[Genetic problems of handedness]

The present review discusses the heredity of the most famous and important lateral sign, namely handedness. There are some problems in assessing the handedness and so it is not ever easy to describe the phenotype of handedness in relation to the genotype. Another important point is the biological foundation. It is possible to argue that genes are left-right agonistic. All available family studies on handedness are presented and altogether they show a clear intrafamiliar relationship. Data of adoption studies on handedness are rare but they indicate that the effects of shared biological heritage are more powerful determinants of handedness than sociocultural factors. Several genetic models are discussed shortly favoring the Annett- and the McManus-model because they calculate a directional and a fluctuating asymmetry. Finally the present review describes the factors favoring a genetic influence (presence of asymmetries in infants, structural and behavioral asymmetries) and those favoring sociocultural determination (twin data). The body of data offers substantial evidence for the influence of genes.