"Well, if the blue eyed individuals in Ancient Egypt and Sumer were few, they could have come from the north, could they not?
I see the argument, though, that blue eyed individuals would be more numerous today in northern countries, due to the fact that it's more healthful for blue eyed people to be there, just as it is far more healthful to live in the north if you have white skin, (or else you risk skin cancer), but I am still not quite convinced that the mutation could not have happened when the individual in question already where in a faviourable place for blue eyes - is it not what Darwin's theory were about, that mutations occur to adopt to the environment you live in?
Anyway, I find it very interesting that all blue eyed people today have a common ancestor!"
Remember that mutations aren't always an adaptive response to the environment; mammalian ~hybridization~ (interbreeding between closely related species) is a prime catalyst for genetic mutations.
(From a scientific study by Peter R. Grant & B. Rosemary Grant, Princeton University, 1994):
"Hybridization increased additive genetic and environmental variances, increased heritabilities to a moderate extent, and generally strengthened phenotypic and genetic correlations. New additive genetic variance introduced by hybridization is estimated to be two to three orders of magnitude greater than that introduced by mutation. Enhanced variation facilitates directional evolutionary change, subject to constraints arising from genetic correlations between characters. The Darwin's finch data suggest that these constraints become stronger when species with similar proportions hybridize, but some become weaker when the interbreeding species have different allometries. This latter effect of hybridization, together with an enhancement of genetic variation, facilitates evolutionary change in a new direction."
The "variations" they refer to, are mutations induced by hybridization between related species; as opposed to natural (environmentally induced) mutations. It's not very difficult for DNA science to logically track down the species involved in the hybrid production of certain mutations.
(Btw, my family has its share of blue & green eyed individuals; red & blond hair, too. And oh yes - there's plenty of evidence to suggest that I might have some of that Viking blood, from their earlier forays into North America; or maybe some Phoenician, from some of their ancient explorations.)