October 12, 2004

A common fitness factor behind intelligence and body symmetry

A new study shows that intelligence and body symmetry are correlated, and the correlation becomes more marked for intelligence tests with higher loading of the general intelligence factor g. This may indicate that both g and body symmetry are influenced by a general "fitness" factor.

Intelligence (Article in Press)

Intelligence tests with higher g-loadings show higher correlations with body symmetry: Evidence for a general fitness factor mediated by developmental stability

Mark D. Prokosch et al.


Just as body symmetry reveals developmental stability at the morphological level, general intelligence may reveal developmental stability at the level of brain development and cognitive functioning. These two forms of developmental stability may overlap by tapping into a “general fitness factor.” If so, then intellectual tests with higher g-loadings should show higher correlations with a composite measure of body symmetry. We tested this prediction in 78 young males by measuring their left–right symmetry at 10 body points, and by administering five cognitive tests with diverse g-loadings. As predicted, we found a significant (z=3.64, p<0.003) relationship between each test's rank order g-loading and its body symmetry association. We also found a substantial correlation (r=0.39, p<0.01) between body symmetry and our most highly g-loaded test (Ravens Advanced Progressive Matrices). General intelligence is apparently a valid indicator of general developmental stability and heritable fitness, which may partly explain its social and sexual attractiveness.


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