Skin Deep: What a person’s skin color really means
Essential Question: How did humans develop a range of skin colors and what are the benefits of diversity in skin color?
Standards:
LS4B: Natural Selection
LS4C: Adaptation
In many cultures and subcultures throughout the world, skin color is a symbol of power and status. People have gone to extreme lengths to change their complexion (eg. bleaching, tanning beds, diets) as companies profit off this social hierarchy. By exploring the evolutionary history of human skin color, students will learn that, just as with any other organ, skin’s properties, including pigmentation, play an important role in their health. Variations in skin color are a symbol of human adaptability rather than aesthetics and social strata.
Start by observing maps of skin color distribution globally and encouraging students to generate questions and/or hypotheses. Students will likely note that sunnier places are correlated with more pigmentation. However, they should also note anomalies including darker skin colors near the coast and variations at similar latitudes. Let student inquiry guide the process, but providing maps, data and information around human migration, vitamin D deficiency (rickets), folic acid deficiency, lactose intolerance, and indigenous diets can provide clues to answer the question.Students should learn that exposure to UV light can produce Vitamin D but can break down folic acid, another important nutrient. Those with limited sources of Vitamin D (fish, milk, sunlight) need lighter skin to allow for more UV penetration. Those with ample Vitamin D (eg. people in sunny areas, Inuit cultures with seafood-rich diets) would benefit from darker skin that preserves their folic acid. (Skin cancer is an issue too but less of an selective force, as it affects primarily people past reproductive age.) Historically, humans had dark skin. As they started to migrate out of Africa and towards colder climates of Europe and Asia, those with dark skin were suffering from vitamin D deficiency and natural selection favored lighter skin. Those who consumed vitamin D in their diet were less likely to see this shift. As populations continued to migrate back towards sunnier climates of the Americas, light skin resulted in folic acid deficiency and natural selection favored those with more melanin. Students can create statistical models to show these selective pressures or predict how human skin color variation will look in the future as migration happens faster and diets change. They may consider how their scientific understanding can challenge the harmful beliefs and cultural values tied to skin color.
Distribution of skin color among people indigenous to regions
Distribution of skin color by the 21st century
