From the end of the second century C.E., Judaism enforced a religious norm requiring any Jewish father to educate his children. We present evidence supporting our thesis that this exogenous change in the religious and social norm had a major influence on Jewish economic and demographic history. First, the high individual and community cost of educating children in subsistence farming economies (2nd to 7th centuries) prompted voluntary conversions, which account for a large share of the reduction in the size of the Jewish population from about 4.5 million to 1.2 million. Second, the Jewish farmers who invested in education, gained the comparative advantage and incentive to enter skilled occupations during the vast urbanization in the newly developed Muslim Empire (7th and 8th centuries) and they actually did select themselves into these occupations. Third, as merchants the Jews invested even more in education–a pre-condition for the extensive mailing network and common court system that endowed them with trading skills demanded all over the world. Fourth, the Jews generated a voluntary diaspora by migrating within the Muslim Empire, and later to western Europe where they were invited to settle as high skill intermediaries by local rulers. By 1200, the Jews were living in hundreds of towns from England and Spain in the West to China and India in the East. Fifth, the majority of world Jewry (about one million) lived in the Near East when the Mongol invasions in the 1250s brought this region back to a subsistence farming economy in which many Jews found it difficult to enforce the religious norm regarding education, and hence, voluntarily converted, exactly as it had happened centuries earlier.