Explain how the continuous nature of evolution presents a challenge to the classification of organisms into discrete taxa, and suggest one approach biologists use to address this challenge.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
1. Evolution is a continuous process, so boundaries between species/taxa are not always clear-cut or distinct.
2. Populations that are diverging may still interbreed, making it difficult to assign them to separate species using the biological species concept.
3. The fossil record and living intermediates reveal ancestral forms that do not fit neatly into any single modern taxon.
4. Biologists address this by using phylogenetic/cladistic classification, grouping organisms by shared derived characters (synapomorphies) and common ancestry rather than by overall similarity, producing clades that reflect evolutionary relationships.
2. Populations that are diverging may still interbreed, making it difficult to assign them to separate species using the biological species concept.
3. The fossil record and living intermediates reveal ancestral forms that do not fit neatly into any single modern taxon.
4. Biologists address this by using phylogenetic/cladistic classification, grouping organisms by shared derived characters (synapomorphies) and common ancestry rather than by overall similarity, producing clades that reflect evolutionary relationships.
Examiner tips
- Use the word ‘continuous’ early to show understanding of the problem. Mention interbreeding and fossil intermediates to hit the key points. Finish with the phylogenetic approach to demonstrate a solution. Keep each point brief but complete.
Common mistakes
- Confusing ‘species’ with ‘taxa’ and vice versa. Failing to mention the biological species concept. Using vague terms like ‘similarity’ instead of ‘shared derived characters’.
Mark scheme (4 marks)
- Evolution is a continuous process, so boundaries between species/taxa are not always clear-cut or distinct.
- Populations that are diverging may still be able to interbreed, making it difficult to assign them to separate species using the biological species concept.
- The fossil record and living intermediates reveal ancestral forms that do not fit neatly into any single modern taxon.
- Biologists address this by using phylogenetic/cladistic classification, grouping organisms by shared derived characters (synapomorphies) and common ancestry rather than by overall similarity, producing clades that reflect evolutionary relationships.
Related
- All IB DP Biology Higher Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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