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Difficulty: MediumEvidence for Evolution: Comparative Biochemistry and Biogeography

Marsupials are naturally restricted to Australia and South America, yet comparative biochemical analysis reveals near-identical amino acid sequences in their cytochrome c proteins. Which of the following best explains this observation?

  1. The organisms share a common ancestor that inhabited the unified landmass prior to continental separationAnswer
  2. B
    The organisms independently evolved identical amino acid sequences as an adaptive response to similar climatic environments
  3. C
    The organisms acquired identical protein alterations during their lifespan due to environmental stress from continental movement
  4. D
    The organisms represent extreme ends of continuous variation within a single geographically continuous population

Answer

The organisms share a common ancestor that inhabited the unified landmass prior to continental separation.
High sequence homology in essential proteins such as cytochrome c demonstrates close genetic relationship. When combined with biogeographical evidence showing Australia and South America were once joined as part of Gondwana, it indicates that marsupial ancestors lived on the shared landmass before continental drift isolated them.

Step-by-Step Solution

1
Analyze the biogeographical evidence presented in the stem.
The presence of related marsupial lineages in South America and Australia reflects a disjunct distribution resulting from tectonic continental drift (breakup of Gondwana).
Geographical isolation on separate continents accounts for spatial distribution patterns of related organisms.
2
Analyze the comparative biochemical evidence.
High amino acid sequence similarity in cytochrome c indicates genetic homology and close evolutionary ancestry.
Conserved proteins accumulate mutations over geological time; minimal sequence divergence points to a shared evolutionary past.
3
Integrate biogeographical and biochemical findings to reach the accurate evolutionary conclusion.
The ancestors of these marsupials inherited the conserved protein structure on a continuous supercontinent before plate tectonics separated the populations.
Combining molecular homology with vicariance models provides robust evidence for macroevolution.

Key Concept

Biogeographical disjunct distribution combined with molecular protein homology provides evidence of common ancestry prior to continental drift.
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Topics

Evidence for Evolution: Comparative Biochemistry and Biogeography

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