# Explain how geographic isolation can lead to the formation of two new species from a single ancestral population.

> IB DP Biology Standard Level (2023 syllabus) — A4.1 Evolution and speciation · Explain · 4 marks

## Mark scheme (4 marks)

1. Geographic isolation prevents gene flow between the separated populations
2. Each population is subject to different selection pressures and/or random mutation, so allele frequencies change independently in each population
3. Over time, genetic differences accumulate to the point where individuals from the two populations are no longer able to interbreed to produce fertile offspring
4. Once reproductive isolation is established, the two groups are defined as separate species (biological species concept)

## Key terms

- [geographic isolation](https://www.gradenine.co.uk/glossary/geographic-isolation)

## Related

- [Revision notes for IB DP Biology Standard Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-geographic-isolation-can-lead-d3283bd8) · Published by Druglandscape Ltd.