# Explain how natural selection could lead to a population of peppered moths becoming darker in colour over many generations, following an increase in air pollution that darkens tree bark in their habitat.

> Cambridge International IGCSE Biology (0610) — 18.3 Selection · Explain · 4 marks

> The peppered moth exists in two forms: a pale, speckled form and a dark form. Before industrialisation, pale tree bark was common. After industrialisation, soot darkened tree bark across large areas.

## Mark scheme (4 marks)

1. There is variation in colour within the moth population, with some moths being darker than others, due to different alleles.
2. Dark moths are better camouflaged on darkened tree bark and are less likely to be eaten by predators, so they have a greater chance of survival.
3. Dark moths are more likely to survive and reproduce, passing on the allele for dark colouration to their offspring.
4. Over many generations, the frequency of the allele for dark colouration increases in the population, so the population becomes predominantly darker.

## Key terms

- [natural selection](https://www.gradenine.co.uk/glossary/natural-selection)

## Related

- [Revision notes for Cambridge International IGCSE Biology (0610)](https://www.gradenine.co.uk/learn)
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