Japanese North–South Gradient in IQ Predicts Differences in Stature, Skin Color, Income, and Homicide Rate

Abstract

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 mortality. The lower IQ in southern Japanese islands could be attributable to warmer climates with less cognitive demand for more than fifteen hundred years.

Introduction

It has become increasingly evident that human populations have different behavioral propensities and intelligence levels. Those who have adapted to the harsh northern climate worldwide are taller, more intelligent, more pro-social, less crime prone, and exhibit less fertility. This is said to be due to the more cognitively demanding long winter season (Lynn, 2006 and Lynn, 2008). In a similar and more speculative vein, the differential r/K theory (Rushton, 1988 and Rushton, 1994) predicts that a more demanding cold climate has induced more intelligent and pro-social personality in general.

While these differences in intelligence and behavioral traits were reported mainly with respect to racial categories in the twentieth century (Herrnstein and Murray, 1994 and Rushton, 1994), even finer gradients of these personality traits from all over the world have been reported in the twenty-first century (Lynn, 2006, Lynn, 2010, Lynn, 2012, Lynn and Vanhanen, 2002, Lynn and Vanhanen, 2006 and McDaniel, 2006).

Since nation states like Italy and Spain exhibit north-south differences in their behavioral propensities in the above expected directions, it is natural to expect the same gradients in other parts of the world. In Japan, although casual observation sometimes admits that regional behavioral and IQ differences result in relatively poor economic performances in the south, there exists only one paper suggesting regional IQ differences on Okinawa, the southernmost region (Agarie, 1959). Serious inquiry on this topic has been effectively prohibited due to the political correctness and self-censorship in Japanese academia. Since various kinds of IQ tests such as the WISCor Progressive Matrices were no longer being conducted after the 1970s, this paper examines this conjecture by utilizing national achievement test scores from Japan’s 47 prefectural populations.

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Method

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Results

In Table 2, except for infant mortality, all variables correlate significantly with the prefectural latitude. People living in the northern part of Japan are taller, more intelligent, and less crime prone. They divorce less often, have lower fertility.

Latitude is correlated with IQ (r = 0.44) and height (r = 0.70). From many collected IQ measurements, the Japanese average IQ has been estimated to be 104, which is slightly lower than the Chinese and Korean averages (Lynn & Vanhanen, 2006; Lynn, 2008,Lynn and Meisenberg, 2010 and Lynn and Vanhanen, 2012). Assuming that the Japanese population has a standard deviation of 15 as in England, north–south IQ difference is estimated to be 11 points, with the prefecture with the highest IQ prefecture (Akita) having 107 while the one with the lowest (Okinawa) having 96. This is surprising in that it challenges the much-touted homogeneity of Japanese people.

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Discussion

Many people worldwide seem to have an image of Japan as a highly homogeneous nation. However, the Japanese islands were initially populated by the hunter–gatherer Jomon people (Y haplogroup C1, C3 & D1) and experienced a great deal of immigration from the Korean peninsula and mainland China from 2900 to 1500 years ago. These incoming Yayoi people (Y haplogroup O2b from Korea and O3 from China) brought wet-rice agriculture and bronze and iron tools to the islands. Because of these cultural advancements, they had shown much more fecundity and have in number dominated the native Jomon people. There still exists a genetic cline from the Western Yayoi population in the Eastern Jomon population in Japan (Hammer et al., 2006). Haplogroups, C1, C3 and D2 are most common among the Ainu people in the northmost Japan (almost 100%) and in the Okinawans in southmost Japan (about 60%),while the western regions closer to the Korean peninsula are more densely populated by Yayoi descendant haplogroup of O2b and O3 (60–70%).

Since the continental Northeast Asians (Han Chinese and Korean) have a higher intelligence compared to the rest of the Eurasian population, it would be natural to assume that these Yayoi people were more intelligent. This conjecture is based on the facts: 1. The fossil evidence shows that the Yayoi people were 5–8 cm (2–3 in.) taller than the Jomon; 2. Modern-day Koreans are about 3 cm (1.2 in.) taller than the Japanese; 3. The IQs of Chinese and Korean people have continuously outscored that of Japanese people (estimated to be 106 and 105, respectively). Hence, it is reasonable to expect that the prefectures closer to the continent exhibit higher intelligence than those in the Northeast.

However, this tendency was not observed and instead there exists a simple intelligence gradient from south to north. This may be due to an almost perfect admixture within the last 1500 year (about more than 60 generations) as far as genes for taller stature and higher intelligence are concerned, as well as the selective pressures of the last 1500 years of civilization, which have been strong enough to reshape the original east–west IQ gradient into the current north–south cline. This conclusion would be in line with the Hawks, Wang, Cochran, Harpending, and Moyzis (2007) idea of ever-accelerating human evolution. They insist that more and more beneficial mutations swept populations, after the advent of agricultural civilizations with metallurgy, letters and complex hierarchical organizations. The Japanese north–south gradient in height and intelligence can be evidence that modern humans have evolved to higher intelligence within the last two millennia.

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