Explain how adaptive radiation can result in the formation of multiple new species from a single ancestral species.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Adaptive radiation is considered one of the most dramatic examples of evolution, with the diversification of Darwin's finches in the Galápagos Islands often cited as a classic case. A single ancestral finch species colonised the archipelago and gave rise to approximately 15 distinct species, each occupying a different ecological niche.
Model answer (4 marks)
A single ancestral species colonises a new environment with unoccupied ecological niches.
Populations become isolated, either geographically or ecologically, and experience different selection pressures in each niche.
Over many generations, genetic divergence accumulates through selection of different mutations and genetic drift.
Reproductive isolation eventually develops, preventing interbreeding and establishing the populations as separate species.
Populations become isolated, either geographically or ecologically, and experience different selection pressures in each niche.
Over many generations, genetic divergence accumulates through selection of different mutations and genetic drift.
Reproductive isolation eventually develops, preventing interbreeding and establishing the populations as separate species.
Examiner tips
- Use the four key points in the order given; each point counts one mark.
- Show clear cause–effect links (colonisation → isolation → divergence → isolation).
- Use terms like ‘geographic isolation’, ‘selection pressures’, ‘genetic drift’, ‘reproductive isolation’.
- Keep sentences short and to the point.
Mark scheme (4 marks)
- A single ancestral species colonises a new environment or enters an environment with available/unoccupied ecological niches.
- Populations become isolated (geographically or ecologically) and are subject to different selection pressures in different niches.
- Genetic divergence accumulates between populations over many generations due to different mutations being selected for and/or genetic drift.
- Reproductive isolation eventually develops between diverged populations, preventing interbreeding and establishing them as separate species.
Key terms in this question
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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