First this: The fact that Chinese, Koreans and Japanese developed lighter skin with
different genes involved than Europeans basically point to evolutionary pressure. So what would that be? Most probably vitamin D. Apart from Rachitis a number of diseases seem to be affected by vitamin D deficiency:
http://anthrogenetics.wordpress.com/...athyway-genes/
The list has a number of interesting health issues. Lower fertility, higher mortality, infectious diseases. Now, as far as I understand the part of mankind that departed Africa carried for a large part a number of genes that give lighter skin. This feature is shared with East-asians , Indian and Amerindians. Apparently this is enough "lightening" of the skin for hunter gatherers as American Indians basically carry these. Off course,
hunter gatherers eat basically game and fish, which is relatively rich in vitamin D. Especially if you'd eat
fish liver. So, we have a number light skinned genes that allow for more sunlight to reach the skin to make vitamin D, but not yet the light skin of European. Remember that the Loschbourg mesolthic hunter-gatherer does not share any of these specifically European light skin genes with us, even if he possibly had blue eyes.
Now the neolithic revolution kicks in. The amount of available food is high but it's
mostly cereals. So far less vitamin D enters the body via food. Since farming is considered to be related to the emerging of a number infectious diseases the notion that vitamin D is highly involved in immune system evolutionary pressure for more light skin is quite relevant. It is also noteworthy that in similar environment both Europeans and East-Asians, heavy cereal using
agricultural cultural conglomerates, develop genes for lighter skin independently, whereas the mostly hunter-gatherer American Indians do not. That may serve as evidence for
neolithic selective pressure.
So, whatever the scenario that brought in the mentioned mutations, I am beginning to get the idea that evolutionary selective pressure assured the ascendancy to 100% of the current genetic make up.