Genetics of skin color variation
Several genes have been invoked to explain variations of skin tones in humans, including SLC45A2,<7> ASIP, TYR, and OCA2.<8> SLC24A5 has been shown to account for a substantial fraction of the difference in melanin units between Europeans and Africans, variations in human skin tones have been correlated with mutations in another gene; the MC1R gene.<9>. Harding found no differences among Africans for the amino acid sequences in their receptor proteins while among certain European non-African individuals there were.
Examination of the variation in MC1R nucleotide sequences for people of different ancestry to determine the most probable progression of the skin tone of human ancestors over the last five million years and comparing the MC1R nucleotide sequences for chimpanzees and humans in various regions of the Earth, Rogers concluded that the common ancestors of all humans had light skin tone under dark hair. By 1.2 million years ago, all people having descendants today had exactly the receptor protein of today's Africans; their skin was dark, and the intense sun killed off the progeny with any lighter skin that resulted from mutational variation in the receptor protein.<10>
However, the progeny of those humans who migrated North away from the intense African sun had another evolutionary constraint: vitamin D availability. Human requirements for vitamin D (cholecalciferol) are in part met through photoconversion of a precursor to vitamin D3. As humans migrated north from the equator, they were exposed to less intense sunlight, in part because of the need for greater use of clothing to protect against the colder climate, under these conditions, evolutionary pressures would tend to select for lighter-skinned humans as there was less photodestruction of folate and a greater need for photogeneration of cholecalciferol.<11> Hence the leading hypothesis for the evolution of human skin color proposes that:-
1. From ~1.2 million years ago for at least ~1.35 million years, the ancestors of all people alive were as dark as today's Africans.
2. The descendants of any prehistoric people who migrated North from the equator mutated to become light over time because the evolutionary constraint keeping Africans' skin dark decreased generally the further North a people migrated.<10><12> This also occurs as a result of selection for light skin due to the need to produce vitamin D by way of the penetration of sunlight into the skin (the exception being if dietary sources of vitamin D are available, as is the case among the Inuit).
3. The genetic mutations leading to light skin, though different among East Asians and Europeans,<13> suggest the two groups experienced a similar selective pressure due to settlement in northern latitudes.<3>
A variation of the vitamin D argument is that humans lived in Europe for several thousand years without their skin lightening and that it only became white after they adopted agriculture.<3><14> It is suggested that in Europe the latitude permitted enough synthesis of vitamin D combined with hunting for health, only when agriculture was adopted was there a need for lighter skin to maximize the synthesis of vitamin D , therefore it is suggested the elimination of game meat, fish, and some plants from the diet resulted in skin turning white several thousand years after modern human settlement in Europe.<15><16>
From my observations, it is impossible to draw a line - there are fair and dark amongst Italians, French, Germans, etc - and sometimes the differences between Jewish and Arabic people are difficult to tell. There is a tribe that has Israeli origins living in southern Africa.
http://en.wikipedia.org/wiki/African_JewsThe most ancient communities of African Jews known to the Western world are the Ethiopian Jews, Sephardic and Mizrahi Jews of North and Middle Africa.
Largely unknown in the West until quite recently are communities of the African Jews such as the Lemba (Malawi, Zimbabwe, and Northern South Africa). Some among the Igbo of Nigeria, the Annang/Efik/Ibibio of Akwa Ibom State and Cross River State of Nigeria, Cameroon, and Equatorial Guinea) claim descent from East Africa and Jews in Algeria and Jews in Tunisia and Jews in Morocco,Jews in Libya and Jews in Egypt Jewish communities.
In the seventh century, many Spanish Jews fled persecution under the Visigoths to North Africa, where they made their homes in the Byzantine-dominated cities along the Mediterranean coast. Some, however, moved further inland and actively proselytized among the Berber tribes. A number of tribes, including the Jarawa, Uled Jari, and some tribes of the Daggatun people, converted to Judaism.<1> Ibn Khaldun reported that Kahina, a female Berber warlord who led the resistance against the Arab invaders of North Africa in the 680's and 690's, was a Jew of the Jarawa tribe. With the defeat of the Berber resistance, none of the Jewish tribes were initially forced to convert to Islam.<2> Remnants of longstanding Jewish communities remain in Morocco, Tunisia and the Spanish cities of Ceuta and Melilla. There is a much-diminished but still vibrant community on the island of Djerba in Tunisia. Many Jews emigrated to North America in the early 20th century. Most other Jews emigrated to Israel, France and Spain, since 1948.