Explain how comparative anatomy provides evidence for the common ancestry of vertebrates.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Homologous structures are anatomical features that share a common underlying structure but may have different functions in different species.
An example is the pentadactyl limb: the fore‑limb of humans, the flipper of whales, the wing of bats and the hind‑limb of frogs all have a similar bone arrangement.
The existence of such homologues shows that these vertebrates descended from a common ancestor that possessed the same limb structure.
Differences in shape or function of the limb in each species are the result of adaptation to different environments, demonstrating natural selection acting on a shared ancestral trait.
An example is the pentadactyl limb: the fore‑limb of humans, the flipper of whales, the wing of bats and the hind‑limb of frogs all have a similar bone arrangement.
The existence of such homologues shows that these vertebrates descended from a common ancestor that possessed the same limb structure.
Differences in shape or function of the limb in each species are the result of adaptation to different environments, demonstrating natural selection acting on a shared ancestral trait.
Examiner tips
- Define homologous structures, give a clear example, explain common ancestry, link differences to natural selection
Common mistakes
- Confusing homology with analogy, omitting the example, failing to mention adaptation or natural selection
Mark scheme (4 marks)
- Homologous structures are anatomical features shared by different vertebrate species that have the same underlying structure/origin but may differ in function.
- Named example of homologous structures across two or more vertebrate groups, e.g. the pentadactyl limb found in humans, whales, bats, and frogs.
- The presence of homologous structures indicates that these species descended from a common ancestor that possessed the same structure.
- Differences in structure/function between species reflect adaptation to different environments/selection pressures over time, consistent with evolution by natural selection.
Key terms in this question
comparative anatomy · common ancestry
Related
- All IB DP Biology Standard Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
More Evolution and speciation questions
- Explain how variation within a population enables natural selection to occur.
- Explain how geographic isolation can lead to the formation of two new species fr…
- Explain how the concept of reproductive isolation is central to the biological s…
- Explain how the accumulation of mutations over time can contribute to speciation…
- Explain how artificial selection differs from natural selection in the mechanism…
- Explain how stabilising selection differs from directional selection in its effe…