DEVELOPMENTAL ORIGINS OF VARIATION IN HUMAN HAND PREFERENCE

Though right-handedness is a prominant characteristic within all human societies, a substantial and stable proportion of individuals are lef t-handed. Any comprehensive approach to the origin of variation in han dedness must account for substantial evidence that left-handedness is associated with reduced fitness, neurodevelopmental disorders, and red uced neuroanatomical asymmmetry. In this paper we investigate the hypo thesis that developmental instability in early fetal development under lies variation in handedness. In two studies we note an increased inci dence of minor physical anomalies (MPAs) and fluctuating asymmetries i n both left-handers and extreme right-handers. Moreover, extreme right -handlers were more apt to have left-handed parents than moderate righ t-handers. These data suggest that deviation from moderate right-hande dness reflect imprecise expression of a near-universal design due to d evelopmental instability. Preliminary attempts to elucidate the mechan isms underlying developmental instability suggest that both polygenic homozygosity and particular HLA alleles may be important factors. Thes e observations are discussed with respect to current genetic theories of handedness and human evolution.