Temperature , skin color , per capita income , and IQ : An international perspective

The impetus for our study was the contention of both Lynn [Lynn, R. (1991) Race differences in intelligence: A global perspective. Mankind Quarterly, 31, 255–296] and Rushton (Rushton [Rushton, J. P. (1995). Race, evolution and behavior: A life history perspective. New Brunswick, NJ: Transaction; Rushton, J. P. (1997). Race, intelligence, and the brain: The errors and omissions of the revised edition of S.J. Gould’s the mismeasurement of man. Personality and Individual Differences, 23, 169–180; Rushton, J. P. (2000). Race, evolution, and behavior. A life history perspective (3rd edition). Port Huron: Charles Darwin Research Institute] that persons in colder climates tend to have higher IQs than persons in warmer climates. We correlated mean IQ of 129 countries with per capita income, skin color, and winter and summer temperatures, conceptualizing skin color as a multigenerational reflection of climate. The highest correlations were 0.92 (rho= 0.91) for skin color, 0.76 (rho= 0.76) for mean high winter temperature, 0.66 (rho= 0.68) for mean low winter temperature, and 0.63 (rho=0.74) for real gross domestic product per capita. The correlations with population of country controlled for are almost identical. Our findings provide strong support for the observation of Lynn and of Rushton that persons in colder climates tend to have higher IQs. These findings could also be viewed as congruent with, although not providing unequivocal evidence for, the contention that higher intelligence evolves in colder climates. The finding of higher IQ in Eurasians than Africans could also be viewed as congruent with the position of Diamond (1997) that knowledge and resources are transmitted more readily on the Eurasian west–east axis. D 2005 Elsevier Inc. All rights reserved. Both Rushton (1995, 1997, 2000) and Lynn (1991) have pointed out that ethnic groups in colder climates score higher on intelligence tests than ethnic groups in warmer climates. They contend that greater intelligence is needed to adapt to a colder climate so that, over many generations, the more intelligent members of a population are more likely to survive and reproduce. Their temperature and IQ analyses have been descriptive rather than quantitative, however. In the present quantitative study, we predicted a negative correlation between IQ 0160-2896/$ see front matter D 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.intell.2005.04.002 * Corresponding author. E-mail address: donaldtempler@sbcglobal.net (D.I. Templer). and temperature. We hypothesized that correlations would be higher for mean winter temperatures (January in the Northern Hemisphere and July in the Southern Hemisphere) than for mean summer temperatures. Skin color was conceptualized as a variable closely related to temperature. It is viewed by the present authors as a multigenerational reflection of the climates one’s ancestors have lived in for thousands of years. Another reason to predict correlations of IQ with temperature and skin color is the product–moment correlation reported by Beals, Smith, and Dodd (1984) of 0.62 between cranial capacity and distance from the equator. Beals et al. based their finding on 20,000 individual crania 06) 121–139 D.I. Templer, H. Arikawa / Intelligence 34 (2006) 121–139 122 from every continent and representing 122 ethnically distinguishable populations. Jensen (1998) reasoned that natural selection would favor a smaller head with a less spherical shape because of better heat dissipation in hot climates. Natural selection in colder climates would favor a more spherical head to accommodate a larger brain and to have better heat conservation. We used an index of per capita income-real gross domestic product (GDP) per capita to compare the correlations of income with IQ to those of temperature and skin color with IQ. There is a strong rationale for predicting a positive relationship between IQ and real GDP per capita. Common sense dictates that more intelligent populations can achieve greater scientific, technological, and organizational advancement. Furthermore, it is well established that conditions associated with poverty, such as malnutrition and inadequate prenatal/perinatal and other health care, can prevent the attainment of genetic potential. Lynn and Vanhanen (2002) did indeed find positive correlations between adjusted IQ and real GDP per capita of nations throughout the world. Their scatter plots vividly show that countries south of the Sahara Desert have both the lowest real GDPs per capita in the world and the lowest mean IQs in the world (in the 60s and 70s). The real GDP per capita in high-IQ countries is much more variable. For example, China and Korea have very high mean IQs but rather low real GDPs per capita. In this study, we considered only countries (N =129) with primarily indigenous people—those with populations that have persisted since before the voyages of Christopher Columbus. It is acknowledged that there have been many migrations both before and after Columbus. However, the year 1492 has previously been used to define indigenous populations (Cavalli-Sforza, Menzoni, & Piazza, 1994).