Human handedness and the concept of developmental stability.

A model is proposed to explain the etiology of pathological handedness. Developmental instability, caused by elevated genotypic homozygosity, environmental disturbances, or their interaction, overrides programmed laterality and handedness in the same way that it perturbs the bilaterally symmetrical expression of morphological and metric traits. The model predicts that pathological handedness should be elevated among individuals with higher than average homozygosity and individuals who have developed under unfavorable uterine environments. Suggestions are offered for specific populations in which the predictions may be tested.