Scientists refute Khazar origins of Ashkenazim

I've just been informed of scientific research that bears on the work of Shlomo Sand, a professor of history at Tel Aviv University who created quite a stir with his book, "The Invention of the Jewish People." When in New York in October 2009 to promote the Verso Press English-language edition, he charmed a packed audience of the "Marxist Theory Colloquium" at New York University with his wit and devastating attacks on ideas that most Jews and Israelis hold dear.  (I blogged on this at the time.)

His notion is that the people we know as Jews are a disparate collection of physically unrelated populations, who are descendants of converts, and mostly not of the original inhabitants of the land of Israel; and that the Palestinian Arabs are actually descended from the ancient Judeans. His basic points of argumentation include:
    1)    that the Romans never "exiled" the Jews from Judea (because there was no Imperial expulsion decree) and that most of the survivors eventually converted to Islam with the Arab conquest about 600 years after the Roman victories over the two great Jewish rebellions;
    2)    that Ashkenazi Jews are mostly descended from the Khazars―a Turkic people, originally from near the Caspian Sea, who largely adopted Judaism over 1000 years ago;
    3)    that Sephardic Jews are mostly descended from Berbers who had a Jewish kingdom that fell to the Arab-Muslim conquest of North Africa;
    4)    that the idea of a "Jewish people" was "invented" by Zionist thinkers in the late 19th century.
 
An article in Newsweek in June, 2010, reported that the Khazar thesis has been refuted in recent DNA research on geographically diverse Jewish communities, which was written up for The American Journal of Human Genetics.  This news led me to survey other articles on this subject, which reveal a complex reality:

1. that descendants of the priestly caste (the kohanim) bear genetic markers that may actually date back to the time of the Biblical story of the Exodus; 
2. that Ashkenazim and Sephardim resemble each other more than they do non-Jews; 
3. that Jews mostly inbred in diaspora communities yet also mixed with local populations among whom they settled, with an impressive number becoming converts during the early years of the Roman Empire. 

In other words, there is a basis in fact for at least some of Dr. Sand's claims, but he presents them tendentiously―especially his exaggerated assertion that most Jews have no common origin in ancient Israel or Judea.