Not jewish, interested in the variations amongst individuals and groups of the human race. I have worked with a number of Ashkenazi Jews in multiple fields and have been astonished at the overwhelming proportion (relative to population). There have been many cultural explanations of the phenomenon (e.g. Talmudic education) which I find unconvincing. Genetic selection supported by hundreds of years of cultural practices and socio-political constraints seems most plausible.
Q: are other populations where similar phenomena have played out?