Evolution and speciation · USMLE Step 1

Which of the following is NOT considered a primary mechanism driving evolution?

  1. Natural selection
  2. Genetic drift
  3. Gene flow (migration)
  4. Somatic cell mutation
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Correct answer: Somatic cell mutation

Somatic cell mutations affect only the individual and are not heritable in a population; evolution requires heritable changes in allele frequencies — mechanisms are mutation (in gametes), natural selection, genetic drift, and gene flow.

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