Blog 8 Give examples of the different types of natural selection. Give an example for each

The different types of natural selection are directional selection, disruptive selection, and Stabilizing selection. In directional selection, one extreme of the trait distribution experiences selection against it. The result is that the population's trait distribution shifts toward the other extreme. In the case of such selection, the mean of the population graph shifts. Using the familiar example of giraffe necks, there was a selection pressure against short necks, since individuals with short necks could not reach as many leaves on which to feed. As a result, the distribution of neck length shifted to favor individuals with long necks.In disruptive selection, selection pressures act against individuals in the middle of the trait distribution. The result is a bimodal, or two-peaked, curve in which the two extremes of the curve create their own smaller curves. For example, imagine a plant of extremely variable height that is pollinated by three different pollinators, one that was attracted to short plants, another that preferred plants of medium height and a third that visited only the tallest plants. If the pollinator that preferred plants of medium height disappeared from an area, medium height plants would be selected against and the population would tend toward both short and tall, but not medium height plants. Stabilizing selection is when natural selection works against the two extremes of a trait to make the population more uniform. For example, stabilizing selection might work on the birth weight of human babies to keep them at an intermediate weight, because babies that are too big or too small have less chance of being born healthy.