Brain size as an explanation of national differences in IQ, longevity, and other life-history variables
Short Communication Brain size as an explanation of national differences in IQ, longevity, and other life-history variables J. Philippe Rushton * Department of Psychology, University of Western Ontario, London, Ontario, Canada N6A 5C2 article info Article history: Received 6 July 2009 Accepted 31 July 2009 Available online 2 September 2009 Keywords: Brain size National IQ Longevity Life-history theory abstract Brain size provides a causal mechanism for why national differences in intelligence correlate with life- history variables such as longevity, health, parental care, and fecundity. Brain size correlates .40 with general intelligence within human populations, .91 with IQ across ten human population groups, and .60–.90 with longevity, fecundity, and infant mortality in non-human animals (just as IQ does within and across nations, albeit often with lower values). Brain size is central to a suite of life-history variables arising during the course of evolution. Traits need to be harmonized, not work independently of each other. The question Wicherts et al. do not ask is – what causes national differences in their preferred the- ory of ‘‘developmental status?” Heritable brain-power is the answer. A life-history theory perspective on heritable brain-power also explains the social-class/longevity paradox within nations. Any theory which explains differences at the individual, national, and cross-national level deserves to be taken very seriously. 2009 Elsevier Ltd. All rights reserved. 1. Introduction Wicherts, Borsboom, and Dolan (2009)showed that even after excluding low scoring countries in sub-Saharan Africa, 60 national IQs correlated with latitude (.50), fertility ( .75), child mortality (.61), education (.60), calories per day (.44), and urbanization (.52). They also found one dominant principal component that explained 65% of the variance across 18 variables. Wicherts et al.’s results corroborated those byTempler (2008), who found a super-factor accounted f…