Ultraviolet rays of Sun are decisive factor in determination of skin color. These high frequency rays are incisive enough to penetrate and burn white skin and produce skin cancer. Therefore, Nature has provided protection to people living in hot sunny areas in the form of a black chemical substance named melanin. This substance stops excessive Sun rays at the skin to protect healthy cells. Hotter the Sun rays higher the proportion of melanin, and higher the melanin blacker the skin. Negroes of Africa have the blackest skin. On the other hand people of Scandinavian countries like Norway, Sweden and Denmark almost completely lack melanin in their skin. Melanin is absent even from their hair so their hair looks white or golden. There is another reason behind Nature’s having almost withdrawn melanin from the Scandinavian people. The cells of body require some sunlight to produce Vitamin-D. In the northern areas of Northern Hemisphere Sun rays are weak and come from an acute angle. If melanin blocks this negligible sunlight how can body produce Vitamin-D? This means that people should continue living where they have always lived. During the Second World War Negro soldiers who fought on Norwegian front were afflicted with a disease named rickets for want of Vitamin-D because they could not get sufficient Sun rays due to protective cover of melanin. In the Korean War some more American Negro soldiers became victims of rickets.
There is still another reason behind blue colored-eyes of the Scandinavians. The hours of sunlight are few there. Sometimes there is only dim light throughout the day. The position of Sun rays is near red on the visible spectrum of light. If there is no melanin in pupil and iris, then the eyes can absorb only that dim light, hence their eyeballs have ultimately become transparent like glass. The Scandinavians settled in hot sunny areas of America since one or two generations have to use goggles regularly to protect their eyeballs from the glare of sunlight and also sunbathe in mild sunlight to increase melanin.