The final chapter of "The 10,000 Year Explosion" expands on their paper from the "Journal of Biosocial Science" on the issue of Ashkenazi Jewish intelligence. Harpending and Cochran argue the cause of the claim of Ashkenazim having higher mean verbal and mathematical intelligence than other ethnic groups (as well as having a relatively high number of genetic diseases, such as Tay–Sachs disease, Canavan disease, Niemann–Pick disease, Gaucher's disease, familial dysautonomia, Bloom syndrome, Fanconi anemia, cystic fibrosis and mucolipidosis IV) is due to the historically isolated population of Jews in Europe.