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Grade 10 Intermediate About 15 min Version 1 Awaiting review Premium

Natural selection: the peppered moth

Peppered moths rest on tree trunks during the day. Most were light, speckled and well hidden on pale, lichen-covered bark; a few were dark, because of an inherited variation. When factories filled the air with soot, trunks turned black. Now the light moths stood out and birds ate more of them, while the dark moths were hidden, survived and laid more eggs. Their young inherited the dark colour, so each generation had a higher share of dark moths. This is natural selection: the environment selects which variations survive and are passed on, and over many generations the population becomes adapted to its environment.

What you will learn

  • Describe how natural selection changes a population over generations.
  • Explain the role of variation, inheritance and predators.
  • Predict what happens when the environment changes back.

Before you start

  • Know that features can be inherited and that individuals of a species vary.

Materials

  • Population record sheet

Equipment

  • None for the virtual lab

Procedure

  1. Start with 10% dark moths on soot-blackened trees with birds hunting. Record the share of dark moths after 1, 5, 10 and 20 generations.
  2. Repeat on clean, pale trees, recording after 5 and 10 generations.
  3. Repeat on blackened trees with no birds, recording after 20 generations.

How this simulation is simplified

  • The population starts with 10% dark moths. When birds hunt, the moths that stand out are 30% less likely to survive and breed each generation.