Final answer:
The different shades of skin color evolved as an adaptation to different levels of sunlight. Dark skin protects against UV radiation in sunny areas, while lighter skin allows for vitamin D production in areas with less sunlight. Skin color varies along a spectrum and doesn't fit into racial categories.
Step-by-step explanation:
The different shades of skin color from pinkish white to dark brown evolved throughout human history as an evolutionary adaptation to different levels of exposure to ultraviolet rays from the sun. The traditional theory of directional selection suggests that dark skin is advantageous in sunny regions as it protects against the damaging effects of the sun's ultraviolet radiation. In contrast, lighter skin is advantageous in areas with less direct sunlight as it allows for the production of Vitamin D.
As humans migrated to different geographical regions, their skin color gradually shifted to adapt to the varying levels of sunlight. For example, people in sunnier regions like central Africa have deep brown skin to protect them from the intense sunlight, while people in northern Europe have lighter beige skin to absorb more vitamin D from weaker sunlight. Skin color variation exists along a spectrum and does not fit into discrete racial categories.