Sunday, April 5, 2009
The Evolution of Skin Color
Carroll, on page 168, brings up the question of whether skin color is a product of evolution, or just a characteristic that people in the same region share. Discuss Carroll's view on this, as well as your own by bringing in examples. Carroll also mentions the works of William Charles Wells and Charles Darwin. Using their examples, and outside research, discuss the changes in skin color over different parts of the world. Compare this to what Carroll has said about evolution and natural selection, as well as the selective advantage of different skin pigmentation.
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ReplyDeleteIt seems as if people living in the same regions have the same skin color. Based on William Wells views skin color is determined by nature and the different variations of mankind are fitted for the country that they inhabit. (169). He believes that the “darker race would in the course of time occurs, and as the darker would be the best fitted for the climate” (169). This is the idea of survival of the fittest, as the darker skinned individuals would adapt better to their hot surroundings they would survive, and the race would become darker and darker. It seems as if Well’s believes that climate is the main reason for change in skin color. Wells also believes that the darker skinned individuals have immunity from certain tropical diseases.
ReplyDeleteDarwin took Wells ideas into further research as he studied the inside of human cells. He studied the pigment melanocyte. Melanin’s synthesis pathway is induced by ultraviolet irradiation. The amount of UV radiation that hits the Earth varies from region to region (171). There has been research done proving that there is a close relationship between the levels of UV radiation in different regions of the world and variations in the skin pigmentation. So the physical environment is responsible for the different skin colors.
It seems as if the sun and the environment have a huge effect on skin color. Also the natural selection is another factor. Different environments demand for different types of skin colors. In Europe people have a relaxed selection in melanin and since less vitamin D is needed, lighter skin is an adaptation to lower levels of sunlight.
http://en.wikipedia.org/wiki/Human_skin_color
http://www.bgsu.edu/departments/chem/faculty/leontis/chem447/PDF_files/Jablonski_skin_color_2000.pdf
http://74.125.95.132/search?q=cache:wj_x4HR17VYJ:www.wonderquest.com/evolution-skin-color.htm+skin+color+evolution&cd=5&hl=en&ct=clnk&gl=us
William Charles Wells made the first clear statement describing natural selection. He used this principle to describe human diversity, primarily skin color. He noted in his essay, “Observations on the Causes of the Differences of Colour and Form between the White and Negro Races of Men,” that the darkest people in Africa would be better fitted than others to survive the diseases of that area. Following the principle of natural selection, he said that those people who were lighter would be less fit for the area and would decrease.
ReplyDeleteHis example that darker people were better fitted to live in Africa turned out to be correct; however, this was not due to disease. It was a matter of man versus the sun.
The lightness and darkness of skin is due primarily to the amount of a pigment called melanin in the skin. This production of this pigment is stimulated by the binding of MC1R to alphaMSH. Melanin is a natural sunscreen that exists in our skin. It absorbs UV radiation. UV radiation is a mutagen that directly causes mutations in the skin DNA. There is a chance that these mutations will be harmful. UV light hits the earth with different intensity at different altitudes. It hits with the most intensity at the equator and with least intensity at northern and southern latitudes. Looking at the MC1R genes of light and dark-skinned individuals, it was found that the gene had no variation of protein produced in darker individuals. In lighter individuals, there are 10 varieties of protein produced by this gene. It can be determined that this gene is under less intense selection among Europeans. UV light is not as intense so harmful mutation occurs less often. It does not matter as much how much melanin is in the skin, so the MC1R gene is permitted to decay. Exactly the opposite is true of Africans.
This example follows from what is known about natural selection. Because the higher amount of melanin was favored in Africans, their MC1R gene was under higher selection. Therefore, skin color is a result of Natural Selection.
http://en.wikipedia.org/wiki/William_Charles_Wells
Carroll pp. 168-173