Human skin color variation evolved as an adaptation to the varying levels of ultraviolet (UV) radiation in different parts of the world. Darker skin colors evolved in regions with high UV radiation, such as the equatorial regions of Africa, Australia, and South Asia. This is because melanin, the pigment responsible for skin color, provides protection against the harmful effects of UV radiation, such as skin cancer and DNA damage.

In contrast, lighter skin colors evolved in regions with lower levels of UV radiation, such as Europe and northern Asia. In these regions, the lighter skin color allowed for more efficient synthesis of vitamin D in the skin, which is necessary for bone health.

Therefore, skin color variation is a result of natural selection, with the evolutionary process favoring skin pigmentation that provides the best protection against the harmful effects of UV radiation and the most efficient synthesis of vitamin D, depending on the environmental conditions of the region.