Due to the haughtiness of some traditional Jews of Eastern/Central European origin they like to fancy themselves “pure” Jews without any gentile admixture. The fact that they are white doesn’t hint to them that reality is otherwise; they imagine that climate alone, over a millennium or so, is enough to noticeably alter the pigmentation of a people. Narrow as many of them are in their outlook on life, they fancy that the ancient Jews were as white as they are or that each tribe had a different appearance and that each one, upon exile, happened to arrive at a place where the gentiles looked the same. No need to waste time debunking the theories of mental children but let it be known that the average Jew, in ancient times, was neither black nor white, but in between. The fact that the majority of the present native Palestinian Arabs are brown would indicate that. The fact that the ancient Egyptians depicted the Canaanites (and there is no reason to suspect they looked any different than the Jews other than hair style and, maybe clothes) as brown also supports that idea. But it also states in the Mishna (Nega’im) “Said Ribbi Yishma’el, the children of Israel… are neither black, like an Ethiopian, nor white, like a German, but in between, like a cedar tree”. I once showed this to a very white Hassidic Jew in Jerusalem and he was dumbfounded, not knowing what to say.
When I was in a Lubavither yeshiva a blond haired, blue eyed Hassid asked where my family was from and I told him “Russia”. He gave a look of surprise and then said “well! Somewhere along the way…” as if to say my forebears had somehow been contaminated. Not that it’s his fault but he is the descendant of Vikings. There is no way to know for sure how much of any Jew’s ancestry comes from ancient Israel but, if you find one who looks radically different from the gentile population from whence he came, and he looks Mideastern, there’s no more likely candidate for “descendant of ancient Jews” than he.
In the old days the Jews placed plenty of emphasis on pedigree and one need not go any further than the books of Chronicles to see that. The emphasis was not to make sure one was Jewish and it was not even purely for halachic reasons but a matter of national pride intertwined with halacha. It was important to them to keep our people as pure as possible – to such an extent that even Ribbi ‘Aqiva wasn’t allowed to be head of the Sanhedrin because he was descended from a convert. See also the “Kuzari” by R. Yehuda haLewi. Over time, due to dispersion and persecution our people became more and more diluted until those making the rules were, themselves, very much mixed. The ancient People of Israel ceased to exist in many ways. The religious aspect of our people, in an adulterated way, continued to thrive among many who professed the faith and, mixed among them, real descendants of the ancient people. Now we are so far gone that no importance, whatsoever, is given to true pedigree. Instead we have a newer kind of pedigree based on ones being a descendant of a famous rabbi. At this point, at least among Ashkenazic Jews, it’s hard to say how much credence should be given to claims like “my family descends from Rashi, and so from Hillel”. That may even be so but that has nothing to do with any type of purity. It’s also hard to say whether or not Ashkenazic “cohanim” are really cohanim. It should be noted however that, among the various Jewish communities among the best at preserving true traditions were the German Jews up until recently. Among the worst were the Eastern Europeans and the Sephardic Jews. The Yemenites, Jarbaim (from an island near Tunisia) and, to a lesser extent, the ‘Iraqis were the most conservative of all.