Temperature, skin color, per capita income, and IQ: An international perspective 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.A population that suddenly increases in size has the potential for rapid adaptive change. Comments on correlations of IQ with skin color and geographic–demographic variables. Temperature and evolutionary novelty as forces behind the evolution of general intelligence Lynn, 1991.The best analogy to recent human evolution may be the rapid evolution of domesticates such as maize (9, 10). Brain Size, Intelligence, and Paleoclimatic Variation. The evolution of race differences in intelligence Lynn and Vanhanen, 2006. Race, evolution, and behavior: A life history perspective Templer and Arikawa, 2006.A review of Gregory Cochran and Henry Harpending, The 10,000 Year Explosion: How Civilization Accelerated Human Evolution.Human populations have increased vastly in numbers during the past 50,000 years or more (1).Can this idea really describe recent human evolution? Only a small fraction of all mutations are advantageous; most are neutral or deleterious.
In contrast, I offer a different evolutionary psychological explanation for the evolution of general intelligence as a domain specific adaptation in the sphere of evolutionary novelty.Its universal and enormous importance today reflects the fact that we now live in an evolutionarily novel world.We also propose a complementary hypothesis that may explain some of the effects of infectious disease on intelligence.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.Rapid population growth has been coupled with vast changes in cultures and ecology during the Late Pleistocene and Holocene, creating new opportunities for adaptation.The past 10,000 years have seen rapid skeletal and dental evolution in human populations and the appearance of many new genetic responses to diets and disease (4).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 found that birds from the harsh northern population, where selection for cognitive abilities is expected to be high, significantly out performed conspecifics from the mild southern population…our results support the idea that environmental severity may be an important factor in shaping certain aspects of cognition.” Selection due to geographic novelty Jensen, 1998. General intelligence as a domain-specific adaptation In a recent book, IQ and the Wealth of Nations, Lynn and Vanhanen (2002) compile a comprehensive list of “national IQs” (the mean IQ of populations) of 185 nations in the world.Population Differences In Intelligence: Causal Hypotheses. In: The g Factor: The Science of Mental Ability Kanazawa, 2004a. One striking feature of their data is that the national IQs in sub-Saharan Africa are significantly lower than those in the rest of the world (68.8 vs. This, of course, makes perfect sense from my perspective of general intelligence as a domain-specific adaptation for evolutionary novelty.Since our ancestors spent most of their evolutionary history in sub-Saharan Africa, it is evolutionarily more familiar to the human brain than the rest of the world, which is more evolutionarily novel.