Human Polygenic Selection as the Source of Race Differences in Intelligence
Davide Piffer
Ulster Institute for Social Research, London.
Weak widespread (polygenic) selection is a mechanism that acts on multiple SNPs simultaneously. The aim of this study is to suggest a methodology to detect signals of polygenic selection using educational attainment, IQ and height as examples. These are polygenic phenotypes, influenced by many genetic variants with small effects. Frequencies of 10 SNPs found to be associated with educational attainment in a recent genome-wide association study were obtained from HapMap, 1000 Genomes and ALFRED. Factor analysis showed that they are strongly statistically associated at the population level, and the resulting factor score was highly related to average population IQ (r=.9). Moreover, allele frequencies were positively correlated with aggregate measures of educational attainment in the population, average IQ. A principal component extracted from 4 IQ increasing alleles is strongly associated with the educational attainment component (r=.90). A separate analysis carried out on an independent set of alleles related to human stature suggests that this trait was subject to different directional selective pressures. One-way ANOVA showed that the average frequencies of height increasing alleles (N=46) for three racial groups (East Asian, Sub-Saharan African and European) differed significantly and that Africans had significantly higher frequencies than East Asians. This study provides a simple method for detecting signals of polygenic selection on genes with overlapping phenotypes but located on different chromosomes. The method is therefore different from traditional estimations of linkage disequilibrium.
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