Answer to Question #90759 in Evolution for amia
Dark skin has a higher level of melanin pigment, which blocks UV light and protects it from the dangerous UV effects. The UV light results in DNA damage, associated with skin cancer, and causes the breakdown of vitamins A and B. On the other hand, skin cells need a certain amount of UV light to produce vitamin D. These competing factors influenced skin color in people who lived near the equator (high amounts of UV light) and in north regions (low amounts of UV light). In addition, after the development of agriculture, the early Europeans began to consume less vitamin D. Therefore, the lightening of the skin, associated with the synthesis of large amounts of vitamin D, was beneficial.
As a result, dark skin protected the human body from dangerous UV light in hot areas, whereas white skin resulted in the production of higher amounts of vitamin D far for equator.