1. What are the causes of skin cancer?
2. Why are Caucasians more at risk of skin cancer than other populations?
3. At what age does skin cancer typically occur? Is the incidence of skin cancer greater in youth or old age?
4. Does the amount of UV light reaching the Earth vary in a predictable manner (Figure 6-3)? If so, describe the pattern you observe.
5. What latitude receives the greatest amount of UV light (Figure 6-3)? The least?
6. Based on these data (Figure 6-3), where might you expect to find the most lightly pigmented and most darkly pigmented people on the planet? Be as specific as you can.
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)?
8. Interpret Figure 6-4 and the trend it describes.
A. Is skin reflectance randomly distributed throughout the globe? If not, how would you describe the pattern?
B. Restate your findings in terms of skin color and UV light (instead of skin reflectance and latitude).
C. How closely do these findings match the predictions of your hypothesis (Question 6)?
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 6-4). What might explain the skin color of these exceptional populations? Propose a few hypotheses.
E. Hypothesize why different skin colors have evolved.
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?
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?
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?
12. Based on Branda and Eaton’s results (Figure 6-5), what is the apparent effect of UV light exposure on blood folate levels?
13. What is the apparent effect of UV light on folate levels in these test tubes? __________________
14. How is folate linked to natural selection?
15. All other things being equal, which skin tone would you expect to be correlated with higher 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.light-skinnedperson living in the tropics? _________________________________________
B. light-skinned person living in the polar region? _____________________________________
C.dark-skinned person living in the tropics? _________________________________________
D. dark-skinned person living in the polar region? _____________________________________
18. Predict the skin tones expected at different latitudes, taking folate needs into consideration. Use the world map (Figure 6-6) to indicate the skin tone expected at each latitude (shade the areas where populations are darkly pigmented).
19. Can folate explain the variation and distribution of light- and dark-skinned individuals around the world?
20. How is vitamin D linked to natural selection?
21. Which skin tone allows someone to maintain the recommended level of vitamin D? ________________
22. Based on this new information, revise your hypothesis to explain the evolution of the variation and distribution of human skin color.
23. Taking only vitamin D into consideration, what would happen to the reproductive success of:
A. light-skinned person living in the tropics? _________________________________________
B. light-skinned person living in the polar region? _____________________________________
C. dark-skinned person living in the tropics? _________________________________________
D. 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 6-8) to indicate the skin tone expected at each latitude (shade a region to represent pigmented skin in that population).
25. Can vitamin D alone explain the current world distribution of skin color? ____________________
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 6-9) to indicate skin tone patterns at different latitudes (shade regions where populations are expected to be darkly pigmented).
27. Are UV light, vitamin D and folate needs sufficient to explain the current world distribution of 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.
29. Conversely, Northern Europeans are slightly lighter-skinned than expected for their latitude. Propose a hypothesis to explain this observation.