Human evolution and skin colour.
As we migrated out of Africa a mere sixty thousand years ago we hit a problem. The sunshine and hence UV light was greatly reduced. We needed that UV light in order to make Vitamin D. Without vitamin D we got ill. When you are living on the edge any small advantage becomes crucial.
In strong UV Light the black pigment melanin provides protection against skin cancer.
We all stem from Africans who had black skin.
Outside of Africa black skin was a disadvantage. A mutation occurred that reduced melanin and resulted in lighter skin that upped our vitamin D production.
Pale skin was selected in subtropical regions.
It is interesting to observe the way natural selection has occurred to optimise protection against skin cancer and vitamin D production. I tropical regions with harsh UV the skin colour is black. In subtropical regions with less intense UV it is brown and in temporate regions it is very pale.
This is a good example of changes in the ratio of genes in a population and hence evolution.