Evolution and speciation · USMLE Step 1

How can sexual selection contribute to speciation within a population?

  1. By steadily increasing overall population size
  2. By shaping mate choice, driving reproductive isolation without geographic barriers
  3. By preventing any genetic divergence among individuals
  4. By promoting continuous gene flow across the population
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Correct answer: By shaping mate choice, driving reproductive isolation without geographic barriers

Sexual selection can lead to preferential mating within subgroups (e.g., based on traits), reducing gene flow across subgroups and facilitating reproductive isolation — an important driver of sympatric speciation.

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