Biological and sociocultural effects on handedness: comparison between biological and adoptive families.

Data from adoption studies on handedness indicate that the effects of shared biological heritage are more powerful determinants of hand preference than sociocultural factors. Biological offspring were found to show nonrandom distributions of right- and non-right-handedness as a function of parental handedness; these distributions were consistent with the results fo previous family studies. In contrast, the handedness distribution of adopted children as a function of parental handedness was essentially random.