# Explain how convergent evolution provides evidence that natural selection, rather than chance alone, drives evolutionary change.

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

> Convergent evolution describes the independent evolution of similar traits in distantly related lineages. Classic examples include the streamlined body form of sharks (Chondrichthyes), ichthyosaurs (extinct reptiles), and dolphins (Mammalia), and the camera-type eye found in both vertebrates and cephalopod molluscs.

## Mark scheme (4 marks)

1. Convergent evolution occurs when distantly related / phylogenetically unrelated organisms independently evolve similar structures or traits
2. The similar traits arise because both lineages experience the same / comparable selective pressures from analogous environments or ecological niches
3. If evolution were driven by chance (random mutation / genetic drift) alone, the probability of the same complex trait arising independently in unrelated lineages would be negligibly small
4. The repeated, independent origin of the same adaptive solution therefore demonstrates that natural selection consistently favours particular phenotypes when selective pressures are equivalent, confirming selection as a directional, non-random mechanism of evolutionary change

## Key terms

- [convergent evolution](https://www.gradenine.co.uk/glossary/convergent-evolution)
- [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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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-convergent-evolution-provides-evidence-ab178713) · Published by Druglandscape Ltd.