I'll give you the ultra Cliff's Notes version:
- Cystic Fibrosis is mostly limited to Caucasians and it clearly peaks in Northwestern Europeans
- The mutation spread around the time Beakerfolk were marauding through Western Europe
- Cystic Fibrosis sucks to death if you have two copies
- But for others, it must have some useful purpose - exposure to heavy metals is a strong possibility
- The ancestral carriers were from the neighborhood of the Black and Caspian SeasNote that in the Cliff's Note version above the reference to "Caucasians" is to white people and not the people specifically from the Caucasus mountains region.