There is also a latitudinal gradient in intelligence

From Stability of Italian Regional Intelligence Differences for 150 Years by Emil O. W. Kirkegaard and Davide Piffer.  From the Abstract:

Italy shows a strong north-south gradient in measures of well-being, with the northern areas being far wealthier than the southern. Less well known is that there is also a latitudinal gradient in intelligence. We combined numeracy scores based on age heaping data for Italian provinces from the censuses of 1861, 1871, and 1881 with modern data about scholastic ability from the INVALSI, and important social outcomes such as mortality and income (up to 107 provinces in analyses). We show that there is a strong stability of the intelligence differences across 150 years for the overlapping set of 69 provinces. Intelligence measured in the 1800s predicts overall well-being just as well as modern data, r’s .78 and .82, for age heaping and INVALSI, respectively. We discuss the findings in light of recent evidence of genetic differences in regional intelligence levels.