Question

What are some examples of directional selection?

Answer 1

Directional selection is a type of natural selection. It favors the selection of the most adapted and extreme phenotype over other traits. Over the time, allele frequency also shifts towards the direction of the favored phenotype. Thus as generations continue, organisms with the desired phenotype increase in the population.

Complete answer:
Directional selection occurs without the direct interruption of any man-made initiatives. Choosing the extreme phenotype, the species overcomes the environment challenges, such as drought period, extreme cold condition etc. Some examples of Directional selection are as follows.
Finches of Galapagos Islands:
-In Galapagos island, trees produce large seeds with hard seed cover due to drought conditions.
-Finches with short beaks are unable to eat these large and hard seeds.
-As the drought results in change in size and toughness of the seeds, in the same way it causes directional selection in the beaks of the finches.
-Thus, the population after drought contains a huge section of finches with large beaks.
Giraffe's neck:
-Giraffe's long neck is selected naturally and is an example of directional selection.
-Due to this adaptation, giraffes can reach to the topmost leaves to avoid food competition.
Black bears in Europe:
-According to fossil records, the black bears in Europe were increased in size during glacial periods due to the extreme cold conditions.
-While during the ice ages, their size decreased.
Industrial revolution:
-The industrial revolution in the 18th and 19th century caused many changes in the environment.
-The cities were polluted due to dust and soot.
-The pollution made the light coloured pepper moth easily visible to the predators.
-Thus, along with the industrial revolution, more number of dark moths appeared to avoid predators.

Notes:
-Directional selection occurs, when a phenotype becomes unable to survive the environmental pressure.
-It is also known as the 'positive selection'.
-Charles Darwin first described the directional selection in his book, 'On the Origin of Species'.