1. Skin Color Natural Selection
Essential Question:
How does our skin color connect with natural selection?
Analyze the map below. What is the map showing us? Why do you think the colors are darker in the middle? Why are they lighter at the top and bottom?
Fig. 1.  Distribution of skin pigmentation among human populations (from Encylopedia Brittanica)

2. Early Humans
Early humans moved into warmer environments in search of food and water, one challenge they faced was keeping their body temperature cool.
Therefore, adaptations were made. Humans started to produce more sweat glands which reduced the amount of body hair needed. With less hair and more sweat glands the body could regulate temperature better.
However, this also produced a problem for early humans.
The closer they moved to the equator, the more their skin was exposed to strong sun and to ultraviolet radiation the sun produces.
So, in the tropical regions, natural selection created darker pigmented individuals to protect them against the sun.

3. Reasons for the Adaptation
Humans need a balance of vitamin D and folate to be healthy. Vitamin D helps absorb calcium for strong bones, while folate is a folic acid which help produce new cells.
Ultraviolet B radiation produces vitamin D in human skin, but can destroy folate. Places with less sun, have less vitamin D accessibility. Destruction of folate or deficiencies in vitamin D are major factors in reproduction. Women with either issue are more likely to have unsuccessful attempts of reproducing.
Therefore, a possible end of man kind.

4. What Changed?
Early humans that traveled to tropical regions or areas near the equator adapted by their skin darkening. Dark skin pigmentation (natural coloring) protects people from folate destruction but also allows them to produce enough vitamin D for successful reproduction.
Early humans who migrated to colder places had to make a different adaptation. Dark skin pigmentation could not absorb enough vitamin D. Therefore, their skin lightened. Lighter pigmentation could absorb the right amount of vitamin D. Therefore, they to had the correct balance of folate and vitamin D for successful reproduction.
Hence a perfect example of natural selection among the human race.

5. Different Variations
The human race still has many different variation in skin pigmentation.
Early humans that migrated to subtropics or areas with changing seasons created another example of natural selection. Tanning became a mechanism to partly protect humans from harmful radiation.
Tanning evolved for humans so that when ultraviolet B radiation increases in early spring the skin gradually darkens. As the sun becomes stronger, the tan deepens. During the winter months, there is less radiation. Therefore, the tan decreases.
This allowed for the appropriate balance for folate protection and vitamin D production.
Coastal people in artic regions sometimes have darker skin pigmentation. Coastal people eat diets rich in vitamin D (seafood). Therefore, they can keep their darker appearance even in low UV areas. In the summer, they get higher UV rays that reflect against the surface of the snow and ice. Their dark skin then protects them from the reflected light.

6. Why is it that we still have so many variations in skin color?
Natural selection can be seen in nearly ever classroom because humans move, visit, and travel around the globe far faster than evolution can adjust to the needed balance. Therefore, we keep the various skin colors.
The variation of skin color comes directly from our ancestors. Skin color originated from where our ancestors lived and how strong the sun was in those particular areas. Therefore, various skin pigmentation were created and those genetics were passed down to humans today.

7. Resource Page
N.p., n.d. Web
"Skin Color: Handy Tool for Teaching Evolution." Penn State University. N.p., n.d. Web. 30 Jan