# A species of ground-dwelling bird lives on a large island. The birds feed on seeds found on the ground. Over thousands of years, a wide sea channel forms, permanently separating the island into two smaller islands. Each island has a different climate and different types of seeds available. Explain how this separation could eventually lead to the formation of two new species.

> Edexcel A-Level Biology A: Salters-Nuffield (9BN0) — 3.4 Evolution and speciation · Explain · 5 marks

> A species of ground-dwelling bird lives on a large island. The birds feed on seeds found on the ground. Over thousands of years, a wide sea channel forms, permanently separating the island into two smaller islands. Each island has a different climate and different types of seeds available.

## Mark scheme (5 marks)

1. The sea channel acts as a geographical barrier / the two populations are now isolated from each other and cannot interbreed
2. Each population has genetic variation due to random mutations producing different alleles
3. Different environmental conditions (different climate / seed types) mean different alleles are advantageous in each population
4. Individuals with advantageous alleles are more likely to survive, reproduce and pass on those alleles to offspring (natural selection)
5. Over many generations the two populations become so different that they can no longer interbreed to produce fertile offspring, forming two new species (speciation)

## Related

- [Revision notes for Edexcel A-Level Biology A: Salters-Nuffield (9BN0)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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