TerryT: regarding the part of your reply: "Selection for white skin is unlikely to have anything to do with vit. D."

I found a 2002 Scientific American article (although I know they can be wrong, as with the shower-curtain effect). It is entitled Skin Deep: Throughout the world, human skin color has evolved to be dark enough to prevent sunlight from destroying the nutrient folate but light enough to foster the production of vitamin D. At <http://www.sciam.com/article.cfm?articleID=000B7732-FC72-1D80-90FB809EC5880000>
~The first paragraph ends with: "Recent epidemiological and physiological evidence suggests to us that the worldwide pattern of human skin color is the product of natural selection acting to regulate the effects of the sun?s ultraviolet (UV) radiation on key nutrients crucial to reproductive success."
Not definitive, but certainly plausible I think.
Thanks,
~Sam

Pyrolysis creates reduced carbon! ...Time for the next step in our evolutionary symbiosis with fire.