“For instance, the gene that gives light skin, an advantage in regions without much sunlight”
How is light skin an advantage in regions without much sunlight?
How was it determined that this is an advantage?
“How is light skin an advantage in regions without much sunlight?”
http://en.wikipedia.org/wiki/Vitamin_D
Try this one instead:
“Humans with light skin pigmentation have skin with low amounts of eumelanin, and possess fewer melanosomes than humans with dark skin pigmentation. Light skin provides better absorption qualities of ultraviolet radiation. This helps the body to synthesize higher amounts of vitamin D for bodily processes such as calcium development.”
http://en.m.wikipedia.org/wiki/Light_skin
“How is light skin an advantage in regions without much sunlight?”
Well, our bodies need to absorb UV radiation through our skin to synthesize vitamin D. Melanin blocks that radiation, and hinders the synthesis. If you live in a region with less sunlight, then having skin that is too dark will lead to vitamin D deficiency (unless you can offset it with your diet), putting you at a disadvantage to people with less melanin.