However, it was not until the 1890s that outward migration from the south became substantial [...], but the north–south differences in per capita income were present before then and go back centuries [...] The north–south differences in IQ also appear to have been present before substantial migration from the south to the north, if the percentages of the populations that were literate in 1880 are adopted as a proxy for IQ, while Murray's data on the far greater numbers of high IQ "significant figures" from northern Italy as early as the period 1400–1600 [...] suggest that the higher IQ of the north predated by several centuries the mass migration from south to north.
A possible explanation for the northern regions having had higher IQs than the southern regions at least from 1880 and possibly from 1400 to 1600 is that the populations of the north and south are genetically different and these genetic differences are related to differences in intelligence.
