Right-handedness tied to walking upright and brain expansion

About 90 percent of people across all human cultures prefer using their right hand for tasks such as writing, eating and throwing. This near universal trait is absent in other primates, which typically show no consistent population level hand preference. A new study published in the journal PLOS Biology suggests that the origins of human right handedness lie in two key evolutionary shifts: walking upright and the expansion of the brain.

Researchers from the University of Oxford and the University of Reading analyzed data from 2,025 individuals representing 41 species of monkeys and apes. Using models that accounted for evolutionary relationships, they tested several leading hypotheses about handedness, including tool use, diet, habitat, body size, social organization and locomotion. None of these factors alone could explain why humans are such outliers in their strong right hand bias.

The picture changed when the researchers added two additional traits to their model: brain size and the ratio of arm length to leg length, a standard marker of bipedal movement. Once these factors were included, human handedness no longer appeared anomalous. The model closely predicted the observed...