Handedness is not a unidimensional trait.

Most theories about the inheritance of hand preference assume that handedness is a unidimensional trait which forms a continuous distribution. This paper demonstrates that sampling a wide range of manual activities reveals dimensions of hand preference that are independent. 180 right handed and 110 left handed adults indicated their hand preference for 55 activities according to a five point scale. A Varimax Factor Analysis revealed four factors which accounted for 80 percent of the variance. Factor 3 was of special interest because it represented behaviors which rely upon the axial musculature and involve strength more than dexterity. Hand preference for items on this factor were less laterally biased than on factors which included such fine motor behaviors as writing or drawing. These results suggest that manual preference is governed by more than one neural system and that these systems may be independently lateralized.