The question of whether left-handedness could be inherited was answered in 2007 when scientist Clyde Francks announced the isolation of a gene—called LRRTM1—that contributes to left-handedness. Francks' research suggests the gene is inherited on the father's side.
Parents can monitor their child's handedness by keeping tabs on which hand reaches for toys and food or by noting which direction a child stirs with a spoon. Righties tend to stir clockwise, while lefties stir counterclockwise.
Babies usually start showing a hand preference at about 7 to 9 months old, but they may not make a final distinction until they start school. "Doodling and eating are not fine motor skills requiring premium dexterity, which is why many babies and toddlers, under the influence of rapidly developing brains, switch between using the left and right hands, often masking underlying handedness and leading parents to conclude falsely that their children are ambidextrous," David Wolman writes in A Left-Hand Turn Around the World. "This is a common error among people who associate ambidextrousness with high intellect."