Explain how a population of peppered moths could change over time if the trees in their habitat became covered in dark soot due to industrial pollution.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Before industrial pollution, most peppered moths in England had light-coloured wings that camouflaged them against pale, lichen-covered tree bark. Over several generations following the growth of industrial factories, the proportion of dark-winged moths in the population increased significantly.
Model answer (4 marks)
Random mutation creates variation in wing colour, so some moths are dark.
Dark-winged moths are better camouflaged on soot‑covered trees and are less likely to be eaten by predators.
Because they survive longer they are more likely to reproduce, passing the dark‑wing allele to their offspring.
Over many generations the frequency of the dark‑wing allele rises in the population (natural selection).
Dark-winged moths are better camouflaged on soot‑covered trees and are less likely to be eaten by predators.
Because they survive longer they are more likely to reproduce, passing the dark‑wing allele to their offspring.
Over many generations the frequency of the dark‑wing allele rises in the population (natural selection).
Examiner tips
- Use the word ‘mutation’ to show the source of variation. Explain the link between camouflage and survival. Mention that surviving moths reproduce, passing the allele. Show the change in allele frequency over generations.
Common mistakes
- Confusing mutation with natural selection. Forgetting to link camouflage to reduced predation. Not stating that surviving moths reproduce. Using vague terms like ‘change’ without explaining the mechanism.
Mark scheme (4 marks)
- Random mutation produces variation in wing colour within the population (e.g. some moths have dark wings)
- Dark-winged moths are better camouflaged on soot-covered trees and are less likely to be eaten by predators
- Dark-winged moths are more likely to survive and reproduce, passing the advantageous allele to offspring
- Over many generations the frequency of the dark-wing allele increases in the population (natural selection)
Related
- Revision notes: Natural selection and evolution →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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