# A population of giraffes living on the African savanna feeds on leaves from trees. Over many generations, the average neck length of giraffes in the population has increased. Explain how natural selection could have caused this change.

> Edexcel GCSE Biology (1BI0) — 4.1 Evolution by natural selection · Explain · 4 marks

> In a population of giraffes, individuals vary in neck length. Giraffes with longer necks are able to reach leaves higher up in trees, giving them access to more food.

## Mark scheme (4 marks)

1. There is variation in neck length within the population (due to mutation)
2. Giraffes with longer necks can reach more food / have a better chance of surviving (named selection pressure: competition for food)
3. Giraffes with longer necks are more likely to reproduce and pass on the advantageous allele/trait to offspring
4. Over many generations, the frequency of the longer-neck trait increases in the population

## Key terms

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

## Related

- [Revision notes for Edexcel GCSE Biology (1BI0)](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/a-population-of-giraffes-living-on-427bdcc7) · Published by Druglandscape Ltd.