Poring around the nets while I’m on holiday is turning out to be quite interesting looking at summaries of science. I’ve been picking out some for discussion here. Here is a post from Knol with a summary on why Europeans are so pale.
They discuss well-known ultraviolet / vitamin D linkage with the consequent diseases.
UV rays produce vitamin D and reduce folate when they hit naked skin. And embryos are terribly vulnerable to both substances in the mother. When it comes to sunlight and skin tone, furless humans are balanced on a knife-blade.
Too much UV penetrating the skin (too pale-skinned under intense sunlight) increases Vitamin D but reduces folate. Lack of folate causes neural tube defects in the fetus, causing such congenital abnormalities as craniorachischisis, anencephalus, and spina bifida, leading to many miscarriages.
On the other hand, too little UV penetrating the skin (too dark-skinned under dim sunlight) increases folate but reduces vitamin D. Lack of vitamin D causes skeletal neonatal abnormalities (skull, chest, and leg malformations), rickets being the best known. Again, this causes miscarriages.
And so, humans adapt very quickly to solar UV. Prehistoric groups that migrated towards the equator got darker. Prehistoric groups that migrated away from the equator got lighter.
Some foods that are eaten also contain vitamin D and therefore break the dependence on the sun. So people like the Inuit, Sammi, Chukchi and Aleut in the north have far darker skins than would be expected because a high proportion of their diet is seafoods.
People who eat grains do not get vitamin D from food; they must get it from sunlight.
This usually works out fine because grains grow only where it is warm. And this means only in latitudes with bright sunlight, with one exception.
People who live in low latitudes, where they can live off grains, get plenty of sunlight. People who live in dim sunlight cannot grow grains, and so they get vitamin D from the meat and fish that they eat.
But this is unsatisfactory for explaining the historical paleness of Northern Europeans who are very pale in skin and hair tones, live inland, and live in a latitude that grains should be hard to grow without high levels of farming technology.
However grains do grow in Northern Europe easily. A climatological quirk explains why. The Gulf stream delivers warmth further north than the latitude would normally allow. This is about the only place where there has been grain grown for a long time in high latitudes. But eating these foods, while good for diet, would cause severe neonatal abnormalities and therefore a severe evolutionary pressure.
Now this is where it gets interesting to me because it is something that I hadn’t realized previously. Because children are not reproductively active, there is less evolutionary pressure on them for vitamin D. So all populations have some children who have lighter hair colour. My hair was quite blond and my skin tone was much fairer when I was child, and then darkened as I hit puberty. My hair went to a dark brown/black and is now going lighter as it goes grey, presumably because by my age my female counterparts would have stopped having children.
When the inhabitants of this region switched to grain about 6 KYA, they suddenly got insufficient vitamin D to survive. They had stopped eating mostly meat and fish in a place where sunlight was too dim to produce vitamin D in normally pigmented skin.
And so they adapted by retaining into adulthood the infantile trait of extreme paleness. Blonde hair and blue eyes were other infantile traits that were just swept along accidentally.
For the detailed text of this topic, complete with footnoted references, citations, and all the peer-reviewed material, visit The Paleo-Etiology of Human Skin Tone.
So Europeans have infantile traits from a neoteny adaption because of a climate quirk. I’m sure that will impress the ‘white’ racists who persist in perpetuating some other childish traits.