Handedness and speech: A critical reappraisal of the role of genetic and environmental factors in the cerebral lateralization of function.

Abstract

Functional predominance of the left cerebral hemisphere with regard to both handedness and speech has usually been assumed to be due to some underlying neural specialization that is predetermined and inborn. However, data from left-handed individuals and animal experiments, together with a consideration of the effects of natural selection on brain and behaviour during hominid evolution, are incompatible with such an explanation. A critical reexamination of the relevant nonhuman and human evidence suggests that although the development of a cerebral lateralization for speech and handedness is dependent on both genetic and environmental factors, the specific role of inborn and postnatal influences is very different. This has significant implications for a fundamental revision of current theory and research orientation.

Posture and laterality in human and non-human primates: Asymmetries in maternal handling and the infant's early motor asymmetries

“…Moreover, from birth, the world of objects (both social and inanimate) influences humans in an asymmetrical manner and this action expresses itself in a prominent way in maternal behaviour. Provins (1997) assumes that cultural biases in human populations tend to favour the use of the right hand. As a result, individuals who begin in infancy by using their right hand in some unimanual tasks would have this tendency strengthened.…”

“…It could be instead that it is behavioural, with infant handedness being determined by the behaviour of the mother. Explanations of this sort include effects of: (1) maternal cradling bias (Provins, 1997); (2) intrauterine fetal position (Previc, 1991); or (3) prenatal hormonal environment (Geschwind and Galaburda, 1985). But for the ti me being, there are no strong data that can be used to support or to challenge any of these views.…”

“…Provins, 1997). A primate (non-human) model of hand preference is likely to advance our understanding greatly of human lateralization and its evolution.…”

Heritability of hand preference in chimpanzees (Pan troglodytes): Evidence from a partial interspecies cross-fostering study.

“…The pervasiveness of human right-handedness has led to numerous debates about the mechanisms involved in the expression of hand preference (B. Hopkins & Ronnqvist, 1998). Both genetic models (Annett, 1985;Corballis, 1997;Laland, Kumm, Van Horn, & Feldman, 1995;McManus, 1985;Yeo & Gangestad, 1993) and environmental models (Collins, 1985;Provins, 1997) have been proposed to explain the origin of human hand preference. The principal data in support of a genetic basis for hand preference are that it runs in families (Curt, De Agostini, Maccario, & Dellatolas, 1995;Laland et al, 1995;McGee & Cozad, 1980;McManus & Bryden, 1992) and that offspring typically exhibit patterns of hand preference more similar to their biological parents compared with offspring who have been adopted or raised by stepparents (Carter-Saltzman, 1980;Hicks & Kinsbourne, 1976).…”

Visual experience affects handedness

“…Historically, there has been the suggestion that genetic variation does not have a significant role in causing left-or right-handedness and that left-handedness is due largely to environmental influences [41,47]. However such purely non-genetic models of handedness are unable to explain the dominance of right-handedness (despite culture-dependent variations) in all human societies [32].…”