Fluctuating asymmetry and intelligence

The general factor of mental ability (g) may reflect general biological fitness. If so, g-loaded measures such as Raven's progressive matrices should be related to morphological measures of fitness such as fluctuating asymmetry (FA: left-right asymmetry of a set of typically left-right symmetrical body traits such as finger lengths). This prediction of a negative correlation between FA and IQ was confirmed in two independent samples, with correlations of -0.41 and -0.29, respectively. Head size also predicted Raven's scores but this relationship appeared to be mediated by FA. It is concluded that g along with correlated variables such as head size are in large part a reflection of a more general fitness factor influencing the growth and maintenance of all bodily systems. with brain function being an especially sensitive indicator of this fitness factor. (c) 2006 Published by Elsevier Inc.