Professor Hans Eiberg of the the Department of Cellular and Molecular Medicine at the University notes that "Originally, we all had brown eyes”, but a genetic mutation affecting the OCA2 gene in our chromosomes resulted in the creation of a “switch”, which literally “turned off” the ability to produce brown eyes.
The “switch” reduces the production of melanin in the iris, effectively “diluting” brown eyes to blue.
Blue-eyed individuals have only a small degree of variation in the amount of melanin in their eyes, and "they have all inherited the same switch at exactly the same spot in their DNA” which means they are all related in the not too distance past. In contrast, brown-eyed individuals have quit a lot of individual variation in the area of their DNA that controls melanin production.
So does this mean that blue-eye individuals are defective?
The mutation of brown eyes to blue does not appear to be either a positive or a negative mutation; it is simply a color variation that is about as meaningful as hair color or the presence, or absence. of freckles or beauty spots.