# A population of mountain hares lives in a cold northern region. The hares have white fur, which acts as camouflage against snow. Over many generations, a small group of hares migrates southward to a warmer region with less snowfall. After thousands of years, scientists find that the southern hares can no longer interbreed with the northern hares to produce fertile offspring. Explain how the southern population of hares could have evolved into a new species.

> Pearson Edexcel A-Level Biology A (9BI0) — 3.4 Evolution and speciation · Explain · 5 marks

> Mountain hares in the northern region have white fur all year round. The southern region has fewer months of snow cover and a greater variety of predators that hunt by sight.

## Mark scheme (5 marks)

1. The two populations are geographically isolated / separated, preventing interbreeding between them
2. Random mutations occur in the DNA of individuals in both populations, producing genetic variation
3. In the southern population, individuals with alleles better suited to the warmer, less snowy environment (e.g. darker/brown fur) have a survival advantage / are better adapted
4. These better-adapted individuals are more likely to survive and reproduce, passing their alleles on to offspring (natural selection)
5. Over many generations the allele frequencies in the two populations become so different that they can no longer interbreed to produce fertile offspring, so they are now different species (speciation)

## Related

- [Revision notes for Pearson Edexcel A-Level Biology A (9BI0)](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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