# Explain how natural selection acts on variation within a population to bring about evolutionary change over successive generations.

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

## Mark scheme (4 marks)

1. Heritable variation exists within a population due to mutation and/or sexual reproduction (recombination / random fertilisation).
2. Individuals with favourable/advantageous phenotypic variants have a greater chance of survival and reproduction (differential reproductive success).
3. Favourable alleles are passed on to offspring at a higher frequency, so allele frequencies in the population change over generations.
4. Accumulated changes in allele frequencies over many generations result in evolutionary change, potentially producing new adaptations or new species.

## Key terms

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

## Related

- [Revision notes for IB DP Biology Higher 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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