Bio 102 Notes on human skin colour.docx

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Simon Fraser University
Biological Sciences
BISC 110
Joan Sharp

Name: Michelle Le Lab day & time: Tuesday PM LAB ASSIGNMENT 6: The Evolution of Human Skin Color Human Skin Color Assignment Evolution of Skin Color – The Conventional Explanation 1. Propose an explanation for how skin cancer risk might have selected for darker skin color in early hominines who lived near the equator. Hint: address all three conditions of natural selection. The pigment produced by skin cells called melanin, protects the skin cells from harmful UV radiation from the sun. As mentioned by the information given, early hominines are thought to originate with light skin and therefore fewer melanin cells. Polygenetic coding for skin pigmentation leads to individuals with varying skin tones. In the high UV radiation zone near the equator, having darker skin, and therefore more melanin to protect skin cells from UV radiation, is advantageous to the health, and therefore fitness, of individuals since that lowers the risk of skin cancer. Based on this theory that the risk of skin cancer is a selective factor and that survival favoured individuals with more melanin, darker skinned early hominines living near the equator had better survival rates than lighter skinned ones. Over generations, the gene pool for early hominines living near the equator had more alleles for traits that contributed to darker skin color. 2. How does the skin cancer explanation account for the relationship between latitude and skin color seen in Figure 2? UV radiation, and proportionately the risk of skin cancer, is highest near the earth’s equator, intermediate near the temperate zones, and low in the upper northern and lower southern latitudes. Early hominines who lived in the temperate or near the poles of the earth had less selective pressures from the risk of skin cancer to favour dark skin (which had protective melanin). In other words, the genetic combinations that resulted in the most efficient amount of melanin to counter the UV radiation were favoured;
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