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How do scientists explain the geographic pattern of human skin color?
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Race
Skin color is one of the variables that has been used to classify people into different racial categories.
Scientists explain the geographic distribution of human skin color as an evolutionary adaptation to varying levels of ultraviolet (UV) radiation across different latitudes. This variation is primarily determined by the amount of melanin produced in the skin.123
Evolutionary Adaptations
- Tropical Regions: Populations residing in areas with intense, high-level sunlight evolved darker skin. Melanin acts as a protective pigment that shields the skin from sunburn and reduces the risk of skin cancer caused by ultraviolet radiation.142
- Northern Latitudes: As human groups migrated into northern temperate climates with limited sunlight, natural selection favored individuals with lighter skin. This adaptation was critical because sunlight is required for the body to synthesize vitamin D, which is essential for bone health. Lighter skin tones enabled better vitamin D production in low-sunlight environments, helping to prevent diseases such as rickets.12
This process resulted in skin color clines—gradations that correlate with latitude and sunlight exposure—reflecting a long-term adaptation of human groups to their specific environments.1