Why Is Light Skin More Prevalent in People Whose Ancestors

Why is light skin more prevalent in people whose ancestors were from higher latitudes far from the equator?

A) Decreased melanin promotes the synthesis of folic acid, but the low light available does not destroy vitamin D
B) Decreased melanin promotes the synthesis of folic acid and vitamin D
C) Decreased melanin promotes the synthesis of vitamin D, but the low light available does not destroy folic acid
D) Melanin is not needed given the low level of light and requires energy to produce
E) Our common human ancestors had light skin, and dark skin arose earlier as humans moved near the equator