The Distribution of Manual Asymmetry

Four different descriptions of lateral asymmetry are reviewed and their probable interrelations examined. Two main features are distinguished: first, a normal distribution of relative efficiency of the two sides which probably applies to all species subject to lateral differences; second, a factor specific to humans which induces a shift of the normal distribution toward dextrality. A brief discussion of the origins of asymmetry leads to the conclusion that the basic normal distribution probably depends on accidental variation while the human shift to the right may be a product of both cultural and genetic influences. The latter could imply that human right handedness is inherited while left handedness is not.