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Sexual Selection Choice of mate, based on his, or her, appearance.

Stabilizing Selection Individuals with an average form of the trait have the highest fitness- variation is reduced. (Small spiders can’t get food, big ones are eaten.).

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Sexual Selection Choice of mate, based on his, or her, appearance.

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  1. Stabilizing SelectionIndividuals with an average form of the trait have the highest fitness- variation is reduced.(Small spiders can’t get food, big ones are eaten.)

  2. Directional SelectionIndividuals with an extreme form of the trait have the highest fitness- the trait moves toward one of the extremes.(The woodpeckers with long beaks are better able to get food)

  3. Disruptive SelectionBoth extremes have greater fitness. The “average” is selected against until 2 separate populations, or species, exist. (The light limpets on the shore are camouflaged, as are the dark ones by the sea.)

  4. Sexual Selection Choice of mate, based on his, or her, appearance.

  5. Artificial SelectionHumans choosing desirable traits.

  6. An Example of Directional SelectionPeppered Moths

  7. An Example of Directional Selection • Originally, the vast majority of peppered moths had light coloration, which effectively camouflaged them against the light-colored trees and lichens which they rested upon. However, because of widespread pollution during the Industrial Revolution in England, many of the lichens died out, and the trees that peppered moths rested on became blackened by soot, causing most of the light-colored moths to die off from predation. At the same time, the dark-colored, (with their dark color resulting from a mutation), flourished because of their ability to hide on the darkened trees. • Since then, with improved environmental standards, light-colored peppered moths have again become common, but the dramatic change in the peppered moth's population has remained a subject of much interest and study, and has led to the coining of the term Industrial melanism to refer to the genetic darkening of species in response to pollutants. As a result of the relatively simple and easy-to-understand circumstances of the adaptation, the peppered moth has become a common example used in explaining or demonstrating natural selectionto laypeople and classroom students.

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