Scientists studying the genetics of eye colour have found that
all people with blue eyes inherited them from a common ancestor, who lived about 6,000 to 10,000 years ago in the northwestern Black Sea region, and developed a very specific mutation which disrupted melanin production in the iris.
It is still not clear why the mutation was selected for and spread as widely, though possible explanations are that it conferred some advantage in northern latitudes, or else that it spread purely because, by some quirk of psychology, it was considered sexually attractive.