Evolution and speciation · USMLE Step 1

Why is speciation considered a macroevolutionary process, distinct from microevolution?

  1. Because it involves adaptive changes within a single generation
  2. Because it involves allele-frequency changes within one population
  3. Because it yields new species through reproductive isolation, not just allele shifts
  4. Because it occurs only in plant lineages and never in animals
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Correct answer: Because it yields new species through reproductive isolation, not just allele shifts

Speciation results in the emergence of reproductively isolated populations (new species), which is a macroevolutionary change — beyond microevolutionary allele-frequency shifts within a single species.

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