Skin color, microevolution, and dehydration.

Article: In human evolution, changes in skin's barrier set northern Europeans apart

An example of microevolution.

It has already been hypothesized that the pale skin of Europeans is due to a natural selection-driven need for vitamin D. More UV-B can be absorbed by paler skin, producing more vitamin D synthesis.

The authors of this article add that paler skin in Europeans may also be due to mutations which reduce the ability of skin to conserve water and prevent dehydration. That is, Europeans have a reduced need to conserve water compared to their African ancestors.

Yet, there was an evolutionary tradeoff for these barrier-weakening [...] mutations, Elias said. Mutation bearers have a tendency for very dry skin, and are vulnerable to atopic dermatitis, asthma and food allergies. But these diseases have appeared only recently, and did not become a problem until humans began to live in densely populated urban environments, Elias said.