moths became obvious to
the hungry birds. Several generations of moths later, it seemed the
species was nearly all dark in wing color, in stark contrast to the
description of the species several years beforehand.
This program exemplifies that scenario. Choose a background color
and click "See It" to see what would happen to a group of butterflies.
Here is how my algoritm is working:
| 1. |
The program creates a set of butterflies with a random wing
color, which is a value between 0 and 255. The butterflies are then
placed onto an image with a background color that has been selected.
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| 2. |
A "bird attack" occurs, in which highly visible moths are eaten.
Visibility is determined by probability: 1 / |background - wing color|
+ 1. (A color difference of 0 yields a visibility of 1.) A randomized
number is compared to the visibility rating, and should that number be
greater than the visibility, the butterfly is considered eaten. This
ensures that butterflies with a low visibility probability are less
likely to be eaten than those with a greater wing-to-background color
difference. |
| 3. |
A random set of surviving butterflies are chosen, and a mutation
of that butterfly is placed into a vacancy made by an eaten butterfly.
The mutation is made by either adding or subtracting a random value
(between zero and the mutation radius, in this case 0.50) from the
"parent" butterfly's wing color ID. Care is taken to ensure
no "child" butterfly creates offspring for the current
generation. |
| 4. |
Using this current pool of butterflies, the process repeats from
step 2 ad infinitum. |
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