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Why did lighter skin evolve among populations living in northern climates?

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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 in populations residing in northern climates is a clear example of human adaptation to environmental conditions through natural selection.1

While melanin provides essential protection against sunburn and skin cancer in regions with intense ultraviolet sunlight, it also acts as a barrier to the production of vitamin D. Humans synthesize vitamin D in the skin when exposed to ultraviolet radiation, a process critical for bone growth and health.123

In northern temperate climates, where sunlight is limited, populations faced the risk of vitamin D deficiency, which can lead to rickets—a condition that would have been devastating to early human groups. Over thousands of years, individuals with lower levels of melanin were better able to synthesize sufficient vitamin D in these low-light environments. Consequently, these individuals survived and reproduced in greater numbers, leading to the gradual loss of skin pigmentation in northern populations as an evolutionary response to ensure survival.13