Blonde Moment

Via Robot Wisdom comes a fascinating map of the density, as it were, of blondes in Europe.

Inevitably the Scandinavians have the most per head, but what struck me immediately is something picked up in the notes:

The southern border of the fairer-haired part of Great Britain seems to correspond quite well with the southern border of the Danelaw, which was ruled and settled by the Danish in the early Middle Ages.