A population of Galápagos finches lives on an island where the main food source is large, hard seeds. Explain how natural selection could lead to finches with larger, stronger beaks becoming the dominant variety in the population over many generations.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
On the island, a random mutation caused some finches to develop slightly larger, stronger beaks. Other finches in the population had smaller, weaker beaks.
Model answer (5 marks)
Variation in beak size and strength exists in the population.
This variation is caused by a random mutation that produces larger, stronger beaks, and the trait is inherited.
Finches with larger, stronger beaks can crack and eat the large, hard seeds more successfully, giving them a selective advantage and a better chance of survival.
Because they survive better, these finches are more likely to reproduce and pass on the alleles for larger beaks to their offspring.
Over many generations the frequency of the alleles for larger, stronger beaks increases, so larger beaks become the dominant variety in the population.
This variation is caused by a random mutation that produces larger, stronger beaks, and the trait is inherited.
Finches with larger, stronger beaks can crack and eat the large, hard seeds more successfully, giving them a selective advantage and a better chance of survival.
Because they survive better, these finches are more likely to reproduce and pass on the alleles for larger beaks to their offspring.
Over many generations the frequency of the alleles for larger, stronger beaks increases, so larger beaks become the dominant variety in the population.
Examiner tips
- Use the word "variation" and link it to mutation and inheritance. Explain the selective advantage in terms of food access. Show the chain: survival → reproduction → allele frequency change. Mention that the change occurs over many generations.
Common mistakes
- Failing to state that the variation is inherited. Confusing survival advantage with reproductive advantage. Not linking the change to allele frequency over generations.
Mark scheme (5 marks)
- There is variation in beak size/strength within the population
- Variation is caused by (random) mutation / inherited genetic differences
- Finches with larger, stronger beaks can crack/eat the large hard seeds more successfully, giving them a selective advantage / better chance of survival
- Finches with larger beaks are more likely to survive and reproduce / pass on their alleles/genes to offspring
- Over many generations the alleles/genes for larger, stronger beaks increase in frequency in the population, so larger beaks become more common
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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