# Explain how natural selection acting on variation within a population can lead to the formation of a new species over time.

> IB DP Biology Standard Level (2023 syllabus) — A3.1 Diversity of organisms · Explain · 4 marks

## Mark scheme (4 marks)

1. Variation exists within a population due to mutation and/or sexual reproduction
2. Natural selection favours individuals with advantageous traits, which survive and reproduce more successfully (differential reproductive success)
3. Allele frequencies in the population change over many generations, accumulating genetic differences
4. When populations become reproductively isolated (e.g. by a geographical barrier), independent natural selection / genetic divergence leads to populations that can no longer interbreed to produce fertile offspring, forming a new species

## Key terms

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

## 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)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-natural-selection-acting-on-353338d6) · Published by Druglandscape Ltd.