Handedness Develops Through Practice, Not Just Biology, Study Finds

A new study published on June 30 in Proceedings of the National Academy of Sciences challenges the common belief that people are born left- or right-handed. Researchers led by John Krakauer at Johns Hopkins University School of Medicine and Ahmet Arac at UCLA found that while biological preference exists, the superior skill of the dominant hand is largely acquired through practice. In experiments with right-handed participants, both arms performed equally in reaching tasks, but the dominant hand excelled when using tools like a stick. Writing tasks showed no advantage when performed with the elbow, suggesting that practice, not innate brain wiring, drives dominance. The study supports the idea that hand preference is culturally transmitted, as learning motor skills from right-handed individuals perpetuates right-handedness. Roughly 90% of people are righties, but genetics alone don't explain it: two left-handed parents have a left-handed child only 25-30% of the time. The findings have implications for stroke rehabilitation, as nondominant limbs can improve with training.