FLUCTUATING ASYMMETRY AND PSYCHOMETRIC INTELLIGENCE

Little is known about the genetic nature of human psychometric intelli gence (IQ), but it is widely assumed that IQ's heritability is at loci for intelligence per se. We present evidence consistent with a hypoth esis that interindividual IQ differences are partly due to heritable v ulnerabilities to environmental sources of developmental stress, an in direct genetic mechanism for the heritability of IQ. Using fluctuating asymmetry (FA) of the body (the asymmetry resulting from errors in th e development of normally symmetrical bilateral traits under stressful conditions), are estimated the relative developmental instability of 112 undergraduates and administered to them Cattell's culture fair int elligence test (CFIT). A subsequent replication on 128 students was pe rformed. In both samples, FA correlated negatively and significantly w ith CFIT scores. We propose two non-mutually exclusive physiological e xplanations for this correlation. First, external body FA may correlat e negatively with the developmental integrity of the brain. Second, in dividual energy budget allocations and/or low metabolic efficiency in high-FA individuals may lower IQ scores. We review the data on IQ in l ight of our findings and conclude that improving developmental environ mental quality may increase average IQ in future generations.