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Of the components of IQ tests, Ashkenazim do well on verbal and mathematical questions but score lower than average on visuospatial questions. In most people, these two kinds of ability are highly correlated. This suggests that some specific force has been at work in shaping the nature of Ashkenazi intelligence, as if the population were being adapted not to hunting, which requires excellent visuospatial skills, but to more urban occupations served by the ability to manipulate words and numerals. So it’s striking to find that Ashkenazim, almost from the moment their appearance in Europe was first recorded, around 900 AD, were heavily engaged in moneylending. This was the principal occupation of Jews in England, France and Germany. The trade required a variety of high level skills, including the ability to read and write contracts and to do arithmetic. Literacy was a rare ability in medieval Europe. As late as 1500, only 10% of the population of most European countries was literate, whereas almost all Jews were.7 As for arithmetic, it may be simple enough with the Arabic numerals in use today. But Arabic numerals did not become widespread in Europe until the mid-16th century. Before that, people used Roman numerals, a notation system that has no zero. Calculating interest rates and currency swaps without the use of zero is not a straightforward computation.
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