I've come across a few cats (read or talked to) who believe white folks, not a genetic mutation, but were originally African but traveled towards the norhtern regions of Europe. No different then the African who migrated out of the motherland and inhabited other parts of the earth like Australia, the Americas, the Far East, etc. Those Africans who traveled north into Europe got trapped below the 51st Parallel around the onset of the Wurm Ice Age. Over time they adapted to the harsh cold climate, minimal sunlight, overcast skies, scarce crops and rough terrain - as opposed to the rich & abunant land that is Africa. I think all that led to their depigmentization of the skin, change of hair and eye color and altogether changed the genotype of that people which set the table for the caucasian we see today. I guess one could say that is a genetic mutation. haha I always found that theory interesting.
As to why they terrorized the world....I cant call it. haha