The show is about how we all started in Africa and migrated north then one group heads west and another group goes east. We lightened up the further north we went to be able to get the most amount of Vit D with shorter days I guess. But then how do you explain why the Inuit were darker in hair and skin and eyes?
Another point is when you are so far north it is very cold and you are bundled up and very little skin is open to the sun. So someplace along the way the lighter pigmented tribes survived better up north because they could now take in more Vitamin D through their skin while others with dark pigments further south could take in vitamin D much better and to screen out too much light. If our genetics could change for Vitamin D, then what else changed to adapt? Does one diet really fit all genetic differences?
I am of Scandinavian decent and have always been on the heavy side and docs would look at my stats and shake their head like they didn't understand why my heart rate was low, blood pressure low, cholesterol was good, no thyroid issues. They would try to find a reason to tell my why I should take off weight but the numbers were good. I wonder if I am designed to be more insulated than others for extreme cold and to survive long harsh cold spells/winters like a bear does.
Maybe down the road they will take a blood test of folks and new babies and from the genetic info they will be able to prescribe the optimum diet for you specifically based on your immune system and the way you process nutrients. Maybe they will be able to create a diet that changes during the different stages of your life that is tailored to your genetics. One size fits all never has worked for me in so many ways.
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.
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
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