How many handednesses: The importance of preference and limb lateralization for the handedness phenotype.

The phenotype of human handedness is likely to be a product of the ecological conditions experienced by our ancestors, with different forms of handedness having different fitness costs and benefits. Human hands, limbs, and bodies move in a coordinated fashion, so that hand lateralization is likely to have also entailed the evolution of limb and body lateralization. Consequently, we suggest that a measure of handedness should incorporate measures of limb lateralization. Measures of handedness that do not represent these differences may not capture the functional properties of an individual's hand use, or the types of handedness that were selected for in ancestral environments. The advantages of measuring lateral preference rather than skill are also highlighted. Finally, we suggest that to determine categories from continuously measured data, it may be better to use algorithmic analysis techniques, such as cluster analysis, latent class analysis, or dual Weibull mixture models. These reduce researcher degrees of freedom, while being able to capture the dimensional and categorical nature of handedness. Ultimately, methods to determine handedness should be suited to the specific research question, and no single method may suit all circumstances.