# Explain how the peppered moth (Biston betularia) population in industrial areas of England changed in colour frequency during the Industrial Revolution through the process of natural selection.

> IB DP Biology Standard Level (2023 syllabus) — D4.1 Natural selection · Explain · 4 marks

> Before the Industrial Revolution, light-coloured peppered moths were more common than dark (melanic) forms in England. As industrial pollution increased, tree bark became coated with soot, darkening the environment. By the late 19th century, dark moths had become the dominant form in heavily industrialised regions.

## Mark scheme (4 marks)

1. Variation existed in the moth population, with individuals differing in body colour (light and dark/melanic forms).
2. Soot darkened tree bark, meaning light-coloured moths were more visible to predators (birds) on dark bark, and dark moths were better camouflaged.
3. Dark moths had a higher survival rate and reproduced more successfully, passing the allele(s) for dark colouration to offspring (differential reproductive success).
4. Over successive generations, the frequency of the dark allele increased in the population, so dark moths became more common — this is natural selection.

## Key terms

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

## Related

- [Revision notes for IB DP Biology Standard Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-peppered-moth-biston-b82abd68) · Published by Druglandscape Ltd.