HAND PREFERENCE AND DEVELOPMENTAL INSTABILITY

The origins of individual variation in hand preference are unclear, wi th some theories emphasizing environmental factors, and others, geneti c factors. In two studies, we investigated the hypothesis that develop mental instability, leading to imprecise expression of a near-universa l neural design, underlies phenotypic variation in hand preference and performance. In Study 1, a composite index of developmental instabili ty was constructed from a checklist of minor physical anomalies and th e left-right asymmetry in a specific dermatoglyphic characteristic of the palms, the atd angle. This composite measure possessed a linear re lationship with a hand preference inventory and both linear and curvil inear relationships with a measure of relative hand skill. Study 2 rep licated these results and extended them to a wider variety of physical left-right asymmetries. Three major implications of these results are discussed. First, variations in early fetal development may be import ant for individual variations in the neural substrate of handedness, l eading to both left-handedness and extreme right-handedness. Second, a s developmental instability likely results from polygenic homozygosity , the present results may be incompatible with single-gene theories of handedness. Third, the theoretical underpinnings of developmental ins tability offer a novel way to account for the association of left-hand edness with some neurodevelopmental disorders.