Dominance of the left hemisphere for many aspects of speech production and perception is one of the best known examples of functional hemispheric asymmetries in the human brain. Classic theories about its ontogenesis assume that it is determined by the same ontogenetic factors as handedness because the two traits are correlated to some extent. However, the strength of this correlation depends on the measures used to assess the two traits, and the neurophysiological basis of language lateralization is different from that of handedness. Therefore, we argue that although the two traits show partial pleiotropy, there is also a substantial amount of independent ontogenetic influences for each of them. This view is supported by several recent genetic and neuroscientific studies that are reviewed in the present article.
Keywords: Functional Hemispheric asymmetries; Laterality; Lateralization; Ontogenesis; Speech.
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