# A population of wild wolves was once found across a vast continent. Around 10 000 years ago, a large glacier advanced and permanently separated the wolves into two isolated groups — one in the north and one in the south. The northern group lived in deep snow environments, while the southern group lived in warm, dry grasslands. After many thousands of years, scientists found that the two groups could no longer interbreed to produce fertile offspring. Explain how the two isolated groups of wolves eventually became two separate species.

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

> A population of wild wolves was once found across a vast continent. Around 10 000 years ago, a large glacier advanced and permanently separated the wolves into two isolated groups — one in the north and one in the south. The northern group lived in deep snow environments, while the southern group lived in warm, dry grasslands. After many thousands of years, scientists found that the two groups could no longer interbreed to produce fertile offspring.

## Mark scheme (5 marks)

1. The glacier acted as a physical barrier, preventing the two groups from interbreeding / mating with each other (geographical isolation).
2. Random mutations produced new genetic variants / alleles within each group, creating genetic variation.
3. In each environment, natural selection acted on the variation — individuals with advantageous characteristics were more likely to survive and reproduce.
4. The beneficial alleles / characteristics were passed on to offspring, so the frequency of advantageous alleles increased in each population over generations.
5. Over time, the two populations accumulated so many genetic differences that they could no longer interbreed to produce fertile offspring, so they became separate 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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