Evidence for a maternal effect on infant hand-use preferences.

Left-handed offspring occur more frequently when one or both parents are left-handed. Among parental pairs with discordant handedness, left-handed mothers have more left-handed offspring than do left-handed fathers. No previous study has looked for this maternal effect in the hand-use preferences of infants. Handedness of 42 infants (21 females) 6-13 months of age (M = 10 months) was assessed by a reliable and valid procedure that provides hand-use preference scores separately for reaching and unimanual manipulation of objects. Equal numbers of age-matched male and female infants were formed into three groups representing different patterns of parental handedness: neither parent left-handed, father left-handed, mother left-handed. Infants of left-handed mothers showed more left hand-use than infants of left-handed fathers or infants of right-handed parents. Indeed, 64% of infants with left-handed mothers had significant left hand-use preference scores whereas none of the infants in the other groups had significant left hand-use preference scores. Possible mechanisms for this maternal effect on infant hand-use preferences are discussed.