The Peppered Moth

Samantha Linberg
Natural Selection: The Peppered Moth

The peppered moth has “changed” over the past 200 years from its lighter white coloration to a darker charcoal, and then back again to it’s original lighter, color. How it this possible? It only appears as though this moth has magically changed but in all actually it is a result of natural selection. These moths are an example of Darwin’s theory of evolution, natural selection being one cause of evolution. A background about these moths, information about natural selection, the natural selection process in this situation, and the outcome will provide you with some insight on how these moths “magically changed.” The Biston betularia, also known as the peppered moth, is the endemic, or native, species that was common throughout Great Britain before the mid-1800s. This moth had the trait in which it was white with black specks, causing it to have a peppered phenotype, or appearance. Since this moth is nocturnal, it would eat and breed during the night, but during the day it would live on trees, which were covered in lichen. Since the lichen was a light color, it protected the hiding white moths during the daytime. In the mid-1800s a naturalist discovered a new species of the moth, called Biston carbonaria. It was completely black. This form of moth remained low until the mid-1900s, but increased in frequency because of natural selection. Natural selection is when members of a population have an enhanced survival characteristic, which will then allow them to reproduce more offspring that will survive to a reproductive age, which will further pass on this enhanced characteristic. The reason natural selection came into play was because of the Industrial Revolution in England. There was an increase in pollution because of the burning of coal and other aspects the new industries produced. This environmental selective agent, soot, caused the lichen on the trees to die, and also caused the trees to have a blackened appearance. The variation in the black moths allowed those moths to have reproductive success. Their offspring in turn produced more moths with the black color trait, thus they displayed a greater fitness; their genotype was an adaptive advantage so increased the black moths frequency. In the late 1960’s there were harsher pollution laws put into place, so the same natural selection process described previously, now resulted in a change from the black moths back to the variation of the white moths. The lower level of pollution was the environmental selective agent in this case, causing a decline in black moths reproductive success. The moths having the trait of being white, was adaptive advantage, and thus caused them to have a higher fitness. Through natural selection, their genotype enhanced their survival. In both circumstances, directional selection had taken place, where the selection for a certain trait is extremely favored. These moths started out as one species with the trait of being white, but over time turned into two species, white and black. One of these traits is extremely favored by the environmental selective agent of pollution or lack thereof, and this selective agent can cause reproductive success. Variation provides the raw material for this process, this process called natural selection.