A Modern Reanalysis of McManus’ Genetic Model of Handedness

We replicate and critically evaluate McManus’ (1985) single-locus genetic model of handedness, which remains influential in laterality research. Using the original familial and twin datasets, we reproduce McManus’ parameter estimates while correcting reporting errors and miscalculations. Our reproduction confirms that the model is reproducible but reveals sensitivity to dataset inconsistencies and outliers. We extend the framework by generalizing correction matrices, implementing simulations, and applying bootstrap methods to estimate confidence intervals. We further analyze a modern dataset from Flores and Adonara, Indonesia, providing a test of the model in a different cultural setting and comparing triplet versus multi-offspring representations. Our findings emphasize both the historical value and the current limitations of the Dextral–Chance framework, offering a modern foundation for testing genetic and cultural theories of handedness with contemporary datasets.