Question

When does directional selection occur?

Answer 1

Hint: Directional selection is a type of natural selection which was introduced by Charles Darwin. It is known to be a key mechanism in evolution of organisms as well as heritable changes of organisms of a population over generations.

Complete answer-
Natural selection is commonly categorized into three types-stabilizing selection, directional selection and disruptive selection. Stabilizing selection is known to occur when there are selective pressures working against two extreme traits which finally results in the selection of an intermediate or middle trait. Example of stabilizing selection is seen in plants, plants that are very tall are exposed to more wind and can be blown away easily whereas plants which are short do not get enough sunlight. As a result, middle height plants are best suited because they get enough e=sunlight and are also not blown away by wind. Directional selection occurs when the selective pressure is working in favor of one extreme trait. Examples of long neck giraffes, directional selection will favor long neck giraffes because it is easier for them to reach the trees and thus the entire population will move towards this direction. Disruptive selection occurs when selective pressures are working on the intermediate trait and in favor of the two extreme traits. This type of selection is rare. Example if an area consists of black, white and brown bunnies disruptive selection will favor black and white ones but not grey ones.

Note:
Natural selection thus plays an important role in shaping the evolution of different organisms in accordance to their living conditions. Organisms that cannot adhere to natural selection ultimately become extinct from the new environment.