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nmdcat.online July 14, 2026

Which of the following is an example of “directional selection”?

A. Male peak tail lengths remaining constant in a stable forest ecosystem.
B. The average beak size of a finch population increasing over several dry years as small seeds become scarce.
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C. Small and large seeds becoming abundant, leading to an increase in both small- and large-beaked birds.
D. Human baby birth weights clustered tightly around 3.5 kilograms.

📝 Explanation

Directional selection shifts the phenotypic distribution toward one extreme (larger beaks), typically in response to a directional change in environmental conditions.

📖 Additional Information

  • Male peak tail lengths remaining constant in a stable forest ecosystem.
  • The average beak size of a finch population increasing over several dry years as small seeds become scarce.
  • Small and large seeds becoming abundant, leading to an increase in both small- and large-beaked birds.
  • Human baby birth weights clustered tightly around 3.5 kilograms.

Directional selection shifts the phenotypic distribution toward one extreme (larger beaks), typically in response to a directional change in environmental conditions.

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