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How does vitamin D production help explain the evolution of lighter skin?

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Overhead view of a diverse group of people standing in a circle, holding each other's hands in a gesture of unity and teamwork. — Race Skin color is one of the variables that has been used to classify people into different racial categories.

The evolution of lighter skin is understood as an adaptive response to environmental conditions, particularly in northern latitudes where sunlight is limited. While melanin provides essential protection against sunburn and skin cancer in high-sunlight tropical regions, it also acts as a barrier to the synthesis of vitamin D in the skin.12

As human populations migrated into northern temperate climates with lower levels of ultraviolet radiation, they faced a different selective pressure: the need to produce sufficient vitamin D for healthy bone growth. Vitamin D is synthesized in the skin through exposure to sunlight, and a deficiency can lead to rickets, a debilitating bone disease.123

Over thousands of years, natural selection favored individuals with lower levels of melanin, as their lighter skin enabled more efficient synthesis of vitamin D in environments with limited sun exposure. Consequently, lighter skin tones became more prevalent in these populations, as those individuals were better able to survive and reproduce in northern latitudes.12