According to an Israeli geneticist who has done a lot of comparative studies of the Jewish DNA, this is not true. There are genes for blondness and light-colored eyes that are native to Jews. They are less common than brown hair, but they exist nonetheless. These are native Jewish phenotypes. Keep in mind that "blond" Jews are not as blond as Scandinavians. They may be tow-heads as babies, but become dish-water blonds when they mature. It's a misconception to think that they have become mixed with the surrounding populations. He has done comparative studies on Jews and the Slavic and Germanic populations among whom they lived. He concluded that there is very little admixture. There is a lot more in common genetically between Ashkenazi Jews and the Kurds, for example, with whom they had no or little contact.
There were conversions all through the middle ages, especially from the Christian clergy and educated Moslems. It was not unusual for a Moslem to travel to a Christian country to convert to Judaism and vice versa. Also DNA evidence supports the hypothesis that the first Jews in many more distant (from Mediterranean culture) areas were men, probably traders, who married local women and founded communities. They were probably joined later by larger migrations of Jews from the south. Also keep in mind that at one time 10 % of the Roman Empire was Jewish. Most Europeans, therefore, probably have some distant Jewish ancestry. Although blond hair isn't common in southern European people, there were some blond hair people that were mixing with the Jews after the great rebelion of 66-70 B.C.E., plus enter the mixing with Europeans and there you have it.
http://www.pnas.org/cgi/content/full/97/12/6769Also, this study based on mitochondrial DNA that reveals that 40% of Ashkenazi Jews are descended from just 4 females from the Middle East 2000 years ago. The remaining 60% cannot be precisely identified but Middle Eastern origin is probable for many them.
The Y-chromosome of course is inherited from the father and the mitochondrial DNA from the mother. This testifies to a striking and remarkable degree of genetic stability over the centuries.
As for the distribution of blond hair in Jewish populations, in those regions where blond hair predominates in the non-Jewish population the proportion of blond hair in the Jewish population is lower; in regions where blond hair in the Gentile population is rare, blond hair in the Jewish population is proportionately higher.
It's worth pointing out as well that the Kabyle of North Africa have golden hair and Esau is supposed to have had red hair. Sefardic Jews also have some blond hair people, but they are in lower number then in Ashkenazi Jewish population.
Oh, no, not Ashkenazi Jews. They don't look like arabs at all. Sefardic Jews are mixed with arabs, though, and look different. Many of them look like arabs. They also have a lower IQ, according to some recent studies. Ashkenazi IQ is 110. Sefardic IQ is below 100. I think it's 91. There was a discussion about it in the Commentary Magazine.
In the past when the Ashkenazi Jewish areas were pretty close the Jews looked darker, but with time they became lighter because of mixing. Most Sefardics are lighter than the Arabs. Plus, the Sefardic Jews in Israel only have lower IQ and that's because what happend to us in the 1950', while Sefardics in other places have pretty high IQ, sometimes higher than Ashkenazi one. If Sefardics would have live in European life style they would have a higher IQ. It's proved that 95% of the Jews in north-Africa, Iraq and Persia (I am not sure about Persia) studied in weastern schools. There are 10,0000 Morrocon Jews in Spain and they have higher number of proffersors than the morrocon Jews in Israel who are numbered in 1,000,000.
