This activity simulates natural selection on two populations of butterflies of different colors. The color of each population relative to the colors of the background environment makes them more or less susceptible to predation and therefore affects their survivorship. To begin, select an initial frequency for Population 1, lock that selection, and then select a color for each population. Then click "Run simulation" to watch how the populations change over time.

Population 1

Initial frequency:

.25 .50 .75

Population 2

Initial frequency: .50

To get the most out of this simulation, try the following two scenarios:

Select one color that matches the background environment well, and one color that matches the background environment poorly. What happens over time?
Try selecting two colors that match the background poorly, and repeat the simulation several times. When a mutation arises that matches the background well, what happens? If the new mutation matches the background poorly, what happens?