IQHSBI and the Health of States SatoshiIQ and the Health of States Kanazawa* Department of Management, London School of Economics and Political Science; Department of Psychology, University College London; Department of Psychology, Birkbeck College, University of London ABSTRACT: Epidemiologists contend that income inequality reduces the health and life expectancy of the whole population, but this argument does not make sense within its own evolutionary framework. Recent evolutionary psychological theory suggests that the human brain, adapted to the ancestral environment, has difficulty comprehending and dealing with entities and situations that did not exist in the ancestral environment, and that general intelligence evolved as a domain-specific adaptation to solve evolutionarily novel problems. Since most dangers to health in the contemporary society are evolutionarily novel, it follows that more intelligent individuals are better able to recognize and deal with such dangers and live longer. Consistent with the theory, and replicating an earlier study of cross-national data, income inequality has no effect on the health and longevity of the population across the American states, when the racial composi- tion (percent black) is controlled, but the average intelligence of the population (state IQ) has a significant effect. The data presented here and in the earlier study challenge the conclusion that income inequality reduces the health of the population. INTRODUCTION damage health. Wilkinson’s conclusion is succinctly captured in the blurb on his In a series of articles and books, Richard book Mind the Gap, “Inequality kills. Peo- Wilkinson argues that economic inequal- ple die younger in countries with greater ity reduces the health of the population inequalities in income.” While Wilkinson’s and lowers its life expectancy (Marmot original observation on the negative asso- & Wilkinson, 1999; Wilkinson, 1992, ciation between income inequality and 2000). He claims that humans and other health involves cross-national comparisons primates have an evolved physiological of nations (Wilkinson, 1992), others have mechanism whereby their cortisol level since documented the same negative asso- goes up when they are under attack or ciation for subnational units, such as the otherwise in submissive situations. American states (Ben Shlomo, White, & Heightened levels of cortisol and other Marmot, 1996; Kaplan et al., 1996; Kawachi stress hormones allow the individuals to & Kennedy, 1997; Kennedy, Kawachi, & deal with the short-term emergencies but Prothrow-Smith, 1996; Lynch et al., 1998; at the cost of long-term health. When the Ross et al., 2000). The negative conse- submissive status prolongs, the continu- quences of income inequality for popula- ously high levels of stress and anxiety tion health and longevity has become part of the established knowledge of epidemiol- *Address correspondence to: Satoshi Kanazawa, ogy and public health. Interdisciplinary Institute of Management, London Wilkinson’s theory, however, does not School of Economics and Political Science, Houghton Street, London WC2A 2AE, United Kingdom. E-mail: make sense within its own evolutionary [email protected] framework. Given that prolonged stress 200 IQ and the Health of States 201 and anxiety lead to health problems and African savanna during the Pleistocene early death, with no apparent compensating Epoch). It may therefore have difficulty benefits in reproductive success,1 any comprehending and dealing with entities genetic mutation that allows its carrier not and situations that did not exist in the to experience stress in the face of perma- ancestral environment (Kanazawa, 2002, nently low status from which it cannot 2004a). On the other hand, an evolution- escape (the “Que sera sera” gene?) will be ary psychological theory of the evolution selected. Chronic low status, being at the of general intelligence2 proposes that bottom of a social hierarchy for life, general intelligence may have evolved as seems dramatically different from the a domain-specific adaptation to solve acute emergency of imminent physical evolutionarily novel problems, for which attack, with which cortisol and other there are no predesigned psychological stress hormones are designed to deal. Any adaptations (Kanazawa, 2004b, 2008a). genotype which makes a distinction The synthesis of these two theories, the between short-term emergencies of physi- Savanna-IQ Interaction Hypothesis, cal attack and long-term chronic low sta- implies that the human brain’s difficulty tus, and which responds differently, with with evolutionarily novel stimuli may a surge of cortisol, prolactin and other interact with general intelligence, such stress hormones to the former, but not to that more intelligent individuals have less the latter, will be favored by natural selec- difficulty with evolutionarily novel stim- tion over another genotype which does uli than the less intelligent individuals. In not make such a distinction and responds contrast, general intelligence may not similarly to both. Since all primate societ- affect individuals’ ability to comprehend ies are hierarchical and there are chroni- and deal with evolutionarily familiar enti- cally high- and low-status individuals in ties and situations. them, suggesting that the origins of Some critics (including one anony- human social hierarchies may go back at mous reviewer) contend that general least 15–20 million years in evolutionary intelligence could not be an adaptation history, it appears that there should have because it is an individual difference vari- been enough time for such a genetic able. Adaptations are universal and con- mutation to emerge and spread. What is stant features of a species shared by all its the ultimate function of stress and anxiety members; in contrast, there are obviously in the face of low status? If there are heritable individual differences in general none, why hasn’t natural selection elimi- intelligence and some individuals are nated it? more intelligent than others. These critics Recent evolutionary psychological argue that adaptations and heritable indi- theory suggests an entirely different vidual differences are mutually exclusive. determinant of health and life expectancy I strongly disagree with these critics. in contemporary society. On the one I believe that a trait could simultaneously hand, evolutionary psychology (Craw- be an evolved adaptation and an individ- ford, 1993; Symons, 1990; Tooby & ual difference variable. Full-time bipe- Cosmides, 1990) posits that the human dalism is a uniquely human adaptation brain, just like any other organ, is among mammals, yet some individuals designed for and adapted to the conditions run faster than others. The eye is a complex of the ancestral environment (roughly the adaptation, yet some individuals have 202 Kanazawa better vision than others. Language is an general intelligence is an adaptation and adaptation, yet some individuals have has zero heritability (in the sense that all greater linguistic facility than others. humans are highly intelligent), even Individual differences in general intelli- though the exact level of an individual’s gence is what Tooby and Cosmides intelligence is not an adaptation and is (1990) call “random quantitative variation highly heritable. And Tooby and on a monomorphic design.” “Because the Cosmides (1990, p. 57) contend that elaborate functional design of individuals “nonadaptive, random fluctuations in [in this case, general intelligence as a the monomorphic design of a mental domain-specific adaptation] is largely organ can give rise to heritable individ- monomorphic [shared by all members of ual differences in nearly every manifest a species], our adaptations do not vary in feature of human psychology.” We their architecture from individual to indi- would therefore expect individual dif- vidual (except quantitatively)” (Tooby & ferences in general intelligence as a Cosmides, 1990, p. 37, emphasis added). domain-specific adaptation. Intraspecific (interindividual) differences As it happens, there has been accumu- in such traits pale in comparison to inter- lating evidence for the Savanna-IQ Inter- specific differences. Carl Lewis and I run action Hypothesis. First, individuals’ at a virtually identical speed compared to tendency to respond to TV characters as if cheetahs or sloths. Similarly, Einstein and they were real friends, first discovered by I have virtually identical intelligence Kanazawa (2002), is limited to those with compared to cheetahs or sloths. I there- below-median intelligence (Kanazawa, fore believe it is possible for a trait to be 2006a); individuals with above-median universal and species-typical (exhibiting intelligence do not become more satisfied virtually no variation in a cross-species with their friendships by watching more comparison) and manifest vast individual television. differences among members of a single Second, less intelligent individuals species. I believe general intelligence is have more children than more intelligent one such trait. individuals, even though they do not want Tooby and Cosmides (1990, pp. 38–39) to, possibly because they have greater make this exact point, using “a complex difficulty effectively employing evolu- psychological mechanism regulating tionarily novel means of modern contra- aggression” as their example. They con- ception (Kanazawa, 2005). Another tend that it is an adaptation, even though indication that less intelligent individuals there are heritable