A population of snowshoe hares lives in a forest that receives heavy snowfall in winter. Some hares have thicker, whiter fur than others due to natural variation. Explain how natural selection could lead to most hares in the population having thick, white fur over many generations.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Snowshoe hares live in forests where the ground is covered in snow for several months each year. Predators such as lynx hunt the hares by sight.
Model answer (4 marks)
1. Variation exists – some hares have thicker, whiter fur.
2. Thicker, whiter fur gives better camouflage in snow, reducing predation.
3. Hares with this fur are more likely to survive and reproduce, passing the alleles on.
4. Over many generations the allele frequency for thick, white fur rises, so most hares become white.
2. Thicker, whiter fur gives better camouflage in snow, reducing predation.
3. Hares with this fur are more likely to survive and reproduce, passing the alleles on.
4. Over many generations the allele frequency for thick, white fur rises, so most hares become white.
Examiner tips
- Use the 4-point structure: variation, selection pressure, survival/reproduction, allele frequency change. Include the word "camouflage" and "predation" to show understanding. Show the causal chain clearly, not just listing facts.
Common mistakes
- Failing to mention variation or selection pressure. Using vague terms like "better fur" without linking to camouflage. Not explaining that the change is in allele frequency, not just individual traits.
Mark scheme (4 marks)
- There is variation / mutation in the population, so some hares have thicker, whiter fur than others
- Hares with thicker, whiter fur are better camouflaged in snow and are less likely to be caught by predators (selection pressure)
- Hares with thicker, whiter fur are more likely to survive and reproduce / pass on their genes/alleles to offspring
- Over many generations, the frequency of the alleles for thick, white fur increases in the population
Key terms in this question
Related
- Revision notes: Evolution by natural selection →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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