There's also evidence that European light skin and different colors of hair might have a lot to do with sexual selection in addition to issues with vitamin D.

The inuit in the snow recieve large doses of reflected long wave ultraviolet radiation. Supposedly, the snow glare can be quite bad and even result in 'snow blindness' which is damage to the eyes from the snow glare. It is believed the dark inuit skin helped protect them from that and since they consumed enough vitamin D through their diet, there was less pressure to have light skin for D production. It should also be considered that some experts believe that natural skin oil (sebum) that is excreted outside the skin is also able to create vitamin D (tests show skin oil is full of D) and then the skin is able to reabsorb the oil and D with it. If this is the case, then skin oil would be a mechanism to bypass dark skin and still get access to D production.

My guess would be that population characteristics according to a complex combo of chance (as far as which mutations occured) mixed with subtle pressures in the environment and diet. THings like more or less snow, more or less D in the diet, sunlight, weather, etc would all compete for determining which strategy was best for survival. In addition, although there are clear patterns for body type and world location, there may have been more than one successful path to take in the same situation and which path was taken may have depended in part by chance and preexisting genetics before the population arrived in that area. If you look in any lake or stream, there are many different kinds of fish in there because each has developed a different survival tactic. There isn't just one survival option for each environmental challenge. The inuit might have developed one strategy and the Scandinavians might have developed another.

Inuit were able to get lots of vitamin D through their diets, so there was not a selection advantage to getting fair skin and the resultant increased vitamin D from the sun.

I had similar questions for many years about following the diet of your ancestors. Have you read Dr. Weston A Price's book Nutrtition and Physical Degeneration? He was a dentist in the 30's? that traveled the world studying primitive and traditional cultures and and how their diets affected their health. When they stayed on their traditional diets they were healthy. When they added white flour/sugar/processed foods their health changed and in their children it showed up first in the teeth and jaw structure. Fascinating book with tons of pics showing both affects. He briefly talks about what each of these cultures ate, so, if you are interested you might read up on that and follow that diet for a while and see how you feel. Also, Sally Fallon (now Sally Fallon Morrell) wrote a cookbook with tons of research based on Price's work.... "Nourishing Traditions" which allows grains, but only when soaked and fermented which neutralizes the phytic acid. I know its not "paleo". I promote and lean towards paleo, but am strongly pulled to eating what your ancestors ate too. They learned how to prepare the foods for optimal nutrition. And the whole focus in on animal based fats/protein too. The cultures that lived chiefly as vegetarians did not fare well. Sorry if you already knew all this, I hope it helped answer part of your question. ~~~s