• The peppered moth is a common insect in Britain with two forms: the dark form and the light form.

• The light form has small black specks just like it has been dusted with pepper. This is variation.

The peppered moth

300 years ago most peppered moths were the light form.

After the industrial revolution the dark form became commonest in city areas.

Natural selection of dark form in industrial areas

Dark moths more likely to survive to breed

Repeated over generations

Dark moth less likely to be seen and eaten by bird predators

Tree surfaces are dark because of air pollutionPale lichens are killed by sulfur dioxide

Natural selection of light form in clean areas

Light moths more likely to survive to breed

Repeated over generations

Light moth less likely to be seen and eaten by bird predators

Tree surfaces are pale.Pale lichens grow on the tree bark.

Two varieties of peppered moth

The proportion of dark and light

peppered moths found in different areas of Britain

today.