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Abstract
Grasp-reflex asymmetry was studied in human newborns with regard to familial sinistrality (FS). In the total sample, the following results were obtained. The mean grasp-reflex strength from the right hand was found to be significantly greater than that from the left hand in FS- subjects. There was no significant difference between these parameters in FS+ subjects. The mean right minus left (R-L) reflex strength was significantly greater than zero in FS- subjects. The mean R-L reflex did not significantly differ from zero in FS+ subjects. The mean reflex strength from the right hand was found to be significantly greater in FS- subjects than FS+ subjects. There was no significant difference between the mean reflex strengths from the left hands of the FS- and FS+ subjects. The mean R-L reflex in subjects FS- was found to be significantly greater than that in FS+ subjects. Similar results were obtained from the male and female subjects. It was concluded that FS is an important factor determining the degree of the grasp-reflex asymmetry in newborns. The relatively left-biased grasp-reflex asymmetry under the influence of FS indicates a genetic origin of the motor asymmetry in newborns. This, in turn, suggests that cerebral lateralization inducing manual asymmetry in humans may have been preprogrammed genetically.