Disruptive Selection: Example, Definition & Graph

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  • 0:00 What is Disruptive Selection?
  • 1:15 Disruptive Selection Examples
  • 2:50 Lesson Summary
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Lesson Transcript
Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

How do new species develop? One evolutionary mechanism that may be at play is disruptive selection. Though rare in nature, this process favors extreme traits over those that are more intermediate.

What Is Disruptive Selection?

The term 'average' is used to describe the middle ground. A teacher looks for a bell-shaped curve for her class grades, with 'C' being the average grade. At one end, there will be students who did poorly and earned grades less than 'C.' On the other end are the students who did very well and earned grades higher than 'C.' This bell shaped curve also appears in nature. While some individuals in a population may be at one end of the spectrum or the other for any number of traits, most are in the average range.

For example, some individuals are very fast runners and some are very slow. Overall, most individuals are close to average; they are neither very fast nor very slow. When the average is expressed in nature, this is referred to as stabilizing selection.

Sometimes, however, one or more extremes is actually what is favored, and the average is selected against. When only one extreme is selected, it's called directional selection. When both extremes are selected for equally, it's called disruptive selection.

Disruptive Selection

Disruptive selection is the rarest of these three types of natural selection, but is a major driving force of evolution. This is because by selecting such opposite traits, directional selection can lead to the development of two separate species.

Examples of Disruptive Selection

Peppered Moths

One of the best-studied examples of directional selection is the peppered moth in England. The moth gets its name from the peppery-looking coloration on its wings and body. The peppered moth may be a light color or a dark color, with very few individuals being a color in between the two extremes.

During the day, the moths sleep on tree trunks that are covered with lichen. Originally, the lighter-colored moths were more common because they blend in very well with the lichen and were not as easily seen by birds, who like to eat them.

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