In those people with light skin, something prevents the enzyme from functioning at full strength. There is apparently a switch that creates this limiting factor. So it turns out that what separates Africans from Europeans is not different numbers of genes or certain genes that provide pigmentation, but rather a collection of tiny genetic differences in the way our genes interact and regulate each other. This provides the chance for mutations to play significant roles in contributing to color variations. In animals, melanin comes and goes at the dictates of evolutionary pressures.
Coloration is one of the easiest changes for organisms.
Some of the most darkly pigmented people in the world live on the Solomon Island. Europeans living in Hawaii, on the other hand, have the highest documented skin cancer rate in the United States. It is clear that darker pigmentation protects from skin cancer. It is less clear how humans benefit from lesser amounts of pigmentation however. The most popular theory is based on the fact that the exposure of our skin to ultraviolet light is necessary for the formation of the precursor of Vitamin D. Vitamin D is necessary for proper bone formation.