[defen]

Something must have happened during the Middle Ages - in antiquity, the Jews weren't regarded as particularly intelligent compared to other groups - that title went to the Ionian Greeks. There's a hypothesis that medieval restrictions on Jewish occupations & land ownership + Christian restrictions on charging interest pushed Jewish people into financial / lending roles in which intelligence was an advantage (meanwhile, many of the smartest Christian men went into the priesthood with its official celibacy). So you had selection on intelligence genes. Further evidence for this hypothesis is the raft of genetic diseases that disproportionately affect Jews, and are related to brain/nerve development - Canavan disease, familial dysautonomia, Joubert Syndrome, MLIV, Niemann-Pick Disease, Spinal muscular atrophy, Tay-Sachs disease, etc. It's possible that being a carrier for some of those provides some sort of boost to intelligence / brain functioning - otherwise you would expect them to be much less common.