Why does the sun effect our skin pigmentation?

Question: Why does the sun effect our skin pigmentation?
- Keywords:
  pigmentation,
  skin,
  sun
Asked by you cant see me to Theresia, Katie, Andy on 12 Nov 2014.
- Andrew Philp answered on 12 Nov 2014:
  
  I thought that skin pigmentation was kind of like a natural sun block. With the greater the pigmentation the higher the protection from sun light. So people that live in hot/sunny environments will have adapted to have higher natural pigmentation.

Question: Why does the sun effect our skin pigmentation?