bicicleur 2
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Here is a global map of skin color reflectance. It may not be exact, but I think the general pattern is probably accurate enough for our purposes. The decreasing cline for "dark" pigmentation seems pretty gradual to me.
http://upload.wikimedia.org/wikiped...abeled_Renatto_Luschan_Skin_color_map.svg.png
For North Africans, a couple of factors might be at play, I think. We don't know much about the pigmentation of the "indigenous" inhabitants. We do know that a large Neolithic migration impacted the area. We also know that there was some movement of Arabian tribes into the area. At the same time, SSA introgression, perhaps fairly constant, but definitely important since the era of the Arab slave trade has resulted in average levels for SSA of 25%. We also know that there were large scale importations of Europeans versus another slave route. So, figuring this one out is beyond me.
Another interesting fact is that studies done on women in these areas show that many of them suffer from Vitamin D deficiencies resulting in serious health problems. It's hypothesized that the cause is the heavy veiling that they wear, particularly in the more conservative rural areas.
plenty of sun in north africa, more than in the equatorial forests
neolithic immigration seems to be at play
neolithic immigration were cattle herders (R1-V88 and T), some 8000 years ago probably
that is 8000 years natural selection could have played to make them darker
of course there is also the late arrival of Arabs
south africa would be interesting to study :
arrival of cattle 2000 years ago (haplo E1b1b and some T)
arrival of Bantu 1700 years ago (haplo E1b1a )
original subsahara : haplo A&B
nice puzzle