In the study of the origin of left-handedness three main areas have been identified: the ‘genetic”, “cultural” and “pathological”.
Since 1871, when a high frequency of family left-handedness among left-handed subjects was found the model of genetic determination of left-handedness is discussed. Currently, two genetic models are the most widely used. According to Ms. Annett, the asymmetry of the brain is determined by the presence of a single gene, which was named by her the “right shift” factor. If this factor is the individual, the latter is prone to be right-handed. If the factor is absent, the person can be either left-handed or right-handed depending on the random circumstances. However, a greater importance is given to brain damage in the prenatal and early postnatal period, which may affect the phenotypic implisicity of “right shift” factor. (more…)