Interesting read --except for the Vikings.  I was just thinking about this the other day when looking at the Fox News gal on the Fox News VS. Denmark thread.

"But naturally fair hair is uncommon: An estimated 2 percent of the world's population—and 5 percent of white Americans—is actually towheaded."

https://www.theatlantic.com/entertainment/archive/2018/08/the-pursuit-of-blondness/567688/?utm_source=feed

>Vikings

Blondes. Blondes everywhere. It's one of the things that struck me most while there.

It is an adaptation for vitamin D absorption.  Most people who historically lived in that high a latitude  were able to get enough vit D from hunting, but the Scandinavians turned to farming early.   Without enough vitamin D from the sun or food they adapted to have less pigment to increase their skin exposure to UV rays.