Mathematical ability and the right-shift theory of handedness.

A genetic theory of handedness, the right-shift theory, associates differential patterns of cerebral functioning with contrasting handedness groups and suggests that individuals with an rs + + genotype will be disadvantaged in mathematical performance. This hypothesis is investigated with contrasting handedness groups drawn from a national sample of over 11,000 children from the National Child Development Study. Some differentiation in cognitive performance between handedness groups is found in the direction predicted by the right-shift theory but the level of the findings is not statistically significant. The rs+ +/mathematical deficit hypothesis is not confirmed.