On the futility of using familial sinistrality to subclassify handedness groups.

Annett's right shift model was used to show that presence of left-handedness in parents or grandparents is an extremely weak indicator of whether or not a person's handedness is influenced by genetic factors. Furthermore, where a genetic influence is present, familial sinistrality is only weakly related to underlying genotype. The usual rationale given for subdividing handedness groups according to familial sinistrality is logically indefensible.