Which one of the following phenomena supports Darwin's concept of nautral selection in organic evolution ?

Explanation

Natural selection is a process by which the organisms are physically, physiologically and behaviorally better adopted to environment, survive and reproduce.
It is mainly of three types : 1. Stabilizing selection, 2. Directional selection, 3. Disruptive Selection.
1. Stabilizing selection (Centrifetal selection) : This selection operates in a stable environment. In this process, the organisms with average phenotype are preserved where as the extreme individuals from both the ends are eliminated. Hence it does not promote any evolutionary change that leads to specification, but maintains the phenotypic stability within the population over generations.
Eg : In England weight of newborn babies were studied in a large sample. Greater mortality was found in the babies whose weight was greater or lesser than the average weight of 8lbs.
2. Directional selection : This selection operates in an environment which gradually undergoes changes. It works by constantly removing the individuals from one end and constantly shifting the average value of fitness towards the other end of phenotypic distribution.
Eg : In case of giraffes the average value of the length of neck shifted towards the long-neck. Stabilizing selection takes over the directional selection. Once the average value of the phenotype coincides with the new optimum environmental conditions.
3. Disruptive selection (Centrifugal selection) : This selection operates when homogenous environment changes into a heterogenous type. In this process, the organism of both the extreme phenotypes are selected while the individuals with average phenotype are eliminated. This can split the population into two or more sub-populations or species populations.
Eg : In California the sunflower population was divided into two sub-populations. One was adapted to dry area and the other was adapted to wet area.