Inbreeding depression and IQ in a study of 72 countries
Michael A. Woodley
In this ecological study, a robust negative correlation of r = − .62 (P less than .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 for GDP per capita (r = − .41, P less than .01); education index (r = − .40, P less than .01); and democracy index (r = − .42, P less than .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, P greater than .05) whereas GDP per capita had the highest (β = .35, P greater than .01). This result is interpreted in light of 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 into much 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.