Why Is Dark Skin More Prevalent in People Whose Ancestors

Why is dark skin more prevalent in people whose ancestors were from lower latitudes near the equator?

A) Increased melanin prevents the breakdown of vitamin D, but enough light is available to make folic acid
B) Increased melanin prevents the breakdown of folic acid and vitamin D
C) Increased melanin prevents skin cancer
D) Increased melanin prevents the breakdown of folic acid, but enough light is available to make vitamin D
E) Increased melanin prevents skin cancer and protects vitamin D