Scientists Have Studied, in Detail, the Evolution of the Peppered

Essay

Scientists have studied, in detail, the evolution of the peppered moth, Biston betularia, over the last two hundred years. The peppered moths rest on tree trunks and are a tempting treat for birds in the area. In the mid -1800's the trees in their England habitat were covered with lichens, which are a light, grayish - green color. Although color variations occurred, the vast majority of the moths were light-colored. Because their light coloration effectively camouflaged them against the lichens-covered trees, they were not as easily seen by birds as darker colored moths. The light colored moths flourished.
The environment changed, as the Industrial Revolution progressed. By 1900, the lichens had died and trees were coated with soot due to the industrial pollution. The lighter colored moths were no longer 'hidden' in their environment, and in fact, were easily seen by their predators. Their numbers dwindled. At the same time, the darker-colored moths flourished because of their ability to hide on the darkened trees.
As environmental standards have been implemented, environmental conditions have shifted, allowing lichens to grow on tree trunks.
a. What type of selection is this?
b. What is the agent of selection?
c. What alleles were favored in the clean environment? The polluted environment?