Natural Selection

The Peppered Moth

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About the Peppered moths

Peppered moths are common insects living in England, Europe and North America. They are small moths, there wing span is only 1.5 to 2.5 inches. Peppered Moths are normally white with black speckles across the wings. The colour of these moths mean that they camouflage against lichen on trees, and make them harder to be seen by predators.

There is also a naturally occurring genetic mutation which causes some moths to have almost black wings. These moths with the mutation are poorly camouflaged and this means that they are more likely to be eaten by predators. There predators include but are not limited to flycatchers, nuthatches and the European robin.

Natural Selection

Charles Darwin's Theory of Evolution by Natural Selection is shown below in the video.

This theory states that a species adapts to their environment and passes down a favorable trait. This leads to an evolutionary change within a species. (survival of the fittest). These characteristics give an animal a greater survival or reproductive rate than other animals of the same species and there offspring have inherent these genetic characteristics. He also suggested that humans share a common ancestor with modern apes. The video below goes into further detail about Darwin and his theory of evolution by natural selection

In order for natural selection to occur there are four things that need to happen, they are called the four rules of natural selection. Click the picture on the left for details.

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The Theory of Evolution (by Natural Selection) | Cornerstones Education
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How Does this Relate To Natural Selection

Because of the mutation that turns some moths black they are easily seen and more likely to be eaten. This greatly reduces there numbers and were less likely to live as long and produce offspring. This means the white moths have a favorable trait and that makes them fitter to survive in that particular environment because the percentages of white to black moths were higher. That means the white moths were more likely to survive longer and produce offspring.
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Peppered Moth

The Industrial Revolution

Industrialization and domestic coal fires had caused sooty air pollution which had killed off lichens from trees and blackened urban tree trunks and walls. which make the Black moths more favorable to survive in and produce offspring. Now it is the white moths that are easily seen to predators. But this is only in urban areas, in rural areas the white moths are still the fittest to survive and reproduced. Before people new what caused the moth to be dark there were many theories, like they could change their colours to match the trees and others thought the chemicals in the smoke darkened the moths.

Dr Henry Bernard Davis Kettlewell

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Between 1952 and 1959 Dr Kettlewell set out to test if natural selection had actually caused the rise of the dark peppered moth. He believed that there must be four things to be true in order to cause this. The four things in order to be true are:
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His findings proved that natural selection was the cause of the of the black moth's high numbers. To this date his findings Today Kettlewell's work is considered to be a classic demonstration of natural selection in action

The Peppered Moth Now and in the Future

As the pollution in the environment is decreasing the lichen on trees is growing back in areas where the peppered moth is commonly found, and the white peppered moth now has a higher percentage of the population compared to black peppered moths. Humans are in control of this of the balance of the peppered moth because of the population we cause. With alternatives to coal the pollution in these areas will continue to decrease.