Natural Selection

This model shows 140 beetles whose body color is heritable. Each generation birds eat a chosen share of them, preferring those most visible against the background, and the survivors breed to refill the population with slightly mutated copies. Students pick a background, set the percent eaten, bird eyesight and mutation size, and can skip to the next generation. Readouts track generation number, average color trait, mean visibility and survivors. It makes variation, selection and inheritance visible and fits the peppered moth story.

• Press Next generation now repeatedly and watch Mean visibility fall as beetles match the ground.
• Change Background to Pale lichen mid-run and see the population re-adapt over several generations.
• Set Mutation size to 0 and see whether the population can still change.
• Raise Bird eyesight and compare how quickly camouflage improves.
• Raise Eaten per generation to 80 percent and read the Survived last round readout.

1. 1Explain how variation, inheritance and differential survival cause adaptation.
2. 2Predict how a change of environment changes which traits are favored.
3. 3Describe the role of mutation in providing new variation.
4. 4Relate the model to the peppered moth example.

Questions teachers ask