What is the Peppered Moth?
The Peppered Moth is native to England and can be either black or mostly white with black markings. Initially, black peppered moths were rare, and you almost always saw the white ones. The lighter color helped the moths blend in with lichens on the trees, while the black moths stood out more which made them more likely to get eaten by predators. This however, changed after the Industrial Revolution. During the Industrial Revolution, coal-burning factories began to pollute the air and the surrounding areas. This pollution began to kill many of the lichens on the trees and eventually led to the trees becoming darker. This change in color made it so that the lighter colored moths now stood out against the new dark color of the trees which made them a much easier target for predators. It also made it so that the rare, dark colored moths no longer stood out, and now they were the ones who were able to camouflage themselves. This led to a drastic decrease of light colored moth populations and a dramatic increase in the populations of dark colored moths.
The photos below shows a light colored peppered moth against lichens on a tree and a dark colored peppered moth against one of the darkened polluted trees.
The peppered moth is also a common example used to show Darwin’s theory of Natural Selection. This is because the more advantageous trait to have in a polluted forest is the dark coloration, while in a non-polluted forest, the lighter colored moths have a higher fitness.
The type of camouflage that the peppered moths display is known as industrial melanism. This type of camouflage has been found in several arthropods and it is when an organism evolves a dark pigmentation as a result of industrial pollution.
Peppered moths are also an example of directional selection. Directional selection causes a population to move in a particular direction because of individuals each having extreme values of a trait.
Proximate vs. Ultimate Causation
Proximate causation is how genetic-development explains a biological function in terms of immediate physiological or environmental factors. In other words, the proximate cause is why these specific traits develop. In the case of the peppered moth, the proximate cause is genetic. The moth has a specific gene that codes for whether they are light or dark colored. The moths that are colored so that they have the highest fitness will reproduce and then pass the genes for a specific color to their offspring.
Ultimate causation is the evolutionary history behind why a trait evolves. In the case of the peppered moth, it was to help the moths blend in. Blending in increases their chances of survival and likeliness of reproducing. In a specific environment, one wing color may help more moths survive than the other wing color. Being able to blend in is a significant advantage to the moth.