Abstract
Traits that are attractive to the opposite sex are often positively correlated when scaled such that scores increase with attractiveness, and this correlation typically has a genetic component. Such traits can be genetically correlated due to genes that affect both traits (“pleiotropy”) and/or because assortative mating causes statistical correlations to develop between selected alleles across the traits (“gametic phase disequilibrium”). In this study, we modeled the covariation between monozygotic and dizygotic twins, their siblings, and their parents (total N = 7,905) to elucidate the nature of the correlation between two potentially sexually selected traits in humans: height and IQ. Unlike previous designs used to investigate the nature of the height–IQ correlation, the present design accounts for the effects of assortative mating and provides much less biased estimates of additive genetic, non-additive genetic, and shared environmental influences. Both traits were highly heritable, although there was greater evidence for non-additive genetic effects in males. After accounting for assortative mating, the correlation between height and IQ was found to be almost entirely genetic in nature. Model fits indicate that both pleiotropy and assortative mating contribute significantly and about equally to this genetic correlation.
Highlights
Traits related to attractiveness are often positively correlated when scaled such that higher scores are more attractive
A non-mutually exclusive alternative for positive inter-correlations between traits related to attractiveness is that genetic effects are shared between such traits
Traits that are attractive to the opposite sex are often positively correlated when scaled such that scores increase with attractiveness, and this correlation typically has a genetic component
Summary
Traits related to attractiveness are often positively correlated when scaled such that higher scores are more attractive. A non-mutually exclusive alternative for positive inter-correlations between traits related to attractiveness is that genetic effects are shared between such traits This may occur either because the sets of genes affecting these traits partially overlap (pleiotropy) and/or because positive assortative mating for overall attractiveness causes cross-trait assortative mating, leading to genetic covariation due to gametic phase disequilibrium. If height and IQ were the only two traits differentiating people on attractiveness, assortative mating on attractiveness would imply that smart people would mate with other smart people, and with tall people at above chance levels Assuming that such traits are heritable, cross-trait positive correlations cause a statistical relationship to develop between the ‘increasing’ alleles across the traits—gametic phase disequilibrium—thereby inducing a positive genetic covariation between the traits [17] (negative cross-trait assortative mating would induce a negative genetic correlation between traits).
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