The mixture distribution of left minus right hand skill in men and women

The distribution of left minus right (L - R) hand skill (peg moving) was studied in 436 men and 247 women. In total sample, the distribution was continuous and a sum of two Gaussian curves. One of them was constituted by subjects with better right hand (79.0%) and better left hand (21.0%). The other curve (2.5% of total) was exclusively due to the subjects with better left hand. In men and women, the total curve was a sum of three overlapping Gaussian curves. Two of them were mostly due to the subjects with better right hand. There was a third curve representing almost entirely the subjects with better left hand. Women were more strongly right-handed than men. There was no significant sex difference at the sinistral side. The overall results were compatible with the right shift theory, but there was not a single Gaussian curve representing a chance distribution with a mean of zero. These results suggested that the distribution of manual asymmetry in skill is continuous, which may be described by probabilities due to subjects with better right and left hands; there is no place for chance in human handedness.