It wasn't until the mid-to-late 17th Century in most European countries that jews were allowed to own property, serve in the rulers' military, practice the learned professions of law, medicine or clergy and most businessmen tradesmmen engaged in patent discrimination by sub rosa not hiring jews or blantly posting notices that ''Jews need not apply.'' Thus, virtually the only areas of commerce and employment available were banking and becoming one's own small business owner. In those fields most showed such adeptness and acumen that many were able to accumulate significant wealth. Without the ability to reinvest such proceeds in real property and since lending and the collection of interest were without any adverse moral taint, they often became the object of even greater and widespred scorn by the rest of society.
And in the fields of merchanting and moneylending, the predominant characteristic that determines success is intelligence. And since up until the last century or so, success was defined as "having enough to keep you and your children from starving", those fields had a powerful effect on genetic natural selection