A population of Arctic foxes lives in a snowy environment. Most Arctic foxes have white fur, but a small number have grey fur. Explain how natural selection could lead to white fur becoming more common in this population over many generations.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Arctic foxes are predators that hunt prey such as lemmings. A fox's fur colour affects how well it is camouflaged against the snow.
Model answer (5 marks)
1. Variation in fur colour exists – some foxes are white, others grey.
2. White fur gives better camouflage in snow, so white foxes are better at hunting prey and avoiding predators.
3. Because of this advantage, white foxes survive more often than grey ones.
4. The surviving white foxes are more likely to reproduce, passing the white‑fur genes to their offspring.
5. Over many generations the proportion of white‑fur foxes in the population increases.
2. White fur gives better camouflage in snow, so white foxes are better at hunting prey and avoiding predators.
3. Because of this advantage, white foxes survive more often than grey ones.
4. The surviving white foxes are more likely to reproduce, passing the white‑fur genes to their offspring.
5. Over many generations the proportion of white‑fur foxes in the population increases.
Examiner tips
- Use the exact terms: variation, camouflage, survival, reproduction, allele(s).
- Show the causal chain: variation → differential survival → differential reproduction → change in frequency.
- Keep each point short and directly linked to the mark scheme.
- Mention "over many generations" to show evolutionary change.
Common mistakes
- Confusing camouflage with hunting efficiency alone; both are important but camouflage is key. Not linking survival to reproduction – need to state that surviving foxes breed. Using vague terms like "better" without explaining why white is advantageous.
Mark scheme (5 marks)
- There is variation in fur colour within the Arctic fox population (white and grey fur)
- White fur provides better camouflage against the snow, so white foxes are better adapted to hunt prey / avoid being outcompeted
- White foxes are more likely to survive / grey foxes are more likely to die (survival of the fittest / differential survival)
- White foxes are more likely to reproduce and pass on the allele(s) / genes for white fur to offspring
- Over many generations, the proportion of foxes with white fur increases in the population
Key terms in this question
Related
- All Pearson Edexcel A-Level Biology A (9BI0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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