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Difficulty: MediumEvidence for Evolution: Comparative Biochemistry and Biogeography

The presence of closely related species of flightless birds, such as the ostrich in Africa, the rhea in South America, and the emu in Australia, across widely separated landmasses is best explained by which of the following?

  1. Geographic isolation of an ancestral population caused by continental driftAnswer
  2. B
    The independent inheritance of acquired flightlessness in response to similar ground environments
  3. C
    Convergent evolution producing analogous structures in unrelated bird families
  4. D
    Discontinuous variations caused by recent cross-continental genetic hybridization

Answer

The distribution of ratite birds across separated continents is best explained by geographic isolation of an ancestral population caused by continental drift.
Biogeography provides strong evidence for evolution by showing how the movement of continental plates (continental drift) fragmented Gondwana. This separated ancestral flightless bird populations, allowing them to undergo divergent evolution and speciation into ostriches, rheas, and emus while retaining ancestral homologous traits.

Step-by-Step Solution

1
Identify the geographical pattern
Closely related flightless bird species (ratites) inhabit isolated southern continents (Africa, South America, Australia).
Understanding spatial distribution across continents provides biogeographical evidence for evolutionary history.
2
Relate species distribution to geological history
The supercontinent Gondwana split apart via continental drift, separating ancestral ratite populations.
Vicariance events (plate tectonics) geographically isolate ancestral lineages into distinct evolutionary pathways.
3
Evaluate evolutionary implications
Common ancestry combined with tectonic movement accounts for homologous traits and current disjunct distributions.
Biogeography demonstrates how geological processes drive speciation from shared ancestral stock.

Key Concept

Biogeographical Evidence for Evolution and Continental Drift
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Topics

Evidence for Evolution: Comparative Biochemistry and Biogeography

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