L ETTERS www.sciencemag.org SCIENCE VOL 309 29 JULY 2005 703 Human Hierarchies, Health, and IQ R. M. SAPOLSKY’S REVIEW “THE INFLUENCE of social hierarchy on primate health” (29 Apr., p. 648) begins and ends with the conun- drum that there is a graded, inverse associa- tion between low socioeconomic position (SEP) and important health outcomes in humans. The nicely described animal work on stress responses and social hierarchies forms the main portion of the piece. The application of these findings to humans is critical, yet, apart from some examples of the physiologi- cal responses to stress, there is no clear series of data-based findings to take us mechanisti- cally, in human samples, from human social hierarchy, to psychosocial stressors, to stress- related physiological responses, to adverse health outcomes and mortality. In humans, there is another factor and other possible mechanisms to consider. It is surpris- ing that there was no mention of intelligence (IQ). Childhood IQ is moderately strongly cor- related with adult socioeconomic position. Lower IQ is also associated with increased rates of all-cause mortality (1, 2), cardiovascu- lar disease (2–4), hypertension (5), contact with psychiatric services (6), and other nega- tive health outcomes (7). These associations remain after controlling for socioeconomic position in early life. Stable population varia- tion in IQ is perhaps more consistent with the highly graded socioeconomic position-health relation than are the shifting effects of small- group rank on psychosocial stress. The well- replicated, although relatively recent finding that lower childhood IQ is related to later mor- bidity (7) and mortality experience affords hypotheses about mechanisms linking cogni- tive resources to health differences. These hypotheses merit consideration alongside the psychosocial stress hypothesis (8, 9). IAN J. DEARY, 1 * DAVID BATTY, 2 LINDA S. GOTTFREDSON 3 1 Department of Psychology,University of Edinburgh, Edinburgh, EH8 9JZ, UK. 2 Medical Research Council Social and Public Health Sciences Unit, University of Glasgow, Glasgow, G12 8RZ, UK, and Department of Psychology, University of Edinburgh, Edinburgh, EH8 9JZ, UK. 3 School of Education, College of Human Services, Education, and Public Policy, University of Delaware, Newark, DE 19716, USA. *To whom correspondence should be addressed. E-mail: I.Deary@ed.ac.uk References 1. L. J.Whalley, I. J. Deary, Br. Med. J. 322, 819 (2001). 2. C. L. Hart et al., Psychosom. Med. 65, 877 (2003). 3. C. L. Hart et al., Soc. Sci. Med. 59, 2131 (2004). 4. G. D. Batty, E. L. Mortensen, A.-M. Nybo Andersen, M. Osler, Paediatr. Perinat. Epidemiol., in press. 5. J. M. Starr et al., J. Hypertens. 22, 893 (2004). 6. N. P. Walker, P. M. McConville, D. Hunter, I. J. Deary, L. J. Whalley, Intelligence 30, 233 (2002). 7. G. D. Batty, I. J. Deary, Br. Med. J. 329, 585 (2004). 8. L. Gottfredson, I. J. Deary, Curr. Dir. Psychol. Sci. 13,1 (2004). 9. L. S. Gottfredson, J. Pers. Soc. Psychol. 86, 174 (2004). Response DEARY ET AL. RAISE TWO IMPORTANT POINTS, with which I agree. The first is that it is immensely difficult to carry out studies in humans that would uncover the series of steps linking social experience all the way down to the reductive biology of health and disease. Thus, the Letter nicely reiterates the rationale for the paper, namely, the usefulness of studies of nonhuman species. Their second point is that IQ may be an important variable in understanding the health/socioeconomic status relationship. This is absolutely so and is likely to be relevant in a number of ways (e.g., having access to the most current information regarding health risk factors, being able to understand the pertinence of such factors, and so on). ROBERT M. SAPOLSKY Stanford University, Stanford, CA 94305–5020, USA, and Institute of Primate Research, National Museums of Kenya. Published by AAAS