Inbreeding depression and IQ in a study of 72 countries

Article history: Received 15 June 2008 Received in revised form 30 October 2008 Accepted 30 October 2008 Available online 5 December 2008 In this ecological study, a robust negative correlation of r=− .62 (Pb.01) is reported between national IQs and consanguinity as measured by the log10 transformed percentage of consanguineous marriages for 72 countries. This correlation is reduced in magnitude, when IQ is controlled forGDPper capita (r=− .41,Pb.01); education index (r=− .40,Pb.01); anddemocracy index (r=− .42,Pb.01).Multiple regression analysis revealed that in the absence of the democracy index; percentage consanguineous marriages, education index and GDP per capita all exhibited stable final standardized β coefficients, however consanguinity had the least impact (β=0, PN.05) whereasGDPper capita had thehighest (β=.35,PN.01). This result is interpreted in lightof cultural feedback theory, whereby it is suggested that consanguinity could subtly influence IQ at larger scales as a result of small IQ handicaps bought about through inbreeding being amplified intomuch larger differences through their effect on factors that maximize IQ such as access to education and adequate nutrition. Finally, consideration is given to future potential research directions. © 2008 Elsevier Inc. All rights reserved.