The theory is fine but several questions then arise. Why didn't the same thing happen throughout Northern Eurasia? Why did selection for a white skin colour occur predominantly in the region of northern deciduous forest, a region where the trait is found in many other species? Is the balance between folate and vitamin D that precarious? Wouldn't humans have been fully-clothed by the time they reached north far enough for it to matter?

Re. the pervasive influence of Judeo-Christian beliefs. The Basque philosopher Unamuno recognised the problem when he said that in Spain even atheists are Catholic.