You watched a TedTalk in this week's lab reading by Dr. Jablonski, a biological anthropologist and leading expert on human skin color variation. She talked about the connection between UV exposure and the essential nutrient folate (a B vitamin), which circulates throughout the body in the blood. A research paper from 1978 discussed how serum (blood) folate concentrations differed between two groups of light-skinned people exposed to different UV light. A figure from that paper is below (Fig. 2). Use Figure 2 to address question 2.
Figure 2. Folate Levels in Two Groups of People. In one group ("patients"), 10 individuals were exposed to intense UV light for at least 30-60 minutes once or twice a week for three months. Sixty-four individuals not receiving this treatment ("normals") served as the control group. The difference between the two groups was statistically significant (p < 0.005). Brackets represent the standard error of the mean, and "ng/mL" means "nanograms per milliliter." (Republished with permission of the American Assn for the Advancement of Science, from Skin color and nutrient photolysis: an evolutionary hypothesis, Branda, RF and Eaton, JW, 201:4356, 1978; permission conveyed through Copyright Clearance Center, Inc.).
2. What is the relationship between folate levels and UV exposure?
3. Low folate levels are linked to severe birth defects. Based on this information, write a hypothesis to explain the selective pressure of folate and UV exposure on the evolution of human skin color. Hint: Recall from your that melanin, the pigment that makes skin dark, is a "natural sunscreen" that blocks UV rays from going through the skin. What shade of skin would be most protective against folate deficiency, and in which environment would this shade be the most advantageous?