I don't usually like to rely on secular science, but when you twist your own 'science' - what studies? 40 % Ashkenazi Jews have been shown to descend from 4 women of Middle Eastern origin (No imagination to work out who they were [Rachel, Leah, Bilhah and Zilpa]), and yes, the other 60 % can be attributed to conversion, where futre converts were expressly mentioned at the giving of the Torah to be true Jews, and share their entire existence with Jews as having always been such and just waiting for the opportunity to convert. As for Palestinians, they have been shown to be an amalgamation of Egyptian, Roman and Turkish, which makes historical sense. Some are descendants of Jews who were forceably converted. They are welcome and encouraged to come back the normal way a convert would come back to Judaism.
Israeli ambassador to U.K.: Elements of left 'in denial' about 'disease' of anti-Semitism (Haaretz)
from the article: Israeli troops, Palestinians clash near Jerusalem