Just to add a couple of points:
In all of Europe, by order of the Pope in 1204, Jews were legally restricted to ghettos and intermarriage with Christians was strictly prohibited (think the segregation and anti-miscegenation laws in the US), and those laws remained in place in many countries until the late 1800s . So hybrid vigor was not really available to European Jews until the spread of democracy in the 20th century, which was of course rudely interrupted by the Nazis.
As Korkscrew noted, 80% of Jews are Ashkenazi, which are western and central European Jews. The other 20% are Sephardic Jews, who originated in Spain (until their expulsion in 1492), Northern Africa (Morocco, Algiers, Tunisia etc) and the Middle East (Syria, Yemen, Persia/Iran etc).
My mother's side is predominantly Ashkenazi, most of whom had/have straight reddish-blonde hair. My boys and I take after my father's Sephardic side, with waves/curls, frizz etc. (Their father is half-Jewish and totally bald, so go figure!)
Jewish identity can be very confusing, I know - part of it is based on beliefs, but there is also an ancestral genetic component. For many Jews, it's more a matter of heritage than anything else.
L'shana tova to all of you, Jewish and non-Jewish alike