Japanese north–south gradient in IQ predicts differences in stature, skin color, income, and homicide rate

Regional differences in IQ are estimated for 47 prefectures of Japan. IQ scores obtained from official achievement tests show a gradient from north to south. Latitudes correlate with height, IQ, and skin color at r = 0.70, 0.44, 0.47, respectively. IQ also correlates with height (0.52), skin color (0.42), income (0.51) after correction, less homicide rate (− 0.60), and less divorce (− 0.69) but not with fertility infant mortaliʹty. The lower IQ in southern Japanese islands could be attributable to warmer climates with less cognitive demand for more than fifteen hundred years.