As I've heard it, the development of both blue eyes and blond hair is thought of as mainly being driven by sexual preferences, i.e. status of novelty. Sexual p

As I've heard it, the development of both blue eyes and blond hair is thought of as mainly being driven by sexual preferences, i.e. status of novelty. Sexual preferences are pretty strong drivers and combined with periods of harsh environments (e.g. where either of the sexes die off early in life) can create really fast evolution.