Peppered Moth Simulator

Clean bark

Each moth shown stands for some moths in the population.

Generation: 0
Dark moths: 0 (0%)
Light moths: 0 (100%)
Eaten by birds: 0

CC (dark) 0
Cc (dark) 0
cc (light) 0

Tree bark Clean (lichen) Sooty (pollution)

Speed 10 generations/sec Bird predation 20% Chance that a moth that stands out against the bark gets eaten. Camouflaged moths are eaten one tenth as often. Mutation rate (light → dark) Population size (restarts the simulation)

Population over time

Dark moths (% of population)
Dark allele C (% of gene copies)
Sooty bark

What happened

How the model works

One gene controls wing colour. The C allele (carbonaria) makes moths dark and is dominant, so CC and Cc moths are dark. Only cc moths are light and speckled.

Every generation, birds hunt the moths resting on tree bark. Moths that stand out are easier to spot. The survivors mate at random to produce the next generation, and new dark mutations can appear by chance.

Things to try

On clean bark, how long does a new dark mutation usually last?
Switch to sooty bark once dark moths appear. How many generations until they are the majority?
On sooty bark, why are light moths so hard to get rid of completely? Look at the Cc count.
Switch back to clean bark. Does the population return to where it started?
Try a population of 100 with no predation. What happens by chance alone?