Final answer:
Lighter skin color is more prevalent in regions with low UV radiation levels to optimize vitamin D production. Skin pigmentation is an evolutionary adaptation to varying exposure to UV radiation, with melanin serving as a protective factor against UV damage and a regulatory element for vitamin D synthesis.
Step-by-step explanation:
In places with low levels of UV radiation, skin color tends to be lighter. Throughout human migration and evolution, varying skin pigmentation has developed as a direct response to the local UV radiation levels. People living farther from the equator, where UV exposure is lower, have evolved with lighter skin pigmentation. This adaptation helps absorb more UV radiation, which is necessary for the production of vitamin D, crucial for bone health and immune function.
UV radiation not only contributes to vitamin D synthesis but also stimulates melanocytes in the skin to produce and accumulate melanin, which protects against UV damage. However, too much melanin can impede vitamin D production, thus skin pigmentation becomes lighter in areas with less UV light to maintain the balance between protecting the body and producing sufficient amounts of vitamin D.