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Understanding Evolution: How Natural Selection Shapes Trait Distributions in Populations

This overview explores the concept of evolution in populations, emphasizing that natural selection acts on distributions of traits rather than on individuals. Traits often follow a normal distribution, represented by a bell curve, where frequencies are highest near the mean and decrease towards extremes. Natural selection can lead to microevolution, observable through changes in allele frequencies. It can take three distinct paths: directional selection, which favors one extreme phenotype; stabilizing selection, which favors intermediate phenotypes; and disruptive selection, which favors both extremes.

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Understanding Evolution: How Natural Selection Shapes Trait Distributions in Populations

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Presentation Transcript

  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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