Shlomo Sand is a self-hating Jew who quit Israel's Communist party because it wasn't radically anti-Zionist enough for him. He is still an admitted Communist and a Marxist historian. He is also a crackpot. His answer to the genetic evidence is, essentially "Hitler would have liked the genetic evidence, so it must be wrong." The only people who take him seriously are Jew-haters.
Now, here's a question. Will you admit you are wrong? Or will you cast your oars with crackpots and Jew-haters over the considerable genetic, linguistic and historical evidence? And if you will, that pretty much says a lot about you.
http://news.sciencemag.org/sciencenow/2010/06/tracing-the-roots-of-jewishness.html