A population of finches lives on a mainland. Some finches migrate to a remote island far out at sea, where they cannot return to the mainland. Explain how, over many generations, the island finches could eventually become a new species.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Finches on the mainland eat hard seeds and have short, strong beaks. The remote island has a very different climate and food supply compared to the mainland.
Model answer (5 marks)
The island finches are geographically isolated from the mainland finches, so they cannot interbreed with them.
Random mutations occur in the DNA of individuals in both populations.
On the island, different environmental conditions mean different alleles are advantageous compared to those on the mainland.
Natural selection favours individuals with beneficial alleles, so they are more likely to survive, reproduce and pass those alleles to offspring.
Over many generations the two populations become so genetically different that they can no longer interbreed to produce fertile offspring, and a new species has formed.
Random mutations occur in the DNA of individuals in both populations.
On the island, different environmental conditions mean different alleles are advantageous compared to those on the mainland.
Natural selection favours individuals with beneficial alleles, so they are more likely to survive, reproduce and pass those alleles to offspring.
Over many generations the two populations become so genetically different that they can no longer interbreed to produce fertile offspring, and a new species has formed.
Examiner tips
- Use the exact wording from the mark scheme – e.g. ‘geographically isolated’, ‘random mutations’, ‘different environmental conditions’, ‘natural selection’, ‘genetically different’, ‘new species’.
- Show the causal chain: isolation → mutation → selection → divergence → speciation.
- Keep the answer concise – 5 points, one sentence each.
Mark scheme (5 marks)
- The island finches are geographically isolated from the mainland finches, so they cannot interbreed with them.
- Random mutations occur in the DNA / genetic material of individuals in both populations.
- On the island, different environmental conditions mean different alleles / mutations are advantageous compared to those on the mainland.
- Natural selection means individuals with beneficial alleles are more likely to survive, reproduce and pass those alleles on to offspring.
- Over many generations the two populations become so genetically different that they can no longer interbreed to produce fertile offspring, and a new species has formed.
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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