# Explain how the concept of punctuated equilibrium differs from phyletic gradualism in describing the pattern of evolutionary change seen in the fossil record.

> IB DP Biology Higher Level (2023 syllabus) — D4.2 Stability and change · Explain · 4 marks

## Mark scheme (4 marks)

1. Phyletic gradualism proposes that evolutionary change occurs slowly and continuously over long periods of time
2. Punctuated equilibrium proposes that species remain largely unchanged (stasis) for long periods, interspersed with rapid bursts of evolutionary change
3. The fossil record tends to support punctuated equilibrium because transitional forms are rare / gaps between morphologically distinct forms are common
4. Under punctuated equilibrium, rapid change is linked to environmental perturbation / isolation of small populations / allopatric speciation events, explaining why change appears sudden rather than gradual

## Key terms

- [punctuated equilibrium](https://www.gradenine.co.uk/glossary/punctuated-equilibrium)
- [phyletic gradualism](https://www.gradenine.co.uk/glossary/phyletic-gradualism)
- [fossil record](https://www.gradenine.co.uk/glossary/fossil-record)

## 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)
- [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-the-concept-of-punctuated-2508226e) · Published by Druglandscape Ltd.