Light skin in northern latitudes offers a selective advantage primarily due to the need for efficient vitamin D synthesis. In regions with less sunlight, especially during the winter months, lighter skin allows for better absorption of ultraviolet B (UVB) rays. This is crucial because UVB rays are necessary for the production of vitamin D in the skin.
Vitamin D is essential for various bodily functions, including calcium absorption, bone health, and immune system support. In areas with limited sunlight, individuals with darker skin may struggle to produce sufficient vitamin D, leading to health issues such as rickets and osteoporosis.
Over thousands of years, natural selection favored lighter skin tones in populations living in northern latitudes. This adaptation helped ensure that individuals could produce enough vitamin D even with reduced sunlight exposure. Thus, the selective advantage of light skin in these regions is closely tied to the environmental conditions and the biological necessity of vitamin D synthesis.