# A population of beetles lives on a large island. Over thousands of years, the island splits into two separate landmasses due to rising sea levels, dividing the beetle population. After many generations, the two groups of beetles can no longer interbreed to produce fertile offspring. Describe how genetic variation and natural selection led to this outcome.

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

> A population of beetles lives on a large island. Over thousands of years, rising sea levels split the island into two separate landmasses, permanently separating the beetle population into two isolated groups. After many generations, the two groups of beetles can no longer interbreed to produce fertile offspring.

## Mark scheme (5 marks)

1. Random mutations occur in the DNA base sequence of individuals in each population
2. This creates genetic variation between individuals within each separated population
3. The two populations experience different selection pressures / environments, so different alleles are advantageous in each group
4. Individuals with beneficial alleles are more likely to survive and reproduce, passing those alleles to offspring (natural selection)
5. Over many generations the two populations become so genetically different that they can no longer interbreed to produce fertile offspring, forming two separate species (speciation)

## Key terms

- [genetic variation](https://www.gradenine.co.uk/glossary/genetic-variation)
- [natural selection](https://www.gradenine.co.uk/glossary/natural-selection)

## Related

- [Revision notes for Pearson Edexcel A-Level Biology A (9BI0)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" 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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Source: [GradeNine](https://www.gradenine.co.uk/q/a-population-of-beetles-lives-on-d8e51997) · Published by Druglandscape Ltd.