Dark skin is thus adaptive to those who live in equatorial regions. People who live in northern latitudes, however, found dark skin a disadvantage because it led to rickets which can be fatal in a world where physical skills determined survival. As humans moved out of their ancestral home in Africa some 200,000 years ago, their skin color was selected for more efficient ultraviolet absorption. Skin colors became lighter and normal bone growth followed. Thus both dark skin and light skin served their purposes over the millennia as humans settled the earth.
Life is filled with agents and substances that are both necessary for health and damaging to health.
Fatalists take it on the chin and just ride their fates hoping for miracles to spare them harm. Scientists try to understand why things work the way they do and thus we can take charge of our lives and enjoy the benefits of vitamin D produced in our skins, the ultraviolet induced protective tanning, the natural skin color adaptive to our latitude, or a variety of sun screens to prevent those chromosome-snapping thymine dimers formed in our DNA whenever ultraviolet penetrates the barriers of our melanin and enters deep within our cells. Today dark skinned people living in the north are protected by diet from rickets and light skinned people living in the south are protected, if they use good sense while outdoors, from sunburn and skin cancers.