# Explain how geographic isolation of a small population from a larger parent population can lead to the formation of a new species through natural selection.

> IB DP Biology Standard Level (2023 syllabus) — D4.1 Natural selection · Explain · 4 marks

## Mark scheme (4 marks)

1. Geographic isolation prevents gene flow between the separated population and the parent population.
2. Each population is subject to different selection pressures in its environment, favouring different heritable traits / alleles.
3. Over many generations, allele frequencies in the isolated population diverge from those in the parent population through natural selection (and genetic drift).
4. Eventually the two populations become so genetically different that they can no longer interbreed to produce fertile offspring, and are therefore classified as separate species (reproductive isolation / speciation).

## 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)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-geographic-isolation-of-a-268fb853) · Published by Druglandscape Ltd.