Example Of Disruptive Selection

In directional selection, one extreme trait is favored over the mean trait or other extreme trait; and this occurs in environments that have undergone changes over time. Changes in terms of climate, weather and food availability are the driving forces for this type of natural selection. If shown on a graph, the population bell curve shifts either farther left or farther right, indicating that one trait, is favored over another for a species. An example of this type of natural selection is the beak length of the Galapagos finches, which changed through time due to changes in food availability. Those with larger and deeper beaks survived the scarcity of insects since they were able to crack seeds. When insects became abundant, finches have developed smaller and longer beaks.

Here, both extremes (traits) are selected. This indicates that most of the individuals in a population exhibit either of the two extremes, with no preference over which extreme is better, while very few individuals show intermediate traits. If shown on a graph, the population bell curve has two peaks with a “valley” in the middle of them. This type of natural selection can lead to speciation, and form two or more different species in areas that go through harsh environmental changes (i.e. pollution). The best example for disruptive selection is the evolution of peppered moth in London at the beginning of the Industrial Revolution. Before the said period, most of the moths were white, and they camouflaged with bark of light-colored trees to avoid being eaten by predators. Then during the Industrial Revolution, when the atmosphere in the city became filled with soot, the light-colored trees became darker and white moths were therefore eaten by predators. To adapt with their environment, most of the moths became