The Evolution of Human Skin Color

1. What are the causes of skin cancer? - A few common causes of skin cancer is over explosion to UV light, moles, and it can also be hereditarily. 2. Why are Caucasians more at risk of skin cancer than other populations? - Caucasians have the lowest amount of melanin in their skin cells. Someone with darker skin tone is better protected against the sun’s UV rays because they produce more melanin. 3. At what age does skin cancer typically occur? Is the incidence of skin cancer greater in youth or old age? - Skin cancer is more dominant in youth with the age range typically anywhere from 20-30 years old. 4. Does the amount of UV light reaching the Earth vary in a predictable manner? If so, describe the pattern you observe. - When you look at the map you can tell that areas where the earth is closer to the sun has a higher UV index. You can also tell that areas where the earth is farther from the sun has a lower UV index. 5. What latitude receives the greatest amount of UV light? The least? - The greatest amount of UV light can be found across the equator. The least amount of UV light can be found from 60-90 and -70-(-90) longitude. 6. Based on these data, where might you expect to find the most lightly pigmented and most darkly pigmented people on the planet? Be as specific as you can. - The more naturally light a person is they would be found in the north or south, the more naturally darker a person is they would be found closer to the equator. This is all assumed that the people are not of mixed races. 7. Provide a rationale to your answer above (i.e., why did you think that more darkly pigmented people would be found in those areas)? - People of darker skin tone provide a lot more melanin which is crucial in countries with high UV exposure. In the farther north and the farther south there is not really a use for a large amount of melanin and therefore people’s pigmentation is more faint. 8. Interpret this graph and the trend it describes. a. Is skin reflectance randomly distributed throughout the globe? If not, how would you describe the pattern? - The skin reflectance is not randomly distributed throughout the globe. In the upper and lower latitude extremes there is a higher skin reflectance. The more moderate numbers, the reflectance is lower so we can conclude that the population is dark skin tone. b. Restate your findings in terms of skin color and UV light (instead of skin reflectance and latitude). - People who live near the equator are more exposed to UV light and so these people are dark skin toned and they need more melanin in order to keep them protected. The people who live farther north or farther south are not exposed to as much UV light and so they don’t need as much melanin and so they are more fair toned. c. How closely do these findings match the predictions of your hypothesis (Question 6)? - These findings do match the predictions of my hypothesis very well. The people who need the melanin the most and the less match. d. Some populations have skin colors that are darker or lighter than predicted based on their location (their data point falls somewhere outside of the line shown in Figure 2). What might explain the skin color of these exceptional populations? Propose a few hypotheses. - Well the people of the south may be of more dark skin because the earth is on a tilt, and so the southern hemisphere would probably receive more UV rays. 9. Hypothesize why different skin colors have evolved. Based on what you know, what factor is most likely to exert a selective pressure on skin color? - Our ancestral origin plays a big role as to why skin colors have evolved. Different people will have different skin tones depending on where they are located on earth. Extreme climatic change could also change skin tones as a more dramatic effect. 10. Review your answer to Question 3. Keeping your answer in mind, how strong a selective pressure do you expect skin cancer (UV-induced mutations) to exert on reproductive success? - Skin cancer can exert a lot of reproductive success especially on the ages of 20-30. If there is more UV radiation then skin will require a lot more pigment. 11. Based on this information, does your hypothesis about the evolution of skin color (Question 9) seem likely? Why or why not? How does skin color meet, or fail to meet, the three requirements of natural selection outlined above? - My hypothesis was actually fairly accurate I think. If someone who is born in areas with higher UV rays with lighter pigmentation then chances are they probably will not survive. 12. Based on Branda and Eaton’s results (Figure 3), what is the apparent effect of UV light exposure on blood folate levels? - The people who were exposed to the UV light had fewer levels of blood folate in them. 13. What is the apparent effect of UV light on folate levels in these test tubes? - The people who were exposed to the UV light had lower levels of blood folate in them, and the people who were not exposed to the UV light had more levels of blood folate in them. 14. How is folate linked to natural selection? - Folate deficiencies during pregnancy can lead to anemia in the mother and malformations of the nervous system, gastrointestinal system, aorta, kidney, and skeletal system in the fetus. It is also linked to a high rate of miscarriages. So natural selection favored people of darker pigmentation because it is said to be believed that they could produce healthy offspring. 15. All other things being equal, which skin tone would you expect to be correlated with higher levels of folate? - Probably lighter skin tones because darker pigmentation deplete the levels of folate. 16. Based on this new information, revise your hypothesis to explain the evolution of human skin color. 17. What would happen to the reproductive success of: a. A light-skinned person living in the tropics? - They would have a lower reproductive success rate. b. A light-skinned person living in the polar region? - They would have a high-percentage of reproductive success rate. c. A dark-skinned person living in the tropics? - They would have a high-percentage of reproductive success rate. d. A dark-skinned person living in the polar region? - They would have a moderate reproductive success rate. 18. Predict the skin tones expected at different latitudes, taking folate needs into consideration. Use the world map (Figure 4) to indicate the skin tone expected at each latitude (shade the areas where populations are darkly pigmented). - Skin tones that are near the equator would have dark pigmentation. Skin tones farther north would have light pigmentation. Skin tones father south would have really fair pigmentation. Skin tones between the north poles and equator would be medium skin tones and same skin tones between the equator and south poles. 19. Can folate explain the variation and distribution of light- and dark-skinned individuals around the world? - Yes, mainly because if the UV rays deteriorate the folic acid, then many different skin tones could appear. 20. How is vitamin D linked to natural selection? - Vitamin D is linked to natural selection because it is what keeps an individual healthy. It helps maintain our nervous system and immune system. This helps organisms better adapt to their environments in order to survive. 21. Which skin tone allows someone to maintain the recommended level of vitamin D? - Darker skin tones are able to maintain the recommended level of vitamin D because lighter skin tones are more affected by UV rays. 22. Based on this new information, revise your hypothesis to explain the evolution of the variation and distribution of human skin color. - The variations and distributions of human skin color all depends on where a person lives. 23. Taking only vitamin D into consideration, what would happen to the reproductive success of: - For all of these people the reproductive success would be the same because I don’t think that vitamin D levels really play a level in who people decide they want to mate with. a. A light-skinned person living in the tropics? b. A light-skinned person living in the polar region? c. A dark-skinned person living in the tropics? d. A dark-skinned person living in the polar region? 24. Predict the skin tones expected at different latitudes, taking only vitamin D needs into consideration. Use the world map (Figure 6) to indicate the skin tone expected at each latitude (shade a region to represent pigmented skin in that population). - Skin tones near the equator would have medium pigmentation. Skin tones near the north would be very dark. Skin tones near the south would be very dark. Skin tones between the north and the equator would be light also the same for the skin tones between the south and the equator. 25. Can vitamin D alone explain the current world distribution of skin color? - No, because there are a lot more factors to take into consideration with distributions of skin color. UV rays help the body utilize the vitamin d levels. 26. Using principles of natural selection, predict the skin tone expected at different latitudes, taking ultraviolet exposure, vitamin D, and folate needs into consideration. Use the map (Figure 7) to indicate skin tone patterns at different latitudes (shade regions where populations are expected to be darkly pigmented). - Skin tones near the equator would be very dark. Skin tones near the north would be dark and skin tones near the south would also be dark. Skin tones between the north and south would be medium and skin tones between the south and the equator would be light to medium. 27. Are UV light, vitamin D and folate needs sufficient to explain the current world distribution of skin color? - Yes, because these are all contributing factors that determine an individual’s skin color. 28. How might you explain that Inuits, living at northern latitudes, are relatively dark-skinned (much more so than expected for their latitude)? Propose a hypothesis. - My hypothesis is that they had an ancestor who lived there before and maybe their traits traveled through generations causing the people to be relatively dark-skinned. 29. Conversely, Northern Europeans are slightly lighter-skinned than expected for their latitude. Propose a hypothesis to explain this observation. - My hypothesis is because the hot weather and the food that they have and grow lack the necessary vitamin D levels that someone with dark- skin would have. 30. Which populations have insufficient amounts of vitamin D in their blood? - East and South Asia 31. What is a common trait to all of these populations? How could this explain their deficiency? - Both of these populations have relatively high UV light exposure, so maybe this makes it harder on the people to get the necessary vitamin D. 32. For several decades, milk and cereals have been fortified with vitamin D to help increase intake of this nutrient. Hypothesize why these fortification programs appear to be failing in some ethnic groups (there may be different reasons for different groups). - Not everyone drinks and eats the same things. Some people are not able to consume milk at all so that could play a role. 33. What should some Canadians do to avoid vitamin D deficiency? - They should try and buy food and products that have high vitamin D levels, and they could even take vitamin D pills to help. 34. If individuals do not take steps to boost their vitamin D intake, hypothesize what might happen to their descendants in the future. - I believe that mutations could occur as a result of pregnancy or people might be more receptive to the UV rays and then as a result could easily get the vitamin D. 35. What might happen to Australians of European descent over time? - They might lose vitamin D components. 36. Think of the forces that affected the evolution of skin color in the past. Contrast these to the factors that affect skin pigmentation today. Hypothesize about the factors that may affect skin pigmentation in the future. a. Do you think the impact of natural selection on skin color is as strong today as it was in the past? - I don’t think it is as today as it was in the past. b. What factors may have decreased or increased selection today? - The amount of awareness that people have about skin cancer now and we have more options to keep ourselves protected. c. Predict skin color distribution in the year 2500. Outline your assumptions and the reasons for your predictions. - I believe that people will have an easier time tanning and this will lead to darker skin tones. 37. During the trip, the lightly-pigmented individual is looking forward to lying on a beach and working on his/ her tan. Will this person be adapting to the environment (in a Darwinian sense)? In other words, will evolution take place by developing a tan in a geographical region of intense UV light? Yes, because it is a good chance that the people who already live there are already tanned. 38. Should the lightly-pigmented person wear sunscreen on the trip?- yes, because they could get really bad sunburned and this could cause damage to their skin. 39. Should this person wear sunscreen when he/she is at northern latitudes (i.e., at home in Canada)? - Yes, because no matter what someone's skin tone is they should still wear sunscreen because even if they don’t see any damage immediately then they could end up developing problems from it later on in life. 40. How might this observation be the result of sexual selection? Explain your reasoning. - Because some people may be attracted more towards darker skin toned individuals. 41. Could this observation be the result of “normal” natural selection (i.e., not sexual selection)? Explain your answer. - Yes, because the amount of melanin that an individual is able to produce depends on their genes.