Question

Until the middle of the nineteenth century, all peppered moths (Biston betularia) observed around Manchester, England, were light in color. In 1845, a single black peppered moth was reported. As Manchester became more industrialized and dark soot began to cover the bark of the trees, the frequency of black moths increased greatly. The change in proportion of light and dark forms resulted from____________.

Select one:

A. disruptive selection.
B. directional selection.
C. stabilizing selection.
D. genetic drift.
E. increased mutation

Answer 1

B. directional selection.

Step-by-step explanation:

Changes in environmental conditions over time makes the natural selection to favor one of the extreme phenotypes due to its better survival and reproductive fitness over the other phenotypes. The favored phenotype gradually becomes abundant in the population. This type of natural selection is called directional selection.

In the given example, industrialization led to the deposition of dark soot over the barks of the tress. The black moths had better survival success as they could blend themselves with the dark background. The light-colored moths were easily picked by predators. This led to a gradual increase in the number of black colored moths in the population. Since one of the extreme phenotypes (black color) was favored, the process is called directional selection.