Evolution and speciation · USMLE Step 1

Which evolutionary scenario is most conducive to rapid speciation — for example, adaptive radiation — when a colonizing species reaches an unoccupied habitat with many available ecological niches?

  1. Large gene flow maintaining ties with the ancestral population
  2. High genetic drift acting with no selection pressure at all
  3. Strong ecological selection combined with ecological opportunity
  4. Constant, unchanging environmental conditions and no new mutation
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Correct answer: Strong ecological selection combined with ecological opportunity

When a species colonizes a new environment with many empty niches, strong ecological selection pressures coupled with ecological opportunity can drive rapid diversification and speciation (adaptive radiation).

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