# Explain how a cladogram can be used to identify the most recent common ancestor of two species, and outline what the position of that ancestor on the cladogram indicates about the evolutionary relationship between those species.

> IB DP Biology Higher Level (2023 syllabus) — A3.2 Classification and cladistics · Explain · 4 marks

## Mark scheme (4 marks)

1. The most recent common ancestor is identified by tracing the lineages of both species back to the node where they first converge/meet on the cladogram.
2. The closer (more recent) the node, the more closely related the two species are / they share a more recent common ancestor.
3. All species that share that node (and all descendant lineages from it) form a clade / monophyletic group, meaning they all descended from that single common ancestor.
4. The branching pattern shows the sequence of divergence events, indicating that the two species diverged from a common ancestral population rather than one species giving rise directly to the other.

## Key terms

- [cladogram](https://www.gradenine.co.uk/glossary/cladogram)
- [most recent common ancestor](https://www.gradenine.co.uk/glossary/most-recent-common-ancestor)

## 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-a-cladogram-can-be-df2a9233) · Published by Druglandscape Ltd.