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KEY CONCEPT Populations, not individuals, evolve.

KEY CONCEPT Populations, not individuals, evolve. Natural selection acts on distributions of traits. . A normal distribution graphs as a bell-shaped curve. highest frequency near mean value frequencies decrease toward each extreme value.

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KEY CONCEPT Populations, not individuals, evolve.

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  1. KEY CONCEPT Populations, not individuals, evolve.

  2. Natural selection acts on distributions of traits. • A normal distribution graphs as a bell-shaped curve. • highest frequency near mean value • frequencies decrease toward each extreme value • Traits not undergoing natural selection have a normal distribution.

  3. Natural selection can change the distribution of a trait in one of three ways. • Microevolution is evolution within a population. • observable change in the allele frequencies • can result from natural selection

  4. Natural selection can take one of three paths. • Directional selection favors phenotypes at one extreme.

  5. Natural selection can take one of three paths. • Stabilizing selection favors the intermediate phenotype.

  6. Natural selection can take one of three paths. • Disruptive selection favors both extreme phenotypes.

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