Breaking the binary: Mixed-handedness and its implications for theoretical and clinical laterality research

For more than a century, handedness has served as a canonical example of functional asymmetry in humans. Traditional perspectives have largely treated handedness as a binary trait, classifying individuals as either right- or left-handed / non-right-handed, with only occasional recognition of a third category such as mixed-handedness. This binary categorization has become deeply entrenched and often remains unquestioned. A consequence of this dichotomous framework is a long-standing bias in the interpretation of findings related to left-handedness, which by some authors has been associated with negative outcomes in clinical research or even has been proposed to be a marker of decreased survival fitness. These interpretations largely reflect methodological limitations, as individuals who do not fit neatly into either category are frequently misclassified or overlooked. This commentary argues that mixed-handedness should be recognized as a central aspect of laterality research. Incorporating this category challenges the conventional dichotomy, addresses limitations of existing classification systems, and has important implications for understanding neurodevelopment, cognition, and clinical outcomes. In the following sections we will shortly line out empirical evidence supporting this view.