In The Chosen Few, Maristella Botticini and Zvi Eckstein offer an explanation for how Jews wound up in high-skilled, urban occupations. They argue (p. 95) that between 200 and 650 AD,
world Jewry became a small population of literate individuals (“the chosen few”). The unintended consequences of the religious ruling that required Jewish fathers to invest in their sons’ literacy and education fully displayed themselves.
Jews became much more literate than other populations, but at a cost of numbers, as those who could not afford to educate their sons converted to other religions. Over this time period (p. 113)
the general population decreased by about 12 percent, whereas the Jewish population collapsed by roughly two-thirds.
In those days, most people were farmers, for whom literacy’s costs generally outweighed its benefits. However, in an urbanized society with skilled occupations, literacy pays off. As urbanization gradually increased in the late Middle Ages, Jews came to fill high-skilled occupations. Botticini and Eckstein argue that literacy, rather than persecution, is what led Jews into these occupations.